Handbook of Cosmic Hazards and Planetary Defense [1 ed.] 9783319039510, 9783319039527

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Joseph N. Pelton Firooz Allahdadi Editors

Handbook of Cosmic Hazards and Planetary Defense

1 3Reference

Handbook of Cosmic Hazards and Planetary Defense

Joseph N. Pelton • Firooz Allahdadi Editors

Handbook of Cosmic Hazards and Planetary Defense With 479 Figures and 48 Tables

Editors Joseph N. Pelton International Association for the Advancement of Space Safety Arlington, VA, USA

Firooz Allahdadi Space Science and Environmental Research Applied Research Associates Albuquerque, NM, USA

ISBN 978-3-319-03951-0 ISBN 978-3-319-03952-7 (eBook) ISBN 978-3-319-03953-4 (print and electronic bundle) DOI 10.1007/978-3-319-03952-7 Library of Congress Control Number: 2015934442 Springer Cham Heidelberg New York Dordrecht London # Springer International Publishing Switzerland 2015 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Printed on acid-free paper Springer International Publishing AG Switzerland is part of Springer Science+Business Media (www.springer.com)

Many cosmic hazards such as comets, asteroids, and extreme solar weather threaten the small six sextillion ton mudball that we call planet Earth. We indeed travel on this quite perilous spacecraft through the cosmos each and every year. An ever-growing cadre of dedicated researchers devote their professional lives to creating a credible planetary defense for our vulnerable planet against such potentially mass destructive events. These dedicated scientists are seeking to develop new engineering and scientific methods to better understand cosmic threats as well as better methods to achieve a planetary defense against the most catastrophic of these dangers. We dedicate this Handbook of Cosmic Hazards and Planetary Defense to all those cosmic warriors who have dedicated their professional careers to the study of cosmic hazards and planetary defense and contributed to the creation of this manuscript. We wish to particularly recognize Lord Martin Rees, Royal Astronomer of the United Kingdom; astronauts Rusty Schwieckart and Ed Lu of the B612 Foundation; Donald Kessler, who first warned of what is now

called the “Kessler Syndrome”; Michael Simpson, of the Secure World Foundation; Simonetta di Pippo, of the Office of Outer Space Affairs of the United Nations; Tommaso Sgobba, Executive Director of the International Association for the Advancement of Space Safety (IAASS); James Green of NASA, who heads planetary and solar research efforts; Michael Potter of the Paradigm Corporation who produced the YouTube video “Cosmic Hazards”, William Ailor, of the Aerospace Corporation; and the quite numerous researchers and officials around the world engaged in this global effort. Dr. Joseph N. Pelton and Dr. Firooz Allahdadi, Executive Editors

Foreword

More than seven billion of us live on this crowded planet. All too often, our focus is on parochial issues and the conflicts that divide different nations and ideologies. There are some concerns that should surely unite us: threats that come from beyond the Earth. This Handbook offers a comprehensive and authoritative survey of these. Throughout its history, the Earth has been impacted by asteroids and comets and buffeted by solar flares. But the consequences of these natural phenomena are more catastrophic today, because the infrastructure on which our civilization depends is more elaborate and more vulnerable. For instance, our remote ancestors were oblivious of solar flares; in contrast, we are now dependent on electronics and networks that could be frighteningly vulnerable to such events. And the ever more valuable infrastructure of our great cities (especially those on the coast) is vulnerable to asteroid impacts. The theme of this book is not only an important one, but also a hopeful one. We understand these cosmic phenomena far better; we have instruments, both on the ground and in space, that can give us forewarning of threatening flares and impacts. We are learning how to make our systems more robust and resilient. Moreover, we will not remain helpless in the face of these threats because we are empowered by advancing technology and engineering. Such advances may within a few decades enable us to actually reduce the risk of impacts by detecting the millions of asteroids and “space rocks” that pass near the Earth and “nudging” the orbits of the bodies that threaten to hit us. This Handbook is hugely impressive and deserves wide readership: it offers us a broad and well-informed perspective on our cosmic environment. More important, I hope it will stimulate appropriate efforts to understand and counter these threats – an enterprise valuable in its own right, but one which offers an opportunity for international partnership, both governmental and private, in a common cause. We are all members of the crew of “Spaceship Earth” – a precious and fragile “pale blue dot” in the wider cosmos. The recipes and insights in this Handbook will help to protect and safeguard it for future generations. Martin Rees UK Astronomer Royal

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Preface

While living aboard the International Space Station for 6 months, my life was affected on a daily basis by cosmic events. From solar flares requiring us to take shelter due to increased radiation as well as causing communications outages to micrometeoroid impacts on the solar arrays, it was clear that we were living in a universe that encompassed more than just the Earth. In fact, from my vantage point I often pondered the large asteroid impact craters on both the Earth and the Moon and realized that the entire history of life on Earth has been shaped by cosmic impacts. People in ancient times believed that the heavens affected daily life and attributed all manner of worldly occurrences to the influence of astronomical events. But since the advent of the scientific revolution and the beginning of our understanding of how the universe works, most of these beliefs have fallen by the wayside (astrologists notwithstanding). But now that we have begun to understand some of the cosmic hazards that affect our Earth and the technologies that we rely upon every day, we are beginning to realize that the heavens do in fact affect our lives on Earth – just not in the way the ancients imagined. As our lives become more dependent on space technology and as our economic sphere expands outward, we cannot afford to ignore these cosmic hazards. And of course, we are still subject to the danger of asteroid impacts, just as the dinosaurs were millions of years ago. Only now, we have the capability to understand these hazards and to do something about them! Edward Lu Astronaut, President and CEO of the B612 Foundation

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Acknowledgments

This project has been over 2 years in the making and has involved the dedicated effort of many people. To all of these expert authors from around the world, we extend our heartfelt thanks. We want to start by thanking our various editors from around the world. These include Dr. James Green of NASA, Dr. William Ailor of the Aerospace Corporation, Prof. Mikhail Marov of the Russian Academy of Science and the International Space University, and Tommaso Sgobba of the the International Association for the Advancement of Space Safety (IAASS). We also wish to thank the dedicated staff at Springer Press that helped give birth to the project, Ms. Maury Solomon and then those who diligently worked to see it through to completion including Ms. Barbara Wolf, Saskia Ellis, Nora Rawn, and Lydia Mueller. We enormously appreciate all of the people that, at some personal sacrifice of time and with expert effort, contributed the many scholarly and informative chapters that this reference work now represents. Joseph N. Pelton Firooz Allahdadi

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The Handbook Sponsors

The Handbook of Cosmic Hazards and Planetary Defense was undertaken under the sponsorship of four organizations. Although each of these four organizations has somewhat different missions, they are all dedicated to the peaceful uses of outer space and a better understanding of the cosmos in terms of its physics, its commercial potential and applications, and improved safety for humanity. The International Space University (ISU) seeks to develop the future leaders of the world space community by providing interdisciplinary educational programs to students and space professionals in an international, intercultural environment. The ISU also serves as a neutral international forum for the exchange of knowledge and ideas on challenging issues related to space and space applications. ISU programs impart critical skills essential to future space initiatives in the public and private sectors, while they also promote international understanding and cooperation; foster an interactive global network of students, teachers, and alumni; encourage the innovative development of space for peaceful purposes; and seek to improve life on Earth and advance humanity into space. It offers a Masters of Space Studies at its home campus in Strasbourg, France, a Space Studies Program that is hosted at sites around the world, an annual symposium, books and articles published by its worldwide faculty, and a wide range of other programs. The International Association for the Advancement of Space Safety (IAASS) was formed with the mission to create an international space safety culture. Its specific goals are to advance the science and application of space safety; to improve the communication, dissemination of knowledge, and cooperation between interested groups and individuals; to improve understanding and awareness of the space safety discipline; to promote and improve the development of space safety professionals and standards; and to advocate the establishment of safety laws, rules, and self-regulatory bodies at national and international levels and industrial level for the civil/commercial use of space. It accomplishes these goals through academic and training programs; the publishing of books, the Space Safety Magazine, and the Journal of Space Safety Engineering; as well as conferences, workshops, and other space safety-related programs. xiii

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The Handbook Sponsors

The Arthur C. Clarke Foundation was established at the White House in 1983 in Washington, D.C., as part of World Communications Year celebrations at the United Nations, an international event sponsored by the United Nations International Telecommunication Union (ITU). The Foundation was created to recognize and promote the extraordinary contributions of Arthur C. Clarke to the world and to promote the use of space and telecommunications technology for the benefit of humankind. The Foundation carries out a wide range of educational, training, publishing, and annual awards programs related to the broad field of science, outer space enterprise, and the relationship between human creativity and the development of scientific knowledge. The Foundation has played a role in the creation of the Arthur C. Clarke Institute for Modern Technologies in Sri Lanka, where Arthur C. Clarke lived for many years, and the creation of the Arthur C. Clarke Institute for Space Science Education that is associated with the National Center for Earth and Space Science Education in the Washington, D.C., area of the USA. Most recently the Foundation led the process that established Arthur C. Clarke Center on the Human Imagination in 2013. This interdisciplinary studies center is based at the University of California, San Diego. The International Institute of Space Commerce (IISC) was created with the goal to become the leading think tank in the study of the economics of space. It is intended to be the intellectual home for the industry and academic community around the world concerned with space activities, exploration, and applications. This institute performs studies and evaluations and provides services to all interested parties with the ultimate aim to promote and enhance world’s space commerce to the general public.

Contents

Volume 1 Part I Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

Introduction to the Handbook of Cosmic Hazards and Planetary Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joseph N. Pelton and Firooz Allahdadi

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Part II

Solar Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

35

Solar Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frederick M. Jonas

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Solar Flares and Impact on Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mikhail Ya. Marov and Vladimir D. Kuznetsov

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Part III

Coronal Mass Ejections . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Coronal Mass Ejections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maher A. Dayeh

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Fundamental Aspects of Coronal Mass Ejections . . . . . . . . . . . . . . . . . Carlos Alexandre Wuensche

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Part IV

Sun and Solar Wind Monitors

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Early Solar and Heliophysical Space Missions . . . . . . . . . . . . . . . . . . . Joseph N. Pelton

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NASA Wind Satellite (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adam Szabo

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Solar and Heliospheric Observatory (SOHO) (1995) . . . . . . . . . . . . . . B. Fleck and O. C. St. Cyr

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Contents

Solar Dynamics Observatory (SDO) . . . . . . . . . . . . . . . . . . . . . . . . . . . W. Dean Pesnell

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STEREO as a ‘Planetary Hazards’ Mission . . . . . . . . . . . . . . . . . . . . . M. Guhathakurta and B. J. Thompson

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Part V The Earth’s Natural Protective Systems and the Van Allen Belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Earth’s Natural Protective System: Van Allen Radiation Belts . . . . . . Sayavur I. Bakhtiyarov

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Part VI

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Cosmic Radiation

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Basics of Solar and Cosmic Radiation and Hazards . . . . . . . . . . . . . . . Joseph N. Pelton Medical Concerns with Space Radiation and Radiobiological Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tore Straume

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Solar Radiation and Spacecraft Shielding . . . . . . . . . . . . . . . . . . . . . . . David F. Medina

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Part VII

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Geomagnetic Storm and Substorm Missions . . . . . . . . . . .........

317

IMAGE Mission: Imager for Magnetopause-to-Aurora Global Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . James L. Green

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Cluster Technical Challenges and Scientific Achievements C. P. Escoubet, A. Masson, H. Laakso, M. G. G. T. Taylor, J. Volpp, D. Sieg, M. Hapgood, and M. L. Goldstein

International Sun Earth Explorers 1 & 2 . . . . . . . . . . . . . . . . . . . . . . . C. T. Russell

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ISAS-NASA GEOTAIL Satellite (1992) A. Nishida and Toshifumi Mukai Part VIII

The NOAA Space Weather Program . . . . . . . . . . . . . . . . .

399

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401

NOAA Satellites and Solar Backscatter Ultra Violet (SBUV) Subsystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Su-Yin Tan

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Dashboard Display of Solar Weather Su-Yin Tan

Contents

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Part IX Micrometeorites, Asteroids, and Comets . . . . . . . . . . . . . .

487

Comet Shoemaker-Levy 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frederick M. Jonas and Firooz Allahdadi

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Key Reports on Cosmic Hazards and Planetary Defense Issues and Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joseph N. Pelton

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Deep Impact and Related Missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michael F. A’Hearn and Lindley N. Johnson

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NASA’s Asteroid Redirect Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michele Gates and Lindley N. Johnson

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OSIRIS-REx Asteroid Sample-Return Mission . . . . . . . . . . . . . . . . . . . Dante S. Lauretta

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Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Harold J. Reitsema and Edward T. Lu Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Mainzer, J. Bauer, T. Grav, R. Cutri, J. Masiero, R. S. McMillan, C. Nugent, S. Sonnett, R. Stevenson, R. Walker, and E. Wright

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Volume 2 Part X

Ground-Based Discovery Efforts . . . . . . . . . . . . . . . . . . . . .

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European Operational Initiative on NEO Hazard Monitoring . . . . . . . Simonetta Di Pippo and Ettore Perozzi

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NEO Discovery and Follow-up Surveys . . . . . . . . . . . . . . . . . . . . . . . . . Donald K. Yeomans

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Part XI Impact Risk Assessment and Estimation . . . . . . . . . . . . . .

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Impact Risk Estimation and Assessment Scales Steve Chesley and Paul Chodas Part XII

Impact Consequences

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Airburst Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mark Boslough

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Water Impact Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Souheil M. Ezzedine and Paul L. Miller

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Part XIII

Contents

Information Resources . . . . . . . . . . . . . . . . . . . . . . . . . . .

717

Minor Planet Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gareth V. Williams and Timothy B. Spahr

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Part XIV

731

Defending Against Planetary Threats . . . . . . . . . . . . . . .

Defending Against Asteroids and Comets . . . . . . . . . . . . . . . . . . . . . . . David P. S. Dearborn and Paul L. Miller

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International Astronomical Union and the Neo Hazard . . . . . . . . . . . . Karel A. van der Hucht and Johannes Andersen

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NEOSHIELD - A Global Approach to Near-earth Object Impact Threat Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L. Drube, A. W. Harris, T. Hoerth, P. Michel, D. Perna, and F. Sch€afer

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United Nation Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joseph N. Pelton and Sergio Camacho-Lara

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Part XV

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Mounting Hazards of Man-Made Threats in Space . . . . .

Hazard of Orbital Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heiner Klinkrad

807

Nature of the Threat / Historical Occurrence . . . . . . . . . . . . . . . . . . . . Frederick M. Jonas

835

Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joseph N. Pelton

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Potentially Hazardous Asteroids and Comets . . . . . . . . . . . . . . . . . . . . Frederick M. Jonas and Firooz Allahdadi

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891

Strategies to Prevent Radiological Damage from Debris Curt Botts Part XVI

Future of Planetary Defense

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919

Active Orbital Debris Removal and the Sustainability of Space . . . . . . Joyeeta Chatterjee, Joseph N. Pelton, and Firooz Allahdadi

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Directed Energy for Planetary Defense . . . . . . . . . . . . . . . . . . . . . . . . . Philip Lubin and Gary B. Hughes

941

Economic Challenges of Financing Planetary Defense . . . . . . . . . . . . . Henry R. Hertzfeld and Pierre-Alain Schieb

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Contents

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International Cooperation and Collaboration in Planetary Defense Efforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007 Joseph N. Pelton International Legal Consideration of Cosmic Hazards and Planetary Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1027 Fabio Tronchetti Major Gaps in International Planetary Defense Systems: Operation and Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1045 Michael Potter Planetary Defense, Global Cooperation and World Peace . . . . . . . . . . 1055 Michael K. Simpson Regulatory Aspects Associated with Response to Man-Made Cosmic Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069 Ram S. Jakhu Risk Management and Insurance Industry Perspective on Cosmic Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1085 Scott Ross Glossary of Key Terms, Concepts, and Acronyms

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About the Editors

Joseph N. Pelton holds a PhD from Georgetown University and is the Executive Director Emeritus of the Space and Advanced Communications Research Institute (SACRI) at George Washington University. He is also the founder of the Arthur C. Clarke Foundation and founding President of the Society of Satellite Professionals International (SSPI). He also served as Dean and Chairman of the Board of Trustees of the International Space University, Director of the Interdisciplinary Telecommunications Program at the University of Colorado at Boulder, and Director of Strategic Policy at Intelsat. In addition, he is the former Executive Editor of the Journal of International Space Communications and is currently on the Editorial Board of Space Policy. Dr. Pelton is a Fellow of the International Association for the Advancement of Space Safety (IAASS) where he serves on the Executive Board and chairs their International Academic Committee. Dr. Pelton’s awards include the Outstanding Educator Award from the International Communications Association, the Public Service Satellite Consortium’s H. Rex Lee Award for Public Service, and the ISCe Award for Outstanding Educational Achievement. He received the 2001 Arthur C. Clarke Lifetime Achievement Award. He has made a number of media appearances on US television and radio, BBC radio, and CBC of Canada. Dr. Pelton is the author of hundreds of articles and 35 books in the fields of telecommunications and space policy and systems, including the Pulitzer Prize-nominated book Global Talk. This book also won the Eugene Emme Literature Award from the American Astronautics Society. Pelton is a member of the International Academy of Astronautics and an Associate Fellow of the AIAA, and most recently the UK Space Conference gave him an “Arthur” for his international space activities and the founding of the Arthur C. Clarke Foundation.

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About the Editors

Dr. Firooz Allahdadi served (1998–2011) at the HQ Air Force Safety Center in multiple capacities. He was the Center’s Senior Technical Advisor, Director of Air Force Space Safety Directorate, and the DoD representative in the Interagency Space Nuclear Safety Review Panel (INSRP). The INSRP is mandated by the US President to ensure the safe launching of all space missions containing nuclear payload. In 1998 Dr. Allahdadi employed rigorous first principle computational analysis as well field experimentation to revamp the Air Force’s operational weapons safety procedures and guidelines. This undertaking produced measurable operational efficiency and considerable real estate savings. Dr. Allahdadi pioneered the Directed Energy Weapons (DEW) Safety initiative and lead teams of experts to identify and quantify the entire DEW hazards spectrum. He authored the governing principals of DEW operation safety policies and procedures, AFPD 91-4, which have been benchmarked throughout the US military. As the DoD representative in INSRP, Dr. Allahdadi initiated far-reaching safety analyses, providing overarching technical oversight and garnering Presidential Launch authorization for the flawless Martian launches of “Spirit” and “Opportunity” in 2003; the “New Horizons Mission,” a journey to Pluto in 2005; and the landing of the nuclear-powered rover “Curiosity” on the surface of Mars in 2010. He founded and directed the Space Kinetic Impact and Debris Division (1990–1999) at the Air Force Research Laboratory in Albuquerque, New Mexico. In this capacity, he led teams of scientists and engineers to develop high-fidelity analytical tools to predict the dynamics of breakup and formation of the debris clouds resulting from space interactions. This technology was employed by a number of DoD contractors and government agencies to simulate potential space collision scenarios for purposes of national security planning. As a faculty member at the University of New Mexico (1980–1990), Dr. Allahdadi lectured on various topics in shock physics and transport phenomenon. At the same time, as a principle investigator he conducted research on a variety of critically important national defense programs which dealt with the dynamics of detonations and vulnerability of US military assets to tactical as well as strategic nuclear bursts. Dr. Allahdadi is a member of the National Research Council, Chief Editor of the International Society for Optical Engineering, and a Board Member and Fellow of the International Association for Advancement of Space Safety. He has authored over 100 scientific refereed journals and chaired many national and international conferences.

Section Editors

Section Editor, Joseph N. Pelton International Association for the Advancement of Space Safety, Arlington, VA, USA [email protected]

Section Editor, Firooz Allahdadi Space Science and Environmental Research, Applied Research Associates, Albuquerque, NM, USA [email protected]

Section Editor, Dr. Jim Green Planetary Science Division Director NASA [email protected] Dr. Green received his PhD in Space Physics from the University of Iowa in 1979 and began working in the Magnetospheric Physics Branch at NASA’s Marshall Space Flight Center (MSFC) in 1980. At Marshall, Dr. Green developed and managed the Space Physics Analysis Network that provided scientists all over the world with rapid access to data, to other scientists, and to specific NASA computer and information resources. In addition, Dr. Green was a Safety Diver in the Neutral Buoyancy tank making over 150 dives until he left MSFC in 1985. From 1985 to 1992 he was the head of the National Space Science Data Center (NSSDC) at Goddard Space Flight Center (GSFC). The NSSDC is NASA’s largest space science data archive. In 1992, he became the Chief of the Space Science Data Operations Office until 2005, when he became the Chief of the Science Proposal Support Office. While at GSFC, Dr. Green was a co-investigator and the Deputy Project Scientist on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission. He has written over 100 scientific articles in refereed journals

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Section Editors

involving various aspects of the Earth’s and Jupiter’s magnetospheres and over 50 technical articles on various aspects of data systems and networks. In August 2006, Dr. Green became the Director of the Planetary Science Division at NASA Headquarters. Over his career, Dr. Green has received numerous awards. In 1988, he received the Arthur S. Flemming award given for outstanding individual performance in the federal government and was awarded Japan’s Kotani Prize in 1996 in recognition of his international science data management activities.

Section Editor, Dr. William Ailor is a Distinguished Scientist with the Center for Orbital and Reentry Debris Studies at the Aerospace Corporation in El Segundo, California. He has chaired or co-chaired nine international conferences, including five on protecting Earth from asteroids, and served on the United Nations subcommittee that developed protocols for international cooperation in the event a threatening asteroid or comet is discovered. He testified to Congress and was featured on NBC Nightly News, CBS Evening News, ABC News, and CNN as an expert on the Leonid meteor storm’s possible effects on satellites during the period of the storm. He is also known for his expertise in space debris and reentry breakup and has appeared on CNN, the Discovery Channel, and the Learning Channel on these topics. He testified to the Columbia Accident Investigation Board on what might be learned from recovered debris. He provided expert commentary during the reentry of the Upper Atmosphere Research Satellite (UARS) in 2011. In his private life, Dr. Ailor founded the Palos Verdes Peninsula Land Conservancy in 1988 and served as its president for 18 years. During that time, the organization preserved over 1000 acres of natural open space.

Section Editors

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Section Editor, Tommaso Sgobba Executive Director, International Association for the Advancement of Space Safety (IAASS) Noordwijk The Netherlands http://iaass.space-safety.org T. Sgobba is Executive Director, former President, and co-founder of the International Association for the Advancement of Space Safety, which gathers top space safety experts worldwide. He is also Board Member of the US-based International Space Safety Foundation (ISSF). Until June 2013 Tommaso Sgobba has been responsible for flight safety at the European Space Agency (ESA), including human-rated systems, spacecraft reentries, space debris, use of nuclear power sources, and planetary protection. T. Sgobba joined the European Space Agency in 1989, after 13 years in the aeronautical industry. Initially he supported the developments of the Ariane 5 launcher, several Earth observation and meteorological satellites, and the early phase of the Hermes spaceplane. Later Mr. Sgobba became product assurance and safety manager for all European manned missions on Shuttle, MIR station, and for the European research facilities for the International Space Station. During his long and close cooperation with the NASA Shuttle/ISS Payload Safety Review Panel, Mr. Sgobba developed at ESA the safety technical and organizational capabilities that eventually led in 2002 to the establishment of the first ESA formal safety review panel and first International Partner ISS Payload Safety Review Panel. He was also instrumental in setting up the ESA Re-entry Safety Review Panel and to organize the first ESA scientific observation campaign of a destructively reentering spacecraft (ATV Jules Verne). T. Sgobba holds an M.Sc. in Aeronautical Engineering from the Polytechnic University of Turin (I), where he has been also professor of space system safety (1999–2001). T. Sgobba has published several articles and papers on space safety and has co-edited with two NASA colleagues the textbook Safety Design for Space Systems, published in 2009 by Elsevier, which is the first of its kind worldwide. In 2011 the book was translated into Chinese. He was Chief Editor of the follow up book Safety Design for Space Operations, published in 2013. Mr. Sgobba also co-edited the book entitled The Need for an Integrated Regulatory Regime for Aviation and Space, published by Springer in 2011. Mr. Sgobba is Managing Editor of the Journal of Space Safety Engineering and member of the editorial board of the Space Safety Magazine. Mr. Sgobba received the NASA recognition for outstanding contribution to the International Space Station in 2004 and the prestigious NASA Space Flight Awareness (SFA) Award in 2007.

The Authors

Michael F. A’Hearn Department of Astronomy University of Maryland 20742-2421 College Park MD USA [email protected] Michael A’Hearn is a Professor Emeritus and Research Professor at the University of Maryland, having retired in 2011 as a Distinguished University Professor of Astronomy. He has been affiliated with the University of Maryland since completing graduate school in 1966. Prior to his work with deep space missions, he studied comets by remote sensing at all wavelengths from the far ultraviolet to the radio regime, using both ground-based and space-based telescopes. He was the Principal Investigator for the Deep Impact mission and for the EPOXI mission (the extended mission for the Deep Impact spacecraft). He was a co-investigator for the Stardust-NExT mission and is currently a co-investigator for two of the instrument teams on ESA’s Rosetta mission. He has twice received the NASA Medal for Exceptional Scientific Achievement, once for Deep Impact and once for EPOXI. He is an author of more than 200 refereed papers in scientific journals, the majority of them related to comets. The photo shows him in the clean room at Ball Aerospace and Technology Corporation in Boulder CO. He is examining the cratering mass, the spherical cap with about 1/3 the mass of the impactor spacecraft and made of copper that was designed to optimize the cratering effects of the impactor spacecraft on the Deep Impact mission. The use of copper, from the noble metal column of the periodic table, minimized reactions with water or ice in the comet that would have led to very bright emission lines if the mass were made of the more usual aluminum or any other material from another column of the periodic table.

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Firooz Allahdadi Space Science and Environmental Research, Applied Research Associates, Albuquerque, NM, USA [email protected]

Johannes Andersen was born in 1943 and graduated in 1969 from the University of Copenhagen, Denmark, where he was first a postdoc, from 1972 a professor of astronomy, earning a DSc degree in 1991. In 2002–2013 he served as Director of the Nordic Optical Telescope, La Palma, Canarias, Spain. His principal research interests are in stellar and galactic evolution and in development of astronomical (mostly spectroscopic) instrumentation and detectors. In these fields he has observed over 700 nights at ESO and other observatories and authored nearly 400 scientific papers with over 10,000 citations. He chaired the ESO Scientific Technical Committee in 1993–1995 and served as General Secretary of the International Astronomical Union (IAU) 1997–2000 and on the Council and Bureau of COSPAR 1997–2002, on the Board and Telescope Directors’ Forum of the EU-funded I3 OPTICON, and on the Board of the ERA-NET ASTRONET (chair 2005–2010).

Dr. Sayavur I. Bakhtiyarov is an Associate Professor at New Mexico Institute of Mining and Technology (Socorro, NM, USA). Dr. Bakhtiyarov obtained a PhD degree from the Russian Academy of Sciences in 1978 and in 1992 a DSC degree from the Azerbaijan National Academy of Sciences. Dr. Bakhtiyarov authored 350+ scientific publications in refereed scholarly journals, books, international conferences, and symposia proceedings and 14 patents. From 2005 to 2010 he was a Program Director of US DOE and NASA research projects. From 2011 to 2014 Dr. Bakhtiyarov was a Chief Scientist at Space Safety Division of the US Air Force Safety Center (Kirtland, NM, USA) and a DOD Permanent Coordinator of Interagency Nuclear Safety Review Panel (INSRP). He was an INSRP DOD Coordinator for NASA’s Mars Science Lab (MSL) mission in 2011. Dr. Bakhtiyarov is a lead organizer of ASME annual symposia and forums; Editor in Chief of two International Journals, Mechanics and Solids (IJM&S) and Manufacturing Science and Technology (IJMS&T); Editorial Board Member of I-manager’s Journal on Engineering and Technology (IJET), Mathematics Applied in Science and Technology (MAST), International Journal of Applied

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Engineering Research (IJAER), International Journal of Dynamics of Fluids (IJDF) and Far East Journal of Mathematics (FEJM).

James “gerbs” Bauer (JPL/IPAC) is Deputy PI of the NEOWISE project and lead scientist for the WISE Moving Object Pipeline Subsystem. He obtained his PhD in Astronomy from the University of Hawaii’s Manoa campus in 2003. He studies comets, centaurs, and related small bodies in the outer solar system.

Mark Boslough received his PhD in Applied Physics from Caltech and joined Sandia National Laboratories in 1983, where he has worked on many aspects of impact physics including NMR spectroscopy of shocked sandstone, testing space-station debris shields, and analyzing satellite observations of fireballs. In 1994 he was a member of a team that gained international recognition for using a supercomputer to correctly predict the effects of the impact of Comet Shoemaker-Levy 9 on Jupiter. His current impact research is focused on computational modeling of airbursts and their effects. He participated in expeditions to airburst sites in the Libyan Desert of Egypt in 2006 and to Tunguska in Siberia in 2008. He has collaborated on research to understand Asteroid 2008 TC3, its spectacular airburst over northern Sudan, the recovery of its meteorites, and its implications for understanding the impact threat. He served on the asteroid mitigation panel for the National Research Council and coauthored the report “Defending Planet Earth” that was delivered to Congress in 2010. In 2013 he was the first US scientist to visit the site of the Chelyabinsk airburst in Russia to begin the process of documentation, appearing in two episodes of PBS NOVA. His simulation of that event appeared on the cover of Nature.

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Mr. Curt Botts is Chief of the Launch Safety Branch, 45th Space Wing Safety Office, Patrick Air Force Base, Florida. The 45th Space Wing executes and maintains Air Force spacelift operations; operates, maintains, and secures the Eastern Range; and supports ballistic missile test launches, aircraft tests, manned civil space launch operations, and commercial spacelift operations licensed by Federal Aviation Administration in accordance with National Space Policy and Public Law. Mr. Botts serves as the senior civilian advisor to the 45th Space Wing Chief of Safety on matters relating to flight analysis, risk analysis, and safety policy. Mr. Botts also serves as the Interagency Nuclear Safety Review Panel Launch Abort Working Group Chairman evaluating risks for space nuclear power system launches and reporting to the President’s Office of Science and Technology Policy. He has 30 years experience with Launch Operations and Safety.

Dr. Sergio Camacho-Lara Sergio Camacho-Lara Centro Regional de Ensen˜anza de Ciencia y Tecnologı´a del Espacio para Ame´rica Latina y el Caribe (CRECTEALC), Tonantzintla, Puebla, Me´xico. Dr. Sergio Camacho-Lara is the secretary-general of the Regional Centre for Space Science and Technology Education for Latin America and the Caribbean. He was Director of the United Nations Office for Outer Space Affairs and Chief of the Space Applications Section and the Committee Services and Research Section in the same office. He worked on the organization of the Third United Nations Conference on the Exploration and Peaceful Uses of Outer Space (UNISPACE III) and on implementing its recommendations, including the establishment of the International Committee on GNSS. Prior to joining the United Nations, he carried out research on the interaction of electromagnetic radiation with matter at the Instituto de Geofı´sica, Universidad Nacional Auto´noma de Me´xico. He obtained his PhD from the University of Michigan.

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Joyeeta Chatterjee recently graduated from the Institute of Air and Space Law, McGill University, Canada. The topic of her master’s thesis focused on the legal aspects of active removal of debris and on-orbit satellite servicing. She was awarded the Nicolas Mateesco Matte Prize 2011–2012 for outstanding performance in space law by the Faculty of Law, McGill University. Joyeeta obtained her undergraduate law degree from Gujarat National Law University, India in 2011. Additionally, she is an alumnus of the International Space University’s Southern Hemisphere Summer Space Program 2011. Joyeeta’s research interests include public international law and international and national space law and policy – particularly, the legal aspects of space sustainability, commercial human spaceflight, and exploitation of planetary resources. Owing to her passion in space outreach activities and international space collaboration, she is involved with the Space Generation Advisory Council, a youth organization in support of the United Nations Programme on Space Applications which works to promote the views of the youth on space activities. In recognition of her contributions to the organization, she was awarded the 2011 SGAC Young Leader Award at the Space Generation Congress, Cape Town.

Dr. Steven Chesley is an expert in asteroid and comet orbit determination with NASA’s NEO Program Office at the Jet Propulsion Laboratory. He led the development of JPL’s Sentry System – an automatic process that updates the orbits of recently observed NEOs and assesses their hazard to Earth. Dr. Chesley led the team that reported the first detection of the Yarkovsky effect acting on a specific asteroid in 2003. His spaceflight project experience includes NEAR-Shoemaker navigation and the comet ephemeris development for the last five NASA cometspacecraft encounters, most recently the EPOXI mission to Comet Hartley 2 and the Stardust-NExT mission to Comet Tempel 1. As a member of the OSIRIS-REx Science Team, he is responsible for the Yarkovsky effect investigation and asteroid ephemeris development. He is a recipient of NASA’s Exceptional Engineering Achievement Medal, and asteroid 12104 Chesley is named in his honor.

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Paul Chodas is a senior scientist at the Jet Propulsion Laboratory where he has computed trajectories of asteroids and comets for over 30 years. He received a B. Math. from the University of Waterloo, Canada, in 1975 and an M.A.Sc. and PhD in Aerospace Engineering from the University of Toronto in 1980 and 1986. He was the principal architect for much of JPL’s small body software that determines orbits of asteroids and comets, computes future trajectories, detects close approaches, and calculates impact probabilities. Paul coined the term “keyhole” in connection with asteroid close approaches that can lead to later impacts and is currently coordinating the search and characterization of candidate targets for NASA’s proposed Asteroid Redirect Mission.

Dr. Cutri, IPAC Deputy Executive Director, was the data processing lead scientist for the Two-Micron All Sky Survey (2MASS) project which involved about two dozen staff members from IPAC, for which he won the 2007 James Craig Watson Medal from the National Academy of Sciences.

Maher Al Dayeh was born in Kefraya, Lebanon. After receiving a Bachelor’s degree in Physics, he moved to the USA where he earned an M.Sc. in Atmospheric Physics and PhD in Space Physics from the Florida Institute of Technology in Melbourne, Florida. He then worked as a postdoctoral researcher at the Space Science and Engineering Division at the Southwest Research Institute in San Antonio, Texas, where he is currently a research scientist. Maher has worked and published in diverse research of areas in space and atmospheric physics. His research interests include atmospheric electricity, microphysics of lightning and thunder, space weather, interplanetary transport and acceleration of solar energetic particles, heliospheric and magnetospheric energetic

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neutral atom emissions, and the development of novel radiation and particle detectors. Maher has served on several NSF and NASA review panels and chaired numerous sessions in relevant scientific meetings. He has authored/coauthored over 50-refereed publications and presented numerous contributed talks/posters at national and international conferences and workshops. He is affiliated with the American Geophysical Union, the American Association for the Advancement of Science, and the Physics Honor Society Sigma Pi Sigma.

Dr. Dearborn is a graduate of UCLA (B.A., 1970) and the University of Texas at Austin (PhD, 1975) and has held positions at the Copernicus Institute in Warsaw, the Institute of Astronomy in Cambridge, the California Institute of Technology, and Steward Observatory in Tucson. For the last 30 years, he has been a research physicist/astrophysicist at the Lawrence Livermore National Laboratory (LLNL). While most of his LLNL research has supported programmatic efforts, he has maintained an active presence in astrophysics and recently become involved in planetary physics (asteroid deflection). He has also published significantly in Andean studies (particularly Inca Astronomy).

Simonetta Di Pippo, Master’s Degree in Astrophysics and Space Physics at the Univ. “La Sapienza” in Rome, Italy, in 1984, joined the Italian Space Agency (ASI) in 1986. Her responsibilities there ranged from Earth observation to automation and robotics and science to human spaceflight. She took up duty as Director of the Observation of the Universe in 2002. After having served as Director of Human Spaceflight at the European Space Agency (ESA) from 2008 to 2011, she went back to ASI leading the European Space Policy Observatory at ASI – Brussels until March 2014. Starting from June 2009, she is President and co-founder of the international association Women in Aerospace Europe (WIA-E), with legal base in the Netherlands and with the main aim of expanding the women representation and leadership in the aerospace sector. Knighted by the President of the Italian Republic in 2006, the International Astronomical Union in 2008 assigned the name “dipippo” to asteroid 21887, in recognition of her effort in space exploration. Author of more than 60 publications and more than 700 articles

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and interviews on magazines and newspapers, member and president of scientific committees of international congresses, and member and president of scientific awards’ jury, she has been teaching at various universities, including the George Washington University in Washington, D.C., and the LUISS Business School in Rome. From November 1, 2013, she was a visiting scholar at CalPoly, CA. She is the author of a blog on LaStampa.it devoted to provide information about the use of satellites and space activities to improve the quality of life on Earth, called SpazioGreen, and she is also member of the editorial board of the NewSpace Journal. In May 2013 she got from St. John University in Vinovo (TO) an Honoris Causa Degree in Environmental Studies. Since April 2013 she is member of the Global Board Ready Women, the list of potential top managers created by European Business Schools in the framework of the Women on Boards Initiative. She was appointed Academician of the International Academy of Astronautics (IAA) in July 2013. She is chairing since July 2012, on behalf of the Academy, the study on “Public/Private Human Access to Space” with the aim of analyzing on a global scale the potential market development for commercial human spaceflight. On March 23, 2014, she took up duty as the new Director of the Office for Outer Space Affairs at the United Nations. She is considered one of the most expert worldwide leaders in international cooperation in the aerospace sector.

Line Drube is a planetary scientist born in Denmark and educated at the Niels Bohr Institute of the University of Copenhagen; the Earth, Planetary, and Space Science Department of the University of California, Los Angeles (UCLA); and the International Space University. She received her PhD in 2011 for a thesis entitled “Martian Airborne Dust – Magnetic Properties Experiment on Phoenix and Dust on the MSL Calibration Target” (supervised by Morten Bo Madsen). While working for her PhD she became a member of the Atmospheric Science Team at the Phoenix Mars Lander Science Operation Center in Tucson and served as downlink engineer for the Robotic Arm Camera on the Phoenix Mission. Her PhD thesis is partly based on the results of research carried out using relevant instruments on the mission. Since 2012 Drube has worked at the German Aerospace Center’s (DLR) Institute of Planetary Research in Berlin as a postdoctoral researcher under the supervision of Alan Harris, the Coordinator of the European Commission’s NEOShield project “A Global Approach to Near-Earth Object Impact Threat Mitigation.” She is researching the physical properties of NEOs from the point of view of mitigation of impact threats and the requirements for NEOs to be used as targets in mitigation demonstration missions. In the Action Team 14 of the UN’s Committee on the Peaceful Uses of Outer Space, she has worked on the team’s recommendations to the UN for a coordinated international response to the NEO impact threat. She plans

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to continue this work as a member of the German delegation to the newly formed UN Space Missions Planning Advisory Group.

C. Philippe Escoubet Mission Manager and Project Scientist for the Cluster mission at the European Space Agency (ESA) Dr. Escoubet obtained his PhD in 1989 at the Universite Paul Sabatier Toulouse, France. After a postdoc at NASA Goddard Space Flight Centre, he joined ESA in 1991, first as postdoc and then as Cluster Deputy Project Scientist in 1993. In 1997 he became Cluster Project Scientist and Cluster Mission Manager in 2007. Dr. Escoubet’s main scientific interest is the Sun-Earth connection and in particular solar wind plasma entry in the magnetosphere. In 2001 he became Project Scientist of the first Chinese-European program called Double Star, of which he became Mission Manager in 2007. From 2007 to 2009 he was also study scientist for the Cross‐ Scale mission study in the ESA Cosmic Vision program. From 2009 to 2012 he was acting coordinator for solar system missions. Dr. Escoubet specializes in data analysis of plasma, electric, and magnetic field instruments on low-altitude spacecraft (Aureol-3 and DE-2) and magnetospheric spacecraft (ISEE-1, Polar, Cluster, Double Star, and THEMIS). He is a co-investigator on various space missions: Cluster (CIS and ASPOC instruments), SMART-1 (SPEDE), Double Star (ASPOC and HIA), THEMIS, BepiColombo (PICAM), and MMS (ASPOC). He is author or coauthor of more than 115 refereed publications.

Dr. Ezzedine is an applied mathematician and statistician at Lawrence Livermore National Laboratory. Dr. Ezzedine earned his PhD from E´cole Nationale Supe´rieure des Mines de Paris, was a postdoctoral researcher at UC Berkeley and UC Davis, and has 10 years of consulting experience. His interests include CFD, structural analysis, probabilistic assessment, uncertainty quantification, reservoir engineering, geophysics, inverse problem, and parallel computing. Dr. Ezzedine serves on several national and international scientific committees and associate editor boards. He is a registered professional engineer with the state of California, a Board Member of the Society of Petroleum Engineering, and a lecturer at several universities around the San Francisco Bay area. Dr. Ezzedine holds several awards and honors.

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Bernhard Fleck received his PhD in Physics from the University of W€urzburg, Germany. In 1993 he joined ESA’s Space Science Department at ESTEC in Noordwijk, the Netherlands, to work on the SOHO project. With the launch of SOHO in 1995, his duty station moved to NASA’s Goddard Space Flight Center in Greenbelt, Maryland. In 1998 he became SOHO Project Scientist. His research interest is the dynamics of the solar atmosphere, in particular wave propagation characteristics in the chromosphere.

Dr. Gates has served the National Aeronautics and Space Administration for more than 20 years. She serves as Senior Technical Advisor to the Associate Administrator for Human Exploration and Operations at NASA Headquarters. She is also currently leading NASA’s Asteroid Redirect Mission planning and implementation efforts. Prior to this role, Dr. Gates served in a temporary assignment as the Deputy Associate Director for Earth Science Projects Continuity Missions at the Goddard Space Flight Center, where she provided overall programmatic guidance during the formulation and baseline of several earth science missions. Dr. Gates began her career in space radiation effects engineering at the Goddard Space Flight Center. She has a Bachelor’s, Master’s, and PhD in Aerospace Engineering from the University of Maryland at College Park. Melvyn Goldstein has been at Goddard since 1972. At present, he is a member of the Heliospheric Physics Laboratory. In 2006, he was elected a Fellow of the American Geophysical Union. He has been involved with the Cluster project since its inception and has served as the NASA Project Scientist since 1984. His research focuses on a variety of nonlinear plasma processes that can be elucidated using data from the four Cluster spacecraft and other spacecraft. In addition, Dr. Goldstein has participated in large and complex simulations of the origin of magnetohydrodynamic turbulence in the solar wind. He is also Principal Investigator of an Interdisciplinary Science grant that supports NASA’s Magnetospheric Multiscale Mission.

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Tommy Grav’s research interests are focused on the study of minor planets in the solar system, particularly the objects heavily influenced by the giant planets, like the Jovian Trojans, Centaurs, Trans-Neptunian Population, irregular satellites, and comets. These populations provide important clues and constraints on the formation and migration of the giant planets in the early solar system. These populations also provide potential sources of material that may have remained more or less unaltered since the early times of our solar system. Dr. Grav got his PhD. (Dr. Scientiarum) in Astronomy from the University of Oslo, Norway, with the thesis “Physical and Dynamical Properties of the Irregular Satellites of the Giant Planets” under supervision of Prof. Kaare Aksnes. The research for his thesis was performed as a predoctoral fellow at the HarvardSmithsonian Center for Astrophysics under the guidance of Dr. Matthew J. Holman. He joined the Pan-STARRS project at the University of Hawaii in 2004 as a Junior Research Scientist and was part of the development team for the Moving Object Processing System (MOPS). In 2007 he joined the Johns Hopkins University as an Associate Research Scientist and joined their efforts as part of the Pan-STARRS 1 Science Consortium. He is a science team member with the Pan-STARRS 1 project and the lead of the Pan-STARRS effort on the study of the Centaur population. In 2008 he joined the science team for the NEOWISE project, a solar system augmentation to the Wide-Field Infrared Survey Explorer (WISE), a NASA Explorer class mission. He is part of the small development team for the WISE Moving Object Processing System (WMOPS), which successfully identified more than 157,000 moving objects, of which more than 33,000 were new discoveries, in the WISE survey. He is leading the NEOWISE project efforts in deriving diameter and albedo distributions for the Hilda and Jovian Trojan populations. He is also intimately involved with the efforts concerning the near-Earth object (NEO), mainbelt, comet, and Centaur populations. Dr. Grav is also a science team member on two of the missions selected for category III as part of the 2010 NASA Discovery Announcement of Opportunity. NEOCam (PI Amy Mainzer, JPL) is a next-generation infrared NEO survey, while Whipple (PI Charles Alcock, Harvard-Smithsonian Center for Astrophysics) is an occultation survey for distant TNOs and Oort cloud objects. Asteroid 12309 Tommygrav has been named after Dr. Grav.

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Madhulika (Lika) Guhathakurta is the Lead Program Scientist for the Living With a Star Program at the National Aeronautics and Atmospheric Administration headquarters in Washington, D.C. LWS focuses on understanding and ultimately predicting solar variability and its diverse effects on Earth, human technology, and astronauts in space. The systems science behind this new kind of weather outside of Earth’s terrestrial atmosphere is known as “space weather.” Dr. Guhathakurta also leads an international initiative known as the International Living With a Star that brings together all the space agencies of the world to contribute towards the scientific goal for space weather (http:// ilwsonline.org/). In addition to leading science missions for the LWS program, she also manages a theory, modeling, and data analysis program to integrate scientific output, data, and models to generate a comprehensive, systems understanding of Sun-Heliosphere-Planets coupling. She is a scientist devoted to the new discipline known as heliophysics. Dr. Guhathakurta has served as co-chair and now serves as an active member on the interagency group known as the Committee on Space Weather of the National Space Weather Program (http://www.nswp.gov/) and NASA lead on the Space Weather Agenda item for UNCOPUOS. Education and outreach is another strong passion of Dr. Guhathakurta. To that effect she has helped create graduate level textbooks in heliophysics (http://www.vsp.ucar.edu/ Heliophysics/). To popularize heliophysics, she has partnered with the American Museum of Natural History, NY, to produce two popular full dome planetarium shows that are being showed internationally and used by teachers to excite the next generation of space scientists. She also helped produce a 3D IMAX show utilizing the observations from the STEREO mission. Dr. Guhathakurta has worked as an educator, scientist, and mission designer, directed and managed science programs, and has built instruments for spacecraft.

M. Hapgood RAL Space/STFC, Harwell, Oxford, UK [email protected]

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Alan Harris was born in Birmingham, UK, and received B.Sc. and PhD degrees in physics from the University of Leeds, UK, in 1973 and 1977, respectively. He has held positions at the Max Planck Institute for Astronomy in Heidelberg, Germany, and at the Rutherford Appleton Laboratory, UK. Harris is now a DLR Senior Scientist at the German Aerospace Center’s (DLR) Institute of Planetary Research in Berlin and holds an Honorary Chair at Queen’s University Belfast, UK. He leads research projects in solar system science, including observations and modeling of the physical properties of asteroids, and has pioneered radiometric data analysis techniques applicable to the study of small asteroids. He supervises research students and lectures at universities. Harris has served as Chairman of the European Space Agency’s (ESA’s) Near-Earth Object Mission Advisory Panel (NEOMAP) and was a member of ESA’s Solar System Exploration Working Group from 2010 to 2012. He is a member of the United Nations Action Team 14 on nearEarth objects, reporting to the UN Committee for the Peaceful Uses of Outer Space, and is a member of the International Asteroid Warning Network and the Space Mission Planning Advisory Group, both of which have been recently established to undertake and coordinate actions relating to NEO impact mitigation under the auspices of the UN. As of January 2012 he is the Coordinator of the 13-partner, 5.8 million euro, European Commission’s NEOShield project “A Global Approach to Near-Earth Object Impact Threat Mitigation.” Harris is a Fellow of the Royal Astronomical Society, a member of the Division for Planetary Sciences of the American Astronomical Society, and a member of the International Astronomical Union. In recognition of his research the main-belt asteroid numbered 7737 was named after him in July 1999.

Dr. Henry R. Hertzfeld is a Research Professor of Space Policy and International Affairs at the Space Policy Institute, Center for International Science and Technology Policy, Elliott School of International Affairs, George Washington University. He is also an Adjunct Professor of Law at GW. He is an expert in the economic, legal, and policy issues of space and advanced technological development. Dr. Hertzfeld has served as a Senior Economist and Policy Analyst at both NASA and the National Science Foundation and is a consultant to both US and international agencies and organizations. He is author of many articles on the economic and legal issues concerning space

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and technology. Dr. Hertzfeld is a member of the Bar in Pennsylvania and the District of Columbia. He can be contacted at [email protected] or hhertzfeld@law. gwu.edu.

Tobias Hoerth is a research fellow at Fraunhofer Institute for High-Speed Dynamics, Ernst-MachInstitut, EMI in Freiburg, Germany. He studied geophysics at Karlsruhe Institute of Technology (KIT). In 2010 he started his position at EMI in the field of experimental impact cratering research as a member of the MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network) research group funded by the German Research Foundation (DFG). Within MEMIN he conducted intensive research in the field of cratering experiments and investigation of the highly transient processes associated with hypervelocity impacts. Within the European Commission’s NEOShield project “A Global Approach to Near-Earth Object Impact Threat Mitigation” he is working on momentum transfer measurements during hypervelocity impact experiments. Furthermore, he is investigating dynamic behavior of geological materials to derive material models required for numerical impact simulations. He is author or coauthor of several peer-reviewed articles in the field of experimental impact cratering.

Gary B. Hughes is an assistant professor in the Statistics Department at California Polytechnic State University in San Luis Obispo, CA. He received his PhD in Earth and Environmental Science from the University of Pennsylvania. His primary work involves numerical and statistical modeling of physical systems, aiming to incorporate stochastic elements in models that mimic natural variability of the systems.

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Dr. Ram S. Jakhu is a tenured Associate Professor at the Institute of Air and Space Law, Faculty of Law, of McGill University in Montreal, Canada, where he teaches and conducts research in international space law, law of space applications, law of space commercialization, government regulation of space activities, law of telecommunications and Canadian communications law, and public international law. He served as Director of the Centre for the Study of Regulated Industries, McGill University, 1999–2004. He served as the First Director of the Masters Program of the International Space University, Strasbourg, France, 1995–1998. He has authored 2 books, more than 60 articles, and more than 20 research reports and edited 4 books, including the one that received the 2011 Social Sciences Book Award from the International Academy of Astronautics. Dr. Jakhu chaired three international interdisciplinary congresses dealing with space debris mitigation, remediation, and on-orbit serving and presented their reports to the United Nations Committee on Peaceful Uses of Outer Space. He is a member of the Space Security Council of the World Economic Forum and a “Fellow” as well as the Chairman of the Legal and Regulatory Committee of the International Association for the Advancement of Space Safety. In 2007, he received a “Distinguished Service Award” from the International Institute of Space Law for significant contribution to the development of space law. He holds Doctor of Civil Law (Dean’s Honors List) and Master of Law (LL.M.) degrees from McGill University, Canada, as well as LL.M., LL.B., and B.A. degrees from Panjab University, India.

Lindley Johnson is NASA’s Program Executive for the Discovery Program of mid-class solar system exploration missions and for the Near-Earth Object Observations Program. Prior to NASA he served 23 years of Air Force active duty, obtaining the rank of lieutenant colonel and 15 major medals and awards while working a variety of national security space systems. After joining NASA, he was the Program Executive for NASA’s Deep Impact mission to Comet Tempel 1, launched in January 2005 to deliver an impact probe to the comet’s surface on July 4 that year and explore the composition of short-period comets. NASA’s NEO Observations program has discovered over 8,000 near-Earth asteroids, over 80% of the total known, since Lindley became its manager. Lindley received NASA’s Exceptional Achievement Medal for his work on comet and asteroid missions. Asteroid 5905 (1989 CJ1) is named Johnson to recognize Lindley’s efforts in detecting near-Earth objects.

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His photo shows him standing in the basement vault of the Smithsonian National Museum of Natural History that contains its extensive meteorite collection. The “layer cake” he is holding is actually a preserved sample of Earth’s sediment from about 65 million years ago. The finger-width layer of light sediment he is pointing out is iridium enriched and believed to have been laid down from ejecta of the asteroid impact thought to have caused the demise of the dinosaurs.

Frederick (Fred) Morgan Jonas, Ph.D. 8208 Copper Leaf Trail, NE, NM 87122 (505) 856-8320 [email protected] Dr. Jonas is an experienced professional aerospace engineer with some 40+ years experience in the design, development, and test of air and space systems. Born and raised in Gallup, New Mexico, Dr. Jonas spent 20 years in the Air Force as a research and development officer and then 20+ years as an aerospace contractor in the defense industry. He has a Bachelor of Science degree in Aeronautical Engineering from the US Air Force Academy, a Master of Science degree in Aeronautical and Astronautical Engineering from Stanford University, and a Doctorate degree in Aeronautical Engineering with a Heat Transfer minor from the Air Force Institute of Technology (Distinguished Graduate). Dr. Jonas is a member of Tau Beta Pi and holds a patent. He has a wide range of research and publications in the fields of space studies and the space environment. Initial activities involved the assessment of engineering models of the orbital man-made debris (space debris) environment developed by NASA in the late 1980s and early 1990s for use by the Air Force. This led to the initial development of more sophisticated computational models of this environment by the Air Force in order to assess the hazard to Air Force space systems. Understanding the man-made space environment then led to a study to define the complete near-earth space environment for typical Air Force systems and orbits. Following this, Dr. Jonas led the contract team supporting the now closed Air Force Malabar Test Facility, a ground-based facility used by the Air Force to image and track space objects and space experiments. Next, Dr. Jonas supported the design and development of an Air Force Space-Based Radar (SBR) concept and specifically performed as the thermomechanical lead for the development of the Transmit/Receive Antenna Module (TRAM) that was being developed for the SBR antenna. This included the design and development of a space experiment for a receive-only TRAM (or RAM) to test the thermomechanical design in the actual space environment. The experiment was successfully launched as part of the STRV-1d research satellite; however, the satellite failed on orbit (and still orbits as “space debris” today). As part of this study Dr. Jonas developed models of the expected thermal response of the antenna in low earth orbits. In the next activity Dr. Jonas led a team

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to develop and demonstrate a soldier-carried integrated sensor and satellite-based communication system for near-real-time information exchange as notionally part of the Space-Based Soldier System. An integrated soldier-carried system was developed that included an uncooled infrared (IR) sensor, GPS, triaxial accelerometers, and an accelerometer. The prototype system was successfully demonstrated in a field exercise that included communication with overhead assets. As part of this activity, Dr. Jonas was part of a patent, #36810293, for a Compact Integrated SelfContained Surveillance Unit (2004). Other space-related experience includes the development of unique space-based transportation concepts, the development of strategic plans for the continued development of space-based IR sensor systems, and an assessment of the state of laser communication technology regarding space applications. Finally, Dr. Jonas is an avid amateur cosmologist and astronomy enthusiast. Living now in Albuquerque, New Mexico, Dr. Jonas and wife Sandra have five children, six grandchildren, and great-grandchildren as well.

Donald J. (Don) Kessler retired from NASA in 1996 as NASA’s Senior Scientist for Orbital Debris Research. He began his career at NASA modeling the interplanetary meteoroid environment and later applied these modeling techniques to artificial satellites in Earth orbit. These models predicted that the hazard from man-made orbital debris soon would exceed the hazard from the natural meteoroid environment. This prediction, combined with an increasing amount of supportive data, led to the development of today’s international orbital debris program. Since retiring, he has continued to consult with NASA and other organizations. Don has published more than 100 technical papers on meteoroids and orbital debris and has been a contributing author or editor of 10 major reports. However, he may be recognized by the general public for the “Kessler Syndrome,” a term propagated by the popular press to describe his 1978 publication. This publication predicted an increasing orbital debris environment from random collisions between satellites, which is being observed today. His awards include the NASA Medal for Exceptional Scientific Achievement, the AIAA Losey Atmospheric Sciences Award, the IAASS Jerome Lederer Space Safety Pioneer Award, and the AAS Dirk Brouwer Award “For first recognizing, then defining and researching the Earth’s orbital debris hazard during his half-century career in astrodynamics.” His recent activities include supporting the National Research Council to assess NASA’s orbital debris program and the NASA Engineering and Safety Center to assess orbital debris models.

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Prof. Dr. Heiner Klinkrad Head of Space Debris Office European Space Agency Heiner Klinkrad graduated from the Braunschweig University of Technology (TUBS) in aeronautical engineering in 1980, and he received his PhD from the same university in 1984. In 1980 he joined the European Space Agency, where today he is head of the Space Debris Office at the European Space Operations Centre, ESOC, in Darmstadt, Germany. In his current position he is ESA’s focal point and senior advisor for space debris matters, and he represents ESA, for instance, in the multinational Inter-Agency Space Debris Coordination Committee (IADC). Heiner is a full member of the International Academy of Astronautics (IAA) and a Fellow of AIAA, and he has served as a member or chairperson of working groups and panels of AIAA, COSPAR, ECSS, IAA, IADC, IAG, ISO, and UNCOPUOS. He is a professor at the Braunschweig University of Technology since 2009, and he published a textbook on “Space Debris – Models and Risk Analysis” in 2006.

Dr. Vladimir Kuznetsov is the Director of the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, a part of the Russian Academy of Sciences known as IZMIRAN. This Institute is located in Moscow, Russia. Dr. Kuznetsov’s areas of expertise include space physics, solar-terrestrial physics, space research, and magnetohydrodynamics. Dr. Kuznetsov’s special field of study relates to solar flares and pre-flare activities of the Sun. Dr. Kuznetsov after defending his doctoral dissertation on “Some problems of the solar atmosphere and cosmic medium dynamics” joined the staff of IZMIRAN as a Research Scientist in 1981 where he has continued to serve for nearly 35 years. While at IZMIRAN he has served as Scientific Secretary and first Deputy Director and is now Director of the institute. He is a graduate of Moscow Institute of Physics and Technology where he received his doctorate in 1981. He is a member of the International Academy of Astronautics, the International Astronomical Union, and the European Astronomical Society. He has received a number of awards including the highest award of the Russian Space Agency, the Tsiolkovsky Sign in 2007, and the Russian Federation Government Prize in the Field of Science and Technology in 2008. He also serves on many scientific councils, commissions, and scientific organizations including the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP). He serves as the

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Chair of the Geomagnetism and Aeronomy Section of the Russian National Geophysical Committee and chairs a section of the Space Council of the Russian Academy of Sciences. Finally he is Editor in Chief of the Journal of Geomagnetism and Aeronomy and serves as a space weather expert to the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). H. Laakso ESA/ESTEC, Noordwijk, The Netherlands [email protected]

Dante Lauretta (born 1970) is a Professor of Planetary Science and Cosmochemistry at the University of Arizona’s Lunar and Planetary Laboratory. He is internationally recognized as an expert in near-Earth asteroid formation and evolution. He is the leader of NASA’s OSIRIS-REx Asteroid Sample Return mission. OSIRIS-REx is the USA’s premier mission to visit one of the most potentially hazardous near-Earth asteroids, survey it to assess its impact hazard and resource potential, understand its physical and chemical properties, and return a sample of this body to Earth for detailed scientific analysis. This mission is scheduled for launch in 2016 and will rendezvous with asteroid Bennu in 2018. Sample return to Earth occurs in 2023. He received a B.Sc. in Physics and Mathematics from the University of Arizona in 1993 and a PhD in Earth and Planetary Sciences from Washington University in St. Louis in 1997. He was a postdoctoral research associate in the Department of Geological Sciences at Arizona State University from 1997 through 1999. He was an Associate Research Scientist in the Department of Chemistry and Biochemistry at Arizona State University from 1999 through 2001. He was hired onto the faculty at the University of Arizona in 2001. His research interests focus on the chemistry and mineralogy of asteroids and comets as determined by in situ laboratory analysis and spacecraft observations. This work is important for understanding the origin of the solar system and the role that asteroids and comets played in the formation of Earth’s oceans and the origin of life. He has received numerous awards including Innovator of the Year – Arizona Governor’s Celebration of Innovation Award (2011), the Antarctica Service Medal of the United States of America (2010), Kavli Fellow of the National Academy of Sciences (2008), and the Alfred O. Nier Prize of the Meteoritical Society (2002). Asteroid 5819 is named Lauretta in his honor.

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Dr. Edward Tsang Lu B612 Foundation Mill-Valley, CA, USA [email protected] Dr. Lu is a trained research physicist working in the fields of solar physics and astrophysics who is a former NASA astronaut and currently heads the B612 Foundation. He first served as a visiting scientist at the High Altitude Observatory in Boulder, Colorado, from 1989 to 1992. From 1992 to 1995, he was a postdoctoral fellow at the Institute for Astronomy in Honolulu, Hawaii. Dr. Lu has developed a number of new theoretical advances, which have provided for the first time a basic understanding of the underlying physics of solar flares. He has published articles on a wide range of topics including solar flares, cosmology, solar oscillations, statistical mechanics, plasma physics, and near-Earth asteroids. Dr. Lu began his service as a NASA astronaut in 1995 and completed three in-orbit missions. He flew as a mission specialist on STS-84 in 1997. His next mission was as payload commander on STS-106 in 2000. He next flew as flight engineer on Soyuz TMA-2 and then went on to serve as NASA ISS Science Officer and flight engineer on ISS Expedition-7 in 2003. Dr. Lu logged over 206 days in space, and accumulated a record of space walks (i.e., EVAs) that totaled 6 h and 14 min. In August 2007, Dr. Lu retired from NASA. Currently Dr. Lu heads the B612 Foundation that is embarked on the launch and operation of the Sentinel Infrared Telescope in 2018. This $400 million project that is funded by private donations is designed to detect potentially harmful near-Earth objects and to do so for asteroids as small as 30–40 m.

Philip Lubin is a professor of Physics at UC Santa Barbara. He received his PhD in Physics from UC Berkeley. His primary work is in studies of the early universe and he is co-recipient of the Gruber Prize for Cosmology in 2006. He has more than three decades of experience in designing, building, and deploying far IR and millimeter wave systems for ground, airborne, and orbital applications.

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Amy Mainzer is a Principal Scientist at JPL who specializes in astrophysical instrumentation and small body science. She is the Principal Investigator (PI) of the NEOWISE mission to search for nearEarth objects using a space-based infrared telescope. She is also the PI of the Near-Earth Object Camera (NEOCam) project, a proposed mission to NASA’s Discovery program to carry out a comprehensive survey for NEOs using a 50 cm infrared telescope located at the Earth-Sun L1 Lagrange point. Mainzer designed and built the fine guidance sensor for NASA’s Spitzer Space Telescope; the sensor has been used continuously throughout Spitzer’s 11 years of science operations. Mainzer has worked on low mass stars and star formation, as well as the First Light Camera for NASA’s Stratospheric Infrared Observatory.

Mikhail Marov is a professor and academician of the Russian Academy of Science and was elected to the International Academy of Astronautics. He was born in 1933 in Moscow and graduated from the Moscow Technical University in 1958. He received his PhD in 1964 and full Doctorate degree in Physics and Mathematics in 1970. He was elected in the Academy of Science in 1990. His principal scientific interests are focused on the fundamental problems of hydrodynamics, gas kinetics, and space physics, with application to solar system studies and planetary cosmogony along with experimental studies of planets. Marov has been deeply involved in many major endeavors of the Russian space program beginning from the first space flights to the Moon and planets up to the present. He worked as Project Scientist and/or Principal Investigator on the VENERA and MARS lander series and made first several in situ measurements in Venus and Mars atmospheres. He has authored above 250 publications in refereed journals and has also published 15 books and monographs. He has occupied a number of distinguished positions in several Russian and international scientific organizations and has also served as an editor for the distinguished international magazines. Since 1989 Mikhail Marov was deeply involved in the International Space University for which he has taught 25 summer sessions as faculty and co-chair of the Physical Sciences department. He also served as a member of the ISU Academic Council and a Trustee. He received two distinguished national (Lenin and State) awards and the International Galabert Award for Astronautics and Alvin Seiff Award for pioneering space studies of planets.

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Dr. Joseph Masiero is a researcher at NASA’s Jet Propulsion Laboratory in Pasadena, CA, and a member of the NEOWISE Science Team. His research of asteroids and comets focuses on the composition and evolution of asteroid families in the main belt, as well as techniques for detecting objects in large-scale surveys. Dr. Masiero is also interested in asteroid polarimetry, instrumentation, and education and public outreach.

Dr. Arnaud Masson Following graduate studies at University of Pierre et Marie Curie, Paris, France (PhD in Space Physics, 2001), Dr. Arnaud Masson spent a year at the Swedish Institute of Space Physics in Uppsala, Sweden, in 1999. He then moved to ESA (ESTEC site, Noordwijk, the Netherlands) in 2000 as a research fellow. In 2002, he became calibration and mission support scientist of the Cluster mission at ESA and was nominated co-investigator of the WHISPER relaxation sounder experiment. He received a group achievement award by NASA (2004) and a science achievement award by ESA (2005). In 2009, he became acting Deputy Project Scientist of the Cluster mission and was nominated Cluster archive scientist in 2011. He received an ESA team award in 2013 as part of the Cluster team.

Robert S. McMillan is at the University of Arizona with joint appointment at the Lunar and Planetary Laboratory and Steward Observatory. He received his B.Sc. degree in Astronomy with High Honors in 1972 from Case Institute of Technology in Cleveland, OH, and his PhD in Astronomy in 1977 from the University of Texas at Austin. His career has been focused on the development of astronomical instruments and their use on stars and solar system objects. He co-founded the Spacewatch Project in 1980 and is its Principal Investigator.

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David Medina is a Senior Research Engineer at the Air Force Research Laboratory who, for over 25 years, has investigated various aspects of spacecraft and ground-based system vulnerability to highenergy effects. His research includes computational physics-based models and methods for predicting laser-material interaction, hypervelocity impact from orbiting debris, blast effects on structures, and passive/ active optical signature prediction. His area of expertise in modeling techniques includes hydrodynamic particles, finite element methods, and finite-difference methods. Modeling research is conducted along with the corresponding laboratory experiments that are needed for validating the models. He received a Master of Science in Mechanical Engineering from the University of New Mexico in 1993.

Patrick Michel is a planetary scientist born in SaintTropez, France, who began his advanced education with a degree in Aeronautical Engineering and Space Techniques in 1993 whereafter he moved to the study of asteroids. He received his PhD in 1997 at the Coˆte d’Azur Observatory in Nice for a thesis titled “Dynamical evolution of Near-Earth Asteroids” (co-supervised by Paolo Farinella). He then spent 2 years at the Torino Observatory (Italy) with a European Space Agency (ESA) external fellowship to study the origin of near-Earth asteroids and asteroid families. He is now a senior researcher at CNRS (French National Center for Scientific Research) where he leads the Lagrange Laboratory Planetology group at the Coˆte d’Azur Observatory in Nice, France. He is a specialist of the physical properties and the collisional and dynamical evolution of asteroids. His work on numerical simulations of collisional disruption and asteroid family formation has been the subject of several publications and made the covers of both international journals Nature and Science. He is author or coauthor of more than 75 publications in international peerreview journals and of more than 40 invited lectures. He belongs to the Near-Earth Object Mission Advisory Panel (NEOMAP) at ESA, wherein he recommends space mission concepts dealing with asteroid hazard. He was a co-chair of the MarcoPoloR sample return mission science team during the ESA M3-class competition and is a co-investigator on the NASA OSIRIS-REx and JAXA Hayabusa 2 sample return missions to primitive asteroids. He leads the European science team of the AIDA project under study with NASA and ESA aimed at deflecting the secondary of the binary asteroid Didymos using a kinetic impactor. He is also responsible of the Work Package on numerical simulations of collisions and asteroid deflection by a

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kinetic impactor in the European Consortium NEOShield funded by the FP7 program of the European Commission. He has wide involvement in the IAU and other international organizations (such as the Action Team 14 of COPUOS at the United Nations devoted to impact hazard). In 2006 he received the “Young Researcher” prize from the French Society of Astronomy and Astrophysics; in 2012, he was awarded the Carl Sagan Medal by the Department of Planetary Science of the American Astronomical Society for Excellence in Public Communication in Planetary Science; and in 2013 he was awarded the Paolo Farinella Prize in recognition of his work on the collisional process. An asteroid is named after him: 7561 Patrickmichel (1986 TR2).

Dr. Miller earned a B.S.E. from Princeton University in Mechanical and Aerospace Engineering (with emphasis in physics) and M.Sc. and PhD degrees from Caltech in Applied Physics. After additional time at Caltech as a postdoctoral fellow, he joined Lawrence Livermore National Laboratory, where he has worked for over two decades and is currently an Associate Division Leader for the AX Division. His background includes multi-physics modeling and simulation; the design, fielding, and analysis of laser-based experiments; high-explosive material testing; and turbulence and mixing processes. He currently leads a project on modeling the physics of asteroid impacts and threat-mitigation approaches.

Toshifumi Mukai is Professor Emeritus of the Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). He has been engaged in space plasma observations for more than 40 years, especially in measurements of low-energy electrons and ions on board numerous spacecraft, such as KYOKKO (EXOS-A), JIKIKEN (EXOS-B), OHZORA (EXOS-C), SUISEI (PLANET-A), AKEBONO (EXOS-D), GEOTAIL, and NOZOMI (PLANET-B). He played an important role in the success of international projects, such as GEOTAIL with the ISAS (now JAXA)-NASA collaboration and BepiColombo with the ESA-JAXA collaboration. He also worked as Senior Chief Engineer of Japan Aerospace Exploration Agency (JAXA) during a time period of October 2005 to March 2009, in which he played a leading role in improving systems engineering and project management processes as well as engineering skill developments in JAXA. He holds a PhD in electrical engineering.

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Atsuhiro Nishida is the former Director-General and Professor Emeritus of Institute of the Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). He received his PhD from the University of British Columbia in 1962 and joined the magnetospheric research in the early days of its development. In the 1980–1990s he proposed and organized the GEOTAIL mission to investigate the physics of the tail region of the magnetosphere where magnetic reconnection plays a key role. This mission was the first launch of the armada of spacecraft, which comprised the ISTP (International Solar-Terrestrial Physics) Program of ESA, IKI, ISAS, and NASA. He is the author of a monograph “Geomagnetic Diagnosis of the Magnetosphere” published by Springer Verlag in 1978 and co-edited an AGU monograph “New Perspectives on the Earth’s Magnetotail” in 1998.

Dr. Nugent is a NASA Postdoctoral Program Fellow working with Dr. Mainzer and the NEOWISE team. She is interested in studying the dynamics and thermal characteristics of asteroids, particularly the asteroids that get close to Earth. She received her PhD in Geophysics and Space Physics from UCLA in 2013.

Joseph N. Pelton International Association for the Advancement of Space Safety, Arlington, VA, USA [email protected]

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Davide Perna is a planetary scientist born in Rome, Italy. His researches focus on the characterization of the physical properties of the solar system small bodies, mainly via the analysis and interpretation of photometric and spectroscopic data at visible and infrared wavelengths. He educated at Tor Vergata University (Italy) and Paris Observatory (France), receiving a Master’s Degree in Physics (2006) after a thesis on the search and physical characterization of near-Earth asteroids and a PhD in Astronomy and Astrophysics (2010) for a thesis titled “Physical properties of asteroid targets of the Rosetta space mission, and of minor bodies of the outer Solar System.” After a postdoc at Capodimonte Observatory (Italy), where he started to study the cometary activity of small bodies at different heliocentric distances, since March 2012 he is a research fellow at LESIA, Paris Observatory, working for the NEOShield project. Within NEOShield he studies how best to obtain the physical and dynamical information required to design an effective mitigation mission once a hazardous asteroid has been discovered, including the necessary reconnaissance observations and design of the appropriate instrumentation for a dedicated space mission. He also deals with the establishment of a global response campaign roadmap to address the asteroid impact threat. He was a co-investigator of the MaNAC camera and of the MaRIS spectrometer being studied for the MarcoPolo-R sample return mission proposed for the ESA M3 mission opportunity. He authors about 30 publications in international peerreviewed journals, including an invited review paper about the near-Earth asteroids and their impact risk. In 2012, the main-belt asteroid 7989 was named Pernadavide after him.

Ettore Perozzi is a planetary scientist involved in celestial mechanics, dynamics of solar system bodies, near-Earth and interplanetary mission analysis, education, and public outreach. He obtained a Laurea degree in Physics in 1981 at the University of Rome and has been working at the CNR Institute for Space Astrophysics (Italy), at the European Space Operations Centre (Germany), at the Observatoire de Paris Meudon (France), and at Telespazio (Italy), and he is presently at Deimos Space (Spain) leading the industrial team operating the ESA SSA NEO Coordination Centre. He is an associated member to INAF (Istituto Nazionale di Astrofisica) and member of the International Astronomical Union (IAU). He has been awarded the ESA Giuseppe Colombo fellowship and the Finmeccanica Innovation Award for Telespazio. Asteroid number 10027 is named after him.

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Dr. W. Dean Pesnell is the Project Scientist of the Solar Dynamics Observatory. He has published more than 90 papers in research areas including variable stars, the Sun-Earth connection, quantum mechanics, and meteors in planetary atmospheres. Dr. Pesnell received his PhD in 1983 from the University of Florida. He started working on SDO in 2004 and became the Project Scientist in 2005. He has lectured extensively on solar activity, including long-term predictions of solar activity.

Michael Potter is a Senior Fellow at the International Institute of Space Commerce, Isle of Man. He serves as Director of Paradigm Ventures, a family investment firm focused on high technology ventures. Potter has served as faculty at the Singularity University. Previously Potter was Vice Chairman, founder, and President of Esprit Telecom PLC, a pan-European competitive telecommunications services provider. He was formerly an international telecommunications analyst at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Potter was also Vice Chairman of the founding Board of the European Competitive Telecommunications Association (ECTA). Potter is an Advisor to Odyssey Moon and Space IL and served as a member of the Board of Trustees of the International Space University. Potter is a member of the TED community.

Martin Rees is an astrophysicist and cosmologist. He is currently the UK’s Astronomer Royal and was formerly Director of the Cambridge Institute of Astronomy. He has also been President of the Royal Society (the UK’s academy of sciences) and is a member of the UK’s House of Lords. He has been much involved in international science policy and also in space science (especially via the European Space Agency). He is an advisor to the B612 project and has written extensively about “extreme risks” stemming from novel technologies.

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Dr. Harold J. Reitsema B612 Foundation Dr. Harold J. Reitsema is a planetary astronomer who has specialized in designing space science missions that probe the solar system and beyond. He is the Mission Director for the B612 Foundation privately funded space mission called Sentinel that is expected identify up to a million unknown near-Earth objects when launched in 2018. He was employed by Ball Aerospace & Technologies Corp. for 26 years during which he led design teams for Hubble Space Telescope instruments and numerous space missions. In 2008, Dr. Reitsema retired as Ball’s Director for Science Mission Development, Civil and Operational Space. He has consulted for NASA, academia, and industry in the areas of project management, team building, and aerospace mission development. Dr. Reitsema has project management experience in space hardware and mission design and a strong background in technology development, including infrared and visible light detectors, calibration, and data analysis. His prior positions at Ball Aerospace include Principal Investigator for a NASA Planetary Instrument Design and Development contract for miniature focal plane development, Flight Project Manager of the Submillimeter Wave Astronomy Satellite instrument program, Lead Systems Engineer in support of science teams for several NASA science instrument programs, and co-investigator and Calibration and Data Processing Team lead for the GIOTTO mission that flew past Halley’s Comet in 1986. He holds memberships in the American Astronomical Society, American Association for the Advancement of Science, the International Astronautical Federation, and the International Astronomical Union and is listed in Who’s Who in America.

Scott Ross Global Aerospace Corporation, MBA, CPCU, ARe, and CAIP Mr. Ross is a Vice President at Global Aerospace underwriting aerospace products liability and space insurance. He works extensively with major aircraft, engine, and satellite manufacturers. His space underwriting involves asset and liability coverage for all space risks from launch and in orbit to space tourism. Mr. Ross’s credentials include B.Sc. in Aeronautical Science from Embry-Riddle Aeronautical University, MBA from Kent State University, Chartered Property

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Casualty Underwriter, Associates in Reinsurance, Certified Aviation Insurance Professional, and NJ Broker license and holds a Commercial Pilot Certificate.

C. T. Russell received his B.Sc. in Physics in 1964 from the University of Toronto and his PhD in Space Physics from UCLA in 1968. He is a member of the faculties of both the Department of Earth and Space Sciences and the Institute of Geophysics and Planetary Physics. He is a Fellow of the American Geophysical Union and the American Association for the Advancement of Science. He is an Associate of the Royal Astronomical Society and the US National Academy of Science. He is a member of the American Astronomical Society, the European Geophysical Society, and the International Academy of Astronautics. In 1977 he was awarded the Macelwane Award by the AGU and, in 2003, their Fleming medal. He was the 1987 Harold Jeffreys lecturer of the Royal Astronomical Society and received the COSPAR Space Science Award in 2002. He is a past chairman of Commission D of COSPAR and of CODMAC, the NAS Committee on Data Management and Computation. He has served as a member of the NAS Space Science Board and NASA’s Space and Earth Science Advisory Committee. He served as President of the Solar-Terrestrial Relationships Section of the American Geophysical Union from 1990–1992. His instruments have been selected for flight on ISEE-1 and ISEE-2 and Pioneer Venus and the ISTP/Polar mission. He has served as a co-investigator on the magnetic field investigations on the Apollo 15 and 16 subsatellites, Galileo, VEGA, Phobos, Mars 96, Cassini, and STEREO missions, and he was an interdisciplinary scientist on the Galileo mission. He is PI of the Dawn Discovery mission to Vesta and Ceres. He has been an editor of EOS, the weekly newspaper of the AGU, and has served as editor of over 30 different books. He has served as associate editor of the JGR and GRL and is presently on the editorial boards of Space Science Reviews and Planetary and Space Science. He is the author of over 1400 articles in journals and books on various aspects of planetary space physics. The Institute of Scientific Information in 2002 named him one of the most highly cited space scientists, with an H-index of currently 88 and lists over 37,000 citations to his indexed publications.

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Frank Sch€afer received a Master of Science degree from the Department of Physics and Astronomy at the University of New Mexico, Albuquerque, USA, in 1991. He graduated from the Physics Department at Julius-Maximilians-Universit€at W€urzburg with a Diploma in Physics in 1993. In 2001, he received a PhD from the Department of Aerospace Engineering at Technische Universit€at M€unchen. He joined Fraunhofer EMI in 1994 and is now head of the Space Business Unit, deputy head of Impact Physics Department, and senior research consultant for homeland security projects. Since 2010 he is lecturer for shockwave physics at the Geosciences Department of Albert-Ludwigs-Universit€at Freiburg, Germany. Frank Sch€afer’s main interests lie in interdisciplinary work in the fields of space, security, and defense research. His research topics include shockwave physics and physical measurement technologies for scientific and engineering applications. He has more than 70 publications (including 20 peer-reviewed) related to hypervelocity impact phenomena, impact cratering in geological materials, characterization of material behavior under high shock loads, and numerical simulations. He is the co-editor of the Proceedings of the 11th Hypervelocity Impact Symposium (2010). He is involved in the MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network) research unit funded by the German Research Foundation (DFG) and the European Commission’s FP7NEOShield project. Frank Sch€afer is a member of Deutsche Physikalische Gesellschaft since 1993, a member of the International Program Committee of the International Astronautical Federation (IAF) since 2004, a member of the Board of Directors of the Hypervelocity Impact Society since 2005, delegate of the German Space Agency of the Inter-Agency Space Debris Coordination Committee (IADC) since 1998, and member of the European Geosciences Union since 2011.

Dr. Pierre-Alain Schieb [email protected] [email protected] Dr. Pierre-Alain Schieb is a French national who is a Professor as well as Chair of the Industrial Bioeconomics Department at the NEOMA Graduate School of Business, France, and Consultant to the OECD. Until April 2013, Schieb was counsellor in the OECD and head of OECD Futures Projects, such as the projects on Future Global Shocks and Infrastructure Needs to 2030/2050. Dr. Schieb was also in

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charge of the OECD Forum on Space Economics, which he contributed to create. He was also the Chairman of the Technical Committee on Space Economy of the International Astronautical Federation. Before joining the OECD in 1994, Dr. Schieb was formerly Executive Vice President of International Business of one France’s major retailing groups (1991–1994) and Dean of a graduate school of business in France (1985–1991) and held an Associate Professorship at the University of Paris, Dauphine. A co-founder of a high-tech start-up company in the early 1980s and involved in venture capital initiatives, Dr. Schieb was also a consultant to numerous French and US companies in the field of alliances, industrial cooperation, licensing, and corporate and marketing strategies. He has also published many articles in the field of international management, risk management, and marketing and corporate strategy. Dr. Schieb earned a PhD (Doctorat d’Etat) in management science from the University of Strasbourg (1981), a DBA in economics and business administration from the University of Aix-en-Provence (1974), and a M.Sc. in quantitative marketing from the University of Sherbrooke (Canada). Dr. Schieb has received numerous distinctions such as the Best Award in Economy (Aix-en-Provence, 1967), Best Dissertation Award (Quebec, Canada, 1974), and Knight in the French Order of Palmes Acade´miques (1991).

Detlef Sieg is employed by the SCISYS Deutschland GmbH as flight dynamics engineer. He is a German native and graduated with honors in geodesy from the Technical University of Darmstadt. He supports the Flight Dynamics Division at the European Space Operations Centre (ESOC) with 15 years of experience in the maintenance of orbit determination and control software and its operational use during several Earth orbiting missions. He is recognized for the design of complex maneuver campaigns for the formation flying missions Swarm and Cluster-II. For the latter he has been flight dynamics routine operations manager since 2008. Whenever snow conditions are good, he performs outdoor activities in the highlands. He can be contacted at [email protected].

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Dr. Michael K. Simpson is Executive Director of the Secure World Foundation and former President of the International Space University. He currently holds a post as Professor of Space Policy and Law at ISU. He is a member of the International Academy of Astronautics, a member of the International Institute of Space Law, and a Senior Fellow of the International Institute of Space Commerce. His practical experience includes service as an observer representative to both the UN Committee on the Peaceful Uses of Outer Space and the Group on Earth Observations.

Sarah Sonnett received her Bachelor’s degree in Physics from the College of Charleston and then went on to earn a Master’s and PhD in Astronomy from the University of Hawaii at Manoa – Institute for Astronomy. Her past work spanned many topics from variable stars to sunspots to small solar system bodies. She is currently a NASA postdoctoral fellow at the Jet Propulsion Laboratory, where she works on the NEOWISE mission studying rotation properties and binaries within the Jovian Trojans and outer main asteroid belt.

Dr. Timothy B. Spahr has been studying asteroids and comets since the early 1990s, and his personal interest in these objects started 15 years before that. Spahr is the Director of the International Astronomical Union Minor Planet Center, operated at the Harvard-Smithsonian Center for Astrophysics. The MPC is the world’s nerve center for asteroid and comet observations. Prior to his work at the MPC, Spahr was a member of the original Catalina Sky Survey team during 1998–2000, where he wrote software to detect moving objects in CCD frames, as well as measure their positions precisely. Tim’s dissertation research was completed at the University of Florida studying celestial mechanics and observational biases present in asteroid surveys.

The Authors

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O. C. St. Cyr received his PhD in Astronomy from the University of Florida. His primary scientific research has focused on understanding the Sun, the causes of space weather, and the impacts on Earth and throughout the solar system. In the early 1990s he was instrumental in developing the ground system for SOHO, and he was the operations scientist for SOHO’s LASCO and EIT during the first 2.5 years of the mission. He went on to become Deputy Project Scientist for STEREO and Senior Project Scientist for NASA’s Living With a Star Program, and he is currently the NASA Project Scientist for the collaborative Solar Orbiter mission with ESA.

Dr. Rachel Stevenson studies rocks in space, such as asteroids and comets, with the goal of improving our understanding of the origins and evolution of the solar system. She obtained her M.Sc. of Astrophysics from University College London in 2006. In 2012 she received her PhD in Geophysics and Space Physics from the University of California, Los Angeles, where her advisor was Prof. David Jewitt. She was then awarded a NASA postdoctoral fellowship and worked on the Wide-Field Infrared Survey Explorer (WISE) mission and its extension, Near-Earth Object WISE (NEOWISE). She is working with the NEOWISE team to discover and characterize asteroids and comets throughout the solar system.

Dr. Straume received a PhD in radiation biophysics from the University of California in 1982 and a B.Sc. and M.Sc. from the University of Washington (1973, 1976). He has held senior scientist and academic positions at the Lawrence Livermore National Lab (1975–1997), the University of Utah (1997–2004), and the NASA Ames Research Center (2004–present). Although his core expertise is radiation science applied to radiobiology, biophysics, and novel radiation detection technologies, he has also pioneered the development of biotechnologies and is inventor or co-inventor of nine patents in the biotechnology field. Dr. Straume’s position at NASA

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The Authors

includes advancing the understanding of health effects from radiation exposure during deep space exploration missions such as Mars and the development of methods and technologies to mitigate such hazards.

Dr. Adam Szabo, born in 1965, received his B.A. degree from the University of Chicago in 1988 and his PhD from the Massachusetts Institute of Technology in 1993. Both of his degrees were awarded in physics. He is currently a civil service scientist and Chief of the Heliospheric Physics Laboratory at the NASA Goddard Space Flight Center. Dr. Szabo specializes in heliospheric and magnetospheric shocks, discontinuities, and coronal mass ejections. He is the Project Scientist for the Wind and the upcoming Deep Space Climate Observatory (DSCOVR) missions and is the NASA mission scientist for the Solar Probe Plus mission currently under development. He is also the Principal Investigator for the magnetometer instrument on the Wind spacecraft and of the Virtual Heliospheric Observatory. He has authored or coauthored over 100 scientific papers.

Dr. Su-Yin Tan is a senior lecturer at the Department of Geography and Environmental Management at the University of Waterloo, Canada. She is the Director of the Applied Geomatics Research Laboratory (AGRL) and teaches courses on environmental remote sensing, geographic information systems, and spatial data analysis. She is a distinguished Gates Scholar and received her PhD degree from the University of Cambridge, UK; two masters degrees from Oxford University, UK, and Boston University, USA; and a B.Sc. (Env) from the University of Guelph (Canada). Dr. Tan is also Adjunct Faculty at the International Space University and Chair of the Space Applications Department at the Space Studies Program. Dr. Tan has an interdisciplinary background in the environmental sciences and spatial data analysis methodologies in a range of application areas, such as climatology, ecosystem modeling, and remote sensing. Dr. Tan has built a diverse record of research experience in North America, Australia, Asia, South America, and Europe. Although born in Canada, she was raised in Papua New Guinea, where she developed an interest in environmental management and conservation. Her interdisciplinary research interests are in the area of space technologies and environmental applications.

The Authors

lxi

Matt Taylor Project Scientist European Space Agency Nationality: British Matt Taylor was born in London. He gained his undergraduate Physics degree at the University of Liverpool and a PhD from Imperial College London. His career has focused on in situ space plasma measurements, working in Europe and the USA on the four-spacecraft ESA Cluster mission, leading to a post at ESA which started in 2005, working in the area of Project Science for the Cluster mission and also the ESA-China Double Star mission, up to 2013. His scientific studies have focused on energetic particle dynamics in near-Earth space and in the interaction of the Sun’s solar wind with the Earth’s magnetic field, particularly focusing on how boundary layer interactions evolve, leading to over 70 first or coauthored papers. Most recently he was appointed as Project Scientist on the ESA Rosetta mission. Dr. Thompson has devoted the majority of her solar research to the study of coronal mass ejections and the dynamics of coronal structures. She has a great deal of experience in analyzing data from multiple sources and has authored or coauthored more than 50 papers using data from more than one instrument, as well as dozens of papers combining observations with model interpretations. Her current research efforts focus on understanding the dynamics of the solar corona and understanding the coupling between small-scale and large-scale structures. Her scientific leadership has emphasized cross-disciplinary development and innovation. She currently serves as a co-investigator for the STEREO/SECCHI and PLASTIC investigations and as the Deputy Project Scientist for the Solar Dynamics Observatory. Fabio Tronchetti is Associate Professor at the School of Law of the Harbin Institute of Technology, People’s Republic of China, and Adjunct Professor of Comparative National Space Law at the School of Law of the University of Mississippi, USA. Before, he was lecturer and academic coordinator at the International Institute of Air and Space Law, Leiden University, the Netherlands. He is regularly invited to give lectures at several European and Chinese Universities. Prof. Tronchetti has participated as a speaker in several international space law conferences

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The Authors

and has published two books and more than 20 articles in internationally peerreviewed space law and policy journals. He holds a PhD in International Space Law (Leiden University) and an Advanced LL.M. in International Relations (Bologna University, Italy). He is a member of the International Institute of Space Law (IISL), European Centre for Space Law (ECSL), and the Asian Society of International Law (ASIL).

Karel A. van der Hucht was born in Nuth, the Netherlands, on January 16, 1946. He obtained his PhD in Astronomy at the University of Utrecht in September 1978. From 1972 to 2011 he was employed at the Space Research Laboratory, Utrecht, the Netherlands, later named the SRON Netherlands Institute for Space Research. He served as senior scientist there until he was appointed to serve from 1978 to 1979 at the Joint Institute for Laboratory Astrophysics (JILA), University of Colorado, Boulder, CO, USA. In those four decades at he was involved in the development and use of UV and IR spectroscopy experiments, annually summer guest lecturer at the ITB Observatorium Bosscha in Lembang, Indonesia. He served on numerous committees and in the organizing committees of 17 astronomy conferences. From 2003 to 2006 he was Assistant General Secretary of the International Astronomical Union (IAU) and from 2006 to 2009 General Secretary of the IAU. Since 2011 he is emeritus senior scientist at SRON in Utrecht. He is (co-)author of 377 astronomical publications, with 6198 citations, as listed by the SAO-NASA ADS.

J€ urgen Volpp Cluster Spacecraft Operations Manager European Space Agency Nationality: German ¨ hringen, Germany. J€ urgen Volpp was born in O He gained a Diploma in Physics and later a PhD at the Institute of Environmental Physics of the University of Heidelberg. For five years he was in the prime contractor team for the European Remote Sensing Satellite ERS-1 at Dornier System, now Astrium. There he was responsible for the operations of the Active Microwave Instrument. He joined ESA at the European Space Operations Centre ESOC in 1990. In the position of the Columbus user interface engineer he formulated the operations concept for the European payload in the Columbus module at the International Space Station. During various Spacelab missions and EuroMir 95 he participated in tests of the remote payload

The Authors

lxiii

operations concept. In early 1999 he joined the Cluster Flight Control Team as an operations engineer responsible for power and thermal control. Since 2002 he has served as the Spacecraft Operations Manager of the Cluster project.

Russ Walker did his undergraduate and masters work in physics, small particle scattering, and molecular spectroscopy at Ohio State University and completed a doctorate in astronomy at Harvard University, where he was coauthor of the first paper to be published in the Astrophysical Journal on the infrared detectability of extraterrestrial civilizations. He has designed and built infrared and optical photometers, interferometers for Fourier transform spectroscopy, and liquid helium cooled infrared telescopes for operation in space. His passion has been performing infrared all-sky surveys and, more recently, the study and exploration of asteroids, comets, and their debris trails. He was awarded the NASA Medal for Exceptional Scientific Achievement for his work as Telescope Scientist of the Infrared Astronomical Satellite (IRAS) and his analysis of the IRAS comet data. Most recently, he was a member of the WISE and NEOWISE science teams, and asteroid 243526 (2010 DY28) has been named Russwalker. Gareth V. Williams obtained his B.Sc. (Hons) in Astronomy at University College, London, and his PhD from the Open University, Milton Keynes, studying the intrinsic brightness of minor planets. He began working at the MPC in 1990 and was responsible for the identification of the last two lost numbered minor planets: (878) Mildred, in 1991, and (719) Albert, in 2000.

Edward L. (Ned) Wright received his AB and PhD degrees from Harvard University and was a Junior Fellow in the Society of Fellows. After teaching in the MIT Physics Department, Professor Wright has been at UCLA since 1981. Prof. Wright is interested in infrared astronomy and cosmology. He is the PI on the Wide-Field Infrared Survey Explorer (WISE) which launched on December 14, 2009, and finished its first coverage of the whole sky on July 17, 2010. He worked on the Cosmic Background

lxiv

The Authors

Explorer (COBE) starting in 1978 and is still using COBE data to study the Cosmic Infrared Background. In 1992 he received the NASA Exceptional Scientific Achievement Medal for his work on the Cosmic Background Explorer. The COBE team received the Gruber Prize in Cosmology in 2006. Prof. Wright was an interdisciplinary scientist on the Spitzer Space Telescope (formerly SIRTF) Science Working Group. He has worked on the SIRTF project since 1976.

Dr. Carlos Alexandre Wuensche (aka Alex Wuensche) graduated in physics from the State University of Rio de Janeiro (1984) and earned a Master’s in Astrophysics (X-ray astronomy) at the National Institute for Space Research (1988) and a PhD in Astrophysics (experimental cosmology) at the National Institute for Space Research (1995), doing a split program in the Physics Department of the University of California, Santa Barbara, under the supervision of Prof. Philip Lubin (1991–1994). Dr. Wuensche maintains collaborations with the University of California, Berkeley and Santa Barbara, USA, and the University of Rome “La Sapienza,” Italy. He is a senior researcher at the National Institute for Space Research (INPE) and a CNPq fellow, holding a productivity grant level 1D. Dr. Wuensche has experience in the area of astronomy, with emphasis on cosmology, acting on the following areas: cosmic microwave background (CMB), cosmology, and galactic emission in microwave and radio astronomy instrumentation. Dr. Wuensche has supervised 10 dissertations and 4 PhD theses. He has participated in several international projects related to the study of CMB since 1991, including ACME, HACME, GEM, BEAST, and WMPol, all published in refereed journals. He worked with the data acquisition system and data analysis of the GEM experiment, which made the first measurements of polarized synchrotron emission of our galaxy at 5 GHz, in collaboration with Prof. George Smoot, at the University of California, Berkeley. Dr. Wuensche is also interested in the CMB polarization measurements and in understanding the Sunyaev-Zeldovich effect. Currently his is Chief of Staff for INPE the Brazilian Space Agency.

The Authors

lxv

Don Yeomans At the Jet Propulsion Laboratory, Don Yeomans is a JPL Fellow, Senior Research Scientist, and manager of NASA’s Near-Earth Object Program Office. Dr. Yeomans was the Radio Science team chief for NASA’s Near-Earth Asteroid Rendezvous (NEAR) mission. He was the NASA Project Scientist for the successful Japanese mission to land upon and return a sample from near-Earth asteroid Itokawa, and he was a scientific investigator on NASA’s Deep Impact mission that successfully impacted Comet Tempel 1 in July 2005 and flew past Comet Hartley 2 in November 2010. He provided the accurate predictions that led to the recovery of Comet Halley at Palomar Observatory on October 16, 1982, and allowed the discovery of 164 BC Babylonian observations of Comet Halley on clay tablets in the British Museum. His group at JPL is responsible for providing predictions for future close Earth approaches and impacts by comets and asteroids. Asteroid “2956” was renamed asteroid “2956 Yeomans” to honor his professional achievements.

Contributors

Michael F. A’Hearn Department of Astronomy, University of Maryland, College Park, MD, USA Firooz Allahdadi Space Science and Environmental Research, Applied Research Associates, Albuquerque, NM, USA Johannes Andersen Niels Bohr Institute, Copenhagen University, Copenhagen Ø, Denmark J. Bauer JPL, Pasadena, CA, USA Sayavur I. Bakhtiyarov NMTech Socorro, Socorro, NM, USA Mark Boslough Sandia National Laboratories, Albuquerque, NM, USA Curt Botts Launch Safety, Air Force Space Command, 45th Space Wing Safety Office, Patrick Air Force Base, FL, USA Sergio Camacho-Lara Science and Technology Education for Latin America and the Caribbean (CRECTEALC), Mexico City, Mexico Joyeeta Chatterjee Institute of Air & Space Law, McGill University, Montreal, QC, Canada Steve Chesley Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA Paul Chodas Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA R. Cutri California Institute of Technology, Pasadena, USA Maher A. Dayeh Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA David P. S. Dearborn Lawrence Livermore National Laboratory, Livermore, CA, USA Simonetta Di Pippo UNOOSA – United Nations Office for Outer Space Affairs, Vienna, Austria lxvii

lxviii

Contributors

L. Drube German Aerospace Center (DLR) Institute of Planetary Research, Berlin, Germany C. P. Escoubet ESA/ESTEC, Noordwijk, The Netherlands Souheil M. Ezzedine Lawrence Livermore National Laboratory, Livermore, CA, USA B. Fleck Science Operations Department, European Space Agency, c/o NASA/ GSFC Code 671, Greenbelt, MD, USA Michele Gates NASA Headquarters, Human Exploration and Operations Directorate, Washington, DC, USA M. L. Goldstein NASA/GSFC, Greenbelt, MD, USA T. Grav Planetary Science Institute, Tucson, AZ, USA James L. Green Planetary Science Division, NASA Headquarters, Washington, DC, USA M. Guhathakurta NASA Headquarters, Science Mission Directorate, Washingto, DC, USA M. Hapgood RAL Space/STFC, Harwell, Oxford, UK A. W. Harris German Aerospace Center (DLR) Institute of Planetary Research, Berlin, Germany Henry R. Hertzfeld Space Policy Institute, Elliott School of International Affairs, The George Washington University, Washington, DC, USA T. Hoerth Fraunhofer Institute for High-Speed Dynamics, Ernst Mach Institute, EMI, Freiburg, Germany Gary B. Hughes Statistics Department, California Polytechnic State University, San Luis Obispo, CA, USA Ram S. Jakhu Faculty of Law, Institute of Air and Space Law, McGill University, Montreal, Canada Lindley N. Johnson Planetary Science, NASA Headquarters, Science Mission Directorate, Washington, DC, USA Frederick M. Jonas Amateur Cosmologist, Gallup, NM, USA Heiner Klinkrad European Space Agency ESA/ESOC, Darmstadt, Germany Vladimir D. Kuznetsov Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation, Russian Academy of Sciences, Moscow, Troitsk, Russia H. Laakso ESA/ESTEC, Noordwijk, The Netherlands

Contributors

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Dante S. Lauretta Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA Edward T. Lu The B612 Foundation, Mill-Valley, CA, USA Philip Lubin Physics Department, University of California, Santa Barbara, CA, USA A. Mainzer JPL, Pasadena, CA, USA Mikhail Ya. Marov Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia J. Masiero JPL, Pasadena, CA, USA A. Masson ESA/ESTEC, Noordwijk, The Netherlands R. S. McMillan University of Arizona, Tucson, AZ, USA David F. Medina Directed Energy Directorate, AFRL/RDLE, U.S. Air Force Research Laboratory, Kirtland AFB, NM, USA P. Michel Lagrange Laboratory, University of Nice Sophia Antipolis, CNRS, Coˆte d’ Azur Observatory, Nice, France Paul L. Miller Lawrence Livermore National Laboratory, Livermore, CA, USA Toshifumi Mukai Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Hino, Tokyo, Japan A. Nishida Institute of Space and Astronautical Science, Machida, Tokyo, Japan C. Nugent JPL, Pasadena, CA, USA Joseph N. Pelton International Association for the Advancement of Space Safety, Arlington, VA, USA D. Perna LESIA – Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, Meudon, France Ettore Perozzi Deimos Space/INAF-IAPS, Madrid, Spain W. Dean Pesnell NASA Goddard Space Flight Center, Greenbelt, MD, USA Michael Potter International Institute of Space Commerce, Douglas, Isle of Man Harold J. Reitsema Reitsema Enterprises Inc., Holland, USA Scott Ross Global Aerospace, Inc., Parsippany, NJ, USA C. T. Russell Department of Earth and Space Sciences, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA F. Sch€ afer Fraunhofer Institute for High-Speed Dynamics, Ernst Mach Institute, EMI, Freiburg, Germany

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Contributors

Pierre-Alain Schieb NEOMA Business School, Reims, France Consultant to the OECD, Paris, France D. Sieg ESA/ESOC, Darmstadt, Germany Michael K. Simpson Secure World Foundation, Broomfield, CO, USA S. Sonnett JPL, Pasadena, CA, USA Timothy B. Spahr Minor Planet Center, Smithsonian Astrophysical Observatory, Cambridge, MA, USA O. C. St. Cyr NASA/GSFC, Code 670, Greenbelt, MD, USA R. Stevenson JPL, Pasadena, CA, USA Tore Straume Space Biosciences Division, NASA Ames Research Center, Mountain View, CA, USA Adam Szabo Heliospheric Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA Su-Yin Tan Department of Geography and Environmental Management, University of Waterloo, Waterloo, ON, Canada M. G. G. T. Taylor ESA/ESTEC, Noordwijk, The Netherlands B. J. Thompson Heliophysics Science Division, NASA/GSFC, Greenbelt, MD, USA Fabio Tronchetti School of Law, Harbin Institute of Technology, Harbin, Heilongjiang, People’s Republic of China School of Law, University of Mississippi, Oxford, MS, USA Karel A. van der Hucht SRON Netherlands Institute for Space Research, Utrecht, The Netherlands J. Volpp ESA/ESOC, Darmstadt, Germany R. Walker Monterey Institute for Research in Astronomy, Monterey, CA, USA Gareth V. Williams Minor Planet Center, Smithsonian Astrophysical Observatory, Cambridge, MA, USA E. Wright UCLA, Los Angeles, CA, USA Carlos Alexandre Wuensche INPE, Sa˜o Jose´ dos Campos, SP, Brazil Donald K. Yeomans Jet Propulsion Laboratory, Pasadena, CA, USA

Part I Introduction

Introduction to the Handbook of Cosmic Hazards and Planetary Defense Joseph N. Pelton and Firooz Allahdadi

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Threat from Near-Earth Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Different Types of Near-Earth Objects and Their Various Kinds of Orbits . . . . . . . . . . . . . . . . . . . Comets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Overview of Threats from Space Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Weather and Coronal Mass Ejections (CMEs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cosmic Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geomagnetic Distortions and “Cracks” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Antimatter and Matter Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiological and Biological Contamination from Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orbital Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure of the Handbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 6 10 13 15 15 21 23 24 26 28 29 29 30 31 31 31 32

J.N. Pelton (*) International Association for the Advancement of Space Safety, Arlington, VA, USA e-mail: [email protected] F. Allahdadi Space Science and Environmental Research, Applied Research Associates, Albuquerque, NM, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_85

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4

J.N. Pelton and F. Allahdadi

Abstract

Each year humans travel through space on their own very special spacecraft called planet Earth, but that trip around the Sun is actually a very hazardous journey. Without the benefit of a space program, the human species has spent millions of years unaware of the wide range of cosmic dangers that lurk out in space. In some ways humans are playing Russian Roulette with a random set of rock and metal bullets that were first fired at this small six sextillion ton planet millions if not billions of years ago. These bullets are potentially hazardous asteroids, bolides, and meteorites. In addition there are comets that streak down toward the Sun from the Oort Cloud every few years. Perhaps an even greater danger to humans come from the nearby nuclear furnace called the Sun. Solar flares, coronal mass ejections, and continuous radiation from the Sun are warded off by the Van Allen Belts, the Earth’s geomagnetosphere, and the ozone layer that sits atop the stratosphere. During the height of the Sun’s activity that follows an 11-year cycle, the radiation and solar eruptions from the Sun hit very dangerous levels. Current research that examines the Van Allen Belts and the Earth’s magnetic shielding suggests that the protective magnetosphere shielding that protects life could be changing. And then there are other hazards from space. These risks include increasing levels of orbital debris and returning spacecraft that may contain nuclear, radiological, or chemical dangers, or even biological dangers. The Handbook of Cosmic Hazards and Planetary Defense seeks to examine in depth the various dangers that the delicate Earth Habitat could be exposed to from outer space risks and what research needs to be done to understand in greater depth the nature of these dangers. And the editors and the authors of this book are defining “cosmic hazards” in the broadest possible terms. Thus, these hazards from outer space include comets, asteroids, and bolides that might collide with Earth. The risks to humans and modern global infrastructure include solar flares, coronal mass ejections, solar proton events, and other space weather events, as well as changes to the Earth’s protective shielding from cosmic hazards such as a lessened magnetosphere, altered Van Allen Belts, and a depleted ozone layer. This chapter also addresses orbital debris (in terms of its impact on Earth and aircraft as well as such debris possibly endangering vital infrastructure and satellite networks). This chapter even considers such hazards as cosmic radiation, antimatter events, and lethal biological agents that could come to Earth in various forms, including via returning spacecraft or astronauts. The last part of the chapter builds on what is known about the dangers of outer space and presents the various types of activities that humans are beginning to undertake to protect life on Earth. This latter part of the handbook sets forth what types of activities can serve to protect humans and indeed all types of life-forms from mass extinctions. Such massive loss of species that include a third or more of all types of life-forms has been documented to have occurred at least five times during the Earth’s existence. These past mass extinction events have come about, on average, every 300 million years or so, over the last two billion years.

Introduction to the Handbook of Cosmic Hazards and Planetary Defense

5

These massive losses of life serve as powerful reminder that not only are there powerful hazards that can wipe out life on a massive scale, but that unless protective measures are undertaken, they could happen again with devastating effect. The rise of mass urbanization that may exceed 70 % of all people living in towns of cities by 2100 coupled with the enormous dependence on modern infrastructure such as electric power grids, telecommunications and information systems, and vast utility plants make twenty-first-century vulnerabilities to cosmic risks far greater than any previous time in human history. The objective of this chapter is thus to present in detail what is known about the hazards of outer space and the scientific and technical nature of these threats. Further this handbook seeks to identify what steps can be undertaken to initiate a creditable planetary defense effort. It is such an effort that can unite all the people of planet Earth in a great and common undertaking. Keywords

Advanced Composition Explorer (ACE) • Antimatter • Bolides • Biological and radiological contamination from space • Carrington event • COPUOS • Coronal mass ejections • Earth guard • ESA • Gamma rays • Geomagnetosphere • Mass extinctions • Millennium ecosystem assessment • Near-Earth objects • NASA • NEOWISE • Orbital debris • Palermo scale • Potentially hazardous asteroids • Sentinel infrared space telescope • Solar and Heliospheric Observatory (SOHO) • Solar flares • Solar max/solar minimum • Sustainability of space • Space weather • Torino impact hazard scale • UNISPACE • United Nations • Van Allen Belts • Van Allen storm probe • Wide-Field Infrared Survey Explorer (WISE) • X-Rays

Introduction The threats that come from outer space are both frightening and numerous in types and nature. The Earth and its various life-forms – both animal and plants – are only protected by a thin atmosphere and a magnetosphere subject to change and weakening over time. There are powerful eruptions from the Sun and a large number of potentially deadly asteroids that only in the last 50 years have become systematically detectable by scientific satellites. Likewise it is only recently that scientific investigation has revealed the true nature and magnitude of mass extinction events where a significant number of species living on planet Earth were wiped out. Today the extent of dangers to human survival and the scope of risks to modern ways of life that come from outer space are much more clearly understood than ever before. And these dangers come from many different sources that include near-Earth objects, potentially hazardous asteroids and comets, solar flares, coronal mass ejections, solar proton events, cosmic radiation as well as solar weather events and even more exotic concerns such as matterantimatter collisions.

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And human activities involving space exploration and applications can also lead to threats and dangers. These include orbital debris that can threaten vital space infrastructure like communications satellites, meteorological spacecraft, and positioning navigation and timing satellites. There is even risk from reentering spacecraft that can bring back chemical, radiological, nuclear, or even biological threats. As orbital debris mounts and more and more satellites deorbit, this could bring physical danger to aircraft or people and facilities on the ground. Today exponential population growth and human industrial activity that generates greenhouse gases when interacting with the Sun’s energy can lead to climate change and global warming that could lead to life-annihilating results such as the runaway heating that occurred years ago on the planet Venus. Even this is a form of risk from the cosmos, but because so much is being written on this subject and is a matter of such broad concern, it is not explicitly addressed in this handbook. This handbook thus defines “cosmic hazards” broadly. The purpose of this book is to explore all of these dangers that come from outer space and shares as much technical and scientific knowledge as is now known about these “space threats.” It continues on to explore what actions might be undertaken to prevent or mitigate these space threats in terms of a concerted effort to undertake a planetary defense against these dangers. This introductory chapter seeks to provide an overview of the various elements addressed in the totality of the handbook to provide a synoptic context as to the nature of the threats and how space research and ground-based observations are constantly seeking to learn about these various potential threats and to begin charting a course forward toward a systematic and hopefully effective planetary defense of life on Earth.

The Threat from Near-Earth Objects In the last few decades, scientists have discovered more and more evidence of the various types of cosmic hazards that lurk out in space. In the 1980s a huge circular crater was discovered that is 180 km across and 900 m deep. This huge and perfectly shaped circular crater ranges along the coast of Mexico’s Yucatan plateau and extends well out into the Gulf. By the 1990s space imaging was able to confirm that this was indeed the remnant of the giant asteroid that smashed into Earth. This event, which was the equivalent to the explosion of tens of thousands of nuclear bombs blocked out the Sun with the cloud of dust that ensued. This was an event termed “Nuclear Winter” during the Cold War era. This mass extinction event (known as the K-T event) not only killed off the dinosaurs some 65 million years ago but it also extinguished about two thirds of all plant and animal species that were alive on the day of this devastating impact. This was Earth’ Big Bang. The ultimate verification that this was the remnant of a huge meteor collision proved that not only could potentially hazardous asteroids could hit Earth but do so in a way that can wipe out human civilization as it is known today (Dinosaur Killer 2003) (Fig. 1). The more recent wake-up call about space hazards that can crash into planets at supersonic speeds came in 1994. This was when astronomers were able to train their

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Fig. 1 The 180 km across meteor crater on the Yucatan plateau (Graphic Courtesy of NASA)

telescopes on Jupiter and watch the impact of a multi-part comet as it crashed at tremendous velocity into the Solar System’s largest planet. This all occurred some 20 years ago when the Comet P/Shoemaker-Levy 9 (note that its formal designation is D/1993 F2) collided with Jupiter. This comet that was first witnessed on March 24, 1993, by Carolyn and Eugene Shoemaker and David Levy at the Palomar Observatory in California had, of course, been predicted well before this catastrophic event actually occurred. There were actually twenty-one discernible parts to the comet “complex” – with some parts being as large as 2 km in diameter (Comet Shoemaker-Levy Collision with Jupiter 1994). During a 6-day period from 16 to 22 July 1994, pieces of the comet bombarded Jupiter with explosive force that could easily be seen through telescopes. This was the first such collision of two Solar System bodies ever to be observed and recorded, and the impact on Jupiter and its atmosphere were truly spectacular. A previous encounter with Jupiter’s gravitational field in 1992 had actually pulled the comet apart to form the 21 pieces. The observed speed of collision was at 216,000 km/h or at134,000 miles/h. The huge scars from the impact left on the surface of Jupiter were larger than the Great Red Spot and remained apparent for many months. Since the size of the Great Red Spot is more than ten times the entire cross section of the Earth, one can only imagine the destructive power of this six day galactic bombardment (Comet Shoemaker-Levy Collision with Jupiter 1994). It is completely plausible that if this 21 piece avalanche of space rocks had hit Earth, human life as it is known with all its modern life and societal infrastructure would have been completely wiped out along with vast numbers of plants and animals.

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The fact that Comet P/Shoemaker-Levy 9 impacted Jupiter rather than Earth is not at all unusual because comets and asteroids hitting Jupiter are calculated to be at least 2000 times more likely because of Jupiter’s huge cross section and its tremendously strong gravitational field. In short Jupiter’s enormous gravity well along with the Sun actually serves as a sort of “cosmic vacuum sweeper” to attract dangerous space rocks to crash into this giant planet or the solar furnace rather than Earth. Saturn and Uranus to an extent help as well, but Jupiter serves a particularly vital function in protecting Earth from comets and potentially hazardous asteroids. For those who say that such threats can be forgotten since they are millions of years away, need to focus on the destructive force of the Shoemaker-Levy comet that would have destroyed human civilization, and to note that this event occurred only two decades ago. Scientists have tried to come to terms with the types of threats that near-Earth objects of various kinds that exist out there and to try to put these dangers into some form of perspective. The result was the so-called Torino Scale that was formally adopted by the scientists that attended the Unispace III Conference in Vienna, Austria. The concept of the Torino Impact Hazard Scale was to create a system analogous to the Richter Scale for Earthquakes. The problem is that the general public has difficulty dealing with very small probabilities combined with hugely disastrous consequences. Tell them they have a 1 % chance of surviving an operation and this makes some sense. Tell them that within a range of 50 years to over a 1000 years, there is a very serious chance of a big space rock doing very serious damage to global society, and they are perplexed but have no clue what to do about it. If it is not immanent, the public tends to say let’s move on to today’s crisis. When the Shoemaker-Levy comet was smashing into Jupiter, the Jet Propulsion Labs web site on this topic had millions of hits in 1994, but today the event is all but forgotten (Fig. 2). The Torino Scale helps us assess the enormity of a threatening collision by a near-Earth object. There is also something called the Palermo Scale that provides a useful assessment of the likelihood that a rogue space object will actually collide with Earth. NASA maintains a so-called Sentry Risk Table that monitors all known near-Earth objects and assigns to those that could come into conjunction with Earth a Palermo Scale number. Near-Earth object 2007 VK384, for instance, will swing by Earth in 2048 and has a Palermo scale number of 1.57 which means a very low probability (NASA Sentry Risk Assessment). The problem is that the needed inventory of the skies is far from complete. But fortunately scientists and engineers are developing improved infrared space telescopes that when combined with Earth observatories, can help us better map the heavens to discover possible threats to Earth with the hope that a major threat could be averted before it could destroy human civilization. The Wide-Field Infrared Survey Explorer (WISE) has helped identify an estimated 80 % of all potentially hazardous asteroids that are greater than 1 km in size that might possibly collide with Earth (WISE: The Wide-field Infrared Survey Explorer). Unfortunately a nearEarth object that is just 30–40 m in size can be a “city killer,” and only a small fraction of these smaller potentially hazardous asteroids have been identified.

Introduction to the Handbook of Cosmic Hazards and Planetary Defense Fig. 2 Torino impact scale for potentially hazardous asteroid (Graphic Courtesy of the UN Unispace Conference) http://neo.jpl.nasa.gov/ torino_scale.html

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Fig. 3 Charting the orbits of potentially hazardous asteroids (Graphic Courtesy of NASA)

Despite the fact Jupiter “vacuums” up many potentially hazardous asteroids, there are a surprising number of space rocks out there that could still do us a great deal of harm. The following graphic shows in blue the orbital characteristic of a “typical” near-Earth asteroid and in red is a “typical orbit for a potentially hazardous asteroid (See Fig. 3 below). It is far from reassuring to know that there are tens of thousands of these potentially hazardous space rocks out there circling the Sun in orbits that could intersect with Earth twice each time they go around the Sun. This “typical” PHA orbit, which relates to asteroids known as the “Apollo” type of near-Earth objects, actually represents about 62 % of the population according to JPL scientists. As can be seen in Fig. 4, there are also asteroids that have larger orbits than that of the Earth and thus are greater than one astronomical unit in size. These types of asteroids could become a problem if their orbits decay over time. These “Amor” asteroids are about 32 % of the population. Then there are the Aten asteroids that have an elliptical orbit that goes near the Sun in their perihelion and then reach an apogee well above the Earth’s orbit and can also cut across Earth’s orbit twice a year. These represent about 6 % of the population (Jet Propulsion Laboratory background on PHAs).

Different Types of Near-Earth Objects and Their Various Kinds of Orbits Former Congressman George Brown, who headed the Congressional Science and Technology Committee for many years was memorialized by a US legislation passed in 2005 to assign the task to NASA and Earth observatories to chart

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Apollo

Aten

Amor

Semimajor Axis ≥ 1.0 AU Perihelion ≤ 1.02 AU Earth Crossing

Semimajor Axis < 1.0 AU Aphelion ≤ 1.0167 AU Earth Crossing

1.02 AU < Perihelion ≤ 1.3 AU

Inner Earth Objects (IEOs) Aphelion < 0.983 AU Always inside Earth’s orbit (aka Apohele)

Type Apollo

Near-Earth Population 62% of known asteroids

Aten Amor

6% of known asteroids 32% of known asteroids

IEO

6 known asteroids

Fig. 4 Different types of orbits for near-Earth objects (Graphic Courtesy of the Jet Propulsion Laboratory)

90 % of all near-Earth objects (larger than 140 m) by 2020 (Section 321 of the NASA Authorization Act of 2005). This initiative is sometimes informally known as Spaceguard. And NASA together with other space agencies and ground observatories has been working on this quite hard for well over a decade. The good news is that the paths of about 80 % of the biggest of these rocks that are a kilometer or more in size are now known. The WISE space telescope and especially the NEOWISE program and Earth observation have given us a good deal of good information. This is reassuring. Yet, those near-Earth objects that are under 1 km in diameter are still 90 % unknown despite the efforts that NASA and others have made. One might be tempted to say: “Probably that is okay because it is the really big space rocks that would really do catastrophic harm.” But they would be wrong. Let us consider something like the space rock known as Apophis, which is only about 300 m in diameter. This particular space rock will whiz by Earth in 2029 and again in 2036. This “small space rock” could do enormous harm. At a speed of 60,000–70,000 km/h, damage from an Apophis-sized rock could be equivalent to thousands of atomic bombs, and at the right location, it could trigger a tsunami that could destroy the Eastern Coast of the USA or Tokyo and Osaka in Japan. When it realizes that over 80 % of the space rocks of this size are still unknown, then any sense of reassurance evaporates away again. NASA has admitted that it cannot achieve the objective of 90 % mapping of all near-Earth objects 140 m in size or larger by 2020 in its formal report to the Congress in 2007. The 2005 Act also required a report to the Congress that analyzed possible options that might be employed to divert a hazardous space rock from colliding with Earth if actual threats were detected. While the NASA report did analyze options, it also indicated

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Fig. 5 Representation of sentinel infrared space telescope deployed in space (Courtesy of B612 Foundation – Not to Scale)

that better technology needed to be developed and no single method (with the possible exception of nuclear devices being used) provided a high level of confidence as to a fully effective response. This lack of progress as reported in 2007 and in the years that have followed is why the B612 Foundation has started its own initiative to launch the Sentinel infrared space telescope to increase a planetary early warning system for lifethreatening space rocks. This new initiative that was formally announced on June 28, 2012, will be dedicated to surveying and identifying all near-Earth objects down to 140 m in size and has the potential to identify threats down to 30–40 m in diameter. As currently designed and engineered, this space telescope could even seek to create over time an inventory of virtually all space rocks that could create major damage. This is a $450 million project that is seeking to build, deploy and operate an infrared space telescope that could provide us consistent and long-range warning of any possible future strikes by a potentially hazardous asteroid that might be lurking out there in space (The B612 Foundation) (Fig. 5). And unfortunately there is much more to be known than just the presence and the precise orbits of these space rocks – even though this is clearly the place to begin. One needs to know about the composition of these asteroids (i.e., rock, dirt, chemicals, or various metals from light to very heavy) and their shape and their relative velocity with respect to Earth. It is also important to know how

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the Sun’s radiation and gravity can impact these asteroids as well. A smaller asteroid consisting of heavy metals and traveling at a relative velocity of 100,000 km/h might actually do more damage than a larger and “softer” space rock traveling at a slower pace. Here is a calculation based on a 30 m asteroid with a radius of 15 m traveling at 100,000 km/h or 27,500 m/s and based on the assumption that, like Earth, the mass density is six times that of water or about 6,000 kg/m3. The amount of power released by the impact would be 7.250 terawatts. If one were to calculate what an asteroid that is at the low end of what the US Congress specified that NASA would use in surveying the heavens for space rocks, i.e., 140 m across, then the calculated power release would be 740 terawatts. And to assess the impact of an asteroid that is 1 km in diameter, the calculated power release would be 260 quadrillion watts. This is 260,000,000,000,000,000 W. This represents enough energy to keep the Earth running for many, many years if converted to electrical energy. The “typical hurricane” power release, which is much greater than a nuclear bomb, is around 50 trillion watts. Knowledge of the composition is important to know not only in terms of the damage that might be done, but this is also key to know in terms of devising a scheme to ward off the impact as well. There is actually a good deal being done to map the orbits of these space rocks. There are research programs to learn about how the Sun’s gravity might create a so-called keyhole effect to change the orbit of a deadly asteroid. These investigations that are seeking information about the Yarkovsky effect are also seeking to learn how the Sun’s radiation can alter over time and thus change the orbit of potentially hazardous asteroids as well. Activities such as NEOShield (2012) and the Spaceguard Foundation (The Working Group 1995) are now underway to study the best methods to ward off a catastrophic collision with Earth. This is the good news. The more sobering news is that humans are not equipped to deal effectively with a killer asteroid or other potentially hazardous near-Earth object. This is particularly true if it was learned that an asteroid would impact Earth in just a matter of weeks. Fortunately no such fate is immanent.

Comets The number one concern with regard to near-Earth objects is actually asteroids and bolides. This is simply because of their sheer numbers. There are many thousands of these objects that are large enough to cause catastrophic damage to Earth if they should actually collide. Their high relative velocity and mass make them a very lethal encounter of the most unwelcome kind. Yet there are other types of space objects that also could come close to Earth that are also worthy of careful study as well. These are the comets that come streaking down from the Oort Cloud region beyond Pluto on a periodic basis and then go zooming back outside of the Solar System. The most famous of these is the

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Fig. 6 The so-called String of Pearls Shoemaker-Levy comet streaking in the sky (Graphic Courtesy of NASA from the Hubble Space Telescope)

Halley’s comet, but in terms of understanding the threat that a comet might pose to planet Earth, the so-called Shoemaker-Levy 9 comet has no peer (See Fig. 6). The Shoemaker-Levy comet (or indeed its multiple elements) that smashed into Jupiter in 1994 with such devastating force demonstrates with an exclamation point that it is important to track and monitor comets as well. This 1994 event was actually helpful to researchers of cosmic hazards in several ways. It allowed us for the first time to observe and record the effects of comet elements as they smashed into a planet. It also helped us to understand even more clearly the extent to which Jupiter does act as a protector of Earth by virtue of its huge gravity well. The gravitational effect of this huge planet helps to capture both near-Earth asteroids, bolides, and comets that might otherwise someday crash into Earth. Although the same could also be said about other elements of the Solar System with gravitational mass, the truth is that the Sun and Jupiter are by far the main line of defense. Thirdly Jupiter and the Sun could also become logical “ultimate destination targets” if it became possible to develop the technology to divert the orbits of nearEarth objects that are directly threatening Earth – assuming the threat is detected early enough in time. This means that it is the current objective to deploy systems out into space that are capable of changing the path of potentially hazardous asteroids and to redirect them so that they would then be captured by the gravity of the Sun or Jupiter. This would be so as to avoid the danger that they could eventually come back and threaten Earth again at a later date. It has been thought for some time that threat from comets is less than that of potentially hazardous asteroids, but recent reexamination of data from observations made in 1883 from Mexico of what is now thought to possibly be a large comet that

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very narrowly missed Earth. The following image suggests that humans and indeed all animal life on Earth may have escaped a very large “cosmic comet-based bullet” just a century and half ago. The only reason that comets are considered less of a concern is really a matter of numbers and statistical probabilities. There are only scores of comets to track and be concerned about, while there are many thousands of asteroids and bolides (which are big space rocks that are smaller than asteroids but larger than mere meteorites or micrometeorites), although programs such as the NASA WISE infrared telescope (especially during its NEOWISE stage) have helped to identify a large number of the potentially hazardous asteroids. Nevertheless there is still a long way to go to get an accurate assessment of the space rocks out there that are in the range of 140 m to 1 k in diameter. The Sentinel infrared telescope might even eventually allow us to do an inventory down to the 30 m range. Statistical evidence indicates that there are tens of thousands of near-Earth objects in this range. As noted in the previous section, even a 30 m space rock can release the power of 7 terawatts which is a pretty powerful wallop.

Overview of Threats from Space Rocks The truth is that despite serious efforts to come to grips with the danger from various types of space rocks in near-Earth orbit, there is still a long way yet to go. Scientists are, in effect, in the infancy of mapping cosmic dangers. There are many hidden dangers within the Solar System still to discover. In order to sum up the various types of danger, it is necessary to be concerned about the information provided in Table 1 below (Types of Near-Earth Objects (JPL)). As can be seen in this chart, the Apollo group of asteroids represents 62 % of the known population, Amors represent 32 %, Atens represent 6 %, and there are only a very few Atiras and IEOs. Yet one must survey the sky for all of these different groups of asteroids because any one could be extremely dangerous.

The Sun The Sun is the largest and most powerful object in the Solar System. The amount of energy that reaches Earth each day some 93 million miles (or 149 million kilometers) away from the Sun’s surface is 10,000 times the total amount that all of humanity actually consumes. To say that the Sun is both the life force for planet Earth as well as a potentially destructive force that could also destroy all life is to state the obvious. Solar activity follows a well-known but not well-understood 11-year cycle that moves from solar minimum to solar maximum. The latest peak in the cycle has reached the during Fall season of 2013. What is known is that there are several types of destructive eruptions that come from the Sun and create hostile space weather for our planet. These are known as solar flares that are associated with sunspot activity and solar proton events (SPEs)

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Table 1 Overview of types of “Space Rocks” constituting cosmic hazards to Earth Brief name NECs NEAs PHAs

Atiras

Atens

Apollos

Amors

IEO

Description of hazard Near-Earth comets Near-Earth asteroid or potentially hazardous asteroid Potentially hazardous asteroids. These are considered the most dangerous. These asteroids that come with 0.05 A.U.s. to Earth are thus within 4.65 million miles or 7.5 million kilometers of Earth NEAs which fly around the same orbit as the Earth (named after NEA Atira Atens cut across Earth Orbit. Since this is at the apogee (or aphelion) Atens are moving at their slowest velocity. This maximizes the likelihood of collision but would likely decrease the speed of impact Apollos have an orbit very similar to Earth. They travel inside Earth orbit at perihelion but above Earth Orbit at aphelion Earth-approaching NEAs with orbits exterior to Earth’s but interior to Mars’s (named after asteroid 1,221 Amor) Inter Earth objects

Definition Typical period is less than 200 years and trajectory within 0.3 AU of Earth Asteroids whose trajectory come within 0.3 AU of Earth Potentially hazardous asteroids: NEAs whose Minimum Orbit Intersection Distance (MOID) with the Earth is 0.05 AU or less and whose absolute magnitude (H) is 22.0 or brighter Asteroids whose orbit around the Sun are within 0.0167 AU of Earth (very few Atiras exist) NEAs which cut across the Earth’s orbit twice. Its semi-major axis is less that 1.0 AU, while apogee is 1.0167 AU or less (see Fig. 4). Atens represent about 6 % of known NEAs These near circular orbit NEAs have a semi-major axis of less than 1.0 AU but an apogee of 1.02 AU or less. Apollos represent 62 % of all known NEAs Those that are considered potentially hazardous are orbits between 1.017 and 1.3 A.U.s. Amors constitute about 32 % of NEAs or PHAs IEOs have a maximum aphelion of 0.983 AU. Only six such asteroids have been identified

Key terms An astronomical unit: Is 93 million miles or 149 million kilometers and is the mean distance between the Earth and the Sun Perihelion and aphelion: Perihelion is the closest approach point to the Sun, while aphelion is when that object is furthest away. (It is like perigee and apogee for a satellite orbiting Earth) Major axis and semi-major axis: The major axis is the long distance across an ellipse, while the semi-major axis is the short distance across an ellipse (This chart is composed from information supplied by the Jet Propulsion Laboratory)

and coronal mass ejections (CMEs) that are typically but not always associated with such flares. These eruptions (in terms of violence and frequency), follow this 11-year cycle. A solar flare perceived from Earth is a sudden brightening on the Sun’s surface and a manifestation of a very large energy eruption, like KABOOM. The amount of this energy release is equivalent to millions of atomic bombs going off all at once. The energy release if one actually uses the precise terms of physics can be up to a

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ISES Solar Cycle Sunspot Number Progression Observed data through Oct 2013 175

150

Sunspot Number

125

100

75

50

25 0

n− Ja

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 −19 n Ja

Smoothed Monthly Values Updated 2013 Nov 4

Monthly Values

Predicted Values (Smoothed) NOAA/SWPC Boulder,CO USA

Fig. 7 Solar cycle for the period 2000–2018 (Graphic Courtesy of the U.S. National Oceanic and Atmospheric Administration)

staggering 60,000,000,000,000,000,000,000,000 J of energy. This is equivalent to one sixth of all the energy the Sun produces each second or the same as 160 million atomic bombs each with a rated explosive power of 1 gigatons of TNT. If one were to try to compare this energy release with the power released in 1 s, it would be 25,000 times greater than the impact power of all of the parts of the comet Shoemaker-Levy when they hit Jupiter. This huge energy release, or solar flare (see Fig. 7), is often also accompanied by a blast of plasma mass (or CME) being expelled from the Sun. It is Earth’s good fortune that any CME must travel 93 million miles (or 149 million kilometers) before it encounters Earth’s protective shield in the form of the Van Allen Belts and the world’s geomagnetic field. Usually these coronal mass ejections go off harmlessly into space. This is because Earth actually constitutes a very small target at its location one astronomical unit away (Fig. 8). Flares occur in active regions around sunspots that develop over a period of only minutes in times. Flares create radiation at all frequencies from highly energetic gamma rays and X-rays down through radio waves. Flares that are directed toward the Earth can and indeed do create radio outages. The blast of radiation can disable satellites and can be quite deadly for astronauts in space as well.

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Fig. 8 A solar flare emission from a sunspot (shown in false color to reflect radiation patterns) (Image Courtesy of NASA)

The power for these eruptions are thought to come from the magnetic energy within the Sun – perhaps just below the corona. These incredibly powerful energy releases are, as noted above, closely associated with coronal mass ejections (CMEs). The exact link between CMEs and flares is still not well established and a flare that is associated with sunspots does not always result in large scale coronal mass ejections. In 1997 the Solar and Heliospheric Observatory (SOHO), a joint undertaking of NASA and the European Space Agency (ESA), was launched in order to study the Sun. The SOHO mission spacecraft was very successful and had a 15-year lifetime that extended through 2012. Although this spacecraft cost $1.5 billion (US), the sharing of costs between the two space agencies made this project more affordable for both of these space agencies. The SOHO research satellite was particularly designed to achieve a better understanding of the concept of harmful space weather from the Sun. Its prime mission was to understand, in greater detail, the cause of the powerful coronal mass ejections and their relation to the powerful solar radiation flares that occur at varying levels of intensity and frequency during the course of the Sun’s 11-year cycle (NASA-SOHO 1997). During solar max, the Sun can each day have as many as three coronal mass ejections that typically accompany violent solar flares. During the solar minimum, however, CMEs can be as few as once every 4 or 5 days. The reason for this periodic cycle of solar turmoil (in terms of both solar flares and related coronal mass

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ejections) is still a matter of intensive research and study. The most puzzling enigma is why intense solar weather eruptions from the Sun can be 15 times more frequent during solar max in comparison to the more dormant conditions solar minimum (in this case “dormant” only makes sense by comparing conditions to the much more turbulent conditions during solar max). There must be a reason why the nuclear fusion engine that generates so much solar heat and generates great loops of magnetic flux follows with such great regularity this well-documented 11-year cycle. Despite targeted research the reason for this rather precise cycle has eluded solar scientists to date. The SOHO mission nevertheless added new levels of understanding. It is now understood that while the mass ejections do indeed spew forth from the corona, solar flares, in contrast, are now thought to be emitted from the layer of the Sun underneath the corona where sunspots form. High-intensity radiation flares and coronal mass ejections can occur in parallel or separately. Both become more intense and frequent during solar max. SOHO has allowed NASA and ESA scientists to capture 3-D images of sunspots that form below the Sun’s super-hot corona (i.e., 1,000,00 C). It also allowed a better understanding of so-called slow and fast solar wind. The greater understanding of flares and CMEs has allowed up to 3 days warning of intense solar weather conditions. NASA also launched the Advanced Composition Explorer (ACE) satellite in 1997 to study solar activities, and then in 2006, it launched two additional solar research satellites appropriately known as “Stereo.” The Stereo name comes from the fact that the two satellites will fly in formation so that eruptions from the Sun can be imaged in 3-D by being able to record these events from two perspectives. The ACE and Stereo satellites are both focused on solar flares and coronal mass ejections, but the main emphasis is on recording slow and fast solar wind as it travels between the Sun and Earth and to study the highly destructive coronal mass ejections (CMEs) as they blast away from the Sun’s corona. These satellites are thus discussed further in the next section and of course later in the handbook. These spacecraft, despite their prime focus on CMEs, have also produced useful information with regard to sunspot activity and high-energy radiation events as well. Of prime interest in terms of studying the extreme radiation solar flares is the NASA satellite known as the Solar Dynamics Observatory. This satellite monitors flares, especially those in the M-Class up through the X-Class levels, since flares of this magnitude can create radio outages and damage to spacecraft and threaten the safety of astronauts in orbit. An X-Class event is at the highest levels, while an M-Class is ten times less energetic (see Fig. 8). Solar flares that emanate from disconnected magnetic loops below the corona dramatically affect all layers of the solar atmosphere. These layers of the outer Sun are known as the photosphere, the chromosphere, and the corona. When the flare occurs it produces a plasma medium that is heated to tens of millions of degrees. This intense plasma accelerates electrons, protons and heavier ions of helium that exist within the Sun to velocities that can reach to near the speed of light. These flares produce radiation at all energy ranges from radio waves up to light and ultraviolet radiation. Most of the

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energy, however, is released as X-rays and gamma rays. The same magnetic surges that create the flares often result in coronal mass ejections as well. Solar flares, as a result of their tremendous power, are dangerous and the ultraviolet radiation, X-rays, and gamma rays can and do blast artificial satellites in Earth orbit and zap the Earth’s ionosphere. Without the Van Allen Belts, without the magnetosphere, and without the ozone layer (which mitigates these blasts and diverts the radiation toward the polar regions), humankind would be in big-time trouble. These flares disrupt long-range radio communications such as shortwave transmissions (i.e., high frequency, very high frequency, and ultra high frequency). This can adversely affect ham radio operators; radar systems; shortwave longdistance, microwave transmission; and over-the-air television transmissions. A solar flare of the highest X-Class range with the exact directionality to hit Earth square on could do even more damage. The so-called Carrington event of 1859 was perhaps the first time that people realized the destructive power of solar events. Carrington, a solar astronomer, was observing the Sun on a “typical Thursday morning” in London when he suddenly saw the development of huge sunspots linked together on the surface of the Sun. These “spots” were many times the diameter of the Earth. Carrington was so excited that he ran downstairs to gather his staff to witness this unique event that he hastily sketched. The massive “fast” solar wind that originated from this flare hit Earth the next day. This flare and then accompanying CME represented an unprecedented blast of solar fury in all of modern times. The Aurora Borealis was witnessed as far south as Hawaii and Cuba. There was at the time very little electrical devices in use at the time, but at several telegraph offices, paper caught on fire as the coronal mass ejection associated with the flare burned through the ionosphere to the Earth’s surface (Pelton 2013). Today in the age of widespread computers and electrical power use that permeates society, no one knows what the consequences would be if such an event were to happen again. The asteroid strike that destroyed the dinosaurs may be a once in every 600 million years event, but a “Carrington event” that involved a solar flare and a coronal mass ejection may be a once in every 100 and 50 years occurrence if not perhaps of greater frequency. On August 31, 2012, a major coronal mass ejection occurred as registered by the Solar Dynamics Observatory (SDO) satellite. The event was actually on a similar scale to the Carrington Event and the ejection speed was at 5.5 km an hour (or about 900 miles a second). If this CME had directly hit Earth, the scale of this hit might well have taken out most of the world’s satellites and destroyed much of the energy grids as well. A solar flare is also potentially dangerous in many ways as well. Its high-energy radiation might take out most communications and navigation satellites and disable much of the radar tracking systems. Fortunately the Earth’s atmosphere and magnetosphere provide us reasonable levels of protection, except for such issues as skin cancer and genetic mutation. Coronal mass ejections (CMEs) will create much more severe consequences. Fortunately we receive more warning against the impact of this massive onslaught of ionic plasma.

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The radiation from a flare can reach Earth in a matter of about 8 min, but the “slower” mass ejections that still travel at millions of kilometers/hour typically reach Earth a day to 2 days later. Billions of tons of the solar ionic mass traveling at these incredible velocities, if they were to travel on a trajectory to hit Earth, would create the most extensive damage possible.

Space Weather and Coronal Mass Ejections (CMEs) As noted earlier solar flares and coronal mass ejections are closely related phenomena. The amount of energy associated with the flare is like millions of nuclear bombs going off at once, and if Earth were not 93 million miles or 149 million kilometers away from the Sun, virtually all life on Earth would be in big-time trouble. If a Carrington event were to happen today, it might actually disable many of telecommunication, remote sensing, meteorological, scientific, and military satellites. And the damage would not stop there. A massive CME could wipe out a large percentage of the world’s computers and processors not only in homes and offices but on airplanes, automobiles, and within vital infrastructure that routes transportation and utilities. Thus, this massive surge of space weather could wipe out the electronic controls for water and sewage plants as well as those that control the delivery of electrical power supplies. But the controls for power plants might quickly become a moot point. This is because there would no power to supply. The CME surge of ions that comes with a massive solar storm would also likely knock out many of the world’s power transformers as well. Underground pipelines carrying fuel would not be exempt. These pipes might suddenly carry a huge electrical surge as the CME ions penetrated the ground and travel hundreds of miles (kilometers) to zap distribution lines or blow up inflammable fuels. A big-time hit by a CME is a disaster for which modern technological society is clearly not prepared. Indeed if the CME of August 31, 2012, had occurred just a week later, the Earth and humanity might have encounter the biggest natural disaster of the modern era. Assessments of this event by NASA scientists have concluded that there is about a 12% chance that a similar extreme solar event could impact Earth within the coming decade. In short the extent of the danger is not known. If a massive CME, like that associated with the Carrington event, did occur, would it indeed send most of human civilization back to the Stone Age? In the most extreme case, such a catastrophe (just like a massive electromagnetic pulse (EMP)) might wipe out most airplanes, trucks, buses, and automobiles by destroying their electronics and making them inoperable. It is possible that a strong enough CME would torch electrical power transformers and eliminate much of today’s electrical power supply. Likewise there is no clear information as to whether such an event might serve to shut down most if not all modern telecommunications and computer networks. Within a brief period of time a truly massive wave of space weather could possibly zap through the Earth’s atmosphere in a way that wipes out most of modern infrastructure. In the worst case condition, much of the world could be

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without power, telecommunications, reliable water and sewage systems, or modern transport. In large cities, at the very least, food supplies would very quickly become a critical problem as transportation and distribution systems rapidly begin to break down. The exact cause of a CME and its specific relationship to a solar flare remains to be definitively explained. Nevertheless recent scientific research has tended toward the conclusion that the phenomenon known as “magnetic reconnection” is responsible for both coronal mass ejections (CMEs) and solar flares. This term refers to the violent shift of magnetic field lines that occurs when two oppositely directed magnetic fields are suddenly brought together. It is now generally believed that “magnetic reconnection” may happen on what are characterized as solar arcades. It is currently thought that there are many loops of magnetic lines of force that occur just below the corona and that these multiple levels or arcades are defined by the extremes of these magnetic loops. These magnetic lines of force can and do quickly reconnect into a lower arcade of loops, leaving a helix of magnetic field unconnected to the rest of the arcade. The resulting unconnected helix of magnetic field is thought to be the cause of a sudden surge of energy. And this is a truly big – like in gargantuan – solar flare. The energy released can be up to 60 septillion joules. The unconnected magnetic helical field and the material that it contains may (or may not) violently expand outward to form the deadly ionic plasma that result in a coronal mass ejection – the CME. This explanation of magnetic loops disconnecting and violently reconnecting helps to provide a rationale as to why CMEs and solar flares typically erupt from sunspot regions where magnetic fields tend to be stronger. What is not at all clear is why there is an ongoing 11-year cycle where solar flares and CMEs are much less common and energetic, and then build up to solar maximum, and then die down again (Holman 2006). There is a constant flow of space weather from the Sun that is characterized by what is called solar wind. The normal flow of particles from the Sun is sometimes called “slow” solar wind. The most recent research data from the Stereo satellites that are able to capture three-dimensional images of coronal mass ejections show that when the explosive mass ejections occur that the faster CME ions overtake the slower solar wind and in “eating up,” the slower particles create an even more powerful solar weather event by the time it reaches Earth. The power of the impact on the Earth’s protective shield is incredibly strong. The artist representation of solar wind blasting into the protective Van Allen Belts and the shockwaves that this creates give some feel for the enormity of space weather. It is really not easy to convey what the force of perhaps billions of tons of ions hitting the Earth’s protective shield at millions of miles (or kilometers) an hour is (Fig. 9). The question that naturally comes to mind is this: “How likely is a CME event likely to cause global devastation to Earth and to human civilization?” The answer at this stage of scientific space exploration is that the answer is not known. Currently modern society is simply not prepared for something like the Carrington CME event to occur. In 1989 a much less powerful CME event, known as the

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Fig. 9 Artist representation of solar weather hitting the Van Allen Belts (Graphic courtesy of NASA – note Earth is the small blue sphere)

Quebec event, fried transformers in Chicago, Illinois, and in Ontario and Quebec, Canada. This knocked out electronic power systems for millions of people. It is known that a very powerful CME event would be in a number of ways akin to an electromagnetic pulse (EMP) that a nuclear explosion in space would create. A single EMP event for instance could disable hundreds of millions of computers and processors that permeate the modern world. What is known is that there are a number of key questions to pursue that fall into these two categories: How can research scientists better understand the workings of the Sun, its 11-year cycle, and especially solar flares and coronal mass ejections (CMEs)? The second set of questions relates to how to develop new or better technology to protect modern human society from a massive solar event that could potentially bring much of human civilization back to the Stone Age in virtually a blink of the eye. The dinosaurs had 1 s of warning against the giant asteroid hitting Earth. Earth might have only short warning against a massive CME, and today there is very little that can be done even if there were a day or two warning.

Cosmic Radiation The Sun is the nearest star and it is the main source of radiation. It showers the Solar System and Earth with a tremendous amount of energy – particularly in the ultraviolet frequencies and a constant stream of X-rays and gamma rays. There are billions and billions of stars that are doing the same throughout the universe. Current understanding of the Sun, solar flares, and coronal mass ejections is derived, in part, by studying other stars in the galaxy and beyond. Stars everywhere seem to perform the same types of nuclear fusion processes and emit flares and mass ejections. Here on Earth there is a constant bombardment not only by solar

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radiation but by cosmic radiation that come from the nuclear reaction in stars, novae and supernovae, and even the mysterious pulsars. Some may think that all needed to be done to protect against cosmic radiation is to put on some sunscreen. Recent experience and scientific study suggest that there are dangers from cosmic radiation that truly need to be taken seriously. It is only through Earth observation satellites that ozone holes in the upper atmosphere layers above the polar regions have been discovered. The Van Allen Belts are formed through the Earth’s magnetic field, and space weather ions are diverted from the higher latitudes toward the polar regions and accelerated as they approach the poles. It is for this reason that the Aurora Borealis and Aurora Australis (i.e., the northern and southern lights) light up the polar regions as well as create eerie noises. This aurora zones are typically 10–20 latitude from the magnetic North and South Poles. Radiation is also shielded by the Van Allen Belt and the ozone layer at the top of the stratosphere also serves to screen the most intense ultraviolet radiation. Since this most intense and powerful radiation in the UV frequencies is above the optical range, it is not directly “seen,” but it can certainly be “felt.” In January during the summer months in the South of Australia (Melbourne and Adelaide), Chile, New Zealand, South Africa, or Antarctica or in July the Northern parts of Canada Europe and Russia, one can certainly “feel” the intense radiation coming through. If over time, in response to climate change and upper altitude jet and rocket combustion, the ozone holes widen even further, the danger can increase beyond concerns about sunburn. Already elevated levels of skin cancer have been recorded among those living in the high latitude areas of the world (Mirsky 2012). Even more alarming has been the detection of increased levels of genetic mutation among frogs and amphibians. There is reason to believe that if the ozone holes widen further and no protective measures taken, humans and other plant and animal lives will be subject to genetic mutation that over time could be deadly to the human species (Norby 2012). Today there has been a connection made between climate change and its impact on many parts of the world’s protective biosphere. Thus, there are concerns that go beyond simply global warming to a range of concerns. Thus, scientists are beginning to explore in much greater depth such aspects as the increase in the ozone holes in the polar regions and how this could have adverse impacts that range from skin cancer to genetic mutation to plants and animals.

Geomagnetic Distortions and “Cracks” It is a human fallacy to assume that today’s reality is somehow a norm and that continuity of experience is the norm. In fact the Earth and the species of life that live on it are quite dynamic. Less than 1 % of all species that have ever lived on Earth over time exist today. The so-called K-T mass extinction event that wiped out the dinosaurs actually wiped out some two thirds of all species. There have been at least four other mass extinction events that have come not from cosmic collisions but from climate change and to be more precise due to heat increases. What is

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Fig. 10 Earth’s magnetic field today and during a reversal (Graphic Courtesy of NASA)

important to learn is the extent to which major changes to the Earth and the biosphere linked to what might be characterized as “cosmic events.” It is thought that about every 66000 years, there is a shift in the Earth’s magnetic poles. It is also suspected that when this reversal of polarity occurs, some rather dramatic shifts also occur, but there are precious little details as to exactly what to expect in terms of the impact on modern infrastructure. Since there was no farming and fixed towns and cities nor scientific investigators before 8000 BCE, there is a great deal that is not known. A study published in 2012 by a group from the German Research Center for Geosciences suggests that a brief complete reversal occurred only 41,000 years ago during the last ice age. The reversal lasted about 440 years with the actual change of polarity lasting around 250 years. During this change, according to this study, the strength of the magnetic field dropped to 5 % of its present strength. This part of the reversal process could be a very bad problem indeed for modern electronic infrastructure. What is currently known is that after some 400 years of relative stability, the Earth’s North Magnetic Pole has moved nearly 1,100 km out into the Arctic Ocean during the twentieth century and at its present rate could move from northern Canada to Siberia within the next half century. The impact that this reversal of the Earth’s magnetic field might have, in terms of the protective levels of the Van Allen Belts that ward off coronal mass ejections, is far from clear. The likelihood is that it could be catastrophic if not for human life – at least for all of a large percentage of today’s computers, processors, and electrical power systems and much of the infrastructure that modern society completely depends on (Fig. 10). If it is true humans do not have to worry about another polar shift and a diminished greatly geomagnetic field for several more thousand years, this would be a great relief. By the year 27,000, for instance, scientists probably will be a

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whole lot smarter. But what if there is not some 25,000 years left? If there is a major magnetic polar shift coming much sooner, there may be big trouble ahead (Vincent et al. 2006). And there are reasons to have some concerns as to whether “cracks” could be occurring in the Earth’s magnetosphere. As early as 1961 James Dungey of the United Kingdom predicted that “cracks” might form in the Earth’s magnetic shield when the solar wind contained a magnetic field that was oriented in the opposite direction to a portion of the Earth’s field. In these regions with the competing two magnetic fields, it is possible that this can create a “crack” in the Earth’s normal geomagnetic patterns. As noted earlier the process of “magnetic reconnection” can trigger solar flares of greater power and intensity. Here on a much more modest scale, a “magnetic reconnection” could lead to the forming of a modest crack in the Earth’s shield. In this case electrically charged particles of the solar wind as well as ions from the Van Allen Belt could flow below the geomagnetic field. This can bring not only deadly radiation but poisonous gases such as hydrogen cyanide. These small “cracks” were first detected using the International Sun-Earth Explorer (ISEE) satellite as early as 1979. This potentially very serious threat has thus been under study since that time (The Earth’s Magnetosphere Shield 2003). A joint space mission funded by NASA and the European Space Agency, named the IMAGE satellite, has been launched to monitor these “cracks” and to determine the degree to which the Earth’s geomagnetic field might be weakening and to explore whether these dangerous conditions might be increased over time. In early January 2011 there what seemed to be a freak phenomenon where perhaps many millions of birds as well as fish were suddenly killed all at once in various locations around the world. The theory put forth by Russian scientists was that hydrogen cyanide had managed to leak through from the lower Van Allen Belt to an altitude where it could kill birds. The further theory is that this hydrogen cyanide was captured in a way that it fell with rain water and thus was able to also kill a large number of fish (Adams 2011; Stewart and Lynch 2007). If it is true that solar wind interacting with the Earth’s magnetosphere can create serious cracks to let through poisonous gases or if the polarity shift is occurring earlier than expected and could cause the geomagnetosphere to reduce in strength by a factor of 20, this development could become the most severe cosmic challenge that humanity will face in the next few decades.

Antimatter and Matter Collisions Another threat that is considered today to be obscure but may well be a hazard that should be considered with some scientific care is that of a collision between matter and antimatter. Today within the CERN nuclear accelerator, scientists are able to

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create minute bits of antimatter that when exposed to matter explode with tremendous force. Some researchers believe that collisions that are ascribed to an asteroid hitting Earth or exploding in the atmosphere might actually be an antimatter and matter collision. In 2007, a supergiant star 200 times bigger than the Sun was utterly obliterated by runaway thermonuclear reactions triggered by gamma ray-driven antimatter production. The resulting blast was visible for months because it unleashed a cloud of radioactive material over 50 times the size of the Sun. SN 2007bi was discovered by the Lawrence Berkeley National Laboratory. The explosion ejected more than 22 solar masses of silicon and other heavy elements into space, including more than six solar masses of radioactive nickel which caused the expanding gases to glow brightly for many months. Giant stars are supported against gravitational collapse by gamma ray pressure. The hotter the core, the higher the energy of these gamma rays – but if they get too energetic, these gamma rays can begin pair production: creating an electronpositron matter-antimatter pair out of pure energy as they pass an atom. The antimatter fueled by gamma rays is generated and then this antimatter is annihilated with its opposite which is regular matter. But this is still a critical delay that allows the gamma-ray pressure to still up the star. As this process occurs the outer layers sag inward and thus compress the core more, raising the temperature, making more energetic gamma rays even more likely to make antimatter, and suddenly the whole star is a runaway nuclear reactor of almost imaginable explosive force. The entire star explodes at once. With this type of super supernova, there is no neutron star or black hole left. The result is an expanding cloud of newly radioactive material and empty space (The Antimatter Super Nova, 2012). The question is whether a fluke event could allow a sizable amount of antimatter to collide with matter in proximity to Earth. Currently it is thought that the bulk of antimatter in the Milky Way is at the very center of the galaxy where it is extremely hot. Currently the Sun does form gamma rays but not in sufficient quantity to generate large amounts of antimatter. The antimatter detector that is now installed on the ISS is telling us a great deal about antimatter and how it is formed. Currently the collision of matter and antimatter in a sufficient amount that it could endanger Earth and humanity seems remote, yet this phenomenon seems worthy of much more detailed study because of the enormous potential energy release – greater than any other single source in the universe known to date (Fig. 11). Up to this point the cosmic threats that have been considered are those that come from “out there” and humanity cannot be thought to be responsible for the creation of these threats and indeed humanity’s role has been to study these threats so as to eliminate or mitigate these threats through technology. But there are two types of “cosmic threat” in which humanity may well have some complicity. These relate to orbital debris and the possibility that elements might return to Earth and bring with them radiological or biological agencies that could threaten life – at least to some degree – back here on Earth.

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Fig. 11 The colossal supernova driven by runaway gamma ray production and antimatter explosions (Graphic Courtesy of Lawrence-Berkley Laboratories)

Radiological and Biological Contamination from Space For over a half century, humans have been launching mass into orbit with little thought to the “sustainability of space.” The result is that there are now about 6,500 t of mass in Earth orbit with about 2,800 t (or over 40 %) of this being low earth orbit. Some of the space objects are active satellites and spacecraft, but a good deal of it is space debris. Some of the defunct space objects contain noxious gases like hydrazine, and others contain nuclear power sources that threaten radiological contamination when they deorbit. Rockets have lifted humans into space to explore the Moon and to carry out missions on “manned platforms.” Scientists are still in early days in studying space biology and the biochemistry of life in outer space. There is far from complete knowledge about how the space environment with zero (or near zero) gravity, radiological phenomena up to gamma rays, and intense thermal gradients might affect not only the human physiology but viruses and bacteriological organisms. A major miscalculation could give rise to pandemics if mutated bacteria returned from space to the Earth environment. Certainly there are sophisticated isolation and decontamination processes for all missions returning from outer space, but only one lapse in these procedures could give rise to a deadly outbreak that could conceivably turn into a pandemic. Even beyond human space exploration exobiology is still a young area of scientific pursuit. Some believe that organic chemistries trapped in falling meteors or bolides could bring new life-forms to Earth. In light of the huge thermal

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gradients that are involved this certainly seems unlikely. Yet some scientists have expressed ideas about “life-forms” that are non-carbon based such as perhaps sulfur-based life-forms that could withstand much greater heat than life-forms known to us here on Earth. As systematic ways are undertaken to prepare for planetary defense, care must be taken in all of these areas. Research activities must not prematurely rule out radiological or biological dangers that are not thought possible.

Orbital Debris Today, concerns about orbital debris are not focused so much on the dangers of radiological or biological contamination or even space junk falling down in such a manner as to damage buildings or to kill or maim people, but rather the prime concern is focused on what is known as the Kessler Syndrome. This is the danger that was first formally anticipated by Donald Kessler in the 1980s. Kessler suggested that a “tipping point” could be reached where the buildup of space debris would continue to increase in the form of a cascade effect and that this deadly rise in space junk could endanger vital space infrastructure and thus in time make it impossible to achieve safe access to outer space. Today radar systems are actively tracking some 22,000 objects that the size of baseball or larger. It is also known that there are some 500,000 objects that are about the size of a marble and over 100 million that are the size of a grain of salt. These space objects that are traveling at speeds of many thousands of kilometers per hour can actually be deadly to an astronaut suit. Even with new voluntary guidelines approved by the United Nation’s Committee on the Peaceful Uses of Outer Space (COPUOS), the problem space debris continues to mount. Efforts are now underway to work toward active debris removal programs with a focus on the largest space debris elements because collisions of large space objects can give rise to thousands of new debris elements. With an increasing number of satellites being launched and a wide range of new small satellite initiatives, there is a need to include active debris removal in an overall program to create a planetary defense effort for Earth.

Sustainability It is in recent times that the whole importance of “sustainability” has become apparent to people who care about the long-term survival of the human species – not for another century but for another eon. Sustainability has been defined by the Merriam-Webster dictionary as “a method of harvesting or using a resource so that the resource is not depleted or permanently damaged” (Merriam-Webster 2012). But at its most basic level, “sustainability” means that Earth can allow human civilization to survive for the long term, and “space sustainability” means that humans will be able to access and to utilize space and space systems to survive.

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At the global scale, scientific data now indicates that humans are living beyond the “carrying capacity” of the spaceship known as planet Earth. There are good rules of physics and mathematics why this cannot continue indefinitely. This scientific evidence comes from many sources but is presented in detail in such sources as the “Millennium Ecosystem Assessment (Turner 2008). A 2012 review in Nature by 22 international researchers expressed concerns that the Earth may be “approaching a state shift” in its biosphere (Barnosky et al. 2012). One very useful measure human consumption is what is called an ecological footprint. This index addresses such aspects as the biologically productive land needed to provide the resources and absorb the wastes of the average global citizen. According to various studies humans are already exceeding that limit by borrowing from either the past or the future. But even if one disputes these calculations, one need only note that the total human population was 800 million in 1800, was 1.8 billion by 1900, over 6 billion by 2000, and will be somewhere in the range of 10–12 billion in 2100. Somewhere along this exponential rise in human population, spaceship Earth has taken on too many passengers to sustain itself and to sustain itself in terms of food, power, climate, jobs, or other measures of sustainability and sanity. If there is to be a credible plan for planetary defense, there will likely need to be some finite limits set for “one planet” consumption. In short it is not possible to divorce entirely space sustainability from sustainability here on Earth.

Structure of the Handbook So what is the purpose of this chapter? It is to cover in a comprehensive fashion all aspects of cosmic hazards and possible strategies for contending with these threats through a comprehensive planetary defense strategy. The earlier portions of the handbook address various forms and types of threats that are poised by our cosmic environment. The middle portion of the chapter addresses the various types of scientific and observational spacecraft that helps us to better understand the physics and behavior of various types of cosmic threats. Likewise there is information presented about various ground observation activities that complement data collected from spacecraft. The editors of this chapter have sought to bring together in a single reference work a rich blend of information about the various types of cosmic threats that are posed to human civilization by asteroids, comets, bolides, meteors, solar flares and coronal mass ejections, cosmic radiation, and other types of threats that are only recently beginning to be understood and studied. These other areas include investigation of the “cracks” in the protective shield provided by the Van Allen Belts and the geomagnetosphere and of matter-antimatter collisions, orbital debris, and radiological or biological contamination. Some areas that are addressed involve areas about which there is a good deal of information that has been collected for many decades by multiple space missions by many space agencies, observatories, and scientific researchers. Other areas involve areas of research and study that have only recently begun.

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Conclusion A concerted attempt has been made to assemble some of the world’s foremost experts in each of these areas. The purpose of this effort has been to provide up-todate and scientifically verifiable information about both the nature of these cosmic threats and possible strategies to alleviate, mitigate, or eliminate these threats. Although much of the work in these various areas have been conducted by space agencies, an expanding range of work is also being carried out by observatories, by universities and other research centers, and even by private foundations and professional organizations such as the B612 Foundation and the Planetary Society. The purpose of this work is thus severalfold. The first objective was to provide the latest information and most systematic research from around the world in a single reference work. Secondly the goal has been to provide not only the most recent information, but where relevant the authors have sought to note where there are significant gaps in our knowledge or where new research, spacecraft, observatories, or other initiatives are needed to fill in critical missing information. Finally the third goal has been to provide the best possible information about preventative actions that might be taken against cosmic threats and to identify various alternative strategies that are now underway or planned to cope with these various threats. Some might argue that this chapter might well have included information about the search for extraterrestrial intelligence since such cosmic life-forms could potentially pose a future threat to humanity. In light of well-documented information about the various SETI programs now underway and the current belief that livable planets are safely hundreds if not thousands of light years away, the editors have chosen not to include this topic in the chapter. Likewise, for reasons noted earlier, the issue of climate change has not been explicitly addressed since there has been so much materials addressed to this topic elsewhere.

Additional Information The Working Group on Near-Earth Objects (WGNEO) of the International Astronomical Union held a workshop in 1995 entitled Beginning the Spaceguard Survey which led to an international organization called the Spaceguard Foundation (1995).

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Directed Energy for Planetary Defense ▶ Earth’s Natural Protective System: Van Allen Radiation Belts ▶ Fundamental Aspects of Coronal Mass Ejections ▶ International Cooperation and Collaboration in Planetary Defense Efforts

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▶ Medical Concerns with Space Radiation and Radiobiological Effects ▶ Planetary Defense, Global Cooperation and World Peace ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris ▶ Potentially Hazardous Asteroids and Comets ▶ United Nation Activities

References Adams M Natural news, Earth’s magnetic pole shift unleashing poisonous space clouds lined to mysterious bird deaths. http://www.naturalnews.com/030996_bird_deaths_pole_shift.html. Accessed 13 Jan 2011 Barnosky AD, Hadly EA et al (2012) Approaching a state shift in Earth’s biosphere. Nat Rev 486:52–58. doi:10.1038/nature11018 Comet Shoemaker-Levy Collision with Jupiter (1994) http://www2.jpl.nasa.gov/sl9/ “Dinosaur-killer” asteroid crater imaged for first time. National Geographic News. http://news. nationalgeographic.com/news/2003/03/0307_030307_impactcrater.html. Accessed Mar 2003 Holman G The mysterious origins of solar flares. Scientific Magazine. http://www. scientificamerican.com/article.cfm?id=the-mysterious-origins-of-solar-flares/. Accessed 26 Mar 2006 Ice age polarity was global event: extremely brief reversal of Geomagnetic field, climate variability, and super volcano. Science News. http://www.sciencedaily.com/releases/2012/10/ 121016084936.htm. Accessed 16 Oct 2012 Jet propulsion laboratory background on different types of orbits for potentially harmful asteroids. http://neo.jpl.nasa.gov/neo/groups.html. Accessed 9 Apr 2014 Merriam-Webster dictionary (2012) www.merriam-webster.com/dictionary/sustainable/ Mirsky S Northern lights make noise, too. Scientific American. July 11, 2012 NASA sentry risk assessment site. http://geology.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn= geology&cdn=education&tm=104&f=20&su=p284.13.342.ip_&tt=2&bt=2&bts=24&zu= http%3A//neo.jpl.nasa.gov/risk/. Accessed 9 April 2014 NASA-SOHO www.nasa.gov/mission_pages/soho/. Accessed August 2014 NEOShield (2012) The near earth object shield: preparing to protect the planet an European Union Project. http://www.neoshield.net/en/index.htm Norby K The sunburned country: skin cancer in Australia. http://www.biology.iastate.edu/ InternationalTrips/1Australia/04papers/NorbySunburn.htm. Accessed August 2014 Pelton JN (2013) Orbital debris and other threats from outer space. Springer Press, New York Section 321 of the NASA Authorization Act of 2005 (Public Law No. 109–155), also known as the George E. Brown, Jr. Near-Earth Object Survey Act. http://www.nasa.gov/pdf/171331main_ NEO_report_march07.pdf Stewart I, Lynch J (2007) Earth: the biography. National Geographic Society, Washington, DC, pp 57–63 The antimatter supernova: one of the largest cosmic explosions ever recorded. The daily galaxy. http://www.dailygalaxy.com/my_weblog/2012/12/the-antimatter-supernova-largest-cosmicexplosion-ever-recorded.html. Accessed 28 Dec 2012 The B612 foundation and the sentinel space telescope. http://b612foundation.org/sentinelmission/ The Earth’s Magnetosphere Shield. http://science.nasa.gov/science-news/science-at-nasa/2003/ 03dec_magneticcracks/. (Last accessed in August 2014) The solar magnetosphere and when does it shift Poles? Global event: extremely brief reversal of GeoMagnetic field, climate variability, and super volcano. Science News. http://www. sciencedaily.com/releases/2012/10/121016084936.htm. Accessed 16 Oct 2012 The Space Guard Foundation spaceguard.iasf-roma.inaf.it/ (Last accessed in August 2014)

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The Working Group on Near-Earth Objects (WGNEO) of the International Astronomical Union (September 18–22 1995) “Beginning the Spaceguard Survey”. Vulcano, Italy Turner G (2008) A comparison of the limits to growth with thirty years of reality. Commonwealth Scientific and Industrial Research Organisation (CSIRO) sustainable ecosystems Types of near earth objects by types and grouping, JPL. http://neo.jpl.nasa.gov/neo/groups.html. Accessed 9 Apr 2014 Vincent WF, Rautio M, Pienitz P (2006) Climate control of biological UV exposure in polar and alpine aquatic ecosystems”. In: Orbaek JB, Kallenborn R, Tombre IM (eds) Environmental challenges in arctic-alpine regions. Springer, New York, pp 117–157 WISE: the wide-field infrared survey explorer: the NASA infrared space telescope. http://www. nasa.gov/mission_pages/WISE/main/index.html. Accessed 9 Apr 2014

Part II Solar Flares

All stars emit radiation. This irradiated electromagnetic energy starts with lower frequency emissions such as infrared and travels up the frequency spectrum to light waves, ultraviolet rays, X-rays, and ultimately very intense gamma rays. The sun, the star in our solar system, emanates a radiation field consisting of various frequency streams. In addition to the normal pattern of electromagnetic radiation that gives us light, there are extremely high-energy emissions known as solar flares. These radiative eruptions are tied to extreme magnetic events which generate intense radiation beams. These solar flares occur more frequently during the height of solar activity known as solar max. Thus, solar flares recur again and again during an 11-year cycle. If it were not for the Earth’s atmosphere (particularly the so-called ozone layer above the stratosphere) and the Van Allen belts that soften the impact of this radiation when these intense beams hit Earth, these solar flares would be quite deadly. Even so solar flares and radiation can create genetic mutations, elevated skin cancer, and other adverse effects. These solar flares often occur in conjunction with so-called coronal mass ejections (CMEs). These CMEs, which instead of sending out electromagnetic radiation that travels at the speed of light, actually spews out slower moving ionic particles that still travel at millions of kilometers an hour. Such CME events can create major disruption and damage on Earth. The topic of CMEs is addressed in the following section.

Solar Flares Frederick M. Jonas

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Carrington Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Similar Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Power of a Solar Flare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hazards to Today’s World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modeling/Predictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

Solar flares are the biggest explosions in the solar system. This tremendous energy release of a single solar flare represents a significant threat to current terrestrial- and space-based systems. This includes any human occupants of space systems who may be exposed to this hazardous energy and radiation environment. Evidence of the deadly nature of these outbursts, and what followed, was clearly demonstrated in 1859 in what has become known as the Carrington Event. Evidence of similar events has been found in the geologic record, most notably Greenland ice cores. From this evidence, it appears events of this magnitude occur approximately once every 500 years.

Frederick M. Jonas has retired F.M. Jonas (*) Amateur Cosmologist, Gallup, NM, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_3

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Storms with a fifth of this energy are estimated to occur several times every 100 years. The good news is that these storms typically last but a few hours. More importantly, we have the technology to protect ourselves, both on Earth and in space. Keywords

Solar flare • Solar system • Carrington • Carrington Event • Earth • Hodgson • Auroras • Solar cycle • Electromagnetic • Coronal mass ejection • CME • Magnetic • Magnetic reconnection • Classification • Radiation • Energy

Introduction Solar flares are the biggest explosions in the solar system. Figure 1 shows a recent image of an M7.9 class solar flare taken March 13, 2012, by the Solar Dynamics Observatory (SDO). Solar flares are identified and characterized by a sudden intense brightening of light on the Sun’s surface or solar limb. The total energy released can be upwards of 6 (1025) Joules of energy. This is equivalent to 160,000,000,000 megatons of TNT equivalent. By contrast, the largest man-made explosion was the hydrogen bomb, Tsar Bomba, detonated on October 30, 1962, by the Union of Soviet Socialist Republics (USSR), now Russia. The estimated yield for Tsar Bomba was 59 megatons TNT, minuscule in comparison. This tremendous energy release of a single solar flare represents a significant threat to current terrestrial- and space-based systems. This includes any human occupants of space systems who may be exposed to this hazardous energy and radiation environment. Evidence of the deadly nature of these outbursts, and what followed, was clearly demonstrated in 1859 in what has become known as the Carrington Event.

Fig. 1 Magnitude 7.9 solar flare observed by SDO March 24, 2012

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The Carrington Event Solar flares were first observed on the Sun in 1859 simultaneously and independently by Richard Christopher Carrington and Richard Hodgson. The first flare observed was characterized as a localized visible brightening within a small area of a sunspot group. The definition still stands. The flare observed by Carrington and Hodgson was part of the solar storm of 1859 during solar cycle 10. This flare and others that followed is known now as the 1859 solar superstorm, the largest geomagnetic storm ever recorded. Richard Carrington (1826–1875) was an amateur English astronomer. His observations of the 1859 solar storm clearly provided the evidence for the existence of solar flares. In addition, his observations also demonstrated the differential rotation of the Sun, the equatorial migration of sunspots during the course of a solar cycle, and the more accurate determination of the Sun’s axis of rotation. All observations were made and recorded at his own observatory built with his home at Redhill, Surrey England. Richard Hodgson was also an amateur English astronomer. Just before noon local on September 1, 1859, while observing and recording sunspots, both observed a marked localized solar brightening in white light, or solar flare, for the first time. Carrington’s recorded observation is shown in Fig. 2. Excerpts from Carrington’s paper (Description of a Singular Appearance seen in the Sun on September 1, 1859) regarding the first observation of a solar flare follow: While engaged in the forenoon of Thursday, September 1, in taking my customary observation of the forms and positions of the solar spots, an appearance was witnessed which I believe to be exceedingly rare. . . . within the area of the great north group (the size of which had previously excited great remark), two patches of intensely bright and white light broke out . . . I hastily ran to call someone to witness the exhibition with me, and on returning within 60 seconds, was mortified to find that it was already much changed and enfeebled. Very shortly afterwards the last trace was gone.. . .)

This fortuitous observation was the precursor to what has become known as the “Carrington Event.” It was during this period of time in solar cycle 10, between August 28 and September 2, 1859, that numerous sunspots were being observed on the Sun. On August 29, auroras were observed in Sydney, Australia. Sydney is at approximately 34 south latitude roughly the same as Roswell, New Mexico, in north latitude. Electromagnetic effects of some sort were also observed as telegraph services were interrupted. On September 1, Richard Carrington and Richard Hobson observed a solar flare for the first time. 17.6 h later during September 1 and 2, auroras and electromagnetic effects begin to occur around the world. They were visible as far from the North Pole as Cuba, 20 north latitude, and Hawaii at approximately 21 north latitude. Reports of auroras came in from around the world. The auroras were bright. Reports from the Rocky Mountains had miners getting up because they thought it was morning and people reading papers in the northeastern USA by the auroras light. A report from the Baltimore American and Commercial Advisor dated September 3 offered the following report:

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20∞

Fig. 2 Carrington’s recorded observation of the September 1, 1859, solar flare

N F

P B

S

D

A 20∞

C

0∞

Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, and the prismatic hues more varied and gorgeous. The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested. Between 12 and o’clock, when the display was at it full brilliancy, the quiet streets of the city resting under this strange light, presented a beautiful as well as singular appearance.

Interesting to note is that a similar event preceded this magnificent display a few days earlier. The electromagnetic effects associated with this second occurrence however were significantly more powerful. Telegraph systems all across North America and Europe failed. Telegraph systems threw sparks and some were set on fire. Some operators were shocked and some systems continued to operate even when disconnected from their power source. Many suspected these events were somehow connected to the solar flare observed. As we now know today, these effects were the result of massive coronal mass ejections or CMEs that impacted Earth (more will be presented on CMEs later). The solar flares were the precursor events. It is also interesting to note that there were at least two CME events, the first one clearing the way for the second as noted by the speed of the second CME effects. Most CMEs today take 3–4 days to travel directly to Earth. The second one made it in half that time. That this overall event was an extremely powerful solar storm is evidenced today by traces left in Greenland ice cores. More importantly, this powerful solar storm has significant implications for us today. We are highly reliant on electronic systems, and these systems are highly interconnected. Failure of one part of these systems, for example, power and power

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distribution systems, can have significant and cascading disastrous effects on our water, banking, and communication systems. And for those systems in the space environment not protected by the Earth’s magnetic shield, the effects can be disastrous leading to the failure of unprotected or poorly shielded systems. We could in effect become disconnected from space and those around us for some unknown period of time if an event such as this were to occur.

Similar Events Evidence of similar events has been found in the geologic record, most notably Greenland ice cores. From this evidence, it appears events of this magnitude occur approximately once every 500 years. Storms with a fifth of this energy are estimated to occur several times every hundred years. The frequency of solar flares goes hand in hand with the 11-year solar cycle, with the number of flares increasing going from solar minimum (less than once per week) to solar maximum (several per day). While perhaps not as powerful as the Carrington Event, other less severe storms occurred in 1921, 1960, and 1989. The latter storm was responsible for knocking out power across large areas of Quebec, Canada. During the recent march to solar maximum, other large solar flares have been observed by not only ground but the increasing number of space systems watching the Sun. Large solar flares occurred in April 2001, October 2003, and September 2005. Approaching solar maximum, this frequency has increased with large storms being observed in February and August 2011, and March and July (two) 2012, and May 2013. On May 12 itself, four X-class (more on classification later) solar flares were observed. While solar maximum is estimated to occur sometime during 2013, solar cycle 24 has been extremely weak compared to other cycles and difficult to predict regarding solar maximum. In fact, solar cycle 24 may actually have two peaks in this cycle.

The Power of a Solar Flare Solar flares affect all the layers of the solar atmosphere, from the photosphere through the chromospheres to the solar corona. Solar flares typically erupt from and are associated with active regions on the Sun. Magnetic reconnection is responsible for and occurs during all solar flares (and CMEs). Magnetic reconnection occurs when the Sun’s magnetic fields join, rearrange, and swap places producing a burst of electromagnetic energy. Captured in action, Fig. 3 shows magnetic reconnection as captured by the RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) spacecraft on August 11, 2012. The event was also captured by NASA’s Solar Dynamics Observatory (SDO). During magnetic reconnection, electromagnetic radiation is produced across the entire spectrum typically released at a rate on the order of 1020J per second. As previously noted, the total energy release can be upwards of 6(1025) Joules. Most of the energy is spread over frequencies outside the visible range.

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Fig. 3 Magnetic reconnection caught by the spacecraft on August 11, 2012

Table 1 Solar flare classification

Classification A B C M X

Peak flux (W/m2) 0.1–0.8 nm 10 3

Typically, there are three stages to a solar flare. The duration of any of these stages can vary from seconds to hours. The first or precursor stage is detected by the release of magnetic energy in the form of soft x-rays. Next, during the impulsive stage, protons and electrons are accelerated tremendously to energies greater than 1 MeV. During this stage, radio waves, hard x-rays, and gamma rays are emitted. X-rays and ultraviolet (UV) emissions affect the ionosphere and thus long range radio communications. Finally, during the decay or third stage, the gradual buildup and decay of soft x-rays can be detected. Temperatures in the solar corona, typically a few million degrees Kelvin, can routinely reach 10 or 20 million degrees, up to 100 million degrees Kelvin on occasion, evidence of the enormous power of these flares. These extreme temperatures result in the electrons, protons, and heavy ions being accelerated to speeds near the speed of light in the impulsive stage. Note that recent detections (2013) have also been made of antimatter particles streaming away from the Sun during these events. This tremendous energy release, combined with coming CME, is the most violent explosion we can observe in the solar system.

Classification Solar flares are classified as either A, B, C, M, or X in increasing order (peak flux or burst intensity, I) as measured near the Earth by the Geostationary Operational Environment Satellite (GOES) satellite in the 0.1–0.8 nm wavelength range (x-rays, Watts per square meter). Intensity levels for each ranking are shown in Table 1. Note that earlier flare classifications were based on qualitative measures of the intensity based on Hα (hydrogen alpha) spectral observations.

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Within each class, there is also a linear scale used to indicate the level within each class. For example, an M3 class flare produced at least 3 (10 5) Watts per square meter. X-class flares have been measured up to X28. The Carrington Event is estimated to have been larger than an X10 class flare.

Hazards to Today’s World Versus the world of 1859, we are highly reliant today on electronic systems, especially microelectronic systems that can fail when exposed to these kinds of energies. Further, most of these systems are interconnected and thus the failure of any one part of these system-of-systems can lead to cascading failures throughout this complex infrastructure. Our electronic systems, from power grids to water to communication and computer networks, including the Internet, are all interconnected. The loss of any of these vital systems can trigger the loss or upset of other vital systems due to this interconnectivity. Massive solar flares, often associated with CMEs, can trigger powerful electromagnetic storms on Earth with the potential to knock out electric power systems for extended periods of time (e.g., Quebec 1989). Power system transformers knocked out by such a storm take time to be replaced, taking months to years depending on the number of systems knocked out and our ability to manufacture new transformers (due to the expense of these transformers, few spares are kept on hand). Cascading system failures could occur as discussed above and illustrated in Fig. 4. Virtually all modern life infrastructure would be affected or disabled. This would include communication networks, financial transactions and banking, transportation water and food distribution systems, medical systems, and any systems that rely on the power grids for power. And note, transportation systems include modern aircraft that are becoming increasingly reliant on electronic systems. These modern electronic aircraft systems are thus more susceptible to damage or upset from these storms than their predecessors. Point is many of the systems we rely on rely on that power coming out of the plug. If that is disrupted for any significant length of time, our lives will be seriously disrupted. More importantly, recovery services will be impacted by any loss of power and associated services (e.g., no water from the fire hydrants for fire fighters to fight fire). The overall recovery becomes more problematic the longer the outage. As a result, large areas of the globe, especially in North America, could be without electricity for a year or more. Our lives would be seriously disrupted. On a more personal level, our personal electronic systems, sensitive to electromagnetic disruptions, would most likely be disabled. This includes of course our personal computers, cell phones, newer cars, and other home systems housing sensitive electronics and computer chips. As noted earlier, long range radio communication systems will be disrupted as well as radars and other systems operating at these frequencies. And there would be no access to the Internet. Our lives would be seriously disrupted. And this is just on Earth.

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Fig. 4 Cascading system failure following power loss

In space, the X-ray flux associated with X-class flares can heat the outer atmosphere and increase the drag on low orbiting satellites leading to orbital decay and reentry. Further, these X-rays (and gamma rays) can interact with exposed space systems leading to system generated electromagnetic pulse that can damage and destroy the internal electronics resulting in the loss of the satellite. This includes systems such as GPS, satellite TV/radio, and weather satellites upon which we have become highly reliant. Such a superstorm could wreak havoc on our orbiting systems. Finally, the radiation itself poses extreme hazards to any astronauts or cosmonauts who might happen to be in space and exposed at the time of this extreme space weather and are of concern for any long duration manned missions to the moon, Mars, or any other planetary bodies. A solar flare occurring January 20, 2005 gave astronauts less than 15 min to reach shelter. That is the good news. We can protect ourselves if given warning. While of course the preceding assumes an Earth-directed event such as the Carrington Event, the geologic record as noted previously gives evidence that such events do occur. It is only a matter of time, and any unprotected electronic

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Fig. 5 NASA Solar Dynamics Observatory (SDO)

systems will be vulnerable to these catastrophic storms. We, in North America especially, if not prepared could find ourselves in a world and technology that existed prior to the Carrington Event of 1859 and for an extended period of time. The economic impact would be devastating, much less to say the impact on everyday life. Suffice it to say, without electricity, our civilization would be turned upside down.

Modeling/Predictions The ability to predict space weather is somewhat akin to the state of the technology regarding terrestrial weather in the 1950s. With the advent of overhead space systems, additional terrestrial weather stations, and computational modeling, the ability to predict terrestrial weather has improved significantly. This improvement can easily be seen by watching any TV news-weather report with the sophisticated graphics and imaging. Although terrestrial weather forecasters may miss the magnitude of the event, they are fairly accurate on the timing. Predictions are usually offered for the following week, but computational models exist that offer predictions for the long term. The same trend is occurring in space weather. Our ability to model and predict (forecast) space weather is improving, especially with the advent of space systems such as the Solar Dynamics Observatory (SDO) (Fig. 5), STEREO (Solar and Terrestrial Relations Observatory), SOHO (Solar and Heliospheric Observatory), and others and improved terrestrially based systems. Through these constant observations of the Sun, we are able to improve our understanding of solar processes, and thus, we are improving our ability to model these phenomena. With these improved models, our ability to predict these events thus improves. Currently, predictions are offered by the NOAA Space

46 Table 2 Space weather predictions for October 14, 2012 (NOAA SWPC)

F.M. Jonas Space weather NOAA forecasts http://spaceweather.com/ Flare 0–24 h 24–48 h Class M 30 % 30 % Class X 01 % 01 %

Weather Prediction Center out to 48 h. These predictions can be found at www. swpc.noaa.gov or spaceweather.com. For example, current solar conditions are given as well as solar flare forecasts for the next 24 and 48 h. Probabilities for geomagnetic storms producing significant disturbances are given for active, minor storm, and severe storm activity levels (Table 2).

Conclusion The good news is that these storms typically last but a few hours. More importantly, we can protect ourselves, both on Earth and in space. If we can accurately predict these storms, especially those aimed at the Earth, then we can shout down our electronic systems to protect them both here on earth and near-space.

Cross-References ▶ Early Solar and Heliophysical Space Missions ▶ International Sun Earth Explorers 1 and 2 ▶ NASA Wind Satellite (1994) ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Dynamics Observatory (SDO) ▶ STEREO as a ‘Planetary Hazards’ Mission

References Baker DN, Green JL (2011) The perfect solar superstorm. Sky Telescope 121(2):28–34 Ferris T (2012) Sunny with a chance of Woe (sun struck). Natl Geogr 221(6):36–53

Solar Flares and Impact on Earth Mikhail Ya. Marov and Vladimir D. Kuznetsov

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification of Solar Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact on Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Characterization of Impacts from Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Historical Highlights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electromagnetic and Corpuscular Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Flares and Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vulnerability of Current Technologies and Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some Quantitative Risk Estimates from Extreme Solar Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49 51 55 55 57 61 72 73 75 76 77 77

Abstract

The Sun exhibits different kinds of activity and its appearance is permanently changing, as it is revealed by numerous ground and space observations. The most well-known phenomenon is the 11-year solar activity cycle with an increasing and decreasing number of sunspots on the Sun surface over this period. These sunspots can be tens of thousands of kilometers across. They usually exist as pairs with opposite magnetic polarity alternating every solar cycle. A number of sunspots tend to peak at the solar maximum and are generally M.Y. Marov (*) Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia e-mail: [email protected] V.D. Kuznetsov Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation, Russian Academy of Sciences, Moscow, Troitsk, Russia e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_1

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manifested closer to the Sun’s equator. Sunspots are darker and cooler than their surroundings because these are regions of the reducing energy convective transport from the hot interiors, which is inhibited by strong magnetic fields. The polarity of the Sun’s magnetic dipole changes every 11 years. This means that the North Magnetic Pole becomes the South one and vice versa. Because solar activity changes from one 11-year cycle to another, the doubled cycles (22 years and longer) are also distinguishable from each other. Irregularity is specifically manifested by a minimum of sunspots and solar activity during several cycles, as significantly occurred in the seventeenth century and is now known as the Maunder Minimum. These cycles strongly impact the Earth’ climate. During the last 11-year cycle, an unusual solar minimum occurred in 2008 and lasted much longer with lower amounts of sunspots than normal. Therefore, solar activity recurrence is not stable. Moreover, theory claims that magnetic instabilities in the Sun core could cause fluctuations with periods that could last tens of thousands of years. Solar flares, coronal mass ejection (CME), and solar proton events (SPEs) are the most characteristic phenomena of these changes in solar activity and their external manifestation. The activity rate as noted above is closely related with the 11-year solar cycle. These solar flare events are often accompanied by the huge ejected amounts of high-energy protons and electrons well exceeding the “normal” energy levels of solar-wind particles. Solar flares, coronal mass ejections (CMEs), solar proton events (SPEs), and normal ejections from the Sun known as “solar wind” have an effect throughout the solar system – especially its inner parts. These phenomena determine the state of geomagnetic fields of planets. Solar plasma and electromagnetic emissions thus have important interactions with the solar system bodies with particular significance for Earth. Solar weather processes impact the Earth’s upper, middle, and lower atmosphere and even can have negative impacts at the surface. Basically, solar activity events determine the space weather which influences planetary environment and, in particular, the life on Earth. This chapter addresses the known science that is associated with solar flares as well as how these solar flares play a key role in triggering other energetic and harmful solar phenomena. Finally it addresses how solar flares, CMEs, and SPEs in particular impact the Earth’s atmosphere and magnetosphere and especially how these phenomena can create significant negative impacts and major infrastructure risks to the world’s current economic and technological systems.

Keywords

Carrington event • Coronal mass ejections (CMEs) • Extreme-ultraviolet (EUV) radiation • Galactic cosmic radiation (GCR) • Gamma radiation • Geomagnetically induced currents (GICs) • Polar cap absorption (PCA) event • Solar corpuscular radiation (SCR) • Solar energetic particles (SEPs) • Solar and Heliospheric Observatory (SOHO) satellite • Solar flares • Solar proton events (SPEs) • Solar wind • Sunspot • X-ray radiation

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Introduction Solar flares (Fig. 1) are caused by the tearing apart and reconnection of the magnetic field lines (the so-called B-field) in the Sun’s chromosphere. This is accompanied by a rapid release of magnetic energy stored in the corona. A flare is a burst exhibited as an instantaneous and intense change in the Sun’s brightness in an active area on the Sun surface. The majority of the flares’ energy is not visible to the naked eye and must be observed with special instruments outside of the visible light range. Temperature inside a flare reaches 108 K, and energy release may reach nearly 1026 J – about a sixth of the total energy output of the Sun each second. This is the equivalent of 160 billion megatons of TNT or the same as the largest type of thermonuclear bomb known to humanity. Flare duration may be as long as 200 min. The typical solar flare is accompanied by strong intensity X-ray and gamma-ray releases of energy. This can and often does lead to a powerful acceleration of clouds of electrons, protons, and heavier particles that are ejected into space. The velocity of these plasma releases can approach a tenth of the speed of light. Unlike solar wind, particles generated by the violent flares and manifested as coronal mass ejections (CMEs) or solar proton events (SPEs) travel very fast, and when and if they reach Earth, they strongly disturb its environment and the atmosphere. Radiation from the flares can be extremely harmful to astronauts and to satellites and spacecraft and create other negative impacts that will be discussed later in this chapter. The exact relationship between the solar flare that originated below the corona and the ionic particle release known as a coronal mass ejections (CMEs) and solar proton events (SPEs) is not entirely understood. Solar flares, CMEs, and SPEs often occur together but are not always linked. The dynamic nature of the Sun’s magnetic fields is key to all of these phenomena.

Fig. 1 An example of solar flares over the Sun’s visible surface – photosphere (Credit: SOHO, ESA)

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A CME represents the most powerful phenomenon in the solar system. They are originated in the corona and represent outbursts of the enormous volumes of the solar plasma also caused by the magnetic field lines reconnection. Some of them are associated with the solar flares or are related with the solar eruptive protuberances maintained above the solar surface by the magnetic fields. CME appears periodically and are composed of very energetic particles. Giant clots of plasma forming giant plasma bubbles expanding outside in the corona and its arms are thrown out in space. Billions and sometimes trillions of tons of matter are ejected and travel in the interplanetary medium with a velocity of greater than 1,000 km/s and form a detached bow shockwave at the front. CMEs are responsible for powerful magnetic storms on Earth. Due to plasma inflow the Earth’s magnetosphere can decrease from about 12 RE to about 6 RE. Solar flares and CME carry very harmful radiation, and in the case of CMEs, they generate a large amount of radiation as they hit the Earth’s atmosphere. Another phenomenon that is less violent than CMEs is solar proton events (SPE). They occur more often than typical solar flares and CMEs. The peak energies of generated proton ions are lower (i.e., typical energy levels are E ~ 30 MeV, and particle flux density is about 1010 cm 3) but SPE duration is longer. These events can last from a few hours to a few days. Whereas solar flares and CME are more characteristic for the maximum phase of the 11-year solar activity cycle, SPE occurs throughout the whole cycle. Their influence on the space environment and their impact on Earth is much lower than CMEs. Solar plasma and electromagnetic radiation impacting planets strongly influences their environment. The biggest impact is on their magnetosphere – either intrinsic or induced depending on whether a particular planet possesses a magnetic field. Such an interaction is referred to as solar-planetary coupling and is substantially dependent on the phase of the 11-year cycle of solar activity. Solar flares, especially when combined with CMEs, exert strong influence on the state of geomagnetic field and space weather on Earth. Changes in the solar activity result in changes to the geomagnetosphere’s shape and to the Earth’s radiation levels. These events can trigger magnetic storms and lead to major changes to the various upper atmosphere properties of the Earth as well. In particular, temperature of the Earth’s atmosphere in the height range 200–1,000 km can change by several times, from about 400 K to as high as 1,500 K, and change the atmosphere’s mass density by one to even two orders of magnitude. These solar storms can dramatically impact artificial satellite lifetime and threaten astronauts in orbit. These variations are caused by the solar flare’s extreme-ultraviolet (EUV) and soft X-ray radiation. Radio emissions from the Sun can be conveniently measured in the decimeter wavelengths. Solar activity can thus be indexed by measuring radiation in the 10.7 cm band. Radiation in this wavelength is today continuously recorded by simple radio antennas over the globe. This index (F10.7) changes from about 70 to about 180 W/m2Hz between solar activity minimum and maximum, respectively, and perfectly reflects the real physical processes depending on the solar energy input. Similarly, indexes of geomagnetic activity (Ap, Kp, Dst, and some others) are recorded by geophysical observatories. These measurements are

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used to characterize the Earth’s magnetic field disturbance. Solar flare effects on Earth (as well as CMEs) display themselves as auroras at high to moderate latitudes. In the case of particularly severe solar flares and CMEs, these auroras can be seen at much lower latitudes and with much greater vividness. Solar flares (as well as CMEs) can also result in the disruption of radio communications, breaks in electric power supply and destruction of electrical power transformers, blocking of radar operations, damage to spacecraft electronics, and even disruption of underwater submarine cable operations. Many of these problems are occasioned by what are called geomagnetically induced currents (GICs).

Classification of Solar Flares Solar flare is a very explosive process. It involves energy release in the Sun’s atmosphere encompassing all its layers – photosphere, chromospheres, and corona. It manifests itself as a sudden brightening observed over the Sun surface or the solar limb. Basically, solar flare implies an event that is localized within an active region on the Sun (Fig. 2). In this way they are distinguished from CMEs which have much larger angular spans encompassing several active regions and enormous power of an explosive nature. The CME leads to an explosion of plasma ejected at a speed of thousand km per second. Flares involve the release of energy as electromagnetic radiation (i.e., extreme-ultraviolet X-rays and even gamma rays) that travels at the speed of light, while CMEs are ionic plasma that travels at speeds up to one-tenth of the speed of light. The top recorded speed of any recent CME was over 5.5 million km/h as registered by the Solar Dynamics Observatory (SDO). This was during a 31 August 2012 event that fortunately was largely directed away from the Earth’s path. Solar flares are extremely complex phenomena observed across the whole electromagnetic spectrum including extreme-ultraviolet and gamma-ray emissions as well as radio wavelength. Solar flares are classified depending on their size, duration, morphology or magnetic topology, and characteristic corpuscular radiation. There are two basic kinds of flares – impulsive and gradual. The duration of flares varies – from a few minutes to tens of minutes and even several hours. A fully developing flare is sometimes a combination of an impulsive and gradual event. A flare’s duration is indicative of its magnetic topology. While long-duration flares are linked to CMEs, impulsive flares are generally completely confined within the Sun’s lower atmosphere though some short-duration flares may also have ionic plasma ejections of various scales. Solar satellite missions are seeking to understand better the relationship between flares and CMEs and SPEs and their causal relationships. There is widely used optical (Hα) classification system that is based on Hα emission line spectral observations, and this classification system addresses flare size (i.e., importance). The classification starts from a character S (means sub-flare) followed by Figs. 1, 2, 3, or 4 for successively larger flares and accompanied by a letter (f = faint, n = normal, b = bright or brilliant). Basically, this classification

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Fig. 2 The massive solar flare X1.2-class on 7 January 2014. This image taken by SDO’s (Solar Dynamics Observatory) Helioseismic and Magnetic Imager shows location of two active regions on the Sun, which straddle a giant sunspot complex. The flare has forced the commercial spaceflight company Orbital Sciences to postpone the planned launch of a private cargo mission to the International Space Station (Credit: NASA/SDO)

system denotes the flare size, i.e., area A (as measured in millionths of a solar hemisphere) and importance class (1–4), i.e., power. The relationship is shown in Table 1. Therefore, the most outstanding flares are classified as 4b and the smallest and faintest as Sf. Another classification system of flare size/power is based on observations of the ˚ ) wavelength in the soft X-ray range. This type Sun in the (1 through 8 Angstrom A of classification became possible when solar research satellites were able to take measurements. The system thus appeared and came into usage since the 1970s. The size of flare (power) is given by the peak intensity of the emission on logarithmic scale. Flares are classified with a letter (A, B, C, M, or X) corresponding to the ˚ flux in Wm 2 power of 10 ( 8, 7, 6, 5, 4, respectively) of the peak (1–8) A units and a number (1–9) that acts as a multiplier (Table 2). For example, a B3 flare has a peak flux of 3  10 7 Wm 2 and an M8 flare has a peak flux of 8  10 5 Wm 2. During the solar cycle minimum X-ray background emissions are low and flares only smaller than C1 are recorded. Generally, X-class flares are confined whereas intense flares are mostly eruptive. Flares occasionally exceed class X9 in intensity; they are simply referred to as X10, X11, etc. events. In turn, B-class flares may be associated with CME events with explosive and prolonged energy release. Moreover, some eruptive flares are regarded as a consequence of CMEs. The relationship of CMEs to long-duration flares is generally interpreted in terms of

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Fig. 3 Solar flares defining space weather and affecting technological systems on the Earth and in space (Credit: L. J. Lanzerotti, Bell Laboratories, Lucent Technologies, Inc)

magnetic reconnection. The large fully developed flares in which an impulsive phase is followed by a gradual main phase (called “hybrid” flares) exert the most profound influence on the planetary environments, and thus they are most important from the geophysical viewpoint. With a soft X-ray classification, it is difficult to indicate whether a flare is eruptive or compact (confined). The decisive argument to distinguish between them is magnetic topology. Thus the critical factor becomes whether magnetic field lines are opened or closed. Unlike the case of the confined flares in a closed configuration, there are clearly distinguishable eruptive events. Here one is likely to find CMEs with newly opened field lines. This is often followed by the closing down or reconnection of the magnetic fields that usually occurs on a timescale of hours and provides the prolonged and violent energy release. Because solar flares exhibit themselves in the radio wavelength ranging from millimeters to kilometers, they are also classified in association with radio events or bursts. This classification is particularly useful in terms of the dividing of flares into confined and eruptive categories. The five (I through V) categories are distinguished from each other. Types II and IV bursts are identified most commonly with eruptive flares, while types III and V bursts are usually attributed to flareaccelerated electrons moving along open field lines into the corona.

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Fig. 4 Electromagnetic and corpuscular solar radiation and its effects (Credit: P. Brekke. Source: P. Brekke. Space Weather Effects. Presentation, ESTEC, 1 December, 2004) Table 1 Optical (Ha) classification system of flare size/importance

S 1 2 3 4

Table 2 Classification system of flares in X-ray flux range (Watts/m2)

A B C M X Z

A 10,000 489 16 to +5 47 1.3 2.0 4.2

et al. 2005, 2006). In this catalog, CMEs are identified by visual inspection. The automated Computer Aided CME Tracking (CACTus) software helped to identify even much lower-level events. This software, in fact, revealed a much higher occurrence rate that varied from 1019 Hz). These cosmic gamma rays not only have extremely high energies but quite miniscule wavelengths that can be less than the diameter of an atom. Gamma decay related to radioactive materials commonly produces energies that typically range between a few hundred thousand electron volts and under 10 MeV (Merdin 2001). The energies of gamma rays from astronomical sources tend to be dramatically different. They can range up to energies that exceed over 10 trillion electron volts (TeV). This is an energy level far too large to result from radioactive decay or any typical solar flare. Astronomical gamma ray emissions thus tend to be extremely powerful releases of high-energy radiation normally referred to as long-duration gamma ray bursts (GRBs). These bursts of gamma rays are often thought to be due to the extreme collapse of stars called hyper novae as well as other galactic phenomena discussed in chapter “▶ Basics of Solar and Cosmic Radiation and Hazards.” These galactic events that produce such super gamma rays (as recorded by the RHESSI satellite described later in this chapter) are the most powerful phenomena ever discovered by scientific researchers since they can have energy levels in the range of 10 to even 100 trillion electron volts (Helios 1 and 2).

Helios-A and Helios-B (Also Known as Helios 1 and 2) (1974 and Remains in Circumsolar Orbit) Helios-A and Helios-B (also known as Helios 1 and Helios 2) are a pair of probes launched into a circumsolar orbit for the purpose of studying solar processes with the closest approach point (i.e., perihelion) for Helios 1 being about 46 million kilometers and for Helios 2 being about 43 million kilometers or inside the orbit of Mercury. This was a joint venture of NASA and the Federal Republic of Germany (West Germany). Helios 1 was launched by NASA on Dec. 10, 1974, and Helios 2 was launched some 13 months later on Jan. 15, 1976.

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Table 1 The instrumentation for the Helios 1 and Helios 2 spacecraft Instrument name Plasma experiment investigation Flux-gate magnetometer Search coil magnetometer Plasma wave investigation Cosmic radiation investigation Low-energy electron and ion spectrometer Zodiacal light photometer Micrometeoroid analyzer

Description Measures the velocity and distribution of the solar wind plasma Measures the field strength and direction of low-frequency magnetic fields in the sun’s environment Compliments the flux-gate magnetometer by measuring the magnetic fields between 0 and 3 kHz Measures and analyzes waves of free ions and electrons in the solar wind plasma, 10 Hz to 3 MHz region Measures protons, electrons, and X-rays to determine the distribution of cosmic rays Investigates the higher-energy portion of the crossover region between the solar wind particles and the cosmic rays Measures the scattering of sunlight by interplanetary dust particles Investigates the composition, charge, mass, velocity, and direction of interplanetary dust particles

These solar research spacecraft are not to be confused with the like named optical military reconnaissance satellites launched by France and Italy known as Helios 1A and 1B and Helios 2A and 2B. The solar research probes are notable for having set a maximum speed record among spacecraft at 252,800 km/h (or about 157,000 mi/h). Helios 2 was sent into orbit 13 months after the launch of Helios 1. The Helios space probes completed their primary missions by the early 1980s, but they continued to send data up to 1985. The probes are no longer functional but still remain in their elliptical orbit around the sun (Helios 2). These solar research satellites were equipped with eight instruments that provided perhaps the most accurate and complete set of data with regard to solar radiation, solar wind, solar ion ejections, and solar magnetic field up to that point. This was not only because of the complexity and capability of the instruments detailed below in Table 1 (the P78-1) but also because of the circumsolar orbit that at perihelion made the closest approach to the sun of any previous probe (Fig. 2).

Skylab (1973–1979) Skylab was the United States first manned space station, and it was conceived as a true laboratory in space. Skylab was also a final element of the Apollo program in 1973 after the final Moon mission of Apollo 17 in 1972. Skylab was configured to include a total of nine different solar experiment projects. This rich combination of solar experiments was designed by a number of different groups that included the Naval Research Laboratory, the NASA Marshall Space Flight Center, the

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Fig. 2 The prototype mockup of the circumsolar Helios 1 solar probe (Graphic: courtesy of NASA)

Harvard-Smithsonian Observatory, and the High Altitude Observatory. These experimental projects can be briefly described as follows (“Skylab”): • There were two X-ray telescopes. These were designated as experiments S-054 and S-056. The instruments were developed under the sponsorship of the NASA Marshall Space Flight Center. • There was a special camera designed to capture X-ray and extreme-ultraviolet radiation. This was experiment S-020 sponsored by the Naval Research Laboratory. • There was an ultraviolet spectro-heliometer. This was experiment designated as S-055 and sponsored by Harvard-Smithsonian Observatory. • There was an extreme-ultraviolet spectroheliograph and an ultraviolet spectroheliograph that were respectively designated as experiments S-082A and S-082B. These experimental packages were also sponsored by the Naval Research Laboratory. • There was a white-light coronagraph (S-052 sponsored by the High Altitude Observatory). • Two hydrogen-alpha telescopes. These were designated as H-alpha no. 1 under the sponsorship of the Harvard-Smithsonian Observatory and H-alpha no. 2 that was sponsored by the NASA Marshall Space Flight Center.

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Fig. 3 Picture of Skylab, the first orbital platform deployed in 1973 (Graphic: courtesy of NASA)

Skylab was launched on May 14, 1973, as the final part of the Apollo program. This in-orbit lab was 36 m long and 6.7 m in diameter and flew at an altitude of 435 km. Three different Apollo crews manned the Skylab during its 9 months of active experiments. The three crews that operated the experiments over this period were as follows. The first crew was Charles (Pete) Conrad, Joseph Kerwin, and Paul Weitz, and they ran experiments from May 25 to June 21, 1973. The second crew was Alan Bean, Owen Garriott, and Jack Lousma who were aboard the Skylab from July 28 to September 24, 1973. The final crew for Skylab was composed of Gerald Carr, Edward Gibson, and William Pogue. This final crew flew onboard the Skylab from November 16, 1973, to February 8, 1974. Skylab actually lost one of its solar panels plus part of its external shielding during its launch and deployment sequence. Skylab astronauts thus had to rig up on an extemporaneous basis an improvised type of shield out of reflective material to keep their habitat comfortable from solar heating and also to keep the instrumentation at reasonable temperatures. Skylab reentered the Earth’s atmosphere in 1979 over Australia on a controlled deorbit. This reentry was over a year earlier than had first been anticipated (Fig. 3). A number of key findings resulted from these intensive series of solar experiments. The “soft” X-ray telescope was able to produce images over the range of ˚ ) as viewed through six different filters. This wavelengths from 6 to 49 angstroms (A data was returned to Earth and processed in the form of a video film. Coronal holes were revealed as dark regions in which the hot coronal material is very thin. X-ray bright points are small, compact, short-lived “brightenings” that are most easily seen in the coronal holes themselves. Coronal holes were observed to rotate fairly precisely and maintain their shape through several 27-day solar rotations in spite of the variations in rotation rate of the solar surface. These videos suggested that the sun was actually brighter during the maximum sunspot

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sequences, since the bright spots on the edge of the sunspots were significantly brighter. This was the first time that these various solar features had been so precisely revealed (Skylab Image).

Solar Maximum Mission (SMM) (1980–1989) The Solar Maximum Mission satellite (or SolarMax) was designed to carry out research with regard to various solar activities, but its special focus was with regard to solar flares. It was launched on February 14, 1980, and ended its mission in 1989. After less than a year of operation, it became limited in its experimental functions due to an onboard failure. It had continued for another 7 years. The SMM was the first satellite based on the Multimission Modular Spacecraft bus manufactured by Fairchild Industries, a platform which was later used for Landsats 4 and 5 as well as the Upper Atmosphere Research Satellite (UARS). Although the spacecraft had seven different experimental instruments, perhaps most significant was the Active Cavity Radiometer Irradiance Monitor (ACRIM) since this instrumentation was used in at least two other satellites including the UARS and ACRIM satellites as noted below. This ACRIM module was used to measure the total solar irradiance (TSI) of the sun for an extended period of time. The other instruments about the SMM included the coronagraph/polarimeter, the ultraviolet spectrometer and polarimeter, soft X-ray polychromator raster imager, hard X-ray burst spectrometer, and a gamma ray spectrometer. In January 1981, the attitude control system failed and limited its pointing ability to focus on the sun. In order to maintain point ability, it was necessary to use the satellites’ magnetorquers to achieve some degree of orientation. In this mode a “wobble” was introduced in the satellite’s solar pointing ability. Only three of the seven solar observing instruments onboard the SMM could continue to be used in this mode of operation since pointing accuracy was greatly impaired. During Space Shuttle Challenger mission, the SMM was intercepted to make some repairs and undertake maintenance. SMM had fortunately been designed so that it could be captured for this purpose. In this way the SMM’s entire attitude control system was retrofitted, and the electronics for coronagraph/polarimeter were updated. Finally a gas cover was installed over the X-ray polychromator to improve its performance (Fig. 4). The Solar Maximum Mission ended on December 2, 1989, when the spacecraft reentered the atmosphere and burned up. The SMM also discovered ten sungrazing comets between 1987 and 1989 (Solar Maximum Mission).

The Upper Atmosphere Research Satellite (UARS) (1991–2005) This satellite was launched in 1991 by the Space Shuttle Discovery. It was 10.7 m (35 ft) long and 4.5 m (15 ft) in diameter, weighed 5,900 kg (13,000 lb), and carried ten instruments. UARS orbited at an altitude of 600 km (375 miles) with an orbital

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Fig. 4 The Solar Maximum Mission (SMM) satellite (Graphics: courtesy of NASA)

inclination of 57 . Designed to operate for 3 years, six of its ten instruments functioned for over 14 years, and it was officially terminated in its mission as of December 14, 2005. The primary purpose of UARS was to study the upper atmosphere and to measure ozone and other polluting chemical compounds found in the ozone layer which affect ozone chemistry and processes. Thus the main focus of UARS related to the Earth’s atmosphere and elements of climate change and issues related to the ozone layer as well as to measure winds and temperatures in the stratosphere. Nevertheless it is included here because it also did measure the energy output from the sun. It has played a key role in measuring total solar irradiance (TSI) over the last nearly 25 years on a continuous basis (The Upper Atmosphere Research Satellite).

The Active Cavity Radiometer Irradiance Monitor (ACRIM) Satellite (1999–2013) The Active Cavity Radiometer Irradiance Monitor Satellite, or ACRIMSAT, is a dedicated satellite and instrument that is one of the 21 primary observational components of NASA’s Earth Observing System program and represents the most recent satellite to measure the total solar irradiance from the sun. ACRIMSAT was launched on December 20, 1999, from Vandenberg Air Force Base as the secondary payload on a Taurus rocket along with KOMPSAT and placed into a high inclination, 700 km sun-synchronous orbit from which the ACRIM III instrument monitors total solar irradiance (TSI). The ACRIM III represented the third generation of this type of device that flew first with the SMM spacecraft, then with the UAR, and finally with the ACRIM satellite. It was thus able to extend for a period of well over 20 years of the total solar irradiance (TSI) database began by the earlier spacecraft (ACRIM I: 1980–1989 on the SMM) and (ACRIM II: 1991–2001) on the Upper Atmosphere Research Satellite (UAR).

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Fig. 5 Results of total solar irradiance monitoring at 1 AU since 1978 (Graphic courtesy of NASA)

ACRIMSAT was a single-purpose satellite manufactured by Orbital Sciences Corporation that has achieved a 14-year lifetime that has gone well beyond its projected 7-year mission lifetime. Upper Atmosphere Research Satellite ACRIMSAT/ACRIM3 tracked the TSI during a 2004 transit of Venus and measured the 0.1 % reduction in the solar intensity caused by the shadow of the planet. It also recorded data for the 2012 transit of Venus which was a particular bonus of this satellite’s extended lifetime. The ACRIMSAT spacecraft included the ACRIM III instrument that represented the perfection of the ACRIM I and II solar irradiance monitors – all of which were designed and built by the Jet Propulsion Lab. This small satellite, which represented NASA’s efforts to create smaller, cheaper, and better spacecraft, was a secondary payload on a Taurus vehicle that launched on December 1999. This satellite thus continued to extend the database first created by ACRIM I, which was launched in 1980 on the Solar Maximum Mission (SMM) spacecraft. ACRIM II followed on the Upper Atmosphere Research Satellite (UARS) in 1991. ACRIMSAT then took over this mission in 1999. As can be seen in Fig. 5, there is now considerable data over decades from solar research and weather satellites that indicate fluctuations in the solar power output over time (Results from the ACRIM).

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The Active Cavity Radiometer Irradiance Monitor (ACRIM) instruments, however, were significantly the first to clearly demonstrate that the total radiant energy from the sun was not a constant, but actually varied a perceptible amount over time. The fact that this variation was only at about 0.1 % was difficult to detect until the first ACRIM instruments flew. This variation is nevertheless significant in that even this small degree of variation can and indeed does impact climate change on Earth. Some scientists believe that as much as 25 % of climate change variations can be attributed to changes in the sun’s energy output. This still confirms that the other variations arise from Earth-based origins. The ACRIMSAT mission was funded by NASA through the Earth Science Programs Office at Goddard Space Flight Center. And additional data on the ACRIM III data measurements are available through the NASA Langley Center (ACRIMSAT).

The Ulysses High-Latitude Solar Space Probe (1990–2008) Ulysses is a decommissioned experimental spacecraft launched on October 6, 1990, as joint mission of NASA and the European Space Agency. The main objective of Ulysses was to study the sun’s radiation and ion emissions from all latitudes. It was able to function from 1994 to 1995 and then again in 2000–2001 and yet again in 2007–2008. These observation periods that were 6 years apart stemmed from the fact that the probe had to be sent to Jupiter first to change its orbit to be able to see the sun from its polar regions. Ulysses also had other mission objectives that included examining the characteristics of tails of comets and to measure the gravitational and magnetic characteristics of the sun. It was amazingly successful in accomplishing all of these objectives and successfully operating some 18 years from October 1990 through July of 2008. It was thus able to complete three cycles of closeup observation of the sun from its polar regions at high latitudes which had not been accomplished previously (Fig. 6). The key determinant of the Ulysses mission design was the objective to observe the sun at all latitudes including the solar polar regions that are difficult to reach from the Earth since we are located in the plane of the planets. To achieve this huge change in the orbital inclination of a spacecraft from essentially 0 to about 80 requires a huge delta increase in velocity. The propulsion system for the Ulysses spacecraft that was chosen was the Space Shuttle plus an Inertial Upper Stage. This would not supply sufficient thrust to accomplish the mission, and thus the solution was to employ a so-called gravity assist maneuver around Jupiter. This created an additional problem in that a trajectory that looped around Jupiter to create the highlatitude orbit around the sun dictated that solar cells could not be used to power the mission because Jupiter was too far away from the sun. This required a radioisotope power system to support the mission. This ended with Ulysses being powered by a radioisotope thermoelectric generator (RTG). Ulysses was originally scheduled for launch in May 1986 aboard the Space Shuttle Challenger. With the loss of Challenger, the launch of Ulysses was delayed until October 6, 1990, aboard Discovery (mission STS-41).

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Fig. 6 The Ulysses space probe as visualized in space observing the sun (Graphic: courtesy of NASA)

The Ulysses probe was equipped with an impressive array of experimental instruments. These included the following: • Radio/plasma antennas. This was a complex arrangement. First there were two beryllium-copper antennas that were the primary sensors. These dipole antennas were unreeled outward from the body and deployed perpendicular to the spin axis of the satellite. This dipole antenna when extended reached an impressive 72 m in length and thus had a high degree of sensitivity. A third antenna in the form of a hollow beryllium-copper tube was deployed from the body. This was extended along the spin axis and opposite the dish that was used to provide the data relay of instrument’s observations. This additional monopole antenna was 7.5 m long. These radio/plasma antennas were developed to measure the strength of radio waves generated by plasma releases from the sun. • Experiment boom. There was also a specially designed boom that contained various sensors. This boom was shorter and extended from the last side of the spacecraft, opposite the radioisotope power supply. This was a hollow carbonfiber tube, of 50 mm diameter. This experimental boom carried four types of instruments. A solid-state X-ray instrument was composed of two silicon detectors to study X-rays from high-energy solar flares. There was also an experiment to detect gamma ray bursts (GRBs). This experiment consisted of two specially designed scintillator crystals with photomultipliers. Two different magnetometers were mounted. These were a helium magnetometer to study the vector of the solar magnetosphere and a flux-gate magnetometer to detect the level of the magnetic flux. Finally there was magnetic search coil antenna. All of these devices were mounted in the experiment boom.

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• Body-mounted instruments. In addition to the experiment boom and the radio/ plasma antennas that extended from the probe, there were detectors mounted in the body of the spacecraft in the so-called quiet section of the probe. These instruments were variously able to detect electrons, ions, neutral gas, dust, and cosmic rays. • SWOOPS (Solar Wind Observations Over the Poles of the Sun). This was the final instrument, and it was designed to measure the existence of both positive ions (i.e., positrons) and electrons. The Ulysses upon its launch became a part of the so-called InterPlanetary Network (IPN). The purpose of the IPN is to detect and record the frequency and nature of gamma ray bursts (GRBs). This is very difficult to do for several reasons, including the fact they cannot be deflected with mirrors. Thus one needs the gamma ray detectors on spacecraft that are very far apart, and then the nature and directionality of the GRB can be determined by triangulation (or if there are enough gamma ray telescopes in play by many multiple observations that can be consolidated). Each spacecraft equipped with a gamma ray detector can record with exact time measurements. The object is to compare the arrival times of gamma showers with the known separations of the spacecraft and adjustment for the speed of light transmission times. Several spacecraft orbiting the Earth, an inner-solar-system probe (to Mars, Venus, or an asteroid), and Ulysses were combined together to form this InterPlanetary Network (IPN) to detect gamma ray bursts. Ulysses, because of its great distance away from the sun, was a particularly demanding yet critical part of the IPN and its gamma ray burst determinations. Ulysses monitored solar flares (i.e., GRBs) but also observed solar weather (ionic emissions) and coronal mass ejections. Specifically Ulysses was able to accomplish the following primary objectives: (i) Ulysses discovered that the sun’s magnetic field interacts with the Solar System in a more complex fashion than previously assumed; (ii) Ulysses discovered that dust coming into the Solar System from deep space was 30 times more abundant than previously expected; (iii) in 2007–2008, Ulysses determined that the magnetic field emanating from the sun’s poles is much weaker than previously observed; and (iv) the solar wind had tended to become weaker during its mission and is currently thought to be at its weakest since the start of the Space Age (Ulysses).

Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) (2002–) This spacecraft was designed by NASA and investigators at the University of California, Berkeley. This satellite was launched in 2002 to study gamma ray emissions from solar flares. RHESSI’s primary mission was to explore the basic physics of particle acceleration and explosive energy release within solar flares by high-energy radiation. This satellite achieved its research goals through imaging spectroscopy of the X-rays and

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gamma rays released during gamma ray bursts. The RHESSI was equipped with precision spectroscopes with precise angular and energy resolution. It was thus able to reveal the spectra of the most rapidly accelerated electrons and ions within even the hottest plasma of the coronal mass ejections. Scientists are still seeking to understand how the energy equivalent of quadrillions of tons of TNT can be suddenly released in the solar atmosphere on time scales measured in only seconds or minutes and how so many electrons, protons, and heavier ions can be accelerated to such high energies so rapidly via magnetic fluxes of the sun. These super-energetic solar eruptive events are the most extreme drivers of space weather and present hazards to astronauts, satellites, electrical grid systems, and indeed any electrical device. The RHESSI and Yohkoh (Solar-A) satellites have been intensive studying for some years the “pattern” and “nature” of solar flares and their relationship to CMEs without developing a firm theoretical understanding of these events other than to understand that they are related to magnetic energy releases within the sun and in sequence with the solar max/solar minimum cycle. There has been scrutiny of recurring patterns of behavior, polarization patterns, plasma composition, intensity of energy release, and geographic patterns. This has occurred over a number of years without a widely agreed understanding of why solar flares of such great intensity occur and why some flares are accompanied by CMEs and others not (The RHESSI Satellite). Perhaps an even greater mystery is the nature of flares from more distant cosmic sources. RHESSI and other satellites allowed astronomers around the world to record in late 2005 the brightest explosion ever of high-energy X-rays and gamma rays. This sudden flash came not from the sun but from the other side of the Milky Way galaxy. Despite coming from many, many light years away, this radiation release was still strong enough to affect the Earth’s atmosphere. The flash, called a soft gamma repeater flare, reached Earth on Dec. 27, 2005, and was detected by at least 15 satellites and spacecraft between Earth and Saturn, swamping most of their detectors. Some of the best observations were recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Kevin Hurley from the University of California-Berkeley’s Space Sciences Laboratory who leads a major international team that studies such cosmic radiation simply said: “It was the mother of all magnetic flares—a true monster.” The current theory is that this is a mighty cataclysm in a superdense, highly magnetized star called a magnetar; it emitted as much energy in two-tenths of a second as the sun gives off in 250,000 years (RHESSI Satellite Captures Giant Gamma Ray Flare).

Coriolis Satellite: (2003–2006) Coriolis was a joint Air Force Space Test Program and Space Naval Warfare Systems Command (SPAWAR) project. This satellite was launched from the Vandenberg Air Force site in 2003. The satellite contains a Solar Mass Ejection

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Imager (SMEI) which is an all-sky set of cameras (each with 180 of view) that was able to monitor over a 3-year period from 2003 to 2006 coronal mass ejections (CMEs). The prime objective of this part of the mission was to detect the degree of geomagnetic disturbance that these superhigh-speed ionic ejections actually created. The Coriolis satellite also included quite unrelated Windsat instrumentation that measured ocean wind velocities. This part of the mission included a Conical Microwave Imager Sounder (CMIS) that allowed the measurement of ocean wind velocities and directional vectors. While the OSO spacecraft and the Skylab experiments concentrated on solar flares and gamma and X-ray emissions, Coriolis focused on coronal mass ejections. The major finding was the coronal mass ejections did indeed create disturbances to the geomagnetosphere. The key instrumentation on the Coriolis spacecraft for experiments related to the sun was the Solar Mass Ejection Imager (SMEI). This was a 35 kg camerabased sensor developed by the USAF Research Laboratory (AFRL), but the actual devise was constructed at the University of Birmingham, UK, and the University of California at San Diego (UCSD). The overall contractor for Coriolis was Spectrum Astron. The SMEI monitored solar activity through three-linked camera that allowed a complete field of view (FOV) or full-sky coverage during each of the space orbits. This allowed not only a correlation between CMEs and changes to the Earth’s magnetosphere but also allowed alerts to potentially damaging Earthbound CMEs. Since the detection traveled at the speed of light (about 8 min from the sun to Earth orbit) and the CMEs travel at only a fraction of that speed (i.e., at millions of kilometers an hour vs. 300,000 km a second), this allowed the protection of space assets. The powering down of satellites which is done for military, governmental, and commercial spacecraft is the main protective action (The Coriolis Satellite).

Yohkoh (Solar-A: Sunbeam) (1991–2001) On August 31, 1991, the Yohkoh satellite was launched into space from the Kagoshima Space Center (KSC) in Southern Japan. This satellite, known as Yohkoh (“Sunbeam”), was a project of the Japanese Institute of Space and Astronautical Science (ISAS) that was designed before ISAS was consolidated with JAXA. The United States and the United Kingdom also collaborated to design and manufacture instruments for the spacecraft as well. The scientific objective of Yohkoh was to observe solar flares in both the gamma and X-ray frequencies. Yohkoh included the two spectrometers to sense gamma rays and two X-ray telescopes as follows: • A Bragg and Wide Band Spectrometer known as BCS and WBS, respectively • The soft X-ray telescope (SXT) and the hard X-ray telescope (HXT)

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The Bragg telescope consisted of four bent crystal spectrometers. Each crystal was designed to observe a limited range of soft x-ray emissions tuned to the spectrum of hot plasma that is produced during solar flares. The observations of these spectral lines provided information on the characteristics of the hot plasma generated by solar flares. The WBS was designed to operate over the complete range of wavelengths from soft x-rays to gamma rays with sensing over this entire spectra being accomplished about once a second. The SXT obtained information about the temperature and density of the plasma that emitted the observed X-rays. This was done by comparing images acquired via different filters set to different X-ray bands. Flare images could be obtained every 2 s. Smaller images obtained via a single filter could be obtained as frequently as once every 0.5 s. The HXT observed hard X-rays in four energy bands in a large number of grids. Images of the higher spectra X-rays could be sensed as frequently as once every 0.5 s. The Yohkoh spacecraft was in a slightly elliptical low-earth orbit with a perigee of 570 km and an apogee of 730 km with a 90 min orbital period and the ability to observe the sun about two-thirds of the time. The satellite was designed so it could operate in several spacecraft modes and several different subsystem modes. The two modes of principal interest were the quiet mode and flare mode. Switching between these two particular modes was controlled by a flare flag generated by the WBS instruments. The Yohkoh satellite completed its mission in 2001, and the Hinode satellite with improved capabilities was deployed in 2006 to obtain new data with much higher-resolution capabilities (Yohkoh (Solar-A)).

Hinode (Solar-B: Sunrise) (2006–2009) The Hinode (or Sunrise) probe was a JAXA mission to study the sun’s magnetic fields that was carried out in cooperation with NASA in the United States and the United Kingdom. It is the follow-up to the Yohkoh (Solar-A) mission. Hinode was launched on the final flight of the M-V-7 rocket from Uchinoura Space Center, Japan, on September 22, 2006. The key participant in this project was the ISAS part of JAXA that developed the M-V rocket and leads the JAXA interplanetary studies effort. Initial orbit has a perigee height of 280 km, an apogee height of 686 km, and an inclination of 98.3 . Then the satellite maneuvered to the quasi-circular sun-synchronous orbit over the day/night terminator, which allows near-continuous observation of the sun. On October 28, 2006, the probe’s instruments captured their first images. Hinode was planned as a 3-year mission to explore the magnetic fields of the sun. It consists of a coordinated set of optical, extreme-ultraviolet (EUV), and X-ray instruments to investigate the interaction between the sun’s magnetic field and its corona. The result will be an improved understanding of the mechanisms that power

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the solar atmosphere and drive solar eruptions. NASA, the space agency of the United States, developed three science instrument components, the focal plane package (FPP), the X-ray telescope (XRT), and the extreme-ultraviolet imaging spectrometer (EIS), and shares operations support for science planning and instrument command generation. Hinode carries three main instruments to study the sun: • Solar optical telescope (SOT). The SOT represented a 0.5 m Gregorian optical telescope made up of three optical instruments. These elements are (i) a Broadband Filter Imager (BFI) which produces images of the solar photosphere and chromosphere, (ii) the Narrowband Filter Imager (NFI) which is capable of producing magnetograms and Doppler-based images of the solar surface, and (iii) spectropolarimeter (SP) which is capable of producing magnetograph maps of the photosphere. What is particularly notable about the SOT is the spatial resolution which is a factor of 5 improvements over previous space-based solar telescopes (e.g., the MDI instrument on the Solar and Heliospheric Observatory (SOHO) satellite and the sensors on the TRACE and Yohkoh satellites.) • X-ray telescope (XRT). This device was designed to image the solar corona’s hottest components and capable of ranging over 500,000–10 million degrees K and also capable of capturing a complete image of the entire sun. • EIS (extreme-ultraviolet imaging spectrometer). This extreme-ultraviolet (EUV) spectrometer was designed to resolve the solar spectrum into two different wavelength bands of 17–21 nm and 24.5–29 nm. This spectra range is designed to align with UV radiation over a range of 50,000  K to 20 million degrees Kelvin. This allows precise mapping of the high-beta plasmas in the solar corona (Hinode (Solar B)).

Transition Region and Coronal Explorer (TRACE) (1998–2010) The objective of the Transition Region and Coronal Explorer (TRACE) satellite, which was launched on April 1, 1998, included the exploration of the threedimensional magnetic structures in the visible surface of the sun’s photosphere. TRACE thus sought, by use of this type of magnetic mapping, to help define both the geometry and dynamic shaping of the sun’s upper solar atmosphere. In essence TRACE sought to achieve a “magnetic mapping” of the Transition Region just below the solar corona as well as the corona itself. The TRACE spacecraft was able to take images of the solar plasma emitted in a range of temperatures that were only at about 6,000  K in the photosphere (i.e., the low-beta plasma area), but then rapidly transition up to millions of degrees Kelvin in the corona (i.e., the high-beta plasma area). In light of the extreme temperature gradients between the photosphere and the corona, this part of the sun’s Transition Region is very difficult to model. TRACE sought to accomplish this type of wide magnetic mapping by observing over time the various wavelength emissions from the low- and

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Fig. 7 This colorized image shows the transitions from “low-beta” plasma to “highbeta” plasma that creates high-energy magnetic loops that are thought to give rise to solar flares and coronal mass ejections (CMEs) (Graphic: courtesy of NASA)

high-beta plasmas. This smaller solar research probe worked in conjunction with the larger and more sophisticated SOHO probe that is addressed later in this chapter. This data from the plasma temperature transitions and the magnetic loops they engender is critical to understanding the sun’s physical process since so many critical functions occur in this Transition Region. These functions include plasma confinement, reconnection, wave propagation, and plasma heating. These functions are considered vital to understanding the relationship between solar flares and coronal mass ejections that appear to originate at different levels of the sun’s surface. TRACE is the first spacecraft designed to study this transitional process from low-beta plasma to high-beta plasma. As a result of the temperature transitions that can range up to 10 million degrees K, new magnetic flux can be detected emerging through from solar surface. These magnetic loops can then organize into local concentrations. The largest of these concentrations or magnetic loops can then become sunspots which are, in fact, strong magnetic loops that roil the sun’s highenergy plasma. The emergence of new magnetic fluxes can have profound effects on the overlying atmosphere of the solar surface. This can then lead to the release of significant amounts of energy (both solar flares and CMEs) as well as result in a restructuring of the corona as well as the interplanetary medium. These events can be sufficiently energetic to impact the Earth’s magnetosphere and certainly impact space weather from the sun. TRACE thus observed and mapped both the “quiet” solar atmosphere and the more episodic active portions of the sun and fortunately was able to do so over an extended period of time (Fig. 7) (TRACE).

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Conclusion Great strides have been made in understanding the sun and its heliophysics since the Orbiting Solar Observatory satellites were first launched in the early 1960s. The various spacecraft probes on behalf of the United States, the United Kingdom, Germany, France, and Japan as carried out through civilian, academic, and military programs have contributed to the knowledge of solar flares, space weather, and total solar irradiance. These missions have also helped to better understand the coronal mass ejections, the low-beta plasma, and the high-beta plasma interactions and how these severe temperature gradients lead to the creation of magnetic loops at the sun’s surface, the generation of sunspots. Also a better understanding of the sun’s magnetic fields has also led to a better understanding of the sun’s cyclic behavior in response to the solar maximum and solar minimum 11-year cycle as well as an understanding that there are longer-term cycles. The various satellites such as OSO, Solwind (P78-1), Helios-A and Helios-B, the Skylab experiments, the Solar Maximum Mission, UARS, ACRIMSAT, Ulysses, Coriolis, RHESSI, Yohkoh (Solar-A), Hinode (Solar-B), and TRACE have advanced the state of solar research in many ways. These pioneering missions have blazed the trail for current solar research that has some of the most sophisticated tools in space ever to study the sun and other galactic phenomena. This does not include every satellite that has produced some information about the sun, but it has sought to include some of the most important missions that have provided information about solar threats from flares, coronal mass ejections, and magnetic anomalies as well as new and useful information about cosmic radiation threats. New initiatives that are just beginning such as the Russian Koronas-Foton solar satellite research program as well as those from space research programs around the world will bring within the next decade important new knowledge forward. The newest NASA solar probe that will, when launched, come within 9 solar diameters of the sun should reveal vital new information. In the chapters that follow, some of the most important recent and current missions and solar research programs, particularly in the context of solar threats, will be described in even greater detail.

Additional Information Also see the relevant web sites of the European Space Agency, ISAS/JAXA, NASA, and its various centers, especially Jet Propulsion Labs and Goddard Space Flight Center. Also see the relevant web sites for the US Air Force.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Fundamental Aspects of Coronal Mass Ejections

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▶ NASA Wind Satellite (1994) ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Dynamics Observatory (SDO) ▶ Solar Flares and Impact on Earth ▶ STEREO as a “Planetary Hazards” Mission

References ACRIMSAT official web page at JPL. http://ww.acrim.jpl.nasa.gov. 9 Apr, 2014 Helios 1 and 2. The encyclopedia Astronautica. http://astronautix.com/craft/helios.htm. 9 Apr 2014 Helios 2. heasarc.gsfc.nasa.gov/docs/heasarc/missions/helios2.html. 9 Apr 2014 Hinode (Solar B). http://solarb.msfc.nasa.gov/. 9 Apr 2014 Merdin P (ed) (2001) Encyclopedia of astronomy and astrophysics. Hampshire, UK Registered No. 785998 Nature Publishing Group and Institute of Physics Publishing Dirac House, Bristol OSO: Orbiting Solar Observatory. http://www.mediahex.com/Orbiting_Solar_Observatory. 9 Apr 2014 Results from the ACRIM solar irradiance monitors and other satellites since 1978. http://acrim. com/. 9 Apr 2014 RHESSI Satellite Captures Giant Gamma Ray Flare. http://www.berkeley.edu/news/media/ releases/2005/02/18_magnetar.shtml. 9 Apr 2014 Skylab Image. https://www.google.com/search?q=skylab+images&tbm=isch&imgil= NZuCQh9i4g5LtM%253A%253Bhttps%253A%252F%252Fencrypted-tbn2.gstatic.com%252 Fimages%253Fq%253Dtbn%253AANd9GcQjF13Njs–nCJro9MqU5uL99GHPMmBwT4u4sz8 Bg6m3pAD0Dx1%253B1258%253B1024%253BDB8mn3aXv4ninM%253Bhttp%25253A% 25252F%25252Fen.wikipedia.org%25252Fwiki%25252FSkylab&source=iu&usg=__yqFku1 DNH98y0m8g7AkqCahq7H8%3D&sa=X&ei=5HjJU6uYMcSxyAS3yoKQBA&sqi=2&ved= 0CB8Q9QEwAA&biw=1043&bih=699#facrc=_&imgrc=NZuCQh9i4g5LtM%253A%3BD B8mn3aXv4ninM%3Bhttp%253A%252F%252Fupload.wikimedia.org%252Fwikipedia%252 Fcommons%252Fthumb%252F0%252F07%252FSkylab_(SL-4).jpg%252F1258px-Skylab_ (SL-4).jpg%3Bhttp%253A%252F%252Fen.wikipedia.org%252Fwiki%252FSkylab%3B1258% 3B1024. 9 Apr 2014 The Coriolis Satellite. http://www.astronautix.com/craft/coriolis.htm. 9 Apr 2014. Also see: http:// www.orbital.com/SatellitesSpace/ImagingDefense/Coriolis/. 9 Apr 2014 The Encyclopedia Astronautica. www.astronautix.com/craft/oso.htm The Orbiting Solar Observatory. The encyclopedia Astronautica. www.astronautix.com/craft/oso. htm. 9 Apr 2014 The P78-1 or Solwind Satellite. heasarc.gsfc.nasa.gov/docs/heasarc/missions/p78-1.html. 9 Apr 2014 The RHESSI Satellite Mission findings concerning solar flares. http://hesperia.gsfc.nasa.gov/ rhessi2/home/mission/science/overview-of-solar-flares/. 9 Apr 2014 The Skylab Program. http://solarscience.msfc.nasa.gov/Skylab.shtml. 9 Apr 2014 The Solar Maximum Mission. heasarc.gsfc.nasa.gov/docs/heasarc/missions/solarmax.htm. 9 Apr 2014 The Upper Atmosphere Research Satellite (UARS). http://uars.gsfc.nasa.gov/. 9 Apr 2014 TRACE Mission Results. http://sunland.gsfc.nasa.gov/smex/trace/mission/trace.htm. 9 Apr 2014 Ulysses web site. http://ulysses.jpl.nasa.gov/. Also see: ESA Ulysses web site http://sci.esa.int/ ulysses/42893-ulysses-spacecraft. 9 Apr 2014 Yohkoh (Solar A). http://solarscience.msfc.nasa.gov/Yohkoh.shtml. 9 Apr 2014

NASA Wind Satellite (1994) Adam Szabo

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Orbit of the Wind Spacecraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spacecraft Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Ambient Solar Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coronal Mass Ejections (CMEs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interplanetary Shocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Energetic Particles (SEPs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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The NASA Wind spacecraft, launched in November 1994, provides comprehensive and continuous in situ solar wind measurements while orbiting the Sun–Earth first Lagrange point upstream of Earth. The spacecraft has a full complement of instruments to measure the local magnetic and electric fields and thermal solar wind and high-energy charged particles at unprecedented high time resolutions. After nearly 20 years of operation, the spacecraft and most instruments are fully operational, and Wind is expected to remain in service for many years to come. While Wind provides real-time solar wind measurements for only about 2 h every day – thus it is not considered an operational space weather monitor – the high-quality and continuous Wind observations have been critical in developing current space weather forecasting techniques. In particular, Wind observations led to better understanding of the propagation and evolution A. Szabo (*) Heliospheric Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA e-mail: [email protected] # Springer International Publishing Switzerland (outside the USA) 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_13

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of coronal mass ejections quantifying their distortions and deflections. Wind radio science results significantly added to the understanding of the inner heliospheric propagation of interplanetary shocks and high time resolution field and particle measurements revealed the mechanisms of how these shocks and magnetic reconnection can accelerate charged particles to very high and harmful energies. Wind is expected to continue its contribution to the development of future space weather forecasting capabilities as its measurements near two complete 11-year solar cycles allowing the identification of long-term trends. Keywords

Wind spacecraft • Solar wind • Interplanetary magnetic field • First Lagrange point • Coronal mass ejections • Magnetic cloud • Magnetic flux rope • Interplanetary shocks • Solar energetic particles • Solar flares • Magnetic reconnection • Heliosphere • Magnetosphere • Bow shock • Space weather • Type II radio burst • Solar cycle

Introduction NASA launched the Wind spacecraft in November 1994 to the Earth’s first Lagrange point (L1) as the interplanetary component of the Global Geospace Science (GGS) program within the International Solar Terrestrial Physics (ISTP) program. An orbit around the L1 point, upstream of Earth, toward the Sun, and four times further away than the Moon, provides a unique opportunity to observe the undisturbed solar wind before it impinges on the Earth’s magnetosphere (see Fig. 1). The original science objectives of the Wind mission were (1) to make accurate in situ measurements of interplanetary conditions upstream of the magnetosphere to complement measurements made inside the magnetosphere by the Polar and Geotail spacecraft, other elements of the GGS program, and (2) to remotely sense interplanetary disturbances for possible future predictive purposes. The spin-stabilized Wind spacecraft – spin axis aligned with ecliptic south – carries eight instrument suites that provide comprehensive and continuous measurements of the thermal solar wind to solar energetic particles, quasi-static magnetic and electric fields to high-frequency radio waves, and γ-rays. After nearly 20 years of operation, Wind is still returning all of these measurements that became essential for solar wind studies and serves as 1 AU baseline for deep space (inner and outer heliospheric) missions and as a reliable input for magnetospheric investigations long after the termination of the GGS and ISTP programs. The sections below review the rich contributions of the Wind mission to the subject of understanding the structure and propagation of coronal mass ejections (CMEs), interplanetary shocks, and corotating interaction regions (CIRs) and to the acceleration and transport of solar energetic particles (SEPs).

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Fig. 1 Artist depiction of the Wind spacecraft orbiting the Sun–Earth first Lagrange point observing the incoming solar wind. The two long booms hold the magnetometers and the four wire antennas, and two axial booms measure the electric magnetic field waves. The other instruments are housed inside of the spacecraft body

The Orbit of the Wind Spacecraft The first Sun–Earth Lagrange point, on the Sun–Earth line between the two objects, marks the position where the combined gravitational pull of the Sun and Earth provides precisely the centripetal force required to orbit with them. Thus a satellite at L1 will have a heliocentric orbit with a slightly smaller orbital radius but the same angular speed as Earth. In effect, the spacecraft will appear from Earth to be motionless, hovering 1.5 million km (or four times further than the Moon) upstream of Earth. In practice, the L1 Lagrange point – named after the eighteenth-century Italian mathematician and astronomer Joseph-Louis Lagrange – is not stable due to the eccentricity of the Earth’s orbit and other forces. Neither is it desirable to park a spacecraft exactly on the Sun–Earth line, making communication with it difficult due to intense radio emissions from the Sun. Fortunately, there exists a class of semi-periodic – not exactly repeating but bounded by a box – orbit around L1, called a Lissajous orbit that keeps the spacecraft outside of a 3–4 solar radio exclusion region, yet keeps it continuously upwind from Earth with minimal orbit correction requirements. The Wind spacecraft was only the second mission to take advantage of this kind of an orbit after the very successful ISEE-3 mission (1978–1982). After a number of petal orbits and a double lunar swingby, Wind reached L1 in 1996. However, it did not stay in the vicinity of L1 for long as it was soon joined

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Fig. 2 The complex orbit of the Wind spacecraft between 2001 and 2004 in ecliptic coordinates. The plot is centered on Earth with the Sun to the left. The lunar orbit is marked by blue dashed lines

there by the Advanced Composition Explorer (ACE), another NASA solar wind mission. With Wind’s very large fuel reserve and with its spin axis perpendicular to the ecliptic (ACE’s spin axis is pointing at the Sun in constant need of realignment as the spacecraft is orbiting around the Sun), it was decided to relocate the Wind spacecraft to various, scientifically advantageous locations. In 1999 Wind executed a number of magnetospheric petal orbits that took it to the rarely sampled geomagnetic high latitudes. Between 2000 and 2002, Wind moved further and further away from the Sun–Earth line (and from ACE) reaching 2.3 million km to the side in a distant prograde orbit (see Fig. 2). Finally in 2003 it completed a second Lagrange (L2) point campaign, taking the spacecraft more than 1.5 million km downstream of Earth and ~3 million km downstream of ACE, to investigate solar wind evolution and magnetotail phenomena. Since 2004 Wind has remained at L1 in a Lissajous orbit bounded by +/ 600,000 km perpendicular to the Sun–Earth line in the ecliptic and +/ 120,000 km perpendicular to the ecliptic. It should be noted that

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this is a very large orbit as the maximum radius of the Earth’s geomagnetic tail is only around 150,000 km. Thus, propagating solar wind observations to Earth is a nontrivial task. The Wind spacecraft has enough fuel left to maintain its current orbit for almost 60 more years.

Spacecraft Design Wind was designed and manufactured by Martin Marietta of Astro Space Division in East Windsor, New Jersey. The satellite is a spin-stabilized cylindrical satellite with a diameter of 2.4 m and a height of 1.8 m (see Fig. 1). It has an approximately 3 s rotation period. With its 1,150 kg mass, two 50 m and two 7.5 m wire antennas, and two 12 m lanyard booms, the spacecraft has an immense angular momentum, rendering it an extremely stable platform, ideal for long-term, continuous solar wind measurements. Wind has body-mounted solar panels, only some of which see the Sun at any given time. At the beginning of the mission, the solar panels generated 472 W of power with a 100 W margin that allowed for ample aging degradation. The spacecraft will be able to operate all its subsystems simultaneously at least for the next 10 years. The instruments record their measurements to a tape deck, from which it is read back at high speed, nominally once a day for 2 h. This downlink telemetry takes place via an S-band system to the NASA Deep Space Network (DSN) at 64 kbps.

Instrumentation The Wind spacecraft carries eight instrument suites that provide comprehensive measurements of the solar wind thermal particles to solar energetic particles, quasistatic electromagnetic fields to high-frequency radio waves, and γ-rays. Table 1 lists all of these instrument suites and their capabilities and current status. Wind’s complement of instruments was optimized for studies of solar wind plasma, interplanetary magnetic field, radio and plasma waves, and low energetic particles. The instrument suite is not equivalent to that on ACE, rather the two missions complement each other. Wind is the only near-Earth spacecraft capable of making remote radio wave measurements and hence tracking interplanetary shocks from the Sun to Earth. Moreover, Wind provides solar wind measurements with an unprecedented accuracy. It measures solar wind particle densities with three different instruments (SWE, 3DP, and WAVES) relying on different measurement techniques. Intercalibrating these three observations yields an absolute accuracy of better than 1 %. Wind also provides the highest time resolution measurements in the near-Earth environment (11 vectors/s for magnetic field and a 3 s cadence for plasma observations). Finally, Wind has accumulated solar wind observations for nearly two complete solar cycles (a solar magnetic cycle is ~11 years long). Thus, Wind is ideally positioned to study solar wind transients that have adverse space weather effects.

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Table 1 The Wind spacecraft instrument suite and its current status Instrument Magnetic field investigation (MFI) Solar wind experiment (SWE) 3D plasma experiment (3DP)

Radio and plasma wave experiment (WAVES) Suprathermal particle experiment (SMS) High-energy particle experiment (EPACT) KONUS Transient gamma-ray spectrometer (TGRS)

Description Slowly varying vector magnetic fields (0–64,000 nT, 0–5.5 Hz)

Status Fully operational

Density, velocity, and temperature of solar wind thermal ions (150 eV–8 keV) and electrons (5 eV–24.8 keV) Full 3D distribution function of solar wind ions and electrons (3 eV–30 keV) Energetic ions (25 keV–11 MeV) and energetic electrons (20 keV–1 MeV) Electric and magnetic field waves (0.3 Hz–14 MHz)

Ion sensors fully operational. Electron measurements limited to energies below 5 keV

Suprathermal ions (H–Fe) in the energy range (0.5–226 keV/e)

Energetic particles (0.04–500 MeV/nuc)

High-time resolution gamma-ray detector High spectral resolution gamma-ray detector in the energy range 15 keV–10 MeV

Fully operational

Fully operational

The low-energy SWICS sensor is not operational The STICS and MASS sensor fully operational Only the lower-energy detectors LEMT and STEP are operational (0.04–10 MeV/nuc) Fully operational All the coolants used up. Instrument turned off

The Ambient Solar Wind The visible surface of the Sun, the photosphere, is at an effective temperature of 5,800 K, and it continuously emits charged particles called the solar wind. This solar wind – composed mostly of protons and electrons, 4 % (by number) helium nuclei (alpha particles), and traces of heavier ions – is heated to over a million degrees of Kelvin in the solar corona, 2,000 km above the photosphere. The solar wind particles are not only heated but also accelerated to 200–800 km/s of speed dragging with them the magnetic field of the Sun. This enormous speed (a fast bullet can reach 1 km/s and the fastest spacecraft launch ever was 16.26 km/s for New Horizon, a mission to Pluto) is faster than information can travel in this medium. Thus, as the solar wind flow approaches obstacles (like planets), information cannot flow upstream fast enough to divert the particles and they pile up

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Fig. 3 Artist rendition of the solar wind flowing around the Earth’s magnetosphere. The blue lines represent plasma flow directions. The yellow lines connected to Earth are magnetic field lines (Courtesy of K. Endo and Prof. Yohsuke Kamide)

forming a shock wave, not unlike a sonic boom in front of a supersonic airplane. In the case of Earth, this shock wave, called the bow shock, forms around 100,000 km, or 15 Earth radii upstream, toward the Sun. At this boundary, the solar wind particles abruptly slow down and change direction to flow around the planet (see Fig. 3). The Earth is a magnetized planet; thus, the obstacle that the solar wind plasma reacts to is not the surface of the planet, but its magnetic field that charge particles cannot cross. In turn, the shocked solar wind flowing around the planet compresses the Earth’s magnetic field into a large bubble, called the magnetosphere, till an energy balance is reached between the kinetic energy of the incoming solar wind flow and the magnetic energy of the magnetosphere. This energy balance boundary, the magnetopause, is just above 60,000 km at the subsolar point. Solar wind particles cannot cross through the magnetopause and thus cannot reach the surface of the Earth except near the magnetic poles where the vertically oriented magnetic field lines can exert only minimal pressure. But even at the magnetic poles, the extremely low-density solar wind of 10 particles per cubic centimeter (compared to 6  1023 particles/cm3 of the surface atmosphere) is quickly absorbed by the neutral atmosphere posing no danger to humankind. Therefore, it is not the ambient solar wind that represents a cosmic hazard. Rather, the large transients embedded in it that cause rapid variations in the compression of the magnetosphere are the chief culprit. These transients are discussed in the next sections.

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Coronal Mass Ejections (CMEs) Coronal mass ejections (CMEs) are the most hazardous solar transients for man-made systems like electric power grids or oil pipelines. Sometimes as frequently as several times a day, but at least once every couple of weeks, the Sun ejects an extra dose of charged particles. Most of these CMEs originate from active regions on the Sun’s surface, such as groupings of sunspots associated with frequent solar flares. These regions have closed magnetic field lines, in which the magnetic field strength is large enough to contain the plasma. These field lines must be broken or weakened – probably via magnetic reconnection – for the plasma to escape from the Sun. The released CMEs have a wide range of velocities between 20 and 3,200 km/s. The slower ones are accelerated and the fast ones are decelerated by the solar wind so that by 1 AU the range of their speeds is much smaller. It takes between 1 and 3 days for them to reach Earth. Even though the average ejected mass in a CME is a staggering 1.6  1012 kg, it is the embedded magnetic field that is responsible for most of the geomagnetic response. CMEs expand their volume faster than the ambient solar wind – the solar wind expands nearly spherically resulting in a 1/r2 reduction in the solar wind density – thus by 1 AU their internal particle density is typically comparable or smaller than that of the ambient solar wind. However, the embedded magnetic field strength is several times – up to an order of magnitude – larger than the 1 AU interplanetary magnetic field. This extra field pressure compresses the Earth’s magnetosphere. Moreover, the CME internal magnetic field often takes a helical flux rope geometry – referred to as magnetic clouds (MCs) – with prolonged periods of large, ecliptic southwardpointing components. When squeezed against the northward-oriented subsolar magnetic field of Earth, they reconnect (cancel), weakening the internal magnetic pressure in the magnetosphere and thus rapidly further compressing the surface magnetic fields. These rapid magnetic fluctuations generate current in all conducting materials like a giant alternator. The amount of excess current generated is proportional to the length of the conducting material. Thus, electric power grid lines and oil pipelines that can span multiple states will experience the most excess current flows overloading transformers and weakening welding lines. Therefore, it is imperative to develop a forecasting capability that can accurately predict the arrival of the largest of these CMEs. Current space weather monitoring spacecraft at L1 (like the ACE spacecraft or the future Deep Space Climate Observatory, DSCOVR) provide 15–45 min of warning time by measuring the local or in situ signatures of an incoming CME. To expand the forecasting interval to 1–3 days, the initiation of CMEs near the Sun has to be observed remotely and the propagation of these CMEs to 1 AU accurately modeled. The primary contribution of the Wind spacecraft to CME forecasting is in the area of developing these CME propagation and evolution models. While there is a very good correlation between CMEs at 1 AU and coronal CMEs (Gopalswamy et al. 2000) observed by white light coronagraphs, the reverse is not true. Even when limiting the study to only front-side full-halo CMEs, Michalek et al. (2004) found that only 83 out of 123 solar events had discernible

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1 AU counterparts. What happened to a third of the CMEs? Were they processed by the solar wind so much that they became indistinguishable from the background flow? Or were they deflected by an unusual amount so that they missed Earth? Measurements made by Wind and other spacecraft give us some clues. Not every visible light CME observed near the Sun will maintain its dangerous magnetic flux rope topology by the time it reaches 1 AU. These irregular ejecta can still be identified by the Wind spacecraft by counter-streaming heat flux electrons, electrons with slightly more energy than the average solar wind component. These heat flux electrons travel faster than the solar wind but follow very precisely the interplanetary magnetic field lines. Thus, no matter what geometrical shape the CME takes at 1 AU, as long as both foot points of the internal magnetic field lines are still encored to the Sun, heat flux electrons will travel in both directions clearly delineating the CME from the ambient solar wind where only one end of the field lines is connected to the Sun, and thus heat flux electrons flow only in one direction. By identifying these irregular ejecta, the Wind measurements clearly identify that these CMEs dissipated harmlessly. What internal or external condition determines whether a CME dissipates or not is the subject of ongoing research. The most harmful CMEs preserve their magnetic flux rope configuration to 1 AU. However, even these powerful transients can be distorted by the ambient solar wind, changing their magnetic impact on the Earth system. Traditionally, CMEs are drawn as large horseshoe-shaped structures with embedded helical magnetic fields, with the field wound up much more near the surface and axial near the center (see Fig. 4). In contrast, STEREO white light images appear to show significant pancaking, not unlike some magnetohydrodynamic numerical simulations suggest (see Fig. 5). However, Wind magnetic field observations can be fitted rather well with simple circular cross-section flux rope models. In fact, even simultaneous three-spacecraft 3D reconstruction of the CME internal magnetic field lines, using magnetic field measurements from Wind and the two STEREO spacecraft, shows very little geometrical distortions. A recent, multi-spacecraft study has solved this dilemma by demonstrating that the white light images suffer from projection effects that make the CMEs look much more elongated than they are (Nieves-Chinchilla et al. 2012). This is a significant result, as it shows that those CMEs that do not dissipate will likely retain their near-circular cross section allowing more reliable forecasting. The shape of CMEs in the third dimension, along their symmetry axis, is much more difficult to observe at 1 AU. There are only a handful of fortuitous in situ observations of the same CME by multiple, well-separated spacecraft, as the CME has to lie nearly perfectly in the ecliptic and propagate toward Earth, a situation that happens only very rarely. But for these few cases, it has been shown that CMEs can twist and change the direction of their propagation significantly before reaching Earth (Mo¨stl et al. 2012). Particularly during maximum solar activity years, when multiple CMEs are ejected in close proximity to each other, CMEs can interact with each other significantly deflecting their propagation. While multi-spacecraft observations cannot be relied on as a space weather forecasting technique, these cases serve as benchmark events for numerical and empirical space weather prediction models.

150 Fig. 4 The idealized horseshoe shape of a CME magnetic flux rope. The internal magnetic field lines follow a helical direction with less and less winding toward the center of the structure (After Marubashi 1997)

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Further insight into the global geometry of CMEs can be obtained using energetic particles as magnetic field line tracers. Solar flares, sudden releases of very energetic particles in the solar atmosphere, spew out simultaneously charged particles at different energies, thus speeds. If the flare happens at the foot point of the CME, the released energetic particles will follow the internal magnetic field lines of the CME with the more energetic and faster particles reaching the 1 AU observer – in this case the Wind spacecraft 3DP instrument – before the slower ones. The start of the energetic electrons is marked by a type III radio burst with the radio signal traveling in a straight line at the speed of light and measured by the Wind spacecraft radio antennas. Using these time differences, the length of the magnetic field lines from the Sun to 1 AU can be computed with great accuracy and compared to the predictions of helical flux rope geometry models. Such studies resulted in good agreements deep inside the CME, but not near the boundary (Kahler et al. 2011). This implies that, in addition to deflection and distortion, CME surface magnetic fields also reconnect with the ambient interplanetary magnetic fields, in effect peeling away one layer at a time of their structure. Thus, wind measurements, together with other spacecraft, have enabled the identification of the key processes of CME interplanetary propagation and evolution. It remains to distill these results into a space weather prediction model.

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Fig. 5 Global magnetohydrodynamic simulation of the evolution of a CME in the inner heliosphere. The injected CME is shown as an iso-surface at 25 % of maximum density. The color scale shows the flow velocities on the iso-surface and from the solar source surface. The small blue box toward the left of the figure shows the Earth’s position (Odstrcil et al. 2004)

Interplanetary Shocks Besides CMEs any sudden pressure increase in the solar wind can compress the Earth’s magnetic field with negative consequences. Especially effective are interplanetary shocks where fast-moving solar wind streams overtake slowly moving parcels with a speed difference greater than any of the plasma wave mode speeds. At shocks, the plasma of the fast-moving stream piles up against the slow stream resulting in a density jump of up to a factor of four in a few seconds. Fastmoving CMEs can act like fast-moving pistons driving an interplanetary shock in front of them. Another source of interplanetary shocks is corotating interaction regions (CIRs) where a stream of fast solar wind overtakes a parcel of slow solar wind that was emitted from the Sun at an earlier time. During solar activity minimum years on the Sun, when the solar magnetic field is nearly dipolar, the Sun emits fast (~800 km/s) solar wind at high latitudes and much slower winds (300–450 km/s) near the magnetic equator (see Fig. 6). Since the magnetic dipole axis of the Sun is tilted with respect to its rotation axis, as the Sun rotates, fast streams are emitted behind slow parcels near the fast–slow wind boundary. These fast streams running into slow ones form CIRs, often steepening into fully formed shocks by 1 AU.

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Fig. 6 Solar wind observations collected by the Ulysses spacecraft during two separate polar orbits of the Sun, 6 years apart at nearly opposite times in the 11-year solar cycle. Near solar minimum (left), the slow solar wind is limited to low latitudes. Near solar maximum (right), the fast and slow streams are more intermingled (Courtesy of Southwest Research Institute and the Ulysses/SWOOPS team)

During solar maximum years, the picture becomes much more complicated with fast and slow streams intermingling at all latitudes (see Fig. 6). Current global heliospheric models can accurately predict the arrival of CIR compression regions at Earth with about 3 days of warning time. Forecasting the arrival of CME-driven shocks is much more complicated. Moreover, unlike CIR shocks that are almost always aligned with the local Parker spiral direction (about 45 relative to the Sun–Earth line at 1 AU), CME-driven shocks can have almost any orientation. This introduces a large uncertainty in the predicted arrival times at Earth even from the L1 monitors (like ACE). As mentioned above, the L1 monitors orbit the L1 point that takes them several times further to the side than the diameter of the magnetosphere. For nonradially aligned structures, this requires the determination of the orientation of these fronts. Local surface normals can be computed based on the in situ measurements; however, these directions reflect the small ripples on the shock surfaces, not their global orientation. Multi-spacecraft

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Fig. 7 Radio spectrogram of the August 24–27, 1998, CME observed by the Wind spacecraft. Red color represents high-intensity emissions. Shortly after 21:00 UT on August 24, the bright feature covering the full frequency range is a type III burst associated with a solar flare. The slowly descending feature is the type II burst related to the outward-propagating CME-driven shock. The shock reaches the Wind and Earth just before 9:00 on August 26 (Courtesy of the Wind/WAVES team)

techniques have been successfully employed, combining measurements from Wind, ACE, SOHO, and the Genesis spacecraft, to reduce the prediction uncertainty from 10–15 min to 1–2 min. However, this technique does require four simultaneous real-time solar wind monitors to operate upstream of Earth. Fortunately, interplanetary shocks are strong radio emitters. The shocks accelerate electrons locally. The faster electrons race ahead, creating a plasma instability that through nonlinear wave–wave interactions produce the so-called type II radio emissions at the local electron plasma frequency and at its second harmonic. As the shock propagates away from the Sun and the local solar wind density drops, the frequency of these type II radio bursts also decreases. The radio receivers on-board the Wind spacecraft observe these radio signals (see Fig. 7) and thus are able to track shocks from the Sun all the way to 1 AU. Moreover, since the Wind spacecraft rotates in the ecliptic plane, it can determine the direction from which the signal is emanating (like a rotating radar dish). Combining the Wind radio measurements with those on STEREO, the signal can even be precisely triangulated to yield an exact location in space for each radio burst. The only unknown in this observational scheme is the precise radial solar wind density profile. Using global magnetohydrodynamic solar wind simulations to obtain the required solar wind density profiles and combining it with STEREO and SOHO white light images, the best current techniques are able to predict the arrival times of these shocks with an error bar of no more than a few hours, 1 or 3 days in advance. Current research is focusing on an interesting subclass of interplanetary shocks that are radio loud near the Sun – that is they produce a well-discernible type II

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radio emission – but result in no observable solar wind compressions in near-Earth, in situ measurements. It is postulated that these shocks somehow have deflected and completely missed Earth (Gopalswamy et al. 2012).

Solar Energetic Particles (SEPs) CMEs ringing the Earth’s magnetosphere are not the only space weather dangers emanating from the Sun. The Sun is also the source of a very wide energy spectrum of energetic particles – called solar energetic particles (SEPs) – ranging from tens of keV to well above 100 MeV. Besides solar flares directly injecting energetic particles onto interplanetary magnetic field lines just above the photosphere of the Sun, interplanetary shocks, discussed in the previous section, produce copious amounts of energetic ions and electrons as they propagate outward. While only the most energetic (~1 GeV) SEPs can reach the surface of the Earth due to the deflection of most charged particles by the protective magnetosphere, they represent a significant danger to astronauts, especially during future deep space missions. Also, SEPs cause havoc in modern satellite microelectronics causing memory bit flips, single-event upsets, and latchups that can significantly harm these components. Due to their near-speed-of-light velocities, SEPs arrive to the vicinity of Earth from the Sun in mere 15–30 min. Thus, viable forecasting schemes rely on remote observations of flares and interplanetary shocks. Tracking interplanetary shocks in the inner heliosphere has been discussed in the previous section. However, knowing the location and speed of a shock is insufficient to accurately predict SEP production rates. In fact, the precise physical mechanisms involved in SEP generation at shocks are not fully understood. The high time resolution solar wind measurements of the Wind spacecraft have recently resulted in a number of discoveries related to the acceleration of charged particles at interplanetary shocks. Analytical studies of the behavior of charged particles at solar wind shock discontinuities derived that the most energetic SEPs would have to be generated at shocks with such large jumps in density and magnetic field strength that are very rarely observed. Yet, even moderate-size shocks appear to be capable of producing harmful SEPs. In observing interplanetary shocks at 1 AU, Wind measurements revealed that shocks often are composed of multiple up/down steps or shocklets (see Fig. 8 upper panel). In observing the charged particles concurrently, evidence was found for diffusive shock acceleration (see Fig. 8 lower panel), whereby particles gain energy by traversing a shock ramp multiple times and diffuse in pitch angle and energy by scattering off of upstream and downstream shocklets or large fluctuations (Wilson et al. 2013). This process enables weaker shocks to still produce higher energy particles. Particularly effective are shock–shock interactions to produce copious amount of energetic particles. Catching the moment of interaction between two extremely fast-moving shocks in interplanetary space is highly unlikely. However, the Wind spacecraft, in cooperation with other near-Earth assets, can readily observe the moments when an interplanetary shock impinges on the Earth’s bow shock.

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Fig. 8 (Upper) Overview of the magnetic field profiles of a series of shocklets and SLAMS observed by Wind/MFI at an interplanetary shock. The green shaded region corresponds to the time period for the lower panel. (Lower) Ion velocity distribution showing contours of constant phase-space density (bulk flow frame) in the plane containing the average magnetic field direction (along the horizontal) and the solar wind velocity vector Vsw. Red peaks left of the plot center show accelerated ions (After Wilson et al. 2013)

It appears that one shock starts the acceleration process of the particles creating a pool of seed population that the second shock further accelerates to the higher energy ranges. In effect, the two shocks as they collide form a magnetic trap that is particularly efficient at accelerating charged particles.

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Finally, Wind observations also shed some light on how magnetic reconnection in solar flares accelerates particles. Magnetic reconnection also operates in the 1 AU solar wind, though it is not nearly as energetic of a process as in solar flares. But 1 AU magnetic reconnection is readily observable by the Wind spacecraft. It appears that magnetic field lines do not have to be oriented precisely in the opposite direction in order to reconnect. In fact, component reconnection is much more prevalent than full magnetic cancelation (Gosling 2007). Wind observations also established that electron two-stream instability is the physical mechanism responsible for transferring magnetic energy of the reconnecting field lines to particle acceleration (Malaspina et al. 2013). These Wind observations and results pave the way for future predictive capabilities of SEP generation and forecasting.

Conclusion Over the past 20 years, the Wind spacecraft has collected valuable observations of the 1 AU solar wind, impinging on the Earth’s magnetosphere to advance our space weather prediction capabilities. Making most of its measurements while orbiting the Sun–Earth first Lagrange (L1) point, Wind has been collecting a comprehensive set of solar wind data at an unprecedented time resolution. The mostly multiply redundant instrumentation on the spacecraft has enabled in-depth studies of the structure and evolution of CMEs, interplanetary shock, and of the physical processes of particle acceleration at shocks and magnetic reconnection sites. Moreover, Wind radio wave observation of type II radio bursts generated by interplanetary shocks heading toward Earth has paved the way for future operational space weather forecasting capabilities with multiday lead times. The Wind spacecraft and its complement of instruments are still fully operational with enough fuel to maintain its current L1 orbit for nearly 60 years. Current NASA plans call for many more years of operations of this venerable spacecraft, most assuredly leading to more groundbreaking scientific discoveries.

Cross-References ▶ Coronal Mass Ejections ▶ Fundamental Aspects of Coronal Mass Ejections ▶ Early Solar and Heliophysical Space Missions ▶ ISAS-NASA GEOTAIL Satellite (1992) ▶ Nature of the Threat/Historical Occurrence ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ STEREO as a “Planetary Hazards” Mission

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References Gopalswamy N, Lara A, Lepping RP, Kaiser ML, Berdichevsky D, St. Cyr OC (2000) Interplanetary acceleration of coronal mass ejections. Geophys Res Lett 27:145–148 Gopalswamy N, MaKela P, Akiyama S, Yashiro S, Xie H, MacDowall RJ, Kaiser ML (2012) Radio-loud CMEs from the disk center lacking shocks at 1 AU. J Geophys Res 117:A08106 Gosling J (2007) Observations of magnetic reconnection in the turbulent high-speed solar wind. Astrophys J Lett 671:L73–L76 Kahler SW, Krucker S, Szabo A (2011) Solar energetic electron probes of magnetic cloud field line lengths. J Geophys Res 116:1104 Malaspina DM, Newman DL, Wilson LB III, Goetz K, Kellogg PJ, Kerstin K (2013) Electrostatic solitary waves in the solar wind: evidence for instability at solar wind current sheets. J Geophys Res 118(2):591–599 Marubashi K (1997) Interplanetary magnetic flux ropes and solar filaments. In: Crooker NU, Joselyn JA, Feynman J (eds) Coronal mass ejections, vol 99, Geophysical monograph. American Geophysical Union, Washington, DC, p 147 Michalek G, Gopalswamy N, Lara A, Manoharan PK (2004) Arrival time of halo coronal mass ejections in the vicinity of the Earth. Astron Astrophys 423:729–736 Mo¨stl C, Farrugia CJ, Kilpua EKJ, Jian LK, Liu Y, Eastwood JP, Harrison RA, Webb DF, Temmer M, Odstrcil D, Davies JA, Rollett T, Luhmann JG, Nitta N, Mulligan T, Jensen EA, Forsyth R, Lavraud B, de Koning CA, Veronig AM, Galvin AB, Zhang TL, Anderson BJ (2012) Multi-point shock and flux rope analysis of multiple interplanetary coronal mass ejections around 2010 August 1 in the inner heliosphere. Astrophys J 758:10. doi:10.1088/ 0004-637X/758/1/10 Nieves-Chinchilla T, Colaninno R, Vourlidas A, Szabo A, Lepping RP, Boardson SA, Anderson BJ, Korth H (2012) Remote and in-situ observations of an unusual Earth-directed coronal mass ejection from multiple viewpoints. J Geophys Res 117:6106 Odstrcil D, Riley PC, Zhao XP (2004) Numerical simulation of the 12 May 1997 interplanetary CME event. J Geophys Res 109. doi:10.1029/2003JA010135 Wilson LB III, Koval A, Sibeck DG, Szabo A, Cattell CA, Kasper JC, Maruca BA, Pulupa M, Salem CS, Wilber M (2013) Shocklets, SLAMS, and field-aligned ion beams in the terrestrial foreshock. J Geophys Res 118(3):957–966

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Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mission Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spacecraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Payload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cleanliness and Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recent Mission Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of Key Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SOHO’s Contributions to Space Weather Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CMEs and Space Weather Before SOHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CMEs and Space Weather After SOHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Additional Scientific Understanding of CMEs from SOHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Future of CME Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MDI Magnetic Field Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Far-Side Imaging of Active Regions by MDI and SWAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Predicting Solar Proton Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CELIAS Proton Monitor Measurements of the Solar Wind and ICMEs . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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B. Fleck (*) Science Operations Department, European Space Agency, c/o NASA/GSFC Code 671, Greenbelt, MD, USA e-mail: [email protected] O.C. St. Cyr NASA/GSFC, Code 670, Greenbelt, MD, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_14

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Abstract

SOHO is the most comprehensive space mission ever devoted to the study of the Sun and its nearby cosmic environment known as the heliosphere. It was launched in December 1995 and is currently funded at least through the end of 2016. SOHO’s 12 instruments observe and measure structures and processes occurring inside as well as outside the Sun and which reach well beyond Earth’s orbit into the heliosphere. While designed to study the “quiet” Sun, the new capabilities and combination of several SOHO instruments have revolutionized space weather research. This article gives a brief mission overview, summarizes selected highlight results, and describes SOHO’s contributions to space weather research. These include cotemporaneous EUV imaging of activity in the Sun’s corona and white-light imaging of coronal mass ejections in the extended corona, magnetometry in the Sun’s atmosphere, imaging of far-side activity, measurements to predict solar proton storms, and monitoring solar wind plasma at the L1 Lagrangian point, 1.5 million kilometers upstream of Earth. Keywords

Sun • Heliosphere • CMEs • Space weather

Introduction SOHO, the Solar and Heliospheric Observatory, is a mission of international cooperation between ESA and NASA to study the Sun, from its deep core to the outer corona, the solar wind, and solar energetic particles. Together with Cluster. Information about the mission as well as material suitable for education and public outreach are also available at the same locations. SOHO was designed to answer the following three fundamental questions about the Sun: What is the structure and dynamics of the solar interior? Why does the solar corona exist and how is it heated? Where is the solar wind produced and how is it accelerated? In the following paragraphs, the “original” SOHO mission will be described as it has been operated for over 15 years until the spring of 2011. Following the launch of NASA’s Solar Dynamics Observatory (SDO), which carries vastly improved versions of two of SOHO’s primary instruments, and in response to budget pressures, SOHO operations have been significantly reduced in recent years. A brief summary of the current status of SOHO and anticipated changes is also given. Detailed descriptions of all 12 instruments, the science operations and data products, as well as a complete mission overview can be found in Fleck et al. (1995). First an overview of the mission (spacecraft, orbit, payload, operations) is given, followed by a short summary of some of SOHO’s main scientific accomplishments. Then SOHO’s contributions to space weather research are discussed, which include the combination of coronal imaging in the EUV and white-light imaging of the extended corona, continuous mapping of the Sun’s magnetic field, imaging of active regions on the far side of the Sun, predicting the arrival of solar energetic

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particles (SEPs) based on measurements of energetic electrons, and in situ measurements of shock fronts of coronal mass ejections (CMEs) as they sweep over the Lagrangian point L1.

Mission Overview Spacecraft SOHO is a three-axis stabilized spacecraft that constantly faces the Sun. Its design is based on a modular concept with two main elements: the payload module, housing the 12 instrument packages, and the service module, providing essentials such as thrusters, power, and communications. SOHO’s mass at launch was 1,850 kg; its dimensions are 4.3  2.7  3.7 m3 (9.5 m with solar arrays deployed). Design life was 2 years, with consumables (hydrazine) onboard for another 4 years. The current hydrazine reserves in fact are sufficient for several more decades of normal operation, and the solar arrays should provide sufficient energy at least until the end of 2018. SOHO has excellent pointing performance, with errors typically smaller than 1 arcsec. SOHO was designed, assembled, and tested by a consortium of European space companies led by prime contractor Matra Marconi Space (now Airbus Defense and Space) under ESA management. NASA contributed the Atlas IIAS rocket on which SOHO was launched and is responsible for telecommunications (using NASA’s Deep Space Network, DSN) and daily operations, while ESA has overall responsibility for the mission. The focal point for spacecraft operations, science planning, and instrument operations is NASA’s Goddard Space Flight Center.

Orbit SOHO was launched on 2 December 1995 and inserted into a halo orbit around the Lagrangian point L1 in February 1996. There the combined gravity of Earth and Sun keep SOHO in an orbit locked to the Earth-Sun line. Nominal science operations started on 2 May 1996. The L1 halo orbit was chosen as it allows: (a) uninterrupted observations of our star, (b) sampling of the solar wind and energetic particles outside Earth’s magnetosphere, and (c) extremely good observing conditions for the detection of solar velocity oscillations with high accuracy and sensitivity by minimizing radial velocity variations.

Payload The payload consists of a set of 12 complementary instruments, developed and furnished by 12 international principal investigator (PI)-led consortia involving 39 institutes from 15 countries. Nine consortia are led by European PIs, the remaining three by US PIs. The payload weighs about 640 kg and consumes 450 W.

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Table 1 Instruments on SOHO and current PIs Instrument Global Oscillations at Low Frequency (GOLF) Na-vapor resonant scattering cell to measure global Sun velocity oscillations Variability of solar IRradiance and Variability (VIRGO) Active cavity radiometers and sun photometers for total and spectral irradiance Michelson Doppler Imager (MDI)a Fourier tachometer to measure velocity oscillation up to l = 4,500 Solar UV Measurements of Emitted Radiation (SUMER)a ˚ ; spectral res. Normal incidence spectrometer; 500–1,600 A 20,000–40,000 Coronal Diagnostic Spectrometer (CDS)a ˚ Normal and grazing incidence spectrometers, 150–800 A Extreme ultraviolet Imaging Telescope (EIT) Full-disk images (1,024  1,024) in He II, Fe IX, Fe XII, Fe XV UltraViolet Coronagraph Spectrometer (UVCS)a UV lines (Ly α, O VI, etc.) in extended corona (1.3–3 RJ) Large Angle and Spectrometric COronagraph (LASCO) Overlapping externally occulted coronagraphs: 2–30 RJ Solar Wind ANisotropies (SWAN) Scanning telescopes operating in Ly α to measure solar wind mass flux Charge, Element, and Isotope Analysis System (CELIAS) Electrostatic deflection, time-of-flight measurements, solid-state detectors Comprehensive Suprathermal Energetic Particle analyzer (COSTEP) p, He: 0.04–53 MeV/n, e: 0;04–5 MeV; solid-state and plastic scintillator detectors Energetic and Relativistic Nuclei and Electron experiment (ERNE) p-Ni: 1.4–540 MeV/n, e: 5–60 MeV; solid-state and plastic scintillator detectors

Principal investigator P. Boumier, IAS, F

C. Fro¨hlich, PMOD/WRC, CH

P. Scherrer, Stanford. Univ., USA W. Curdt, MPS, D

A. Fludra, RAL, UK F. Auche`re, IAS, F

L. Strachan, SAO, USA R. Howard, NRL, USA E. Que´merais, LATMOS, F

R. Wimmer-Schweingruber, Univ. Kiel, D B. Heber, Univ. Kiel, D

E. Valtonen, Univ. Turku, SF

a

No longer operated

SOHO’s 12 instruments, which represent the most comprehensive set of solar and heliospheric instruments ever developed and carried on the same platform, are listed in Table 1. The payload includes three helioseismology and solar irradiance instruments (GOLF, VIRGO, MDI) that have provided unique data for the study of the structure and dynamics of the solar interior, from the very deep core to the outermost layers of the convection zone; a set of five complementary remotesensing instruments, consisting of EUV and UV imagers, spectrographs, and

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coronagraphs (SUMER, CDS, EIT, UVCS, LASCO, SWAN), that have given us our first comprehensive view of the outer solar atmosphere and corona; and three in situ instruments (CELIAS, COSTEP, ERNE) making measurements of the composition and energy of the solar wind and charged energetic particles.

Cleanliness and Calibration UV instruments on earlier solar space missions have sometimes shown rather strong drops in responsivity after being exposed to solar radiation in space, due to polymerization of molecular contaminants. To avoid the danger of permanent degradation of the throughput of the SOHO instruments and to protect the instruments observing the corona against particulate contamination, cleanliness was recognized early in the development of SOHO as a prime concern. As a consequence, a very stringent cleanliness program was implemented in order to assure clean environmental conditions for the sensitive experiments. Considerable effort went into making the radiometric response of the SOHO UV and EUV instruments directly traceable to a primary laboratory standard, namely, synchrotron radiation produced by storage rings. Because of unavoidable detector aging, a rigorous in-flight intercalibration program was implemented to monitor and maintain the calibration of instruments in orbit. For some instruments, that included suborbital intercalibration rocket flights. For details about SOHO’s cleanliness and calibration program, see Pauluhn et al. (2002).

Operations The SOHO Experimenters’ Operations Facility (EOF), located at NASA’s Goddard Space Flight Center (GSFC), served as the focal point for mission science planning and instrument operations. There the experiment teams received real-time and playback telemetry, processed those data to determine instrument commands, and sent commands directly from their workstations through the ground system to their instruments, both in near real time and on a delayed execution basis. From the outset, SOHO was conceived as an integrated package of complementary instruments, being once described as an “object-oriented” mission, rather than an “instrument-oriented” mission. There was therefore great emphasis on coordinated observations. Internally, this was facilitated through a nested scheme of planning meetings (monthly, weekly, daily), and externally through close coordination and data exchange for special campaigns and collaborations with other space missions and ground-based observatories over the Internet. In response to budget pressures and the increased feasibility of remote science operations via the Internet, the SOHO EOF and the SOHO Experimenters’ Analysis Facility (EAF) at GSFC were closed at the end of November 2010. Most remote sensing instruments are now being operated remotely from the PI home institutions. The SOHO spacecraft was originally designed for 24/7 manual operations. Starting in late 2006, SOHO engineers began an in-house reengineering effort to

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automate the spacecraft operations in an effort to reduce operations cost. This required the development of new ground software (pass generator, anomaly detection, and notification) as well as modifications of the Central On-Board Software. Since September 2008, all DSN contacts (except nonroutine passes such as station keeping and momentum management maneuvers) are automated.

Recent Mission Changes NASA’s Solar Dynamics Observatory (SDO – see chapter on “▶ Solar Dynamics Observatory (SDO)” in this volume), which was launched on 11 February 2010, carries vastly improved versions of SOHO’s MDI and EIT instruments, as well as an EUV irradiance monitor. After the cross-calibration of EIT with SDO/AIA at the end of July 2010, the EIT image cadence has been reduced to two synoptic sets of images in all four wavelengths each day to track detector behavior and to maintain the uniform data set, spanning now over 1½ solar cycles. The telemetry bandwidth that had been used by EIT is now being used by LASCO to improve the cadence of its observations of the fastest CMEs. After the successful completion of the cross-calibration with SDO/HMI, MDI was commanded to stop taking science data on 12 April 2011 at 23:22:31UT. MDI operated exceptionally well for more than 15 years and has produced data that form the basis of over 1,700 papers in the refereed literature. On 23 January 2013, 17 years after the Ultraviolet Coronagraph Spectrometer (UVCS) obtained its first ultraviolet spectra of the extended solar corona, it was commanded to end operations because the detectors were no longer capable of producing scientifically meaningful observations. The SUMER detectors are very close to end of life and NASA’s Interface Region Imaging Spectrograph (IRIS), which was successfully launched on 27 June 2013, has vastly improved performance characteristics compared to SUMER. Following a final cross-calibration campaign in July 2014, SUMER science operations was terminated on 8 August 2014. CDS, which has been superseded to a large degree by Hinode/EIS, was commanded to end operations on 5 September 2014 because of budget constraints in the UK. All other instruments (VIRGO, GOLF, LASCO, SWAN, CELIAS, COSTEP, ERNE) are fully functional and continue to make unique and important contributions to the “Heliophysics System Observatory.”

Summary of Key Findings SOHO has provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, out to the solar wind and its interaction with the interstellar medium (e.g., Fleck et al. 2000, 2006). SOHO’s findings have been documented in an impressive and growing body of

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scientific literature and popular articles. It is impossible to do justice to the 4,900plus articles published in the refereed literature (as of end of 2014) and an even greater number in conference proceedings and other publications, representing the work of more than 3,200 scientists worldwide. Here, only a brief summary of a few selected results based on data from SOHO can be given. In the following section, space-weather-related results will be discussed in some more detail. SOHO provided the first-ever images of structures and flows below the Sun’s surface and of activity on the far side of the Sun. Analysis of the helioseismology data from SOHO has shed new light on a number of structural and dynamic phenomena in the solar interior, such as the absence of differential rotation in the radiative zone, subsurface zonal and meridional flows, subconvection zone mixing, a very slow polar rotation, and shear zones in the solar rotation rate just below the surface of the Sun and at the tachocline (transition between radiative and convection zone). SOHO discovered sunquakes and eliminated uncertainties in the internal structure of the Sun as a possible explanation for the “neutrino problem.” It allowed the detection of sunspots in the deep interior of the Sun 1–2 days before they appeared at the solar surface. The ultraviolet imagers and spectrometers on SOHO have revealed an extremely dynamic solar atmosphere where plasma flows play an important role. They discovered new dynamic solar phenomena such as coronal waves and solar tornadoes and provided evidence for upward transfer of magnetic energy from the surface to the corona through a “magnetic carpet” (a weave of magnetic loops extending above the Sun’s surface). SOHO measured the acceleration profiles of both the slow and fast solar wind and identified the source regions of the fast solar wind. SOHO discovered that heavy solar wind ions in coronal holes both flow faster and are heated hundreds of times more strongly than protons and electrons and that they have highly anisotropic temperatures reaching hundreds of millions of degrees Kelvin in the direction perpendicular to the magnetic field. SOHO revolutionized our understanding of solar-terrestrial relations and dramatically boosted space weather forecasting capabilities by providing, in a nearcontinuous stream, a comprehensive suite of images covering the dynamic atmosphere and extended corona. SOHO has measured and characterized over 20,000 CMEs. CMEs are the most energetic eruptions on the Sun and the major driver of space weather. They are responsible for all of the largest solar energetic particle events in the heliosphere and are the primary cause of major geomagnetic storms. SOHO has measured for over 1½ solar cycles the total solar irradiance (the “solar constant”), spectral irradiance, as well as variations in the extreme ultraviolet flux which are important for the understanding of the impact of solar variability on Earth’s climate. High-precision visible light measurements of the Sun’s shape and brightness during two special 360 roll maneuvers of the SOHO spacecraft have produced the most precise determination of solar oblateness. Besides watching the Sun, SOHO has become the most prolific discoverer of comets in astronomical history: as of May 2014, over 2,700 comets have been found by SOHO, most of them by amateurs accessing SOHO near-real-time data via the Internet. Moreover, UVCS provided plasma diagnostic measurements of many of the sungrazing comets from both planned and serendipitous observations.

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SOHO’s Contributions to Space Weather Research CMEs and Space Weather Before SOHO Coronal mass ejections, or CMEs, are eruptions of magnetized plasma from the Sun’s atmosphere. For recent reviews of many aspects of CMEs, see, e.g., Kunow et al. (2006), Chen (2011), Webb and Howard (2012), or the chapters on “▶ Coronal Mass Ejections” and “▶ Fundamental Aspects of Coronal Mass Ejections” in this volume. CMEs striking Earth’s magnetosphere are known to be the cause of the most significant geomagnetic storms. They also drive magnetohydrodynamic shocks that accelerate energetic particles and fill the heliosphere with energized particles. At the end of the 1980s, two developments highlighted the importance of understanding, or at least predicting, CMEs. The first was the collapse of the HydroQuebec power grid in 1989 due to a severe geomagnetic storm. This encouraged policy makers in the United States to formulate a cross-Agency National Space Weather Plan to coordinate resources and undertake new programs, such as NASA’s Living With a Star program. The second development was a shift in the research community from a focus on solar flares to CMEs as primarily important for solar-terrestrial physics. These developments set the stage for two space-based platforms that followed in the second half of the 1990s that revolutionized the understandingdriven science of solar and space physics into the applied science called space weather. Those two spacecraft were NASA’s Advanced Composition Explorer (ACE) and SOHO. ACE also resides at the Lagrangian point L1, and it was designed to send a continuous stream of highly compressed telemetry of in situ measurements of solar wind parameters just upstream of Earth’s magnetosphere that were relevant to the short-term (30–60 min) prediction of the onset of geomagnetic activity. For broader accounts of space weather, see Schwenn (2006), Bothmer and Daglis (2007), Schrijver and Siscoe (2009), or Song et al. (2001). CMEs were originally detected in the early 1970s when specialized telescopes called coronagraphs were first flown in space. Coronagraphs produce artificial eclipses of the Sun, occulting light from the million-times brighter solar disk so that the extended atmosphere, or corona, can be seen. As such, these telescopes are critically susceptible to stray light in order to detect the corona. Significant questions about CMEs remained unanswered prior to the launch of SOHO: What was their relationship to other forms of solar activity, particularly in terms of timing and causality? Although the morphology of some CMEs appeared to be a three-part structure (bright leading edge, dark trailing cavity, and bright prominence material trailing), what factors determined the variations of that form? Finally, there was the dispute about the interpretation (indeed, even the existence) of “halo” CMEs that surrounded the occulting disk and appeared to be directed toward the observer – could those events presage geomagnetic storms?

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Fig. 1 CME eruption in white light as observed by SOHO/LASCO C2. The relative size and location of the Sun can be seen by the inset cotemporaneous EIT image on the LASCO occulting disk. Two bright coronal streamers can be seen at the 4 and 7 o’clock position extending from underneath the LASCO occulting disk. The CME appears in the southwest streamer and proceeds to disrupt it (upper right frame at 10:29). Note the distinct magnetic flux rope structure which can be seen as a series of almost concentric windings in the 11:27 image (lower left). The CME is associated with a bright prominence that trails behind the flux rope (This and all subsequent images of this chapter are covered under the SOHO copyright policy, available at http://soho. nascom.nasa.gov/data/summary/copyright.html)

CMEs and Space Weather After SOHO The questions posed above were answered within the first year of operation of SOHO’s LASCO and EIT, primarily due to significant improvements in these instruments compared to earlier ones. In Fig. 1, one can see a typical coronagraph series of images of a CME taken by LASCO C2. The dynamic range of LASCO’s CCD detectors was orders of magnitude larger than vidicon tubes used in previous coronagraphs, and the location of SOHO at L1 provided a greatly reduced and more stable stray-light background so that fainter CMEs could be detected and tracked than ever before. Earlier coronagraphs on Skylab, SMM, and P78-1 were in low-Earth, low-inclination orbits with 15 day-night transitions every 24 h. Two problems arose from this: (a) an approximately 40 % loss of coverage and

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˚ channel of Fig. 2 A time series of running difference images spanning 34 min in the Fe XII 195 A SOHO/EIT. Centered on a flaring active region just to the north on the central meridian, one can see a nearly circular disturbance (the “EIT wave”) as it propagates across the disk. The wave appears as the patchy bright features, leaving a region of reduced emission behind (dimming region) (Image covered under the SOHO copyright policy)

(b) thermal distortions which resulted in a large and continuously changing straylight background because of small changes in the sensitive alignment of the optical benches. The relatively rapid (e.g., 10–20 min) cadence of EIT images allowed many CMEs to be unambiguously associated with various forms of activity in the low corona for the first time. Of particular interest were the “EIT waves” that appeared to map the expansion of the CME across the solar surface (Fig. 2). Also, the intentional overlap (or nesting) of fields of view between EIT and LASCO’s C1-C2-C3 meant that events could be tracked from their initiation in the low corona out to the extent of the C3 field of view. The superior imaging capability of LASCO revealed that the three-part structure seen in many CMEs appeared to be a magnetic

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flux rope, thus giving physical insight to the myriad of morphologies that had been reported earlier (cf. Fig. 1). This understanding was critical to the subsequent physics-based modeling of the initiation and propagation of CMEs, and many of our current space weather forecasting tools are now built on this fact. The existence of halo CMEs (St. Cyr 2005) was confirmed because of the aforementioned improvements in detecting faint events. The combination of LASCO and EIT allowed observers to be able to distinguish between halo CMEs directed toward Earth and those originating on the far side. During the development of SOHO, as was evident from their original allocation of onboard resources, LASCO and EIT were considered “context” instruments for the spectrometric telescopes. However, during the first year of SOHO’s operation, it became clear that the significant improvements in image quality, combined with real-time return of LASCO and EIT images (almost 20 h per day), would define the “gold standard” for midrange (1–3 day) space weather forecasting (Fig. 3). SOHO operations personnel established a protocol to contact NOAA’s Space Environment Center (now Space Weather Prediction Center) with timely information on the appearance of Earth-directed CMEs. Many researchers then began using the LASCO and EIT data in various techniques, and combined with different auxiliary observations, to predict the arrival time of CMEs and interplanetary shocks. In 1998, additional telemetry was allocated to LASCO and EIT to improve the cadence of observations, and the midterm forecasting capabilities were significantly expanded.

Additional Scientific Understanding of CMEs from SOHO Observers have continued to populate the LASCO CME catalogue with information about the appearance, size, speed, and mass of individual events, now numbering more than 20,000, and researchers internationally compare these with their own observations of associated phenomena. With the growing size of that database and the launch of STEREO with multiple coronagraphs, some researchers began experimenting with the automated detection and measurement of CMEs. The algorithms were developed using archival data, and that has become a veritable cottage industry in recent years with almost a dozen technical approaches appearing to have some levels of success. Another SOHO instrument has also provided significant new insights into CME research. UVCS was able to obtain spectroscopic observations of over 1,000 CMEs imaged by LASCO, during both planned and serendipitous observation. For the first time, UV emission lines of the pre- and posteruption coronal plasma, as well as the CME itself, have been observed, and diagnostics such as the line-of-sight velocity, density, composition, ionization state, and temperature allow researchers to link the CME onset characteristics to the coronal white-light images. Using the UVCS observations, the thermal history of the ejected plasma can be constrained, and realistic three-dimensional models of CMEs can be compared with simulations. Numerous shock waves and current sheets associated with CMEs have also been observed by UVCS, and this has allowed comparison of plasma densities and compression factors with radio bursts.

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Fig. 3 Top left: MDI visible light image of the solar disk taken on 28 October 2003, where multiple large active regions can be seen. Top right: MDI magnetogram on the same day, ˚ illustrating the magnetic complexity of these active regions. Lower left: EIT Fe XII 195 A image at the time of the X17 X-ray flare, seen as the bright emission just south close to the central meridian. The linear horizontal feature is an artifact due to saturation of the CCD detector. Lower right: LASCO C3 image at minutes after the flare (11:30 UT) where a halo CME completely surrounding the occulting disk is visible. The flare location and the existence of the halo CME were a clear indication that the event was heading toward Earth (Image covered under the SOHO copyright policy)

The Future of CME Research The heliophysics community wants to understand the initiation of CMEs, their propagation into the heliosphere, their impact at Earth and throughout the solar system, and the large-scale structure of the corona through a full magnetic cycle. The success of SOHO LASCO in advancing the understanding of CMEs, combined

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with the inherent limitations of a single vantage point in tracking events to Earth, led directly to the development of the STEREO mission (see chapter on “▶ STEREO as a ‘Planetary Hazards’ Mission” in this volume). The success of combining EIT and LASCO, as well as the high-cadence/high-resolution EUV imaging from the TRACE Small Explorer mission (1998–2010), led to the development of SDO. In order to further our understanding and modeling of the initiation of CMEs, researchers are using high-cadence EUV and vector magnetic field information from SDO and combining them with white-light coronal data from SOHO/LASCO. Reconstructions of the propagation of CMEs into the heliosphere can only be modeled accurately using as many viewpoints as possible, for example, the two STEREO spacecraft and SOHO. Only LASCO provides a continuous record of the large-scale corona over more than an entire solar cycle from one viewpoint.

MDI Magnetic Field Maps The Sun’s magnetic field is the driver of all solar activity. Without a magnetic field, there would be no flares, no particle events, no CMEs, and probably not even a corona. Knowledge of the Sun’s magnetic field is therefore of paramount importance for our understanding of energetic and eruptive events, and the only path to reliable predictive capabilities – the “holy grail” of space weather research – will be through measurements and understanding of the magnetic field topology throughout the Sun’s atmosphere, from the photosphere through the chromosphere to the base of the corona (e.g., Mackay and Yeates 2012). Unfortunately, magnetic field measurements in the chromosphere and corona are very difficult, and it may be many years until it will be possible to measure and interpret them reliably and on a routine basis. Most magnetic field measurements are therefore done in the photosphere and then extrapolated into the higher layers (e.g., Wiegelmann and Sakurai 2012), despite the considerable difficulties of transforming the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona. Since MDI provided only longitudinal magnetograms, extrapolations are limited to linear force-free field models. The Helioseismic and Magnetic Imager (HMI) on SDO, which superseded SOHO/MDI with several major improvements (significantly improved spatial resolution and image cadence), offers full Stokes vector magnetic field measurement capabilities and thus the application of nonlinear force-free field models. While the primary objective of SOHO/MDI was to obtain spatially resolved velocity time series of the solar atmosphere for the helioseismic study of the Sun’s interior, as a by-product, MDI also generated longitudinal (line-of-sight) ˚ line, formed at a height of about magnetograms in the photospheric Ni I 6768 A 100 km above τ5000 = 1. MDI provided both full-disk magnetograms with a spatial resolution of 4 arcsec as well as higher-resolution (1.25 arcsec) magnetograms. The latter were limited to the MDI “high-res” field of view, a square of about

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11  11 arcmin centered about 160 arcsec north of the equator. They were taken during special campaigns, when SOHO high rate telemetry was available. The temporal resolution of some of the MDI magnetic field data products obtained during special campaigns is as short as 1 min. In addition to higher time resolution campaign data, MDI provided synoptic full-disk magnetograms at a regular cadence of 96 min (15 per day) throughout the mission. While there are magnetograms available with much higher spatial resolution (e.g., from the Stokes Polarimeter on Hinode, but also from ground), the unmatched consistency, availability, and coverage of the MDI 96-min full-disk magnetogram series have proven to be invaluable in nearly all research areas of solar physics, in particular also in space weather research. MDI synoptic magnetograms have been used in countless investigations aimed at reconstructing the magnetic field topology of active regions and eruptive events (e.g., Schrijver 2009). They form the basis of a large database of global potential field source surface (PFSS) models, which are frequently used as input for large-scale MHD models of the corona and heliosphere.

Far-Side Imaging of Active Regions by MDI and SWAN Solar active regions are the centers of energetic phenomena that produce flares and coronal mass ejections, whose resulting electromagnetic and particle radiation interfere with telecommunications and power transmission on Earth and pose significant hazards to astronauts and spacecraft. Imaging of far-side solar activity allows anticipation of the appearance of large active regions more than a week ahead of their arrival on the East limb of the Sun, greatly improving midrange space weather forecasting capabilities from 1–3 days to 1–2 weeks. To use an analogy from terrestrial storm forecasting, far-side images of solar active regions would offer the space weather forecaster a similar lead time to potentially hazardous events as geosynchronous satellite data of a strong tropical depression or hurricane cell far out in the Atlantic. Just a little over 4 years after the launch of SOHO, in March 2000, scientists published an astonishing result: the first successful holographic reconstruction of features on the far side of the Sun. An active region on the far side reveals itself because its strong magnetic fields speed up the global sound waves. Because these waves travel from the near side of the Sun to the far side and back, they interfere with their multiple reflections. The result is a standing wave with a sharply defined frequency, called a p-mode (“p” for pressure), similar to the harmonics that resonate in an organ pipe. An active region can be compared to a small dent in the organ pipe, slightly reducing its internal volume and thereby slightly raising its resonant frequency. Soon after the initial publication of this result, the astonishing became routine, and MDI (and later also GONG and SDO/HMI) offered daily far-side images online. MDI was not the first SOHO instrument that provided information about activity on the Sun’s far side. Half a year before the MDI release, in June 1999,

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the SWAN team announced a new technique to map solar activity on the Sun’s far side. SWAN, short for Solar Wind Anisotropies, is used to map the whole sky in ultraviolet light. It sees a huge cloud of interstellar hydrogen that bathes the entire Solar System and interacts with the solar wind. The cloud is relatively tenuous – about 0.1 atoms per cc – yet it is thick enough to shine when illuminated by the Sun’s ultraviolet light (Ly α). This kind of observation is impossible from Earth because the atmosphere completely filters the short-wavelength ultraviolet light. Even spacecraft in orbit around the Earth are blinded to the hydrogen haze of the Solar System by a large swarm of hydrogen atoms that surrounds our planet (geocorona). SWAN full-sky maps reveal “hot spots” when the hydrogen cloud beyond the Sun glows more strongly than would be expected if the Sun were uniformly bright on its far side. The strong ultraviolet emissions from active regions on the far side of the Sun behave like beams from a lighthouse on the landscape (Fig. 4). They move in the sky in accordance with the Sun’s rotation, which takes about 28 days. This allows monitoring activity on the far side of the Sun without looking at it directly and is currently used by space weather researchers in France, in combination with MDI/GONG/HMI far-side helioseismology results to recreate the solar activity pattern at any time and any point on the Sun. With the two STEREO spacecraft (in combination with SOHO and SDO) providing full 360 coverage of the Sun, the far-side imaging techniques have been validated and hence are less frequently used for space weather predictions now than before the availability of STEREO data. However, in a few years, when the two STEREO spacecraft won’t be able to provide full 360 coverage anymore, these techniques will become very important and valuable again. The SWAN full-sky images are also used to predict the UV flux received by the Earth 2 weeks in advance and to compute the UV flux emitted toward any planet or object in the solar system. These values are produced on a regular basis and distributed through the SWAN web page. One application of this data set is the prediction of Earth’s thermospheric temperature, which is the main parameter used to compute the drag effect on satellites on low earth orbit. Multiple SOHO observations were then successfully used in October 2003 when some of the biggest active regions containing some of the largest sunspots of Cycle 23 appeared coming at the East limb of the Sun (Figs. 3 and 5) – already spreading X-rays, extreme ultraviolet radiation, high-energy particles, and coronal mass ejections into interplanetary space. At that time, space weather predictors had an earlier warning since the regions were seen on the far side of the Sun with seismic holography and other techniques developed with SOHO. The significance of that 2-week outburst of solar activity has been documented in a NOAA Service Assessment (http://www.swpc.noaa.gov/Ser vices/SWstorms_assessment.pdf). Not only were the MDI far-side techniques presaging intense activity on the Sun’s backside, but two other SOHO instruments also provided “early warning” that there was unusual activity on the Sun’s far side: the LASCO observers noted extremely fast CMEs without associated

Fig. 4 SWAN full-sky maps from 20 July 1996 (top) and 10 days later (30 July 1996; bottom). The left circles show the sky brightness in Ly α on the far side of the Sun, the right circles the same for the sky behind the spacecraft (i.e., behind Earth). Note the distinct bright patch in the upper left image, resulting from an active region on the far side of the Sun. Ten days later, when the Sun’s rotation has moved that active region to the visible face of the Sun (see lower right green EIT image), the sky behind the spacecraft is now illuminated (lower right blue image) (Image covered under the SOHO copyright policy)

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Fig. 5 A sequence of LASCO C3 images following the event depicted in Fig. 3 (“Halloween Storms” of 28 October 2003). In the upper left image (11:18), the halo CME is still behind the occulting disk. Planet Mercury is the bright feature at about 10 o’clock near the edge of the

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activity counterparts on the Earth-facing hemisphere of the Sun, and SWAN noted unusual EUV intensity coming from the Sun’s far side.

Predicting Solar Proton Events Sudden increases in the fluence of >30 MeV protons in SEP events pose a hazard to human space activities and robotic space missions (cf. Fig. 5). A new method, based on SOHO/COSTEP measurements of relativistic (150 keV–10 MeV) electrons, permits up to an hour of warning for the later arriving protons in SEP events (Posner 2007). The electrons act as test particles by probing the continuously changing heliospheric transport conditions in the same region of the heliosphere through which the slower-moving protons have to propagate. The new method was for the first time tested under operational conditions during the February 2008 Space Shuttle Atlantis mission, which transported ESA’s Columbus laboratory to the International Space Station. NASA-Goddard’s Space Weather Research Center has included this method in its array of research-grade forecasting tools that routinely provide information to the human and robotic exploration fleet.

CELIAS Proton Monitor Measurements of the Solar Wind and ICMEs In addition to interplanetary shock fronts associated with CMEs, corotating interaction regions (CIRs) and their associated high-speed wind streams can drive geomagnetic activity. Upstream measurements of the solar wind plasma are therefore important for the short-term (30–60 min) prediction of the onset of geomagnetic activity. The CELIAS/MTOF proton monitor provides measurements of bulk speed, density, thermal speed, and north/south flow direction in near real time during DSN contact times. The only other available real-time data set is from ACE, which is seriously degraded during intense energetic particle events, and from the STEREO spacecraft, which are now on the far side of the Sun. Unfortunately, there is no magnetometer onboard SOHO (it was de-scoped very early during SOHO’s development), and hence no measurements of the solar wind plasma’s magnetic field. This is arguably the biggest shortcoming of SOHO’s in

ä Fig. 5 (continued) occulting disk; numerous bright coronal streamers can be seen extending out to the edge of the field of view; the dark linear feature at 7 o’clock is the shadow of the pylon holding the occulting disk; numerous stars are seen in the background. Upper right: The halo CME has emerged from behind the C3 occulting disk at 11:42. The remaining images are a time sequence showing the progression of the halo CME and the onset of one of the most intense energetic solar proton events in SOHO’s lifetime. The energetic protons are racing ahead of the CME plasma at nearly the speed of light and an hour after the eruption start bombarding the CCD detector. After about 12 h, the images are practically useless because of the intensity of the proton storm (Image covered under the SOHO copyright policy)

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situ solar wind measurements and explains why ACE solar wind data are more widely used by the space weather community.

Conclusion SOHO is a robust solar observatory that has revolutionized both the understandingdriven science of solar physics and the application of heliophysics that is now known as space weather. During the first year of SOHO’s operation, it became clear that the significant improvements in image quality, combined with near-real-time return of LASCO and EIT images (almost 20 h per day), would define the “gold standard” for midrange (1–3 day) space weather forecasting. Researchers and forecasters have relied on LASCO and EIT data in various techniques, and combined with different auxiliary observations, to predict the arrival time of CMEs and interplanetary shocks at Earth.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Solar Dynamics Observatory (SDO) ▶ Solar Flares ▶ STEREO as a ‘Planetary Hazards’ Mission

References Bothmer V, Daglis IA (2007) Space weather – physics and effects. Springer-Praxis, Chichester Chen PF (2011) Coronal mass ejections: models and their observational basis. Living Rev Solar Phys 8:1 Fleck B, Domingo V, Poland AI (eds) (1995) The SOHO mission. Reprinted from Solar Phys 162(1–2). Kluwer Academic, Dodrecht. Fleck B, Brekke P, Haugan S, Sanchez Duarte L, Domingo V, Gurman JB, Poland AI (2000) Four years of SOHO discoveries – some highlights. ESA Bull 102:68. http://soho.nascom.nasa.gov/ publications/ESA_Bull102.pdf Fleck B, M€uller D, Haugan S, Sanchez Duarte L, Siili T, Gurman JB (2006) 10 years of SOHO. ESA Bull 126:24. http://soho.nascom.nasa.gov/publications/ESA_Bull126.pdf Kunow H, Crooker NU, Linker JA, Schwenn R, Von Stieger R (eds) (2006) Coronal mass ejections. Space sciences series of ISSI, vol 21. Reprinted from Space Sci Rev J 123/1–4 Mackay D, Yeates A (2012) The Sun’s global photospheric and coronal magnetic fields: observations and models. Living Rev Solar Phys 9:6 Pauluhn A, Huber MCE, von Steiger R (eds) (2002) The radiometric calibration of SOHO, ISSI scientific report SR-002, ESA Publications Division, Noordwijk Posner A (2007) Up to 1-hour forecasting of radiation hazards from solar energetic ion events with relativistic electrons. Space Weather 5(5):05001 Schrijver CJ (2009) Driving major solar flares and eruptions: a review. Adv Space Res 43(5):739–755

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Schrijver CJ, Siscoe GL (2009) Heliophysics – plasma physics of the local cosmos. Cambridge University Press, Cambridge Schwenn R (2006) Space weather: the solar perspective. Living Rev Solar Phys 3:2 Song P, Singer HJ, Siscoe GL (eds) (2001) Space weather, vol 125, Geophysical monograph. American Geophysical Union, Washington, DC St. Cyr C (2005) The last word: the definition of Halo Coronal mass ejections. EOS 86(30):281–282 Webb DF, Howard TA (2012) Coronal mass ejections: observations. Living Rev Solar Phys 9:3 Wiegelmann T, Sakurai T (2012) Solar force free magnetic fields. Living Rev Solar Phys 9:5

Solar Dynamics Observatory (SDO) W. Dean Pesnell

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Solar Dynamics Observatory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SDO Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Data Volume and Completeness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SDO Science and Cosmic Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Late-Phase Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prominence and Filament Eruptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Global Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Magnetic Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Helioseismology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

NASA’s Solar Dynamics Observatory (SDO) stands sentinel for the cosmic hazards created by solar activity. The instruments on SDO provide immediate knowledge and understanding of solar eruptive events such as flares and coronal mass ejections. In the longer term SDO provides scientific understanding to better predict the trends of solar activity over the next few months to years. SDO comprehensively observes the magnetic field of the Sun. It measures the surface magnetic field and observes the response of the solar atmosphere to changes in the magnetic field. SDO also gathers helioseismic observations that are analyzed to look inside the Sun and deduce the workings of the solar convection zone – the roiling motions inside the Sun that create the magnetic field. SDO, the data it produces, and some of the science results that help with planetary defense will be described. W.D. Pesnell (*) NASA Goddard Space Flight Center, Greenbelt, MD, USA e-mail: [email protected] # Springer International Publishing Switzerland (outside the USA) 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_16

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Keywords

Solar Dynamics Observatory • SDO • HMI • AIA • EVE • Solar dynamo • Extreme ultraviolet • Magnetic field • Helioseismology • Solar activity • Space weather • Solar flares • CME

Introduction The environments of the Earth and planets are both affected by the energetic particles and photons that cause space weather. Two major cosmic hazards caused by the Sun are solar flares and coronal mass ejections. Both of these can affect nearEarth space and our technology in space and on the ground. Solar flares and CMEs come from the destruction and expulsion of the solar magnetic field. NASA’s Solar Dynamics Observatory (SDO) was designed to study that magnetic field and learn the causes of solar flares and CMEs. One science goal of SDO is to improve our understanding of solar activity to such a degree that we can predict the output of the Sun over next few hours, years, or longer. Solar flares are incredibly bright flashes of electromagnetic radiation with wavelengths spanning from γ-rays to radio (Fig. 1). Flares occur when a part of the Sun’s magnetic field is rapidly converted into the kinetic energy of energetic particles, heat, and radiation. Because the most common emissions from solar flares are at short wavelengths that are completely absorbed by the atmosphere, they are best studied from space. If solar flares are the lightning of space weather, coronal mass ejections, or CMEs, are the storm clouds. They arise when a filament (an arch of solar plasma that is also called a prominence) is ejected from the Sun. If pushed away with sufficient force, the material leaves the Sun and moves out into interplanetary space. CMEs do not spread out to fill the solar system as they move away from the Sun. This leads to one of the fundamental differences between flares and CMEs. Photons from a flare will strike anything that can see the part of the Sun where the flare occurred. The particles and magnetic field of a CME can only strike an object that lies within its much narrower zone of influence. Understanding the impact of a solar flare or a CME requires different data sets and models. Individual solar flares are able to cause errors in radio communications and navigation systems, but they do not cause long-lasting changes in our natural environment. The cumulative effects of solar activity over millions of years, however, can change or even remove a planetary atmosphere (Catling and Zahnle 2009). Measuring the solar X-ray and EUV output over many solar cycles is necessary to determine how the Sun affected the evolution of planetary ionospheres and atmospheres. SDO’s observations guide the study of such effects and also help improve predictions of the Sun of both short and long timescales. One major assumption that has been made in the past is that solar output changes in a similar way each solar cycle. This flies in the face of the evidence from the sunspot number record. Each 11-year sunspot cycle differs from all others. It should not be surprising that

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Fig. 1 An example of a solar flare. This X1.9 flare happened on the eastern limb of the Sun over Active Region 1302. This flare started at 1029 UTC, peaked at 1101 UTC, and ended by 1144 UTC. Illustrated here at 1157 UTC is the remaining bright region of the flare, sitting above post-flare loops that formed during the initial part of the flare. Background loops are behind the flare and survived the magnetic field changes that caused the flare. Foreground loops grew during the flare. They are darker (and hence cooler) than the material behind them

the magnetic field or the X-ray and EUV spectral irradiances would also be different in each cycle. Solar Cycles 23 and 24 have been the best-studied sunspot cycles to date, with many satellites making measurements of different aspects of solar activity. Ground-based observatories, such as the National Solar Observatory, made visible-light measurements at the same time. We know what happened inside and outside of the Sun better than ever before. Even so, the predictions of the amplitude of Solar Cycle 24 spanned a wide range of values. This shows the limits of our knowledge of the solar dynamo inside the Sun that creates the solar magnetic field and the processes above the surface of the Sun that destroy or expel that field.

The Solar Dynamics Observatory The Solar Dynamics Observatory (SDO, illustrated in Fig. 2) was launched on February 11, 2010, and began normal science operations on May 1, 2010. SDO flies in a geosynchronous orbit inclined at 28 near the longitude of the dedicated ground station in New Mexico. All three science instruments are returning excellent data. SDO is the first mission to be launched for NASA’s Living With a Star (LWS) Program, a program designed to understand the causes of solar variability and its impacts on Earth. SDO data will help us understand the Sun’s influence on Earth and near-Earth space by studying the solar atmosphere on small scales of space and time and at many wavelengths simultaneously. SDO’s goal is to understand

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Fig. 2 An illustration of the SDO showing the positions of the instruments (AIA, EVE, and HMI), the deployed solar panels, and one of the high-gain antennas

the solar variations that influence life on Earth and our modern technological environment. The mission is designed to determine how the Sun’s magnetic field is generated, structured, and then converted into variations in the solar irradiance and the motion of energetic particles and the solar wind. One major aspect of SDO science is to develop the capability to predict when the solar magnetic field will change. That predictive capability would allow us to anticipate space weather hazards at all of the planets and the space in between. The cosmic hazards that SDO helps to defend against are produced by the energetic photons and particles emitted by the Sun: 1. Changes in planetary atmospheres that increase satellite drag and cause the loss of the atmosphere 2. Changes in planetary ionospheres that interfere with radio communications, GPS navigation, and power grids 3. Damage to satellites in space, especially the electronics 4. Harm to astronauts in space from increased radiation dose

SDO Measurements The instruments on SDO, which are pointed out in Fig. 2, provide data that continues to lead to a better understanding of the underlying physics of critical solar variations. Each instrument was built and is run by a Science Investigation Team (SIT). Each SIT receives their data from SDO, after which they process, analyze, archive, and serve the data. The instruments and their measurements are:

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Fig. 3 Three views of the Sun at 2030 UTC on January 19, 2014. From left to right are a Dopplergram, intensity image, and LOS magnetogram from HMI. The Dopplergrams are displayed with red shifts in black and blue shifts in white. The color scale for the magnetogram uses white for field pointing toward the observer and black for field pointing away. Several active regions are identified in the intensity image. You can see several active regions in the Dopplergrams. You can also see several regions of strong magnetic field that cannot be seen in the other two images

HMI: The Helioseismic and Magnetic Imager (HMI) produces full-disk Dopplergrams, magnetograms, and visible-light images of the Sun with high spatial resolution (Schou et al. 2012). Dopplergrams are full-disk photospheric velocity maps that are created every 45 s with a pixel size of 730  730 km, a data recovery of 98 %, and a data completeness of 99 % for each Dopplergram (Fig. 3, left). One of the images used to create the Dopplergrams is available as a visible-light image of the Sun (Fig. 3, middle). HMI is also creating full-disk longitudinal magnetic field measurements every 45 s (Fig. 3, right) and full-disk vector magnetic field maps every 12 min. HMI data is available from the SDO JSOC (2014). AIA: The Atmospheric Imaging Assembly (AIA) takes eight images every 12 s. It images the solar atmosphere in multiple wavelengths to link changes above the surface of the Sun to changes inside the Sun (Lemen et al. 2012). The ˚ , Fe XVIII at 94 A ˚ , Fe VIII and XXI EUV channels measure the emissions of He II 304 A ˚ , Fe IX at 171 A ˚ , Fe XII and XXIV at 193 A ˚ , Fe XIV at 211 A ˚ , and Fe XVI at at 131 A ˚ . The diversity of iron ions allows AIA to sample many temperatures in the 335 A corona and chromosphere, including hot flare channels. Every 12 s, AIA captures all seven EUV channels while alternating between chromospheric images of C IV ˚ ) and continuum at 1,700 A ˚ from one 12 s cycle to the next. One image at (1,600 A ˚ is included at low cadence to help align AIA with other imagers. Figure 4 4,500 A shows three images from AIA, taken at the same time as the HMI images in Fig. 3. AIA data have a pixel size of 875  875 km and are available from the SDO JSOC (2014). EVE: The Extreme Ultraviolet Variability Experiment (EVE) measures the solar extreme ultraviolet (EUV) irradiance with unprecedented spectral resolution, temporal cadence, and precision (Woods et al. 2012). EVE EUV spectral irradiances allow us to understand variations on the timescales that influence the Earth’s climate and near-Earth space.

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Fig. 4 Three views of the Sun at 2030 UTC on January 19, 2014. From left to right are the AIA ˚ , AIA 171 A ˚ , and AIA 193 A ˚ images. You can see the active regions listed in Fig. 3 as bright 304 A regions, with coronal loops extending above the limb from ARs 11959 to 11960. Coronal loops are seen above the other active regions as well. There is also a coronal hole in the center of the northern hemisphere and several filaments

Fig. 5 A day-averaged EUV spectral irradiance for January 19, 2014, as measured by EVE, plotted against the wavelength in nm. The seven AIA passbands are identified with vertical dashed ˚ line is the brightest in this wavelength range, with the C III 977 A ˚ line the lines. The He II 304 A next brightest. Although the total radiant energy in this spectrum is 4.7 mW m 2, about 10 5 times the total solar irradiance, it is responsible for most of the ionization in the thermospheres of the Earth, Venus, and Mars. Such spectra, at a 10-s cadence, are the primary data produced by EVE

EVE produces spectra covering 0.1–105 nm with a 10-s cadence and a spectral ˚ line. The accuracy of the spectra resolution of 0.1 nm. This includes the He II 304 A at the bright spectral lines is about 10 %. An example of an EVE EUV spectrum is shown in Fig. 5.

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Fig. 6 Six day-averaged EUV line irradiances from May 1, 2010, to January 20, 2014, as ˚ line is the brightest, followed by the C III 977 A ˚ line and H I measured by EVE. The He II 304 A ˚ . The peak He II 304 A ˚ irradiance was in late December 2013 and a horizontal line is drawn 1,026 A ˚ irradiance, also marked with a horizontal line, has been reached at that value. The peak H I 1,026 A several times in Solar Cycle 24

EVE data is available from the EVE website (EVE 2014). Two SDO instruments return measurements of the Sun in EUV wavelengths. EUV radiation is a probe of the solar corona as well as a major source of ionization in planetary atmospheres. Energetic electrons in the solar corona produce solar EUV photons by a two-step process. First, the electrons must create highly ionized atomic ions in the corona; then they must excite the electrons that remain on those ions. The presence of different ions acts as a thermometer of the coronal plasma. ˚ passband, are created by For example, Fe XII ions, which are seen in the AIA 193 A ˚ passband. When higher temperatures than the Fe IX ions seen in the AIA 171 A EUV photons are absorbed by a planetary thermosphere, they create ions and electrons whose lifetime can exceed the length of a night. This results in a persistent layer of ionization that can interfere with radio-based technologies. The density of each planetary ionosphere and the temperature of the planetary thermosphere tend to track the solar cycle variation in the solar EUV output. The EUV output of the Sun increases during solar maximum, due to both flares and a slower varying background glow. Figure 6 shows that slower varying part, which is important in heating the thermosphere, causing it to expand and increase satellite drag (Odenwald et al. 2006). Each wavelength varies in its own way. At this point in Solar Cycle 24, the ˚ have increased 75 % to reach a local emissions of the chromosphere at He II 304 A maximum, above their brightness in November 2011 when the highest sunspot number so far in Solar Cycle 24 was reached. By comparison, the coronal Fe XVI ˚ line has increased a factor of ten since the launch of SDO, with larger rotation 335 A

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Fig. 7 The history of measurements of the solar EUV spectral irradiance. The F10.7 solar irradiance, a widely used measure of solar activity, is plotted as a solid line. Appended to that curve is a prediction of the remainder of Solar Cycle 24 from Pesnell (2014). At the top of the figure are the satellites that have measured the EUV spectral irradiance since the launch of OSO-3 in March 1967. The spectral coverage is shown by the height of the colored box (from 1 to 150 nm) although some missions provide measurements to longer wavelengths. The temporal coverage of each mission, taken from the NSSDC mission summary pages, is shown by the horizontal extent of the colored boxes. The right sides of the SOHO, TIMED, and SDO boxes are drawn at the end of the currently funded missions

variations. Even with the utility of these measurements, the EUV spectral irradiance between 0.1 and 105 nm has been measured on only about 70 % of the days since 1967 (Fig. 7). Understanding these spectral irradiances is necessary to construct accurate models of their emission at the Sun and how they create the ionospheres and thermospheres of planetary atmospheres. HMI returns information about the surface magnetic field and surface velocity fields. The former is immediately useful as it provides the state of the magnetic field as well as the boundary conditions for extrapolating that field into the corona with magnetic field models. Flares and CMEs are a direct result of the buildup of the magnetic field above the surface. Most of that buildup can be tracked to what emerges through the surface. Models of the coronal magnetic field are an essential tool in understanding and forecasting space weather hazards. The HMI Dopplergrams are an integral part of our understanding of the solar convection zone, the seat of the solar dynamo. Just like seismic waves on the Earth can be inverted to tell us about the interior of the Earth, the solar p-modes can be inverted to measure conditions inside the Sun. Additional analyses can show when localized changes are present and can indicate a magnetic field about to erupt. Other wave patterns are seen in the Dopplergrams. These include the supergranulation pattern that tracks conditions in the outer part of the solar convection zone. SDO has a prime mission of 5 years. This allows us to make our measurements over a significant portion of a solar cycle. By capturing the solar variations that exist

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in different time periods of a solar cycle, SDO can quantify the differences between the rising, maximum, and declining phases of Solar Cycle 24. If SDO continues into the extended mission phase, it will be able to make those comparisons over an even wider range of solar activity.

Data Volume and Completeness The raw data from all three instruments on SDO are CCD images. As a result, SDO produces about 3.4 million images every month. One of the design challenges for SDO mission was to ensure the timely delivery of that data to the SITs and on to other users. To reduce aliasing in the Fourier transforms used in the helioseismic data, the goal was that 95 % of the Dopplergrams must contain 99 % valid pixels. Because Dopplergrams are composed of 5–6 individual CCD images, or filtergrams, measured closely in time, a comprehensive data completeness budget was developed. An onboard recorder was determined to be too difficult to manage, so SDO uses a continuous downlink of the data to a dedicated ground station. This also means that near-real-time, rapid cadence, and low-latency SDO data is available for space weather forecasters.

SDO Science and Cosmic Hazards SDO is a science mission that produces data useful for space weather forecasters. But SDO also produces research into the causes of solar activity. Understanding those causes will help with predicting solar activity, the linchpin of LWS science and a primary science objective of SDO. Warnings of cosmic hazards coming from the Sun can be separated into categories according to how far in advance the warning is needed. Tactical awareness of the Sun comes from an assessment of the near-real-time data. Understanding begins when the analysis and correlation of that data produces short-term predictions and then tests those predictions. Long-term forecasts arise when the science analysis produces accurate and verifiable forecasts that are validated after ever-increasing forecast lead times. SDO produces data and science results in all of these categories: Knowledge: By releasing the near-real-time data as rapidly as possible, SDO provides a tactical awareness of when flares occur, the location on the Sun, duration, and spectral content. The filament liftoffs that can produce CMEs can also be quickly detected. The SDO data is also run through detection and classification software that determines what features are present. A database of discovered features is maintained at LMSAL’s Heliophysics Events Knowledgebase (HEK 2014). This near-real-time data is available at a variety of websites. Short term: Predictions of the timing and strength of solar flares, especially anticipating the next several hours to days, are critical for protecting space assets

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and astronauts. SDO provides line-of-sight magnetic fields that are used in empirical flare predictions. It also provides vector magnetic fields and spatially resolved temperature and radiance maps that should allow more accurate shortterm predictions to be developed. Long term: Predicting solar activity at longer times in the future, weeks to years, is needed for mission planning and designing mitigation techniques for power systems, GPS, and other technologies threatened by space weather. The atmospheres of all of the planets are sensitive to the evolution of the photon and particle output of solar activity. SDO science results provide models of the solar interior, spectral irradiance, and magnetic field that can be adapted to these predictions. Here are a few examples of how SDO data is changing our view of solar activity.

Late-Phase Flares Even after 100 years of solar flare research, the launch of SDO provided new information about the spectral content of long-lasting flares. Radiative energy from flares has been monitored in X-rays since 1976 by GOES. A great deal of work has been done to understand the association of X-rays with other measures of solar activity (Aschwanden and Freeland 2012). These analyses assumed that most, if not all, of the radiated energy was being captured by the GOES radiometers. Soon after EVE began regular observations of the solar EUV spectral irradiance, it was noticed that the spectral irradiance at longer wavelengths often increased long after the X-ray irradiance had faded. Because few flares had been occurring each day at this point in this solar cycle, and by verifying the source of the radiation in AIA images, it was determined that more energy can be emitted at the longer wavelengths than in X-rays as the loops over an active region return to a non-flaring condition (Woods et al. 2011). This additional energy is absorbed higher in the Earth’s atmosphere than are X-rays (Fig. 8), creating ions and electrons in the F-region ionosphere and heating the thermosphere. More energy and longer duration should mean a measurable change in the densities and temperatures within the ionosphere and thermosphere. Any increase in the density of the thermosphere increases the drag on satellites in low-Earth orbit. Unfortunately, the duration is so long that any effects are masked by the normal diurnal variation. Research continues to see if late-phase flares are an important component of space weather or simply an essential clue of how solar flares work.

Prominence and Filament Eruptions Solar prominences and filaments are long arcs of relatively cool material suspended above the surface of the Sun by the solar magnetic field. Prominences are bright

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Fig. 8 An illustration of the absorption of ultraviolet radiation in the terrestrial atmosphere. Red colors denote unattenuated solar radiation at that altitude and wavelength. Black regions are altitudes where light at that wavelength was completely absorbed above that point. Contours are drawn at 25 %, 50 %, and 75 % absorption. Horizontal blue lines show the dividing lines for the named atmospheric layers. The absorption in the EUV occurs above 150 km altitude, making the solar emissions at those wavelengths critical to understanding the density and temperature of the thermosphere

arcs at the solar limb while filaments are the same structures seen as dark arcs on the disk. Their presence and dynamics are often used as an early indicator of the eruptive events that drive space weather. When either erupts from the surface, they can form a coronal mass ejection (or CME). The energetic particles in a CME can disable spacecraft and interfere with radio communications. Compared with flares, the effects of CME take longer to arrive at a planet but can last several days as the magnetic field of a planet (the magnetosphere) relaxes from the impact of the CME. During the initial passage of the CME by a planet, the magnetosphere is distorted and then relaxes after the CME has left. Particles within the magnetosphere are energized by the relaxation of the magnetic field toward a quiet state. During the several days this relaxation takes, the energetic particle fluxes are higher and chances of harm to satellites or the built environment are increased. Predicting that a CME will strike a planet is the first step to mitigating this cosmic hazard. Knowing how filaments form and why they erupt is a crucial step toward making this prediction. Continuous, high-cadence SDO observations have enabled scientists to observe in detail how filaments are formed. Their work shows that filaments can be formed by hot gas cooling within a coiled magnetic field. Once cooled the material finds itself trapped in the magnetic field, which keeps it from falling back toward the solar surface or at least significantly slows that fall for some time. This means filaments are long-lived patterns where material cycles through them: cool material

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Fig. 9 An example of how material in a prominence unwinds. This prominence eruption occurred February 24, 2011, between 0700 and 0930 UTC. These images were taken 36 s apart near 0730 UTC. The material in the hook has rotated counterclockwise between the two images. The multiple images radiating in an “X” from bright areas are caused by the diffraction pattern of the telescope. A movie of this event can be viewed at the SDO website (SDO 2014b, Item 60)

rains out, while new material is added as it descends from the hot corona above them. New, hot material bubbling up along pathways that thread through the descending cooler material refills the reservoir above the filament. The SDO observations also show how filaments may become unstable and how they subsequently erupt as part of a solar coronal mass ejection. The combined SDO and STEREO data reveal rolling motions that are signs of electrical currents and the cause of the filament material sloshing around within the coronal magnetic field. The observations are interpreted by measuring the twist or number of turns in the filament material. Figure 9 shows prominence material unrolling as it moves away from the solar surface. Once the buildup of twist exceeds a critical value, the magnetic configuration erupts, displaying a characteristic kinking and twisting motion (Sterling et al. 2012; Su and van Ballegooijen 2013). SDO data gives an unprecedented view of these eruptions, at a rapid cadence, excellent spatial resolution, and multiple temperatures.

Global Magnetic Fields SDO data has been used to observe and explain rapid changes in the solar corona under the control of the global magnetic field. Many examples have been seen where one part of the solar corona rapidly changes because of a change in another part far away. SDO observations have shown the entire corona can respond to an explosive eruption by a crowning of the magnetic field, much like a forest fire moving through the tops of trees. (An example from 01-AUG-2010 is described in Fig. 10.)

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Fig. 10 An example of how filaments are coupled by the global magnetic field. White arrows ˚ image from 0600 UTC on August 1, 2010. Cyan arrows point at two filaments in this AIA 304 A point at two active regions. A small flare in the upper active region (AR1) at 0300 UTC started a cascade of eruptions, first in the larger active region (AR2), then the upper filament (P1), and finally the lower filament (P2). In this image the upper filament has just begun to erupt. The lower prominence will erupt at 1000 UTC. A movie of this event can be viewed at the SDO website (SDO 2014a, Item 52)

A model of the sympathetic eruptions on this date shows how they are triggered and even how the order of eruption does not progress in distance from the first event (Titov et al. 2012). More frequently, waves are seen to move across the disk of the Sun, covering a large area of the Sun as they pass. These EUV waves can be analyzed to measure the magnetic field in the corona (Liu et al. 2012). Global models of the solar magnetic field start from the surface of the Sun. SDO is providing the first measurements of the strength and direction of the vector magnetic field over the visible disk of the Sun. These data are available every 12 min. This data set is used as the boundary condition for coronal magnetic field models and for developing an understanding of how the field emerges from inside the Sun. One interesting area of study is whether projections of the vector field, summed over an active region and followed in time, can be used to predict when that active region will flare or erupt. This reduction in complexity of the data set is essential for assessing the hazard of an active region. If you combine the vector magnetic field with velocities derived by tracking features at the surface, you can calculate the electric field in the photosphere. The electric and magnetic fields determine how much electromagnetic energy flows into the corona and chromosphere. Although the solar magnetic field has been measured for over 100 years, the electric field has rarely been measured and this Poynting flux is poorly determined. The ohmic heating can also be determined from these

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calculations. In magnetically dominated plasma like the corona, the Poynting flux and ohmic dissipation join thermal conduction and radiative losses as important parts of the energy balance. SDO is also using two small-scale probes of the solar global magnetic field. The brightenings seen when a comet passes through the corona or when material from an eruption falls back onto the Sun may be very small in size but are important checks on our understanding of how the corona works. These observations help calibrate our models of the coronal magnetic field and add to our understanding of how the emissions are created. For example, the energy emitted by the material as it stops must be about the same as the kinetic energy of the material falling back onto the Sun (Innes et al. 2012). The multiple passbands of AIA can resolve the heating of this material as it falls onto the chromosphere. The atomic components of ice evaporated from Sun-grazing comets must be heated to 105–106 K to be seen in the AIA passbands. The motion of the ionized material tests our understanding of how the magnetic field deflects the material, and the emission tests how cooler material is excited to become visible in the SDO passbands (Schrijver et al. 2012). Models of the solar magnetic field were improved to explain the observations, and models of the emission of material in the corona were adjusted to allow for the input of new material (Bryans and Pesnell 2012). Results from these probes shed new light on the long-standing key question of what causes the heating of the solar corona and the solar wind.

Other Magnetic Features Solar flares and CMEs are not the only cosmic hazards from the Sun that endanger the planets and our modern technological environment. High-speed streams emanating from coronal holes and the current sheet that forms throughout the solar system are two other cosmic hazards coming from the Sun. Coronal holes are dark areas of the corona with low densities (one can be seen in Fig. 4). These parts of the corona have open field lines, meaning a magnetic field line that leaves the Sun within a coronal hole will not trace back to the surface of the Sun. Any plasma that moves up a field line in a coronal hole can escape as the fast solar wind. Magnetic field measurements from SDO are used to calculate models that predict the magnetic field line connecting the Sun to the Earth. Highspeed streams moving along that field line will often hit the Earth. When that happens the magnetosphere responds by creating a geomagnetic storm lasting several days. A geomagnetic storm produces high fluxes of energetic electrons and protons. A similar magnetic connection can be found between the Sun and other planets. Coronal holes and high-speed streams are more common in the declining phase of a sunspot cycle. Long-lived coronal holes can survive for several solar rotations. That means if a high-speed stream from a coronal hole hits the Earth today, it probably will hit it again in 27 days. These are two simple predictions of solar activity.

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These same magnetic field models can calculate the position of the current sheet that modulates the flux of the cosmic rays as they enter the solar system and the Earth.

Helioseismology HMI Dopplergrams are maps of wave patterns that are used to probe the inside of the Sun, the location of the solar dynamo that generates the magnetic field. The raw Dopplergram in the left panel of Fig. 3 shows three different kinds of motions. The first is solar rotation, with the left side of the Sun moving toward the viewer and the right side moving away. Next is a set of large cells, looking much like craters on the Moon and visible better around the outer part of the image, called supergranulation. These cells are a motion of material and magnetic field in the top layers of the convection zone. The third motions are the 5-min oscillations or p-modes. These acoustic waves are best seen near the center of the Sun, where their line-of-sight (LOS) velocity is the highest. All of these motions provide clues about the solar dynamo, but the p-modes can be used to look deep inside the Sun. One example of how p-modes help to understand the solar dynamo is their use to determine the pattern of the bulk velocities of the plasma within the Sun. The main result is a profile of the meridional velocities within the solar convection zone. Meridional velocities move plasma and magnetic field from the equator to the pole, down inside the Sun, and back toward the equator, where they emerge to start a new cycle. They are similar to wind patterns seen in the Earth’s atmosphere. The first profile, obtained using data from SOHO and GONG in Solar Cycle 23, showed that the plasma moves upward at low latitudes, poleward near the surface, and then downward at high latitudes. To close the flow pattern, it was necessary to assume some pattern deep in the solar interior. Assuming the flows have a single cell means that an unseen equatorward flow takes place somewhere deep inside the Sun. We were not sure how deep in the Sun that return flow happened and why was there only one cell. If we look at the Earth’s atmosphere, there is a single cell of circulation in the thermosphere but three cells (Hadley, Ferrel, and polar) in the troposphere. Just ask any sailor who gets stuck in the calm winds of the horse latitudes whether a single cell would be better! Having three cells instead of one has profound effects on our weather patterns and climate. Why should the Sun be limited to only a single cell? HMI has extended the observations into Solar Cycle 24. New techniques in local helioseismology were developed by Zhao et al. (2013). to extend the view of the flows to greater depth and with better accuracy. This new result is illustrated in Fig. 11. It was determined that material circulated in two cells, one above the other, rather than the single cell that had been assumed from earlier work. Other work has determined that the shape of the cells changes as solar activity comes and goes. Sometimes it is a single cell from equator to pole and other times there are several

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Fig. 11 Schematic plot showing the double-cell meridional circulation structure inside the Sun. Meridional circulation, which transports solar materials between low and high latitudes inside the Sun, may be a fundamental property of the Sun but it was poorly known. It is thought that meridional circulation plays an important role in creating the 11-year solar activity cycle by redistributing solar angular momentum and transporting magnetic flux (Image courtesy of Zhao and Stanford University)

upwelling and downwelling regions. The complexity of this circulation pattern means that predictions based on these motions are less certain. The variation of the torsional oscillations is examined for even longer-term predictions. Rings of slightly faster and slightly slower rotation gird the Sun and drift slowly from high latitudes toward the equator as the solar cycle progresses. The motion of these rings appears to indicate the timing of the solar cycle. Sunspots begin to appear as one ring passes by the 35 latitude line. These results have only been known for two sunspot cycles, but they show that we are moving toward developing the models we need to predict the amplitude and timing of an upcoming sunspot cycle.

Conclusion The behavior of Solar Cycle 24 shows that even a below-average solar cycle can produce significant solar eruptive events. The first X-class flare of Solar Cycle 24 happened on February 14, 2011, and was accompanied by a halo CME, which means it was heading for Earth. SDO and other observatories have studied Active Region 11158, the site of the February 2011 flare, in great detail in many wavelengths. A series of filament eruptions on August 1, 2010, was a casebook study on sympathetic eruptions. Precipitated by the emergence of magnetic flux on the far side of the Sun, three filaments erupted as the magnetic field high above them changed (Fig. 10). A flare in July 2012 produced the fastest CME yet seen (Russell et al. 2013). If that CME had struck the Earth, it might have caused the largest geomagnetic storm since the Carrington Event in 1859. SDO is part of a research and operational system of observatories, both spaceand ground-based, whose combined data is used to fill the holes in each individual

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part. An excellent example of combining data is the picture of the entire Sun produced by merging views from SDO and the twin STEREO spacecraft. Since February 6, 2011, the EUV images from these three spacecraft have produced a view of the complete EUV Sun. This means that scientists and space weather forecasters are able to watch the evolution of active regions from emergence to decay as they rotate around the Sun. Several cosmic hazards to whose mitigation SDO has contributed were described. The presence of late-phase flares may show that the X-ray irradiance is not sufficient to track the effect of solar activity on planetary atmosphere or stellar activity on planets in other solar systems. The formation and eruption of filaments to create coronal mass ejections has been well documented by SDO observations and analysis. Large eruptions in the global magnetic field of the Sun have been shown to come from modest changes in regions quite remote from the erupting region. This is an important consideration when predicting CMEs. SDO is producing the data and models needed to address the cosmic hazards of solar activity for Solar Cycle 24 and beyond. As of April 30, 2014, it has recorded over 166 million images with high spatial resolution, spanning multiple wavelengths in the corona and including measurements of the EUV spectral irradiance, Doppler velocity, and magnetic field at the solar surface. SDO provides the most accurate, continuous measurements of the EUV photon irradiances that are critical for understanding and predicting the hazards produced by solar activity at the Earth and planets. Research models available at the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center use SDO data to broaden the usefulness of the data to locations throughout the heliosphere. With almost two complete sunspot cycles (a whole solar cycle) measured by spaced-based assets carrying a wide range of instruments, the predictions of solar activity during Solar Cycle 25 should be the most accurate ever. This allows us to anticipate the cosmic hazards caused by the Sun in our planetary atmospheres and in our modern technological environment. Acknowledgments This work was supported by NASA’s Solar Dynamics Observatory (SDO). The SDO data is courtesy of the NASA/SDO and the AIA, HMI, and EVE Science Investigation Teams.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Fundamental Aspects of Coronal Mass Ejections ▶ Medical Concerns with Space Radiation and Radiobiological Effects ▶ Nature of the Threat/Historical Occurrence ▶ Solar Flares ▶ Solar Flares and Impact on Earth ▶ Solar Radiation and Spacecraft Shielding

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References Aschwanden MJ, Freeland SL (2012) Automated solar flare statistics in soft x-rays over 37 years of GOES observations: the invariance of self-organized criticality during three solar cycles. Astrophys J 754, eid: 112 Bryans P, Pesnell WD (2012) The EUV emission from sun-grazing comets. Astrophys J 760, eid: 8, 18 pp Catling DC, Zahnle K (2009) The planetary air leak. Sci Am 300:36–43 Extreme Ultraviolet Variability Experiment (EVE) (2014) Retrieved 1 June 2014 from http://lasp. colorado.edu/home/eve/ Heliophysics Events Knowledgebase (HEK) (2014) Retrieved 1 June 2014 from http://www. lmsal.com/hek/ Innes DE, Cameron RH, Fletcher L, Inhester B, Solanki SK (2012) Break up of returning plasma after the 7 June 2011 filament eruption by Rayleigh-Taylor instabilities. Astron Astrophys 540, did: L10 Lemen JR, Title AM et al (2012) The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Sol Phys 275:17–40 Liu W, Ofman L, Nitta N, Aschwanden M, Schrijver C, Title A, Tarbell T (2012). Quasi-periodic fast-mode wave trains within a global EUV wave and sequential transverse oscillations detected by SDO/AIA. Astrophys J 753, eid: 52 Odenwald S, Green J, Taylor W (2006) Forecasting the impact of an 1859-calibre superstorm on satellite resources. Adv Space Res 38:280–297 Pesnell WD (2014) Predicting solar cycle 24 with geomagnetic precursor pairs. Sol Phys 289:2317–2331 Russell CT et al (2013) The very unusual interplanetary coronal mass ejection of 2012 July 23: a blast wave mediated by solar energetic particles. Astrophys J 770, eid: 38 Schou J, Scherrer PH et al (2012) Design and ground calibration of the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO). Sol Phys 275:229–259 Schrijver CJ, Brown JC, Battams K, Saint-Hilaire P, Liu W, Hudson H, Pesnell WD (2012) Destruction of Sun-grazing comet C/2011 N3 (SOHO) within the low solar corona. Science 335:324–328 SDO (2014a) Item 52. Retrieved 1 June 2014 from http://sdo.gsfc.nasa.gov/gallery/main/item/52 SDO (2014b) Item 60. Retrieved 1 June 2014 from http://sdo.gsfc.nasa.gov/gallery/main/item/60 SDO Joint Science Operations Center (JSOC) (2014) Retrieved 1 June 2014 from http://jsoc. stanford.edu Sterling AC, Moore RL, Hara H (2012) Observations from SDO, Hinode, and STEREO of a twisting and writhing start to a solar-filament-eruption cascade. Astrophys J 761, eid: 69 Su Y, van Ballegooijen A (2013) Rotating motions and modeling of the erupting solar polar-crown prominence on 2010 December 6. Astrophys J 764, eid: 91 Titov VS, Mikic Z, To¨ro¨k T, Linker JA, Panasenco O (2012) 2010 August 1–2 sympathetic eruptions. I. Magnetic topology of the source-surface background field. Astrophys J 759, eid: 70, 17 pp Woods TN, Hock R et al (2011) New solar extreme-ultraviolet irradiance observations during flares. Astrophys J 739, eid: 59 Woods TN, Eparvier FG et al (2012) Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO): overview of science objectives, instrument design, data products, and model developments. Sol Phys 275:115–143 Zhao J, Bogart RS, Kosovichev AG, Duvall TL Jr, Hartlep T (2013) Detection of equatorward meridional flow and evidence of double-cell meridional circulation inside the Sun. Astrophys J Lett 774, eid: L29

STEREO as a ‘Planetary Hazards’ Mission M. Guhathakurta and B. J. Thompson

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mission Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mission Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scientific Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STEREO Space Weather Beacon Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Key Findings and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CME Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Drivers of Solar Eruptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sun-to-Earth Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interplanetary Space Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modern Superstorms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interplanetary “Nanodust” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . “Sun as a Star” Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

NASA’s twin STEREO probes, launched in 2006, have advanced the art and science of space weather forecasting more than any other spacecraft or solar observatory. By surrounding the Sun, they provide previously impossible early warnings of threats approaching Earth as they develop on the solar far side. M. Guhathakurta (*) NASA Headquarters, Science Mission Directorate, Washingto, DC, USA e-mail: [email protected] B.J. Thompson Heliophysics Science Division, NASA/GSFC, Greenbelt, MD, USA e-mail: [email protected] # Springer International Publishing Switzerland (outside the USA) 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_17

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They have also revealed the 3D shape and inner structure of CMEs – massive solar storms that can trigger geomagnetic storms when they collide with Earth. This improves the ability of forecasters to anticipate the timing and severity of such events. Moreover, the unique capability of STEREO to track CMEs in three dimensions allows forecasters to make predictions for other planets, giving rise to the possibility of interplanetary space weather forecasting too. STEREO is one of those rare missions for which “planetary hazards” refers to more than one world. The STEREO probes also hold promise for the study of comets and potentially hazardous asteroids. Keywords

Sun • Heliosphere • CMEs • Space weather

Introduction As planetary hazards go, few perils eclipse the Sun. The iconic example is the Carrington Event of 1859. At 11:18 AM on the cloudless morning of Thursday, September 1, 1859, 33-year-old astronomer Richard Carrington was in his well-appointed private observatory. Just as usual on every sunny day, his telescope was projecting an 11-in.-wide image of the Sun on a screen, and Carrington skillfully drew the sunspots he saw. Suddenly, before his eyes, two brilliant beads of blinding white light appeared over an enormous sunspot group. Realizing that he was witnessing something unprecedented and “being somewhat flurried by the surprise,” Carrington later wrote, “I hastily ran to call someone to witness the exhibition with me. On returning within 60 s, I was mortified to find that it was already much changed and enfeebled.” He and his witness watched the white spots contract to mere pinpoints and disappear. Thus, solar flares were discovered. Before dawn the next day, skies all over Earth erupted in red, green, and purple auroras so brilliant that newspapers could be read by their light. Stunning auroras pulsated as far south as Cuba, the Bahamas, Jamaica, El Salvador, and Hawaii. Even more disconcerting, telegraph systems worldwide went haywire. Spark discharges shocked telegraph operators and set telegraph papers on fire. Even when telegraphers disconnected the batteries powering the lines, aurora-induced electric currents in the wires allowed messages to be transmitted. The “Victorian Internet” was simultaneously energized and brought to its knees. What would happen if such an event occurred today? The National Academy of Sciences has framed the problem in a landmark report entitled “Severe Space Weather Events – Societal and Economic Impacts” (National Research Council, 2008). It noted how people of the twenty-first century rely on high-tech systems for the basics of daily life. Smart power grids,

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GPS navigation, air travel, financial services, and emergency radio communications can all be knocked out by intense solar activity. A century-class solar storm could cause 20 times more economic damage than Hurricane Katrina. It was once thought that the Carrington Event was an extraordinarily rare thing, but that idea is beginning to change. The Carrington Event is indeed the undisputed champion of radiation storms: Energetic particles accelerated by the flares of September 1859 enveloped Earth, possibly leaving a record in the nitrates of ice cores. By this measure, the Carrington Event may be the biggest in 500 years and nearly twice as big as the runner-up. However, there is more to space weather than radiation storms. Another measure is geomagnetic activity – the shaking of Earth’s magnetic field due to the impact of a coronal mass ejection (CME) (a magnetized cloud of plasma from the Sun). In this respect, the Carrington Event has rivals in modern times. A geomagnetic storm at least half as strong as the Carrington Event erupted in May 1921. Researchers examined geomagnetic records from that storm and modeled its effect on the modern power grid (National Research Council 2008). In North America alone, he found more than 350 transformers at risk of permanent damage and 130 million people without power. The loss of electricity would ripple across the social infrastructure with water distribution affected within several hours; perishable foods and medications lost in 12–24 h and the loss of heating/ air conditioning, sewage disposal, phone service, fuel resupply, and other services persisting for unknown periods of time. A more recent example occurred in March 13, 1989, when a strong flare provoked geomagnetic storms that disrupted electric power transmission from the Hydro-Que´bec generating station in Canada. More than six million people were plunged into darkness for 9 h. Aurora-induced power surges melted power transformers as far away as New Jersey. Much of the damage can be mitigated if managers know a storm is coming. Putting satellites in “safe mode” and disconnecting transformers can protect these assets from damaging electrical surges. Preventative action, however, requires accurate forecasting – a job that has been assigned to NOAA. Space weather forecasting is still in its infancy. Many observers liken it to terrestrial weather forecasting – 50 years ago. Nevertheless, researchers at NOAA’s Space Weather Prediction Center in Boulder, Colorado, are making rapid progress. Space weather forecasting is actually a collaboration between NASA and NOAA. NASA’s fleet of heliophysics research spacecraft provides NOAA with up-to-the-minute information about what is happening on the Sun. The NASA fleet complements NOAA’s homegrown GOES and POES satellites, which focus more on the near-Earth environment. Among many capable solar observatories operated by NASA, one stands out as particularly unique: the twin STEREO probes. STEREO, short for “Solar TErrestrial RElations Observatory” (Kaiser et al. 2008), is the third mission in NASA’s Solar Terrestrial Probes program. It consists of two nearly identical 3-axis-stabilized space-based observatories – one

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ahead of Earth in its orbit, the other trailing behind – which observe the Sun from multiple (and sometimes stereoscopic) points of view. The two solar-powered probes were launched on October 25, 2006, and they have been beaming back unprecedented data about the Sun ever since.

Mission Overview The original objective of the STEREO mission was not to provide planetary defense, but rather to conduct fundamental investigations in solar physics. Researchers wanted to investigate the 3D structure and internal magnetohydrodynamic physics of coronal mass ejections (CMEs). CMEs are key agents of planetary space weather. They are powerful eruptions that can blow up to 10 billion tons of the Sun’s atmosphere into interplanetary space. A typical CME has a speed of .5–2 million mph (1–3 million kph), but extremely energetic eruptions have been observed exceeding 5 million mph (8 million kph). When CMEs sweep past Earth, their interaction with our planet’s magnetic can spark pronounced geomagnetic activity and storms. By observing CMEs from multiple points of view and tracking their progress across the Sun-Earth divide, researchers have been able to make progress on a number of previously intractable questions. The authors of the mission’s 1997 Science Definition Report wanted to know the following: • Are CMEs driven primarily by magnetic or nonmagnetic forces? • What initiates a CME? • What is the origin of waves, shocks, and particle radiation that often precede a CME’s arrival at Earth? “In order to understand and forecast CMEs,” they wrote, “we need 3D images of them and of the ambient solar corona and heliosphere.” It is notable that even in the earliest thought-pieces about the STEREO mission, forecasting CMEs appeared alongside understanding them. Planetary hazards were on the minds of mission planners from the very beginning. To accomplish these goals, two spacecraft would be required: one probe orbiting just inside the orbit of Earth and one probe orbiting just outside. STEREO-Ahead (inside) and STEREO-Behind (outside) would drift away from one another, STEREO-A moving ahead of Earth’s orbit and STEREO-B behind at a rate of 22.5 /year, providing the necessary points of view (see Fig. 1). This scheme had another advantage. Within a few years of launch, the separating probes would gain an excellent view of the far side of the Sun. For the first time, NASA could monitor the entire 360 circumference of our star. The Sun has a vexing habit of surprising forecasters with sunspots that developed on the far side of the Sun, spitting flares and hurling CMEs when they rotated toward Earth. With STEREO, those days would be a thing of the past.

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Fig. 1 Diagram of STEREO spacecraft positions from 2007 through 2015 (Courtesy of NASA)

Mission Characteristics As with many nascent space missions, one of the first challenges for STEREO was financial. The NASA budget allowed for a single rocket to launch the mission, yet the two probes needed to be placed in significantly different orbits. Mission planners called on the Moon for assistance. Mission designers realized that they could use the Moon’s gravity to redirect the probes to their appropriate orbits – something the launch vehicle alone could not do. For the first 3 months after launch, the two observatories flew in highly elliptical orbits extending from very close to Earth to just beyond the Moon’s orbit. STEREO Mission Operations personnel at the Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, nudged the spacecraft’s orbits closer and closer to the Moon itself. About 2 months after launch, STEREO-B was close enough to use the Moon’s gravity to fling it to a position “behind” Earth. Approximately 1 month later, STEREO-A encountered the Moon again and was flung to its orbit “ahead” of Earth. This was the first time a “double lunar flyby” had been used to manipulate orbits of multiple spacecraft at the same time. After their encounters with the Moon, the two STEREO probes were in nearly 1-AU orbits with periods slightly less and slightly more than 1 year. From the point

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of view of Earth, STEREO-A would slowly drift ahead of our planet, gaining a view of solar “terrain” previously hidden on one side of the Sun, while STEREO-B would lag behind, providing a view of the other side. Early in the mission, when the spacecraft separation was small, the viewing angles were ideal for stereoscopic reconstruction of CMEs. In situ investigations were able to provide multipoint measurements of the same eruption, providing insight into the structural variation within a particular event. Later, as the separation increased, STEREO undertook different challenges, such as tracking eruptions all the way from the Sun to Earth. Also, the coronal imagers began to see more and more of the Sun that was hidden from Earth’s view, providing the first global observations of the atmosphere of a star. At first, the twin spacecraft saw only a fraction of the Sun’s far side, but as they continued to drift apart, the view improved. On February 6, 2011, STEREO reached “opposition.” The two probes were 180 apart, each looking down on a different hemisphere. Coincidentally, this occurred on Super Bowl Sunday in the USA, and NASA Public Affairs took advantage of the occasion to release a “first light” 3D movie of the Sun. For the first time in the history of astrophysics, researchers could see and study a star as a fully realized sphere as we regularly do with Earth (see Figs. 2 and 3). NASA’s Earth-orbiting Solar Dynamics Observatory is also monitoring the Sun from its location in Earth’s orbit. Working together, the STEREO-SDO fleet will be able to image the entire 3D Sun until May/June 2019 (apart from periods when the STEREO spacecraft are too close to the Sun-Earth line to allow communication). Can STEREO last that long? Originally, STEREO was conceived as a 2 ½ year mission, but that idea was quickly scrapped. Such a short mission would never reveal the full expanse of the far side of the Sun. Also, in early designs, there had been a limit on the movement of the high-gain antenna which would have curtailed operations to approximately 2013. The Applied Physics Lab removed that limit at the request of the NASA project office, and now there is no impediment (other than funding) to continuing on for many more years. The spacecraft’s solar arrays can provide power for any reasonable extension of the program. Both spacecraft have passed the point of “infant mortality” – that is, systems failing early – but of course electronics can fail at any time in response to cosmic rays and, ironically, solar storms.

Scientific Investigations Getting the probes into their correct orbits and engineering them to last more than a decade were significant technical challenges. Even more challenging, however, are the mission’s scientific requirements. To fully understand the genesis, evolution, and planetary impacts of CMEs, the STEREO probes would have to have a dynamic range of sensitivity unlike any other observatory in NASA’s history. Researchers needed to see (1) intensely bright explosions near the Sun’s surface, (2) moderately bright CMEs ramrodding out of

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˚ images onto a solar sphere. Fig. 2 Left: 3D reprojection of STEREO EUVI and SDO AIA 304 A Right: 360 maps of the full solar corona in September 2012, when the STEREO and SDO spacecraft achieved maximum average separation (120 ). From top to bottom, the EUVI/AIA ˚ , 171 A ˚ , and 193/195 A ˚ (Courtesy of the STEREO/SECCHI wavelengths represented are 304 A consortium)

the Sun’s atmosphere, and (3) the vanishingly faint remains of CMEs expanding into the near-vacuum of interplanetary space. Moreover, to understand the environment of CMEs, STEREO would also need to image the solar wind itself, flowing almost transparently in and around the storm cloud. No single telescope could do the job alone. Designers therefore equipped STEREO with a package of five telescopes in the SECCHI investigation (Howard et al. 2008), each operating in a different range of brightness and observing events at different distances from the Sun. The first SECCHI telescope is the Extreme Ultraviolet Imager (EUVI) built at the Lockheed Solar and Astrophysics Laboratory in Palo Alto, California. EUVI is able to make high-resolution (2 k  2 k) images of the Sun and its lower atmosphere in four different extreme ultraviolet emission lines: 171, 193, 284, and 304 angstroms. The four wavelengths were selected to trace plasma temperatures and magnetic conditions of special interest to solar physicists who wish to study the onset of explosions such as flares and CMEs. The Extreme Ultraviolet Imager

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Fig. 3 Four of the SECCHI telescopes from both STEREO-A and STEREO-B were used to reconstruct the 3D propagation toward Earth. Not shown is the HI2 outer heliospheric imager (Figure reproduced from Byrne et al. 2010)

observes the Sun between 1 and 1.7 radii from disk center – in other words, it monitors the bright solar surface, the chromosphere, and the inner corona. Next is the inner coronagraph, known as COR1. Coronagraphs are devices that create an artificial eclipse using an opaque disk to block the glare of the Sun. Built at Goddard Space Flight Center, COR1 is a classic “Lyot internally occulting refractive coronagraph” adapted for the first time to be used in space. COR1’s field of view ranges from 1.4 to 4 solar radii, so there is some overlap with the Extreme Ultraviolet Imager. Unlike EUVI, however, COR1 is designed to observe fainter things – primarily the gossamer solar corona and CMEs which plow through it en route to Earth. Although the Sun is blocked by an occulting disk, scattered light in the optical path of COR1 can still be a problem. To mitigate this, COR1 is equipped with a linear polarizer to suppress scattered light and to extract the polarized brightness signal from the solar corona. When engineers have to build a telescope that spends all of its time staring into the Sun, special measures must be taken to handle thermal loads and protect sensitive components. COR1 is a good example of how STEREO engineers dealt with these problems. Because the two STEREO spacecraft are in elliptical orbits about the Sun, the COR1 instruments experience considerable variation in solar irradiance, from 1,264 to 1,769 W/m2 for STEREO-A and from 1,068 to 1,482 W/m2 for STEREO-B. When these loads are combined with expected changes in the telescope’s material thermal properties from beginning to end of life, the worst-case temperature variation in the COR1 instrument is from 2.5 to 30  C. There is also an axial gradient in temperature from the front to the back of the telescope, ranging from 3 to 7  C.

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To deal with such gradients, designers placed software-controlled heaters with programmable set points at strategic locations throughout the instrument. They keep the instrument within the 0–40  C operational temperature range. There are also survival heaters controlled by mechanical thermostats to keep the instrument within the 20 to +55  C nonoperational range. Other measures also help the instrument deal with intense solar heat. For instance, specialized composite coatings of oxides over silver are deposited onto many exposed surfaces around the telescope’s aperture, such as the objective lens holder and door assemblies. These stable coatings absorb little sunlight and do a good job reradiating what they do absorb as infrared radiation. Another “hot spot” is the tip of the coronagraph’s occulting device. A majority of the solar load collected by the telescope’s main lens is concentrated there, raising its temperature as high as 125  C. This tip is made of titanium and is diamondturned to direct the sunlight into a light trap. The tip is also coated with a composite silver coating for high reflectivity. To further cool things down, the shaft of the occulting device is coated with black nickel to radiate away even more heat. Managing heat is a challenge for any solar observatory. A detailed discussion of heat management techniques and the extensive thermal engineering required for all of STEREO’s telescopes is beyond the scope of this chapter. Suffice it to say that all five telescopes have employed an innovative array of tricks to keep things cool.

The third SECCHI telescope is the outer coronagraph, known as COR2. Unlike COR1, which blocks the Sun inside the telescope assembly, COR2 is an externally occulted Lyot coronagraph. Designed and built at the Naval Research Laboratory in Washington DC, COR2 is a descendant of the highly successful LASCO C2 and C3 coronagraphs onboard the Solar and Heliospheric Observatory (SOHO). COR2 has approximately the same field of view as the two SOHO coronagraphs combined and is able to take pictures with a much shorter exposure time to reveal faster dynamics of CMEs, all while fitting into a smaller space inside its spacecraft. COR2 can track CMEs out to 15 solar radii when they are exiting the Sun’s atmosphere and entering interplanetary space. SECCHI’s COR1 and COR2 observations are complementary to SOHO’s C2 and C3 coronagraphs, which provide observations from Earth’s point of view. With SOHO’s view from Earth and SECCHI’s additional views, the three comprise a powerful 3D viewing assembly for CMEs. Fourth and fifth are, arguably, the most amazing telescopes of all – STEREO’s Heliospheric Imagers. The Heliospheric Imagers monitor a vast realm of space extending from the Sun’s upper atmosphere all the way to the orbit of Earth. They can track CMEs uninterrupted over a gulf of more than 93 million miles. By the time these storm clouds travel so far from the Sun, they are very faint, 13–15 orders of magnitude fainter than the solar disk. The HI instruments must be able to see them against a busy background of stars, planets, and even comets that sometimes get in the way. The Heliospheric Imagers consist of two small wide-angle telescopes mounted on the side of the STEREO spacecraft. They are sheltered from the glare of the Sun by a series of linear occulters. Unlike the coronagraphs, which put an occulter directly in

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Fig. 4 Composite imagery from the five SECCHI telescopes showing three CMEs on January 9, 2009: one in the COR2 field of view, one in HI-1, and one reaching 1 AU in HI-2. Three planets are also shown: the blue dot represents Earth, pink indicates Venus, and yellow indicates Mercury (Courtesy of C. E. DeForest; see DeForest et al. 2011, 2013)

front of the Sun to reduce glare, HI operates in the shade of a more conventional baffle. The concept is not unlike observing the night sky after the Sun has gone below the horizon. One telescope (HI-1) sees a patch of sky about 20 wide; the other (HI-2) sees 70 , extending beyond the orbit of Earth. The fields of view overlap by about 5 , to allow continuous tracking from the inner heliosphere to beyond 1 AU. The greatest challenge for HI is the extreme faintness of CMEs. Background starlight from the Milky Way and the glow of sunlight scattered by interplanetary dust (zodiacal light) tend to overwhelm the gossamer clouds. In order to extract the CME signal, the signal-to-noise ratio must be increased over what is possible with a single exposure. Exposures are therefore summed onboard. This requires that the images be scrubbed for cosmic rays, which can make bright streaks and flashes in individual exposures, prior to summing. A 2  2 binning results in angular sizes of 70 arc second per pixel for HI-1 and 4 arcmin per pixel for HI-2. The combination of summing 50 images and 2  2 binning results in an increase in signal-to-noise ratio of about 14 times for HI-1. The effective exposures are 20 and 60 arc minutes for HI-1 and HI-2, respectively. Powerful image processing techniques, specifically developed for STEREO’s HI imagers, have further enabled the ability to view event faint eruptions. Figure 4 shows three different CMEs in the STEREO-A SECCHI combined field of view, tracking their transit over the course of several days. The result of this processing is a high dynamic range, wide-field image capable of recording stars as faint as 12th magnitude alongside planets orders of magnitude brighter. Indeed, Earth itself often appears in HI images. From their locations over the far side of the Sun, the STEREO probes can look back and see our home planet – a key requirement in tracking CMEs across the Sun-Earth divide.

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Fig. 5 Detection of radio bursts associated with a flare, CME, and post-eruptive loops on the Sun (shown in the upper left corner). CMEs do not propagate through a vacuum. On their way to Earth, they interact with shock waves, solar wind streams, and other gaseous “obstacles.” Indeed, the interaction of CMEs with the interplanetary medium can be a source of hazards to Earth and astronauts: Shock waves at the leading edge of CMEs can accelerate particles in the interplanetary medium to dangerous velocity. Studying the CME by itself is not enough. The structure of the medium it propagates through is equally important (Courtesy of N. Gopalswamy)

When all of its telescopes are operating nominally, STEREO can simultaneously observe objects as bright as the Sun (astronomical magnitude 27) and as dim as a 12th magnitude star. That gives the probes a dynamic range approximately ten billion times greater than the human eye. STEREO can detect flashes as intense as a solar flare and as faint as a charcoal-black asteroid approaching Earth from the direction of the Sun – and everything in between. No other astrophysics observatory has this kind of Olympic range. STEREO is also able to detect radio emissions from a variety of shock waves and plasma oscillations excited by flares and CME. It does this using the SWAVES instrument package: Three mutually orthogonal monopole antenna elements, each 6 m in length, jut out of the spacecraft to sample electrostatic and electromagnetic waves. The antennas are connected to five radio receivers variously sensitive to frequencies between 10 kHz and 50 MHz. Working together, these receivers can pick up type II, III, and IV “solar radio bursts” indicative of shocks and energetic particle interactions (see Fig. 5) as well as a variety of in situ plasma modes such as Langmuir, whistler, Z-mode, and electrostatic solitary waves (Bougeret et al. 2008).

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In situ measurements of particles and fields are provided by two STEREO investigations: IMPACT and PLASTIC. The IMPACT (In Situ Measurements of Particles and CME Transients; Luhmann et al. 2008) investigation is comprised of seven instruments: SWEA (Solar Wind Electron Analyzer), STE (Suprathermal Electron Telescope), MAG (Magnetometer), SEPT (Solar Electron Proton Telescope), SIT (Suprathermal Ion Telescope), LET (Low Energy Telescope), and HET (High Energy Telescope). SWEA measures solar wind electrons from below an eV to several keV, while STE covers 2–20 keV electrons, SEPT covers 20–400 keV, and HET covers.7–6 MeV. Protons are measured by SIT, SEPT (20–7,000 keV), LET (2–30 MeV), and HET (13–100 MeV), while measurements of helium and heavier elements are provided by SIT, LET, and HET. The MAG system provides magnetic field measurements in three dimensions and is divided into eight ranges to allow the capability of measuring a wide variety of magnetic field strengths. The PLASTIC (Plasma and Suprathermal Ion Composition; Galvin et al. 2008) investigation consists of three main components. The Solar Wind Sector (SWS) Small Channel provides a 45 field of view of solar wind protons and alpha particles, while the SWS Main Channel measures elemental composition and charge state properties and velocities for heavier ions. The Wide-Angle Partition (WAP) Sector has a 225 field of view on STEREO-A (210 on STEREO-B), representing the remaining unobstructed directions not covered by the SWS components. All three components deliver measurements at a time resolution of 1 min. The PLASTIC entrance system is an energy-per-charge analyzer, and the resulting energy ranges are .3–10.6 keV/e for SWS Small Channel, .3–80 keV/e for SWS Main Channel, and.3–80 keV/e for WAP. The IMPACT/PLASTIC in situ suite on STEREO has advanced our understanding of interplanetary hazards for several major reasons. Multipoint in situ measurements of major events have provided a dramatic improvement in our understanding of the 3D structure of space weather phenomena. The manifestations of hazardcausing phenomena are far from homogeneous in structure. When two spacecraft are able to sample the same event, the data frequently reveal great variations. Multipoint measurements have improved our ability to complete a 3D picture of these complex phenomena. Notably, both STEREO probes detected the historic radiation storm of July 2012, when a sunspot erupted and produced one of the most prolific streams of energetic protons in the history of the Space Age. Earth was not in the line of fire, and without STEREO, researchers might not have known the event occurred at all. By sampling the storm from points far from Earth, the STEREO probes replaced that cloud of ignorance with a wealth of IMPACT/ PLASTIC data that researchers are still studying years later. The IMPACT/PLASTIC combination has also drastically improved our ability to understand the 3D structure of the heliosphere. It has long been known that the Sun is only the beginning of the story. CMEs, energetic particles, and shocks are strongly modulated by the solar wind through which they propagate. Heliospheric structure is capable of speeding up, slowing down, or even deflecting CMEs. It can also enhance or decrease the magnitude of the hazard; for example, extremely highenergy proton events, which pose the greatest risk to assets in space, are produced

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by the interaction of a CME and shocked solar wind. These protons then travel along the solar wind magnetic field; without knowledge of the magnetic structure of the heliosphere, it is impossible to determine where or how strongly an energetic particle event will manifest itself.

STEREO Space Weather Beacon Data In support of space weather forecasting capabilities, each of the investigations on the two STEREO spacecraft also generate a special low-rate telemetry stream known as the Space Weather Beacon. Outside of the regular Deep Space Network contacts, which deliver the full science data, this Space Weather Beacon stream consists of a low-rate subset of the data specifically designed to allow rapid assessment of the space environment. Various antenna partners around the world collect this telemetry and pass it on to the STEREO Science Center (SSC) in near real time via a socket connection over the open Internet. The Space Weather Beacon allows forecasters and other users to access critical data days before the high-rate science data becomes available.

Key Findings and Results CME Topology The STEREO mission has achieved its major goal – the three-dimensional modeling of CMEs. From our single vantage point on Earth, CMEs flying in all directions away from the Sun appear to have a confusing variety of forms. Indeed, researchers had spent years examining thousands of CMEs recorded by Earth-orbiting cameras without finding the answer. As soon as STEREO was added to the mix, however, a common form emerged: CMEs resemble croissants (Figs. 6 and 7). Actually, theoretical models had predicted this for some time. A croissant shape naturally results from coiled magnetic fields called “flux ropes” widely believed to thread through the hearts of CMEs. Three-dimensional STEREO observations removed any doubt that this was the case (Vourlidas et al. 2013). Follow-up observations by NASA’s Solar Dynamics Observatory have revealed flux ropes near the solar surface that twist and break away to form CMEs (Patsourakos et al. 2012). Although the structure of CMEs can evolve significantly as they propagate, the croissant/flux rope model is now on a very firm footing. This is crucial for two reasons. First, even with STEREO on duty, CMEs leaving the Sun are not always observed from multiple points of view. Knowing the common shape of a CME allows forecasters to model its speed and trajectory using less-than-complete data. This improves the precision of forecast CME impact times. Second, the ability of a CME to foment a magnetic storm on Earth depends critically on its inner magnetic structure. Knowing the form of the magnetic structure – it is a flux rope – helpfully narrows the options for modelers who try

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Fig. 6 3D flux rope reconstruction of a CME on March 7, 2011, using the Thernisien, Howard, and Vourlidas (2006) “croissant” model. The model allows an accurate determination of the spatial extent of a CME and can track the temporal evolution as the CME propagates in the inner corona (Courtesy of the STEREO/SECCHI consortium and A. Thernisien)

to anticipate what a CME will do when it arrives. In 2014, forecasters are still struggling to weave this information into their forecasts. It is just a matter of time, however, before flux rope models improve the fidelity of geomagnetic storm warnings.

The Drivers of Solar Eruptions The full-sun view afforded by STEREO and supporting observatories does more than improve space weather forecasts. It has led to a whole new understanding of solar activity. For decades, astronomers have understood solar activity in terms of localized regions on the Sun. When the magnetic fields of individual sunspots crisscross and reconnect, powerful explosions ensue. This is how flares and CMEs happen. On August 1, 2010, this simple idea was upset. On that date the STEREO-SDO fleet observed a massive global series of explosions engulfing more than two-thirds of the Sun. Researchers catalogued more than a dozen significant shock waves, flares, filament eruptions, and CMEs spanning 180 of solar longitude and 28 h of time (Schrijver and Title 2011). At first it seemed to be a cacophony of disorder

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Fig. 7 Sunspot AR1429 unleashed a powerful X5-class solar flare on March 7, 2012, commencing the “St. Patrick Day storms” of 2012. The blast also propelled a massive coronal mass ejection (CME) toward Earth. Left: NASA’s Solar Dynamics Observatory recorded the flare at multiple extreme ultraviolet wavelengths (Courtesy of the SDO/AIA consortium). Right: A 3D CME model run from CCMC/iSWA shows how the CME would propagate through the inner solar system (Courtesy of the Community Coordinated Modeling Center)

until they plotted the events on a map of the Sun’s magnetic field. The events were connected by magnetism, one explosion triggering another like a series of falling dominoes. Solar physicists had long suspected this kind of magnetic connection was possible. The notion of “sympathetic flares” goes back at least three quarters of a century. Sometimes observers would see flares going off one after another – like popcorn – but it was impossible to prove a link between them. Arguments in favor of cause and effect were statistical and often full of doubt. For this kind of work, STEREO and SDO are game changers. Together, the three spacecraft allow researchers to see connections that they could only guess at in the past. To wit, only a fraction of the August events were visible from Earth, yet all of them could be seen by the SDO-STEREO fleet. Moreover, SDO’s measurements of the Sun’s magnetic field revealed direct connections between the various components of the “Great Eruption” – no statistics required. Much remains to be done. Researchers are still unsure about the timing: Was the event one big chain reaction, in which one eruption triggered another – bang, bang, bang – in sequence? Or did everything go off together as a consequence of some greater change in the Sun’s global magnetic field? The next global eruption observed by STEREO – and, yes, there will be a next one – could answer these questions.

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Sun-to-Earth Observations For many years, a “holy grail” of space weather forecasting has been to track a CME all the way from the Sun to Earth. STEREO has accomplished this, too. In December 2008, STEREO-A was 65 million km from Earth when a CME sped away from the Sun. The cloud remained in STEREO-A’s field of view as it propagated all the way across the Sun-Earth divide. When CMEs first leave the Sun, they are bright and easy to see. Visibility is quickly reduced, however, as the clouds expand into the void. By the time a typical CME crosses the orbit of Venus, it is a billion times fainter than the surface of the full Moon and more than a thousand times fainter than the Milky Way. CMEs that reach Earth are almost as gossamer as vacuum itself and correspondingly transparent. Even with STEREO’s onboard image enhancements described earlier in this chapter, it was an enormous challenge to pull such a faint cloud out of the confusion of starlight and interplanetary dust. Indeed, it took almost 3 years for the researchers to learn how to do it. Footage of the 2008 storm was not released until 2011! Now that the technique has been perfected, it can be applied on a regular basis without such a long delay (DeForest et al. 2011). If Sun-to-Earth CME tracking can be sped up and perfected, it would lead to a revolution in space weather forecasting. For one thing, forecasters would know exactly when and where a CME is going to strike. Uncertainties could be narrowed to the point that forecasts of space weather effects on Earth could become regional, rather than merely global as they are now. Tracking a CME continuously from Sun to Earth also means that forecasters could watch the cloud’s magnetic evolution and accurately anticipate its degree of “coupling” with Earth’s own magnetic field. They would know exactly what kind of geomagnetic storm is in the offing. These dramatic improvements, however, are still in the future. They require processing times to be reduced from years to hours, so there are huge practical challenges yet to overcome. Nevertheless, STEREO has shown us the possibilities.

Interplanetary Space Weather While one revolution waits, another is already under way – the revolution of interplanetary space weather forecasting (Guhathakurta 2013). Researchers working with STEREO’s 3D CME models quickly realized that they could make predictions not only for Earth but also for any other target in the solar system. The “planet” in “planetary hazards” could be any world from Mercury to Neptune. Tracking CMEs through the plasma-filled interplanetary medium takes more than a quick glance at data streaming in from the fleet. High-power computing is required. Around the time STEREO was launched, international researchers began to install their best physics-based models of the heliosphere on a bank of highspeed supercomputers at the Community Coordinated Modeling Center (CCMC),

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an interagency facility located at Goddard. NASA also established the Integrated Space Weather Analysis System (iSWA) to fetch space weather information from a wide array of spacecraft and sensors. Together, these programs can take raw data from the STEREO-SDO-SOHO fleet and turn them into meaningful space weather forecasts for any point in the solar system. Interplanetary space weather forecasting is important to NASA and other space agencies as probes are now orbiting or en route to Mercury, Venus, the Moon, Mars, Ceres, Saturn, Jupiter, and Pluto. Each mission has a unique need to know when a solar storm will pass through its corner of space. This is illustrated by the ironic example of MARIE on Mars Odyssey. The sensor, designed to measure space radiation in the vicinity of the Red Planet, was disabled by a fusillade of solar protons during the Halloween storms of 2003. Turning MARIE off during the storm might have saved it, but no one knew the protons were coming. Controllers of ongoing missions such as MAVEN and Curiosity would like Mars-specific warnings to help them safeguard their hardware. Earth’s satellite fleet is similarly exposed. A widely reported example is Galaxy 15: In April of 2010, a minor CME swept past Earth just as the massive telecommunications satellite was coming out of Earth’s shadow. What happened next is still controversial, but many researchers believe events unfolded as follows: Suddenly exposed to hot, energetic electrons stirred up by the CME, the satellite began to bristle with electricity. Electrons accumulated on the surface of Galaxy 15 until a sudden discharge turned the comsat into a “zombiesat.” It stopped accepting commands from Earth and spent the next 8 months drifting through the Clarke Belt broadcasting its own signals atop those of other satellites until it was recovered. Future episodes like this may be prevented if NOAA forecasters can pinpoint when CMEs will arrive and warn satellite operators to put their assets in safe mode at crucial moments. It might seem that Galaxy 15 hardly calls for an interplanetary forecast. However, the same 3D CME modeling that permits forecasts for Mercury, Venus, and Mars also offers substantially improved forecasts for our own planet.

Modern Superstorms As mentioned previously, the iconic example of space weather hazards is the Carrington Event of 1859. Because of STEREO, researchers were able to study a recent eruption that has been compared to the Carrington Event in terms of geoeffectiveness, and few events exemplify STEREO’s full capability better than the July 23, 2012, CME. The eruption was, for the most part, directed away from geospace; however, the STEREO spacecraft were able to record one of the fastest CMEs ever observed (Russell et al. 2013) and the most intense solar energetic particle event in decades (Mewaldt et al. 2014). Baker et al. (2013) demonstrated, by combining observations and state-of-the art models, that if the CME had been directed toward Earth it likely would have had a much larger impact than the

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Fig. 8 Three views of the July 23, 2012, CME: STEREO-B COR2, SOHO LASCO C3, and STEREO-A COR2 (Courtesy of the STEREO/SECCHI consortium)

Carrington storm. Despite being launched into the weakest solar cycle of the space age, STEREO was able to capture what could have been the storm of the century, had it impacted Earth. Figure 8 shows three views of the coronal mass ejection on 23 July 2012 as observed by the SOHO C3 and STEREO C2 coronagraphs. The multiple viewpoints allowed for a clear determination of the speed and direction of the eruption, and detection in the STEREO heliospheric imagers and in situ extended the speed measurements to 1 AU. The CME’s initial speed was determined to be 2,500  500 km/s, with a width of 140  30 . These parameters were used to drive simulations to determine the CME’s propagation through the heliospheric medium. Figure 9 shows the density impact of the CME as determined by the Wang-SheeleyArge (WSA)-ENLIL (Arge and Pizzo 2000; Odstrcil et al. 2004) simulation. SWAVES added valuable information about the leading edge of the shock of the CME, determining from type II drift frequencies that the leading edge of the shock was traveling at 3,000 km/s (Fig. 9). The shock extended over 240 in longitude, as most of the inner heliosphere felt the impact of the eruption. The increased energetic particle fluxes were detected almost immediately, and the shock and CME were detected in situ later in the day (around 21:00 UT), when solar wind speeds spiked to over 2,000 km/s and the magnetic field strength increased to over 100 nT (see Fig. 10). The 19-h CME transit time from the Sun to 1 AU is the fastest ever measured directly, as the 17-h transit time of the Carrington Event was inferred from the flare and the geospace impacts (Figs. 11, 12, and 13). Although the transit time was slightly longer than the Carrington Event, the estimated geomagnetic impact based on models described in Baker et al. (2013) indicates that if the CME had impacted Earth, the storm would have been even greater than the famous 1859 Carrington storm. Without STEREO, little information would have been available on this “modern” Carrington Event, and we would have missed the opportunity to study what could have been the storm of the century. In addition, thanks to STEREO, we now know that huge potentially damaging events can occur at any phase of the solar cycle irrespective of the degree of sunspot activity.

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Fig. 9 Left: The measurements derived from the multiple viewing angles of the July 2012 CME were then used as input to simulations. 3D models forecast the propagation and evolution of the CME in the inner heliosphere. Although the CME had a dramatic impact on much of the inner heliosphere, fortunately the majority of inner heliospheric space assets were clustered in less impacted longitudes (Courtesy of the Community Coordinated Modeling Center). Right: Radio bursts from the CME shock front as measured by STEREO-A SWAVES (Courtesy of N. Gopalswamy)

Interplanetary “Nanodust” Another discovery by STEREO is not a hazard to planets, but it could be a hazard to spacecraft moving rapidly through interplanetary space. The discovery is “nanodust.” The solar system is choked full with dust. We see these particles disintegrating in the night sky as meteors, and we see them in even greater numbers scattering sunlight from the plane of the solar system. Observers call it the “zodiacal light.” Nanodust is much smaller than these ordinary forms of space dust. Nanodust particles lie at the frontier between macroscopic objects and atomic structures. Unlike regular dust, which is mainly controlled by the gravitational field of the Sun, nanodust grains have a high electric charge relative to their mass and therefore strongly interact with the solar wind’s magnetic field. The solar wind sweeps up grains of nanodust and accelerates them to velocities of hundreds of kilometers per second (a million mph) near Earth’s orbit. These microscopic bullets can create surface charges on the hulls of interplanetary spacecraft. Indeed, this is how STEREO found them, using SWAVES. Each of the twin probes has a long antenna for sensing radio waves generated by CMEs plowing through the Sun’s atmosphere and, later, through the interplanetary medium. When a grain of nanodust hits STEREO at high velocity, it “craters out” and ionizes some of the spacecraft’s surface material. Impacts close enough to an SWAVES antenna

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Fig. 10 The July 23, 2012, CME was detected at STEREO-A only 19 h after the eruption, the fastest transit ever measured. The bottom panel shows the local solar wind speed detected by STEREO-A PLASTIC, the middle panel shows the magnetic field measurements from STEREOA IMPACT, and the upper panel shows the IMPACT SEPT, LET, and HET energetic proton measurements (Figure adapted from Russell et al. 2013)

produce a voltage pulse. Researchers counted these pulses to determine the flux of grains in the 5–20 nm size range. They found, surprisingly, that the population of nanodust makes up a significant fraction of the total mass of dust in interplanetary space (Le Chat et al. 2013).

Comets Finally, the STEREO probes have made exciting new observations of comets. It started with Comet Encke in 2007. Amateur astronomers know Comet Encke is the source of the Taurid meteor shower, a slow display of midnight fireballs that occurs every year in early- to mid-November. Every 3.3 years, the comet dips inside the orbit of Mercury where it is exposed to solar activity at point blank range.

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Fig. 11 Dust trails as detected by the STEREO-A HI1 imager on May 1, 2007. The image at the right shows the HI-1 image in the left image with a prior image subtracted from it, thereby enhancing the dust trails (Courtesy of the STEREO/SECCHI consortium. See St. Cyr et al. 2009)

Fig. 12 These series of three still images were taken from a visualization of Comet Encke flying through the solar storm as witnessed by the STEREO satellite. Note Encke’s tail being torn off by the coronal mass ejection, highlighted by the red line, in the second and third frames (Courtesy of A. Vourlidas and R. A. Howard, see Vourlidas et al. 2007)

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Fig. 13 NASA’s STEREO Spacecraft Discovers New Eclipsing Binary Stars: A STEREO Heliospheric Imager (HI-1A) image taken on March 7, 2010 (left), with two variable stars highlighted in the image. The varying brightness of the two stars V837 Tau and V1129 Tau are shown (right top and bottom, respectively) (Courtesy of D. Bewsher and the STEREO/SECCHI consortium)

In April 2007, only 6 months after the mission launched, STEREO-Ahead watched a CME strike the comet and rip off its tail. CMEs have surely collided with comets before, but this was the first time a spacecraft had witnessed the process. At first glance, it might seem surprising that a CME could rip off Encke’s tail. For all their mass and power, CMEs are spread over a large volume of space. The impact of a gossamer CME exerts little more than a few nanopascals of mechanical pressure – softer than a baby’s breath. Therefore, the ripping action must be due to something else. Researchers now believe the explanation is “magnetic reconnection.” Magnetic fields around the comet bumped into oppositely directed magnetic fields in the CME. Suddenly, these fields linked together – they “reconnected” – releasing a burst of energy that tore off the comet’s tail. A similar process takes place in Earth’s magnetosphere during geomagnetic storms powering, among other things, the aurora borealis. In a sense, the comet experienced a geomagnetic storm. It is the first time astronomers witnessed such an event on another cosmic body. Four years later, in December 2011, STEREO was joined by an armada of solar observatories in watching Comet Lovejoy plunge through the Sun’s atmosphere. In this case, it was the Solar Dynamics Observatory, not STEREO, which had the best view. Dramatic SDO movies showed the sungrazing comet’s tail veering back and forth as it was buffeted by magnetic structures in the solar corona. Movies of these interactions have sparked a number of studies on how comets can be used

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as “solar probes.” Just as you can learn about the hydrodynamics of a pond by tossing a stone into it and watching the ripples, you can learn about the magnetohydrodynamics of the solar corona by watching comets fly through. STEREO took center stage again when Comet ISON approached the Sun in 2013. The Heliospheric Imagers on STEREO-A tracked the comet from the orbit of Earth all the way to the doorstep of the Sun’s atmosphere. No other observatory in space or on Earth could match the quality of the movies STEREO obtained. Footage showed gusts of solar wind buffeting the comet, whirls, and eddies of plasma propagating down the comet’s tail and even a remarkable conjunction between Comet ISON and Comet Encke. When ISON entered the Sun’s atmosphere, STEREO’s coronagraphs followed the action as the comet, lamentably, broke apart. It turns out that Comet ISON was not as tough as its predecessor Comet Lovejoy, so it did not survive its brush with solar fire. STEREO’s coronagraphs and Heliospheric Imagers watched as a cloud of dust emerged where Comet ISON was supposed to be – and quickly faded into the black void of space. On the bright side, STEREO and other observatories such as SOHO had a ringside seat for the disruption of a comet, an event which researchers are enthusiastically studying even now.

“Sun as a Star” Studies Although STEREO is primarily a solar mission, the team realized that the stability of the Heliospheric Imagers (HI) aboard the twin spacecraft could be used to monitor variations in the brightness of stars (Wraight et al. 2012). Researchers have discovered 122 new eclipsing binary stars and observed hundreds more variable stars in an innovative survey using STEREO. STEREO’s ability to sample continuously for up to 20 days, coupled with repeat viewings from the spacecraft during the year, makes it an invaluable resource for researching variable stars. Observations from the HI cameras are enabling scientists to pin down the periods of known variables with much greater accuracy. In addition, HI measurements may be useful for exoplanet and asteroseismology research (Wraight et al. 2011). Very small changes to the brightness of stars can be detected, which could reveal the presence of transiting exoplanets or trace a star’s internal structure by measuring their seismic activity. One such case has been already identified using HI data. The twin STEREO probes have proven to be among the most versatile spacecraft ever launched. Nevertheless, there is still one area where they have not yet “spread their wings” – the search for potentially hazardous asteroids. Asteroids approaching Earth from the direction of the Sun are among the most difficult to detect by groundbased observatories. Detecting faint objects in the vicinity of the Sun, however, is STEREO’s specialty. The Heliospheric Imagers could prove to be useful tools for asteroid hunters, but this is not a capability that researchers are exploiting. This should be considered a small omission, though, given the scope of STEREO’s accomplishments so far.

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Conclusion When the words “planetary hazards” are spoken, most people (lay and scientist alike) probably think of asteroids. Yet when was the last time an asteroid did serious damage to human civilization? The Tunguska Event of 1918 leveled a forest, not a city, and the Chelyabinsk Meteor of 2013, which exploded over a populated area in the Urals of Russia did little more than break some windows. This is not to say that asteroids are safe; they most certainly are not. However, to find a recent example of substantial damage to human interests caused by a heavenly body, the place to look is the Sun. There are multiple examples in the last 25 years alone. During the great Quebec Blackout of 1989, for instance, more than nine million people spent a cold autumn night without lights or power. The same storm that blacked out Quebec damaged multiton transformers as far away as New Jersey and Great Britain and caused more than 200 power anomalies across the USA from the eastern seaboard to the Pacific Northwest. A similar series of “Halloween storms” in October 2003 triggered a regional blackout in southern Sweden and may have damaged transformers in South Africa. And eruptions like the July 23, 2012, CME demonstrate how even weak solar cycles have the ability to produce historic events. Strong solar storms are not far-fetched and improbable. They have happened in our lifetime. The problem we face is, ironically, progress. Since the beginning of the Space Age, the total length of high-voltage power lines crisscrossing North America has increased nearly tenfold. This has turned power grids into giant antennas for geomagnetically induced currents. With demand for power growing exponentially, modern networks are sprawling, interconnected, and stressed to the limit – a recipe for trouble, according to the 2008 report of the National Academy of Sciences: “The scale and speed of problems that could occur on [these modern grids] have the potential to impact the power system in ways not previously experienced.” Storms akin to the Carrington Event or the Quebec Blackout could cause lasting damage to these modern smart power grids, irreparably damaging transformers and knocking out power for months in areas hundreds to thousands of miles wide. Clean water supplies, financial services, telecommunications, and even some aspects of medical care could be crippled. These dangers are the reason why we can call STEREO a “planetary hazards mission.” Although the twin probes were dispatched to do research, they have quickly produced practical benefits, arguably advancing the art and science of space weather forecasting more than any other solar observatory. As humankind expands into the solar system, STEREO will be remembered as the mission that gave a new broader meaning to the term “planetary hazards.” Earth is not the only world in the crosshairs of the Sun. With STEREO, and follow-up missions like it, we may be able to protect them all. Acknowledgments The authors would like to thank the STEREO SECCHI, SWAVES, IMPACT, and PLASTIC investigations for their support in the preparation of this manuscript. Additionally, the authors gratefully acknowledge contributions and editorial support from Nat Gopalswamy, Joseph Gurman, Russell Howard, Ian Richardson, William Thompson, and Angelos Vourlidas.

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Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Early Solar and Heliophysical Space Missions ▶ Fundamental Aspects of Coronal Mass Ejections ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Dynamics Observatory (SDO)

References Arge CN, Pizzo VJ (2000) Improvement in the prediction of solar wind conditions using near-real time solar magnetic field updates. J Geophys Res 105:10465 Baker DN et al (2013) A major solar eruptive event in July 2012: defining extreme space weather scenarios. Space Weather 11:585 Bougeret JL et al (2008) S/WAVES: the radio and plasma wave investigation on the STEREO mission. Space Sci Rev 136:1–4 Byrne JP, Maloney SA, McAteer RTJ, Refojo J, Gallagher PT (2010) Propagation of an Earthdirected coronal mass ejection in three dimensions. Nat Commun 1:74 DeForest CE, Howard TA, Tappin SJ (2011) Observations of detailed structure in the solar wind at 1 AU with STEREO/HI-2. Astrophys J 738:103 DeForest CE, Howard TA, McComas DJ (2013) Tracking coronal features from the low corona to earth: a quantitative analysis of the 2008 December 12 coronal mass ejection. Astrophys J 769:43, and references therein Galvin AB et al (2008) The Plasma and Suprathermal Ion Composition (PLASTIC) investigation on the STEREO observatories. Space Sci Rev 136:1–4 Guhathakurta M (2013) Interplanetary space weather: a new paradigm. EOS Trans Am Geophys Union 94(18):165 Howard RA et al (2008) Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI). Space Sci Rev 136:1–4 Kaiser ML et al (2008) The STEREO mission: an introduction. Space Sci Rev 136:1–4 Le Chat G et al (2013) Interplanetary nanodust detection by the solar terrestrial relations observatory/waves low frequency receiver. Sol Phys 286:549 Luhmann JG et al (2008) STEREO impact investigation goals, measurements, and data products overview. Space Sci Rev 136:1–4 Mewaldt RA et al (2014) A 360 view of solar energetic particle events, including one extreme event, submitted to the Proceedings of the International Cosmic Ray Conference 2014 National Research Council (2008) Severe space weather events – understanding societal and economic impacts, space studies board report. National Academic Press, Washington, DC, pp 3 and 77 Odstrcil D et al (2004) Initial coupling of coronal and heliospheric numerical magnetohydrodynamic codes. J Atmos Solar-Terrestrial Phys 66:1311 Patsourakos S, Vourlidas A, Stenborg G (2012) Direct evidence for a fast coronal mass ejection driven by the prior formation and subsequent destabilization of a magnetic flux rope. Astrophys J 764:125 Russell CT et al (2013) The very unusual interplanetary coronal mass ejection of 2012 July 23: a blast wave mediated by solar energetic particles. Astrophys J 770:38 Schrijver CJ, Title AM (2011) Long-range magnetic couplings between solar flares and coronal mass ejections observed by SDO and STEREO. J Geophys Res 116:A4

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St. Cyr OC et al (2009) STEREO SECCHI and S/WAVES observations of spacecraft debris caused by micron-size interplanetary dust impacts. Sol Phys 256:475–488 Thernisien A, Vourlidas A, Howard RA (2006) Modeling of flux rope coronal mass ejections. Astrophys J 652:763 Vourlidas A, Lynch BJ, Howard RA, Li Y (2013) How many CMEs have flux ropes? Deciphering the signatures of shocks, flux ropes, and prominences in coronagraph observations of CMEs. Sol Phys 284:179 Vourlidas A et al (2007) First direct observation of the interaction between a comet and a coronal mass ejection leading to a complete plasma tail disconnection. Astrophys J 668:L79 Wraight KT, White GJ, Bewsher D, Norton AJ (2011) STEREO observations of stars and the search for exoplanets. Mon Not R Astron Soc 416:2477 Wraight KT, Fossati L, White GJ, Norton AJ, Bewsher D (2012) Bright low mass eclipsing binary candidates observed by STEREO. Mon Not R Astron Soc 427:2298

Part V The Earth’s Natural Protective Systems and the Van Allen Belts

The existence of the Van Allen belts was unknown prior to the Explorer 1 experiments conducted on the United States first successful space launch in 1958. Since that time there has been a great deal of new information gathered about the nature of the radiation and the ionic particles that exist in these belts and how they serve to divert incoming radiation and ionic particles originating from the sun and other cosmic sources. In general, the Van Allen belts redirect the ongoing torrent of radiation and high-speed ions away from the central parts of Earth and toward the polar regions. In recent spacecraft probes, it has been detected that the geomagnetosphere has weaken in its force and that the Van Allen Belts are also changing in their ability to divert the energy of the sun. This section discusses these changes and some of the implications for the future.

Earth’s Natural Protective System: Van Allen Radiation Belts Sayavur I. Bakhtiyarov

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation Electron Anomalies and Seismic Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remediation of Natural and Artificial Radiation Belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feasibility of an Electric Generator Converting Kinetic Energy of Particles of the Radiation Belts into Electric Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

In this chapter the reviews of radiation electron anomalies and seismic activities, remediation of natural and artificial radiation belts, and feasibility of an electric generator converting kinetic energy of particles of the radiation belts into electric power are provided. Keywords

Space radiation • Van Allen radiation belts • Geomagnetic disturbance • Radiation remediation • Geomagnetic storm • Ring current • Corpuscular stream • Plasmapause • South Atlantic Anomaly • Radiation belt remediation • L-shells • MeV

S.I. Bakhtiyarov (*) NMTech Socorro, Socorro, NM, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_19

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Introduction Van Allen radiation belts consist of layers of plasma (charged particles) around the Earth. These belts extend 1,000–60,000 km above the Earth’s surface and are supported by its magnetic field. There are suggestions that the particles that form the Van Allen belts come from solar wind and cosmic rays. The belts are located in the inner section of the geomagnetosphere. The outer belt is formed mainly by energetic electrons and the inner belt by a combination of protons and electrons. Both radiation belts contain small amounts of other nuclei. These radiation belts are harmful to artificial space satellites orbiting a considerable time in the radiation belts. Therefore, an ample shielding is required to protect their electronic components. A third (transient) radiation belt was discovered by NASA’s Goddard Space Flight Center in 2013 using the Radiation Belt Storm Probes launched on August 30, 2012. The mission is expected to last from 2 to 4 years. This belt was observed for 4 weeks, and it was destroyed by a strong Sun’s shock wave (Fig. 1). The toroidal-shaped outer electron radiation belt is extended from 13,000–60,000 km above the Earth. Its maximum radiation intensity is at 24,000–30,000 km above the Earth. The outer belt is produced by the inward radial diffusion and local acceleration due to transfer of energy from plasma waves to radiation belt electrons. The outer belt consists of high-energy (up to 10 MeV) electrons ensnared by a magnetosphere of the Earth. The trapped particles of the outer belt consist of electrons and different ions such as energetic protons, alpha particles, and O+ oxygen ions. This mixture of ions suggests that ring current particles probably comes from more than one source. The particles in the outer belt have higher fluctuation amplitudes than the inner belt. The inner belt contains high concentrations of electrons and energetic protons with energies more than 100 MeV. The inner electron belt extends from an altitude of 1,000–6,000 km above the Earth. During strong solar activities, the inner Rotational Axis Magnetic Axis

Outer Radiation Belt Inner Radiation Belt

Fig. 1 Van Allen radiation belts

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Fig. 2 NASA’s Van Allen Probe (Credit: JHU/APL, NASA)

periphery can reach 200 km above the Earth. Also, the inner belt is closer to the South Atlantic Anomaly (SAA) area due to the offset of the belts relative to the Earth’s geometric center. The magnetic field and plasma disturbances produced by the Sun result in geomagnetic storms which consequently impact energetic (radiation) particle fluxes. It is suggested that injections and acceleration of particles from the tail of the magnetosphere would increase particle flux. The NASA’s Institute for Advanced Concepts developed a technique to collect natural antimatter existed in the Van Allen belts (Fig. 2). It is estimated that only several micrograms of antiprotons are present in the whole belt. It is believed that the radiation belts exist around other planets of the solar system as well. The NASA’s Voyager program discovered the existence of similar magnetic belts around other planets such as Neptune and Uranus. Two most important features of geomagnetic storms are (1) an initial increase in the horizontal magnetic force at the Earth’s surface and (2) a subsequent larger and more prolonged decrease (Akasofu and Chapman 1961). In 1917 Schmidt (1917) ascribed the decrease to the influence of a westward electric current (now called the geomagnetic ring current) that encircles the Earth. Schmidt concluded that it must wax and wane as magnetic disturbance increases or decreases. From a study of the monthly means of the horizontal component, he suggested that the electric current never dies away completely but is a permanent companion of the Earth. Schmidt attributed magnetic storms to the influence of corpuscular streams or clouds from the Sun. The obvious proposition of his conclusions was that some of the solar matter remains near the Earth for a significant period. In other words, the solar material is partially trapped by the Earth’s magnetic field, and one consequence is the enhancement of the ring current and its geomagnetic effects. Schmidt did not

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consider the scale or the location of the current. Chapman and Ferraro (1931a, b, 1933, 1940) and Ferraro (1952) attempted to understand by mathematical deduction the consequences of the impact of a neutral ionized solar stream upon the Earth. Their theory discussed an idealized “model” which did not consider significant features of the real situation. Their idealized and simplified presumptions indicate the fundamental mechanism of the first phase of magnetic storms and the scale of the penetration of the solar gas. The deflection of the gas particles by the geomagnetic field, by which most of the gas is continuously reflected or scattered away from the Earth, produces the first phase of the storm. It was established that some of the gas found its way into the Earth’s atmosphere in high latitudes and there produced auroras. But some gas was retained in the field for a time in the form of a ring current. The authors were unable to explain or describe the motions of these two subgroups of the solar particles. However, they postulated the existence of the ring current, on the basis of the geomagnetic evidence, and discussed the equilibrium, stability, and decay of the current. They assumed a toroidal current ring model with protons and electrons circulating around the geomagnetic axis, with vaguely different speeds, the motion of the protons, at least, being westward. According to Alfven (1957), this type of ring current is unstable. Singer (1957) proposed a different model of the trapped component of the solar gas, based on the work of Stormer (1955) and Alfven (1957). Instead of a toroidal form and a simple circular motion for most of the particles of the gas, Singer indicated that the gas would have the form and motions proved by later satellite and cosmic rocket exploration (Van Allen and Frank 1959; Vernov et al. 1959). According to Singer, the particles oscillate rapidly between mirror points in fairly high northern and southern latitudes. At the same time, they circle round the magnetic field lines and also drift round the Earth – the protons westward and the electrons eastward. Singer concluded that these motions necessarily correspond to a ring current around the Earth. Later, the ring current and its field were discussed by Dessler and Parker (1959) and by Akasofu (1961). Dessler and Parker (1959), for example, developed a formula relating the total energy of the ring current to the magnetic field perturbation at the center of the Earth. Their analysis considered two particle distributions, isotropic and completely equatorial, and the validity of this formulation for all pitch angle distributions were extended by other researchers later. Dessler and Parker (1959) also extended the arguments that the main phase of the geomagnetic storm is caused principally by protons or electrons with kilovolt energies trapped in the geomagnetic field, and the authors concluded that the main contribution arises from protons trapped at a geocentric distance of 3–5 Re. For the time being, satellite observations bearing on these problems have been made during magnetically quiet and disturbed periods. The radiation belts have been much observed, and some magnetic measurements have been made by the USSR Mechta and the US Explorer VI. The Mechta found magnetic deviations that indicated a ring current in the outer Van Allen belts. The Explorer VI found evidence of a ring current much farther out, in a region beyond 5 Earth radii, and its presence was supposed from auroral and magnetic data. The large decrease in the horizontal component of the Earth’s field during the main phase of magnetic storms has been ascribed to the formation or enhancement

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of a geomagnetic ring current. Akasofu and Chapman (1961) discussed the motions of particles trapped in the Earth’s dipole field and the resulting ring current. These calculations deal only with a steady state, though during storms the state is changing. The general equations for the current intensity, to obtain the total current and the magnetic field at the Earth’s center, were applied to the outer radiation belt (V2) and to a special “model” belt V3. The V3 belt had a particular type of pitch angle distribution and a number-intensity distribution of Gaussian type along an equatorial radius. The results are considered in connection with magnetic records for several storms and with satellite data. The authors suggested that during magnetic disturbance, protons of energy of the order of a few hundred keV are occasionally captured between 5 and 8 Earth radii and that they produce a transient belt V3. The variety of development of the ring current from one storm to another may be connected with irregularities in the distribution of particles in the solar stream, which may contain tangled magnetic fields. As was shown by Alfven (1950), the motion of a charged particle in a magnetic field can in certain circumstances be analyzed into the motion of a “guiding center” associated with the particle (this motion being partly along and partly across the lines of force) and virtually circular motion around the lines of force, relative to the guiding center. The motion of the guiding center across the lines of force is often called a drift. The guiding center approximation is valid (i) when the average radius R of the circular motion is much less than the scale length of the system considered and (ii) when the period T of the circular motion is much less than the other scale times associated with the phenomenon. According to Chapman (1961), in the Earth’s undisturbed dipole field, the scale length is of the order of 8000 km, and the scale time is of the order of 104 s in the ring current problem. It is generally assumed that the naked Earth bears a large negative electric charge, Qs, generating a vertical electric field at its surface. In the fair-weather area, the magnitude of this electric field is about 100 V/m, corresponding to a charge Qs = 4πe0rs2E = 4.5  105 C (rs = 6371 km) at Earth’s surface (Uman, 1974). However, an almost equal amount of positive charge is distributed throughout the Earth’s nearest atmosphere. Apart from QE, it is assumed that the two Van Allen belts (Van Allen and Frank 1959) also bear a net electric charge: a positive charge Qi for the inner torus and a negative charge Qo for the outer torus. The two described belts are separated by a region with zero net charge, the so-called electron slot. The magnetic field around the Earth is important for the orientation of the Van Allen belts, and the electric interactions between the charges QE, Qi, and Qo were investigated by many researchers. Starting from the three tori model, recently developed for pulsars and black holes (Biemond 2007), equilibrium between the charges QE, Qi, and Qo appears to be possible. From the same model, three different expressions for the Coulomb electric field, depending on the distance from the Earth’s center, have been derived by Biemond (2007). The deduced Coulomb electric field at the plasmapause is put equal to the so-called corotation field. Values for the charges QE, Qi, and Qo were calculated for the solar maximum or minimum, respectively. The results of the idealized model were discussed, and the contributions to the

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Earth’s magnetic field caused by the proposed charges QE, Qi, and Qo were calculated. Since the latter contributions appear to be almost negligible, a previously proposed gravitational explanation of the Earth’s magnetic field was considered (Biemond 2007). Especially, the so-called Wilson–Blackett law was discussed. In order to obtain agreement between observed and predicted magnetic fields, the existence of a large toroidal current in the Earth was assumed. Stoffle et al. (2011) carried out FLUKA simulations of energy deposition within the silicon layer using models describing the particle flux within the Van Allen Radiation Belts as well as for Galactic Comic Ray particle interactions. The approach taken in the simulation of tracks for individual frames within the Timepix detector necessitates a time resolution on a scale sufficient to differentiate between points within the vehicle trajectory which are less than 1/10th of an orbit. This is necessary to differentiate between portions of the vehicle orbit that are well shielded and portions that traverse regions of the geomagnetic field open to the Van Allen belts and lower energy Galactic Cosmic Rays. Timepix is a version of the technology developed by the Medipix2 Collaboration (Llopart et al. 2007), which is based at CERN. It is a pixel-based ASIC wherein the electronics for each of the individual 55 μ m square pixels is contained within the footprint of that pixel. The Timepix version of the Medipix2 detector has a charge-sensitive preamp and an associated discriminator attached to a logic unit capable of being employed in one of the several different modes including as a simple counter for the number of times that the externally applied common threshold value has been exceeded (Medipix mode), as a time-to-digital converter (TDC), or for the application described here, as a Wilkinson-type analog-to-digital converter (ADC). Each pixel has a 14-bit pseudorandom shift register for data storage and transfer, and there is an adjustable global “shutter” that gates the data-taking active time. Current ground-based applications take advantage of the technology’s dynamic range and radiation hard design. These same characteristics make it an ideal candidate for use in space radiation environments. To that end, work toward simulation of tracks from individual particles has begun in order to understand both the detector response as well as provide initial input for design of hardware and software based on the Timepix technology for use aboard both manned and unmanned space vehicles. While the initial intent is simulation of the space radiation environment, the same approach can be utilized with other radiation sources, and the method can be adapted to simulations of medical diagnostics as well as larger scale experiments utilizing the Timepix technology. The fundamental approach for the simulation of tracks in a Timepix silicon detector is outlined and initial results are presented by Stoffle et al. (2011). In addition, several areas are identified that allow enhancement in the simulation fidelity. The Timepix readout chip is a hybrid pixel detector with over 65 k independent pixel elements. Each pixel contains its own circuitry for charge collection, counting logic, and readout. When coupled with a Silicon detector layer, the Timepix chip is capable of measuring the charge, and thus energy, deposited in the Silicon detector layer. Such simulations are useful in characterizing the Timepix Si detector response in a mixed radiation field with application to similar detectors, future use as dosimeters and area monitors aboard

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manned spaceflight missions. The core technology is also applicable to purely scientific instrumentation. The ISS orbit inclination is high enough that it traverses both the South Atlantic Anomaly and low rigidity cutoff regions, and as a result sees both inner and outer Van Allen belt populations, as well as accessing locations in the geomagnetic field containing lower energy galactic cosmic rays (GCRs) populations. The Space Environment Information System (SPENVIS) trajectory generation tool was used to generate the trajectory of interest. Latitude, longitude, altitude, as well as B and L coordinates were generated for one-minute increments along the orbit trajectory. Additionally, the two-line element historical data was used to interrogate the trajectory to identify 1/10th of an orbit track lengths that traversed both the geomagnetic cusp regions and well-shielded regions of the vehicle orbit.

Radiation Electron Anomalies and Seismic Activities Inside the Van Allen belts, electrons and ions trail spiral trajectories around the field line of the Earth’s magnetic field, while drifting perpendicular to the magnetic field, in opposite direction to protons and electrons. Simultaneously, ions and electrons moving toward higher latitudes are reflected in the strong magnetic field and are trapped within the inner and the outer Van Allen belts. A considerable effort has been made to detect and interpret electromagnetic phenomena related to seismic activity, and, a number of characteristic physical changes have been confirmed as antecedent signals of preparing earthquakes. Several methodologies have been developed, which use Earth-based instrumentation to detect electromagnetic variations occurring in the lithosphere (Kopytsenko et al. 1990; Hayakawa et al. 1996a; Varotsos et al. 1998). Other studies have shown that, before strong earthquakes, characteristic electromagnetic interactions occur in the ionosphere, which are observed as plasma variations or electromagnetic emissions, by either Earthbased (Hayakawa et al. 1996b; Pulinets and Boyarchuk 2004) or space-based (Parrot 2006; Li and Temerin 2000) instrumentation. In addition to the earthquake-related electromagnetic phenomena taking place in the lithosphere and ionosphere, electromagnetic processes related to seismic activity affect the trapped population of the radiation (Van Allen) belts, and several authors have reported satellite measurements suggesting radiation belt energetic particle flux variations during enhanced very-low-frequency (VLF) electric field activity before earthquakes (Ginzburg et al. 1994; Galper et al. 1995; Aleksandrin et al. 2003; Pulinets and Boyarchuk 2004; Sgrigna et al. 2005). Research results based on DEMETER satellite measurements suggested no relationship between anomalous electron flow and seismic activity within 18 h from the earthquake incidence (Buzzi 2007), while more recent studies suggested that energetic electron precipitation occurs several days before strong earthquakes and that this phenomenon follow a distinct temporal pattern, at least for earthquakes in Japan, which were studied statistically (Anagnostopoulos et al. 2010). Consequently, the question whether radiation electron anomalous bursts are earthquake preliminary signals seems that it

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has not been obviously answered. As a result, the phenomenon of energetic electron rainfall in the upper ionosphere has not been critically considered as an important earthquake prediction instrument until now (European Space Agency).

Remediation of Natural and Artificial Radiation Belts The dipole structure of the Earth’s magnetic field has the ability to trap energetic charged particles in regions near the Earth (Hoyt and Minor 2005). Within these regions (Van Allen Radiation Belts) energetic electrons and ions generated through natural and man-made events can persevere for many years. These high-energy particles cause considerable hazard to missions in the Earth’s orbit, damaging electronics and materials in spacecraft systems and causing biological harm to people in space. The costs associated with hardening electronics and other systems to survive and perform reliably in the radiation environment are a major driver in the high costs of space systems (Hoyt and Minor 2005). The radiation belts could become more hazardous to space systems if a nuclear device is detonated at high altitude. Experiments conducted in the 1960s, such as the Starfish experiment, have shown that a high-altitude nuclear detonation (HAND) can produce an intense artificial radiation belt that can persist for several years (Hoyt and Minor 2005). Even a very-low-yield nuclear device could produce a radiation belt with a radiation flux several orders of magnitude greater than the natural environment. The intense artificial radiation belts created by a HAND event could cause rapid failure of many government and commercial space systems and could result in tremendous damage to both the global economy and national defense capabilities (Hoyt and Minor 2005). Radiation belts, both natural and artificial, tend to follow the contours of the geomagnetic field. The size and geometry of the region affected by a HAND can vary significantly depending upon the geographic location and altitude of the explosion, with high-altitude detonations generating wide, diffuse belts and low-altitude detonations creating very narrow, intense belts. A method for rapidly remediating a HAND-induced radiation belt could provide a means for preserving a significant portion of the operational lifetime of existing satellites (Hoyt and Minor 2005). It could also provide a means of reducing the threat posed by the natural Van Allen belts to manned space missions as well as the rate of degradation of Earthorbit satellites. Numerous concepts have been proposed for remediating natural and artificial radiation belts. One of the concepts proposes to place a dense material into orbit to absorb the radiation. Unfortunately, this method would necessitate a very large amount of mass and the high launch costs to place the mass in orbit. The other concepts that have been proposed do not require to absorb the radiation but rather to scatter the charged particles, reducing the “pitch angle” between their velocity vector and the geomagnetic field vector (Hoyt and Minor 2005). If their pitch angle is reduced below a certain value, called the “loss cone angle,” the particles are no longer trapped by the convergence of the Earth’s magnetic field lines at the poles and can follow the magnetic field lines down into the upper atmosphere, where they dissipate their energy through collisions with atmospheric particles. Among the

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scattering-based concepts that have been proposed are the use of very-low-frequency (VLF) waves to cause resonant scattering of high-energy electrons and the use of large current loops to create localized distortions in the geomagnetic field that will scatter charged particles (Hoyt and Minor 2005). Scattering of energetic charged particles by high-voltage electrostatic tether structures may present a technically and economically viable method of rapidly remediating radiation belts caused by both natural processes and man-made events. Hoyt and Minor (2005) described a concept for a system of electrostatic tether structures designed to rapidly remediate an artificial radiation belt caused by a high-altitude nuclear detonation. The authors investigated the scaling of the system size and power requirements with the tether voltage and other design parameters. These scaling analyses indicated that a conventional single-line tether design cannot provide sufficient performance to achieve a system design that is viable. The authors proposed the innovative multi-wire tether geometry and showed that this tether design can significantly improve the overall performance of the electrostatic system, enabling the requirements for total power and number of satellite systems to be reduced to levels that are both technically and economically viable. The behavior of high-energy electrons trapped in the Earth’s Van Allen radiation belts has been extensively studied both experimentally and theoretically. During quiet times, energetic radiation belt electrons are distributed into two belts divided by the “electron slot” at L ~ 2.5, near which there is relatively low energetic electron flux (Rodger et al. 2006). Since the discovery of the radiation belts (Van Allen et al. 1958; Van Allen 1997), it has proven difficult to confirm the principal source and loss mechanisms that control radiation belt particles (Walt 1996). The largescale injections of relativistic particles into the inner radiation belts are associated with geomagnetic storms which can result in a 105-fold increase in the total trapped electron population of the radiation belts (Li and Temerin 2000). In some cases, the relativistic electron fluxes present in the radiation belts may increase by more than two orders of magnitude (Reeves et al. 2003). In most cases, however, these injections do not penetrate into the inner radiation belt. Only in the biggest storms, for example, November 2003, do the slot region fill and the inner belt gain a new population of energetic electrons (Baker et al. 2004). Even before the discovery of the radiation belts, high-altitude nuclear explosions (HANEs) were studied as a source for injecting electrons in the geomagnetic field. This was confirmed by the satellite Explorer IV in 1958, when three nuclear explosions conducted under Operation Argus took place in the South Atlantic, producing belts of trapped electrons from the β-decay of the fission fragments. The trapped particles remained stable for several weeks near L = 2 and did not drift in L or broaden appreciably (Hess 1968). Both the USA and USSR conducted a small number of HANEs, all of which produced artificial belts of trapped energetic electrons in the Earth’s radiation belts. One of the most studied was the US “Starfish Prime” HANE, a 1.4 megaton detonation occurring at 400 km above Johnston Island in the central Pacific Ocean on July 9, 1962. Again, an artificial belt of trapped energetic electrons was injected, although over a wide range of L-shells from about L = 1.25 out to perhaps L = 3 (Hess, 1968). The detonation also caused artificial aurora observed as

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far away as New Zealand, and an electromagnetic pulse which shut down communications and electrical grids in Hawaii, 1,300 km away (Dupont, 2004). The effect of the Starfish Prime HANE on the radiation belts was observed by multiple spacecrafts. However, the intense artificial belts injected by the HANE damaged three of the five satellites operating at the time. Within a small number of days, data transmissions from the Ariel, Transit IVB, and TRAAC satellites became intermittent or ceased altogether (Massey, 1964), primarily due to degrading solar cells. Other effects were also noted even in this early case; the transistors flown in the first active communications satellite, Telstar, failed due to radiation exposure, even though the satellite was launched after the Starfish Prime HANE. The artificial belts produced by this Starfish Prime HANE allowed some understanding of the loss of energetic electrons from the radiation belts, as demonstrated by the comparison of calculated decay rates with the observed loss of injected electrons (Walt 1994). Collisions with atmospheric constituents are the dominant loss process for energetic electrons (>100 keV) only in the innermost parts of the radiation belts (L < 1.3) (Walt, 1996). For higher L-shells, radiation belt particle lifetimes are typically many orders of magnitude shorter than those predicated due to atmospheric collisions, such that other loss processes are clearly dominant. Above L ~ 1.5 C collision-driven losses are generally less important than those driven by whistler mode waves, including plasmaspheric hiss, lightning-generated whistlers, and man-made transmissions (Abel and Thorne 1998, 1999; Rodger et al. 2003). It is recognized that HANEs would decrease the operational lifetime of low-Earthorbit satellites (Parmentola 2001; US Congress 2001; Steer 2002), principally due to the population of HANE-injected >1 MeV trapped electrons. It has been suggested that even a “small” HANE (~10–20 kt) occurring at altitudes of 125–300 km would raise peak radiation fluxes in the inner radiation belt by 3–4 orders of magnitude and lead to the loss of 90 % of all low-Earth-orbit satellites within a month (Dupont, 2004). In 2004, there were approximately 250 satellites operating in low Earth orbit (LEO) (Satellite Industry Association, 2004). These satellites fulfill a large number of roles, including communications, navigation, meteorology, military, and science. In the event of a HANE, or an unusually intense natural injection, this large population of valuable satellites would be threatened. Due to the lifetime of the injected electrons, the manned space program would need to be placed on hold for a year or more. However, recent theoretical calculations have led to the rather surprising conclusion that wave–particle interactions caused by man-made very-low-frequency (VLF) transmissions may dominate non-storm time losses in the inner radiation belts (Abel and Thorne 1998, 1999). This discovery has attracted significant interest, suggesting practical human control of the radiation belts (Inan et al. 2003) to protect Earth-orbiting systems from natural and man-made injections of high-energy electrons. The man-made control of the Van Allen belts has been called “Radiation Belt Remediation” (RBR). An RBR system involved an assemblage of around ten satellites (Dupont, 2004), which would transmit VLF waves so as to enormously increase the loss rate of energetic electrons by precipitation into the upper atmosphere, basically dumping the HANE-produced artificial radiation belt. In order to be effective, an RBR

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system needs to flush the HANE-produced 1MeV electrons in a short time scale, which has been suggested to be as low as ~1–2 days or perhaps as long as 10 days (Papadopoulos 2001). Rodger et al. (2006) consider the upper atmospheric consequences of an RBR system in operation. The dumping of high-energy relativistic electrons into the atmosphere would generate strong energetic particle precipitation, leading to large ionization changes in the ionosphere. This type of precipitation is expected to direct to large changes in atmospheric chemistry and communications interruption, mainly for the case of HANE injections. Particle precipitation results in augmentation of odd nitrogen (NOx) and odd hydrogen (HOx), which play a crucial role in the ozone balance of the middle atmosphere because they devastate odd oxygen through catalytic reactions (Brasseur and Solomon 1986). Ionization changes produced by a 1 MeV electron will have a propensity to peak at ~55 km altitude (Rishbeth and Garriott 1969). Ionization enhances occurring at similar altitudes caused by solar proton events are known to lead to local perturbations in ozone levels (Verronen et al. 2005). Changes in NOx and O3 consistent with solar protondriven modifications have been observed (Seppala et al. 2004; Verronen et al. 2005). It is well known that the precipitation of electrons at high latitudes produces additional ionization leading to increased HF absorption at high latitudes (MacNamara 1985), in extreme cases producing a complete blackout of HF communications in the polar regions. In order to estimate the importance of RBR-driven precipitation to the upper atmosphere, the authors consider two cases of an RBR system operating to flush the artificial radiation belt injected by a Starfish Primetype HANE over either 1 or 10 days. In the first case, they consider the effect of a space-based system, while in the second case, they also consider a ground-based RBR system. This research work examines the range of practical prospective environmental and technological effects due to this man-made precipitation, including changes to the ozone balance in the middle atmosphere and disruption to HF communication. Although, nanomaterials have found broad applications in the exploration of space, however, the emerging new generation of carbon nanoparticles doped with different clusters is not well characterized for space radiation protection purposes. An experimental approach to design and develop nanostructured materials is one of the pivotal challenges facing the nanotechnology and modern space material science. The ability to control material properties at the nano-size level by using nanoparticles in order to create arrays, patterns, and networks is an important requirement in fabricating new multifunctional nanomaterials. A utilization of the magnetic field in manufacturing nanomaterials is quite new and has the promise of broadest applications. This method is quite effective in controlling the macro- and microstructures of synthesized materials with unique properties. Rukhadze et al. (2010a, b, c, 2011a, b, c, 2012, 2013a, b) and Kutelia et al. (2012) presented the results on the characterization of the newly developed carbon nanoparticles doped with clusters and synthesized via a novel technology for space radiation protection. The authors showed based on the obtained results the possibility of using nanocomposite for spacecrafts. The objective of their work was a development of

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the carbon nanoparticles doped with ferromagnetic iron oxide and clusters of cobalt atoms synthesized via a novel technology which combines the method of pyrolysis of ethanol vapors and the chemical vapor deposition (CVD) process in horizontal continuous reactor with certain temperature gradients and controlled partial oxygen pressure. Scanning electron microscope (SEM) and Auger electron spectroscopy (AES) studies of synthesized magnetic carbon nanopowders showed that under freely deposited state in the absence of the external magnetic field, the nanopowder consists of the randomly distributed carbon nanoparticles’ aggregates of 200 nm diameter doped with the magnetic clusters. Under the exposure to the low external magnetic field (~0.01 T), the nanoparticles were assembled into the large-scale linear nano-chain structures.

Feasibility of an Electric Generator Converting Kinetic Energy of Particles of the Radiation Belts into Electric Power A power plant providing for power supply of operation of onboard service devices and science and technology instrumentation is one of the foremost elements of any spacecraft (Kolesnikov and Yakovlev 2008). Currently, designing the power plants transforming the natural energy of space environment into power supply is the most promising technology of development of space power engineering. This type of power source includes firstly various converters of electromagnetic radiation of the Sun (semiconductor photoelectric cells, thermoelectron, thermionic, and thermoelectric converters). Along with manufacturing the power plants that use the energy of electromagnetic radiation of the Sun, the scientists and engineers are developing fundamentally new space electric power generator concepts that are based on utilizing other types of energy available in space medium such as energy of the Earth’s magnetic field (Vignoli et al. 1987), energy of the solar wind plasma (Bolonkin 1992), etc. The viability of constructing a high-voltage electric generator (HEG) transforming kinetic energy of particles of the radiation belts into electric power is considered by Kolesnikov and Yakovlev (2008). The maximum specific power of a generator was theoretically evaluated for particular cases where a generator was positioned in the Earth’s polar region inside the Earth radiation belts (ERB). The authors demonstrated that from the viewpoint of weight parameters, the suggested design of HEG is quite competitive with power sources of low-thrust spacecraft operating on conventional principles. The estimations show that specific power of HEG inside the natural radiation belts of the Earth is no more than 3.3 W/kg, but inside the auroral zone, it can exceed 100 W/kg. In its weight characteristics, the HEG construction is quite competitive with the power plants for small spacecraft operating on conventional principles. Studying the influence of leakage currents through the high-voltage vacuum gap on functioning of HEG, the authors concluded that a further substantiation of the suggested concept of power supply should include investigations of the problem of maintenance of the stiffness and stability of the generator construction and calculations of its strength characteristics. It was

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indicated that the Earth is not the single planet in the solar system with radiation belts. The powerful radiation belts have been found in the vicinity of other planets, such as Jupiter, Saturn, and Uranus.

Conclusion The following reviews on the Earth’s natural protective system are provided: • Radiation electron anomalies and seismic activities • Remediation of natural and artificial radiation belts • Feasibility of an electric generator converting kinetic energy of particles of the radiation belts into electric power Future space missions and research should focus on determining the origins of relativistic electrons and ions in space and their dynamic response to solar activities. Further studies are required to estimate the flux levels in the inner and outer Van Allen belts and specifically the beta radiation levels which are dangerous to humans if they were exposed for an extended period of time during space missions.

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Part VI Cosmic Radiation

Most radiation that reaches Earth comes from the sun, but there are other intense radiation fields and ionic particles that come from sources beyond our solar system. These so-called cosmic rays are actually a combination of intense cosmic rays (gamma rays) as well as super velocity alpha particles and other types of ionic phenomena that can contain enormous power even while traveling vast cosmic distances. These phenomena help us to understand the workings of the universe and how galaxies are formed.

Basics of Solar and Cosmic Radiation and Hazards Joseph N. Pelton

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sources of Cosmic Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A Better Understanding of the Energy Flow from the Sun and Space Weather . . . . . . . . . . . . . . Antimatter as a Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation Protection for Astronauts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation Protection for Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Relationship Between the Sun and Cosmic Radiation Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

There is a wide range of radiation and particles that stream to Earth from the Sun and the universe at large. This hostile array of high-energy ionic particles and electromagnetic radiation impacts Earth on a constant basis. The exact nature of this bombardment can be confusing to understand. This is because the blanket term of “cosmic radiation” includes not only intense and high-energy electromagnetic radiation in the form of gamma and X-rays but also ionic particles and nuclei accelerated to speeds even nearing the speed of light. This radiation when it hits Earth’s atmosphere generates a number of different particles including positrons (or antimatter) as well as high-energy photons. This chapter seeks to provide some basic information and definitions related to solar and cosmic

J.N. Pelton (*) International Association for the Advancement of Space Safety, Arlington, VA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_60

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“radiation” and to explain that both high-energy X-rays and gamma (γ) rays as well as ionic particles are included in the general and generic phrase “cosmic radiation.” Keywords

Accretion disk • Acute radiation syndrome • Active galactic nuclei (AGN) • Air shower • Alpha particles • Antimatter • Beta particles • Beta decay black hole and supermassive black hole • Chandra X-ray space telescope • Coronal mass ejection (CME) • Cosmic radiation • Electron volt • Electrons • Fermi Space Telescope • Gamma rays (γ) • Ionic nuclei • Ozone layer • Positron • Protons • Radiation sickness • Sunlight • Solar flares • Spitzer Space Telescope • Van Allen belts • X-rays

Introduction The first step to understanding solar and cosmic radiation is to learn some key terms. The most basic and obvious fact is that there is a benign and indeed essential flow of energy from the Sun that is simply called “sunlight.” This steady flow in the form of lower-energy electromagnetic radiation comes from the Sun in the form of infrared, visible light, and the less powerful ultraviolet radiation. This generally benign and life-enabling phenomenon is known as “sunlight,” although humans are only able to see the relatively narrow spectrum known as visible light. This ongoing radiation provides the energy on which the Earth depends for survival. But, in addition to “normal sunlight,” there is also higher-energy radiation as well. Of particular significance are occasional solar flares that zap planet Earth with much higher energy in the form of very energetic ultraviolet, X-rays, and solar gamma rays. When these solar flares occur, they can disrupt the Earth’s ionosphere and can also disrupt shortwave radio, radar, and power distribution grids and even disrupt our cell phone conversations. Very often these solar flares are accompanied by even more disruptive coronal mass ejections (CMEs) as well as lower-energy solar proton events (SPEs). When these so-called CMEs and SPEs occur, they bring a surge of ions in the form of ions and even atomic nuclei. These hazardous phenomena, i.e., that of solar flares, solar proton events, and coronal mass ejections, have been described in some detail in earlier chapters, but it is necessary to return to these subjects to provide background understanding and clear definitions. It is important to explain different types of solarrelated as well as cosmic radiation threats. High-energy cosmic rays and ionic bombardment that come from beyond the Sun are a particular threat issue for not only astronauts but key infrastructure such as application satellites that orbit in outer space. This extremely high radiation can be measured in billions, trillions, quadrillions, and quintillions of electron volts. Such high-energy cosmic radiation would be deadly indeed unless Earth was protected by an atmosphere and a magnetosphere that allows the formation of the Van Allen belts. This cosmic radiation comes from stars, distant galaxies, quasars, and a phenomenon known as active galactic nuclei (AGI). This is a threat element beyond the

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high-energy threats from the Sun. When emissions from the Sun are low during solar minimum, cosmic radiation threats are highest. When solar emissions are highest during solar maximum, the cosmic radiation threat is lowest since these two phenomena directly interact. It is important to start with the rather confusing fact that the generic term “cosmic radiation” is actually a misnomer. In truth “cosmic radiation” is a combination of radiation and ionic particles which was mistakenly thought to be radiation since the ionic particles were so energetic and moved at such high velocities. Only later was it sorted out that cosmic radiation was indeed a mix electromagnetic radiation and ionic particles. When extremely high-energy cosmic radiation, in the form of high-energy cosmic gamma rays (which is indeed super-energetic radiation), hits the Earth’s atmosphere, this also serves to generate a cascade of secondary radioactive particles known as alpha and beta particles. This process of cosmic radiation creating a highenergy cascade is known as an “extensive air shower” (EAS). Some of the superhigh-energy cosmic gamma rays have power levels that have been measured up to 3  1020 EVs. (This energy level that represents 300 quintillion electron volts is many millions of times more energetic than that can be achieved by accelerating particles in the large Hadron accelerator at the CERN facility in Switzerland) (Chow). These superhigh-energy cosmic gamma rays were once thought to come exclusively from supernova explosions. Recent data from the Fermi Space Telescope (as well as the Chandra X-ray Telescope and the Spitzer Space Telescope) provides support for the idea that some of the ultrahigh-energy particles also come from quasars and from the center of galaxies (i.e., from a configuration described later in the chapter) and which is specifically called “active galactic nuclei.” It has even been recently learned that violent lightning storms can create gamma rays and can even be created on Earth. In addition, this chapter also briefly addresses the subject of antimatter and positrons and photoneutrons and photoprotons. Positrons and electrons can be generated from cosmic gamma rays as they encounter the Earth’s atmosphere. Positrons are the opposite of electrons. When a cosmic ray hits the Earth’s atmosphere, it generates several kilometer wide “extensive air showers” that also can produce a cascade of alpha and beta particles and photons. These photons can create photoprotons and photoneutrons. Thus the purpose of this chapter is to explain the key and diverse sources of extremely high-energy particles and radiation. This “cosmic radiation” represents a hazard to people, plants, and animals on Earth. But this threat is minimal because the air shower cascade within the Earth’s atmosphere breaks down the energy within the ionosphere, even though there can be secondary cascades (called delta particles) and even tertiary cascades (called epsilon particles). This cosmic radiation only becomes an especially severe hazard for those traveling on space missions beyond the Earth’s protective systems. In addition some of the radiation is “trapped” in the Van Allen belts before it reaches the Earth’s atmosphere, and in this case cosmic radiation “energizes” the Van Allen belt and ups their level of radiation.

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Finally this chapter also seeks to explain briefly how the interaction between the Sun’s magnetic field and solar radiation impacts – and even diminishes – the dangers created by “cosmic radiation” that comes from beyond the solar system. In fact, the Sun plays a key aspect of the protective process for planet Earth and its infrastructure. The Sun therefore helps to ward off asteroids and comets via its massive gravitational field, while its powerful magnetic field and its solar radiation ionic emissions also help to minimize the danger of cosmic radiation from beyond the solar system. This introductory chapter to this section seeks to provide some basic definitions and background. In this regard it may to some degree duplicate earlier chapters that address solar flares and coronal mass ejections. Nevertheless it is a useful prologue to understanding the chapters that immediately follow. It can also serve as an aid to nonscientists who are seeking to learn more about cosmic radiation, solar flares, and coronal mass ejections for the first time. In sum, this chapter seeks to provide a context for the chapters that follow and in particular seeks to define basic terms in the field.

Sources of Cosmic Radiation A solar flare is a sudden brightening observed over the Sun’s surface or a solar limb. A particularly energetic solar flare can equate to one sixth of all the energy released by the Sun per second or a power release on the order of 6  1025 J of energy. The same phenomena that occur on the Sun in terms of solar flares – and frequently closely associated coronal mass ejections (CMEs) – are not unique to our solar system since the same phenomena have been observed to occur in distant stars. While solar flares and CMEs represent a very definite hazard to Earth and can present a particular threat to astronauts as well as infrastructure such as satellites and electronic grids, a typical flare and CME from another star system are too distant to represent a threat to Earth (Active Galactic Nuclei). The so-called cosmic radiation comes to Earth from thousands if not millions of light years away and originates from such sources as distant supernovae, single and binary neutron stars, quasars, and so-called active galactic nuclei (AGN). In the case of AGN, the source is a jet of gamma rays that spew forth from supermassive black holes. This “cosmic radiation” consists of X-rays and gamma rays as well as superaccelerated ionic particles that can also be spectacularly powerful. These cosmic rays can and do represent a real threat in at least two ways. There is the threat to astronauts when they travel beyond the Earth’s protective shield and the danger to satellites and other space infrastructure that is increasingly vital to modern civilization. There are indeed web sites that describe a scenario as “A Day without Satellites,” and impacts on energy systems, global commerce, transportation, broadcasting, communications, and the Internet are quite significant (Allaby and Allaby 1999). In the following pages, we seek to provide briefly a better understanding of the basics of both solar and cosmic electromagnetic radiation as well as ionic particle emissions. Clearly the best way to begin is to define some of the basic terms and

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also to explore the many roles that the Sun plays – as a source of energy and light, as a source of threats in terms of flares and CMEs, and as almost ironically a partial protector against intergalactic cosmic radiation. This chapter thus further explains how the Sun both bombards us with solar radiation and high-energy gaseous ions and serves at the same time to help protect us from cosmic radiation that comes from beyond our solar system by means of its huge magnetic and gravitational fields and its own solar weather.

A Better Understanding of the Energy Flow from the Sun and Space Weather Sunlight: Energy pours forth from the Sun’s core as the result of a thermonuclear fusion process that largely operates by transforming hydrogen into helium. As a consequence, the Sun irradiates enormous power out into the solar system in the form of electromagnetic radiation. Much of that energy issues from the Sun in the infrared, visible, and ultraviolet wavelengths, and this process serves to heat the inner part of the solar system as well as light. Stored energy has come from the Sun over time and is now available to us in the form of petroleum, natural gas, geothermal, ocean, and wind energy. These energy sources that have, in fact, originated from the Sun now help to fuel the modern world on planet Earth. The Sun is an incredible source of energy. Every day ten thousand times more energy flows from the Sun and impacts Earth than human’s currently use to power machines and electrical instruments worldwide. Without sunshine, no plants or animals could live and Earth would be a dead planet. Sunlight is vital commodity on which Earth survives. Solar Flares: The Sun’s thermonuclear fusion process seems to follow an 11-year cycle, and the Sun’s magnetic poles switch back and forth over a 22-year time frame. During this cycle that is lowest during the solar minimum, we see emissions building up to a solar max and then subsiding again. There are also longer-term cycles of solar energy releases that we are just beginning to understand. We are currently at the lower-energy cycle when measured on a longer-term basis. Solar flares generate from just below the corona layer of the Sun and become more and more frequent during solar max. These tremendously powerful solar events lead to enormously powerful energy release of gamma rays that travel outward from the Sun at the speed of light. In a large percentage of cases, the solar flare serves to also “trigger” or “accompany” a parallel explosion of ionic nuclei from the corona of the Sun. These events are known as coronal mass ejections (CMEs). In this energy release, known as solar weather, the “radiation” is actually ionic ejections in forms such as protons, neutrons, and alpha and beta particles. Coronal Mass Ejections: CMEs are huge ejections of ionic gas (i.e., these are largely proton nuclei, electrons, and some positrons) that travel at enormous speeds but well below the speed of light. Solar flares as photons traveling at the free space speed of light (300,000 km/s) reach Earth in 8 min, but CMEs typically travel at velocities calculated in millions of kilometers per hour and reach Earth 1 to 2 days later.

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Coronal mass ejections (or CMEs) are, in fact, huge bubbles of ionic gas threaded with magnetic field lines that are ejected from the Sun in events that can last minutes to several hours. Although the Sun’s corona has been observed briefly during total eclipses of the Sun for many, many years, the existence of coronal mass ejections, as opposed to solar flares, was unrealized and documented only during the Space Age. The earliest evidence of these dynamical events came from observations made with a coronagraph on the Orbiting Solar Observatory (OSO 7) in the early 1970s. (Note: A coronagraph has a disk that blocks out the brightest part of the solar orb so that the corona and its arms are more clearly revealed.) With ground-based coronagraphs, only the innermost corona is visible above the brightness of the sky. From space the corona is visible out to large distances from the Sun and can be viewed continuously. From solar minimum to solar maximum, CMEs are perhaps 15–20 times more prevalent during solar max when these events can occur as often as two to three times per day. Coronal mass ejections, because of their magnetic effect, disrupt the flow of the solar wind and normal solar weather. When the ionic gases from a CME hit the Van Allen belts and the Earth’s magnetic field, it creates an enormous shockwave. When the so-called Carrington event of 1859 occurred, this unusually large CME generated auroras that could be seen as far south as Cuba and Hawaii and served to set telegraph offices on fire. We have no clear idea what the impact of such an event would be if it would happen today. Gamma Rays: These are the most powerful form of electromagnetic radiation – even more energetic than X-rays. Gamma rays, as electromagnetic radiation, travel at the speed of light and are enormously powerful. They can involve incredibly rapid frequencies that are in excess of 300 quadrillion Hz (i.e., 300  1017 cycles per second). When gamma rays strike matter, they often generate the emission of alpha or beta particles. Also when an electron and positron strike each other, this also generates gamma rays. When a nucleus ejects an alpha or beta particle, it is left in an excited or higher-energy state, and it can fall to a lower-energy state by releasing a gamma ray photon. This in turn can generate a photoproton or a photoneutron. Gamma rays, as the highest energy level of electromagnetic radiation, have much higher penetrating power than alpha or beta particles. Gamma rays have so much power that they can penetrate through buildings or bodies. Thick concrete or lead shields are usually needed to ensure complete protection. The highfrequency gamma rays have sufficient energy to ionize molecules in your body, which can cause damage to important macromolecules like DNA inside your cells and also create anomalous cell growth that leads to cancerous growth (Brennan). For years the source of gamma rays has represented one of the key questions in the field of astrophysics. The answer seems to be a variety of sources such as supermassive black holes, pulsating neutron stars that are created by supernovae, quasars, and from the center of actively forming new galaxies when supermassive black holes exist, i.e., the previously mentioned AGNs. Recently it has been discovered that even lightning bolts in massive thunderstorms can generate gamma rays that can strike matter and generate superspeed electrons and positrons (i.e., antimatter). Some theorists even suggest that gamma rays can originate from so-called dark matter, but this is currently merely a theory (Todor 2010).

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Fig. 1 Fermi Gamma-Ray Space Telescope (Figure; courtesy of NASA)

Key to the current discovery process is the Fermi Gamma-Ray Space Telescope that has now completed a 5-year mission in space that has allowed a mapping of gamma rays over one billion electron volts in intensity. The Fermi Gamma-Ray Space Telescope (see Fig. 1), the Chandra X-ray Telescope, and the Spitzer Space Telescope have contributed greatly to our understanding of gamma rays and how they are formed, but much remains to be learned. Of particular interest is how supermassive dark holes form so-called accretion disks that generate jets of gamma rays and X-rays of enormous power (see Fig. 2) (Fermi Gamma-Ray Space Telescope). X-Rays: Radiation levels that are above ultraviolet emissions and below gamma rays in frequency are deemed to be X-rays. These powerful emissions involve wavelengths that are of an atomic scale and thus can be generated by high-powered radio tubes to use for medical imaging. As high-powered gamma rays are generated, lower-powered X-rays are generated as well. Strong radioactive galaxies, star systems, and pulsars can be tracked by X-ray or gamma ray space telescopes. Alpha Particle: An alpha particle is a helium nucleus stripped of its electrons – two protons and two neutrons. It has a much greater mass than beta particles and consequently a much shorter range. Ordinarily, it travels at a velocity of about a

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Fig. 2 Model of massive black hole in a forming galaxy that emits gamma rays (Graphic: courtesy of NASA)

tenth of the speed of light. As nuclei experiencing radioactive decay eject alpha particles, their atomic number decreases by 2, and their mass decreases by 4 (Brennan). Beta Particle: A beta particle is an electron. When a nucleus is bombarded and emits a beta particle, one of its neutrons changes into a proton, so the atomic number increases by 1 and it is now a different element. Beta particles can travel at velocities of up to 90 % or more of the speed of light and have a hundred times more penetrating power than alpha particles. Since they are particles, a thick sheet of aluminum will stop them. A beta particle can penetrate up to about a centimeter into human flesh (see positron emission and beta plus decay). Ionic Bombardment from Space: At one time it was thought that cosmic radiation consisted of gamma rays and alpha and beta particles. Experiments that have been carried out by sending very high-altitude balloons aloft with photographic plates have revealed that the cosmic ionic bombardment consists of not only helium nuclei ions (i.e., alpha particles) but the nuclei of heavier elements such as oxygen, carbon, and even iron. These high-energy ions fortunately encounter the Van Allen belts (which they energize) and the Earth’s upper atmosphere and thus do not normally penetrate to the ground. In light of their size and mass, these ions do not have the penetration capabilities of gamma rays, X-rays, and ultraviolet radiation. Positron Emission: Positron emission can occur as a by-product of a type of radioactive decay known as beta plus decay. In the process of beta plus decay, an unstable balance of neutrons and protons in the nucleus of an atom can trigger the conversion of an excess proton into a neutron. During the conversion process, a neutrino and a positron are also emitted. The positron is a positively charge electron

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that is also known as “antimatter” because when it collides with matter, it is annihilated with a large release of energy in the form of a gamma ray. A positron is also classed as a beta particle, because it is a by-product of beta decay. This process of beta plus decay occurs at random all the time in elements with the potential to experience this type of radioactive decay with the available energy sufficient to transform a proton into a heavier neutron. Radioactivity: When gamma rays hit the Earth’s atmosphere, they tend to create a cascade of alpha and beta particles as well as additional gamma rays, positrons, and neutrinos. When radioactive materials such as uranium, plutonium, and radium experience natural decay, they emit alpha and beta particles as well as gamma rays which are extremely high energy photons that occur with electron decay. Radioactivity is thus simply the spontaneous emission of radiation, either directly from unstable atomic nuclei as a form of natural decay or as a consequence of a nuclear reaction that can trigger atomic bombardment such as in a nuclear bomb, an ionic accelerator, or from a cosmic source that triggers nuclear reactions to take place. Supernovae, pulsars, massive black holes, active galactic nuclei, and even nuclear fusion inside of a star like the Sun can radiate highly energetic photons that reach the Earth’s atmosphere. There will be these high-energy emissions (i.e., photons) if there is sufficient power to trigger a new stream of radioactive reaction. Cosmic radiation in the form of gamma rays represents a very high level and energetic form of photon that comes across the cosmos from galactic sources. Acute Radiation Syndrome (ARS): This is also known as radiation poisoning, radiation sickness, or radiation toxicity. This condition is the result of exposure to high amounts of ionized radiation that can come from being exposed to radioactive materials or from cosmic radiation – particularly in the case of astronauts above the protective Van Allen belts that are exposed to solar storms or cosmic gamma rays. There is today a further danger of solar and cosmic radiation creating the danger of radiation sickness in the case of pilots or passengers that fly frequently polar routes that are under the ozone holes that occur on a seasonal basis. Current studies suggest that these dangers could increase in future years (“Definition of Radioactivity”). Radiation causes cellular degradation due to damage to DNA and other key molecular structures within the cells in various tissues. The result of such damage is that it can affect the ability of cells to divide normally. This can in turn cause the symptoms of radiation poisoning, and if severe enough, this can cause death. There is not only the danger of various forms of radiation sickness but also of damage to genes. Irradiated genes, if sufficiently severe, can lead to mutated births for people or animals. Those living under the ozone holes where gamma rays, X-rays, and ultraviolet radiation can most easily penetrate to the Earth’s surface must be particularly concerned about not only mutations of their genes but also the danger of an accelerated risk of cancer. Already, there are clearly accelerated rates of skin cancer that have been documented in Southern Australia where the ozone hole is present. Also frogs in this region have shown higher levels of mutant births. Earth’s Protective Systems: The radiation and ionic bombardment from the Sun and the cosmos beyond would make life impossible on Earth without the

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Rotational Axis Outer Radiation Belt

Inner Radiation Belt

Inner Radiation Belt

Outer Radiation Belt

Magnetic Axis

Fig. 3 The outer and inner Van Allen belts that shield Earth from cosmic radiation (Graphic: courtesy of NASA)

natural protective barriers. The Van Allen belts that were discovered with the launch of Explorer I in 1958 are the first line of defense against space weather, solar flares, CMEs, and cosmic radiation that bombard Earth on a constant basis. The Earth’s magnetic field shapes the Van Allen belts that are at the highest altitude near the equatorial region and arc downward at the polls. Incoming ionic particles hit the Van Allen belts and the high-energy particles that are trapped there by the Earth’s magnetic field. The outer belt is largely composed of electron ions, while the inner belt is largely composed of proton ions. Anyway these two radiation belts and the geomagnetosphere plus the ionosphere and the ozone layer protect life on Earth by intercepting much of the incoming radiation and ionic bombardment. Incoming ionic particles and radiation are thus prevented from smashing into the Earth in this manner, and incoming ions are pushed off from Earth impact toward the magnetic poles. As major CME events occur, the Van Allen belts and Earth’s atmosphere are nevertheless zapped hard. The Earth’s atmosphere and the Van Allen belts can suddenly extend up to 20 Earth diameters away from the center of the world. Fortunately the Earth’s gravitational pull and magnetic attraction bring the upper atmosphere back to its spherical shape (Fig. 3).

Antimatter as a Hazard Positrons carry a tremendous amount of power since when they collide with matter, the result is the conversion of the mass of the positron to equivalent energy based on the famous Einstein equation E = mc2. This energy is released as high-powered gamma rays, but fortunately positron emissions in beta plus decays are much less common than “normal” beta decays. The Ozone Layerand Screening Out of Ultraviolet Radiation: Well below the Van Allen belts in the stratosphere (i.e., 10–50 km altitude), nitrogen, dioxygen,

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and ozone serve to screen out harmful ultraviolet radiation. Actually the ozone is created by ultraviolet light (especially UV-B) striking oxygen molecules (i.e., O2). The UV radiation splits the oxygen molecule into two oxygen ions that then combine with an available oxygen molecule to form O3. Although the ozone molecule is fairly unstable, it remains in this form for some time in the low-density stratosphere. Anyway this so-called ozone-oxygen cycle serves as an important screen against the higher-energy solar radiation. About 90 % of the ozone in our atmosphere is contained in the stratosphere, although it is actually quite sparse and typically only present in the range of only two to eight parts per million. On a seasonable basis, there tends to be an “ozone hole” in March through May in the northern polar regions and August through October in the southern polar regions. Fortunately nitrogen and dioxygen are in greater supply and serve to screen out ultraviolet radiation in the UV-A and UV-C bands (Gaughan). Health Risks Due to Cosmic and Solar Radiation: The bottom line is that the Earth’s magnetic field traps the broad Van Allen belts and holds them more or less in place. This serves to create a protective band of ionic particles around the Earth. If this were not in place, solar and cosmic radiation would wipe out life on Earth. In fact without these protective bands, life on Earth may never have evolved, or if it had, it would be a much different form of life from that was somehow able to survive under intense radiological conditions.

Radiation Protection for Astronauts NASA as well as the Russian and Chinese space agencies all have the objectives of sending astronauts to the Moon within the next decade. In addition there has been increasing discussion of sending astronauts to Mars that would involve something like a mission lasting months or even years. Recently private ventures, such as the Golden Spike Corporation, have suggested that they could send a two-person crew to the Moon and return on a paid commercial basis – although the projected cost of such a private mission was set at $1 billion per flight. Key to such future missions is the need to achieve a better understanding of solar and cosmic radiation dangers. NASA has long known that astronauts on long-duration flights to the Moon or Mars will be subjected to higher levels of radiation from solar flares and cosmic rays. These radiation levels would be well above experienced aboard the International Space Station (ISS), which flies within the Earth’s protective magnetic field and under the Van Allen belts. For the Apollo missions, NASA set a maximum operational dose (MOD) limit of 400 Rads for the Apollo astronauts covering the entire duration of the flight. In August 1972, right between the Apollo 16 and 17 missions, however, there was a high-energy solar flare, but fortunately no solar flares or CMEs occurred during the actual Apollo lunar missions. The average exposure rates for Apollo 7 through 15 provided below show that the levels were, in fact, well below the set MOD limits of 400 Rads. Had there been a mission in August 1972, however, the levels would have been much higher and potentially lethal. Since the Apollo missions were only a few days long, the radiation

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Table 1 Astronaut radiation exposure levels during the Apollo flights Average exposure levels to radiation for Apollo astronauts Apollo mission Average skin radiation experienced (in Rads) Apollo 7 0.16 Rads Apollo 8 0.16 Rads Apollo 9 0.20 Rads Apollo 10 0.48 Rads Apollo 11 0.18 Rads Apollo 12 0.58 Rads Apollo 13 0.24 Rads Apollo 14 1.14 Rads Apollo 15 0.30 Rads

experience for Apollo 14 would represent a significant level if experienced on a yearlong mission (English et al.) (Table 1). NASA’s current guidelines set career caps on the radiation exposure for astronauts with the limits designed to lead to a less than 3 % increase in the risk of death from cancer. These radiation limits vary greatly, however, with age and gender. For 30-year-old astronauts, the maximum allowable mission length for a female is set at 54 days and reaches 91 days for males. By age 55, the total days in space max out at 159 days for female astronauts and 268 days for their male counterparts.

Radiation Protection for Infrastructure Solar flares, CMEs, positrons, and gamma rays can all pose risks to satellites, especially those in orbits above the protective shields of the Van Allen belts. Satellites in geosynchronous orbit such as communications satellites and meteorological satellites or in medium Earth orbits such as for navigation or communications can be designed for some level of protection. There can be shielding of electronic components, heavy-duty circuit breakers, and other design elements that can allow such satellites to be powered down when there is advanced warning such as of a coronal mass ejection. Solar flares and cosmic radiation, however, do not allow advance warning because the X-rays, gamma rays, and high-energy ultraviolet travel at the speed of light. There can be sufficiently high-powered solar and cosmic radiation that the bombardment penetrates the Earth’s protective systems. The Carrington event of 1859 that we now know as a coronal mass ejection created sparks that ignited paper in telegraph offices (Klein). In 1989 another CME was sufficient to burn out a transformer in Chicago and affect the electrical grid from Chicago to Montreal. Such events when they reach pipes or underground cabling can travel along these conduits for very long distances. There is concern that computer processors and smart grid systems could be adversely impacted by super solar flares or CMEs.

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Unless a Faraday Cage is installed around an electrical system, cosmic radiation of various sorts – if of sufficiently high power – could adversely affect electrical power lines and transformers, microprocessors in ground vehicles and aircraft, and a wide range of infrastructure that are powered by or electronically controlled by processors (Pelton 2012). At this time there is no clear indication as to how frequently a CME of enormous power, such as the Carrington event of the mid-nineteenth century, might hit Earth again. Nor do we know what impact such an event might make on our modern electronic infrastructure since it has all been created since 1859. Clearly as the smart grid that allows effective integration of electrical power systems is deployed, it is critical to install very high-performance circuit breakers to protect against such a catastrophic event. Most recently, probes that have been launched by NASA to explore more thoroughly the Van Allen belts have suggested that the protective capabilities of these radiation belts might change over time as there are variations in the geomagnetosphere. It is believed that the Earth’s magnetic poles shift from north to south and vice versa every 66,000 years and that this transition can take decades to transpire – perhaps even a century. During these transitions, the protective nature of the Van Allen belts might be reduced by a factor as much as 20 times. Such a situation could be catastrophic for modern infrastructure of many types – computers, electrical distribution systems, and most vehicular and aircraft systems. These recent NASA probes suggest that we are currently experiencing some shifts in the Earth’s magnetosphere and the Van Allen Belts that are worrisome. If there are nearer-term shifts in the Van Allen belts that reduce their protective capabilities, this is a very worrisome development for most of our electrical infrastructure around the world.

The Relationship Between the Sun and Cosmic Radiation Levels The interaction between the Sun and the Earth is far from simple. In fact it is quite complicated. In many ways the Sun poses a threat to life on Earth. Yet it is also a key source of life and often plays a role as protector. The gravitational fields of the Sun and Jupiter actually serve to capture many asteroids, meteors, and comets, but quirks in the Sun’s gravitational field can make an asteroid do a “loop de loop” that hurls a rock right at Earth. The Sun’s solar flares and CME represent an ongoing threat to Earth. The peak period represented by the solar max is a time when scientists around the world and operators of communications satellites in geo orbit are on constant alert. Satellites, for instance, are often powered down, and electronics switched off when a violent CME comes our way. It is ironic, however, that when the Sun is most active, it serves to shield Earth more effectively against incoming cosmic rays in the form of highly energetic X- and gamma rays and even positrons. This incoming radiation can trigger an avalanche of beta and alpha particles that can do considerable damage if not stopped in upper regions of the atmosphere or trapped within the Van Allen belts.

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There are now indications that the Sun is going into a quieter stage on a longerterm cycle with the consequence being that highly energetic gamma rays from long-distance cosmic sources will be bombarding our solar system with greater frequency and intensity. Galactic cosmic rays (GCRs) are extremely difficult to shield against because of their enormous energy levels and atomic-level wavelengths. Once an astronaut is beyond the Earth’s magnetic field and the Van Allen belts, any astronaut is at considerable risk. The Sun (beyond its shorter-term 11-year cycle) appears to be in a prolonged period of reduced solar activity and is displaying a low interplanetary magnetic field strength. As a result, the Sun’s magnetic field and its ability to “modulate” or control cosmic radiation are low. This means that the flux density of cosmic gamma rays is near their highest levels in the last 25 years as of late 2009. Measurements by NASA’s Advanced Composition Explorer (ACE) spacecraft indicate that cosmic rays are 19 % more abundant than any previous level seen since space flight began a half century ago. This has also been confirmed by the Lunar Reconnaissance Orbiter (LRO) and the Cosmic Ray Telescope for the Effects of Radiation (CRaTER). These satellites are monitoring gamma ray strength in the lunar environment. These cosmic rays have subsided during solar max in 2013, but will continue to rise in subsequent years (Schwadron et al. 2010).

Conclusion This chapter has sought to provide some basic background and definitions with regard to various types of solar and cosmic radiation. It has explained that infrared, visible light, ultraviolet, X-rays, and gamma rays represent electromagnetic radiation. This type of radiation of increasing intensity, smaller wavelength, and incredibly high frequencies comes from the Sun and star systems beyond. In addition there are various types of ionic particles that also bombard Earth, and these highenergy particles can be accelerated to velocities that approach the speed of light and appear to be much like electromagnetic radiation but are particle based. These include ions from coronal mass ejections that include beta particles (i.e., ionic electrons), protons, alpha particles (i.e., helium nuclei of 2 protons and 2 neutrons), and beta decay particles (i.e., positrons). There are also super-accelerated gamma rays from the cosmos that trigger beta and alpha particles when they hit the Van Allen belts and the Earth’s atmosphere. When positrons collide with matter, they can trigger gamma rays and neutrinos. All of this incoming “cosmic radiation” poses threats to astronauts, satellites, and spacecraft, especially above the Van Allen belts, and can also create threats to infrastructure and to animal and plant life even after penetrating the Van Allen belts and the atmosphere. These dangers can include genetic damage to DNA and mutation in future births, cellular damage that leads to cancer or other diseases, and potentially damage to a wide range of electronic and other infrastructure. The chapters that follow examine further the types of damage that might occur, examine the nature of cosmic radiation in greater details, and address potential protective and mitigation strategies to minimize these dangers.

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Cross-References ▶ Solar Flares and Impact on Earth ▶ Solar Radiation and Spacecraft Shielding

References Active Galactic Nuclei http://www.heasarc.gsfc.nasa.gov/docs/objects/agn/agntext.html, 9 Apr 2014 Allaby A, Allaby M (1999) Galactic cosmic rays. In: A dictionary of earth sciences. Encyclopedia. com, http://www.encyclopedia.com. 15 Oct 2014 Answer.com/definitions Definition of radioactivity. http://www.answers.com/defintions/ radioactivity. 9 Apr 2014 Brennan J What are alpha, beta and gamma particles. http://www.ehow.com/info_8374623_alphabeta-gamma-particles.html. 9 Apr 2014 Chow D Sun releases strongest solar flare in 2 months. Space.com. http://news.yahoo.com/sununleashes-strongest-solar-flare-2-months-video-142132626.html. July 2014 English RA, Kelsey-Sybold Clinic, Benson RE, Vernon Baily J, Barnes CM Apollo experience report protection against radiation. NASA report no TN D-7080, Mar 1973 Fermi Gamma-Ray Space Telescope. http://fermi.gsfc.nasa.gov/ Gaughan R What percent of UV does the ozone absorb? Demand Media. http://science. opposingviews.com/percent-uv-ozone-absorb-20509.html. 9 Apr 2014 Klein C A perfect solar Superstorm: the 1859 Carrington event history. http://www.history.com/ news/a-perfect-solar-superstorm-the-1859-carrington-event. 14 Mar 2012 Orbiting solar observatory. http://www.mediahex.com/Orbiting_Solar_Observatory. 9 Apr 2014 Pelton JN (2012) Orbital debris and other space hazards. Springer Press, New York Schwadron NA, Boyd AJ, Kozarev K, Golightly M, Spence H, Townsend LW, Owens M (2010) Galactic cosmic ray radiation hazard in the unusual extended solar minimum. Space Weather 8(5). http://earthref.org/ERR/127816/ Todor S (2010) High energy cosmic radiation, 2nd edn. Praxis Springer Press, New York

Medical Concerns with Space Radiation and Radiobiological Effects Tore Straume

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Space Radiation Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiobiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energy Transfer to Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation Effects on Cells: Models and Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation Effects on Cells: Factors that Influence Dose–response . . . . . . . . . . . . . . . . . . . . . . . . Radiation Effects on Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Human Health Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cataracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chromosomal Abnormalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cardiovascular Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Central Nervous System Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acute Effects from Large SEP Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fertility Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transmitted Genetic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

An overview is provided of the radiation health challenges associated with extended human missions into deep space with the understanding that this is a complex endeavor presently under active research and development. Hence, this chapter necessarily reflects present limitations and the need for research to make such exploration missions possible. The space radiation environment is

T. Straume (*) Space Biosciences Division, NASA Ames Research Center, Mountain View, CA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_4

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introduced followed by a brief discussion of the radiobiology. The remainder of the chapter is focused on human health concerns from radiation exposure during extended deep space missions. Although the challenges are many, the greatest radiation-related concern from a mission perspective would be an exceptionally large solar-energetic-particle (SEP) event. Such an event, should it occur during extravehicular activity (EVA), or while in a spaceship insufficiently shielded, could potentially result in acute radiation sickness. Fortunately, radiation from SEP events can be shielded and therefore should be manageable through a combination of shielding design and early warning systems. In contrast, the ever-present chronic exposure to galactic cosmic radiation (GCR) is difficult to shield and will likely have to be accepted at some level. Although GCR produces a much lower dose rate than a large SEP event, there are significant uncertainties concerning the effects from the high-charge, high-energy (HZE) component of GCR. It has been estimated that GCR radiation may induce a significant lifetime cancer risk. It is less clear whether health effects such as cardiovascular or central nervous system problems will result from protracted GCR exposure. It is hoped that these and many other uncertainties will be reduced through research and development prior to sending humans to Mars. Keywords

Radiation • Space • Mars • Moon • Asteroid • Dose • Galactic Cosmic Radiation (GCR) • Solar Energetic Particles (SEP) • Radiobiology • Cancer • Genetic • Cardiovascular • Central Nervous System • Chromsosome • Cataract • Acute • Chronic • Protection

Introduction Human exploration of space requires an understanding of the space radiation environment, its effects on health, and how to protect the spacefarers. With extended human missions into deep space drawing ever closer – an asteroid by 2025 and onward to Mars in the 2030s (Obama 2010) – these are becoming active areas of research with contributions from scientists and space programs around the world. The objective here is to provide an introduction to the space radiation environment, the radiobiological concepts, and the radiation-related health challenges.

The Space Radiation Environment The sources of ionizing radiation of greatest concern for deep-space missions (Moon, asteroid, Mars) are galactic cosmic rays (GCR), solar energetic particles (SEP), and secondary neutrons produced by these radiations. The space environment is complex, consisting of a broad range of radiations and energies, and is a formidable challenge to the protection of humans and equipment during extended missions.

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Flux density, particles/cm2-sec

1015

Solar Wind Protons Auroral Electrons

1010

105

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Trapped Electrons Trapped Protons (Outer Zone)

Trapped Protons (Inner Zone)

Solar Storm Protons 100

10–5 10–4

Solar Flare Protons

Galactic Cosmic Rays 10–2

100

102

104

Particle energy, MeV

Fig. 1 The space radiation environment (Wilson 1978)

Near the Earth, there are energetic protons and electrons trapped by the Earth’s magnetic field. These particles are located in belts that extend torroidally around the Earth called Van Allen Belts, named after their discoverer Dr. James Van Allen. The Van Allen radiation belts extend from an altitude of about 1,000–60,000 km above the surface of the Earth. Most of the radiation particles that form the belts are thought to come from the solar wind and cosmic rays. Early atmospheric nuclear tests contributed some to the inner belt but that has substantially decayed since the end of atmospheric nuclear testing. These belts do not pose a significant threat to deep-space exploration because spacecrafts would pass through them quickly, but are a concern for spacecrafts and satellites orbiting the Earth. Beyond the Van Allen belts, in interplanetary space, GCR radiation is a pervasive source of exposure that consists of about 85 % high energy protons, 14 % helium nuclei, and the remaining 1 % are high-Z, high-energy (HZE) nuclei that include all elements heavier than helium. HZE particles consist of nuclei stripped of their electrons and have positive charges according to Z, their atomic number. Although the flux density of GCR radiation is comparatively low, as seen in Fig. 1, their high energies are difficult to shield against and their biological effectiveness makes them a hazard for human space exploration. SEP consists of about 98 % protons and the rest helium nuclei and heavier elements accelerated to high energies by the Sun in proximity to solar flares and coronal mass ejections. The Sun’s activity cycles from low to high with a period of about 11 years. During solar maximum, there is increased probability for SEP events, including a large event. The capability to forecast such events is not yet available. The Sun’s activity modulates the intensity and properties of GCR radiation in our solar system. For example, at a distance of one astronomical unit (AU) from the

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Sun (the distance from the Sun to the Earth) the dose rate from solar minimum to maximum can change by factors of about 3–5. The largest dose rate from GCR ocurrs during solar minimum because the Sun’s weaker magnetic field permits more GCR charged particles to enter our solar system. During solar maximum, the GCR contribution is reduced due to the Sun’s expanded magnetic field deflecting charged particles entering our solar system. To assess the potential hazards of these radiations for space exploration, we must first consider their penetrating power, i.e., their ability to penetrate shielding and other materials likely to be used to protect astronauts in space. The most vulnerable condition would be astronauts performing extravehicular activity (EVA) either in free space or on a planetary surface. Under such conditions, the shielding would be the spacesuit itself. EVA spacsuits for deep-space missions are not yet fully defined so final shielding characteristics are not available. It is also likely that spacesuits may differ depending on the mission because of differences in radiation and other environmental factors. Prior assessments of radiation shielding characteristics of EVA spacesuits (accounting for suit, backpack, cooling systems, etc.) suggest protons must be at least 20-MeV to penetrate the spacesuit (Wilson et al. 2006). Therefore, protons (and HZE particles) with energies below this should not pose a danger to astronauts although these radiations could pose a problem for electronics if unshielded on the surface of a space vehicle. Some of the radiations present in the Van Allen belts could also penetrate a spacesuit, but there would be no need to perform EVAs during the brief transit through the belts when departing the Earth on a deep-space mission. Inside a space vehicle in interplanetary space, only the higher-energy charged particles from SEP and GCR can penetrate the structural materials that make up the vehicle. As seen in Fig. 2, SEP protons are much easier to shield than GCR. A few cm of Al would dramatically reduce dose from SEP but not from the much higherenergy GCR particles that extend well into the GeV/n range. The dose from GCR is only modestly reduced after the penetration of almost 30-cm of Al shielding! It is also seen in Fig. 2 that the relatively low penetrating power of SEP protons results in reduced dose to the blood forming organs (BFO) compared to skin, even when inside a space vehicle, although this difference is observed to diminish with depth of shielding. Protons require at least 70-MeV to penetrate to the BFO (Wilson et al. 2006). Mass is a major constraint during deep space missions, hence the development of efficient shielding approaches is needed. In addition to their penetrating power, high-energy GCR particles produce secondary radiations when they interact with materials such as the spacecraft, planetary surface, base structures, and even the astronauts themselves. In particular, secondary neutrons represent a hazard because of their high biological effectivenss. Depending on the biological effect considered, the ability of neutrons to cause biological damage can be 10–50 times greater than observed for radiations such as X-rays, gamma rays, and the high-energy protons in space. Hence, although the absorbed dose produced by secondary neutrons may be only a few percent of the total absorbed dose, their “biologically effective” dose can be a significant fraction of the total. For example, the effective dose from neutrons on the surface of the

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Fig. 2 Shielding GCR and SEP radiations. Calculations for GCR assume 1977 solar minimum conditions and those for SEP assume radiation from the August 1972 solar event. Calculations are based on particle spectra and fluences in free-space at 1 AU. Based on data in Wilson et al. (1997) for lunar regolith, which attenuates SEP and GCR radiations similarly to Al when depth is normalized to g/cm2. The x-axis was obtained by dividing g/cm2 in Wilson et al. (1997) by 2.7 g/cm3, the density of Al

Moon can be almost a third of the total depending on environment, shielding material, and shielding thickness (Slaba et al. 2011). Neutrons have recently been measured on the surface of Mars by the radiation assessment detector (RAD) aboard the Curiosity Rover (Kohler et al. 2014). The RAD detector measured the radiation environment during transit from Earth to Mars (Zeitlin et al. 2013) and has continued to measure after landing. Results show that neutrons contribute about 10 % of the total dose-equivalent on the surface of Mars (Kohler et al. 2014). SEP events begin without much warning and can last for several days. Typically, many SEP events occur per year but only rarely are they large enough to represent a health hazard inside a space vehicle. The August 1972 event (Fig. 2) was one of the largest recorded during the past 50 years. This event was between Apollo 16 and 17 and had it occurred during a mission the astronauts would have received substantial radiation exposure, and given the 4.5 g/cm2 (1.7-cm Al) shielding of the command module (Wilson et al. 1997) could possibly have approached or even exceeded the threshold for acute radiation effects. Estimates of doses from a large SEP event and GCR are provided in Table 1 for various mission destinations and assumed shielding conditions. It is observed that during transit and on the Moon (or asteroid), large doses could be received from SEP events if insufficiently shielded. For those, a “storm shelter” would be needed along with early warning capabilities that would include real-time radiation sensors and communication with space-weather centers that monitor solar events. Such warning systems would permit astronauts to seek shelter very early in an event

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Table 1 BFO dose estimates for SEP and GCR for various shielding conditionsa Shielding condition Interplanetary space – spacesuit only Interplanetary space – 3.7-cm Al shielding Moon surface – spacesuit only Moon surface – habitat Moon surface – habitat storm shelter Mars surface – spacesuit only Mars surface – regolith habitat

SEP event (mSv per event) 2,400b 270d 1,033 200 78 100 30

GCR (mSv per yr) 210–1070c 200–850c 354 310 270 330 260

a

SEP dose estimates are based on the unusually large events in August 1972 or October 1989. GCR dose estimates are for solar minimum conditions except as indicated. From Straume et al. (2010) and Adamczyk et al. (2011) b Dose to skin can be much higher because protons between 20- and 70-MeV can penetrate the spacesuit but not to the BFO c Range of GCR dose rates for solar maximum and minimum, respectively d Calculated for October 1989 SEP, Al sphere shielding, and BFO distribution (Dr. S. Blattnig, personal communication 2014)

when dose rates are minimal. The significance of these dose estimates will be appreciated when comparing them with the thresholds for radiation-induced health effects in humans summarized in the “Summary and Conclusions” section. On a planetary surface, about half of the radiation in intereplanetary space is shielded by the planet itself. Therefore, as seen in Table 1, the dose rate on the surface of the Moon (spacesuit only) for both SEP and GCR is lower than estimated in interplanetary space. On the surface of Mars, which has a thin CO2 atmosphere, the dose rate is substantially lower for the less penetrating SEP radiation but only somewhat lower for the more penetrating GCR. It should be noted that on both the Moon and Mars there would be an opportunity to enhance the shielding of future habitats using regolith materials available on the surface. In summary, the complexity of the space radiation environment and the differences in the kinds and energies of radiations from those typically encountered on Earth, provide novel challenges to the protection of astronauts during future space exploration missions. Shielding against dose from GCR will be difficult with current technologies. Protection against SEP radiation should be more feasible. Efforts are actively underway to deal with these challenges (e.g., Adamczyk et al. 2011; Slaba et al. 2011; Walker et al. 2013; Simon et al. 2013).

Radiobiology Extensive radiobiological research has been performed since the discovery of ionizing radiation more than 100 years ago. Collectively, these data provide an understanding of the effects of ionizing radiation at the molecular, cellular, and organism levels, which, together with data from human studies of irradiated populations, provide the basis for assessing radiation-induced health risk both on Earth and in space.

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The most common radiations on Earth (X-rays, gamma rays, alpha particles, beta rays, and fission neutrons) have been studied using a variety of experimental systems. In contrast, the most common radiations in space (high energy protons, HZE nuclei, and secondary neutrons) have been studied much less. Whether on Earth or in space, the effects of radiation on biological systems begin with the transfer of energy to molecules and tissues. To help interpret the radiobiological data, including the data most relevant to the potential health effects from exposure to space radiation, some background information concerning the nature of radiation energy transfer is needed.

Energy Transfer to Molecules Because the majority of available radiobiological data for penetrating radiations are from X-rays, gamma rays, and fission neutrons, it is important to understand how these radiations transfer their energy. High-energy photons such as X-rays and gamma rays transfer energy primarily via compton scattering (the photoelectric effect occurs at lower energies and pair production at very high energies) by ejecting an electron from an atom thus producing an ion plus an energetic electron that usually has sufficient kinetic energy to produce additional ionizations. Neutrons (which have no charge) transfer their energy by colliding with a nucleus in the medium setting it in motion and producing a charged particle that can ionize nearby atoms and molecules. In tissues, this energy transfer is primarily via elastic (“billiard ball”) collissions with hydrogen resulting in an energetic proton that can produce a track of many ionizations. Neutron elastic scatter with hydrogen results in an average of about 50 % energy transfer per collission because neutrons and protons have nearly the same mass. This means that the proton will on average have about half of the kinetic energy of the neutron. All ionizing radiations produce free radicals when interacting with tissues. Since soft tissues are about 70 % water, the hydrolysis of water is an important mode of energy transfer and is called indirect action because the initial energy transfer in a cell is to the water molecules creating highly ractive free radicals that can go on to damage biomolecules such as DNA. These reactive species have very short lifespans and therefore must be created in close proximity to a molecule such as DNA to produce damage (Ward 1994). This is the primary mode of action for low-linear-energy-transfer (LET) radiations. As LET increases, the direct mode of action becomes more important because the dense particle tracks are more likely to directly hit a critical target molecule. At very high LET, the effect from indirect action is comparatively negligible. Direct and indirect action on molecules have implications for dose–response relationships and for the biological effectiveness of the radiations in causing subsequent health effects. For space radiation, the charged particles of primary concern can produce dense tracks of ionizations as they pass through matter. It is observed in Fig. 3 that these tracks have a central core of dense ionizations surrounded by a penumbra of lower

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Better

Biological knowledge

Poor

γ –rays

silicon

B Ca H He C Ti Fe Be Li Si Z = 1 Z = 2 Z = 3 Z = 4 Z = 5 Z = 6 Z = 14 Z = 20 Z = 22 Z = 26

50 μm

iron

Fig. 3 Tracks in cell nuclei (left) and in emulsion (right) produced by space-type particles. Ionization pattern from γ-rays is shown for comparison. The cell nuclei (left panel) were stained for the detection of a protein (γ-H2AX) associated with the repair of DNA double-strand breaks. Each green focus corresponds to a DNA double-strand break (Figure from Cucinotta and Durante (2009). Also available from Cucinotta et al. (2012) and Cucinotta and Durante (2006))

density ionizations eminating from the core. The central core is produced by the primary particle itself and the surrounding penumbra is produced by delta rays, which are electrons set in motion by the primary particle and eminate radially from the core. The density of the core increases with increasing charge (Z) of the primary particle. The LET in the core is related to Z and inversely related to the velocity (kinetic energy) of the primary particle. Also seen in Fig. 3 are the sizes of the ionization tracks. A comparison to the scale indicates that the tracks with penumbra have diameters larger than most mammalian cells, which are typically about 12-μm diameter and a nuclear diamter of about 8-μm. It is also seen in Fig. 3 (left) that radiations have very different distributions of DNA damage within the cell nucleus. Gamma rays produce relatively random, sparse patterns in the cell nucleus while HZE particles (in this illustration, silicon and iron) produce tracks of damage that traverse the nucleus

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Fig. 4 Illustration of typical cell survival curves produced by high LET (A) and low LET (B) radiations (modified from Alpen 1998)

in essentially a straight line. These patterns have implications for space radiobiology and risk assessment. Importantly, the present radiobiological knowledge available for these radiations is much less than that for X-rays and gamma rays.

Radiation Effects on Cells: Models and Concepts Much of the knowledge available from radiobiology has been learned by studying survival curves obtained using a variety of cell types and radiations. Cell survival curves are illustrated in Fig. 4 where the log surviving fraction of cells is plotted as a function of dose. Such data have provided theoretical underpinnings for the field of radiobiology and have been used to identify and quantify factors that influence radiation dose–response relationships. Target Theory: A useful theoretical framework for interpreting cell survival curves was provided by Target Theory (Lea 1946). Target Theory provides parameters that are related to the inactivation of sensitive targets within the cell. It should be pointed out that by the time D. E. Lea developed Target Theory, it was already suspected that the lethality target(s) in cells was in the cell nucleus. This came from the ground-breaking results of R. E. Zirkle published in the American Journal of Cancer in 1935 “Biological Effectiveness of Alpha Particles as a function of Ion Concentration Produced in their Paths” where he concluded that “when the spore of the fern Pteris longifolia is irradiated with alpha particles, the resulting inhibition of cell division, of chlorophyll development, and cracking of the spore wall, is due primarily to irradiation of the nucleus” (Zirkle 1935). The reader is referred to Alpen (1998) for additional information on Target Theory. The fundamental principle of target theory is that inactivation of the target(s) inside a cell by radiation results in the cell’s death. The locations of the targets

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within the cell and/or their nature do not have to be known. The assumption is that the “target” is a unit of biological function such that if inactivated the cell will die. Hence, if a cell has one lethality target that can be inactivated by a single hit, such a survival curve would exhibit one-hit kinetics, i.e., would be exponential (log-linear) with no shoulder and expressed by: S ¼ eDo D

(1)

Equation 1 is an expression of Curve A in Fig. 4 where D is the dose delivered to the cells and Do is the mean lethal dose (dose at 37 % survival). If the cell requires the inactivation of more than one target and each target is inactivated by one hit, the cell survival is expressed by:  n D S ¼ 1  1  eDo

(2)

Equation 2 represents curve B in Fig. 4 where D is the dose delivered to the cells, Do is the mean lethal dose determined from the slope (k) of the linear portion of the survival curve (k = 1/Do), and n is the number of lethality targets per cell (extrapolation number). In this model, each of n targets within the cell must be hit at least once and inactivation of all the targets leads to death of the cell. Sublethal Damage: The concept of sublethal damage and repair pioneered by Elkind and Sutton (1959) represents a major advance in radiobiology because they demonstrated that the shoulder of the survival curve in mammalian cells resulted from the repair of radiation-induced damage in the cell. That is, the shoulder observed in Curve B of Fig. 4 could be explained by repair of low LET sublethal radiation damage. To demonstrate this they irradiated cells using a dose that produced 10 % survival and then used those cells for further irradiations after holding them for various lengths of time to permit repair. They observed that as time passes the cells become less and less radiosensitive to the follow-up dose. After 6 h the radiosensitivity of the cells approached that observed for the previously unirradiated cells. From these studies it was concluded that after radiation exposure the surviving cells contain injury that can be repaired with time and that the extent of this injury can be revealed by a suitably timed follow-on dose interacting with the prior damage leading to cell death. Such damage was termed “sublethal” because it had the capacity to be repaired to prevent cell death. Potentially Lethal Damage: Another approach to advance the understanding of cellular repair following radiation exposure emerged from the work of Phillips and Tolmach (1966). They developed a concept termed potentially lethal damage (PLD). PLD is injury that will inevitably kill the cell unless intervention occurs to alter the outcome. Note that under Sublethal Damage, the intervention was time for the cells to repair. The modern understanding is that the “intervention” is DNA repair processes that begin shortly after radiation exposure. Linear-Quadratic Model: The linear-quadratic model to describe dose–response relationships is by far the most widely used today (e.g., NRC 2006). This model

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assumes a combination of one hit and two hit events, resulting in the following relationship: Response ¼ αD þ βD2

(3)

Here, α and β are the linear and quadratic coefficients, respectively, and D is the dose. This model is used extensively in radiotherapy, experimental radiobiology, human cancer epidemiology, and radiation risk assessment. The most common mechanistic description is that radiation tracks produce DNA double-strand breaks (DSB). If there were two broken DNA molecules in close proximity at the same time they would have an opportunity to rejoin incorrectly. If the two broken DNA molecules were produced by the same track, the dose–response relationship would be linear (hence, αD). If they were produced by different tracks, the dose–response would be quadratic (hence, βD2). At low doses or low-dose rates, the linear term dominates because it is unlikely that there will be two tracks in close proximity at the same time. For low-LET radiations, large doses delivered at high-dose rate results in many simultaneous breaks in close proximity from different tracks and thus the quadratic term dominates. For high-LET radiations, the linear term dominates due to the high probability of intra-track interactions. Microdosimetric Models: Dose–response models based on microdosimetry have been developed to deal with the limitations of LET and absorbed dose in cellular and sub cellular volumes (e.g., Kellerer and Rossi 1974; ICRU 1983). It was recognized that energy deposition by ionizing radiation is a stochastic process that can deposit very different amounts of energy in small volumes due to chance alone. That is, an absorbed dose determined on the macro scale could produce a broad range of doses in critical subcellular targets such as DNA (or in genes within DNA) and that this would depend strongly on the radiation type. As it became clear that the radiosensitive targets within cells are small (on the micro or nano scale), the discipline of microdosimetry emerged to deal with such non-homogeneous dose delivery. This is particularly important for HZE space radiations that produce low fluence (less than one traversal per cell) but very high “microdose” in the cells that are actually hit.

Radiation Effects on Cells: Factors that Influence Dose–response Many factors in addition to dose can influence radiation dose–response relationships and have been discovered and studied using cells, including dose rate, dose fractionation (typically used in cancer radiotherapy), biological effectiveness of various radiations, and understanding the influence of oxygen on the radiosensitivity of cells (particularly important for anoxic tumors). More recently, cells have been used to identify and study bystander effects and adaptive responses (e.g., Wolff 1996, 1998; Morgan 2003a, b; Dauer et al. 2010). Dose Rate: For low-LET radiations, the length of time to receive a particular dose has substantial effect on biological response. Delivering the radiation at

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high-dose rate can result in greater response than if delivered over a longer period of time, or as typical in radiotherapy delivered in many small fractions. The response per unit dose has been observed to reach a constant minimum at low dose rates or at low total doses, i.e., below about 0.1 mSv/min and below about 100 mSv (NRC 2006). Response per unit dose tends to reach a maximum at very high-dose rates (typically above about 1,000 mSv/min). Between these two extremes, the response per unit dose has been observed to vary by factors of 2–10 for different biological systems (NCRP 1980; NRC 1990). The extrapolation of health effects from high-dose rate to low-dose rate (and low dose) is discussed under the section on “Human Health Concerns.” Biological Effectiveness: For a given absorbed dose of radiation, the biological response can differ substantially for various types of radiations. The concept of relative biological effectiveness (RBE) was established to provide a quantitative measure of this. RBE is defined as the dose to produce an effect with X-rays or gamma rays (the comparison radiation) divided by the dose required to produce the same effect with a radiation under investigation. RBE has been shown to vary between effects and experimental systems, but generally increases with increasing LET, reaching a maximum at around 100–150 keV/μm and then declines at higher LETs due (at least in part) to the killing of affected cells. The RBE is also influenced by dose and dose rate and typically increases with both decreasing dose and decreasing dose rate due primarily to the decreased effectiveness of the comparison radiation. A maximum (constant) RBE is reached at low doses (or low dose rates) where dose–response curves tend to become linear. RBE values have been obtained for a large number of radiations and biological systems (e.g., NCRP 1990) and range from near unity to more than 50. Such broad ranges of RBEs are observed for both Earth-based and space-type radiations. Oxygen Effect: Normal air at sea level is about 21 % oxygen. This is equivalent to an oxygen tension of about 160 mmHg. 100 % O2 is 760 mmHg. Breathing air with only 16 % O2 (122 mmHg) results in dizziness and 10 % (76 mmHg) results in immediate unconsciousness. Radiation experiments performed using cells in vitro where the concentration of O2 can be evaluated from ~0 % to 100 % have provided information on radiosensitivity as a function of O2 concentration. This is illustrated in Fig. 5 for low-LET radiation (X-rays and gamma rays) and shows that the concentration of O2 has an overall effect on radiosensitivity approaching a factor of 3. It is noted that the influence on radiosensitivity is only appreciable at the very lowest O2 concentrations. Little difference (if any) in radiosensitivity is observed between normal air and 100 % O2. The oxygen effect is highly dependent on indirect action and therefore is very much influenced by the LET of the radiation. This is illustrated in Fig. 6 for low and high LET. For low-LET radiations there is a marked difference observed in cell survival when cells are irradiated in N2 versus O2 conditions. In contrast, when cells are irradiated with high-LET particles the oxygen concentration does not influence the radiation response. The explanation for this difference is that low-LET radiation kills cells indirectly via oxygen free radicals whereas high-LET radiation kills cells by directly damaging the lethality target. The oxygen enhancement ratio (OER) is

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Fig. 5 Effect of oxygen concentration on radiosensitivity for low-LET radiation (Modified from Gray 1958)

Fig. 6 Effect of oxygen concentration on cell survival following low-LET and high-LET radiations

defined as the dose required to produce a given effect under low O2 divided by the dose required to produce the same level of effect under normal O2 conditions. The OER typically ranges from 1 to 3 and is particularly important in radiotherapy where the centers of tumors can become anoxic resulting in difficulties achieving tumor control. Oxygen is also a consideration in space due to different pressures and oxygen atmospheres, especially during EVA. However, O2 concentrations will likely remain in the 21–100 % range, which would not be expected to result in substantial differences in radiosensitivity. Bystander Effect: It has been generally assumed in radiobiology that the detrimental effect of radiation results from radiation-induced damage in the irradiated cells, not in adjacent cells that were not hit by the radiation. However, more recent radiobiological evidence has shown that assumption may not be correct. So-called “bystander” or “non targeted effects” are observed when the effected cell has not received any radiation at all. The effect appears to involve cell-cell communication

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and could have implications for how radiation risks are extrapolated to low doses and low dose rates, where actual health-effects data are difficult to obtain. This is a matter for further research (e.g., Wiley et al. 1997; Little 2000; Baulch et al. 2001; Morgan 2003a, b; Dauer et al. 2010). Adaptive Reponse: A so called “adaptive response” has been observed in some (but not all) experimental systems when a small dose is followed later (within hours) by a much larger dose. A small pre-dose (too small to produce detectable effects by itself) results in substantially less biological damage (up to factor of 2) than if the pre-dose was not received (e.g., Wolff 1996, 1998). The pre-dose appears to enhance repair mechanisms that reduce the effect from the subsequent large dose (see Dauer et al. 2010). Could this have relevance for astronauts in deep space? Astronauts would be exposed to constant low-level GCR radiation, but occationally could be exposed to larger doses from SEP events. Would the constant low-level GCR enhance cellular repair enough to significantly mitigate damage from the more acute SEP radiation? The potential relevance of bystander effects and adaptive responses to the radiation-induced risks associated with human space exploration remains open and in need of further research.

Radiation Effects on Organisms Radiation dose–response relationships for effects such as tumorigenesis and mutagenesis are generally represented by those seen in Fig. 7. Curves are for low- and high-LET radiation as well as for chronic and acute dose delivery. As mentioned previously, low-LET radiations include X-rays and gamma rays, but they also include high-energy protons from GCR and SEP events that are of similar biological effectiveness as X-rays and gamma rays. In space, the high-LET radiations are primarily HZE nuclei in GCR and secondary neutrons produced when energetic particles interact with materials in space. The general relationships illustrated in Fig. 7 are valid for many organisms and effects studied. That is, low-dose rates tend to be less effective than high-dose rates for low-LET radiations and high LET is usually more effective than low-LET radiation. This is consistently observed for early effects that result from DNA double-strand breaks, such as genetic mutations and chromosome aberrations, but is less consistent for late effects such as tumor formation or cancer induction that involve complex damage processing over a long time period (e.g., cancer promotion). In Fig. 8 (data from Fry and Storer 1987) we see the dose–response relationships for Harderian gland tumors induced in mice using various heavy ions and compared with chronic 60Co gamma rays. It is observed that for this biological system the effectiveness increases with increasing LET, similar to that illustrated in Fig. 7 (a similar pattern is also observed for chromosome aberrations, data not shown). For the data in Fig. 8, the LETs span almost a thousand fold from 0.22 keV/μm for 60Co gamma rays to 190 keV/μm for 56Fe ions. There is a noticable “saturation” observed for the highest LET particles. This bendover appears to begin at doses of 10-cGy or

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Fig. 7 Curves representing many (but not all) dose–response relationships for carcinogenesis and mutagenesis in organisms, including rodents and humans. The high-LET curves are for neutrons and heavy ions and the low-LET curves are for gamma rays, X-rays, and high-energy protons. The solid curves are for single acute (high-dose rate) exposures and the dashed curves are for chronic (low-dose rate) exposures. The solid straight line is a linear fit to the high dose-rate low-LET data, generally referred to as the linear-no-threshold (LNT) curve

60 40Ar

50 Incidence of tumors, %

20Ne

40 56Fe

12C

30

4He

20

10 60Co

γ-rays

0 0

50

100

150

200

Dose, cGy Fig. 8 Incidence of harderian gland tumors in mice (From Fry and Storer 1987). 100 cGy = 1 Gy (see Fig. 9)

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Fig. 9 Incidence of hepatocellular carcinoma (left) and incidence of acute myeloid leukemia (right) induced in mice by exposure to 137Cs gamma rays (open circles) or 1-GeV/n 56Fe ions (closed circles) (Plotted from data in Weil et al. (2009))

less for the highest LETs and is believed to be caused by cell killing resulting in less than the expected tumor incidence, i.e., a dead cell can’t become a tumor. An example of exceptions to the dose–response relationships in Figs. 7 and 8 is illustrated in Fig. 9 (plotted from data in Weil et al. 2009). Here two different cancers were induced by low- and high-LET radiation in the same mouse strain. In Fig. 9 (left panel) we see the dose–response relationships for hepatocellular carcinoma induced by 137Cs gamma rays or by 1-GeV/n 56Fe ions. 137Cs gamma rays are low LET (0.4 keV/μm) whereas the 56Fe ions are much higher LET (150 keV/μm). In this case, consistent with those seen in Figs. 7 and 8, the high-LET 56Fe radiation is substantially more effective than the sparsely ionizing gamma rays. However, when acute myeloid leukemia is induced in the same mouse strain using the same radiations the response pattern is very different (right panel of Fig. 9). In this case, the two radiations have indistinguishable responses. This clearly illustrates that different cancers can exhibit very different RBE responses to space-type radiations. Such large RBE variations have been observed among animal models in many prior sudies as well using other high-LET radiations, including neutrons (e.g., Broerse et al. 1982), and translate into substantial uncertainties when using radiobiological animal data to estimate radiation-induced health risk in humans. This is a particular challenge for the assessment of risk to astronauts on deep space missions, where the high-LET radiation component is a significant concern.

Human Health Concerns A major uncertainty for determining the radiation-induced risk in space is that human health-effects data do not exist for HZE particles. Therefore, this requires extrapolation from human data that are available for other radiations

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(mostly gamma rays) and from animal data obtained using simulated space radiations from ground-based accelerator facilities. It has been observed from epidemiological investigations of irradiated human populations (e.g., Japanese a-bomb survivors) that radiation does not produce new types of health effects (some acute radiation syndromes may be exceptions), but rather increases the frequency in a dose-dependent manner of certain kinds of diseases and abnormalities already present in populations. These include cancers, mutations (genetic abnormalities transmitted from irradiated parent to child have not yet been observed in humans, but are well documented in animals), cardiovascular effects, central nervous system effects, effects on fertility, cataracts, chromosomal abnormalities, developmental abnormalities if radiation is received in utero (should not be an issue during early exploration missions), and various acute responses caused by large doses. Information available from human epidemiological studies, together with a large body of radiobiological data, provide the basis for radiation risk assessment and radiation protection standards on Earth. Many of the radiation-induced health concerns on Earth are also of concern in space, hence the available data provide a necessary (but insufficient) basis for risk asessment in space.

Cancer Radiation-induced cancer in human populations has been studied extensively for well over half a century and provide information critical to the assessment of risk and to the establishment of radiation protection standards (e.g., ICRP 1991; NRC 2006; UNSCEAR 2006). The population studies that have provided much of the information on radiation-induced cancer risk from penetrating external whole-body irradiation are from the atomic bomb survivor cohorts of Hiroshima and Nagasaki (e.g., Ozasa et al. 2012). The atomic bomb survivors received almost entirely high dose rate, high energy gamma rays, which were penetrating and resulted in wholebody dose. The neutron exposures were small, about 2.5 % at 1-Gy total free-in-air dose in Hiroshima and about 0.5 % in Nagasaki (RERF 2005). The neutron dose would be further reduced relative to the gamma-ray dose after penetrating to deep organs, but because of their large RBE could impact dose–response relationships of more superficial tissues such as lens of the eye and female breast. The survivors have been followed medically with regular updates. Extensive efforts were undertaken to quantify doses for survivors in the study cohorts, including computational modeling to internal organs of importance for cancer risk assessment (RERF 2005). These attributes have made these data critical to the estimation of cancer risk in humans following exposure to external whole body radiation. Before such cancer risk estimates can be applied to risk assessment generally, and to space in particular, several adjustments are required. These include dose-rate differences (high dose rate a-bomb versus low dose rate space), population differences (Japanese vs. astronaut), and radiation differences (gamma rays vs. space radiation).

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Table 2 Lifetime risk of cancer attributable to exposure to low dose (or low dose rate) low-LET radiationa

Incidence Mortality

Solid cancer (% per 100 mSv) Males Females 0.8 (0.4–1.6) 1.3 (0.7–2.5) 0.4 (0.2–0.8) 0.6 (0.3–1.2)

Leukemia (% per 100 mSv) Males Females 0.10 (0.03–0.30) 0.07 (0.02–0.25) 0.07 (0.02–0.22) 0.05 (0.01–0.19)

a

Low dose is defined as doses in the range from near zero up to about 100 mSv of low LET radiation. Risk is assumed to be dose-rate independent in this range. Numbers in parentheses are 95 % confidence intervals. Based on data in NRC 2006

As mentioned, it is well known from radiobiology that dose rate can influence biological response (e.g., NCRP 1980). Hence, a challenge is to extrapolate from the high dose rate a-bomb data to the much lower dose rates (and doses) of more general concern by the radiation protection community. To quantitatively deal with this, radiation protection organizations (e.g., ICRP 1991; UNSCEAR 2006; NRC 2006) have adopted a dose and dose rate effectiveness factor (DDREF) to scale from high dose-rate data to low dose rate. For example, the risk from the high dose rate a-bomb data would be divided by the DDREF to estimate risk from low dose rates. DDREF values recommended for low-LET radiation range from 1.5 to 2.5. Population characteristics such as age distributions and spontaneous rates of cancer can differ between populations and those differences must be taken into account as well when extrapolating risk from one population to another. Results from such adjustments are seen in Table 2. These are radiation-induced cancer risks estimated for a U.S. population receiving low dose (or low dose rate) gamma rays (NRC 2006). The risk estimates are based on the a-bomb data adjusted for dose rate and population characteristics. Cancer risk estimates of the kind illustrated in Table 2 can be used as a starting point for estimating cancer risk in space. However, for space, the cancer risk must account for radiations that are very different from the gamma rays experienced by the a-bomb survivors. Efforts are underway by space agencies around the world to advance the science of radiation-induced health risks for human exploration missions into deep space. Many disciplines converge to develop such estimates, including radiobiology, dosimetry, shielding, and risk analysis. Listed in Table 3 are point estimates of cancer risk for a hypothetical 1 year mission in interpanetary space at 1 AU (Cucinotta et al. 2013a). These estimates are for men and women and include never smokers and an average based on the characteristics of the U.S. population. The results in Table 3 indicate that age at exposure is an important factor in lifetime cancer risk from radiation exposure, i.e., risk diminishes with age at exposure. This is in part because the young have more time to express cancer during their remaining lifetime. The latency (time between irradiation and appearance of cancer) for solid cancers can be two or more decades, therefore, the chance increases with age that the individual will die from a competing cause before developing cancer from the radiation. This age effect appears to be a bit larger for women than for men. Table 3 also suggests that the history of smoking may influence the lifetime cancer risk from radiation exposure. Although not shown in

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Table 3 Estimates of lifetime risk for exposure induced cancer from hypothetical 1-year mission in deep spacea

Women Never smoker U.S. average Men Never smoker U.S. average

Risk (%) exposure at age 30 year

Risk (%) exposure at age 45 year

Risk (%) exposure at age 60 year

5.7 7.1

3.8 5.2

2.5 3.7

4.2 5.0

3.4 4.1

2.5 3.0

a

Assumes 20 g/cm2 (7.4 cm) Al shielding and average solar minimum (From Cucinotta et al. 2013a). Values rounded to nearest tenth

Table 3, the uncertainties associated with the estimation of cancer risk in space are substantial – upper 95 % confidence limits are perhaps 3–4 times the mean estimates (See Fig. 10). Reducing the uncertainties in cancer risk estimates is an important priority for space exploration. However, substantial reductions in these uncertainties will be difficult to achieve. This is because a-bomb survivors who were adults in 1945 have almost reached their full life expectancy so limited new information is expected, other population studies are unlikely to improve substantially upon the precision of the a-bomb data by the 2030s, and DDREF and RBE values are unlikely to become significantly more accurate because of the variability between species and endpoints. This would suggest that the uncertainty in estimates of radiation-induced cancer risk is likely to remain large unless novel approaches (not yet available) can be developed. Lifetime risk of cancer death from exposure to various sources of radiation is illustrated in Fig. 10. The width of each box represents the 95 % confidence interval of the risk. It is seen that extended human missions beyond low Earth orbit could potentially result in substantial lifetime cancer risk, particularly when the present uncertainties are considered. For example, at the +95 % confidence level a mission to Mars could add almost 20 % to the baseline cancer mortality risk (baseline is risk without space radiation). The NASA career exposure limit is 3 % radiation exposure induced death (REID) from cancer (NASA 2007). NASA further assures that this risk limit is not exceeded at a 95 % confidence level using a statistical assessment of the uncertainties in the risk projection calculations to limit the cumulative effective dose received by an astronaut throughout his or her career. Estimates have been made of the length of time permitted in deep space by the current NASA exposure limits. Assuming 20 g/cm2 (7.4 cm) Al shielding and average solar minimum conditions the maximum duration would be about 150–200 days (Cucinotta et al. 2013b), not sufficient for a mission to Mars (see “Summary and Conclusions” section). Uncertainties in the present risk

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Fig. 10 Estimates of lifetime risk of cancer death resulting from radiation exposure. The width of each box represents the 95 % confidence interval (From Cucinotta and Durante 2009; also available from Durante and Cucinotta 2008)

estimates contribute substantially to the limitation on the length of time permitted in deep space and place a premium on defining and reducing those uncertainties.

Cataracts It is well established that large doses of radiation can cause cataracts to form in the lens of the eye. This risk has been considered in radiation-protection guidelines, which have generally assumed a threshold for vision-impairing cataracts in humans of 5,000 mSv high dose rate X-rays (ICRP 1991). This is substantially more radiation than expected during space missions. However, a recent study of a-bomb survivors observed radiation-induced cataracts at much lower doses (Neriishi et al. 2012). In that study, a clear dose–response relationship for visionimpairing cataracts requiring surgical removal was observed at doses above 1,000 mSv. Their threshold estimate was about 500 mSv. These new data have been considered by international radiation protection organizations and have resulted in updating the threshold for radiation-induced cataracts to 500 mSv (ICRP 2011). Cataracts have also been studied in astronauts (Cucinotta et al. 2001; Chylack et al. 2009; Blakely et al. 2010). Results suggest an increased risk following average doses in space of only 45 mSv to the lens of the eye when compared with astronauts receiving less than 8 mSv. This is a factor of 10 less than the threshold for a-bomb radiation and heightens concerns that the threshold for cataract formation in space may be less than on Earth and well within the dose range expected for space exploration missions. These observations in astronauts need continued followup and confirmation.

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Chromosomal Abnormalities Chromosome rearrangements are linked to both cancers and genetic disorders. Shortly after the discovery of oncogenes in the early 1980s (Bishop 1982), it was observed that there were close positional relationships between oncogenes and chromosomal translocations in human malignancies. This was particularly evident for leukemias and lymphomas (e.g., the associations between abl and 9;22 in CML and myc and 8;14 in Burkitts lymphoma). It is also well established that chromosomal aneuploidy (too many or too few chromosomes) is associated with healthrelated outcomes, including trisomy 21 which causes Down’s syndrome in humans. However, the association between such specific chromosomal abnormalities and radiation exposure has not been demonstrated. Chromosome aberrations have been used in an attempt to identify individuals that may have increased sensitivity to radiation. For example, individuals with DNA repair deficiencies such as Ataxia Telangiectasia have higher than normal aberration frequencies, and also are more susceptible to radiation damage (e.g., McKinnon 1987; Sanford and Parshard 1990). But these are rare – typically a few percent of the population, although somewhat more in the heterozygous condition. It has been suggested that the frequency of chromosome aberrations in human blood lymphocytes is predictive of cancer risk (Norppa et al. 2006; Bonassi et al. 2008). However, chromosome aberration studies in experimental animals do not appear to support such a conclusion (e.g., Brooks et al. 2003). The association suggested between chromosome aberration frequencies in human blood lymphocytes and cancer risk could reflect prior clastogenic exposure, which can induce both aberrations and cancer in a population. The frequency of chromosome aberrations measured in blood lumphocytes has also been used as a “biological dosimeter” to determine prior exposure to radiation (Bender et al. 1967, 1968; Littlefield and Lushbaugh 1990; Straume et al. 1992; Lucas et al. 1992a; Straume and Lucas 1995). Astronauts who spend at least 3 months on the ISS have been analyzed for chromosome aberrations in their blood lymphocytes prior to flight and upon return. The frequency of translocations (translocations/ cell) measured prior to flight is subtracted from the frequency after flight and the difference attributed to radiation exposure during flight. Such biodosimetry employs a calibration curve for human blood lymphocytes exposed to known doses in vitro to convert the increase in translocation frequency to radiation dose. Because a chromosome translocation is a biological response to radiation (not a physical dose) it includes the relative biological effectiveness of the radiations as well as the individual’s own DNA repair capabilities. Hence, one would expect that such a “ biodose” would be more consistent with the measured dose equivalent (absorbed dose times the quality factor) than with the absorbed dose. This was verified by comparing “biodose” with physical dosimetry results (George et al. 2001). In that study, dose estimates were compared for six ISS crew members. The average doses based on the chromosome aberrations were consistent with those based on physical personnel dosimetry, but the chromosome data exhibited considerable inter-individual variation limiting the precision for individual dosimetry.

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Subsequently, this group also evaluated the stability of chromosome aberrations with time following the missions (George et al. 2005). They measured chromosome translocations in six astronauts from 5 months to more than 5 years post flight and observed a decline in the translocation frequencies with half-lives ranging from 10 to 58 months. Although the frequency of simple chromosome translocations measured in human blood lymphocytes has been shown to be remarkably stable with time post exposure following uniform whole-body irradiation (Lucas et al. 1992a, b, 1996), their stability is highly dependent on the uniformity of radiation dose within the body (Straume and Bender 1997). Non-uniform dose to the organs that repopulate the blood lymphocytes will result in reduced translocations per cell over time in the blood because the organs with lower dose will produce cells with lower translocation frequencies thereby dilluting the frequency in the peripheral blood. This could possibly explain the rapid decline and variability between individuals in the translocation frequency observed for ISS astronauts. Human-like phantoms placed on the ISS have been used to measure the variation in the distribution of dose within the body (Berger et al. 2013). Results show substantial variations in internal body dose, which could perhaps be consistent with the temporal instability observed.

Cardiovascular Effects Large therapeutic doses of radiation can cause harmful effects to the cardiovascular system in humans. For example, patients exposed during radiotherapy may develop enhanced plaque formation in arteries in the radiation field and may develop heart disease if the heart is directly exposed (Glanzmann et al. 1998; Darby et al. 2005). However, these are much larger doses than expected during space missions. Evaluations of the a-bomb survivor data suggest that cardiovascular effects may actually emerge decades following doses substantially lower than those received during radiotherapy (Preston et al. 2003; Shimizu et al. 2010). Their analyses found statistically significant radiation induced mortality from heart disease and stroke in the Life Span Study (LSS) cohort at doses between 500 and 2,500 mSv. Radiation effects at doses below 500 mSv were not statistically significant. Likewise, a recent 24-year prospective follow-up of a-bomb survivors in the Adult Health Study (AHS) cohort observed that the association between radiation exposure and stroke increased with radiation dose in both men and women (Takahashi et al. 2012). For women, the apparent threshold was 1,300 mSv. For men, the risk was significant in the 500–1,000 mSv dose group. In both sexes, dose was only related to haemorrhagic, not ischaemic stroke. These observations are potentially important for human space exploration because an extended mission may result in doses within this range and underscores the need to better estimate the cardiovascular risks for space-relevant radiations and how they may translate to astronaut risk on long-duration missions. A special concern for astronauts would be the potential combined effects from stress, microgravity, immobility, and continuous long-term exposure to GCR.

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Central Nervous System Effects For humans, it is known from radiotherapy that the adult brain is comparatively insensitive to radiation because of the resistance of neurons to cell killing (Belka et al. 2001) and redundancy in cognitive capacity. For example, doses of gamma rays or X-rays from whole-brain radiotherapy are typically 12 daily fractions of 2,500 mSv each for a total dose of 30,000 mSv. Although it is also known that such treatment can cause some detectable impairment in learning and memory function (Chang et al. 2009) it has been an acceptable treatment for the past 30 years. A recent prospective study evaluating neurocognitive impairment after fractionated photon radiotherapy for benign or low-grade adult brain tumors (Gondi et al. 2013) found that for the 18 patients that completed both the baseline and 18-month follow-up testing, a dose greater than 7,300 mSv to the hippocampus was required to produce a detectable impairment in long-term list-learning delayed recall. The effect of radiation on dementia has also been studied in a-bomb survivors (Yamada et al. 2009). The incidence of dementia was evaluated for three dose categories: 1,500

2,500 >500

6,000 7,300 fract.

Cardiovascular effects

500–1,000

Most likely larger

Eye cataracts – vision impairing

500–1,000

Most likely larger

Acute radiation sickness

500–1,000

Larger

Skin effects – erythema Skin effects – moist desquamation

2,000 20,000

10,000a 50,000 fract.

References UNCREAR (1982) ICRP (1984) NRC (1990) ICRP (1984) NRC (1990) Yamada et al. (2009) Gondi et al. (2013) Preston et al. (2003) Shimizu et al. (2010) Takahashi et al. (2012) Neriishi et al. (2012) ICRP (2011) Young (1987) Anno et al. (1989) Conklin and Walker (1987), Fabrikant (1972)

a

Based on DDREF of 5 for early skin effects (UNSCEAR 1982)

standards is to prevent deterministic effects and reduce the risk from stochastic effects to acceptable levels. An additional requirement for stochastic effects is the application of the ALARA principle (NCRP 1999), which requires that risk be maintained “as low as reasonably achievable.” It is observed that most thresholds are at or above 500-mSv for acute low-LET radiation. An exception is temporary infertility in men, which is about 150-mSv acute gamma or X-rays. The dose rate in space (with the exception of radiation from a large SEP event) would be chronic, which generally results in higher threshold limits although these are not well established for some effects following low-LET radiations and even less known for space-type radiations. Comparing the threshold doses in Table 4 with the doses estimated for space (Table 1) would suggest that deterministic effects could be a risk if exposed to a very large SEP event while EVA on the Moon or in a spacecraft without sufficient shielding. However, deterministic effects would appear unlikely from GCR or from SEP events in a habitat on the Moon or on the surface of Mars. This comparison underscores the importance of shielding, especially against the radiation from an unusually large SEP event while in transit or on a surface that is not protected by an atmosphere, such as the Moon or an asteroid. It must be emphasized that the threshold doses listed in Table 4 are based on information obtained from humans exposed to primarily X-rays or gamma rays. Such threshold information does not exist for space radiations and therefore

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extrapolation of these data to space must be made with caution. It is inferred from radiobiology that the high-energy protons in space have similar biological effectiveness to X-rays and gamma rays. However, the biological effectiveness of the HZE component of GCR (and secondary neutrons) is largely unkown for these effects in humans. For stochastic effects, it is assumed that there is no threshold dose, i.e., the risk is proportional to dose at all doses. In the present NASA standard, the limit is 3 % radiation exposure induced death (REID) over the lifetime of the individual (NASA 2007). For comparison, the lifetime cancer mortality risk in the U.S. population is about 20 %. Also, 3 % compares with the career mortality risk estimated for hazardous occupations on Earth (e.g., fishing and logging), which are in the 3–5 % range in the US (Bureau of Labor Statistics 2012). It is important to note that NASA further requires this risk limit not to be exceeded at an upper 95 % confidence level during an astronaut’s career. Due to the large uncertainties in the current risk estimates (factor of about 3 for ISS and somewhat larger for deep space) this additional requirement effectively limits the lifetime risk to about 1 %. Given the many uncertainties remaining in the risk estimates for space radiation this approach provides an added safety factor. These stochastic risk limits strongly influence shielding requirements and mission duration. For example, based on the present NASA standard and assuming 20-g/cm2 (7.4-cm) Al shielding and average solar minimum conditions, mission duration would be limited to about 150–200 days in deep space (Cucinotta et al. 2013b). This is not long enough for a human mission to Mars, which may require at least 500 days without landing (fly-by) and over 900 days with landing. Hence, for such missions, there would be substantial premium on the development of improved shielding, improved risk estimates (including capabilities for individual susceptibility assessments), and biological countermeasures. In space as on Earth, radiation-protection standards are established to prevent deterministic effects and limit stochastic effects. For human space exploration, mission requirements (shielding, duration, and other protective measures) would be designed to accomplish this. Radiation protection guidance has been provided for human space operations in low Earth orbit, e.g., for the International Space Station and space shuttles (NCRP 1989, 2000). This guidance was subsequently updated with the eye toward human missions beyond LEO (NCRP 2006). It is observed from these reports as well as from space-agency regulations (e.g., NASA 2007) that exposure limits for space are substantially larger than those recommended for radiation workers on Earth (e.g., ICRP 1991, 2007). For example, the annual dose limit to BFO for radiation workers on Earth is 20 mSv (ICRP 1991) while in space it is 500 mSv. However, in practice, the NASA lifetime limit of 3 % REID controlled at +95 % would effectively limit the exposure to about 300 mSv during an astronaut’s entire career. This is compared with a radiation worker on Earth receiving 20 mSv/year for 50 years which would be 1,000 mSv during a life-long career and result in 3.6 % probability of attributable death (ICRP 1991). It is important to emphasize that additional research is needed to quantify and validate the risks that will serve as the basis for establishing dose limits for future deep space missions such as Mars.

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Finally, although human exploration of deep space faces many risks and challenges (including many serious risks that have nothing to do with radiation), it is worthwhile to ponder how much risk one should accept to go beyond where our species has gone before. Acknowledgments The author would like to thank the Springer editorial office for their guidance related to editorial matters. A very special thanks is extended to Ms. Saskia Ellis for her guidance and extraordinary patience in answering all my questions and uploading the text and figures into the website. The author would also like to thank Dr. Marvin Goldman for providing helpful suggestions on the manuscript and Dr. Stephen Blattnig and colleagues of NASA Langley Research Center for providing a reality check on the dose estimates as well as their recent papers on lunar radiation modeling and shielding. Finally, I would like to express my thanks to Dr. Firooz Allahdadi, an editor of this book, for inviting me to submit this chapter. This work was perfomed under the auspices of the NASA Ames Research Center.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Earth’s Natural Protective System: Van Allen Radiation Belts ▶ Solar Flares ▶ Solar Flares and Impact on Earth ▶ Solar Radiation and Spacecraft Shielding ▶ Strategies to Prevent Radiological Damage from Debris

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Solar Radiation and Spacecraft Shielding David F. Medina

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Ionizing Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sources of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Galactic Cosmic Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Distribution of Radiation in Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ionizing Radiation Effects on Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spacecraft Charging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface Erosion Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Total Ionizing Dose Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shielding Concepts for Spacecraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forecasting the Space Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

296 297 298 298 300 301 301 303 305 306 309 310 311 312 312 312

Abstract

The space environment in the vicinity of spacecraft orbits is replete with a variety of natural and manmade threats from impact of high-speed objects. Setting aside the massive objects such as meteorites and orbital debris, it is apparent that the seeming serenity left behind is still punctuated with a boiling assortment of invisible hazards in the form of high-energy charged particles, plasmas, and electromagnetic radiation. Effects from such threats can reach down into the atmosphere to highaltitude aircraft, ground technologies, and into the DNA of living systems. D.F. Medina (*) Directed Energy Directorate, AFRL/RDLE, U.S. Air Force Research Laboratory, Kirtland AFB, NM, USA e-mail: [email protected]; [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_10

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Here, focus is made on the spacecraft material itself including effects on the associated subsystems. The fundamental nature, source, and temporal-spatial variation of the radiation environment affecting present and future spacecraft traffic is the subject of much in-depth research but is described broadly in order to conceptualize the hazard. Spacecraft material damage is described as either localized material damage at the atomic level or damage to the overall satellite from charge accumulation and surface erosion. The localized hazards apply mostly to susceptible spacecraft sub-components at the particle level, particularly in solid-state microelectronics composed of miniaturized circuitry. The macro hazards have a broad effect over entire surfaces or can be an accumulation of localized damage over the mission of the spacecraft. Surface erosion and contamination is of less immediate consequence but can be eventually disruptive to mission objectives. The environmental sources and distribution of ionizing radiation are addressed including how they couple to the magnetic fields influencing their trajectories and flux concentrations. Given this background, the topic is concluded by addressing the established methods for radiation hazard avoidance and shielding. Keywords

Solar radiation • Spacecraft susceptibility • Microelectronics • Energetic particles • Coronal mass ejections • Solar flare • Spacecraft damage • Satellite • Galactic cosmic radiation • Shielding

Introduction Mankind’s first successful attempt to reach past the protective blankets enveloping earth occurred with the launch of Sputnik 1, on 4 October 1957 by the USSR. Simultaneous with this reach, however, humanity has had to recoil the other hand into a protective stance when facing the unmitigated brunt of the cosmic radiation environment. Historically, mankind is accustomed to the encroachments of massive objects such as asteroids and large meteorites since they are capable of trespassing, with impunity, our protective atmosphere. Ionizing radiation hazards, on the other hand, have been largely ignored prior to the space age since radiation is thankfully ameliorated in an exponential fashion on its way to the earth’s surface. Conversely, the stark vacuum of space is a free range for radiation energy to propagate, subject primarily to magnetic field constraints. The term “radiation,” in this context, serves to distinguish energy and particles of interest that have propagated sufficiently far from their source such that any prescribed spherical boundary through which they pass contains the same amount of energy regardless of the radial extent of the sphere. Modifying the term “radiation” with the term “ionizing” serves to further distinguish those components of the electromagnetic spectrum and subatomic particle population with sufficient energy to liberate or add electrons to the atoms or molecules of the material they strike leaving behind ions with a net electric charge. The most energetic radiation elements can also induce a cascade of

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secondary particles that can, in turn, be ionizing as well. The high-energy content, along with the charged state of these particles, acts in missile-like fashion to deliver a lethal payload. Principal damage mechanisms to technology include localized disruption of sensitive onboard electronics and computer memory states. This results when ions penetrate into the atomic structure, or when multiple penetrations lead to the accumulation of disruptive charge. Hazards exist on two fronts consisting of the localized atomic-level disruptions and broader effects such as body-wide charge accumulation and radiation ageing. The NOAA Space Weather Prediction Center (Speich and Poppe 2005) summarizes the scope of radiation effects on spacecraft to include: • Surface charging resulting in electrostatic discharge and/or contaminate accumulation • Deep dielectric or bulk charging resulting from relativistic electron penetration • Single event effect (SEE) and single event upsets (SEU) in particle penetration • Spacecraft drag (3 composing 1 % of GCR flux Negatively charged electrons with a +1 (positron) or
1 (electron) charge and very small mass, electron beta particles moving near the speed of light are called “relativistic” Subatomic hadron particle, neutral charge, designation n0, GCR sources can have energies on the order of several joules Composed of photons at very small wavelengths, the corresponding energy can be approximated as E(eV) = 1.24/λ(μm) Produced by nucleon transition, designation, γ, wavelengths are 1019 Hz, produced by a variety of causes but in space, principally the result of particle-photon or particle-particle collision Produced by electron orbital transition, wavelength of 0.01–10 nm and frequencies ranging from 3  1016 to 2  1019 Hz At the high UV spectrum, wavelengths in the range of 10–400 nm have sufficient energy to ionize and to break up nuclei

particles resulting from collisions of space particles with the atmospheric such as pions and muons. These can, nevertheless, present a radiation hazard to highaltitude aircraft (Norbury 2010).

Sources of Radiation Ionizing radiation sources include galactic cosmic radiation (GCR) from outside our solar system and solar particle events (SPE) such as solar flares and coronal mass ejections from our sun. Both sources consist of electromagnetic and particle radiation. The relative abundances of the elemental composition of GCR compared to that of solar origin were compiled from various sources and reported by George et al. (2009) in Fig. 1. The abundance is scaled to silicon = 1,000 which is intermediate in weight. Notable differences are the relative lack of hydrogen and helium from GCR sources and the abundance of light elements (lithium, beryllium, and boron) in GCR which are rare in the solar system.

Solar Contributions Clouds of subatomic particles emanating in sporadic surges from the sun are known as solar particle events (SPE). The US National Oceanic and Atmospheric Administration (NOAA) quantitatively defines SPEs to occur when instruments on the

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Fig. 1 Solar and galactic cosmic ray (GCR) composition (George et al. 2009)

Geostationary Operational Environmental Satellite (GOES) measure an average solar proton flux greater than or equal to ten particles/(cm2 ster s) in three consecutive 5-min periods (Friedberg and Copeland 2011). At these times, peak radiation contributions are a result of localized active regions on and near the sun’s surface often solar flares and coronal mass ejections (CME). The exact nature and precipitating causes of SPE is the subject of ongoing research, but SPEs tend to be random occurrences that vary in severity following the 11-year solar activity cycle. Particle distributions consist of high atomic number and energy (HZE) nuclei, protons, electrons, and other energetic ions. It is thought that HZE particles are accelerated by coronal mass ejections (Kahler 2003), but a causal relationship is still being investigated. The proton flux is the highest component of SPE; however, the energetic “relativistic” electrons constitute a formidable threat capable of penetrating spacecraft shielding and depositing accumulated charge on dielectric materials leading to harmful discharge events (Baker 2005) (Fig. 2). Solar flares, with the sudden visible brightening, make for dramatic photography and news headlines, but hidden in this light show are ionizing particles and photons beyond the visible spectrum. Non-visible signatures can be detected at the earth’s surface even if the flare occurs on the back or side of the sun’s surface in areas not directly within the line of sight of the earth. After a solar flare occurs, particles start arriving to earth within tens of minutes with peak intensity occurring in a day or two. The ensuing clouds of charged particles, in addition to protons, include energetic electrons with some heavier elements interspersed. Of the heaviest elements such as iron (Z = 26), there are about 27,000 protons for every iron particle (Shea) with similar ratios within one order of magnitude for carbon, nitrogen, and

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Fig. 2 Giant prominence erupts 16 April 2013 (Figure Source: NASA)

oxygen. In addition to particles, electromagnetic emissions include massless ionizing radiation in the form of X-rays and gamma rays. The ensuing release and acceleration of particles during an SPE can reach fluxes exceeding 100 particles cm
2 s
1 ster
1 with energies greater than 10 MeV with some identified energies as high as 25 GeV. It would take 3  1010 of proton particles at this energy level to equal the kinetic energy of a baseball traveling at 90 mph. From 1970 to 2002, some catalogs record 253 SPEs with energy >10 Mev and peak fluxes of ten protons/cm2 s ster (Kurt et al. 2004). Lest the correct perspective be lost, it should be pointed out that solar flare activity and intensity has been fairly constant in the last ten million years (Shirley) only becoming relevant with the introduction of spaceborne technology.

Galactic Cosmic Sources Galactic cosmic radiation (GCR), originating from outside the solar system, is relatively stable and isotropic but contributes very high-energy particles, above 100 keV, to the total radiation environment. Particles from GCR consist mostly of atomic nuclei stripped of their electrons in the form of protons, alpha particles, and the nuclei of high Z elements. The most abundant particles are hydrogen and helium nuclei with fewer contributions from lithium, beryllium, boron, carbon, nitrogen, and oxygen in decreasing order of abundance. The GCR streams are relatively devoid of electron particles, which have been stripped by the magnetic fields surrounding the supernovae from which they originate (ASTM Special Technical Publication No. 330, Oct 1962). The species distribution of GCR particles is approximately 87 % protons, 12 % alpha nuclei (helium atoms), 1 % heavier nuclei, and 3 % high-energy electrons (Prantzos and Takahashi). The energy levels range

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from tens of MeV to about 1019 eV (Castellina and Donato 2010/2011), but the peak of the energy distribution is close to 0.3 eV. At these high energy levels, it would now only take 73 particles of 1019 eV energy to equal the energy of a baseball traveling at 90 mph. The high-energy content can produce showers of secondary particles through the process of spallation as they impact the atmosphere or spacecraft materials.

Plasmas Plasmas in space consist of disassociated protons and electrons in similar quantities resulting in an overall neutral charge but highly conducting. Because the energy content of the plasma particles considered here is lower than particles capable of ionizing, the charge accumulation collects on the surface of exposed spacecraft rather than deeply penetrating. The accumulation of a surface charge can lead to disruptive and lethal electrostatic discharge (ESD) events. The particles which make up the plasmas are on the order of 1 keV for protons in contrast to the energetic particles of tens to hundreds of keV capable of ion generation. Energy and density variation of the plasma environment ranges from about 0.1 eV and 103–105 particles/cm3 in LEO to 1 eV and 10–1,000 particles/cm3 in the magnetosphere to 1 particle/cm3 and thousands of eV in GEO (Valtonen 2005). Spacecraft surfaces such as solar panels and thermal control surfaces that start with a net positive charge will attract electrons from the plasma. This leads to a parasitic loss of power, surface charging, electrostatic discharge, and surface degradation over long-term exposure. Surface charging can encompass the entire satellite uniformly with a single potential relative to the ambient plasma potential, or it can consist of differential charge over the surface or between surfaces. Primary consequences of imbalanced spacecraft charges include disruption to onboard electronics and anomalous sensor signals but can also include material damage from arching. In addition, charged surfaces will attract contaminates, which affect thermal and optical properties of solar panels and optical sensors (Garrett and Whittlesey 2012). However, ESD was shown to be a primary cause of spacecraft mission anomalies and mission loss across the board of all potential causes. This conclusion was drawn from a survey of the cumulative number of anomaly reports across several agencies and databases (Koons et al. 2000).

Distribution of Radiation in Space Given the charged state of these particles, the spatial ordering in the vicinity of the primary satellite orbits is governed by the earth’s magnetosphere, which also acts as a global shield by attenuating all but the most energetic particles. As the earth’s magnetic field lines converge near the poles, the amount of shielding decreases, affecting spacecraft in high-inclination orbits. To be expected, along with magnetic repulsion is the confluence of the entrapment potential as well.

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Fig. 3 Van Allen belts (Figure Source: NASA)

The Van Allen radiation belt consists of trapped energetic charged particles that follow the earth’s magnetic field lines. The outer belt extends from 12,000 to 25,000 km altitude with a region of high intensity 5,000 km wide centered at an altitude of about 17,000 km. The outer belt consists mostly of electrons and occupies more volume than the inner belt. The inner belt, consisting of mostly protons, ranges from 1,000 to 8,000 km centered at 3,000 km, the region of the highest density of particles. Relative to popular satellite orbits, the majority of the traffic residing in LEO overlaps with the low-altitude portion of the inner Van Allen belt outside of the severest region. Estimates of the total number of active satellites are difficult to obtain but range from 800 to 1,000 with 50 % residing in LEO, 40 % in geostationary orbits (GEO), and the rest dispersed around MEO and other elliptical orbits. The second largest quantity of active satellites, those in GEO, resides at 35,863 km altitude just above the outer belt. Areas of highest concentration are typically avoided by spacecraft. However, flight through the Van Allen belts and into space beyond the geomagnetic shielding is necessary for interplanetary flight. Despite the constraining nature of the earth’s magnetic field lines, the abundance of ionizing particles in the Van Allen belts is by no means static but is continuously relieved and replenished as they interact with the solar activity and neutral particles in the earth’s atmosphere. It is in the regions of highest concentration that disruption to sensitive electronics, disruption to command and control functions, and damage to satellite thermal and power systems and tracking systems are of most concern (Fig. 3).

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Ionizing Radiation Effects on Electronics The race to achieve ever smaller electronic components is now graded by numbers of atoms. Innovative research has concluded that magnetic data storage unit sizes as small as 12 atoms are already feasible (Loth et al. 2012). As a result, radiation effects must also be resolved on a particle-by-particle basis. Single-particle incursions causing an immediate localized effect are known as a single event effect (SEE). The path leading to a SEE begins upon particle penetration leading to the transfer of ionizing energy to the atoms in the electronic materials along its trajectory. This incursion results in the creation of secondary ions, which constitute the mechanism that induces an SEE. SEE encompasses a range of corresponding electrical disturbances (recoverable or permanent) typically in the form of a bit flip in memory or a register. Latch-up can occur when the ion particle charge leads to large currents through the parasitic base regions of integrated circuits. Integrated circuits affected in this manner typically apply the use of complementary metal-oxide-semiconductor (CMOS) technology. The latched region can be permanently disabled through thermal runaway. Nondestructive SEE results in soft errors which are recoverable and do not change the functionality of the device but can disrupt or damage system functionality through a chain of fault events. SEE events can be further categorized into single event upsets (SEU), single event functional interrupts (SEFI), and single event transients (SET). As microelectronic technology advances, new disruptive mechanisms will likely be identified (Maurer et al. 2008). Solar ultraviolet and X-ray radiation have less potential than high-energy particles and gamma rays for deeply penetrating spacecraft skin even during solar flares and are thus not a threat to interior electronics. However, they do play a role in surface degradation of solar panels or other exterior surfaces. Particles, on the other hand, with sufficient initial energy upon entry (>25 eV) to liberate or add electrons to the atoms they strike along their path can have hazardous effects on interior electronics. The depth of penetration is a function of the energy content of the particle. For electrons of 50 keV or less and 1 MeV for protons, the penetration depth into aluminum is on the order of 0.01 mm, and the result is that most of the charge is deposited at the surface. Internal charging requires energies >100 keV for electrons and >5 MeV for protons resulting in penetration depths >0.1 mm (Valtonen 2005). The energy density along the strike path transferred into the ionization process is proportional to the energy lost as the particle is slowed along its trajectory into the material medium. As particles skid to a halt, the damage left in their wake includes the disruption of atoms in the medium potentially causing secondary ions. This is depicted in Fig. 4. The metric used to quantify the deposited energy is referred to as the linear energy transfer (LET) expressed as the differential dE/dx with units of keV/μm. The dependency of LET on the density of the traversed material can be taken into account by scaling LET with mass density resulting in LET units of MeV-cm2/mg. Cumulatively these lead to imbalanced charge states that upset the precise electronic states needed for binary control in

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Fig. 4 Mechanisms for single event effects (Sturesson 2009)

microelectronics. In silicon, for example, an LET of 97 MeV-cm2 corresponds to a charge deposition of 1 pC/μm (Schwank et al. 2008). In semiconductor materials, silicon in particular, the energy gap or bandgap energy between the conduction band and the valence band is small enough that a few electrons can cross the gap into the conduction band. Radiation energy disrupts this feature by contributing to the creation of electron-hole pairs when exciting an electron into the conduction band. The result is a hole left behind in the valence band which sets off a cascade of complex effects leading to a net charge buildup disrupting the state of the circuit. The disruption of the electron-hole pairs is cumulative and dependent on the total ionizing dose (TID) over the duration of the spacecraft mission. Maurer et al. (2008) describes the effects on digital microcircuits as being a result of a shift in metal-oxide-semiconductor (MOS) transistor threshold voltage (related to digital circuit power consumption and speed) from trapped charge. Linear microcircuits are said to exhibit performance changes as input bias current, offset, and drift are affected. Since the characteristics of the penetrating particle into the microelectronic material are initially fashioned by interaction with the spacecraft itself, an end-toend assessment is necessary with computational methods that take into account the governing principles. The NASA HZETRN (Wilson et al. 1995) is one such code that allows the design engineer to study the effects of various shielding materials on the internal radiation environment of a spacecraft. The prediction of particle impact as a stochastic event warrants the selection of an appropriate probabilistic method such as Monte Carlo for assessing overall risk. Once this is determined, an understanding of the physics of particle interaction can be assessed as a function of material properties and then multiplied by the number of expected events to arrive at the total ionizing dose (TID) accumulated during mission duration. Evaluated together, an end-to-end hazard assessment is possible that enables appropriate protective hardening, operational maneuvers, or other protective measures to be incorporated into the design of shielding concepts and deployment strategies for satellites and space probes.

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Spacecraft Charging Spacecraft charging research began in earnest with the launch of the SCATHA (Spacecraft Charging at High Altitudes), which sought to monitor the charging phenomena as a function of the parameters governing the plasma environmental and to detect the corresponding discharge events. Principle findings resulted in an understanding of the interaction of plasma and UV in the charging of dielectric materials and the need for incorporating enhanced conductivity in spacecraft materials (Fennel et al. 1985). Since then, advances in thin polyimide film research have led to specialized treatments such as indium tin oxide (ITO) coating or polyimide modifications such as Conductran™. Lai reports that current observations have further validated theoretical understanding of the critical electron temperature and voltage that delineates the onset of charging as predicted by a Maxwellian model (Lai 2007). Spacecraft charging effects generate the most interest for satellites at geosynchronous orbits. At these altitudes, communication satellites are predominate in the presence of higher-energy plasma particles albeit of lower density. The exact plasma boundaries are dynamically influenced by solar events that push against the sun-facing magnetosphere and elongate the opposite side out to hundreds of earth radii. The distortion of earth’s magnetosphere fields is depicted in Fig. 5 obtained from “Planet and Comets” published by the Max Planck Institute for Solar

Fig. 5 Magnetosphere (Figure source: Max Planck Institute for Solar System Research) (http:// www2.mps.mpg.de/en/forschung/planeten/)

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System Research. Also shown are important research satellites (SOHO, Wind, Cluster, Polar, Geotail). For low earth orbits on the other hand, charging is not as much of a concern since the energy content of the plasma is less than an eV. Exceptions to this include spacecraft with differentially charged external components or large aspect ratios that move perpendicular to the magnetic field lines. Depending on the type and energy content of the radiation exposure, surface orientation, and material type, spacecraft charging can take the form of either deep dielectric charging or surface charging. Deep dielectric charging is primarily driven by relativistic electrons capable of deeper penetration than ions of similar energy states. Conductive materials are not affected below the surface because penetrating electrons move back to the surface via Coulomb repulsion. However, surface charging can occur for both materials primarily as a result of less energetic particle plasma surface charge deposition. In both cases, detrimental effects can range in severity from electrical disturbances such as noise and anomalous measurements to mechanical damage from electrostatic discharge (ESD). Arching is induced by potential differences of 500 V or greater. As stated above, ESD was shown to be a primary cause of spacecraft mission anomaly and mission loss across the board of all potential causes as evidenced in the cumulative number of anomaly reports across several agencies and databases (Koons et al. 2000). The Low Earth Orbit Spacecraft Charging Design Handbook (NASA-HDBK-4006) includes a rare photograph example of arc discharge damage sustained on orbit. This occurred on a solar panel on the European Space Agency (ESA) European Retrievable Carrier (EURECA) spacecraft that was recovered by the Space Shuttle (Figs. 6, 7, and 8). Spacecraft charging is mitigated with three basic approaches as described in the Low Earth Orbit Spacecraft Charging Design Handbook (NASA-HDBK-4006). “One is to place the structure at the most positive potential generated by the LEO spacecraft power system (the positive ground option). The second is to ground the structure by brute force to the ambient plasma (the plasma contactor solution). The third is to prevent any plasma exposure of high-voltage conducting surfaces (the encapsulation solution).” Other solutions derived from here are included in Ferguson et al. (2002).

Surface Erosion Damage Mechanical effects are an issue primarily with susceptible external surfaces in direct exposure. Radiation alone is not to blame. A coupled damage process occurs which includes debris impacts, atomic oxygen interaction, and thermal cycling. Radiation contributes to the damage by inducing embrittlement. Because a majority of these surfaces are covered with various types of metalized polymer films, a great deal of research is focused on the development of resistant materials. This has led to a substantial amount of spacecraft material being composed of polymers and polymeric composites which exhibit favorable multipurpose characteristics. Prominent among the materials used are polybenzimidazole (high-performance fabrics

Solar Radiation and Spacecraft Shielding Fig. 6 Sustained arcing damage on the EURECA solar panel array (Ferguson and Hillard 2003)

Fig. 7 Photograph of embrittled and cracked Teflon FEP retrieved from the Hubble Space Telescope (Figure Source: NASA Glenn Research Center)

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Fig. 8 NASA image: ISS003E5863 – close-up of the experiment trays in MISSE, open and exposed to space

such as space suits), polyimide (cables, multilayer insulation), polyether ether ketone or PEEK (cable insulation, high-vacuum applications), perfluorinated polymers (Teflon ®, dielectric applications, coatings), epoxies, and silicones because of their favorable electrical, thermal, and mechanical properties (Bhowmik 2011). Degradation from radiation can include either embrittlement or softening (loss of tensile strength), depending on whether the polymer chains are cross-linked or degraded. In both cases, undesirable outgassing is also a result (Miller 1959). More recently developed polymers include high-temperature polyimide PMR (polymerization of monomer reactants). Radiation induced hardening of the materials can be caused by ionizing particles, vacuum UV, and possibly the X-ray component. Atomic oxygen effects can work synergistically to degrade exposed surfaces already embrittled by radiation. Mechanical effects from particle incursions include regions of disrupted lattice ordering that can affect mechanical properties and point defects which can combine to impede free lattice motion. This results in hardening and embrittlement. An accumulation of individual impacts can exacerbate these effects depending on the type of material and the length of time they are exposed. Particularly susceptible are external multilayer insulation (MLI) surfaces that rely on maximum surface area for effective thermal control. Necessary properties of the surface material are high reflectance, low solar absorptance, and high thermal emittance which are salient properties of optimized films such as MLI Kapton# with vapor-deposited aluminum (VDA) coatings and Teflon fluorinated ethylene propylene (FEP) (Dupont).

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Surface measurements and detailed microscopy of exposed surfaces retrieved from the Long Duration Exposure Facility (LDEF, 5.8 years in space) experimental satellite in 1990 and the Hubble Space Telescope (3.6 years in space) indicate a synergistic effect between solar-induced embrittlement and atomic oxygen-induced erosion with thermal cycling also playing a role. The mechanism is thought to be enhanced erosion facilitated by a hardened condition (de Groh and Smith 1997; Guo et al. 2012). Starting in 2001, the Materials International Space Station Experiments (MISSE) investigated the response of over 1,500 samples to the space environment. In MISSE 1 and 2, trays consisting of holders for over 750 samples of candidate spacecraft materials arranged side-by-side were affixed to the exterior of the international space station. After up to 2 years of exposure, the samples were retrieved for analysis. Various stages of damage were observed in the plastics and coatings including embrittlement, darkening, and severe erosion. In addition to these localized damage effects, a secondary consequence could be the associated change in reflective properties of external surfaces which is referred to as space ageing. From the perspective of ground observation and tracking functions, the actual optical signature of a spacecraft affected by space ageing will diverge from the expected signature when pristine material conditions are assumed. Validation of mathematical models for predicting spacecraft signatures by comparison with observational data will erroneously differ, particularly around expected specular peaks, depending on the severity and surface area of the aged material. Recognizing this discrepancy, databases of optical properties for aged materials are being assembled (Khatipov 2006). Because of the large trade space available for external MLI blanket design, advanced materials research appears to be the best avenue for hazard mitigation. For highly developed materials composing microelectronics, other mitigating options are needed.

Total Ionizing Dose Rates The accumulation of single-particle events from both GCR and SPE must be taken into consideration over the mission life of spacecraft. Highest dose rates are encountered at geosynchronous altitudes, high-inclination orbits, and the inner radiation belt region, particularly following a major solar flare. Low-inclination orbits allow for better geomagnetic shielding of the GCR and solar radiation sources. The deposition of ionizing energy by a charged particle per time is known as the dose rate measured as energy per mass per time. In terms of energy loss along the particle trajectory in the material (stopping power), the governing expression, known as the Bethe-Bloch formula, is extensive but has been reduced to a proportionality by Valtonen:


ðdE=dxÞ / nz2 Z = mv2 Where z is the charge number, m is mass, and v is velocity of the impacting particle, n is the number density and Z is the charge number of the medium (Valtonen 2005).

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Integrating this expression times the particle flux rate over the life of the mission provides the total ionizing dose (TDI). Although the overall dose rate is low for most spacecraft, ranging from 10
4 to 10
2 rad/s, the exposure time of typical spacecraft mission lifetimes can accumulate 105 rad depending on incident particle energy and the charge or Z of the particle (Maurer et al. 2008).

Shielding Concepts for Spacecraft The remarkable creativity seen in the development of various radiation shielding concepts invokes an analogy to ancient development of shield and armor defensive concepts against lethal projectiles. However, the simple analogy breaks down when considering the complex nature of radiation effects on spacecraft components. For this reason, decades of research have been required. First steps involve some type of passive shielding. Passive shielding relying on mass to deflect and absorb energetic particles has been the baseline concept for spacecraft radiation protection. Here also, the concept is not simple. Spacecraft shielding itself can contribute to secondary radiation as highly energetic particles transverse the atomic lattice of the shielding material creating secondary radiation. Studies (Kim et al. 1994) have shown that shielding materials composed of the least amount of nucleons (protons and neutrons) such as liquid hydrogen, water, and polyethylene provide more protection from secondary radiation than heavier elements such as aluminum or lead. Low nucleon materials will also minimize the occurrence of bremsstrahlung photons, but the shielding requires increased thickness to simultaneously shield against beta radiation incursion as well. One shielding concept that seeks to achieve high strength while leveraging on the benefits of low nucleon hydrogen suggests the need to apply high hydrogen polymers combined with boron nitride nanotube (BNNT) technology to formulate a composite material suitable for load bearing applications (Thibeault 2012). High-density shielding materials, on the other hand, have the advantage of requiring less volume, which is important in areas of restricted space such as compartments for microelectronic components. Additionally, there is the potential advantage of heat-sink cooling through the superior conductive properties inherent in high-density metals. In terms of electron repulsion, high Z atomic properties make these materials effective at reducing radiation from low-energy electrons and protons because they are more effective at scattering electrons. However, they are less effective at stopping the high-energy electrons and secondary ions resulting from cosmic rays. They also generate higher bremsstrahlung photons. Because of these additional considerations, high-density shielding has little effectiveness at preventing SEE. For now, mitigation of SEE is better achieved by a combination of error detection and correction (EDAC), anomaly detection and reboot, and redundancy. A combination of shielding, derating (intentionally reducing operating parameters such as supply voltage and junction temperature), and operational control is best suited for reducing cumulative ionization and displacement damage (Maurer et al. 2008).

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At first glance, the concept of active shielding against radiation appears futuristic. Active shielding, as opposed to passive shielding, involves dynamic protective measures that require some type of ongoing energetic or informational input to function. These types of shielding concepts have, in fact, been investigated for more than 40 years (Sussingham 1999). Most of the concepts are based on the fundamental property of electromagnetic deflection of charged particles. Initial concepts involved enveloping the spacecraft with an electric or plasma shield but were eventually abandoned for various reasons having to do with the complexity of the required systems. Other notional concepts involve the application of superconductors or artificial magnetospheres, but this is problematic due to high energy requirements. Viable concepts have yet to gain momentum. The achievement of an optimum balance of protective properties is the subject of intense continuing research and model development. But it can be broadly stated that optimization of passive shielding design must consider weight constraints, durability, flexibility, and particle stopping effectiveness to list a few. Simulation of secondary radiation effects has been practically applied to the engineering design of shielding concepts. A combination of first-principles transport codes and Monte Carlo probabilistic codes can address both the statistical nature of the impact and the physical phenomena occurring once the impact has taken place.

Forecasting the Space Environment An important aspect of spacecraft protection is the avoidance of the hazard in the first place. For this to be feasible, our current understanding of space weather requires a significant leap ahead. Having access to accurate space weather forecasts would reduce the need for costly shielding design by allowing overly conservative criteria to be relaxed. However, the advantages extend beyond shielding to include avoidance of continent-wide terrestrial power disruptions. For purposes of spacecraft protection, however, the origin, dynamic evolution, and forecasting of damaging radiation in the vicinity of spacecraft orbits are also an important motivating factor spurring the advancement of the space weather research. As the theoretical basis is better understood, we are gaining a significant hazard-avoidance advantage – the ability to forecast the space weather ahead of time. At present, the physical complexity of the coupled phenomena remains formidable. Normally, with theoretical model development, initial understanding can be gained with the application of empirically based methods, as used by Martin, to understand the magnetic field geometry of CME events (Martin and McAllister 1997). In 1997, the relationship between solar flares and CME was only beginning to be understood (Cane 1997). As the physics basis improves, so does the confidence and flexibility of application to a broader range of weather conditions that can be predicted further into the future. In 2002, Huston reported that uncertainties in the standard AP8 and AE8 models for predicting trapped proton and electron environments were a factor of two and an order of magnitude, respectively, when compared with several sets of flight data (Huston 2002). At the present time, protection schemes are primarily

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based on conservative designs to withstand the upper threshold of severity. This has functioned well up to now as there are few catastrophic failures among the multiple hundreds of civilian and military spacecraft (Baker 2005). Nevertheless, the ability to forecast space weather will be revolutionary for satellite protection.

Conclusion This chapter covers a broad range of multidisciplinary fields that only scratches the surface of the depth involved in each. However, it provides a bird’s-eye view of the enormity of the task needed to take us to the point where we can forecast space weather as confidently as we do now with atmospheric weather. This is essential for long-term spacecraft protection. Present shield design has relied on conservative estimates, which have served well up to now. In the long term, shield design based on these conservative assumptions will become prohibitively expensive given the population increase in space and heavier reliance on everincreasing miniaturization of microelectronic systems. High fidelity models based on an understanding of the governing physics will be necessary to optimize shield design and to estimate consequences. While radiation in space threatens the entire satellite, the consensus of research seems to point to microelectronic components (with the exception of biological systems) as the Achilles heel leading to mission failure. Research and development will have to make exponential progress to keep pace with the increasing access and sustainment needs of the space environment.

Cross-References ▶ Coronal Mass Ejections ▶ Dashboard Display of Solar Weather ▶ Economic Challenges of Financing Planetary Defense ▶ Fundamental Aspects of Coronal Mass Ejections ▶ Medical Concerns with Space Radiation and Radiobiological Effects ▶ NOAA Satellites and Solar Backscatter Ultra Violet (SBUV) Subsystems ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Flares

References American Society for Testing Materials, committee E-10 on radioisotopes and radiation effects (1962). Space radiation effects on materials. (ASTM special technical publication no. 330) Philadelphia Baker DN (2005) Introduction to space weather. Lect Notes Phys 656:3–20 ¨ chsner A, Adams RA (eds), Bhowmik S (2011) Effect of radiation and vacuum. In da Silva LFM, O Handbook of adhesion technology (pp. 823–844). Berlin/Heidelberg: Springer

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Cane HV (1997) The current status in our understanding of energetic particles, coronal mass ejections, and flares. Appearing in the geophysical monograph 99 series, Coronal Mass Ejections, The American Geophysical Union Castellina A, Donato F (2011). Astrophysics of galactic charged cosmic rays. Springer Reference Library. doi:10.1007/978-94-007-5612-0_14 de Groh KK, Smith DC (1997) Investigation of teflon FEP embrittlement on spacecraft in low-earth orbit. NASA Technical Memorandum 113153 Fennel JF, Koons HC, Leung MS, Paul MF (1985) A review of SCATHA satellite results: charging and discharging. Air Force Systems Command (AFSC) report, SD-TR-85-27, 12 Aug 1985 Ferguson DC, Hillard GB (2003) Low earth orbit spacecraft charging design guidelines. NASA/ TP—2003-212287 Ferguson DC, Hillard GB, Vayner BV, Galofaro JT (2002) High voltage space solar arrays. In: 53rd international astronautical congress of the International Astronautical Federation (IAF), Houston, IAC paper 02 IAA.6.3.03, 10–19 Oct 2002 Friedberg W, Copeland K (2011) Ionizing radiation in earth’s atmosphere and in space near earth. Final report DOT/FAA/AM-11/9, May 2011 Garrett HB, Whittlesey AC (2012) Guide to mitigating spacecraft charging effects, 1st edn. Wiley, Hoboken, # 2012 John Wiley & Sons George JS et al (2009) Elemental composition and energy spectra of galactic cosmic rays during solar cycle 23. Astrophys J 698:1666. doi:10.1088/0004-637X/698/2/1666 Guo A et al (2012) Embrittlement of MISSE 5 polymers after 13 months of space exposure. NASA/TM—2012-217645, Sept 2012 Huston SL (2002) Space environments and effects: trapped proton model. NASA/CR-2002211784 Kahler SW (2003) Energetic particle acceleration by coronal mass ejections. Adv Space Res 32(12):2587–2596 Khatipov SA (2006) Simulated aging of spacecraft external materials on orbit. In: Advanced Maui Optical and Space Surveillance (AMOS) technologies conference, Maui, Hawaii, 2006 Kim MY et al (1994) Performance study of galactic cosmic ray shield materials. NASA technical paper 3473, Nov 1994 Koons JE et al (2000) The impact of the space environment on space systems. In: 6th Spacecraft charging technology conference, Hanscom air force base, Massachusetts, 1 Sept 2001 Kurt V et al (2004) Statistical analysis of solar proton event. Ann Geophys 22:2255–2271 Lai ST (2007) Spacecraft charging – present situation and some problems. In: AIAA plasmadynamics and lasers conference, 28 June 2007, Miami, Fl Loth S et al (2012) Bistability in atomic-scale antiferromagnets. Science 335(6065):196–199. doi:10.1126/science.1214131 Martin SF, McAllister AH (1997) Predicting the sign of magnetic helicity in erupting filaments and coronal mass ejections. Coronal mass ejections, geophysical monograph 99, The American Geophysical Union Maurer RH, Fraeman ME, Martin MN, Roth DR (2008) Harsh environments: space radiation environment, effects and mitigation. John Hopkins APL Techn Digest 28(1):17–29 Miller AA (1959) Effects of high-energy radiation on polymers. Ann N Y Acad Sci 82:774–781. doi:10.1111/j.1749-6632 NOAA Space Weather Prediction Center Space weather prediction center topic paper: satellites and space weather. http://www.swpc.noaa.gov/info/Satellites.html Norbury JW (2010) Pion production data needed for space radiation. In: 40th international conference on environmental systems, Obtained from NASA Technical Reports Server (NTRS), 12–15 July 2010 Prantzos N, Takahashi J Cosmic rays (in the Galaxy). Springer Reference Library Schwank JR, Shaneyfelt MR, Dodd PE (2008) Radiation hardness assurance testing of microelectronic devices and integrated circuits: radiation environments, physical mechanisms, and

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Part VII Geomagnetic Storm and Substorm Missions

Similar to the deep space probes that are instrumented specifically to measure solar radiation, there are many Earth-monitoring spacecraft especially designed to monitor the Earth’s magnetic field and how it serves as a protective shield against solar storms and coronal mass ejections. This section presents descriptions of the many spacecraft that have provided – and in some cases continue to provide – the critical data needed to understand the current state and longer-term functioning of the geomagnetosphere. Also presented in this section are the results of earlier missions as well as the latest data from the recently launched Van Allen Storm Probes.

Cluster Technical Challenges and Scientific Achievements C. P. Escoubet, A. Masson, H. Laakso, M. G. G. T. Taylor, J. Volpp, D. Sieg, M. Hapgood, and M. L. Goldstein

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Building, Integrating, and Testing Four Spacecraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ariane V Launcher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Payload: 55 Instruments to be Built, Calibrated, and Integrated . . . . . . . . . . . . . . . . . . . . . . . . . . Electromagnetic Cleanliness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cluster Rebuilt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orbit and Constellation Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operations: Four Spacecraft for the Cost of One . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recovery of the Five Wave Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Science Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ripples on the Bow Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electric Current and Kelvin-Helmholtz Waves at the Magnetopause . . . . . . . . . . . . . . . . . . . . .

319 319 319 320 322 323 324 325 327 329 330 331 332

C.P. Escoubet (*) • A. Masson • H. Laakso • M.G.G.T. Taylor ESA/ESTEC, Noordwijk, The Netherlands e-mail: [email protected]; [email protected]; [email protected]; [email protected] J. Volpp • D. Sieg ESA/ESOC, Darmstadt, Germany e-mail: [email protected]; [email protected] M. Hapgood RAL Space/STFC, Harwell, Oxford, UK e-mail: [email protected] M.L. Goldstein NASA/GSFC, Greenbelt, MD, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_30

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Bifurcated Current Sheet in the Plasmasheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electron Pressure Tensor Near Magnetic Reconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acceleration of Electrons by Coronal Mass Ejections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cluster Guest Investigator Programme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cluster Open Access to all High-Resolution Data Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

333 333 336 337 337 341 341 342

Abstract

The Cluster mission has been operated successfully for 14 years. As the first science mission comprising four identical spacecraft, Cluster has faced many challenges during its lifetime. Initially, during the selection process where strong competition with SOHO was almost fatal to one of them, finally both missions were merged into the Solar Terrestrial Science Programme with strong support from NASA. The next challenge came during the manufacturing process where the task to produce four spacecraft in the time usually allocated to one demanded considerable flexibility in the production process. The first launch of Ariane V was not successful, and the rocket exploded 40s after takeoff. The great challenge for the Cluster scientists was to convince ESA, the National Agencies, and the science community that Cluster should be rebuilt identical to the original one. The fast rebuilding phase, in 3 years, and the 2nd launch on two Soyuz rockets, paved the way to numerous ESA launches afterward. Finally in the operational phase, the challenge was to operate four spacecraft with the funding for one, to solve serious anomalies, and to extend the spacecraft lifetime, now seven times its initial duration with some vital elements such as batteries not working at all. After the technical challenges, the key scientific achievements will be presented. The main goal of the Cluster mission is to study in three dimensions small-scale plasma structures in key plasma regions of the Earth’s geospace environment: solar wind and bow shock, magnetopause, polar cusps, magnetotail, plasmasphere, and auroral zone. Science highlights are presented such as ripples on the bow shock, 3D current measurements and Kelvin-Helmholtz waves at the magnetopause, bifurcated current sheet in the magnetotail, and the first measurement of the electron pressure tensor near a site of magnetic reconnection. In addition, Cluster results on understanding the impact of coronal mass ejections (CME) on the Earth’s environment will be shown. Finally, how the mission solved the challenge of distributing huge quantity of data through the Cluster Science Data System (CSDS) and the Cluster Archive will be presented. Those systems were implemented to provide, for the first time for a plasma physics mission, a permanent and public archive of all the high-resolution data from all instruments. Keywords

Sun-Earth connection • Magnetosphere • Multi-point measurements

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Introduction Cluster was selected, together with the Solar and Heliospheric Observatory (SOHO), as the Solar Terrestrial Science Programme, the first cornerstone of ESA’s Horizon 2000 program. The selection process took four years since both Cluster and SOHO were in competition and ESA funding was only available for one. Substantial descoping took place during Phase A where the payloads of both Cluster and SOHO were reduced. Furthermore, a large collaboration was opened with NASA, and a memorandum of understanding was agreed where NASA was providing the launch and conducting the operations of SOHO as well as providing support to Cluster and SOHO spacecraft and payload elements. The Science Programme Committee approved Cluster and SOHO in 1986, and, following an announcement of opportunity, the 11 Cluster instruments were selected in 1988.

Technical Challenges Building, Integrating, and Testing Four Spacecraft The main challenge of the Cluster mission was to produce four identical spacecraft in the time allocated and for the cost of one spacecraft (Credland et al. 1997). Since four spacecraft are not really a series, such as nowadays GPS or Galileo satellites, and at the same time are much more than one spacecraft, the production line has to be adapted in between a one-off, which is usually used in the Science program, and a series production line. The spacecraft were designed to be modular, where integration of instruments and subsystems could be rearranged to fit the delivery of the various units. All elements that constituted the spacecraft were so numerous that they had to be built in series. For instance, the four spacecraft were equipped with 16 deployable rigid booms for communications and magnetometers, 16 43 m long wire booms to measure electric field and waves, 320 m of pipes for the propulsion system connecting four main engines and 32 thrusters, 20 km of harness, 1,500 connectors, and 56,000 electrical connections. An invitation to tender was issued by ESA in 1988 to build the four spacecraft, and the prime contractor, Dornier GmbH (Friedrichshafen, Germany), was selected in 1989. After a design phase of about 1.5 years, the building of the spacecraft took place between April 1991 and April 1995. Parallel integration of the four spacecraft was the norm as well as parallel system testing. The system level testing required over 2 years in IABG (Ottobrunn, Germany), making it one of the longest in an ESA program. When a problem was occurring with one subsystem, it was quickly exchanged with the second model, and the test could be continued without losing significant time waiting for repair. This flexibility in integration and testing was possible due to the full traceability of hardware and software. Since it was mandatory to achieve identical spacecraft and instruments, knowing that each unit may have been slightly different, performances and calibration curves of each unit had to be tracked carefully.

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Fig. 1 The four Cluster spacecraft displayed in the clean room at IABG (Ottobrunn, Germany). The background pair is in a stacked launch configuration, while the two front spacecraft show the instruments and booms on the main equipment platform

The Cluster spacecraft are large cylinders of 2.9 m diameter and 1.3 m height. Their mass at launch was 1,200 kg, including 650 kg of propellant to achieve the delta V of 2,300 m/s required by the mission. Most of the propellant (500 kg) was used to transfer the spacecraft from geo-transfer orbit to the operational orbit. The rest was used for attitude maneuvers and to change the separation between the spacecraft. For the orbit injection, a large 400 N engine was used a few times and once in the operational orbits, and after deploying the instrument and communication booms, only the 10 N thrusters were used. Figure 1 shows the four spacecraft after testing in the clean room at IABG, Ottobrunn (D). The original proposed payload was significantly different from the final one, mainly because the original proposal was based on a main spacecraft with a complete payload and three companions with a reduced payload. However, it turned out to be simpler and cheaper to build, integrate, test, and launch four identical spacecraft. The final payload flown on each spacecraft (Table 1) is therefore close to the original main spacecraft.

Ariane V Launcher Cluster and Ariane V were developed in parallel. It brought a number of challenges on the Cluster side since the specifications and especially shock requirements were not really known when Cluster was being built. The shock

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Table 1 The 11 instruments on each of the four Cluster spacecraft. History of PI ships is also given Instrument/principal investigator (current and previous) ASPOC (Spacecraft potential control) K. Torkar (IRF, A) W. Riedler (IRF, A) 1988–2001 CIS (Ion composition 0 < E < 40 keV) I. Dandouras (IRAP/CNRS, F) H. Reme (IRAP/CNRS, F) 1988–2007 EDI (Plasma drift velocity) R. Torbert (UNH, USA) G. Paschmann (MPE, D) 1988–2006 FGM (Magnetometer) C. Carr (IC, UK) E. Lucek (IC, UK) 2005–2012 A. Balogh (IC, UK) 1988–2005 PEACE (Electrons, 0 < E < 30 keV) A. Fazakerley (MSSL, UK) A. Johnstone (MSSL, UK) 1988–1997 RAPID (High energy electrons and ions) P. Daly (Gottingen U., D) B. Wilken (MPAe, D) 1988–1999 DWPa (Wave processor) M. Balikhin (Sheffield, UK) H. Alleyne (Sheffield, UK) 1996–2011 L. Woolliscroft (Sheffield, UK) 1988–1996 EFWa (Electric field and waves) M. Andre´ (IRFU, S) G. Gustafsson (IRFU, S) 1988–2000 STAFFa (Magnetic and electric fluctuations) P. Canu (LPP, F) N. Cornilleau-Werhlin (LPP, F) 1988–2010 WBDa (Electric field and wave forms) J. Pickett (IOWA, USA) D. Gurnett (IOWA, USA) 1988–2008 WHISPERa (Electron density and waves) J.-L. Rauch (LPC2E, F) J.G. Trotignon (LPC2E, F) 2007–2012 P. Decreau (LPC2E, F) 1988–2007 Total

Mass (kg) 1.9

Power (W) 2.7

10.8

10.6

10.5

9.1

2.6

2.2

6.0

4.2

5.7

4.5

2.9b

4b

16.2

3.7

5.0

2.8

1.8

1.7

1.8

1.8

65.2

47.3

a

Members of the wave experiment consortium (WEC) b Including power supply

requirements were therefore very high, and the Cluster spacecraft and instruments had to be built extremely solidly in order for them to survive during launch. Furthermore, very late in the program when the Cluster spacecraft were built, Ariane V engineers realized that shocks could indeed be even higher during the separation of launcher elements. Cluster had to demonstrate that it could also survive these shocks.

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The launch mass available for the four spacecraft was very constrained since for a long time Cluster had to be compatible with an Ariane 4 launch, which was the backup launcher. The spacecraft mass limit was 4,800 kg for the four spacecraft, and the total Cluster mass ended up at 4,707 kg. Continuous efforts were necessary on both the spacecraft and the payload side to keep the mass below the limit during the manufacturing process. Experiment box walls had to be made thinner, and some instruments even used magnesium for their electronic box (e.g., WBD). The monitoring of both project and instrument teams was essential to achieve the required result.

Payload: 55 Instruments to be Built, Calibrated, and Integrated The payload of Cluster (Table 1) (Escoubet et al. 1997 and reference therein) posed a great challenge to the Europeans and American institutes involved. This was the first time that small teams of engineers were requested to build, test, and calibrate five identical suites of instruments (four flight units and one spare). Altogether, with 11 PI teams, the total number of instruments was 55. Something that could be done in industry by bringing more manpower could not be done easily in small institutes that had fixed numbers of engineers and scientists. The institutes had therefore to allocate more manpower to Cluster, but also the engineers had to work longer hours and sometimes weekends to deliver their instruments on time. The fact that one model had to be built, another one to be calibrated, another to be delivered, and the last one to be tested on the spacecraft at the same time posed great difficulties to the PI teams. It was almost unbearable to the point that when Cluster II had to be rebuilt, some engineers did not want to repeat the experience and it was necessary to train new people to do the work. The major challenge, which was driven by the science goal to derive plasma parameters from the four Cluster measurements, was to make the instruments as identical as possible. Some instruments, which were simpler in design, were easier to produce; however, their requirements were also more difficult to achieve. For instance, the PEACE (electron instrument) PI (Johnstone et al. 1997) required that their two sensors on two different Cluster spacecraft to differ by less than 1 % in the same plasma. To achieve that goal, the design of the instrument required a positioning of the hemispheric deflectors to within 40 μm. The first model could only achieve 80 μm, and a complete redesign was performed to finally reach 37 μm. These efforts were essential to measure for the first time the divergence of the electron pressure tensor and to better understand the magnetic reconnection process (see below). For the five wave instruments, their key requirement was to get the best time accuracy possible to compare measurements at high frequencies between the four spacecraft. The accuracy of the Cluster onboard clock was 2 ms which was clearly not enough to compare wave data at 180 Hz (frequency of the wave form data collected by STAFF and EFW in burst mode). The Cluster spacecraft time accuracy could not be improved significantly at that time due to cost constraints. This is why

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the Digital Wave Processor (DWP) was charged to coordinate all five wave instruments and to improve significantly the time accuracy (Woolliscroft et al. 1997). This finally was achieved using DWP, the spacecraft time correlation performed by ESOC on regular basis and the NASA Wide Band (WBD) time measurements. The accuracy of the wave instrument time is now down to 20 μs (Yearby et al. 2013). One of the prime objectives of the Cluster mission was to measure electric currents in space. To achieve it, a very precise measurement of the magnetic field was required since the magnetic field gradients between the spacecraft are used to deduce the current. With a very extensive electromagnetic cleanliness program (see below) and in-flight calibration, the goal of 0.2 nT accuracy was successfully achieved (Balogh et al. 2001; Carr et al. 2013).

Electromagnetic Cleanliness The Cluster scientific objectives required measuring the electric and magnetic fields and electromagnetic waves in the plasma around the spacecraft with very high accuracy. Therefore the spacecraft and its subsystems as well as the instruments needed to be electromagnetically clean. The importance of this requirement was recognized very early in the Cluster development program, and a special Electromagnetic Cleanliness (EMC) review board was set up, made of scientists and engineers, to monitor the EMC program. First all components used to manufacture the instruments and subsystems were selected to be nonmagnetic, so far as was possible. Then magnetic moments of all units were measured before integration, and an overall spacecraft model was produced. The magnetometers, FGM (flux gate) and STAFF (search coil), were put at the tip of a 5 m solid boom to minimize any magnetic field produced by the spacecraft. However, verification was needed to see if the spacecraft would produce a strong magnetic field at the end of the boom. The 5 m boom had therefore to be deployed, which constituted a challenge for a rather heavy device in the Earth’s gravity (this boom was supposed to deploy only in space). A smart Dornier engineer found a great and simple system to overcome this problem: he hung the boom from a helium-filled balloon, which compensated for the weight of the boom. A small propeller was then attached to the boom to simulate deployment at the proper speed. In the late 1980s, space batteries were usually made of nickel-cadmium (e.g., SOHO) and were strongly magnetic. On Cluster, which required a very low magnetic field produced by the spacecraft, such batteries could not be used. It was therefore decided to use silver-cadmium batteries, which were nonmagnetic. These batteries have been much less frequently used in space missions because they degrade quickly and can crack and expel electrolyte when overcharged. Consequences on operations will be detailed later. Once the four spacecraft were assembled, they were brought to the IABG MSFA (Ottobrunn, Germany) Magnetic Test Facility where the Earth’s magnetic field is compensated and the real spacecraft magnetic field could then be measured.

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Three of the spacecraft were found outside of the specification of 0.25 nT at the end of the 5 m boom. They were in the range 0.6–1 nT. A long compensation program started where small magnets had to be glued on strong magnetic spot found on the spacecraft (e.g., the thruster valves) to decrease the spacecraft magnetic field. After this meticulous work, the spacecraft magnetic field at the end of the boom was found to be around 0.12 nT, better than the requirement of 0.25 nT. Another important element in EMC is conductivity. In sunlight, a spacecraft produces photoelectrons on its sunlit side and therefore charges positively. On the other hand its shadowed side does not charge since there are no photons to extract electrons. If the spacecraft is not fully conductive, then there will be buildup of charges, and these will greatly affect the motion of low energy particles that must be measured by the plasma instruments. The Cluster spacecraft needed therefore to be fully conductive. All external layers of Cluster, solar panels, and the multilayer insulations (MLI) were coated with indium tin oxide to achieve that requirement. Then conductivity was checked over the surface of the spacecraft with many local measurements. During testing it was found that the MLI lost its conductivity when folded at spacecraft corners, and special conductive bridges were then added in those places to maintain conductivity. Sensitive electromagnetic wave measurements also require a very clean spacecraft since some of the waves are coming from large distances away from the spacecraft and have a weak signal that can be swamped by spacecraft subsystems or instruments. Special radiated emission and radiated susceptibility tests were performed to verify that the spacecraft would not perturb the very sensitive wave instruments. After launch and after the first switch on of the STAFF instrument, the PI stated that Cluster was one of the cleanest spacecraft she had put an instrument on. This was a real achievement that all teams were very happy to hear. However, some interference which was inherent to the experiment techniques employed could not be totally suppressed. For instance, the EDI instrument, measuring electric fields by sending an electron beam around the spacecraft, had an effect on the measurements of high-frequency electric waves and sometimes on the spacecraft potential. After analyzing the data, the PIs agreed to start time sharing: EDI would alternate every orbit their operation mode in low, normal, and high beam current, and the ASPOC instrument, controlling the spacecraft potential control, would be switched on during EDI high-current mode. This helped all PIs to get clean data for their investigation. Furthermore a special interference campaign was conducted at the end of the instrument commissioning where the active instruments run through various modes and instrument disturbances could be checked.

Cluster Rebuilt After the failed launch on 4 June 1996 of the Ariane V carrying all four Cluster spacecraft, the team of engineers and scientists saw their hopes dashed in less that 40 s. However, shortly after the failure, the Cluster Science Working Team (SWT)

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and the project team investigated ways to recover the mission (Credland and Schmidt 1997; Schmidt et al. 1997a). To keep the teams in place and not to lose time if a decision to rebuild the four Cluster spacecraft would be taken, it was decided to refurbish the spare model of the spacecraft and instruments. This model was called Phoenix as a reminder to the four original Cluster spacecraft that had burned in the explosion of the first Ariane V rocket. However, the community, although agreeing to build Phoenix, was clearly stating that one spacecraft only would not recover the science objectives of Cluster. It was therefore decided to study two options to recover the original Cluster scientific objectives; the name given to this new mission was Cluster II. The first option (Option 1) was to rebuild four original Cluster spacecraft, including Phoenix. The spacecraft and instruments would be identical to the original ones and could therefore be built in a fast track to be ready less than 3 years later. The launch could be a single one or multiple ones using spare capacity on already planned launches. The second option (Option 2) was based on a small spacecraft platform to be launched in pairs on a Ukrainian Tsyklon rocket. A kickstage would raise apogee to 18.5 RE, and the fuel needed on the spacecraft would be limited to constellation and attitude maneuvers. Such option would have required changes to ESA’s management structure. Option 1 was preferred by the Cluster SWT and by the majority of delegations in the Science Programme Committee since it carried less risk, was not substantially more expensive, had minimal cost for the payload, and could be launched one year earlier than Option 2. Furthermore ESA, after long negotiation, managed to keep the overall Cluster II option 1 cost to under 214 Meuros, including two Soyuz rockets for 60 Meuros and a contribution to the payload of 17.5 Meuros. In addition, NASA agreed to support rebuilding the US-provided instruments. This was accomplished, in part, by lifting several Quality Assurance requirements. At its meeting on 3 April 1997, the Science Programme Committee agreed to the recovery of the Cluster mission, called Cluster II, using identical spacecraft and payload as the original Cluster mission. Phoenix and three new spacecraft were then built in three years and successfully launched on 16 July and 9 August 2000 with two Soyuz rockets from Baikonur (Escoubet et al. 2001). With Cluster I and Cluster II, the teams of engineers and scientists had built 8 science spacecraft and more than 100 instruments in a total of 11 years, which is an extraordinary achievement, rewarded by fundamental science and discoveries made over the past 14 years.

Orbit and Constellation Changes The orbit of Cluster was designed to cross key regions of the Earth’s environment: bow shock, magnetopause, polar cusp, magnetotail, plasmasphere, and the auroral zone. The polar cusp, being above the pole of the Earth, required the orbit to have a high inclination, close to 90 . On the other hand, to study the magnetotail and bow

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Fig. 2 Sketch of the Cluster orbits in 2001, when it was polar, and in 2010, when the inclination and perigee decreased. The yellow orbit is during fall when the apogee is in the tail, and the red orbit is during spring when the apogee is in the solar wind. Two tetrahedra were formed at two locations along the orbit to maintain a good 3D configuration throughout apogee

Table 2 Cluster II spacecraft mass Dry mass (kg) Propellant (kg) Total launch mass

C1 FM5 532 650 1,182

C2 FM6 541 650 1,191

C3 FM7 529 650 1,179

C4 FM8 544 650 1,194

C2 and C4 are heavier since they carry the separation system for the other two spacecraft

shock required an apogee above 15 RE. The selected orbit was 4  19.6 RE with 90 inclination (Fig. 2, solid lines). Each spacecraft had a slightly different orbit to form two tetrahedra along the orbit in the key scientific regions: in the Northern polar cusp and Southern magnetopause in spring and at two places above and below the plasma sheet in the magnetotail in fall. Although requiring a bit more fuel to set up, these two tetrahedra had the great advantage to get an almost perfect tetrahedron in a large area of the magnetotail and the solar wind, which was essential for 3D measurements. With the Soyuz launch into a transfer orbit, a major change in the orbit was required to reach the nominal required operational orbit. This was done using the spacecraft themselves, which carried more than 600 kg of fuel representing more than half of each spacecraft mass (Table 2). Out of such large amount of fuel, about 80 % was used to increase the apogee and perigee altitudes and change the inclination. With the 63 kg of fuel left (not counting oxidizer) on each spacecraft, the separation distances between the spacecraft, as well as the points where the perfect tetrahedron was placed, were changed during the course of the mission (Fig. 3). At the beginning of the mission, constellation maneuvers were performed every 6 months; then after two years it was changed to once a year with two tetrahedra of different sizes for the tail and the polar cusp. A multi-scale formation is flown since 2006 with C1, C2, and C3 forming a large triangle of a few 1,000 km and the C4 distance with C3 being varied from a few km to a few 1,000 km. Since 2011, with the opening to Guest Investigator operations, maneuvers were performed every 3–4 months.

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Fig. 3 Cluster constellation from the beginning of mission up to now. The distance between the spacecraft is given as a function of time: C1-C2-C3 separation distance in magenta and C3-C4 in green. The distance is given at one point along the orbit defined by the symbol and color in the legend

At the beginning of the mission, the smallest inter-spacecraft distance that was considered safe was 100 km. This was achieved at the beginning of 2002 and brought a wealth of new results and discoveries (Paschmann et al. 2005). However the science investigations required smaller distances, and the distance of 40 km was reached between two Cluster spacecraft in 2008–2009, 20 km in 2011, and finally 4 km in 2013. Careful preparation is required to achieve such small distance since it approaches the accuracy in knowing the position of the spacecraft. Furthermore, the Cluster spacecraft have very long wire booms of 88 m tip to tip, which makes their cross section fairly large. The requirement on the accuracy of the position, which is determined using ground station ranging with the spacecraft, was initially 10 km for an inter-spacecraft distance of less than 1,000 km. After launch, the European Space Operations Centre (ESOC) flight dynamics team could achieve an accuracy below 1 km. This experience could be useful for future multi-spacecraft missions, such as the soon-to-be-launched NASA MMS mission.

Operations: Four Spacecraft for the Cost of One The major challenge in operating Cluster was the strong constraint to operate the four spacecraft for the cost of one. The operation teams, for the spacecraft at ESOC (Darmstadt, Germany) and for the science at the Joint Science Operation Centre (RAL, UK), were therefore built to operate, as much as possible, the four spacecraft in parallel. For instance, the payload commanding was prepared simultaneously on

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the four spacecraft. This is fine when everything goes according to plan but can create more stressful situations when anomalies occur, since the teams have to solve anomalies and at the same time still operate the other three spacecraft. Fortunately, the Cluster spacecraft have been very stable with their fast spin rate (15 rotations per minute) and solidly built to withstand harsh space conditions and have not had very many anomalies. However, due to the degradation of some key spacecraft elements such as batteries and solar panels, the flight control team have had to invent new procedures to return the science promised to the community. A few of these challenges are listed below. As presented in section “Electromagnetic Cleanliness,” the Cluster spacecraft were required to be magnetically “clean” and therefore carried nonmagnetic silvercadmium batteries. Due to the relatively rapid degradation of the cathodes in this type of battery, they were expected to last for only 3 years. Thanks to the careful management by the Cluster team, they kept providing power for 6 years. After that time, the ESOC flight operation team had to invent new procedures, which the satellite builder never thought of, to survive eclipses with very little or even without battery power. The first step was to put a new thermal strategy in place: since active heating was not possible anymore during eclipse, it was decided to heat the fuel tanks before eclipse to keep the spacecraft reasonably warm during eclipse. The second step was to reduce drastically the power consumption. A new procedure, called “decoder only,” was introduced, requiring a minimum battery capacity to keep-alive lines, while all spacecraft subsystems, including the onboard computer, were switched off at eclipse entry. The spacecraft were then switched back on at eclipse exit. A few years later, when none of the batteries were usable, a more drastic procedure was introduced, which switched the spacecraft completely off before eclipse and switched it back on at eclipse exit. This procedure was then automated when eclipse seasons increased in length, up to 9 months in 2011 (Fig. 4). Four spacecraft had to

Fig. 4 Eclipses during 2010–2011. The long period of eclipses in 2011 lasted 9 months

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be recovered, every 57 h, within a limited interval of ground station visibility. Speeding up the recovery allowed to keep the ESOC team small and gave more time to operate the scientific instruments, enabling measurements during 85 % of the orbit. At this time, 795 eclipses have been passed successfully, demonstrating the robustness of this procedure.

Recovery of the Five Wave Instruments On 5 March 2011, the digital wave processor (DWP), controlling the five wave instruments, was found switched off at acquisition of the signal of spacecraft 3. Subsequent attempts to switch it back on did not succeed since the current consumed by DWP was going over the spacecraft limit and the onboard current limiter was switching it off automatically. The cause was not clear: it could have been a short circuit or another problem with the instrument. After a few weeks of investigations by the instrument team and ESA, a new attempt was done to switch the instrument using the redundant power line, without success. The instrument technical manager looked then at all possibilities of failure and identified the most likely one: after the abnormal switch off of DWP, which controls the five wave instruments, all instrument relays were most probably stuck in a position on, preventing the subsequent switch on with their overall inrush current. A typical switch on of DWP switches on two or three instruments at once but not five. He went back to ground tests done in 1994 (almost 20 years back, available only on paper) and found the raise of current with three instruments, and he estimated the current raise to be up to 2 A within 11 ms for the five instruments. This was clearly well above the current limit of 1.29 A that the spacecraft could provide. Overconsumption of current is a difficult anomaly since, in case of short circuit, regular switch-on attempts increase the risk of losing the spacecraft if the current monitoring system fails. The next objective was to get more information about the actual ramp-up of the instrument current at switch on. Sampling of current is done on Cluster every 5 s, and the ramp-up, before automatic switch off by the onboard monitoring, was most likely less than 0.1 s. The solution was found by using special application software that had been used to record pyro firing during the launch and early orbit phase. This was tested on spacecraft 4 first and then applied on spacecraft 3 in early April: the ramp-up of the failed instrument current was characterized with a time resolution of one sample every 0.5 ms and confirmed that the switch off occurred after 21 ms as expected if all five relays in the instrument were closed. After intense discussion within the team, the idea emerged to try to switch on the redundant power line before the main one was switched off by the onboard current limiter, which would double the current available from the spacecraft. This would need to be done within 11 ms reaction time of the current limiter to have a chance of success. However, the fastest time allowed between two commands by the onboard computer was only 39 ms, too slow to recover the instrument. After further discussions, the team came up with a clever trick to “hack” the onboard computer

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and the power distribution unit. The trick was to execute the switch on of prime and redundant power lines with only one command, by changing the command register during the execution of the first command. Nobody knew, including industry experts who built the spacecraft, if that would work. However, everybody was convinced that it was the only solution. The first test was executed on another spacecraft with two spare current lines, and the trick worked: the two power lines could be switched on with one execute command in less than 2 ms. Everybody was then awaiting the “real” switch-on test with both current lines simultaneously, planned for the week after. When this was executed, the first test failed. Then the team tried it a second time, and the instrument switched on successfully on 1 June 2011. Fifty percent of the Cluster payload was finally recovered on Cluster 3. Another example of delicate operation was following the science request, from the WHISPER (electric waves and sounder) PI, to tilt the axis of one of the Cluster spacecraft with respect to the others. The goal was to study propagation of an electromagnetic emission called nonthermal continuum and observe its polarization. Since this was not a configuration described in the spacecraft user manual, the instrument teams had to confirm that their instrument would cope with such a change, and ESOC, Astrium, and ESTEC experts had to verify that it was also possible on the spacecraft side. The main issues were the risk of not being able to slew back to the initial attitude in case of a hardware failure, the thermal behavior of the spacecraft and instruments, and the possibility to get sunlight directly into some instruments. After the feasibility and low risk were confirmed in 2006, it was found that May 2008 was the best period of time for these operations, when having the optimal spacecraft constellation and being outside of an eclipse season. Finally Cluster 3 was tilted by 45 for a month. This operation was successful and unique science could be performed. A science paper showing that only the tilted conditions give the accurate location of the source of nonthermal continuum has recently been published (De´cre´au et al. 2013).

Science Results As part of a cornerstone, Cluster science was required to be a major step forward in fundamental plasma physics with many expected discoveries and a large community involved in data analysis. This is clearly being fulfilled with the total number of refereed papers currently above 1959 papers (Fig. 5) and the continuous growth of the community using the data. In the last five years, the publication rate has been above 175 papers/year, with a peak at 232 in 2011 demonstrating that Cluster data usage by the community continues to be very high even after 14 years in orbit. The new science targets and mission goals, obtained by the evolving orbit in combination with different separation strategies, have been a key driver of this vibrant scientific activity. Certainly the public access to all high-resolution data, about 1 year after acquisition, through the Cluster Active Archive has also been a determining factor for success. As of the end of 2013, 1,794 scientists from all over the world have been using the Cluster Active Archive.

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Fig. 5 Cluster and Double star referred publications up to the end of 2013

The following sections will describe a few Cluster science highlights that demonstrate the unique capability of the four spacecraft constellation such as ripples on the bow shock, 3D current measurements and Kelvin-Helmholtz waves at the magnetopause, bifurcated current sheet in the magnetotail, and the first measurement of the electron pressure tensor near magnetic reconnection. In addition, Cluster results on acceleration of energetic electrons in the Earth’s magnetosphere when it was hit by a CME will be highlighted.

Ripples on the Bow Shock The Earth’s bow shock is the first obstacle for the solar wind plasma when it enters the Earth’s environment. It is, however, a rather porous obstacle that mainly slows down and heats the plasma. The bow shock can also be the place where surface waves can form and propagate, similarly to waves on the ocean. Moullard et al. (2006) presented the first evidence of such waves at the bow shock when the Cluster spacecraft were approximately at 250 km from each other (Fig. 6). These waves were observed in the foot and the ramp of the bow shock on both magnetic field and plasma density data. Their period was 16 s, their wavelength 1,000–2,000 km, and they were propagating along the magnetic field. Two possible

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Fig. 6 Magnetic field magnitude (top panels) and electron number density (bottom panels) from C1 for two shock crossing events (From Moullard et al. 2006). The oscillations can be seen in the foot and ramp of the shock, when the density and magnetic field start to increase

explanations have been proposed: these waves are produced by the shock itself, or since it was observed in the flank of the shock, the solar wind flow may have produced it through the shear instability. Such surface waves have been observed by Cluster almost everywhere on the boundaries of the magnetosphere, and they could only be fully characterized and distinguished from a boundary motion by having the four spacecraft in a constellation.

Electric Current and Kelvin-Helmholtz Waves at the Magnetopause The magnetopause is the boundary where the coupling between the solar wind and the Earth magnetic field takes place, and it is the place where a strong current (Chapman and Ferraro 1930) is flowing. Dunlop et al. (2001) first published fourpoint measurements of the magnetic field at the magnetopause during November 2000. They could show that the magnetopause speed along the normal was varying continuously from a minimum of 17 up to 124 km/s. Haaland et al. (2004) presented a new method for estimating the orientation and motion of the magnetopause. They used Cluster when it was in a tetrahedron

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configuration of 100 km, in spring 2002, to obtain the minimum variance of the current density. The small separation distance was essential to make sure that all four spacecraft were inside the current layer of the magnetopause at the same time. The variance analysis was used to estimate the orientation of the magnetopause, and the integration of the current density gave the magnetopause velocity. The motion of the magnetopause on that event was found around 34 km/s, slightly larger than the plasma flow measured by the ion instrument of around 28 km/s, which would indicate an outflow of plasma from the magnetosphere into the solar wind (Fig. 7). At the flanks of the magnetosphere, Hasegawa et al. (2004) observed for the first time Kelvin-Helmholtz (K-H) waves rolling up into vortices that would allow plasma transfer from the solar wind to the magnetosphere. This was demonstrated when the spacecraft located further inward observed higher density than the three others located outward. These observations were supported by a magnetohydrodynamic (MHD) simulation. Since there was no sign of plasma acceleration due to magnetic stress, they speculated that magnetic reconnection was not taking place locally in that event. A few years later however, Nykyri et al. (2006) found that reconnection was occurring inside a rolled-up vortex, and Hasegawa et al. (2009) found it on the trailing edge of the vortex. More recently, K-H vortices have been found even during southward IMF (Hwang et al. 2011) and at high latitudes (Hwang et al. 2012).

Bifurcated Current Sheet in the Plasmasheet The four Cluster spacecraft have also significantly advanced our knowledge of the magnetotail and especially the plasmasheet, the big reservoir of plasma that regularly releases large quantity of energy toward the Earth and produces the northern lights. Once again, being able to distinguish between spatial and temporal variations using measurements at four points separated in space is a key aspect to understand the physics since it is a very dynamic region. These four-point measurements allow for the first time to distinguish the spatial characteristics of the plasmasheet from its quick motion. Runov et al. (2003) showed without ambiguity that the electric current is not maximum in the middle of the plasmasheet but a few 1,000 km away (Fig. 8); this is the so-called bifurcated current sheet. Bifurcations of the current sheet were proposed before (Sergeev et al. 1993; Hoshino et al. 1996), but Cluster observations helped to remove the ambiguities inherent in using single- or two-spacecraft measurements.

Electron Pressure Tensor Near Magnetic Reconnection Magnetic reconnection is a universal physical process, playing a major role in various phenomena such as star formation or solar explosions, but also preventing

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Fig. 7 Magnetopause crossing on 2 March 2002 (From Haaland et al. 2004). From top to bottom, the parameters shown are the electron density deduced from the spacecraft potential, the magnetic field components in GSE, the current density estimated from the curlometer technique, and div B which gives an indication of the validity of the current estimation

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Fig. 8 Current sheet bifurcation on 29 August 2001 (From Runov et al. 2003). The top panel shows Bx as a function of time from the four spacecraft. The middle and bottom panels show two sketches of the bifurcated current sheet for a sausage or kink wave disturbance, respectively. Dark and light gray indicate the region of maximum current

plasma confinement in fusion reactors on Earth. However, a lack of precise measurements at the heart of this physical process prevents a full understanding of this phenomenon. At the heart of the reconnection process, magnetic field lines from different magnetic domains collide and tie together, changing the overall magnetic field topology, usually forming an X line. This topological change leads to the mixing of previously separated plasmas, like the entry of solar material into the magnetosphere. It also efficiently converts magnetic field energy to particle energy, generating plasma heating and reconnection jets as in the magnetotail. But the magnetic field is not the only physical parameter to consider. The electric field also plays a crucial role in the microphysics of reconnection since it accelerates particles. After considerable efforts by the PEACE (electron) team to perfect the PEACE calibration, the multi-spacecraft nature of the Cluster mission was used to derive the first measurements of the divergence of the full electron pressure tensor (Henderson et al. 2008); this parameter is one of the contributions to the electric field. They were able to directly compare quantitatively, for the first time, this quantity to the Hall term (J  B). In agreement with simulations, they found in particular that both terms generate oppositely directed electric field contributions, clearly anticorrelated (Fig. 9, last panel). These observations used small inter-spacecraft distances of about 200 km. This fundamental property of the reconnection process can then be applied elsewhere in the solar system and beyond.

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Fig. 9 The first four panels show the magnetic field from the four spacecraft (From Henderson et al. 2008). The 5th panel shows the electron pressure. The 6th panel shows the parallel electric field derived from the electron pressure tensor. The 7th to 9th panels show the perpendicular electric field deduced from the electron pressure tensor (black) and the Hall term (J  B). The Z component of the perpendicular electric field shows that the electric field from the electron pressure tensor and the one from the Hall term are anti-correlated

Acceleration of Electrons by Coronal Mass Ejections Coronal mass ejections (CMEs) are huge clouds of plasma emitted by the Sun during solar storms. Their characteristics vary greatly, but CMEs can sometimes be as fast as 3,000 km/s and contain strong magnetic field and dense plasma. The effect

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on the Earth’s environment could be dramatic, since it induces fast and large changes of the Earth’s magnetosphere, which in turn energizes particles to very high energy. “Space Weather” was created to study the effect of the Sun on the Earth and on human systems. Cluster is not a space weather mission as such, but its measurements, especially the study of dynamic structures, are providing key input for the models that are being developed for space weather predictions. Cluster capabilities were enhanced when in 2002 the SPC agreed to add a second ground station to record the Cluster observations twenty-four hours a day, seven days a week (originally the mission was designed to cover about 50 % of the orbit focused on magnetospheric boundaries, bow shock, magnetopause, cusp, and plasmasheet). Without it the following observation would not have been possible. CMEs are very often associated with interplanetary shocks that can then accelerate electrons to very high energy when they hit the Earth’s environment. Zong et al. (2009) observed a strong enhancement of energetic electrons in the magnetosphere associated with the passage of the CME shock (Fig. 10). After the shock passage the electric field oscillated in correlation with the flux of energetic electrons, suggesting that the magnetic field compression produced ultralow frequency (ULF) waves that then accelerated electrons. Energetic electrons can penetrate through components of spacecraft and produce deep dielectric charging. If vital components are affected, it could eventually kill a spacecraft. Measurements of energetic electron events and their associated plasma parameters are therefore fundamental to improve models and in the longer term predict their occurrence.

Cluster Guest Investigator Programme As customary for space physics missions, the decisions on how to operate the spacecraft and instruments have been the role of the Science Working team made of the Principal Investigators and the Project Scientist. In 2010, however, as part of activities for that extension period, science operations were opened to scientists from the community, turning Cluster into an “observatory,” similarly to what is commonly done with astronomy missions. An Announcement of Opportunity was opened in July 2010, soliciting Guest Investigator (GI) proposals for special operations of the instruments or the spacecraft, including changing the separation between the spacecraft. Six GI proposals were selected (Table 3). The GI-proposed operations were executed from 2011 up to the end of December 2013. A new AO is in preparation and should be open in the first quarter of 2014.

Cluster Open Access to all High-Resolution Data Sets Since the beginning of the Cluster mission preparation, it was realized that for Cluster to be a success, data should be easily accessible to the community (Schmidt et al. 1990). The Cluster Science Data System (CSDS) was set up to achieve that

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Fig. 10 Energetic electron flux measured by Cluster RAPID instruments around the time of the arrival of the interplanetary shock at 18:27 UT on 7 November 2004 (From Zong et al. 2009). The four top panels show the electron flux in energy-time spectrogram (C1) and in pitch-angle-time spectrogram (C2-C4). The black line on top of each spectrogram represents the azimuthal electric field. The bottom panel shows the magnetospheric magnetic field (Bz component) measured on the four spacecraft; its increase (compression) is clear after 18:27 UT

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Table 3 List of Cluster guest investigators selected in 2011 Guest investigator B. Walsh E. Yordanova

GI proposal title High latitude magnetopause electrons Small-scale turbulence

A. Retino`

Multi-scale observations of magnetic reconnection in the magnetosphere

C. Foullon

Magnetopause boundary layer: evolution of plasma and turbulent characteristics along the flanks Generation and 3D features of flux transfer events at the dayside magnetopause Particle acceleration and field aligned currents in the cusp

Z. Pu

F. Pitout

Laboratory Boston University (USA) Institutet for Rymdfysik, Uppsala (Sweden) LPP/UPMC/ Ecole Polytechnique/ CNRS (France) Exeter University (UK)

Implementation period Spring 2011 February until April 2012 May and August 2012

November 2012

Peking University (China)

January and February 2013

IRAP/Paul Sabatier University/CNRS (France)

Autumn 2013

objective (Schmidt et al. 1997b). CSDS started in the early 1990s, and, at that time, the network bandwidth was much lower than nowadays, only able to distribute e-mail and view simple web pages. It was therefore not suited to distribute the very large quantity of data collected by Cluster, in the range of 1–3 CDroms per day. The only solution was to get data burned on CDroms and to distribute these to PI and CoI institutes (around 70 at that time). It was a big challenge for ESOC to produce between 70 and 200 CDroms per day and to ship them to the scientists. A large operation of PCs and CDroms burners was put in place with substantial manual intervention. Since 2006 the raw data are automatically transferred via public Internet to the Cluster Active Archive (see below). Once at PI and CoI institutes, the data were calibrated, and key parameters at medium and low temporal resolution could be extracted. The CSDS Implementation Working Group had defined the parameters that each instrument would produce (Daly et al. 2005). This had the advantage of decreasing the amount of data from 700–2,100 MBytes down to 20 MBytes per day. The production and distribution of these products were performed by eight data centers, located close to PI institutes and spread worldwide (Fig. 11). Since each data center was processing only data for a few instruments, special software (Cluster data management system) was produced, enabling them to exchange data. This process ensured that all data centers had the full database from all instruments. For Cluster I, public Internet could not guarantee sufficiently fast exchange of data. Consequently, dedicated lines were provided by ESOC to interconnect the data centers. For Cluster II, starting in the late 1990s, public Internet was fast enough to be used.

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Fig. 11 The Cluster Science Data System (CSDS) made of eight interconnected data centers (yellow), processing data for the 11 instruments indicated. Three additional operation centers at ESTEC, ESOC, and RAL are indicated in red

During the first two years (2001–2002) of the Cluster mission, it was realized that Cluster scientific output would be greatly enhanced if the science community would have access to all high-resolution data and not only to medium and low resolution. At that time the network capacity had grown by a few orders of magnitude, and it was not a problem anymore to send high quantity of data through public network. In early 2003, the ESA SPC agreed to the development of the Cluster Active Archive (CAA) that was designed to: • Maximize the scientific return from the mission by making all Cluster data available to the worldwide scientific community. • Ensure that the unique data set returned by the Cluster mission is preserved in a stable, long-term archive for scientific analysis beyond the end of the mission. • Provide this archive as a major contribution by ESA and the Cluster science community to the International Living With a Star program. After a few years of development to define the metadata and the Cluster Exchange Format (ASCII based), to process the first few years of data, and to develop the user interface, the Cluster Active Archive was open to the public in February 2006 (Laakso et al. 2010). The science community using CAA data has been growing continuously since 2006 at a rate around 20 new users every month, and now more than 1,790 scientists are using the data. The download rate has also been continuously growing, and at the beginning of 2014, it was above 2 TB/month. Furthermore a large portion of Cluster-published papers (Fig. 3) are using data from CAA, and their number has clearly increased since 2006, the year of CAA opening.

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Conclusion The Cluster mission is one of the most successful space missions dedicated to the study of the Sun-Earth connection. This is primarily due to the determination of the Cluster scientists who never compromised on the number of spacecraft necessary to achieve the objectives: during the development of the original Cluster mission and its successor Cluster II, the total number of spacecraft was always challenged in order to decrease cost. The answer from scientists was however always the same: four spacecraft is the minimum. They are now continually rewarded by the results achieved by Cluster. Another key aspect that helped to maximize science return was the fast and easy access to data that was first achieved by CSDS and then with the CAA. Cluster for the first time with four identical spacecraft has discovered many aspects of plasma physics by measuring for the first time the 3rd dimension. A few highlights have been presented in this paper such as ripples on the bow shock, 3D current measurements and Kelvin-Helmholtz waves at the magnetopause, bifurcated current sheet in the magnetotail, and the first measurement of the electron pressure tensor near magnetic reconnection. In addition, acceleration of energetic electrons in the Earth’s magnetosphere, which was hit by a CME, was demonstrated. Extreme solar storms and their associated CMEs could have dramatic effects on human life (see US NSF report “Severe space weather eventsunderstanding societal and economic impacts, 2008” or the UK Royal Academy and engineering report “Extreme space weather: impacts on engineered systems and infrastructure, 2013”). The growing interest by governments, especially in the very rare extreme events, has made space weather a permanent agenda item of the United Nations Committee on the Peaceful Uses of Outer Space. Cluster is not a space weather mission as such, but its measurements, especially on the study of dynamic changes in the Earth’s environment, are providing key input for the models that are being developed for space weather predictions. Acknowledgements The authors thank the PI teams for keeping the instrument in very good shape after more than 14 years in space: K. Torkar (IWF, Austria), I. Dandouras (IRAP/CNRS, France), R. Torbert (UNH, USA), C. Carr (IC, UK), A. Fazakerley (MSSL, UK), P. Daly (Gottingen U., Germany), M. Balikhin (Sheffield, UK), M. Andre´ (IRFU, Sweden), P. Canu (LPP, France), J. Pickett (U. Iowa, USA), and J.-L. Rauch (LPC2E, France). We also thank the ESOC and JSOC teams for spacecraft and science operations as well as industry (Astrium, Germany) for their continuous spacecraft operation support. We also thank the archiving teams at ESTEC and ESAC and the CSDS teams at National data centres.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Early Solar and Heliophysical Space Missions ▶ Earth’s Natural Protective System: Van Allen Radiation Belts

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▶ ISAS-NASA GEOTAIL Satellite (1992) ▶ International Sun Earth Explorers 1 and 2 ▶ Introduction to the Handbook of Cosmic Hazards and Planetary Defense ▶ NASA Wind Satellite (1994) ▶ Nature of the Threat/Historical Occurrence ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Dynamics Observatory (SDO) ▶ Solar Flares and Impact on Earth ▶ Solar Radiation and Spacecraft Shielding ▶ STEREO as a “Planetary Hazards” Mission

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IMAGE Mission: Imager for Magnetopause-to-Aurora Global Exploration James L. Green

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mission Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technique: Neutral Atom Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technique: Photon Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technique: Radio Plasma Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Key Finding and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Wind Plasmas and Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polar and Ionospheric Plasma Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plasmaspheric Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Buildup and Decay of the Ring Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

Since the launch of Explorer 1 in 1958, physicists have studied magnetospheric plasma regions by only being immersed in them. This was done by creating large databases of in situ observations taken at vastly different times and under different magnetospheric conditions. This approach allowed models of these regions to be created that offered some insight as to global processes. In most cases these models were also pushed beyond their limits in an effort to try and describe the structure and dynamics of our geospace environment under all solar wind conditions. That all changed with the launch of the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft on March 25, 2000. The overall objective

J.L. Green (*) Planetary Science Division, NASA Headquarters, Washington, DC, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_29

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of the IMAGE mission was to answer the key question: How does the magnetosphere respond globally to the changing conditions in the solar wind? IMAGE was designed to observe vast plasma regions of the inner magnetosphere before, during, and after geomagnetic storms using neutral atom imaging (NAI) at various energies, far ultraviolet imaging (FUV), extreme ultraviolet imaging (EUV), and radio plasma imaging (RPI). These revolutionary instruments provided detailed images of aurora, the ring current, and the plasmasphere at minutes to tens of minute resolution that have greatly changed our view of magnetospheric dynamics. It is not possible to discuss all the results that IMAGE observations have contributed to the understanding of space weather, but we will provide a brief overview concentrating on the ring current and plasmasphere. Keywords

Aurora • Disturbance storm time (DST) index • Geocorona • Geomagnetic storm • IMAGE mission • Imaging • Magnetosphere • Neutral atom imaging • Plasmasphere • Radio plasma imaging (RPI) • Radio sounding • Ring current • Substorm • Ultraviolet imaging

Introduction The IMAGE mission was designed to image the magnetosphere for the first time using a variety of new imaging techniques. The IMAGE mission was the first in NASA’s Heliospheric Division Mid-size Explorer or MIDEX program. The Earth’s magnetosphere contains large reservoirs of extremely tenuous plasmas of both solar and terrestrial origin. Both the Earth’s magnetic field and plasmas constantly rearrange themselves in response to changes in the solar wind. These invisible populations of ions and electrons have traditionally been studied by making in situ measurements with charged particle detectors, magnetometers, and electric field instruments. Instead of taking such in situ measurements, IMAGE used a variety of imaging techniques to “see the invisible” and to produce the first comprehensive global images of plasma regions in the inner magnetosphere showing their variations and responses to solar wind changes.

Mission Objectives The overall objective of IMAGE is best expressed by the question: How does the magnetosphere respond globally to the changing conditions in the solar wind? In fact, with all its implications, this question is a statement of the fundamental problem facing magnetospheric physics at that time. Unlike other disciplines such as astrophysics and solar physics, magnetospheric physics did not have the benefit of images showing a global perspective of the constituent regions under study prior to the IMAGE mission. The magnetospheric images from IMAGE allowed

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Fig. 1 Top panel shows the initial orbit of IMAGE at launch, and the bottom panel shows how the orbit precessed with time showing the changing view of the mission to the plasmas in the inner magnetosphere (Graphic courtesy of NASA)

scientists to observe, in a way never before possible, the large-scale dynamics of the magnetosphere including interactions among its plasma populations. In order to ensure a favorable location for imaging the magnetosphere during its prime mission (i.e., the first 2 years), the IMAGE spacecraft was launched on March 25, 2000, into a highly elliptical north polar orbit (inclination of 90 ), as shown in the top panel of Fig. 1, with initial geocentric apogee of 8.22 Earth radii (RE) and perigee altitude of 1,000 km. IMAGE was launched during the year of the maximum in the sunspot cycle. During the 2-year nominal mission, the line of apsides

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precessed over the pole and returned to 40 . (Note: The apsides in this case represent the points in the orbit where the spacecraft is either closest or furthest away from Earth.) From 2002 through 2005, the IMAGE orbit precessed, as shown in the bottom panel of Fig. 1, until operations terminated due to an unrecoverable anomaly in December 2005. The extended IMAGE mission focused on geomagnetic activity during the declining phase of the solar cycle. The evolution of the IMAGE orbit provided a new, mid- and low latitude, and ultimately southern hemisphere viewing perspective (Graphic courtesy of NASA).

Technical Characteristics The IMAGE mission used three new plasma imaging techniques: neutral atom imaging (NAI) over an energy range from 10 eV to 500 keV, far ultraviolet imaging (FUV) at 121–190 nm, extreme ultraviolet imaging (EUV) at 30.4 nm, and radio plasma imaging (RPI) over the density range from 0.1 to 105 cm 3 throughout the magnetosphere. Table 1 provides an overview of the IMAGE instrument characteristics. Neutral Atom Imaging was thus conducted over the range of Low-Energy Neutral Atom (LENA) imaging, Medium-Energy Neutral Atom (MENA) imaging, and High-Energy Neutral Atom (HENA) imaging over a wide field of view (FOV) of 90 by 90 .

Technique: Neutral Atom Imaging The geocorona is the extended exosphere of the Earth in which relative low-energy neutral hydrogen atoms perform ballistic trajectories and thus form a spherical globe of atoms for several RE around the Earth. In the same region as the geocorona, there exist different populations of energetic ions. Because energetic ions are trapped by the Earth’s magnetic field, they can only be imaged on a global scale from remote locations only if they are converted into energetic neutral atoms through a charge exchange process with the higher-density colder geocorona. In this process, a few percent of the energetic ions in a particular population pick up these electrons from the neutral hydrogen geocorona atoms. Once converted into energetic neutral atoms, they are released from their magnetic confinement allowing them to travel along line-of-sight trajectories to a remote imager. The charge exchange process preserves the parent ion’s direction, speed, and mass so that suitable energetic neutral atom imagers can obtain detailed information about the origin of the energetic magnetospheric ion populations. For the IMAGE mission, a suite of three neutral atom imagers provided energyand composition-resolved images at energies from 10 eV to 500 keV with a time resolution of 2 min. Three separate instruments are needed because the physical processes that convert neutral atoms to ions and then detect the ions differ over the three energy regimes (LENA 1 keV, MENA 1–30 keV, and HENA 10–500 keV).

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Table 1 IMAGE science instrument measurement objectives Imager NAI

Objectives Neutral atom composition and energyresolved images by three instruments 10–300 eV (LENA) 1–30 keV (MENA) 30–500 keV (HENA)

EUV

30.4 nm imaging of plasmasphere He+ column densities

FUV

Far ultraviolet imaging of the aurora and geocorona. Instruments: Wideband Imaging Camera (WIC), Spectrographic Imager (SI), Geocorona (GEO)

RPI

Remote sensing of electron densities and magnetospheric boundary locations using radio sounding. 500 m tip-to-tip X- and Y-axis antenna and a 20 m Z-axis antenna

Measurements FOV: 90  90 (image ring current at apogee) Angular resolution: 4  4 to 8  8 (depending on energy and mass) Energy resolution (ΔE/E): 0.8 (above 1 keV) Composition: distinguish H and O in magnetospheric and ionospheric sources and interstellar neutrals Image time: 2 min (resolve substorm development) FOV: 90  90 (image plasmasphere from apogee) Spatial resolution: 0.1 Earth radius (RE) from apogee Image time: 10 min (resolve plasmaspheric processes) FOV: 16 for aurora (image full Earth from apogee), 60 for geocorona Spatial resolution: 70 km (Wideband Camera), 90 km (Spectrographic Imager) Image time: 2 min (resolve auroral activity) Density range: 0.1–105 cm 3 (determine electron density from inner plasmasphere to magnetopause) Spatial resolution: 500 km (resolve density structures at the magnetopause and plasmapause) Image time: 1 min (resolve changes in boundary locations) to 20 min (polar cap and plasmaspheric density structures)

Technique: Photon Imaging The imaging wavelengths on the IMAGE mission have many unique features that are designed to observe important plasma features where they observe resonate scatter solar illumination or delineate auroral precipitation phenomena. The EUV instrument on IMAGE uses the resonance scattering of He+ at 30.4 nm to observe the global structure of the plasmasphere. He+ is typically the second most abundant ion in the plasmasphere. The time resolution of a EUV image is about 10 min with typically a spatial resolution of 0.1 RE at apogee. The design of the EUV instrument is described in much greater detail by Sandel et al. (2000).

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The FUV investigation on IMAGE uses three basic instruments that observe at several important wavelengths. The FUV-Wideband Imaging Camera (WIC) provided broadband ultraviolet images of the aurora for maximum spatial and temporal resolution by imaging the LBH N2 bands of the aurora. The FUV-Spectrographic Imager (SI) provided maps of the hydrogen (121.8 nm) and oxygen (136 nm) components of the aurora. The FUV auroral imagers WIC and SI both have wide fields of view and take data continuously as the auroral region proceeds through the field of view. The FUV/GEO instrument observed the distribution of the geocoronal emission (121.6 nm), which is a measure of the neutral hydrogen background density and the source for charge exchange in the magnetosphere supporting the LENA, MENA, and HENA measurements. For a detailed description of the Wideband Imaging Camera (WIC), Spectrographic Imager (SI), and Geocorona (GEO) far ultraviolet imagers, see Mende et al. (2000a, b, c).

Technique: Radio Plasma Imaging The Radio Plasma Imager (RPI) on IMAGE was designed as a long-range magnetospheric radio sounder, a relaxation sounder, and a passive plasma wave instrument. The RPI was a highly flexible instrument that was programmed to perform these three types of measurements at times when IMAGE was located in key regions of the magnetosphere. RPI is the first radio sounder ever flown to large radial distances into the magnetosphere. The long-range sounder echoes from RPI allowed remote sensing of a variety of plasma structures and boundaries in the magnetosphere. Like a radar, a radio sounder transmits and receives coded electromagnetic radio pulses. A basic radio sounder measures the time delay between the transmitted pulse and the echo. The time delay measurement is then converted into a distance from the reflection point. This is the point that is typically where the plasma frequency (which can be converted into a plasma density that is known as Ne) matches the wave frequency. As the sounder frequency is increased, the waves penetrate to greater distances, into regions of larger Ne, yielding echoes with larger delay times. By inverting the resulting echo delay as a function of frequency, Ne as a function of distance from the spacecraft can be determined. The RPI would generate selected narrow-band radio frequency pulses in the frequency range from 3 kHz to 3 MHz with a receiver bandwidth of 300 Hz covering the spectrum in about a 2-min cycle. The returned echoes and their directions would be received on all three-axis antennas creating echo traces over each cycle. A profile inversion technique for the RPI echo traces provided a method for determining the density distribution (Ne versus distance) of the plasma from either direct or field-aligned echoes. This technique has enabled the determination of the evolving density structure of the polar cap and the plasmasphere under a variety of geomagnetic conditions. The design of the RPI is described in much greater detail by Reinisch et al. 2000.

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Key Finding and Results IMAGE was the first satellite mission dedicated to imaging the Earth’s magnetosphere. Soon after launch, it began providing global images of the important plasma populations in the inner magnetosphere under a variety of solar wind conditions. These images led immediately to numerous new discoveries and confirmation of several existing theories regarding magnetospheric plasma dynamics. IMAGE addressed: (1) solar wind plasmas and injection, (2) polar and ionospheric plasma dynamics, (3) plasmaspheric dynamics, and (4) the injection, buildup, and decay of the ring current. This brief overview will emphasize the new findings relative to plasma and radiation environment.

Solar Wind Plasmas and Injection Although designed to observed low-energy neutral atoms originating from within the Earth’s magnetosphere, the IMAGE/LENA instrument also observes the interstellar neutral atom flow coming through the inner heliosphere (Moore et al. 2001; Collier et al. 2001, 2004). IMAGE/LENA discovered a neutral atom component of the solar wind, caused by charge exchange with interstellar neutrals and exospheric atoms in the magnetosheath (Moore et al. 2001; Collier et al. 2001). Since these neutral atoms do not pose a comic hazard, only a brief review of these results will be given. Due to LENA instrument look-angle constraints, the interstellar neutral atom observations occurred during the winter season, beginning when the Earth passes across the weak interstellar neutral gas flow downstream line and continuing as the Earth begins to turn upstream into that flow. A density enhancement of He atoms is expected owing to their focusing by solar gravity as they pass the Sun, and indeed this is seen to be the case for He+ pickup ions formed from thermal He atoms. However, the inferred location of maximum LENA density for these fluxes is later by about 30 days than the passage of Earth through the downstream line or the peak in the He+ pickup ions. The variations of the direction of arrival of these neutrals now suggest that they are a combination of the known He focusing cone together with an inner heliospheric secondary stream of H that is shifted from the established thermal hydrogen arrival direction by ~30 whose exact origin is unknown.

Polar and Ionospheric Plasma Dynamics The IMAGE mission observed that the ionosphere responds rapidly and dramatically to changes in the solar wind. Images of the ion outflow from the ionosphere from IMAGE/LENA demonstrated that rapid changes in the solar wind dynamic pressure result in episodic bursts of ion outflow (Fuselier et al. 2002) from the auroral zone and into the Earth’s magnetotail and into the plasma sheet.

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By combining these images with auroral images from FUV, it was also shown that the bursts are confined to regions of the auroral oval where there are intense auroral emissions. IMAGE made the first global images of the proton aurora, establishing its source with correlative measurements of proton precipitation on the FAST satellite and determining the dynamic relationship between electron and proton auroras during substorms (Frey et al. 2001; Mende et al. 2001).

Plasmaspheric Dynamics The plasmasphere is a toroidal region of dense cold plasma (tens of eV) surrounding the Earth whose origin is the Earth’s ionosphere. It encircles the Earth at geomagnetic latitudes less than about 65 , occupying the inner magnetosphere out to a boundary known as the plasmapause. There, the plasmaspheric density can drop by 1–2 orders of magnitude in less than 1 RE. The configuration and dynamics of the plasmasphere and the location of the plasmapause are highly sensitive to geomagnetic disturbances. The plasmapause is the location where the cold co-rotating plasma mixes and interacts with the hot plasmas of the ring current and plasma sheet. EUV plasmasphere imaging was able to solve the problem of the time-dependent structure of the plasmasphere. EUV observal a complexity of interactions, as never before imagined, that takes place within the plasmasphere and particularly at its outer boundary, the plasmapause. Figure 2 shows six EUV images of the plasmasphere that provide examples of plumes, notches, shoulders, fingers, channels, and crenulations. The brightness of the emission is proportional to the line integral of the He+ line-of-sight abundances in each pixel of the image. The shadow region behind the Earth prevents resonance solar radiation from occurring and therefore would not be imaged. These new views of the plasmasphere were largely unpredicted features prior to the IMAGE mission (Sandel et al. 2001). Another unexpected consequence of the variation in the plasmaspheric structure was the determination that the origin of kilometric continuum comes from the equatorial plasmapause deep within plasmaspheric notch structures (Green et al. 2002, 2004). The plasmapause is traditionally considered to be the boundary between closed and open convection trajectories. Accordingly, Grebowsky (1970) proposed that when the open/closed convection boundary moves inward, filled plasmasphere flux tubes become entrained in sunward convection flow to the magnetopause and form long tails or detached regions that move outward to the magnetopause where the cold plasma is vented into the magnetosheath or its boundary layer and lost into the solar wind. The bottom four panels of Fig. 3 show the evolution of the plasmasphere during a geomagnetic storm in late June 2000 as observed by the EUV instrument. The plasmasphere shrinks significantly from its extended shape in the first panel to a well-confined plasmasphere in the last panel. The top panel of Fig. 3 shows an expanded version and labels the key plasmaspheric features. The plasmaspheric drainage plume is clearly seen. These EUV images proved the existence of the

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Fig. 2 The complexity of the longitudinal structure of the plasmasphere is shown in six EUV images over the life of the IMAGE mission (Graphic courtesy of NASA)

plasma drainage plumes or tails (Burch et al. 2001a, b) that were predicted to occur during geomagnetic storms by the global magnetospheric convection model originally proposed by Grebowsky 1970. In addition, it was also shown by Goldstein et al. 2002 that a south–north transition in the IMF produces observed plasmasphere shoulders. A plasmaspheric shoulder is prominently shown in Fig. 3. The first remote measurements of plasmaspheric densities and refilling using radio sounding have been reported by Reinisch et al. 2001, 2004. RPI echoes were observed being ducted (to understand the physics of the ducting process see Fung and Green 2005) along geomagnetic field lines during times of refilling after geomagnetic storms. These results show that the plasmasphere refills in slightly greater than a day at L values of 2.8 and that ion heating is probably playing a major role in the overall density distribution along the field line.

Buildup and Decay of the Ring Current A geomagnetic storm is measured on the Earth by combining data from several near-equatorial magnetometer stations. These stations measure the Earth’s field and other magnetic fields that arise within the Earth’s magnetosphere producing space weather events. The disturbance stormtime index, DST, is based on the average value of the horizontal component (in nanotesla) of the Earth’s magnetic field

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Fig. 3 The evolution of the plasmasphere during a geomagnetic storm is shown in the four bottom panels. A labeled version of the final plasmasphere state is shown in the top panel as having a much-reduced size and a drainage plume as predicted by theory (Graphic courtesy of NASA)

measured hourly at four near-equatorial stations. A negative DST value means that the Earth’s magnetic field has been weakened due to a ring current that has developed within the inner magnetosphere. Ring currents can last for days and are due to the injection of particles into the inner magnetosphere from the Earth’s magnetotail. Prior to IMAGE, ring current observations were made by in situ spacecraft making a very localized measurement of a global phenomenon. The IMAGE HENA and MENA instruments provided global images of all phases of the ring current from development to dissipation in addition to compositional differences. The ring current is largely carried by ions in the 20–200 keV energy range and contains the most energy phenomena within geomagnetic storms with only solar activity being the more energetic space weather event. The ring current plasma is believed to come from both the solar wind and the ionosphere. Previous in situ ring current measurements have found that O+ is larger than H+ in large storms with the O+ indicating an ionospheric origin, while the H+ can be both ionospheric or solar wind in origin. It will be up to the HENA instrument to determine. Geomagnetic storm energy, initially resident in the ring current, is lost to energetic neutral atoms (change exchange) and to the aurora (by precipitation).

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Fig. 4 HENA observations of a developing ring current at 20 keV. The Earth and L shells of 4 and 8 are shown (Graphic courtesy of NASA)

The charge exchange process between ring current ions and the geocorona is believed to be the dominant loss mechanism. Pitch-angle diffusion of ring current ions, leading to precipitation, is due to collisions with the low-energy plasma of the plasmasphere and to wave–particle interactions. Through correlated study of auroral images from FUV, plasmasphere images from EUV and RPI, and hot plasma images from NAI, an assessment which can be made of the importance of plasma waves in the loss of the ring current was accomplished. HENA observations have allowed for the determination of the energy-dependent injection and drift of energetic ions during magnetospheric substorms (Burch et al. 2001a; Pollock et al. 2001; Mitchell et al. 2001). As an example of ring current observations by the HENA instrument, Fig. 4 is a neutral hydrogen atom image at 20 keV during the beginning phases of a geomagnetic storm on June 10, 2000. The image is a view looking down from the north, with the Sun direction to the right and labeled. The Earth and L shells of 4 and 8 are shown in black outline. The anti-sunward direction or the tail direction is where the injection of ring current protons first began. These ring current protons will continue to move clockwise around the Earth starting from this partial ring current (as shown) and rapidly forming a complete current encircling the Earth. The injection from the tail region occurred around an L value of 7. It is important to note that since the geocorona drops in density rapidly with distance, the energetic neutrals hydrogen atoms observed are more intense closer to the Earth, but the ring current itself will be very intense in the range of L values from 4 to 8. Geostationary satellites orbit the Earth at a location of ~6.6 L value and therefore are typically in the ring current region. Ring current plasma environment can produce spacecraft charging since the high-energy ambient ring current can

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Fig. 5 The large increases in integrated oxygen energetic neutral atom flux are shown in association with auroral brightening during substorms. The hydrogen energetic neural atom fluxes do not show these increases but remain relatively constant during the entire geomagnetic storm period (Graphic courtesy of NASA)

“stick” to spacecraft surfaces producing a charge buildup. Spacecraft in low-density regions of the magnetosphere (outside the plasmasphere) can build up hundreds of kilovolt charge. A sudden discharge can affect onboard electronics, breakdown thermal coatings, and degrade solar cells and sensors. By combining observations from both HENA and FUV/WIC instruments, two very important relationships were determined by Mitchell et al. 2003. The HENA instrument observes both energetic neutral hydrogen (top two curves in Fig. 5) and oxygen neutral atoms (third curve in Fig. 5) and found that the hydrogen component of the ring current builds up quickly and decays gradually in concert with the DST geomagnetic storm index. However, energetic oxygen is injected into the ring current from the plasma sheet during magnetospheric substorms that occur during the recovery phase of a geomagnetic storm. As shown in Fig. 5, the oxygen neutral fluxes rise and fall impulsively, following more closely the substorm AE index (shown by auroral brightening), while the hydrogen neutral fluxes remain about the same over the entire storm time. This supports the idea that at the start of a long and

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intense geomagnetic storm, the ionospheric oxygen outflows from the ionosphere and into the plasma sheet, but it takes several hours of negative IMF (interplanetary magnetic field) Bz to enhance the O+ densities in the plasma sheet and then be energized and injected into the ring current impulsively. Once in the ring current, they charge exchange with the geocorona and become energetic oxygen neutral atoms that are observed by the HENA instrument.

Conclusion For the first time, IMAGE observations allowed imaging global dynamics of all the major magnetospheric plasma regions and their boundaries simultaneously. IMAGE observations provided critical tests for hypotheses involving: hot–cold plasma interactions, detached plasma regions and plasma tails, plasmaspheric filling processes, substorm plasma injections, and ring current injection and decay. A thorough understanding of the above processes is necessary to model and predict the Earth’s magnetospheric response to changes in solar wind conditions and form a fundamental understanding of space weather. Since the protection against the solar wind and especially the accelerated ions from coronal mass ejections depends heavily on the Earth’s magnetosphere, all IMAGE data are key to understanding the ability of the Earth to withstand the super energetic explosive particles that come from the Sun, especially during sunspot maximum. There are three major book compilations of IMAGE results and modeling that provide a rich background of scientific results for those who seek more detailed information. These compiled science paper reviews are by Burch (2000, 2003) and Darrouzet et al. (2009).

Cross-References ▶ Cluster Technical Challenges and Scientific Achievements ▶ ISAS-NASA GEOTAIL Satellite (1992)

References Burch JL (ed) (2000) IMAGE mission overview. Space Sci Rev, IMAGE special issue, 91(Issues):1–4 Burch JL (ed) (2003) Magnetospheric imaging: the IMAGE prime mission. Space Sci Rev, IMAGE special issue, 109(Issues):1–4 Burch JL et al (2001a) Views of Earth’s magnetosphere with the IMAGE satellite. Science 291(5504):619–624, 626 Burch JL et al (2001b) Global dynamics of the plasmasphere and ring current during magnetic storms. Geophys Res Lett 28(6):1159–1162 Collier MR et al (2001) Observations of neutral atoms from the solar wind. J Geophys Res 106:24893–24906

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Collier MR et al (2004) An unexplained 10–40 shift in the location of some diverse neutral atom data at 1 AU. Adv Space Res 34(1):166–171 Darrouzet F et al (ed) (2009) The Earth’s plasmasphere: a cluster and IMAGE perspective. Space Sci Rev 145(Issues):1–2 Frey HU et al (2001) The electron and proton aurora as seen by IMAGE-FUV and FAST. Geophys Res Lett 28:1135–1138 Fung SF, Green JL (2005) Modeling of field-aligned radio echoes in the plasmasphere. J Geophys Res 110, A01210. doi:10.1029/2004JA010658 Fuselier SA et al (2002) Localized ion outflow in response to a solar wind pressure pulse. J Geophys Res 107(A8). doi:10.1029/2001JA000297 Goldstein J et al (2002) IMF-driven overshielding electric field and the origin of the plasmaspheric shoulder of May 24, 2000. Geophys Res Lett 29. doi:10.1029/2001GL014534 Grebowsky JM (1970) Model study of plasmapause motion. J Geophys Res 75:4329–4334 Green JL et al (2002) On the origin of kilometric continuum. J Geophys Res 107(A7). doi:10.1029/ 2001JA000193 Green JL et al (2004) Association of kilometric continuum radiation with plasmaspheric structures. J Geophys Res 109, A03203. doi:10.1029/ 2003JA010093 Mende SB et al (2000) Far-ultraviolet imaging from the IMAGE spacecraft. 1. System design. Space Sci Rev, IMAGE special issue, 91:243–270 Mende SB et al (2000) Far-ultraviolet imaging from the IMAGE spacecraft. 2. Wideband FUV imaging. Space Sci Rev, IMAGE special issue, 91:271–285 Mende SB et al (2000) Far-ultraviolet imaging from the IMAGE spacecraft. 3. Spectral imaging of Lyman-alpha and OI 135.6 nm. Space Sci Rev, IMAGE special issue, 91:287–318 Mende SB et al (2001) Global observations of proton and electron auroras in a substorm. Geophys Res Lett 28:1139–1142 Mitchell DG et al (2001) Imaging two geomagnetic storms in energetic neutral atoms. Geophys Res Lett 28:1151 Mitchell DG et al (2003) Global imaging of O+ from IMAGE/HENA. Space Sci Rev, IMAGE special issue 109(Issues):1–4, 63–75 Moore TE et al (2001) Low energy neutral atoms in the magnetosphere. Geophys Res Lett 28(6):1143–1146 Pollock CJ et al (2001) First medium energy neutral atom (MENA) images of Earth’s magnetosphere during substorm and storm-time. Geophys Res Lett 28(6):1147–1150 Reinisch BW et al (2000) The radio plasma imager investigation on the IMAGE spacecraft. Space Sci Rev, IMAGE special issue 91:319–359 Reinisch BW et al (2001) First results from the radio plasma imager on IMAGE. Geophys Res Lett 28:1167–1170 Reinisch BW et al (2004) Plasmaspheric mass loss and refilling as a result of a magnetostorm. J Geophys Res 109, A01202. doi:10.1029/2003JA009948 Sandel BR et al (2000) The extreme ultraviolet imager investigation for the IMAGE mission. Space Sci Rev, IMAGE special issue 91:197 Sandel BR et al (2001) Initial results from the IMAGE extreme ultraviolet imager. Geophys Res Lett 28(8):1439

International Sun Earth Explorers 1 & 2 C. T. Russell

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The ISEE-1 and 2 Missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Key Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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The ISEE-1&2 Explorers were a joint NASA-ESA program with instruments on both spacecraft from the USA and Europe with ISEE-1 built in the USA and ISEE-2 in Europe, launched on a single rocket into the same orbit. The interspacecraft distance was variable, allowing the velocities of the boundaries traversed by the spacecraft to be measured and hence their thickness to be determined and compared quantitatively with theory. The missions’ major discoveries included determining that magnetic reconnection controlled magnetospheric dynamics, what factors controlled the rate of reconnection, and which plasma physical processes provided the dissipation for collisionless shocks. Together with ISEE-3 stationed in orbit around the L-1 Lagrangian point, this was the first space weather mission. Keywords

Bow shock • Magnetopause • Magnetotail • Reconnection • Charged-particle acceleration

C.T. Russell (*) Department of Earth and Space Sciences, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_26

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Introduction The Earth’s magnetosphere and its interaction with the supersonic flow of plasma from the Sun and the solar wind, are dynamic, constantly in motion and constantly changing. Initial studies of this region with high-altitude elliptical orbiters, especially on the Orbiting Geophysical Observatories 1, 3, and 5, had shown the rapid motion and oscillations of the bow shock and the magnetopause. Not knowing the speed of the motion meant that the temporal profiles could not be converted to spatial profiles. Hence, quantitative comparison with theory was difficult in the early days. Nevertheless, qualitative studies did point to the role of the southward magnetic field in magnetic flux transport from the dayside of the magnetosphere to its magnetotail (Aubry et al. 1970; Russell and McPherron 1973), and later reconnection in the tail returning this magnetic flux and stored energy to the nightside magnetosphere. These observations provided the context for the design of the ISEE-1 and 2 mission and its companion spacecraft ISEE-3 that was for the prime ISEE-1 and 2 mission period (with some delay due to its later launch), in orbit about the L-1 Lagrangian point, 237 Earth radii (RE) in front of the Earth. The ISEE-1 and 2 spacecraft would co-orbit the Earth at low latitudes in an elliptical orbit with sufficient distance to probe the magnetopause, bow shock, and nearEarth magnetic tail using a variable separation to measure the velocity of the boundaries and hence translate temporal profiles into spatial. The mission was conceived as a joint NASA-ESA program with instruments provided by both the USA and Europe, with the launch provided by the USA. ISEE-1, the larger “mother” spacecraft, was built by NASA, while ISEE-2, the smaller daughter spacecraft, was built under contract to ESA. ISEE-1 and 2 were successfully launched from the Eastern Test Range at the Cape Canaveral Air Force Base in Florida in October 1997 and, after 10 years of operation, entered the Earth’s atmosphere in 1987. ISEE-3 was moved out of the forward Lagrangian point and used to probe the distant magnetotail and then sent to intercept comet GiacobiniZinner in 1985, despite not being instrumented to optimally make either distant magnetotail or cometary measurements. Thus, most space weather studies could only be undertaken using the periods when Earth-orbiting spacecraft were in the solar wind until the launch of the Wind spacecraft in late 1995. The lack of continuous interplanetary field measurements throughout the 1970s, 1980s, and early 1990s also reduced the number of detections of interplanetary field enhancements that have been associated with collisions of small asteroids and meteorites in the solar wind, some of which could produce hazardous debris near 1 AU (Lai et al. 2013a, b).

The ISEE-1 and 2 Missions The ISEE 1 and 2 missions were launched into an elliptical orbit that penetrated the bow shock and magnetopause into the solar wind, centered in October of each year, and crossing through the center of the tail in March and April

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Fig. 1 The ISEE-1 and 2 orbit illustrating its annual “precession” through the magnetosphere due to its motion around the Sun (Russell 2000)

(Ogilvie 1982; Formisano 1982), as illustrated in Fig. 1. The separation of the two spacecraft was variable and was measured in terms of the time delay between the crossings of the same radial distance by the spacecraft. This time was varied through the mission, as shown in Fig. 2. One second delay is equivalent to 2 km separation at 15 RE. Since the separation time could exceed 5,000 s, the spatial separation could approach 2 RE at 15 RE. At apogee where the spacecraft traveled more slowly, the separation was less, but near perigee where the speeds were much faster, the spacecraft were separated by a very great distance. The large occasional separations meant that one antenna could not view both spacecraft, and the inability often to get a second antenna for the two spacecraft meant that the spacecraft went into single-spacecraft mode as they had no memory devices, because of the technology of the time, and had decided not to use tape recorders. Eventually the project stopped using large separations. The use of time delay to obtain the speed of a boundary along the normal to the boundary depends on the ability of the spacecraft instruments to determine the direction of the normal in other ways. At times, the direction of the normal can be specified by the geometry of the boundary to the accuracy needed. At least on the large scale, it was possible to occasionally obtain four spacecraft measurements which provide an unambiguous velocity and normal direction, as shown in Fig. 3 for an interplanetary shock. Such four-spacecraft observation opportunities were used to calibrate single-spacecraft techniques such as shock co-planarity formulas (Russell et al. 1983). The ISEE-1 spacecraft carried 13 instruments led by different investigators. These covered the thermal plasma, the energetic particles up to cosmic ray energies, plasma waves, and the magnetic and electric fields. The ISEE-2 spacecraft had

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Fig. 2 The separation strategy of the ISEE-1 and 2 spacecraft from launch to 1984. One second of separation is equivalent to 2 km at a distance of 15 RE (Russell 2000)

8 instruments, each led by a different investigator providing a subset of the ISEE-1 measurements, not a duplicate set of measurements. These measurements are listed in Tables 1 and 2 (Ogilvie 1982; Formisano 1982). The ISEE-1 and 2 spacecraft continued to operate for 10 years with most instruments still functioning at the end of the mission. The re-entry into the atmosphere was caused by gravitational torques that increased the eccentricity of the orbit forcing perigee into the atmosphere. The mission achieved its objectives. The motions of the boundaries were measured and the physics of the processes

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Fig. 3 Four encounters with the same interplanetary shock on August 18, 1978, as seen in the magnitude of the magnetic field. Location of the measurement points shown by asterisks in the X-Y solar ecliptic plane (Russell 2000)

involved were determined. Not all the problems of the magnetosphere were solved. In particular, it became clear that the magnetospheric system required simultaneous measurements in the solar wind, in the tail, in the equatorial plane, and at high latitudes in the polar cusp. Such a mission, International Solar Terrestrial Probes (ISTP), including Wind, Polar, and Geotail, was designed and launched in the mid-1990s, but a key element, the equatorial measurements, was descoped. The next major mission solar terrestrial mission was Cluster, a four-spacecraft mission to the polar cusp. The most recent major magnetospheric mission, Magnetospheric

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Table 1 ISEE-1 investigations Principal investigator K. Anderson L. Frank D. Gurnett C. Russell S. Bame C. Harvey R. Helliwell J. Heppner D. Hovestadt D. Williams F. Mozer K. Ogilvie R. Sharp

Measurement Electrons and protons Electrons and protons Plasma wave electric Magnetic Magnetic field Plasma ions Plasma electrons Plasma density/active/passive Wave receiver Plasma waves Cosmic rays Energetic protons Electrons Electric field Plasma electrons Ion composition

Range 8–380 keV 1–50 keV 5.6 Hz–2 M Hz 5.6 Hz–10 k Hz 256 nT; 8,192 nT 5 eV–40 keV 5 eV–20 keV

0.1–3,200 Hz 0.05–20 MeV/nucleon 25 keV–2 MeV 25 keV–1 MeV 0–12 Hz 7 eV–7 keV 0–40 keV/q; 1–138 AMU

Table 2 ISEE-2 investigations Principal Investigator K. Anderson L. Frank D. Gurnett C. Russell C. Harvey E. Keppler A. Egidi G. Paschmann

Measurement Electrons and protons Electrons and protons Magnetic and electric field Magnetic field Electron density/propagation Protons/electrons Solar wind ions Fast plasma, ions Electrons

Range 1.5–280 keV 1.0 eV–45 keV 5.6 Hz–31 kHz 256 nT; 8,192 nT 25–800 keV 50 eV/q–25 keV/q 50 eV–40 keV 5 eV–20 keV

Multiscale (MMS) may recover some of these objectives. It is an equatorial four-spacecraft mission with simultaneous solar wind and magnetotail measurements made by other spacecraft not originally associated with MMS.

Technical Challenges A mission always involves some design trades. One trade was made that reduced the useful data by about half, and that was the decision to obtain only real-time data. It apparently was not appreciated that on many occasions the separation of the two spacecraft would not allow data acquisition from both spacecraft. It should be noted that earlier missions did have tape recorders.

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The most serious instrumental problems involved electric field measurements and the spacecraft potential. The spacecraft potential affects the ability to obtain measurements of the cold and low-energy plasma. The electric field measurements are affected by this and also have their own design problems. Basically, on ISEE-1 and 2, it was difficult to understand the electric field surrounding the spacecraft, either DC or AC. For example, it is unknown whether many of the identified plasmapause boundaries were real density changes or whether the flow of the plasma just was in the direction away from the inlet to the instrument. This problem has been addressed on other spacecraft with electric potential control and better electric antenna design.

Key Findings The ISEE-1 and 2 missions were designed first and foremost to measure the speed of motion of plasma boundaries. This it was able to do very well in most instances. Figure 3 shows four measurements of the magnetic field measured by ISEE-1, 2, and 3 and IMP-8, all in the solar wind during the passage of an interplanetary shock. Measurements like this one could provide an accurate orientation of the shock normal and the speed of the shock. These were then compared with the normal derived at each location for the single-spacecraft techniques such as magnetic co-planarity. While some single-spacecraft techniques were found to be less accurate than expected, it was possible to develop good techniques based on the comparisons possible when four spacecraft were present. Some of these comparisons and improvements, especially at the magnetopause, have continued with the Cluster mission. Some of the key findings were in the area of plasma physics. Figure 4 shows a series of bow shock encounters as seen in the magnetic field strength and displayed versus the ion inertial length. One can see that at low Mach number (top panel), there are standing whistler-mode waves decaying over some distance and higher frequency waves (1 Hz) generated in the shock and moving upstream. At a higher Mach number (but still subcritical), the wavelength of the standing whistler shortens and the noise is more confined to the shock ramp and vicinity. As the shock strengthens further, the noise increases over the entire region around the shock. However, at even higher frequencies, the turbulence cannot be resolved well because the fast motion of the shock has interacted with the instrument’s antialiasing filter and smoothed the data. The ISEE-1 and 2 spacecraft’s most important discovery was the proof that the process known as reconnection exists in a magnetized plasma as predicted, and it controls the behavior of the magnetosphere. This discovery had been presaged by the motion of the magnetopause controlled by the southward component of the magnetic field with OGO-5 observations, but until ISEE-1 and 2 observed the predicted accelerated flow in the magnetopause (Paschmann et al. 1979), it was not accepted by the scientific community. Figure 5 shows these critical data. Here the VZ component (seen by ISEE-1) is the northward flow predicted to occur within the magnetopause. Furthermore, the accelerated flow is present steadily. When the

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Fig. 4 Evolution of the magnetic field profile of the Earth’s bow shock as the Mach number of the shock increases with respect to the critical Mach number. Distance is measured in terms of the ion inertial length (Russell 2000)

boundary rocks back and forth across the spacecraft, the flow is always seen at the magnetopause on this day with “antiparallel” magnetic fields in the magnetosheath and magnetosphere. ISEE-1 and 2 also revealed the unexpected. One important discovery about reconnection that makes perfect sense in retrospect is that when the plasma pressure far exceeds the magnetic pressure (called high beta conditions), the magnetic reconnection rate is minimal. This occurs because the forces in the plasma are nonmagnetic under these conditions. Only when the plasma pressure is low can the magnetic stress control the plasma flow (Scurry et al. 1994). A totally unexpected discovery at the magnetopause was transient reconnection or what was called a flux transfer event. In this process, limited bundles of magnetic flux became reconnected about 10 k Webers at a time. Figure 6 shows the magnetic field observed on both ISEE-1 and ISEE-2 as the two spacecraft approach the magnetopause. Periodic disturbances then appear moving across the two spacecraft

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Fig. 5 Plasma and magnetic field measurements across multiple crossings of the magnetopause when reconnection was taking place almost continually (Russell 2000)

with field not parallel to the magnetospheric field (Elphic and Russell 1979). This phenomenon is common at the Earth’s magnetopause, present but rare at Jupiter (Walker and Russell 1985), and very frequent at Mercury (Russell and Walker 1985).

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Fig. 6 The magnetic field in boundary-normal coordinates across the magnetopause in the presence of FTEs on November 29, 1977 (Russell 2000)

One of the key findings from the ISEE-1, 2, and 3 data that was not fully appreciated at the time was the interplanetary field enhancement (IFE) which is a nearly pure magnetic compression that is traveling nearly at the solar wind speed (Arghavani et al. 1985). Because of the correlation with the phase of the asteroid 2201 Oljato with the appearance of IFEs at Venus (Russell 1987), and because of its evolution in rate of occurrence between the PVO and VEX missions, this phenomenon is now understood to be due to collisions between small bodies (meteoroids) with debris co-orbiting with Oljato (Lai et al. 2013a). The long-term record of data at 1 AU was not originally explored, but recently has been, and it has been found that IFEs at the same longitude as today were present 40 years ago. Thus, collisions with material orbiting the Sun near the Earth are occurring and archives of interplanetary magnetic records can provide insight to where these debris trails are.

Conclusion The ISEE-1 and 2 measurements were obtained over 30 years ago, but they are still providing insight to this day. It is fortunate that some of these records have been preserved. However, it is unfortunate that the data have not been better preserved. The data are difficult to access, many of them are missing, and the documentation has become separated from the data in many cases. Thus, while with time some insight into the phenomena has been gained, often this later insight cannot be exploited. It must not be forgotten that data can become useful at future times for

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reasons not presently understood. Planetary defense is now an important issue, and old records aid in understanding processes whose time scale is measured in decades for which there is no way to get these long databases except to use historical records. Acknowledgments We are grateful to NASA and the teams of scientists and engineers who staffed the ISEE-1 and 2 missions. ESA’s support was equally invaluable. Many of the data were preserved by the National Space Science Data Center and can be still accessed today.

References Arghavani MR, Russell CT, Luhmann JG, Elphic RC (1985) Interplanetary magnetic field enhancements in the solar wind: statistical properties at 1 AU. Icarus 62:230–243 Aubry MP, Russell CT, Kivelson MG (1970) Inward motion of the magnetopause before a substorm. J Geophys Res 75:7018–7031 Elphic RC, Russell CT (1979) ISEE-1 and -2 magnetometer observations of the magnetopause. In: Battrick B (ed) Magnetospheric boundary layers, volume ESA SP-148. European Space Agency, Paris, pp 43–50 Formisano V (1982) The International Sun-Earth Explorer mission – ISEE-2, data from ISEE-1 for the IMS period. In: Russell CT, Southwood DJ (eds) IMS source book. American Geophysical Union, Washington, DC, pp 27–36 Lai HR, Russell CT, Wei HY, Zhang TL (2013a) The evolution of co-orbiting material in the orbit of 2201 Oljato from 1980 to 2012 as deduced from Pioneer Venus Orbiter and Venus Express magnetic records. Met Planet Sci. doi:10.1111/maps.12102 Lai HR, Wei HY, Russell CT (2013b) Solar wind plasma profiles during interplanetary field enhancements (IFEs): consistent with charged-dust pickup. AIP Conf Proc 1539:402–405. doi:10.1063/1.4811070 Ogilvie KW (1982) Data from ISEE-1 for the IMS period. In: Russell CT, Southwood DJ (eds) IMS source book. American Geophysical Union, Washington, DC, pp 21–26 ¨ , Papamastorakis I, Sckopke N, Haerendel G, Bame SJ, Asbridge Paschmann G, Sonnerup BUO JR, Gosling JT, Russell CT, Elphic RC (1979) Plasma acceleration at the Earth’s magnetopause: evidence for reconnection. Nature 282:243–246 Russell CT (1987) Interplanetary magnetic field enhancements: further evidence for an association with asteroid 2201 Oljato. Geophys Res Lett 14:491–494 Russell CT (2000) ISEE lessons for Cluster. In: Harris RA (ed) Proceedings of the Cluster-II workshop: multiscale/multipoint plasma measurements, ESA SP-449. European Space Agency, Noordwijk, pp 11–23 Russell CT, McPherron RL (1973) The magnetotail and substorms. Space Sci Rev 15:205–266 Russell CT, Walker RJ (1985) Flux transfer events at Mercury. J Geophys Res 90:11,067–11,074 Russell CT, Mellott MM, Smith EJ, King JH (1983) Multiple spacecraft observations of interplanetary shocks: four spacecraft determinations of shock normal. J Geophys Res 88(A6):4739–4748 Scurry L, Russell CT, Gosling JT (1994) Geomagnetic activity and the beta dependence of the dayside reconnection rate. J Geophys Res 99:14,811–814,814 Walker RJ, Russell CT (1985) Flux transfer events at the Jovian magnetopause. J Geophys Res 90:7397–7404

ISAS-NASA GEOTAIL Satellite (1992) A. Nishida and Toshifumi Mukai

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spacecraft, Scientific Payload, and Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic Structure of the Magnetotail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Near-Earth Reconnection and Substorm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure of the Reconnection Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sources of Magnetotail Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Wind Entry Following Magnetic Reconnection on the Dayside Magnetopause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Wind Entry from the Flanks of the Tail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plasma of the Terrestrial Origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waves in the Magnetotail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

GEOTAIL spacecraft launched on 24 July 1992 has explored the Earth’s magnetotail across the range of 10–210 RE from the Earth. GEOTAIL not only clarified the basic structure of the magnetotail both in quiet and active times, but it also revealed the kinetics of the plasma that underlies macroscopic dynamics. In the magnetotail magnetic reconnection is the key process which governs energy dissipation and acceleration of ions and electrons. GEOTAIL has A. Nishida and T. Mukai are retired A. Nishida (*) Institute of Space and Astronautical Science, Machida, Tokyo, Japan e-mail: [email protected] T. Mukai Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Hino, Tokyo, Japan e-mail: [email protected]; [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_27

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addressed the relation between the reconnection and auroral phenomena and clarified the kinetics of the energy conversion process in the reconnection region that operates on the scale of the ion inertia length. Understandings have also been advanced on the entry of the solar wind plasma into the magnetotail due to turbulence generated on the magnetopause and the excitation of plasma waves on account of prevalent nonequilibrium velocity distributions of plasma particles. The processes addressed by in-situ observations by GEOTAIL in space should be common to collisionless plasmas that prevail in astrophysical objects. Keywords

Magnetotail • Plasma sheet • Plasmoid • Lobe • Solar wind • Aurora • Substorm • Acceleration • Heating • Reconnection • Neutral line • Convection • Kelvin-Helmholtz instability • Hall current • Ion-electron decoupling

Introduction Cosmic rays, that is, energetic ions and electrons having energies up to ~1021 erg, pose the greatest threat to life in the universe. However, the life on the Earth has been protected from the most part of the spectrum by the magnetic field generated by the dynamo action in the core region. Under the pressure of the solar wind that flows continually from the solar corona, the geomagnetic field is enclosed in a domain called magnetosphere which shields much of the cosmic rays. The magnetosphere is not quiet and static. Solar wind produces a complex structure and activates the magnetosphere. This is the subject of this chapter. Energy and momentum imparted from the solar wind generate global convection in the magnetosphere which circulates between the day and the night side. Geomagnetic field lines are stretched at the same time and form the magnetotail extending behind the Earth. The magnetic energy is converted to the kinetic energy in the magnetotail. This energy conversion occurs primarily through the magnetic reconnection at the neutral sheet in the magnetotail. The collapse of extended field lines produces a variety of disturbances such as substorms on the earthward side of the reconnection region, while plasmoid is ejected on its anti-earthward side. Thus the magnetotail plays a key role in the dynamics of the magnetosphere. The GEOTAIL spacecraft was uniquely designed to address the physics of the Earth’s magnetotail. The prime target was the magnetic reconnection in the nearEarth magnetotail: its location and development, relation to substorms, and microscopic structure of the energy conversion process. Also studied are the solar wind entry into the magnetosphere, outflow of ionospheric ions to the magnetotail, and excitation of plasma waves in the tail plasma. These are the basic processes that make the foundation of the space weather phenomena. GEOTAIL was implemented as a joint mission between ISAS (Institute of Space and Astronautical Science) of Japan and NASA of USA. ISAS developed the spacecraft and NASA launched it. Responsibilities for onboard instruments were

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shared. It was launched on 24 July 1992 and has been working soundly for more than two solar cycles by now. Acquired data have been openly disseminated to the international space science community.

Spacecraft, Scientific Payload, and Orbit The configuration of the GEOTAIL spacecraft is shown in Fig. 1. It has a cylindrical shape with diameter of 2.2 m and height of 1.6 m. Two masts with 6-m length are deployed symmetrically to separate the magnetometers from the main body, and four 50-m wire antennas are deployed to measure the electric field from DC to 800 kHz. Particular attention was paid to make the spacecraft electromagnetically clean. The spacecraft attitude is spin stabilized with the rate of 20 rpm and with the axis being nominally perpendicular to the ecliptic plane; more exactly, the spin axis was controlled to be inclined sunward and make an angle of 87  with respect to the solar ecliptic plane for 11.5 years after launch until the fuel was exhausted. Seven sets of science instruments are on board GEOTAIL, as listed in Table 1. Measured items constitute basic elements of space plasmas. Magnetic field represents the framework of the magnetosphere. Electric field reflects the plasma dynamics. Waves in these fields are essential ingredients of the collisionless plasma. A unique feature in the plasma wave instrument is the waveform capture (WFC), which was

MST-S

WANT-B PANT-B

HGA LGA-A

RCS THRUSTERS

WATN-A LGA-B

MGA

PANT-A MST-F

Fig. 1 Configuration of the GEOTAIL spacecraft (Nishida 1994)

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Table 1 Science instruments on board GEOTAIL (Nishida 1994) Item Electric field (EFD)

Magnetic field (MGF)

Description Spherical probe and wire antenna Electron boomerang Ion emitter Fluxgate Search coil

Plasma (LEP)

Plasma (CPI)

Energetic particles (HEP)

Energetic particles (EPIC)

Ion/electron 3-dim.velocity distributions Solar wind ions Ion mass/energy spectrum Ion/electron 3-dim velocity distributions Solar wind ions Ion mass/energy spectrum Low-energy particles Ion/electron burst Medium-energy ion isotope ratio High-energy ion isotope ratio Ion charge state/mass/energy Ion mass and energy

Plasma waves (PWI)

Electron energy Frequency sweep Multichannel analyzer Waveform capture

Range dc – 32 Hz (2 comp) dc – 10 Hz (3 comp) dc – 16 Hz (3 comp) 1–50 Hz (3 comp)

PI, co-I K. Tsuruda F.S. Mozer R. Schmidt S. Kokubun M. Acuna

10 eV–40 keV/q

D.H. Fairfield T. Mukai

150 eV–8 keV/q 0.1–25 keV/q 1 eV–50 keV/q

L.A. Frank

150 eV–7 keV/q 1 eV–50 keV/q 30 keV–1.5 MeV/n 0.7–3.5 MeV/n 5–50 MeV/n 10–230 MeV/n 30–230 keV/q > 50 keV–5 MeV > 30 keV E: 25 Hz–800 kHz H:25 Hz–12.5 kHz 10 Hz–4 kHz

T. Doke B. Wilken

D.J. Williams

H. Matsumoto R.R. Anderson

quite a new technique in those days (although it has become common to plasma wave instruments on board recent spacecraft). Plasma and particles are measured by four sets of experiments because of their vital importance in physics of the magnetosphere. Energy ranges for the ion measurements covered by these experiments are shown in Fig. 2. For detailed description of each instrument, refer to the special section “GEOTAIL Instruments and Initial Results” of the Journal of Geomagnetism and Geoelectricity (vol. 46, pp. 3–95 and 669–733, 1994). One of the plasma instruments, the low-energy plasma (LEP) experiment, became inoperative on 22 August 1992, when a latch-up occurred in the key part

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Fig. 2 Energy coverage of plasma and particle experiments on board GEOTAIL

of the electronic circuit due to electrical arcing, but this instrument was revived on 1 September 1993, by turning off the spacecraft power in the lunar shadow which was created on purpose. No experiments were adversely affected by this special operation. The recovery of LEP was critical for the success of the GEOTAIL mission, since most of the results to be described in the subsequent sections have been brought forth by the LEP observations. A key feature of the LEP energy-per-charge analyzers is geometrical factors which are larger than the conventional ones in those days; the geometrical factor of the LEP ion analyzer is more than 20 times larger than that of the CPI hot plasma analyzer. The large geometrical factor of LEP means high sensitivity so that high time resolution measurements can be made with sufficient counting statistics. This has proved to be vital especially for the studies of magnetic reconnection and plasma transport processes across boundary layers (i.e., magnetopause as well as internal boundaries such as the plasma sheet boundary layer). On the other hand, the detection efficiency of micro-channel plates (MCP), the particle detectors used along with the energy analyzers, generally degrades with the total counts integrated over the measurements when they are operated with a fixed bias voltage. Therefore, the degradation would be faster if the count rate is higher. The bias voltage is increased if the detector gain of LEP decreases in order to keep the detection efficiency at a reasonable value. The degradation rate, however, was much slower than had been anticipated, and as of 2014 after more than 20 years have elapsed, the LEP instrument is still providing useful observations of magnetospheric plasma. It is mandatory to calibrate the detection efficiency with in-flight data, since the efficiency varies with the instrument operation time. In LEP, the ion detectors are calibrated as follows. At first, after subtraction of background noise, relative

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Fig. 3 Comparison of proton energy distributions measured by three different instruments, LEP-EA, EPIC-STICS, and EPIC-ICS, on board GEOTAIL (Courtesy of ISAS/JAXA)

efficiencies between different channels (detectors at different elevation angles) are examined. Fortunately the relative efficiencies of the ion detectors have not changed throughout the observation, so that those measured in the preflight calibration experiment in the laboratory have been used. Then, ion velocity moments are calculated, and the resultant ion density is compared with electron density estimated from the plasma wave data: cutoff frequency of the continuum radiation in various regions including plasma sheet, lobe, and magnetosheath. From this comparison, the absolute value of the ion detection efficiency can be obtained. Correction of the electron detection efficiency needs a more complicated procedure, since the electron data are sensitive to the spacecraft potential and contain spurious data due to photoelectrons and secondary electrons. In addition, the detector efficiency depends on the electron energy. The detail of the calibration method is described elsewhere (Saito and Mukai 2007; McFadden et al. 2007). Figure 3 shows an example of proton energy distribution measured by three different instruments, LEP-EA, EPIC-STICS, and EPIC-ICS. Although calibrations of the three instruments were carried out independently, agreement among data of these instruments is excellent, which demonstrates high reliability of the respective calibration procedures. For the first 2 years, the spacecraft surveyed the distant magnetotail (with apogees on the nightside at 80–210 RE from the Earth) by executing doublelunar-swingbys orbits. The orbits in this distant-tail phase are shown in Fig. 4 (left) with xy projection on top and xz projection at bottom. The apogee was lowered to 50 RE in mid-November 1994 and then further down to 30 RE in order to focus on the magnetic reconnection in the near-Earth magnetotail. The inclination was set at 7 in order that the apogee is to be on the tail midplane, which is

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Fig. 4 Orbits of the GEOTAIL spacecraft (Courtesy of ISAS/JAXA)

hinged to the geomagnetic equatorial plane at about 10 RE at midnight, around the December solstice when the spacecraft is free from shadowing by the Earth. The perigee was about 10 RE so that the spacecraft skimmed the magnetopause on the dayside; it was further reduced later to 9–9.5 RE to increase the chances of observing the low-latitude boundary layer of the magnetosphere. The orbits in 1999 are shown in Fig. 4 (right). After 2007 the orbit is no longer controlled and currently the inclination is about 30 .

Basic Structure of the Magnetotail Figure 5 shows the noon-midnight meridional section of the magnetotail in quiet (a) and active (b) conditions (Hones 1984, modified). The x direction is toward the sun, the z direction contains the Earth’s magnetic dipole, and the y direction is perpendicular to x and z. Magnetic field is directed earthward in the northern half of the tail and anti-earthward in the southern half. The “tail lobe” in high latitudes is filled by open field lines which have only one root on the Earth. In low latitudes field lines are closed, that is, they have both roots on the Earth. The interface where the sunward component Bx is zero is called the neutral sheet. Actually the neutral sheet is often inclined to the (x,y) plane. In the absence of the reconnection, Bz should be northward everywhere. However, magnetic field lines are reconnected in the magnetotail and hence Bz is southward beyond certain distance. In quiet times the magnetic neutral line, where Bz changes from northward to southward, is located in the distant tail (Fig. 5a).

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Fig. 5 Basic structure and terminology of the magnetotail in (a) quiet and (b) active states (After Hones (1984), modified)

This neutral line, called “distant neutral line,” marks the demarcation between the closed field lines and the open field lines. The open field lines have been produced by reconnection on the dayside magnetopause, move from the lobe region toward the neutral sheet, and are closed by reconnection at the distant neutral line. Plasma which has been heated in the process flows earthward on the earthward side of the neutral line and anti-earthward on the anti-earthward side. The earthward flow accompanies closed field lines, and the anti-earthward flow accompanies the field lines that are no longer rooted on the Earth and extended to the solar wind. The hot plasma deposited on the closed field lines constitutes the “plasma sheet.” Magnetic flux transported by the flow is represented by Ey = VxBz. To find the location of the distant neutral line, seven orbits of GEOTAIL are selected when the geomagnetic activity index Kp was higher than 3 for 24 h or more, and the sums of Ey are calculated separately for intervals of the tailward flow and the earthward flow. The ratio between them is plotted in Fig. 6. A sharp drop of the ratio is seen at a distance of about 130 RE from the Earth, suggesting that the neutral line tends to be located around this distance in moderately active times (Nishida et al. 1996). This does not necessarily mean, however, that the distant neutral line stays at any fixed position, because it could be pushed tailward by the outflowing plasma from a new reconnection line produced later on the earthward side (Maezawa and Hori 1998).

Near-Earth Reconnection and Substorm In active times another neutral line is formed in the near-Earth region (Fig. 5b) where field lines were formerly closed. Distance to the “near-Earth neutral line (NENL)” is in the x range of 20 to 30 RE (Nagai et al. 1998). The major factor

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Fig. 6 Ratio between magnetic fluxes transported tailward and earthward is plotted against the distance x from the Earth. The drop of this ratio from >1 to 10 keV) stream outward while low-energy electrons (100 Mev) are a better indicator of radiation risk to passenger and crews. Pregnant women are particularly susceptible

Moreover, operational challenges still exist with updating and keeping dashboard links and pages current and up to date. Implementing a vision of free and worldwide public space weather data dissemination via dashboard displays and web-based platforms raises fundamental computational challenges at the intersection of computer science, engineering, operations research, information management, and even social sciences. Space weather response and data sharing requires optimization of interdependent infrastructures, collecting and aggregating data in real time, reducing uncertainty in predictions, and understanding decisionmaker requirements for formulating effective response and management plans to space weather events. Leadership is required in community-wide model validation efforts for defining physical parameters and metrics formats relevant to dashboard applications and addressing uncertainties and challenges in model-data comparisons. Forecasting scores depend on a combination of probability of detection and probability of false detection. Space weather models themselves are evaluated on their strategic importance, operational significance, implementation readiness, and cost of operation, maintenance, and improvement. Empirical models also serve as a valuable baseline and possible independent product. Organizations such as the CCMC and SWPC have key roles in the independent validation of models and transitioning from research to weather operations. However, establishing standardized metrics for model and forecast evaluations remains a challenge.

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Table 3 NOAA Space Weather Scale for radio blackouts (http://www.swpc.noaa.gov/ NOAAscales/ – Accessed 19 Feb 2014)

Radio Blackouts R5 Extreme

R4

Severe

R3

Strong

R2

Moderate

HF Radio: Complete HF (high frequencyb) radio blackout on the entire sunlit side of the Earth lasting for a number of hours. This results in no HF radio contact with mariners and en route aviators in this sector Navigation: Low-frequency navigation signals used by maritime and general aviation systems experience outages on the sunlit side of the Earth for many hours, causing loss in positioning. Increased satellite navigation errors in positioning for several hours on the sunlit side of Earth, which may spread into the night side HF Radio: HF radio communication blackout on most of the sunlit side of Earth for one to two hours. HF radio contact lost during this time Navigation: Outages of low-frequency navigation signals cause increased error in positioning for one to two hours. Minor disruptions of satellite navigation possible on the sunlit side of Earth HF Radio: Wide area blackout of HF radio communication, loss of radio contact for about an hour on sunlit side of Earth Navigation: Low-frequency navigation signals degraded for about an hour HF Radio: Limited blackout of HF radio communication on sunlit side of the Earth, loss of radio contact for tens of minutes Navigation: Degradation of low-frequency navigation signals for tens of minutes

GOES X-ray peak brightness by class and by fluxa X20 (2  10 3)

Number of events when flux level was met; (number of storm days) Fewer than 1 per cycle

X10 (10 3)

8 per cycle (8 days per cycle)

X1 (10 3)

175 per cycle (140 days per cycle)

M5 (5  10 5)

350 per cycle (300 days per cycle)

(continued)

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Table 3 (continued)

Radio Blackouts R1 Minor

HF Radio: Weak or minor degradation of HF radio communication on sunlit of the Earth, occasional loss of radio contact Navigation: Low-frequency navigation signals degraded for brief intervals

GOES X-ray peak brightness by class and by fluxa M1 (10 5)

Number of events when flux level was met; (number of storm days) 2,000 per cycle (950 days per cycle)

a

Flux, measured in the 0.1–0.8 nm range, in W-m 2. Based on this measure, but other physical measures are also considered b Other frequencies may also be affected by these conditions

The development and evolution of digital dashboards and online reporting tools is in recognition that addressing space weather needs requires innovative, collaborative, and cost-effective ways (Kuznetsova 2012). Prior to such services, space weather models and data were first accessed and used exclusively by researchers and developers only. Models were later then used and validated by the entire community. Subsequent developments in real-time data flow monitoring and controlling systems meant that models could then continuously run in real time. Advantages were more robust processing and real-time data drivers. This led to the development of space weather displays that were customized for specific applications and missions. These had the benefits of being ready to be used by forecasters, while combining model output and data, but were still limited in availability to specific user groups. The advancement of current digital dashboards, such as the iSWA, has enabled flexible collection and dissemination of space weather information. This has revolutionized the transition from research to operations, addressing the custom needs of user communities. Tools are now available for forecasters worldwide via the Internet and mobile app platforms. Customized dashboard displays not only provide prototype innovative web-based forecasting and analysis tools but also serve to educate operators, students, and the general public. This has helped to lead joint operations and innovative partnership between space weather research, educational, and operational institutions worldwide. The International Space Environment Service (ISES) has engaged international coordination of space weather services since 1962. One of its mandates is to assist transition of research results into operations, with a commitment to free and open exchange of data and products, long-term data stewardship, and compliance with agreed-upon data standards and conventions. ISES provides mechanisms to facilitate and improve access to data and services, enhancing data availability, and information exchange. Such mandates are largely achieved by real-time imagery and data disseminated by dashboard services.

Sudden Impulse Warning

CANCELLATION

Latest Update

Extends Beyond

Feb 24

Feb 25

NOAA/SWPC Boulder, CO USA

Feb 23

Begin: 2014 Feb 18 0000 UTC

Fig. 31 Space weather alerts and warnings timeline (http://www.swpc.noaa.gov/alerts/warnings_timeline.html – Accessed 21 Feb 2014)

All data in Universal Time

WATCH (G-based)

Feb 22

WARNING (Onset) WARNING (Persistence)

Feb 21

SUMMARY

Feb 20

ALERT cr Continuatiion

Feb 19

Space Weather Alerts and Warnings Timeline

Updated 2014 Feb 21 2354 UTC

Legend Key:

Feb 18

>1pfu ELECTRON FLUX >2MeV >1Kpfu GEOMAGNETIC Sudden Impulse K=4 K=5 (G1) K=6 (G2) K>=7 (G3) K>=8 (G4) K>=9 (G5) WATCH G1 G2 G3 G4 or greoter STRATOSPHERIC Stratwarm

PROTONS >100Mev

X-Ray Events Flux >M5 Event >M5 (R2) Event >X1 (R3) Event >X10 (R4) Event >X20 (R5) RADIO EVENTS Type-II Type-IV 10 cm PROTONS >10Mev >10 pfu (S1) >100 pfu (S2) >1K pfu (S3) >10K pfu (S4) >100K pfu (S5)

ALERT (NOAA Scale)

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Conclusion Knowledge that a significant space weather event is occurring, as well as timely and accurate forecasts of the future state of the space environment, provides the means to take proactive measures to mitigate the impacts of these potentially damaging space weather events. The dependencies and interconnectedness of key infrastructure reaffirms that solar weather phenomena are not only a concern to scientists and physicists, but are critical knowledge for supporting a multitude of planners and decision-makers. Such user groups require access to accurate and real-time data about space weather phenomena to assess risks and to plan mitigation, response, and recovery measures. To this end, dashboard displays offer robust and integrated systems that provide information about past, present, and future space weather conditions. Unlike many other systems, dashboards provide a web-based interface that the user can customize to suit a unique set of data requirements in real time. There is a unique level of customization and flexibility available, drawing together information from various data sources from ground- and space-based observations. Moreover, information is publicly available and accessible via the Internet and mobile systems, providing a valuable resource for educating the public about space weather. Dashboard displays for dissemination of space weather information are continuously evolving. There are new resources increasingly appearing from various agencies, institutions, and operators to provide real-time views of space weather. Access to such tools provides users with a personalized “first look” at space weather information, detailed insight into space weather conditions, as well as tools for historical analysis of solar events. Such initiatives will continually support the open free exchange of space weather data and products worldwide for real-time forecasting and monitoring of space weather. In turn, this will contribute to improving the prediction of damaging space hazards for reducing and mitigating space weather impacts on technology, critical infrastructure, and human activities.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Early Solar and Heliophysical Space Missions ▶ Fundamental Aspects of Coronal Mass Ejections ▶ Introduction to the Handbook of Cosmic Hazards and Planetary Defense ▶ Medical Concerns with Space Radiation and Radiobiological Effects ▶ NASA Wind Satellite (1994) ▶ Nature of the Threat / Historical Occurrence ▶ NOAA Satellites and Solar Backscatter Ultra Violet (SBUV) Subsystems

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▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Dynamics Observatory (SDO) ▶ Solar Flares ▶ Solar Flares and Impact on Earth ▶ STEREO as a ‘Planetary Hazards’ Mission

References CCMC (2002) Concept of operations for the Community Coordinated Modeling Center (Prepared by Interagency Consortium – AFOSR, AFRL, AF/XOW, NASA GSFC, NASA HQ, NOAA, NSF, ONR, SMC) DashboardInsight.com (2014) What is a dashboard? http://www.dashboardinsight.com/articles/ digital-dashboards/fundamentals/what-is-a-dashboard.aspx. Accessed 19 Feb 2014 ExcelDashboardWidgets (2014) What is dashboard reporting? http://www.exceldashboardwidgets. com/what-is-dashboard/what-is-dashboard.html. Accessed 18 Feb 2014 Gordon B (2013) State of the Space Weather Prediction Center 2013. Space Weather Workshop, 16 April 2013. http://www.swpc.noaa.gov/sww/SWW_2013_Presentations/Tuesday_Morn ing/StateoftheSpaceWeatherPredictionCenter2013_BrentGordon_NOAASWPC.pptx Ideum.com (2011) Over 100K downloads for NASA Space Weather iPhone App in March. http://www.ideum.com/blog/2011/03/100k-downloads-for-nasa-space-weather-iphone-app/. Accessed 19 Feb 2014 ISES (2014) http://www.ises-spaceweather.org Kuznetsova M (2012) CCMC: models, tools and systems for operational space weather forecasting and analysis. Space Weather Workshop, 16–19 April 2012 Lloyd’s (2013) Solar storm risk to the North American electric grid. http://www.lloyds.com/~/ media/lloyds/reports/emerging%20risk%20reports/solar%20storm%20risk%20to%20the% 20north%20american%20electric%20grid.pdf. Accessed 19 Feb 2014 NASA (2011) http://www.nasa.gov/mission_pages/sdo/multimedia/20110907_briefing_materials_ prt.htm. Accessed 19 Feb 2014 NASA (2014) http://www.nasa.gov/mission_pages/hinode/solar_004.html. Accessed 19 Feb 2014 NASA CCMC (2014) http://ccmc.gsfc.nasa.gov. Accessed 19 Feb 2014 NASA Goddard Space Flight Center (2013) iSWA Wiki. http://iswa.ccmc.gsfc.nasa.gov/wiki/ index.php/Main_Page. Accessed 19 Feb 2014 NASA SDO – Solar Dynamics Observatory (2014) http://sdo.gsfc.nasa.gov. Accessed 19 Feb 2014 NASA Sun-Earth Connection Program (2014) http://sec.gsfc.nasa.gov. Accessed 19 Feb 2014 National Research Council (2008) Severe space weather events – understanding societal and economic impacts: a workshop report. The National Academies Press, Washington, DC NOAA (2000) New scales help public, technicians understand space weather. http://www.swpc. noaa.gov/NOAAscales/EosNewScales.html. Accessed 19 Feb 2014 NOAA SWPC (2000) SWPC Center review presentation materials http://www.swpc.noaa.gov/ AboutUs/Review2000/index.html. Accessed 19 Feb 2014 Space Science Division (2014) Compact coronagraph http://www.nrl.navy.mil/ssd/branches/7680/ CCOR. Accessed 19 Feb 2014 U.S. Department of Homeland Security (2011a) National infrastructure protection plan. Department of Homeland Security

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U.S. Department of Homeland Security (2011b) http://www.dhs.gov/xlibrary/assets/rma-geomag netic-storms.pdf. Accessed 19 Feb 2014 University Corporation for Atmospheric Research (2009) 2009 Community review of the NCEP Space Weather Prediction Center http://www.ncep.noaa.gov/director/ucar_reports/SWPC_ Report_UCAR_Final.pdf. Accessed 19 Feb 2014 White House (2013) Report on space weather observing systems: current capabilities and requirements for the next decade. http://www.whitehouse.gov/sites/default/files/microsites/ostp/ spaceweather_2013_report.pdf. Accessed 19 Feb 2014

NOAA Satellites and Solar Backscatter Ultra Violet (SBUV) Subsystems Su-Yin Tan

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Instrument Calibration and Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Applications and Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Future Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

450 453 457 459 463 468 473 480 483 483 484

Abstract

Ultraviolet radiation is a component of cosmic radiation that represents a health hazard to humans and indeed to many types of flora and fauna. Ultraviolet and X-ray radiation has the ability to penetrate the Earth’s atmosphere. Ultraviolet (UV) and even more energetic X-ray radiation can have harmful effects on human health, including cellular damage in living tissues that can cause genetic mutations and skin cancer. Stratospheric ozone generally prevents damaging ultraviolet radiation from reaching the Earth’s surface. This protective function of ozone plays an important role in regulating the temperature structure of the atmosphere and climate system. Monitoring stratospheric ozone is an important endeavor for many reasons, including assessing the recovery of ozone levels following the implementation of the Montreal Protocol and subsequent S.-Y. Tan (*) Department of Geography and Environmental Management, University of Waterloo, Waterloo, ON, Canada e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_31

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amendments. Long-term and global mapping of total column ozone and the ozone vertical profile are thus essential functions. These ozone monitoring functions can be provided by satellite-based remote sensing instruments. This chapter examines the Solar Backscatter Ultraviolet (SBUV) instruments on weather satellites operated by the US National Oceanic and Atmospheric Administration (NOAA). SBUV instruments have captured the longest continuous record of ozone measurements since the Nimbus-4 satellite was launched in April 1970. This chapter first details the development of the SBUV instrument and its operational timeline. A technical overview of SBUV instrument mechanics and operation is provided, as well as a review of calibration procedures, retrieval algorithms, and sources of error. Finally, primary applications and benefits of SBUV subsystems for measuring global ozone distribution are presented in some detail. In addition, future challenges and developments for collecting high vertical resolution and temporal ozone data are addressed. The long-term operation of the SBUV family of instruments has supported a successful ozone monitoring program. However, combined instrumentation from next-generation NOAA weather satellites is required in order to continue an unbroken ozone record. Such observations are necessary for supporting trend studies and model testing for forecasting what global ozone levels will be in the future. Keywords

Atmospheric chemistry • Backscatter ultraviolet (BUV) • Climatology • Cloud Cover Radiometer (CCR) • Global Ozone Monitoring Experiment (GOME) • JPSS polar-orbiting environmental satellite • Meteorology • Montreal Protocol • National Aeronautics and Space Administration (NASA) • National Oceanic and Atmospheric Administration (NOAA) • Nimbus • Ozone • Ozone Mapping Profiler Suite (OMPS) Satellite Aerosol and Gas Experiments (SAGE I and II) • Satellite remote sensing • Solar Backscatter Ultraviolet (SBUV) • Suomi NPP • Total Ozone Mapping Spectrometer (TOMS) • Ultraviolet (UV) radiation • United Nations Environmental Programme (UNEP) • UVB radiation

Introduction Ozone is an important constituent gas of the atmosphere that protects life on Earth from harmful ultraviolet (UV) radiation from the Sun. Without the layer of ozone in the atmosphere, conditions on Earth would not be favorable for life – photosynthesizing plants would not be able to grow and plankton would not survive to support ocean life. For humans, overexposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems, which may even lead to death. Unabsorbed UV rays can cause direct DNA damage in living tissues in both plants and animals. The abundance of ozone directly affects the Earth’s biosphere, since the total column ozone overhead determines the amount of UV radiation that reaches the ground. Increased UV could lead to reduced crop yield, disruptions in the marine food chain, and other harmful effects on Earth.

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Fig. 1 The distribution of ozone in the Earth’s atmosphere (Courtesy of NOAA 2008)

It can be argued that the most important hazard of cosmic radiation is the damaging effects of ultraviolet radiation due to its ability to penetrate the protective shield of the Earth’s atmosphere because of ozone layer depletion. The ozone layer is mainly found in the lower portion of the stratosphere, just above the troposphere, approximately 20–30 km (12–19 miles) above the Earth’s surface, although its thickness varies seasonally and geographically (Fig. 1). In addition to filtering biologically damaging ultraviolet sunlight, namely, UVB (280–315 nm), ozone absorbs some of the infrared energy emitted by the Earth’s surface and acts as a greenhouse gas by creating a source of heat. Thus, ozone plays an important role in the temperature structure of the Earth’s atmosphere. The combination of ground-level and tropospheric ozone and the depletion of stratospheric ozone is widely believed to contribute to global warming and climate change (IPCC 2001). There is widespread scientific and public concern about losses of stratospheric ozone. The ozone hole refers to the seasonal depletion of the ozone layer in the lower stratosphere above Antarctica, which is primarily caused by the presence of chlorine-containing source gases, such as chlorofluorocarbons (CFCs) and related halocarbons. The release of CFCs, which catalyze ozone destruction, is mainly produced by industrial processes – a clear example of man’s effect on the global environment. The key observation is that chemical depletion of column ozone occurs primarily during Antarctic spring months (September to November) when triggered by sunlight, which results in associated increases in surface UVB radiation (Fig. 2). Similar losses in stratospheric ozone have been observed at other smaller regions on Earth from both ground-based and satellite-borne instruments. Scientific evidence has been accumulated over more than 20 years by the international research community, with the first man-made ozone-destroying pollutants (CFCs) identified in 1973 (Molina and Roland 1974). CFCs and halocarbons are ozone-depleting compounds that are often produced by many anthropogenic applications, including refrigeration, air conditioning, foam blowing, and cleaning

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Fig. 2 Antarctic ozone depletion (Courtesy of the WMO Global Ozone Research and Monitoring Project 2006)

of electronic components, and used as solvents. The full extent of ozone depletion by CFCs is not known, but marked decreases in total column ozone have been observed. A 1976 report by the United States National Academy of Sciences concluded that credible scientific evidence supported the ozone depletion hypothesis. Ozone depletion emerged as a major international issue in the 1980s. This led to the formulation and ratification of the 1985 Vienna Convention for the Protection of the Ozone Layer, which embodied an international environmental consensus that ozone depletion was a serious problem and to take steps to prevent further damage to the ozone layer. The 1987 Montreal Protocol outlined specific steps that nations should take to phase out ozone-depleting chemicals, stating a 50 % cutback in CFC production by 2000. It has been an example of exceptional international cooperation due to its widespread adoption and implementation. The 1990 London Amendments to the protocol committed member states to completely halt the production and consumption of CFCs, CCI4, and halons by the year 2000. These steps include a requirement that scientists regularly assess and report on the health of the ozone layer, particularly the annual Antarctic ozone hole. A long-term monitoring program requires an accurate time series of ozone data records in order to document how the ozone layer has changed and the expected recovery of ozone as a result of the Montreal Protocol and other policy measures adopted to limit the release of ozone-depleting substances. Long-term data records are also required to verify the accuracy of models that predict the expected behavior of ozone in the next 100 years (Randel and Wu 2007). Predictions of ozone levels remain difficult. Although scientists are now confident that stratospheric ozone is being depleted worldwide, there are still many unanswered questions remaining. To understand global atmospheric changes, it is necessary to understand the composition and chemistry of the Earth’s atmosphere, to account for all of the factors affecting ozone creation and destruction, and

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to conduct simultaneous, global studies over the course of many years for trend analysis. A global picture of total ozone in both the stratosphere and troposphere is mainly derived by using space- and ground-based measurements. Remote sensing instruments that measure ultraviolet albedo of Earth include the Total Ozone Mapping Spectrometer (TOMS), the Solar Backscatter Ultraviolet Instrument (SBUV), and the Global Ozone Monitoring Experiment (GOME). This chapter examines the SBUV instruments on National Oceanic and Atmospheric Administration (NOAA) operational weather satellites used to create ozone time series data. (The term SBUV will be used generically for BUV, SBUV, and SBUV/2 instruments.) These operational remote sensors on NOAA spacecraft were used to monitor the density and distribution of ozone in the Earth’s atmosphere and continue to monitor the Antarctica ozone hole. Ozone measurements via satellite have been made by this type of backscatter ultraviolet instrument since the launch of the Nimbus-4 satellite in April 1970. The improved SBUV was launched in November 1978, while the second generation instrument, the SBUV/2, began operations since the NOAA TIROS series of weather satellites in 1984. Therefore, a continuous long-term record of ozone measurements exists of similar design and high accuracy. This chapter will first detail the development of the SBUV instrument and provide a technical overview of its mechanics and operation. Available products and their contributions to the evolution of global climate observing systems will then be discussed. SBUV instruments and data will be evaluated for their ability to track long-term changes in atmospheric ozone. Finally, primary applications and benefits of SBUV subsystems for mapping global ozone distribution, as well as future developments and missions for collecting high temporal and spatial resolution ozone data, will be discussed.

Background A successful ozone monitoring program must address three scientific concerns in order to successfully detect long-term atmospheric changes. These include improving (a) our theoretical understanding of ozone variations, (b) limitations inherent to scientific techniques for measuring and detecting stratospheric ozone, and (c) hardware and technological limitations. Hence, a viable measurement program requires sensors that are capable of detecting ozone concentrations over a decade-long time period to provide data for trend analysis and model testing. The Solar Backscatter Ultraviolet Radiometer (SBUV) is an operational remote sensor, which is flown onboard NOAA weather satellites, and has provided more than three decades of global ozone records. It monitors the density and distribution of ozone in the Earth’s atmosphere, inferring total column ozone and the ozone vertical profile by measuring scattered solar energy from the atmosphere at middle ultraviolet wavelengths, which is characteristic of ozone. The SBUV is capable of determining the global ozone concentration in the stratosphere to an absolute accuracy of 1 % and the vertical distribution of atmospheric ozone to an absolute accuracy of 5 % (WDC 2008).

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The first backscatter ultraviolet (BUV) experiments were designed to measure stratospheric profile and total column ozone with primary instrumentation consisting of a double monochromator containing all reflective optics and a photomultiplier detector. Satellite measurements of ultraviolet solar radiation scattered by the atmosphere for deducing ozone profiles were first suggested by S.F. Singer and R.C. Wentworth in 1957. D.F. Heath and J.V. Dave proposed the satellite-based instruments for the BUV experiment that was placed into orbit aboard the Nimbus-4 satellite on April 8, 1970. These instruments measure the solar irradiance incident on the atmosphere and of sunlight backscattered from the earth-atmosphere system at 12 discrete wavelengths from 250 to 340 nm. The ratio of the backscattered radiance for π units of solar flux to the solar irradiance, the geometric albedo of the earth is inverted to yield the total column ozone amount and vertical ozone profiles up to an altitude of about 55 km. This double monochromator experiment was launched into a circular polar orbit at an altitude of 1,100 km. The BUV was designed to measure the solar irradiance at the top of the atmosphere and the atmospheric radiance in the satellite nadir direction to derive vertical profiles and total ozone amounts, with a spatial resolution of 230 km (Heath et al. 1973). The BUV instrument sounded ozone in the nadir direction only, and under certain orbital conditions, the data were influenced by charged particles in the Earth’s radiation belts. Evaluation of collected BUV data led to a number of design changes and expanded capability in the follow-on Solar Backscatter Ultraviolet and Total Ozone Mapping Spectrometer (SBUV/TOMS) experiment flown on Nimbus-7 on October 24, 1978. Compared to the BUV, the SBUV instrument had a wider wavelength range, a cross-course mapper, and special provisions for minimizing the effects of space radiation. The SBUV had a similar design to the BUV, consisting of a double EbertFastie spectrometer and a filter photometer. It measured spectral intensities at 12 wavelengths between 0.25 and 0.34 μm, with a spectral bandpass of 0.001 μm. The SBUV had added capabilities of a stowed diffuser plate when not in use driven by a stepper motor to three positions on command, as well as an added continuous scan (sweep) mode covering 0.16–0.4 μm for detailed examination of the extraterrestrial solar spectrum and its temporal variations. The TOMS was an ozone mapping system utilizing a close replica of the first monochromator of the SBUV, consisting of a single Ebert-Fastie spectrometer with a fixed grating and an array of exit slits (Heath et al. 1975). Both SBUV and TOMS had five scanner modes and a shared electronic module design. Improvements for mapping total ozone concentrations and vertical profiles of ozone in the atmosphere continued with the second-generation instrument, called the SBUV/2. The SBUV/2 series was first launched on the NOAA-9 satellite on December 12, 1984. There have been eight instruments launched to date produced by Ball Aerospace & Technologies Corp. under contract to NASA/Goddard Space Flight Center and NOAA. The instrument design was based on the technology developed for the SBUV/TOMS flown on Nimbus-7. The solar irradiance was determined at the same 12 wavelength bands, but changed to a programmable grating drive for wavelength selection. An onboard calibration system was added

NOAA Satellites and Solar Backscatter Ultra Violet (SBUV) Subsystems Fig. 3 Timeline of SBUV satellite instrument ozone monitoring (Courtesy of NASA 2013)

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N4 BUV N7 SBUV N9 SBUV/2 N11 SBUV/2 N14 SBUV/2 N16 SBUV/2 N17 SBUV/2 Data Used in Release 3 N18 Data not Used in Release 3 Data to be used In Future Release

SBUV/2 N19 SBUV OMPS

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with a mercury lamp to track diffuser reflectivity changes. The SBUV/2 instruments flown on the NOAA series of spacecraft are described in more detail by Frederick et al. (1986) and Hilsenrath et al. (1995). Successive generations of the SBUV/2 sensor have flown on NOAA-11 (September 1988 through March 1995) and NOAA 14 (December 1994 through September 21, 2000). NOAA-14 is replaced by NOAA-16 (September 21, 2000 through present). NOAA-17 was launched in June 2002, NOAA-18 was launched in May 2005, and NOAA-19 was launched in February 2009. The launch and operational timeline of SBUV instruments are summarized in Fig. 3. The Shuttle Solar Backscatter Ultraviolet Spectrometer (SSBUV) is a calibration unit that began as an engineering model of SBUV/2, but was modified for use on the Space Shuttle to underfly orbiting SBUV/2 instruments and to provide calibration check. This was meant to permit in-space calibration procedures to assess the degree of calibration drift with coincident SBUV/2 measurements onboard NOAA satellites and to obtain correlative measurements of ozone parameters. Eight missions were flown between October 1989 and January 1996 as a Getaway Special (GAS) payload aboard the Space Shuttle before it was retired from service. The first flight with SSBUV instrumentation occurred on the Shuttle Atlantis (STS-34) with Shuttle flight coincident observations taken with the SBUV on Nimbus-7 and the SBUV/2 on NOAA-9 and NOAA-11 satellites (Table 1) (eoPortal 2008). The SSBUV flight on Shuttle Endeavour (STS-72) provided the first opportunity to compare space observations from instruments which had been intercalibrated on the ground. The Ozone Mapping Profiler Suite (OMPS) is the next generation nadir-viewing BUV instrument that will continue measuring the global distribution of ozone. The OMPS is a limb- and nadir-viewing UV hyperspectral imaging spectrometer ( Fig. 4). It consists of three spectrometers: (a) a nadir mapper that will map global ozone with about 50 km ground resolution, (b) a nadir profiler that will measure the vertical distribution of ozone in the stratosphere, and (c) a limb profiler that will measure ozone in the lower stratosphere and troposphere with high vertical resolution.

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Table 1 Survey of space shuttle flights with the SSBUV calibration experimental payload (Courtesy of eoPortal 2002c) Shuttle flight STS-34, Atlantis STS-41, Discovery STS-43, Atlantis STS-45, Atlantis (ATLAS-1) STS-56, Discovery (ATLAS-2) STS-62, Columbia STS-66, Atlantis (ATLAS-3) STS-72, Endeavour

Date Oct. 18–23, 1989 Oct. 6–10, 1990 August 2–11, 1991 Mar. 24 to April 2, 1992 April 8–17, 1993 March 4–18, 1994 Nov. 3–14, 1994 Jan. 11–20, 1996

SSBUV flight SSBUV-1 SSBUV-2 SSBUV-3 SSBUV-4 SSBUV-5

SSBUV flight coincident ozone observations with instruments on the following satellites Nimbus-7 (SBUV/TOMS), NOAA-9, NOAA-11 (SBUV/2) NOAA-9 and NOAA-11 (SBUV/2) Meteor-3–6/TOMS, NOAA-9 and -11 (SBUV/2) NOAA-11, Meteor-3–6/TOMS, UARS (CLAES, ISAMS, HALOE) NOAA-11, Meteor-3–6/TOMS, UARS (CLAES, ISAMS, HALOE)

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NOAA-11, UARS (ISAMS, HALOE)

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Meteor-3–6/TOMS, NOAA-11, UARS (ISAMS, HALOE) NOAA-11, -14, UARS (ISAMS, HALOE), ERS-2 (GOME)

SSBUV-8

VIIRS CrlS ATMS OMPS

Nadir Limb CERES

MEB

Fig. 4 Schematic view of the Ozone Mapping Profiler Suite (OMPS) on the left and JPSS-1 flight configuration identical to the Suomi-NPP on the right (Courtesy of NASA (2000) and eoPortal (2002a))

The OMPS was launched onboard the Suomi National Polar-orbiting Partnership (Suomi-NPP) spacecraft (renamed from the NPOESS Preparatory Project) on October 28, 2011. The OMPS is also planned for the next generation Joint Polar Satellite System (JPSS) program, which will be launched in early 2017, called JPSS-1. The JPSS represents a joint interagency partnership between NASA and NOAA consisting of a series of three satellites with five instruments including the OMPS. The OMPS measurements will fulfill the US treaty obligation to monitor global ozone concentrations, continuing three decades of ozone concentration measurements with no gaps in coverage.

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Measurements This section provides a brief overview of the BUV ozone measurement technique using satellite remote sensing. In general, global measurements of ozone can be made from passive remote sensing techniques, such as backscatter ultraviolet (BUV), occultation, limb emission, and limb scattering (Fig. 5) (Wallace and Hobbs 2006). Viewing geometry indicates in which direction instruments field of view is pointing. The instrument can be pointed directly downward which is called nadir viewing, or it can be pointed into the side of the atmosphere which is called limb viewing. Examples of active remote sensing for detecting ozone include using lidar and radar technologies. No single instrument or technique is capable of measuring ozone concentration at all altitudes with complete global and temporal coverage. All passive remote sensing techniques can be used on satellite platforms, although based on different viewing geometry concepts. The advantage of satellite-borne instruments is their extensive spatial coverage over relatively long time periods, which enables long-term ozone trends to be measured. However, compared to in situ techniques (i.e., ground-based, aircraft, and balloon platforms), measurements of atmospheric constituents are not direct and have to be derived from radiation measurements using a retrieval algorithm. Satellite measurements typically have poor vertical resolution in the region below the ozone peak (30 km) due to effects of increased multiple scattering and reduced sensitivity to the shape of the profile. In situ measurements are generally more direct and provide higher

Fig. 5 Four passive remote sensing techniques for measuring ozone from satellite platforms (Courtesy of NASA Stratospheric Ozone Electronic Textbook, NASA Goddard Space Flight Center 2008)

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Fig. 6 Techniques for measuring ozone in the atmosphere (left) and launching of NOAA ozone balloons at the South Pole Station (right) (Courtesy of WMO Global Ozone Research and Monitoring Project 2006)

vertical spatial resolution, although observations are very intermittent. Airborne in situ measurements, such as using ozonesondes carried on radiosonde balloons (Fig. 6), have often been used to validate satellite measurements. The BUV remote sensing method of ozone was first proposed by J.V. Dave and C.L. Mateer (1967). It requires two pairs of measurements: (a) incoming UV light (irradiance) and backscattered UV light (radiance) at a wavelength that is strongly absorbed by ozone and (b) similar measurements at a wavelength that is absorbed only weakly by ozone. The difference between these measurements can be used to infer total column ozone present in the atmosphere. Since ozone absorbs more strongly at shorter wavelengths, solar radiation with progressively shorter wavelengths is absorbed at progressively higher altitudes. Therefore, the radiation at a particular wavelength in the UV range can be scattered only above a certain height. This enables the vertical measurement of ozone by measuring backscattered radiation at a number of wavelengths. Each radiance measurement is converted to an atmospheric quantity using a retrieval algorithm. Satellite BUV observations have provided valuable data for monitoring seasonal and latitudinal variations of ozone in the stratosphere. It has also provided the first direct evidence of ozone variations following a major solar proton flux into the atmosphere. A solar proton flux event is when large-scale explosions on the Sun associated with a coronal mass ejection lead to an intense flux of charged solar particles in interplanetary space. This interacts with the Earth’s magnetosphere with ozone-destroying solar particles tending to precipitate into polar regions due to the geomagnetic dipole field. Nimbus-4 BUV data showed a 20 % decrease in stratospheric ozone after a solar proton event in August 1972, suggesting possible

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catalytic loss of ozone by halogens (Heath et al. 1977). This thus leads to a depletion of northern polar stratospheric ozone for extended periods of time, lasting several weeks past the events. There have been numerous modeling studies focused on understanding and predicting the atmospheric influence of solar proton events over the years, documenting evidence that ozone can be depleted by such solar eruptions (Jackman et al. 2008). A significant advantage of the BUV technique is its nadir-viewing nature (i.e., looking directly down at the atmosphere below), which enables a good horizontal resolution. The total area of the field of view seen by the instrument is referred to as the footprint, while the subsatellite point is the location on the Earth’s surface directly beneath the satellite. A disadvantage of the BUV technique is the effects of increased multiple scattering and reduced sensitivity to the shape of the profile. This can lead to poor vertical resolution in the region below the ozone peak of about 30 km. Examples of BUV instruments include the SBUV and TOMS on NOAA satellites, as well as the Global Ozone Monitoring Experiment (GOME) launched by the European Space Agency’s European Remote Sensing-2 (ERS-2) satellite in April 1995. SBUV instruments provide one of the longest hemispheric total ozone measurement records based on nadir-viewing geometry and sampling in 12 wavelengths. It provides near global coverage of ozone outside the polar night region, and it takes 1–7 days to create a global map.

System Mechanics A series of nine SBUV instruments have been launched by NASA to produce longterm ozone data records. This includes the BUV instrument on Nimbus-4, SBUV on Nimbus-7, and SBUV/2 instruments on NOAA-9, NOAA-11, NOAA-14, NOAA16, NOAA-17, NOAA-18, and NOAA-19 covering the period 1970–1872 and 1979 to present (Fig. 7). The SBUV instruments onboard NOAA satellites are all of similar design in terms of being non-scanning, nadir-viewing double-grating monochromators (Fig. 8). The instruments take measurements through 12 wavelengths in the middle ultraviolet (between 255 and 340 nm) over 32 s, while obtaining an instantaneous field of view (IFOV) on the ground of approximately 200 km by 200 km. The eight shortest wavelength channels are sensitive to ozone profiles from about 20 hPa to about 1.0 hPa, while the four longest monochromator channels detect radiances that reach the Earth’s surface and thus are sensitive to the ozone column amount. The overall spectral resolution is approximately 1 nm (nm). More detailed description of satellite hardware is available from Ball Aerospace & Technologies Corp., who designed and built the hardware under contract to NASA/Goddard Space Flight Center and NOAA (Ball Aerospace and Technologies Corp. – Systems Division 1985). SBUV instruments are flown in polar orbits to obtain global coverage and are taken on the day side of each orbit. There are about 14 orbits per day with 26 of separation at the equator. The instrument carries two modules, which are the sensor module (with optical elements/detectors) and the electronics module (houses main

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Fig. 7 NOAA-18 was launched on May 20, 2005 with the SBUV/2 instrument monitoring the ozone layer (Courtesy of NESDIS 2013b)

Fig. 8 Photo of the SBUV/2 instrument (Courtesy of eoPortal 2002b)

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Fig. 9 Mechanical configuration of the SBUV/2 instrument (Courtesy of NOAA National Climatic Data Center 2009)

electronics and power supplies). The heart of the instrument is two optical radiometers: (a) a nadir-viewing double monochromator of the Ebert-Fastie type and (b) a Cloud Cover Radiometer (CCR, a filter photometer) (McPeters et al. 2013). The monochromator measures Earth radiance directly and the Sun selectively when a diffuser is deployed. The only difference in the radiance and irradiance observations is the instrument diffuser, while the remaining optical components are identical. A photomultiplier tube detects light exiting the monochromator (Fig. 9). During normal operation, the backscattered radiance from the nadir is measured at 12 near-UV wavelengths from 252 to 340 nm with a bandpass of 1.1 nm about 100 times per orbit on the sunlit portion. The CCR makes measurements at 379 nm wavelength with a bandpass of 3 nm and is used to detect scene reflectivity changes during a scan. Co-aligned to the monochromator, the CCR output represents the amount of cloud cover in a scene and is used to remove cloud effects in the monochromator data (NOAA 2013).

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Table 2 The SBUV/2 makes 12 monochromator measurements in wavelengths from 252 to 340 nm for ozone calculations (Courtesy of WDC 2008) Band Band 1 (VIS) Band 2 (VIS) Band 3 (VIS) Band 4 (VIS) Band 5 (VIS) Band 6 (VIS) Band 7 (VIS) Band 8 (VIS) Band 9 (NIR) Band 10 (VIS) Band 11 (VIS) Band 12 (VIS)

Wavelength (μm) 0.252 0.273 0.283 0.288 0.292 0.298 0.302 0.306 0.312 0.318 0.331 0.34

Bandwidth (nm) 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1

Resolution (m) 170,000 170,000 170,000 170,000 170,000 170,000 170,000 170,000 170,000 170,000 170,000 170,000

Swath width (km) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170) 120 (170)

An important improvement of SBUV/2 over the SBUV is the ability to measure changes in solar diffuser reflectivity in flight, using a mercury lamp as a light source (which also provides wavelength calibration). This system did not work onboard NOAA-9, but was subsequently redesigned and operationally successful on NOAA-11 (Hilsenrath et al. 1995). The SBUV/2 operates in five modes. In the discrete mode, measurements are made sequentially in 12 discrete spectral bands from which the total ozone and vertical distribution of ozone are derived (Table 2). The data from this configuration corresponds to the Earth radiance. In the Sweep Mode, a continuous spectral scan from 160 to 406 nm is made primarily for computation of ultraviolet solar spectral irradiance. Ground and in-flight calibration data are used to convert the detector data and diffuser mode data to solar irradiation or Earth radiance units. Wavelength Calibration Mode is the same as discrete mode, except that only the calibration lamps are scanned. Monochromator Stop Mode interrupts the spectral scan mode. Finally, the Monochromator Caged Mode has the monochromator stored in a predetermined position. The sensor module houses the monochromator optical hardware, which uses a movable grating to select the measured wavelength. The grating mechanism can be commanded to any one of 8,192 positions and providing approximately 0.1 nm wavelength resolution. Commands corresponding to grating positions come from a read-only memory (ROM). SBUV retrieval algorithms are a series of algorithms for deriving total ozone and ozone profile from SBUV measurements. The total ozone retrieval algorithm is a three-step process of successive estimation improvement (NESDIS 2006). First, the algorithm uses a pair of wavelengths 331 nm and 318 nm (340 nm and 331 nm for high solar zenith angle) to derive reflectivity and total ozone as a first guess linearization point. Second, adjustments due to seasonal and latitudinal variations in ozone and temperature profiles are made. Third, a procedure based on N-value residues is implemented to correct errors related to aerosol, sea glint, and profile

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shape deviation. The ozone profile retrieval algorithm is based on the optimal estimation (OE) technique and combines SBUV measurements and a priori profile information to achieve the maximum likelihood estimate.

Instrument Calibration and Errors Overlapping SBUV data sets provide the opportunity to create a continuous profile ozone data set spanning more than 40 years. However, accurate instrument calibration is necessary to produce high-quality ozone data for comparison with other measurements, for use in data assimilation systems, and for long-term trend analysis (DeLand et al. 2012). Algorithm upgrades and calibration changes are continuously implemented with the goal of measuring the global total ozone column to an accuracy of 1 % and the vertical distribution of ozone in the stratosphere to an accuracy of 5 %. Reprocessed SBUV data are able to achieve these accuracy values by correcting for problems such as stray light, out-of-band response, and wavelength shifts. A variety of calibration needs exist, including evaluating absolute calibration, characterizing time dependence, and intercalibration between instruments. Longterm calibration of SBUV instruments is established with specifically designed measurements in the laboratory and on orbit, including solar irradiance measurements and an onboard mercury lamp that tracks diffuser reflectivity changes on orbit. Diffuser degradation-corrected solar measurements capture time-dependent and wavelength-dependent response changes with an estimated long-term accuracy of 2 km) to simplify targeting; (b) that it be a predictable comet, active at previous apparitions; and (c) that it allow for a launch in the window specified in the AO. The trajectory (Fig. 1) was designed to launch in January 2004 into a slightly elliptical orbit that would encounter the Earth again in January 2005, at which point the Earth’s gravity would divert the spacecraft into a much more elliptical orbit that would encounter the comet near its perihelion and near its crossing of the ecliptic, both of which occurred within a week of 4 July 2005, the chosen date for the encounter. Additional details are available from Blume (2005). It was clear from the outset that, in order to excavate a deep, large crater and allow sufficient time after excavation to observe the results, the mission would require two coupled but independent, fully functional, intercommunicating spacecraft – an impactor and a flyby spacecraft. It was also clear (and emphasized by the panel review of the proposal in 1996) that the impactor would need to be released early and carry out autonomous navigation to ensure an impact with enough time to observe the results before the flyby spacecraft flew past the comet.

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To keep things simple, moving parts were limited to four items – the separation mechanisms between the flyby and the impactor, filter wheels in the two cameras on the flyby spacecraft, and a gimbal on the high-gain antenna of the flyby spacecraft with sufficient range to keep it pointed at Earth during the attitude changes expected between release of the impactor and closest approach to comet Tempel 1. Since the backup mission was just to launch 1 year later to reach the same comet with similar geometry, there was no requirement for communication with Earth at all attitudes. Similarly, thermal stability at low operating temperatures was ensured by keeping the instrument bench thermally isolated from the rest of the spacecraft and designing the combination of instruments and solar panels so that the entire instrument suite was shielded from direct sunlight at all attitudes expected during the encounter with comet Tempel 1. The impactor was designed to operate on battery power for a day (with significant margin), since release a day prior to impact would allow the flyby to decelerate sufficiently (by 100 m/s) to view the entire impact event. The trajectory design yielded an encounter at 10.3 km/s, the impactor having a mass of 370 kg including estimated residual hydrazine fuel, of which roughly 50 % was copper, chosen to minimize oxidation reactions with the cometary water that would lead to contaminating bright emission lines. The instruments were also developed, assembled, and integrated with the spacecraft at BATC based on specifications from the science team (see Hampton et al. 2005 for full details). The instruments on the flyby spacecraft included a Medium Resolution Instrument (MRI), which consisted of a 12.1-cm aperture, Cassegrain telescope with a 2.1-m focal length feeding a CCD camera through a filter wheel. Filters in this camera were chosen to isolate emission bands and continuum in the coma of the comet from the OH band in the near UV (305 nm) to a near-IR filter for the continuum at 850 nm. An identical system, but with the filter wheel omitted, constituted the Impactor Targeting Sensor (ITS), the camera used for navigation and for science on the impactor. The High Resolution Instrument (HRI) on the flyby spacecraft was much more complex. The Cassegrain telescope had a 35-cm aperture and a focal length of 10.5 m. This made it, at least for a short time, the largest telescope on any deep-space mission. The telescope fed a dichroic beam splitter, which sent the infrared to a spectrometer for the 1.05–4.80 μm band and the visible to a CCD camera (300–1,000 nm) with a filter wheel. Filters in the camera were chosen to measure colors on the nucleus, a series of medium-band filters spanning the near UV to the CCD sensitivity cutoff near 1 μm. The spectrometer was a two-prism design to avoid order separation problems with a grating (since the spectral range was more than a factor two in wavelength). The IR detector was HgCdTe, bonded to Rockwell’s model Hawai’i-1R multiplexer, part of their development of detectors for the HST Wide Field Planetary Camera 3. Figure 2 shows the final system, with the flyby spacecraft being lowered onto the impactor spacecraft in the clean room at BATC. The system was launched with the impactor attached to the launch vehicle and the flyby spacecraft riding on top of the impactor in their mated positions. The figure shows the compact size of the two

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Fig. 2 Spacecraft system. The white stand simulates the adapter ring on the launch rocket, to which the impactor is attached. The flyby is being lowered to mate with the impactor, much of which was encased by the flyby during flight. The very long tube pointing at the engineer on the left is the HRI telescope, with the infrared spectrometer at the upper right (Credit: Ball Aerospace)

spacecraft, including the solar panels that power the flyby, compared to the large size of the instruments, particularly the HRI.

Development Challenges As with any planetary mission, there were numerous challenges in development. Perhaps one of the most surprising, and one which was not discovered early enough, was that each of the three partners used the same words to refer to different things. This derived from the three organizations having very different cultures and fundamentally different approaches to the mission, but it was ultimately due to the fact that two of the three partners had minimal experience with deep-space planetary exploration. This led to misunderstandings of requirements and assumptions among the partners. At a very early stage after selection, both spacecraft were redesigned from what had been proposed. The flyby spacecraft was redesigned due in large part to accommodation issues. The impactor was redesigned on the basis of numerical simulations of impacts, which showed that the original design (a cylindrical can)

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would be very inefficient in excavating a crater. The redesign emphasized an inert copper spherical cap forward in the impactor, constituting roughly one third of the total mass of the impactor and hollowed out in order to better impedance-match the impactor to the low-density cometary nucleus. This significantly increased costs but led to a much better scientific result. The impactor’s attitude control system was also changed from a cold nitrogen system to a more complicated hydrazine system, in which the experienced engineers had more confidence. The most common challenge of course continued to be cost, despite what appeared at project start to be nominally sufficient reserves. The original design of the spacecraft computer, based on a well-established RAD600 chip, turned out to have inadequate capacity for the complex software being developed. This required switching to the newly developed RAD750 chip as the CPU and, although at the time of the switch it was understood that other missions would fly the chip before DI, it turned out that DI became the first civilian space mission to fly the newly developed chip as the CPU. Development of the entire computer system presented major challenges. Ultimately, late delivery of the spacecraft (not the instruments), due in part to the delays in delivery and testing of the computer system, led to a 1-year launch delay. The HRI presented challenges also. The first primary mirror broke from one of its mounts during vibration testing, but fortunately a spare had been purchased. The instructions for preparing the mirror bonding surfaces were revised after consultation with the mirror provider. Ultimately, the HRI was also out of focus when launched (focus mechanisms had not been included in any of the instruments, partly for cost reasons but, in the case of HRI, also because of the difficulty of designing one with sufficient mechanical range). There had been two independent focus tests in cold vacuum, both of which gave the same result for the focus position. These gave a different result than did a theoretical model of the structure of the telescope. In order to maintain schedule (before it was known that a launch delay would be required), the decision was made to accept two independent experimental measurements of the focus. Ultimately, it turned out that there was one piece of optics in common between the two tests, a flat used to measure the curvature of the window in the vacuum chamber. That flat had been inherited from the Spitzer program, and it had not been realized that the flat developed curvature when cold. Fortunately, the PSF of an out-of-focus Cassegrain telescope retains considerable high-frequency information, so that deconvolution worked well on all images and the resultant images were invaluable in understanding the structure of the nucleus (Busko et al. 2007; Lindler et al. 2013). The short flight time of the mission (6 months from launch to encounter), coupled with a lack of complete flight sequences before launch, resulted in a very heavy workload to learn all the quirks to flying the spacecraft while simultaneously developing all the observational and pointing sequences. Intensive interactions between the activity leads from JPL and the science team led to success despite the issues. But this resulted in the inability to get flat-fields on the moon, particularly for the IR spectrometer, before the spacecraft left the Earth-moon system.

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Failure to communicate with the spacecraft immediately after separation from the launch vehicle caused a temporary panic, until it was realized that the spacecraft was in safe mode. This was caused by the fault protection software, which had been set with too restrictive limits for some parameters, in this case the catalyst-bed heater temperature in the hydrazine thruster system. Fortunately, those limits were easily resettable. The area that led to the most tension was the targeting software. This had been a major challenge because the shape of the nucleus was unknown except for its average radius, close to 3 km. The flyby of comet Borrelly by Deep Space 1 had revealed a very elongated nucleus with a bend in the middle. This led to the realization that certain shapes for the nucleus could lead to the center of light not always being on the nucleus (such as an extreme banana shape for the nucleus). Thus more sophisticated algorithms were required and developed by Mastrodemos et al. (2005). This allowed inclusion of a “bias” to push the impact site toward the side of the nucleus from which the flyby spacecraft would observe the impact. The challenge in the more complicated algorithms was ensuring that the flyby spacecraft would choose the same impact point that the impactor chose, despite seeing the nucleus from a different direction. In the end this worked exactly as desired.

Encounter Spacecraft observations of the comet began 2 months before encounter with a regular monitoring program of images both for science and for navigation. Due to the narrow range of solar elongations over which the spectrometer would remain cold and due to anticipated limited sensitivity, spectra were obtained regularly beginning only 2 weeks before encounter. On 3 July 2005, with the combined spacecraft targeted to impact the nucleus, the impactor spacecraft was released from the flyby via spring mechanisms, turned on for autonomous operation, and allowed to separate gently from the flyby spacecraft. When the impactor had separated by a safe distance, the flyby spacecraft used its thrusters to divert by ~5 m/s laterally in order to miss the nucleus by 500 km and then to slow down by 100 m/s, from 10.3 to 10.2 km/s. This provided a window of 800 s to view the impact and its effects before the flyby spacecraft passed the nucleus. As the impactor approached the nucleus, it made three trajectory correction maneuvers to optimize the targeting. When it got very close (within about 22 s to impact or 230 km), four cometary grains impacted the spacecraft with sufficient effect that the attitude control system had to respond to them and images showed the spacecraft attitude displacement. Three of the particles had masses of 1–10 mg, while the fourth (the last in time at a distance of 30 km or 2.5 s from the nucleus) had a mass of order 0.5 g. Buffering delays in telemetry from the impactor to the flyby resulted in the last transmitted data having been taken roughly 2 s (24 km) prior to impact. The smallest surface features resolved in the last images from the impactor had sizes of 2–4 m. The impactor delivered 19 GJ (~5 t of

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TNT equivalent) of kinetic energy to the nucleus, more than the energy possible if the entire mass of the impactor had been only the most efficient chemical explosives known, a totally unrealistic scenario. In addition to being offset significantly toward the side of the nucleus facing the flyby spacecraft at closest approach, the final trajectory of the impactor at impact was only 30 above the local horizontal, thus providing a valuable separation of up-range and down-range phenomena, altogether a most successful targeting. Because all instruments were body mounted, the flyby spacecraft rotated to track the nucleus. At 500 km (41 s) before its closest approach, the spacecraft rotation was halted to remain in an orientation with maximum shielding against cometary dust. This had been chosen to be somewhat less than the spacecraft’s maximum attitude rate. After passing through the densest parts of the comet’s coma, the flyby spacecraft turned and looked back at the comet to obtain further data on the ejecta over 2 days (additional data beyond 2 days were not obtained due to memory management issues). All data, raw and calibrated, were delivered to NASA’s Planetary Data System (PDS) before the end of the calendar year and they are available at the Small Bodies Node of PDS (2014), many of them in recalibrated versions delivered at later times as the calibration of the instruments was better understood. Since the limited instruments that could be carried on a Discovery-class mission could not possibly probe all aspects of the phenomena, a significant effort was devoted to organizing a campaign of Earth-based observing using telescopes both on the surface of the Earth and in space. Nearly every major astronomical facility on Earth observed comet Tempel 1 at or near the time of the DI encounter. These data proved invaluable in understanding the larger picture of cometary behavior in response to an impact.

Deep Impact Results This section will address only the results obtained directly from the Deep Impact prime mission. Other results that came from more of a synthesis of the prime mission and the extended mission will be addressed after discussing the extended mission. It is particularly important to point out at the start what has become a truism of science, which might be called the Harwit principle after his book on this topic (Harwit 1984): Whenever one enters a new measurement regime, the most interesting results and the ones for which the experiment/mission will be remembered are likely to be the unanticipated results. The results for which the mission was designed may be important but they are likely to be less interesting than the totally new phenomena that are discovered. This has been particularly true of DI and its extensions. The key event, of course, was the impact and its resultant ejecta, events that were quickly summarized in the literature by A’Hearn et al. (2005). Figure 3 shows successive images from the ITS with the ultimate impact site shown in each. The three white spots nearest the impact site are each no more than 2–3 m in diameter.

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Fig. 3 Impact site combination. The yellow arrows indicate the impact site in the successive images, the times of which (prior to impact) are given in red. The images are successively smaller subframes of the camera to allow transmission to the flyby spacecraft at a rapidly increasing rate (Credit: NASA/UMD)

Figure 4 shows a pseudo-color image derived from blue, green, and red images with the HRI visible imager (deconvolved). The bluish regions on the upper part of the nucleus are actually as dark as charcoal but brighter than the rest of the nucleus. The bluish color is a clue to the fact that they are 3 % ice-covered (Sunshine et al. 2006). The ejecta are by far the brightest features in the image. They also are slightly bluish since they include a large amount of ice.

Physical Properties of the Nucleus Two independent approaches were used to estimate the density of the nucleus. The first method uses the flash that occurs immediately after the impact and is due to the hydrodynamically ejected hot material. This flash was unusually faint, and comparison with laboratory experiments using the Ames Vertical Gun Range showed that the outer layers at the impact site, within a few meters (a few impactor diameters) of the surface, had a porosity of at least 75 % (Ernst and Schultz 2007).

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Fig. 4 Impact ejecta (HRI 937–1). A color-composite image from the HRI Vis imager shows the very bright ejecta and the less bright icy patches on the morning portions of the nucleus (the upper left portion in this picture). The sun is to the right (Credit: NASA/JPL/ UMD)

The other approach used the fallback of ejecta onto the surface on ballistic trajectories after being excavated. This approach used the look-back images of the plume and led to a surface gravity and thus an estimate of the bulk density of the nucleus of 0.4 g/cm3 (Richardson et al. 2007). For any reasonable mix of dust and ice, this also implies a porosity for the bulk nucleus of order 75 % or higher, consistent with the result for the surface layer. Both results are consistent with previous models of the nongravitational acceleration of cometary orbits due to outgassing that suggest bulk densities less than 1 g/cm3, but these new approaches are less sensitive to model assumptions. The analysis of the ejecta plume also leads to an estimate of the tensile strength of the cometary material. Since the ejecta plume was “over the limb” when the spacecraft looked back at it, only upper limits can be set on whether the plume separated from the surface. Thus only upper limits can be set on the strength, of order 10 kPa, but the data are consistent with zero strength (Holsapple and Housen 2007; Richardson et al. 2007; Richardson and Melosh 2013). An examination of the nucleus in Fig. 4 (and in pre-impact images) shows extensive layering of materials, some of which may be primordial while other layers may have been more recent flows. There are also two large features that appear to be the eroded bases of large (200–300 m) impact craters that have been exhumed. These craters may date back to the formation era. The combination of obvious layering together with large bulk porosity suggests that the accretion of cometary nuclei does not proceed quite as models of asteroid and TNO (transNeptunian object) formation would have it. They also suggest that cometary nuclei are not fragments of TNOs as had been widely thought to be the case. Moderately gentle accretion of porous bodies can lead to spreading of the impactor, thus

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forming layers on the nucleus. These layers are generally orthogonal to the radius, but they are totally unrelated to the onion-skin layering that might be expected from evolutionary models of the nucleus due to a variety of processes. Building a nucleus in this way was discussed by Belton et al. (2007).

Volatiles in the Comet The primary goal of DI was to look inside a cometary nucleus and search for differences between the surface and the interior, particularly in the volatiles, as had been predicted by numerous theoretical models of the nucleus. Observations of the volatiles released in the impact were made by DI itself using the HRI, by numerous ground-based observatories, by space observatories including HST and Spitzer, and even by ESA’s Rosetta mission. From the vaporization and dissociation to OH of the excavated ice, it is known from at least three different independent observatories that roughly 7  2  104 kg of water ice was excavated (Schleicher et al. 2006; Biver et al. 2007; Keller et al. 2007) and that it was mostly in the form of micronsized grains of ice rather than large chunks of ice (A’Hearn et al. 2005). Adding a comparable amount for refractory grains and using a density of 0.4 g/cm3 for a cometary nucleus, this yields a minimum radius for the crater of ~20 m. The biggest unknown is in estimating what fraction of the excavated ice fell back to the surface and was buried cold enough to remain as ice. Typically most of the excavated material returns to the surface, but some of the returned ice might have been warm enough to sublimate even buried under the refractory ejecta. Nevertheless it seems safe to assert that material was excavated from depths of 20 m or more. More interestingly, observations at ultraviolet, visible, and infrared wavelengths were all consistent in showing that the relative abundances of ALL volatiles excavated in the impact (numerous individual papers on different species) were the same, to within a factor two, as the relative abundances in the ambient outgassing prior to the impact. This includes organic species and simple, very volatile ices such as CO. Thus the principal conclusion is that the surface of a cometary nucleus erodes away fast enough in active areas to keep up with the progress of the differentiation front into the nucleus and that primitive material is always therefore near the surface. On the other hand, it was also clear that the relative abundance of different volatiles in the ambient outgassing varied considerably from place to place on the nucleus. The ratio of CO2 to H2O was much higher above the south polar region (the pole itself had just entered winter night 2 months earlier) than along the subsolar meridian. There appeared to be a deficit of CO2 relative to H2O above the pole that had recently entered summer day (Feaga et al. 2007). Whether this is a seasonal effect or an effect due to the nucleus being formed of cometesimals formed with different primordial abundances is not yet resolved (Fig. 5). The ease with which CO2 could be observed and its relative abundance (5–10 % relative to H2O) implied that CO2 might be an important volatile in many comets. Furthermore, the visible-light monitoring on approach showed that the comet had

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Dust

>0.030 0.025 0.020 0.015 0.010 6.75e−4 5.40e−4 4.05e−4 2.70e−4 1.35e−4 0.00e−4

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Fig. 5 Volatile maps of Tempel 1. The upper panel shows a map of the continuum at 2 μm (dominated by reflected light from solid grains) of the innermost cometary coma. The middle panel shows the distribution of gaseous H2O around the nucleus and the bottom panel shows the distribution of CO2, all from the HRI infrared spectrometer. The distributions of the gaseous species are very different from each other and the grains (seen in the top panel) are better correlated with the CO2 than with the H2O (Credit: NASA/UMD)

frequent outbursts, typically occurring at particular rotational phases. Analysis of these outbursts has shown the presence of CO2 in these outbursts (Moretto and Feaga, private communication). Ice was also observed on the surface of the nucleus but only in a few locations in the early morning regions of the surface and typically associated with depressions (Sunshine et al. 2006). This ice was coarser (grains many tens of micrometers in diameter) than the ice excavated in the impact, as was also true for the refractory grains in the ambient outgassing versus those excavated by the impact. Even in the icy patches, the ice coverage is only about 3 % of the surface, making those parts of the surface slightly brighter than charcoal while the rest of the surface is darker than charcoal. An interesting question is whether those ices are morning frost deposits that disappear every day or topographically shaded regions of bulk ice that only outgas slowly until much later in the day. We note that the icy patches on the surface were not the source of prominent jets in the coma. There was enhanced activity above these areas but it was so weak that it was only observable when the icy patch was almost precisely on the limb as seen from the spacecraft, so that the activity could be seen against the darkness of deep space. These plumes, which may have been composed of either icy grains or dirt

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grains, driven by sublimation of water from the icy patches, were visible for only a small fraction of a nuclear radius above the limb. A collection of all the results available in mid-2007 is contained in the special issue published as volume 191 of the journal Icarus.

Extended Mission Development and Execution As the prime mission was being developed and safety margins were being considered on lifetimes and expendables, there had been preliminary examination of possible extended missions to other comets. Margins were decided with these possibilities in mind, particularly the margin on hydrazine fuel. One of the targets identified at that time was comet 103P/Hartley 2, which had been considered a backup target for the prime mission. After the flyby of Tempel 1, the flyby spacecraft was on a heliocentric trajectory with a period very close to 3 years. Thus the spacecraft would return to its perihelion near Earth in December 2007, and this close approach could then be used for a gravity assist to redirect the spacecraft to a new target. After the prime mission was completed, it was nearly 2 years before there was an opportunity to propose an extended mission. A combined mission was proposed, carrying out a flyby of comet Boethin (DIXI = Deep Impact extended Investigation), with comet Hartley 2 as a backup, and studying extrasolar planets (EPOCh = Extrasolar Planet Observation and Characterization). The combination of two scientific missions, which was essential to ensuring an experienced operations team throughout the years of cruise prior to Boethin encounter, was selected for funding by NASA (with the EPOCh project mostly funded outside the Planetary Science Division and not discussed in this chapter). Since approval for the extended mission arrived only months before the Earthflyby to redirect the spacecraft, an intensive campaign was organized to recover comet Boethin. Ultimately this campaign showed that the comet had disintegrated and that no remaining fragments could be larger than 200 m in radius (Meech et al. 2013). This triggered a change to the backup target, Hartley 2, which had always been foreseen as a scientifically more interesting target, albeit one for which the mission would be more expensive due to a very long cruise phase. The flyby of Earth on 31 December 2007 was therefore targeted for comet Hartley 2. There were several technical problems but also some scientific breakthroughs during the cruise phase. The most significant technical problem was discovered shortly after the flyby of Earth, when it was realized that RF power was being reflected back into the transmitters. This was attributed to a problem with the waveguide switch. It was only discovered after many flips of that switch, and ultimately it was concluded that the problem was most likely caused by thermal issues in the communications package due to the perihelion of the post-Tempel 1 orbit bringing the spacecraft closer to the sun than ever before. This had cost some observing time for EPOCh, but the switch to Hartley 2 as a target provided the opportunity for EPOCh to more than make up for the lost observations.

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The spacecraft trajectory in the EPOCh phase brought the spacecraft back to Earth roughly every 6 months with either close or distant encounters depending on the orbital geometry. This allowed numerous observations of Earth as an archetypical exoplanet. It also allowed numerous calibration observations of the moon in order to obtain flat-fields for the IR spectrometer. This is one of the most challenging tasks in calibrating spectrometers and the process worked very well. Fortuitously, it also put DI in a position to be the conclusive factor in favor of the discovery of lunar OH radicals by the Moon Mineralogy Mapper (M3) team on Chandrayaan (Pieters et al. 2009; Sunshine et al. 2009). The data taken with DI covered the OH absorption much better in wavelength than did the spectra from M3, and they were more extensive, allowing demonstration that the OH abundance on the lunar surface was stronger at high latitudes than near the equator and that it varied diurnally. The encounter with Hartley 2, on 4 November 2010, was executed almost perfectly. A slight pointing error due to a numerical value stored deep in the software during the encounter with Tempel 1 led to an unplanned off-pointing that helped in the discovery of the chunks of ice surrounding the nucleus of Hartley 2. In real time, surprising phenomena were observed as discussed below. As in the prime mission, an extensive program of Earth-based observations was also organized by the team, taking particular advantage of the very close approach of the comet to Earth less than 2 weeks prior to the flyby.

Extended Mission Results The most immediate surprise during the flyby of comet Hartley 2 was the presence of tens of thousands of large grains in the vicinity of the nucleus (Fig. 6). Grains ranged in size up to order 10–20 cm, assuming they had the reflectivity of ice (A’Hearn et al. 2011; Kelley et al. 2013). The many images of the coma from very different directions allowed reconstruction of the 3-D velocity vectors, showing that the grains were moving at speeds of only a few meters per second relative to the nucleus and that a significant fraction (10–30 %) was moving at less than escape velocity (Hermalyn et al. 2013). Such grains had been anticipated at previous encounters but never seen, so finding them at Hartley 2 was surprising. However, Hartley 2 had been known for some time to be hyperactive, i.e., it produced more water vapor than should be possible from a nucleus of its size if the whole surface were active and these grains are likely the source of the excess water vapor. This process probably also explains the hyperactivity of a small number of other cometary nuclei. Some of the best data on the size distribution of the icy grains were obtained using deconvolved images from the out-of-focus HRI visible imager. Furthermore, the grains were clearly being released from the nucleus in the immediate vicinity of a strong jet of CO2 gas (A’Hearn et al. 2011). Thus CO2 is likely the driving gas for the activity, unlike the situation in most comets, for which H2O is the driving gas. Organics also are concentrated in the major jet with the CO2 (Fig. 7). Interestingly, CO was not detected with DI, but contemporaneous

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Fig. 6 Icy grains. A deconvolved image from the HRI visible camera showing the individual chunks of ice near one end of the nucleus of Hartley 2 (Credit: NASA/ JPL/UMD)

observations with HST showed that Hartley 2 has the lowest CO fractional abundance ever measured, ~0.003 relative to H2O (Weaver et al. 2011). Another surprise is that the nucleus appeared as though it might have once been a contact binary, with the “waist” between the two lobes filled in with extremely fine material (Figs. 7, 8). The smaller lobe is clearly more active than the larger one throughout the rotation of the nucleus. The only large feature in the coma when imaged in H2O emission is a straight feature (cylindrical or fan-shaped) immediately above the smooth neck between the two nuclei. The dynamics of the gas are not yet well understood. The nucleus also appeared to be in an excited state of rotation with periods that changed by tens of % over the 2 months of approach to the comet (Belton et al. 2013). Simple models show that torques from the jets could provide enough angular acceleration. If the smooth waist is assumed to be an equipotential (as it might be if composed of very fine, loose grains), then the bulk density of the nucleus is 0.2–0.4 g/cm3, even more porous than Tempel 1. Note that for Hartley 2, the centrifugal force due to rotation must be taken into account in estimating the equipotential. Water ice was found on the surface of the nucleus, much more widespread than on Tempel 1 but following the same pattern of being confined to morning areas with very rough topography. A collection of the detailed results from the encounter available in late 2011 appeared in volume 222 of the journal Icarus. After the flyby of Hartley 2, operations were continued using divisional reserve funds at NASA HQ. These allowed significant observations of C/Garradd (2009 P1) and limited observations of C/ISON (2012 S1). However, the project was clearly

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Fig. 7 Coma spectral maps of Hartley 2. The gases in the innermost coma are shown, together with the distribution of icy grains (as measured by an absorption feature of H2O-ice). The icy grains and the organics and even the refractory grains are much better correlated with CO2 than with H2O (Credit: NASA/UMD)

Fig. 8 Nucleus. This deconvolved HRI image of the nucleus of Hartley 2 (sun at right) shows the very clear distinction between the smooth waist and the two lobes, which might once have been the components of a contact binary (Credit: NASA/JPL/UMD)

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understaffed and contact was lost with the spacecraft between the two observing windows for comet ISON. This was traced to an overflow of a time-conversion calculation in the fault protection software. Nevertheless, the data collected on C/Garradd led to a surprising result (at 2 AU post-perihelion, the highest CO relative abundance ever measured inside 3 AU) that required rethinking all the observations by other groups and showed that, unlike the normal behavior of wateroutgassing (peaking near perihelion), the release of CO increased monotonically from more than 2 AU pre-perihelion to approximately 2 AU post-perihelion (Feaga et al. 2014). This result calls into question any measurements of relative abundance at only a single point in a comet’s orbit and clearly requires rethinking the key features of cometary outgassing.

Stardust NExT The extended mission of the Stardust spacecraft, called the New Exploration of Tempel (NExT), was also a direct consequence of Deep Impact in that it was targeted to fly past Tempel 1 a full orbital period (5½ years) after the DI encounter. It had three goals – to search for evolutionary changes over an orbital period in terrain that had first been seen by DI, to observe terrain that had not been seen with DI, and to examine the impact site. The key challenges for this mission were twofold. The first was to predict the rotational phase of the comet accurately enough a year prior to encounter that the time of encounter could be adjusted so that the impact site would be on the observable side of the nucleus. Two independent studies disagreed on the prediction by a large amount, but the compromise solution averaging the two resulted in an ideal encounter that included visibility of the impact site, visibility of a lot of previously observed terrain, and visibility of considerable previously unseen terrain. The other key challenge was to predict the amount of hydrazine fuel remaining after the expected maneuvers. This set a maximum of about 8 h on the time period over which the arrival could be varied, and it turned out that the spacecraft was actually “running on vapor” by the end of the Tempel 1 encounter. Results from this mission have been summarized by Veverka et al. (2013), and only selected results are discussed here. Examination of the region of the impact by DI’s impactor spacecraft shows a depression consistent with diameter 50 m, consistent with the 40 m inferred above from adding up the estimated excavated ice that sublimed in the coma (Schultz et al. 2013). However, the terrain has been covered out to much larger distances, and there is a bright circular arc with diameter 120–180 m, which is a likely candidate for the raised rim of the crater. This would be consistent with the excavated ice and the observation that, at least in higher gravity environments, most of the ejecta, of order 90 %, falls back to the surface (Richardson and Melosh 2013; Schultz et al. 2013). There is not yet a consensus on the interpretation of all aspects of the resultant crater, but all interpretations imply very weak, low-density material and widespread ejecta. There were two other key results from Stardust NExT mission regarding the evolution of comets that will help to separate evolutionary effects from primordial

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properties on comets. There is reasonably strong evidence that the jets commonly seen in cometary comae likely arise, in most cases, from very steep surfaces (scarps, cliffs, crater walls) rather than from horizontal surfaces (Farnham et al. 2013) and comparisons of surface features seen both by DI and by Stardust NExT show that the average loss of material from the surface (estimated at ~1/3 m) is episodic at least spatially and plausibly temporally. Changes observed, all in the sense of loss of material, had spatial scales of tens of meters (Veverka et al. 2013).

Conclusions Importance of Cometary Missions for Solar System Origins Nuclei of five comets have now been imaged in varying degrees of detail (Fig. 9). They are remarkably diverse in overall shape and in surface topography, without obvious signs of different processes being important. This makes it difficult to

Fig. 9 Five comets. Images of all cometary nuclei visited in situ show dramatic differences in gross shape and also in the nature of the topographic features. Although all comets have jets in the coma, only for Halley and Hartley 2 is it possible to see the jets without using special image enhancements. Given the results at Hartley 2, it seems likely that jets (normally seen in white light reflected by solid particles) are only seen easily when the jets contain many nearly pure icy grains (Credit: NASA/JPL/UMD)

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interpret the differences and/or to separate evolutionary processes from primordial properties. The Stardust NExT mission helped considerably in identifying clearly defined evolutionary changes. Deep Impact’s most significant contributions to the larger picture were twofold. The DI mission and its follow-on activity have played a key role in rethinking the origin of comets and helped to bring comets back as a viable source of the Earth’s water. Hartogh et al. (2011) showed that the D/H ratio in the water from comet Hartley 2 was equal to that in terrestrial mean ocean water (contrary to what had been previously measured only for long-period comets). A’Hearn (2008) discussed the developments prior to the encounter with Hartley 2, but the understanding has evolved considerably since then. The studies of CO2 by DI coupled with the publication of measurements of CO2 from the Japanese AKARI satellite (Ootsubo et al. 2012) led the team to reexamine the whole question of relative abundances of volatiles in different dynamical classes of comets. This was coupled with the new studies of migration of the giant planets by Walsh et al. (2011) and led A’Hearn et al. (2012) to argue that short-period comets did not form in the classical Kuiper belt, but rather formed in a region that significantly overlapped the formation of the Oort cloud comets, but which on average was closer to the sun than the region in which the Oort cloud comets formed, the opposite of previous understanding. They were then ejected, by migration of the giant planets, to the Scattered Disk. This also explained several other aspects of comets, such as the D/H ratios in short-period and long-period comets. Contemporaneously, Belton (2014) studied a variety of properties of cometary nuclei and the size distribution of TNOs (Trans-Neptunian Objects) to argue strongly that cometary nuclei are not fragments of large TNOs, but rather primitive bodies of small size from the Scattered Disk. Formation in the classical Kuiper belt, based on size distributions there, had predicted that most cometary nuclei would be fragments.

Cosmic Hazards and NEO Defense One of the advantages of scientifically driven missions is that they collect enough data to find surprising results of relevance to practical issues. DI made significant contributions to understanding the hazard from NEOs and the required planning for mitigation campaigns. Although Tempel 1 is not an NEO, roughly 10–15 % of NEOs are either fragments of cometary nuclei (a large number of them are independently orbiting fragments of comet Schwassmann-Wachmann 3!) or asteroids with many of the dynamical and physical characteristics of cometary nuclei. In fact, a recent paper (Mommert et al. 2014) argues that (3552) Don Quixote, the third largest known NEO, does exhibit cometary activity. The properties deduced for Tempel 1 are therefore very likely representative for cometary NEOs. First and foremost, DI emphasized the wide variation in many properties among cometary nuclei, this contrasting with a few properties that are common. Many nuclei appear, from indirect measurements, to be very porous, as more directly

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measured by DI for comet Tempel 1 and inferred indirectly by DI for comet Hartley 2. Unpublished results from the numerical modeling of the ejecta plume of Tempel 1 (J. Richardson, private communication) imply that the momentum transfer efficiency, the so-called beta factor, would be only about 2, provided the geometry of the impact was on a line through the center of mass. This is relatively low compared to the value expected for competent, rocky bodies. Shape is one of the most variable properties among comets, and the experience of DI is that rotational light curves are not reliable indicators of the shape of the nucleus, at least with the limited (but typical) range of observational geometries that were available for the targets of DI. DI’s algorithms for targeting a small body of unknown shape are a major step forward in targeting hazardous NEOs for mitigation. However, it is clear that targeting an impactor (or even an explosive device) to impact on a line through the center of mass is still a difficult challenge to our present capabilities. Fortunately, the average radius, and thus a crude volume, appears to be reliably determined from remote sensing, thus enabling early estimates of the mass of a hazardous NEO using a bulk density of 0.5 g/cm3. This in turn allows a more reliable estimation of the energy that would be delivered by an impacting NEO. A totally unanticipated result was an ability to deduce the mass of impacting cometary grains from the attitude fluctuations that they induced in the impactor. At hypervelocity, milligram grains had a large effect on the attitude of a 1/3 t impactor. Although these impacts would not significantly affect the trajectory of an impactor, they could have serious effects on, e.g., proximity fusing for an explosive device or the effectiveness of any device shaped for penetration. These results all suggest fertile areas requiring further study for development of effective mitigation of hazardous NEOs.

Cross-References ▶ Defending Against Asteroids and Comets ▶ International Astronomical Union and the Neo Hazard ▶ Potentially Hazardous Asteroids and Comets ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE

References A’Hearn MF (2008) Deep impact and the origin and evolution of cometary nuclei. Space Sci Rev 138:237–246 A’Hearn MF, Belton MJS (2005) Deep impact: a large-scale active experiment on a cometary nucleus. Space Sci Rev 117:1–21 A’Hearn MF, Belton MJS, Delamere WA, Kissel J, Klaasen KP et al (2005) Deep impact: excavating comet temple 1. Science 310:258–264

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Ootsubo T, Kawakita H, Hamada S, Kobayashi H, Yamaguchi M et al (2012) AAKARI nearinfrared spectroscopic survey for CO2 in 18 Comets. Astrophys J 752:15 (12pp) Pieters CM, Goswami JN, Clark RN, Annadurai M, Boardman J et al (2009) Character and spatial distribution of OH/H2O on the surface of the moon seen by M3 on Chandrayaan-1. Science 326:568–572 Richardson JE, Melosh HJ (2013) An examination of the deep impact Collision site on Comet Tempel 1 via Stardust-NExT: placing further constraints on cometary surface properties. Icarus 222:492–501 Richardson JE, Melosh HJ, Lisse CM, Carcich B (2007) A ballistics analysis of the deep impact Ejecta plume: determining Comet Tempel 1’s gravity, mass, and density. Icarus 190:357–390 Schleicher DG, Barnes KL, Baugh NF (2006) Photometry and imaging results for Comet 9P/Tempel 1 and deep impact: gas production rates, Postimpact Light Curves, and Ejecta Plume Morphology. Astron J 131:1130–1137 Schultz PH, Hermalyn B, Veverka J (2013) The deep impact crater on 9P/Tempel-1 from StardustNExT. Icarus 222:502–515 Small Bodies Node of PDS. http://pdssbn.astro.umd.edu/. Accessed July 2014 Sunshine JM, A’Hearn MF, Groussin O, Li J-Y, Belton MJS et al (2006) Exposed water ice deposits on the surface of Comet 9P/Tempel 1. Science 311:1453–1455 Sunshine JM, Farnham TL, Feaga LM, Groussin O, Merlin F et al (2009) Temporal and spatial variability of lunar hydration as observed by the deep impact spacecraft. Science 326:565–568 Veverka J, Klaasen K, A’Hearn M, Belton M, Brownlee D et al (2013) Return to Comet Tempel 1: overview of Stardust-NExT results. Icarus 222:424–435 Walsh KJ, Morbidelli A, Raymond SN, O’Brien DP, Mandell AM (2011) A low mass for Mars from Jupiter’s early gas-driven migration. Nature 475:206–209 Weaver HA, Feldman PD, A’Hearn MF, Dello Russo N, Stern SA (2011) The carbon monoxide abundance in Comet 103P/Hartley 2 During the EPOXI Flyby. Astrophys J Lett 734:L5

NASA’s Asteroid Redirect Mission Michele Gates and Lindley N. Johnson

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NEA Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Asteroid Redirect Mission Robotic Capture Concept Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Asteroid Redirect Mission Robotic Capture Concept A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Asteroid Redirect Mission Robotic Capture Concept B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Asteroid Redirect Crewed Mission Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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NASA is examining concepts for the Asteroid Redirect Mission, in which the agency would launch a robotic spacecraft to capture and redirect an asteroid into a stable orbit in the Earth-Moon system. This would be followed by an early use of the powerful Space Launch System (SLS) launch vehicle and Orion crew spacecraft to ferry astronauts to retrieve samples and return to Earth. NASA is examining two options for the robotic segment: one to redirect a small asteroid to a lunar distant retrograde orbit (LDRO) and another to extract a cohesive mass from a larger asteroid and return it to this same orbit. A preliminary set of mission objectives includes opportunities for planetary defense deflection demonstrations. This brief chapter describes the mission concepts currently under examination in preformulation, including aspects and potential applications to planetary defense.

M. Gates (*) NASA Headquarters, Human Exploration and Operations Directorate, Washington, DC, USA e-mail: [email protected] L.N. Johnson Planetary Science, NASA Headquarters, Science Mission Directorate, Washington, DC, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_46

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Keywords

Arecibo • Asteroid redirect mission • Asteroid redirect mission robotic concepts • Asteroid initiative • Asteroid Grand Challenge (AGC) • Asteroid Terrestrial-impact Last Alert System (ATLAS) • Catalina Sky Survey • DARPA Space Surveillance Telescope • Goldstone • InfraRed Telescope Facility (IRTF) • LINEAR • Near Earth Asteroid (NEA) • NEOWISE • Pan-STARRS • Planetary defense deflection demonstrations • Solar Electric Propulsion (SEP) • Spitzer Space Telescope

Introduction NASA’s Asteroid Initiative was announced in April 2013 and consists of two separate but related activities: the Asteroid Redirect Mission (ARM) and the Asteroid Grand Challenge (AGC). The Asteroid Redirect Mission comprises of three segments: the detection and characterization of candidate near-Earth asteroids for the robotic redirect mission; the robotic rendezvous, capture, and redirection of the whole or part of a selected target asteroid to the Earth-Moon system; and the crewed mission to explore and sample the captured asteroid mass using the SLS and Orion. The Asteroid Grand Challenge is an enhanced and accelerated effort to find all asteroid threats to human populations and to know how to protect our planet against these threats. As of January 1, 2014, 10,576 near-Earth objects (NEOs) have been found, including 94 comets (Chamberlain 2014). Current systems in NASA’s NEO Program include two data processing and analysis nodes: the Minor Planet Center hosted at the Smithsonian Astrophysical Observatory Center for Astrophysics, Cambridge, MA, and the NEO Program office at the Jet Propulsion Laboratory (JPL), Pasadena, CA. Four dedicated NEO search teams support NASA’s observation efforts: the Catalina Sky Survey of the University of Arizona; the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) of the University of Hawaii; the Lincoln Near-Earth Asteroid Research (LINEAR) team at the Massachusetts Institute of Technology Lincoln Laboratory; and the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) space observatory operated for NASA by JPL. The discovery of NEOs in general has slowly increased in rate in the last few years. NASA also uses planetary radar from its own Goldstone Deep Space Network facility in California and the Arecibo Radio Telescope Facility in Puerto Rico to provide additional information about NEOs, such as high-precision orbit data, size and shape to within ~2 m, spin rate, and surface roughness. Seventy to 80 NEOs are observed with radar every year. Both aspects of the initiative will utilize enhancements to NASA’s NEO observation activities to accelerate the search for potentially hazardous asteroids and characterize NEOs. The ARM concept was proposed in 2011 during a feasibility study at the Keck Institute for Space Studies (Brophy 2014). Important ongoing activities across NASA’s Human Exploration and Operations, Space Technology, and Science Mission Directorates will be leveraged for the mission, including searching for

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potentially hazardous asteroids, advancing high-power solar electric propulsion, and developing the high-capacity SLS rocket and the Orion multipurpose crew vehicle. The robotic segment will demonstrate interaction with low-gravity, noncooperative targets along with high-power and lifelong solar electric propulsion (SEP) for cargo delivery and extensibility to human missions. The human part of the mission planned for the mid-2020s will also utilize advanced technologies and systems for rendezvous and extravehicular activities (EVA), the International Docking System, and integrated vehicle stack operations. The ARM involves sending a high-efficiency (ISP 3000 s), high-power (40 kW) SEP robotic vehicle that leverages advanced space technology development to rendezvous with a near-Earth asteroid (NEA) and returns asteroidal material to a stable lunar distant retrograde orbit (LDRO) (Strange et al. 2013). Once the retrieved asteroidal material is placed into the LDRO, a two-person crew would launch aboard an Orion capsule to rendezvous and dock with the robotic SEP vehicle at its LDRO position. After docking, the crew would conduct two EVAs to collect asteroid samples and potentially deploy instruments prior to Earth return. The crewed mission will use a lunar gravity assist for both the outbound and inbound trajectories and is anticipated to be about 27–28 days in duration. There are two options for asteroid capture currently under examination: one that captures an entire 2–10-m-mean diameter NEA (Muirhead and Brophy 2014) and another that retrieves a 2–4-m-mean diameter boulder from a 100+-meter class NEA (Mazenek et al. 2014). Both robotic segment options include potential slow-push planetary defense demonstrations of NEA deflection techniques, which could include ion beam deflection, gravity tractor, and/or enhanced gravity tractor (in the case of the boulder retrieval).

NEA Observations NASA’s NEA discovery enhancements include plans to bring into operation a second colocated 1.8-m Pan-STARRS telescope and to increase the time devoted to NEO searches. NASA is also working to utilize for observing time the Defense Advanced Research Projects Agency Space Surveillance Telescope for NEO detection. The Asteroid Terrestrial-impact Last Alert System (ATLAS) will be an extremely wide-field new survey capability, covering the entire night sky every night, but not as deeply as other systems (Johnson 2013) (see Figs. 1 and 2). In addition to the reactivation of NEOWISE, NASA’s NEO characterization enhancements include increased time on the Goldstone and Arecibo radars for NEO observations, as well as streamlining rapid response capabilities. At the InfraRed Telescope Facility (IRTF), increased on-call time is improving the rapid response capability and instrumentation modifications will be installed for spectroscopy and thermal signatures (Johnson 2013). The defined nomenclature for asteroid target selection for the ARM includes four tiers. A “potential candidate” is one for which orbit parameters satisfy the

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Total Discovered

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Estimated Diameter (m) Fig. 1 Known NEA population by size bins as of January 1, 2014 (Credit: Chamberlain 2014)

Near-Earth Asteroid Discoveries All Asteroids

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LINEAR NEAT Spacewatch LONEOS Catalina Pan-STARRS NEOWISE all others

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Half Year Intervals Fig. 2 NEAs discovered by observation sites as of January 1, 2014 (Credit: Chamberlain 2014)

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rough constraints on launch and return dates, and absolute magnitude indicates the size lies roughly in the right range. A candidate is “characterizable” when it approaches the Earth (or the Spitzer Space Telescope) close enough and with suitable enough observing geometry that it can be adequately characterized. A “valid candidate” is one for which detailed mission design has been performed for feasible launch and return dates, yielding a maximum returnable mass, and physical properties have been characterized and lie within acceptable ranges to achieve mission goals. A “selectable target” meets programmatic constraints (e.g., on achievable schedule and minimum return size) and has identified but manageable risks.

Asteroid Redirect Mission Robotic Capture Concept Summary NASA has examined two robotic mission concepts for the ARM, both of which utilize a high-efficiency (Isp 3000 s), high-power (40 kW) SEP-based robotic spacecraft to return a cohesive asteroid mass to a stable LDRO. The flight system is largely common to both mission concepts and several permutations of these two concepts exist. The SEP module consists of large solar arrays, xenon propellant tanks, and power processing units. The mission module contains the spacecraft attitude control system, the communication and data handling system, the communications system, the power system, and the thermal control system. The capture system could be a deployable structure that is either an inflatable bag that captures an entire small asteroid or robotic manipulators that remove a boulder from an asteroid’s surface. Integrated navigational sensors used during asteroid rendezvous, proximity operations, and capture could be located on the mission module or capture system. A docking mechanism attached to the aft end of the robotic spacecraft will allow it to dock with the Orion spacecraft. Figure 3 presents a concept drawing of the robotic flight system (Dr. Paul Chodas, Jet Propulsion Laboratory, personal communication). The robotic spacecraft will demonstrate high-power, long-life SEP technology in deep space. The mission concepts call for at least 6 years of deep-space flight. The flight system concept includes four Hall thrusters operating at approximately 10 kW each, 50 kW advanced high-power solar arrays, and approximately 10 tons of xenon propellant. This flight system is envisioned to serve as a building block for future exploration, i.e., it will have a design scalable up to 150 kW, enabling future versions to maneuver larger masses into interplanetary space, such as habitation modules or consumable cargo. The component and system capabilities emerging from this development effort could become standard for the SEP industry.

Asteroid Redirect Mission Robotic Capture Concept A One asteroid capture option, “concept A,” for the robotic capture segment involves a small single NEA, which has a mean diameter of 10 m or less and a mass of less than 1,000 tons. Here, the SEP-based robotic spacecraft will rendezvous with the

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Fig. 3 Conceptual drawing of the robotic flight system (Credit: NASA)

small rotating NEA and match its motion and then deploy an inflatable system to envelop and “capture” the asteroid, provided that it is not spinning too fast or composed of materials that prohibit capture. The orbits of the potential asteroid targets are such that the robotic spacecraft would nudge them over time spans on the order of 2–4 years into the desired capture orbit around the Moon. After capture, the spacecraft will despin the small asteroid using the reaction control systems and maneuvers it using SEP to a stable, crew-accessible LDRO. For concept A, the NEA used for the reference mission concept design is 2009 BD, which is estimated to be less than 145 tons. There are seven other small asteroids identified as potential candidates for this option: 2007 UN12, 2008 EA9, 2010 UE51, 2013 LE7, 2009 BD, 2013 PZ6, and 2011 MD (Dr. Paul Chodas, Jet Propulsion Laboratory, personal communication). These asteroids could be put into NASA’s desired LDRO between 2020 and 2024. Mission concept A is reliant on the NEO Program to identify a selectable target. A demonstration of ion beam deflection can be accomplished through mission concept A by using the SEP system to impart thrust directly onto the asteroid. The spacecraft would use its reaction control system or flip-turns to maintain position. Current calculations indicate that for an asteroid less than 500 t, the concept flight system will impact 1 mm/s change in velocity in less than an hour (Mr. Brian Muirhead, Jet Propulsion Laboratory, personal communication).

Asteroid Redirect Mission Robotic Capture Concept B Another capture option, “concept B,” for the robotic segment involves a larger NEA, which is 50–100 m in diameter or larger, and acquisition of a 2–4-m-diameter coherent boulder with mass approximately 10–70 tons (Mr. Dan Mazanek, NASA Langley Research Center, personal communication). This concept utilizes the

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SEP-based spacecraft and robotic arms to capture a boulder and return it to the same stable, crew-accessible LDRO. This mission leverages data from previous robotic asteroid missions and is enhanced by the NEO Program. Here, the SEP-based robotic spacecraft will perform approach and flyby operations and in situ characterization of the asteroid. This capture concept assumes 44 days to verify and refine the shape, spin, and gravity models of the asteroid and obtain centimeter-scale imagery of the majority of the surface. Rendezvous with the larger rotating NEA includes two dry-run operations for up to three sites to refine local gravity, verify navigation, and obtain sub-centimeter-scale imagery prior to a collection attempt. The concept allows for up to five boulder-collection attempts to provide contingency against surface and boulder anomalies. Larger asteroids from which boulder-sized samples could be collected and redirected are: Itokawa, a sample of which was returned to Earth in 2010 under Japan’s Hayabusa mission; Bennu, from which NASA’s Osiris-REx mission, launching in 2016, plans to study and return a small sample to Earth in 2023; 1999 JU3; 2008 EV5; 2011 UW158; and 2009 DL46 (Dr. Paul Chodas, Jet Propulsion Laboratory, personal communication). The candidate object used for the conceptual design of mission concept B is Itokawa. A 2019 launch of the concept spacecraft could return a 19-ton boulder to the LDRO in 2025. A demonstration of gravity-tractor deflection can be accomplished through the mission concept B by using the gravity attraction of the robotic spacecraft to change the velocity vector of the asteroid. This concept of operations provides 260 days for operations and proper Earth-Itokawa alignment to verify deflection. This concept could also accommodate an enhanced gravity-tractor demonstration using the acquired boulder to significantly increase the robotic spacecraft’s mass, which would be planned for an estimated 180 days of mission operations, with 60 days required for measurable deflection (Mr. Dan Mazanek, NASA Langley Research Center, personal communication).

Asteroid Redirect Crewed Mission Concept Once the asteroid is returned to the stable LDRO in cislunar space, NASA will send two crew members in the Orion vehicle, launched atop the SLS, to study, explore, and sample it. The versatile Orion spacecraft will serve as the in-space crew transportation vehicle, habitat, and airlock for this mission. It will rendezvous and dock with the asteroid-carrying spacecraft to demonstrate early human exploration capabilities including longer duration operations in deep space, rendezvous and proximity operations, life support, and EVA capabilities. Two four-hour EVAs are planned to explore, select, and obtain samples using a variety of sample collection techniques such as core drilling into the asteroid and using sample containers to collect loose material. Once the samples are obtained, the crew will ingress Orion, repressurize the spacecraft, and return the samples to Earth with an entry into the Pacific Ocean off the coast of California.

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Conclusion NASA is in the early stages of formulation for the Asteroid Redirect Mission, which will draw upon key ongoing activities across the agency. One of the primary objectives of the Asteroid Redirect Mission is to enhance the detection and observation of near-Earth asteroids. These enhancements are designed to increase the search for potentially hazardous asteroids for planetary defense and characterization of all potential mission candidates possible within the range of the assets. Substantial progress has been made to examine two approaches to the Asteroid Redirect Robotic Mission: one to redirect a small asteroid to a lunar distant retrograde orbit and another to extract a coherent mass from a larger asteroid and return it to this same orbit. NASA is examining opportunities for planetary defense deflection demonstrations in both approaches.

References Brophy J (2012) Asteroid retrieval feasibility study. Keck Institute for Space studies report Chamberlain A (2014) Near earth asteroid discovery statistics. Near Earth Object Program website. www.neo.jpl.nasa.gov/stats/ Johnson L (2013) NASA near earth object observation program. Presented at the asteroid initiative ideas synthesis Mazenek D et al (2014) Asteroid redirect robotic mission: alternate concept overview. American Institute of Aeronautics and Astronautics, Space 2014 conference, San Diego Muirhead B, Brophy J (2014) Asteroid redirect robotic mission feasibility study. Presented at IEEE aerospace conference, Big Sky Strange N et al (2013) Overview of mission design for NASA asteroid redirect robotic mission concept. Presented at the 33rd international electric propulsion conference, The George Washington University, Washington, DC

OSIRIS-REx Asteroid Sample-Return Mission Dante S. Lauretta

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The OSIRIS-REx Target: Asteroid Bennu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Science Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Touch-and-Go Sample-Acquisition Mechanism (TAGSAM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OSIRIS-REx Camera Suite (OCAMS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OSIRIS-REx Laser Altimeter (OLA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OSIRIS-REx Thermal Emission Spectrometer (OTES) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radio Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Regolith X-ray Imaging Spectrometer (REXIS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample-Return Capsule (SRC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flight System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contamination Control and Knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Baseline Science Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Science Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objective 1: Return and Analyze a Sample of Pristine Carbonaceous Asteroid Regolith in an Amount Sufficient to Study the Nature, History, and Distribution of Its Constituent Minerals and Organic Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objective 2: Map the Global Properties, Chemistry, and Mineralogy of a Primitive Carbonaceous Asteroid to Characterize Its Geologic and Dynamic History and Provide Context for the Returned Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objective 3: Document the Texture, Morphology, Volatile Chemistry, and Spectral Properties of the Regolith at the Sampling Site In Situ at Scales Down to the Sub-centimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objective 4: Measure the Yarkovsky Effect on a Potentially Hazardous Asteroid and Constrain the Asteroid Properties that Contribute to This Effect . . . . . . . . . . . . . . . . . . . . . Objective 5: Characterize the Integrated Global Properties of a Primitive Carbonaceous Asteroid to Enable Direct Comparison with Ground-Based Telescopic Data of the Entire Asteroid Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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D.S. Lauretta (*) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_44

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Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564 Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565

Abstract

The primary objective of the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission is to return pristine samples of carbonaceous material from the surface of a primitive asteroid. The target asteroid, near-Earth object (101955) Bennu, is the most exciting, accessible, and volatile- and organic-rich remnant from the early Solar System. OSIRIS-REx returns a minimum of 60 g of bulk regolith and a separate 26 cm2 of fine-grained surface material from this body. Analyses of these samples provide unprecedented knowledge about presolar history, from the initial stages of planet formation to the origin of life. Prior to sample acquisition, OSIRIS-REx performs comprehensive global mapping of the texture, mineralogy, and chemistry of Bennu, resolving geological features, revealing its geologic and dynamic history, and providing context for the returned samples. The instruments also document the regolith at the sampling site in situ at scales down to the sub-centimeter. In addition, OSIRIS-REx studies the Yarkovsky effect, a non-Keplerian force affecting the orbit of this potentially hazardous asteroid (PHA), and provides the first ground truth for telescopic observations of carbonaceous asteroids. Keywords

101955 Bennu • Asteroids • B-type Asteroid • Carbon • Carbonaceous asteroid • New Frontiers Program • OSIRIS-REx • Potentially hazardous asteroid • Resources • Sample return • Sample return capsule • Spacecraft • Spectroscopy • Stardust mission • Telescopes • Touch-and-Go Sample-Acquisition Mechanism (TAGSAM) • Volatiles • Volatile and organic-rich asteroid • Water • Yarkovsky effect

Introduction OSIRIS-REx provides exceptional science return. For the first time in US spaceexploration history, a mission will return a pristine sample of a carbonaceous asteroid. Maintaining geological context is critical to linking the chemical and physical nature of the sample to the bulk properties of Bennu and the broader asteroid population. Since high-priority NASA science objectives are to understand the initial stages of planet formation and sources of organics delivered to Earth that may have ultimately led to the development of life, samples of a primitive carbonaceous object such as Bennu are highly desirable. A major advantage of the OSIRIS-REx mission is that the evolving capabilities of state-of-the-art laboratory analytical instrumentation, which is impossible to duplicate on a spacecraft, can

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repeatedly be brought to bear on OSIRIS-REx samples to advance NASA science objectives by many future generations. OSIRIS-REx ushers in a new era of planetary exploration by developing unprecedented operational capabilities in small-body proximity operations. OSIRIS-REx executes precise spacecraft navigation to “kiss” the surface and acquire samples of Bennu. These operational capabilities (and the hardware/software inherent to them) are essential as humanity explores near-Earth space to increase our understanding of Solar System bodies and develop in situresource utilization processes. OSIRISREx also serves as a demonstration of what has been termed a “transponder mission,” a type of mission to a potentially hazardous asteroid (PHA) with the dual objectives of refining the orbit to ascertain whether an impact is impending and characterizing the object to facilitate a possible deflection mission. OSIRIS-REx thus seeks to understand the Solar System scientifically, prepare for human exploration, and assess the risk of one of the most threatening PHAs.

The OSIRIS-REx Target: Asteroid Bennu The first step in achieving the mission objectives was selection of the optimum target asteroid. OSIRIS-REx seeks to return samples from a primitive body that represents the objects that may have brought prebiotic seeds of life and volatiles to Earth. The most plausible sources of these compounds are primitive asteroids and comets. Geochemical and dynamic constraints suggest that 200 m (estimated by selecting those brighter than 21.5 absolute magnitude) reduced the list of accessible asteroids to 26. Of these, a dozen had been spectrally characterized and taxonomically classified, and five were known to be carbonaceous. Bennu rose to the top of the list of potential sample-return targets based on both its high science value and its extensive characterization by ground- and space-based telescopes, which greatly reduce the risk for proximity operations planning. Bennu was discovered in September 1999 and is an Apollo NEO with a semimajor axis of 1.126 astronomical units (AU) (Williams 1999). It is a B-type asteroid characterized by a linear, featureless spectrum with bluish to neutral slope (Bus and Binze 2002; Clark et al. 2010; Lantz et al. 2013). Near-infrared spectroscopic data show evidence of a thermal tail longward of 2 μm, suggesting a very low albedo (3.5  1.5 %) that is consistent with a carbonaceous surface. Thermal infrared data show that there is no observable dust or gas in the proximity of Bennu (Emery et al. 2014). Light-curve observations give a rotational period of 4.2834 (0.0065) hours (Hergenrother et al. 2013). The light curve displays no evidence of satellites in orbit about Bennu. Bennu is a PHA that comes within 0.002 AU of the Earth and has one of the highest probabilities of impacting the

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Fig. 2 Bennu’s orbit crosses the Earth every revolution – making a close approach every 6 years

Earth of any known asteroid (Milani et al. 2009; Chesley et al. 2014). Bennu is therefore an extremely high science-value sample-return mission target (Fig. 2). Members of the OSIRIS-REx Science Team observed Bennu with the Arecibo Planetary Radar System in 1999, 2005, and 2011 and with the Goldstone Planetary Radar System in 1999 (Nolan et al. 2013). Because of these observations, Bennu has formal uncertainty of 6 m in the semimajor axis, the lowest of any asteroid (Chesley et al. 2014). This knowledge ensures accurate navigation for rendezvous. Delay-Doppler imaging provides shape information at a spatial resolution of 7.5 m/pixel. These data reveal a 492-m (20 m, mean diameter) asteroid undergoing retrograde rotation. The pole orientation is nearly perpendicular to the ecliptic plane, resulting in favorable lighting conditions for the entire asteroid during rendezvous. Radar observations also display no evidence of satellites. The radar polarization ratio (0.18) suggests a smooth surface of fine-grained material. These data provide high confidence in the presence of regolith on the surface of Bennu (Lauretta et al. 2012, 2014; Fig. 3). Members of the OSIRIS-REx team observed Bennu with the Spitzer Space Telescope in May 2007 (Emery et al. 2014; Muller et al. 2012). These observations provide additional information about the nature and distribution of regolith on the surface of Bennu. The Spitzer observations confirm that Bennu is extremely dark and further constrain the albedo to 4.3  0.3 %. The Spitzer data yield a thermal inertia of Bennu of 310  70 J m 2 s 0.5 K 1, suggesting that the regolith is comprised of fine gravel (sub-cm). These data strongly support the concept that there is abundant regolith on the surface of Bennu available for sampling (Lauretta et al. 2012). Thus, Bennu is the ideal mission target: our knowledge allows for detailed mission operations planning with minimal risk and exceptional science return.

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Fig. 3 The planetary radar system provided highresolution shape information for Bennu – facilitating mission planning

Science Implementation Touch-and-Go Sample-Acquisition Mechanism (TAGSAM) TAGSAM is an elegantly simple device that satisfies all sample-acquisition requirements. TAGSAM consists of two major components: a sampler head and an articulated positioning arm. The head acquires the bulk sample by releasing a jet of high-purity N2 gas that “fluidizes” the regolith into the collection chamber. The articulated arm, which is similar to, but longer than, the Stardust aerogel deployment arm, positions the head for collection, brings it back for visual documentation, and places it in the Stardust-heritage SRC. The team has performed extensive hardware development and testing combined with dynamics simulations. Using a series of Engineering Development Units (EDUs), TAGSAM has been tested separately in vacuum and microgravity conditions. In every case, these tests resulted in acquisition of sample mass substantially above the baseline requirement of 60 g.

OSIRIS-REx Camera Suite (OCAMS) OCAMS is composed of three cameras: PolyCam, MapCam, and SamCam (Hancock et al. 2013; Smith et al. 2013). PolyCam, an F/3.2 Ritchey-Chretien telescope, acquires Bennu from 1 M-km range, refines its ephemeris, and performs high-resolution imaging of the surface. Its focal length is 625 mm. At 0.8 its FOV

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Fig. 4 The OSIRIS-REx Camera Suite (OCAMS) will characterize Bennu from 1 M km to 2-m range – and all distances in between (Figure from Smith et al. (2013))

is five times smaller than MapCam. It uses a 1,024  1,024-pixel CCD array and it is equipped with a focus mechanism that translates one of its field-flattening lens to allow it to focus anywhere within a 200-m to infinity object range. The mechanism includes a shutter that, on every one of its 25 rotations over the focus range, allows it to assume three nominal focal positions while still being able to be safe (if necessary) (Fig. 4). MapCam searches for plumes and satellites, provides narrow-angle optical navigation, performs filter photometry, maps the surface, and images the sample site. MapCam uses the same 1,024  1,024-pixel CCD array as the PolyCam. Optically, it is a five-element refracting telephoto lens with the aperture set to f/3.3. The focal length is 125 mm, with a 4.0 field of view and a 68 μrad IFOV. It is also equipped with a filter wheel populated with four filters consistent with the Eight Color Asteroid Survey (ECAS) photometric system, as well as two panchromatic filters, one allowing imaging from 100 m to infinity and the other allowing imaging around 30 m range. The filters are the v, w, x filters (550, 770, 860 nm) from the ECAS standard set in addition to a blue filter shifted from the ECAS b from 437 to 470 nm to allow better camera performance. Each of the filters can be sequenced and images taken on 5 s centers so that it takes 20 s to collect the 5 images needed (4 colors + 1 panchromatic). SamCam is a 22 -FOV camera that documents the sample-acquisition event from a range of 3–30 m. It uses the same detector as the other two imagers and is also equipped with a filter wheel; this one contains three identical panchromatic filters that allow backup imaging if one or more filters get contaminated by the sampling event. It also contains a diopter, similar to that mounted within the MapCam’s filter wheel, that allows it to refocus at a range of 2 m, in order to achieve higher-resolution imaging of the TAGSAM head after the sampling event. All three cameras are able to back up each other’s functions to a significant degree. The alternate imaging campaigns would occur from different ranges and at

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different stages of the mission but represent a reliable functional redundancy to guard against failures resulting in the loss of a single camera’s functionality.

OSIRIS-REx Laser Altimeter (OLA) OLA provides ranging data out to 7 km and maps the shape and topography (Barnouin et al. 2012; Dickinson et al. 2012). OLA is an advanced lidar (Light Detection and Ranging) system that is a hybrid of the lidar on the Phoenix Mars Lander’s Canadian weather station and an instrument flown on the 2005 US Air Force Experimental Satellite System-11 (XSS-11). OLA will scan the entire surface of the asteroid to create a highly accurate, 3D model of Bennu, which will provide the team with fundamental and unprecedented information on the asteroid’s shape, topography, surface processes, and evolution. OLA uses a receiver and two complementary lasers to provide the information about the asteroid surface. OLA’s high-energy laser transmitter will be used for scanning from further distances (from 1 to 7.5 km from the surface of Bennu). The low-energy laser will be used for rapid imaging at shorter distances (500 m to 1 km) to contribute to a global topographic map of the asteroid as well as local maps to assist the team in selecting the best site for sample collection. OLA will deliver high-density 3D point cloud data, enabling reconstruction of an asteroid shape model at the highest density yet recorded on any small body and providing much needed slope information at the sample site leading up to acquisition. These data will be important for determining the geological context of the samples obtained by the OSIRIS-REx mission as well as for minimizing the risk of encountering hazards during sampling. In addition, OLA will be important for the accurate determination of the gravity field of Bennu by providing an accurate measure of the distance between the spacecraft and asteroid in support of Radio Science. Finally, OLA will provide ranging in support of other instruments and navigation.

OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) OVIRS is a point spectrometer (4-mrad FOV) with a spectral range of 0.4–4.3 μm, providing full-disk Bennu spectral data, global spectral maps, and local spectral information of the sample site (Reuter and Simon-Miller 2012; Simon-Miller and Reuter 2013). OVIRS spectra will be used to identify volatile- and organic-rich regions of Bennu’s surface and guide sample-site selection. OVIRS obtains a full spectrum over all wavelengths simultaneously using linear variable filter segments. OVIRS has three broad filter strips with sufficient resolution to resolve key spectral features across its entire wavelength range. In addition, OVIRS contains a fourth narrow filter strip to measure key spectral signatures of organic functional groups with higher spectral resolution (Fig. 5). The OVIRS signal-to-noise ratio is dependent upon detector sensitivity, the wavelength region of interest, and phase angle of the observation.

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Fig. 5 The OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) provides high-resolution spectral data – helping us find the optimum site for sampling (Figure from Simon-Miller and Reuter (2013))

Thermal emission will fill in spectral features in the near-IR for higher surface temperatures. To obtain full compositional information about Bennu, observations will be obtained at multiple stations during the detailed survey, each optimized for different portions of the spectrum and different science objectives. For absolute spectral and radiometric calibration, OVIRS utilizes two internal calibration sources, filaments and blackbodies, and a solar calibration port. Throughout the mission, occasional solar observations will allow an absolute calibration check of the entire system, while more frequent internal lamp calibrations will be used for an instantaneous relative check of calibration.

OSIRIS-REx Thermal Emission Spectrometer (OTES) OTES is an uncooled, FTIR point spectrometer that maps the thermal flux and spectral properties of Bennu from 5 to 50 μm with a signal-to-noise ratio (SNR) of >325 between 7.4 and 33.3 μm for a 325 K target (Fig. 6). The design of the spectrometer is heritage from the Mars Global Surveyor TES and the Mars Exploration Rovers Mini-TES instruments. The heart of the instrument is a Michelson interferometer that collects one interferogram every 2 s (where each 2-s data acquisition is called an ICK, for Incremental Counter Keeper). OTES’s spectral resolution is 10 cm 1 and its field of view is 8 mrad, achieved with a 15.2-cm f/3.91 Ritchey-Chretien telescope. At Bennu, OTES will have an accuracy of better than 3 % and a precision (noise equivalent spectral radiance, NESR) of 2.3  10 8 W cm 2 sr 1/cm 1 between 300 and 1,350 cm 1. OTES calibration

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Fig. 6 The OSIRIS-REx Thermal Emission Spectrometer (OTES) provides information on the temperature, mineralogy, and grain size of the asteroid surface

in flight is achieved via a two-point calibration that uses space and an internal, conical blackbody calibration target. To map the compositional variation of Bennu at global and site-specific scales, OTES collects data at multiple times of day during the Detailed Survey and Reconnaissance phases, respectively. The data for thermal mapping are collected during the Orbital B, Detailed Survey, and Reconnaissance phases.

Radio Science Radio Science plays several key roles in determining the environment on, within, and about the asteroid (Scheeres et al. 2012). Radio Science reveals the mass, gravity field, internal structure, and surface acceleration distribution. These analyses provide information on the dynamic environment about the nominal asteroid model, the gravity field down to the surface of the asteroid, and the internal structure and mass distribution within the body. The asteroid mass and gravity field coefficients will be determined during two main mission periods. First, upon arrival the spacecraft will undertake a few slow hyperbolic flybys of the asteroid to determine the total mass and detect the lower degree and order gravity coefficients. Then later in the mission there is a period of low, near-polar orbits dedicated to determining the asteroid spherical harmonic gravity field coefficients. Analysis shows that these should be detectable up to fourth degree and order, at least.

Regolith X-ray Imaging Spectrometer (REXIS) The REXIS Student Collaboration Experiment is a joint venture of the Massachusetts Institute of Technology and Harvard-Smithsonian Center for Astrophysics

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Fig. 7 The Regolith X-ray Imaging Spectrometer (REXIS) combines education with enhanced science at Bennu (Figure from Allen et al. (2013))

(Fig. 7; Allen et al. 2013). REXIS significantly enhances OSIRIS-REx by obtaining a global X-ray map of elemental abundance on Bennu. REXIS was conceived as a student-led project whose primary goal is the education of science and engineering students who will participate in the development of flight hardware in future space missions. Additionally REXIS also augments the observation capabilities of the OSIRIS-REx mission at the high end of the electromagnetic spectrum, which will enable characterization of the asteroid elemental abundances from a global scale down to 50 m, a capability unique to REXIS among instruments of this type that have previously flown. REXIS is designed to observe induced X-ray fluorescence lines emitted from the asteroid surface that arise as a result of exposure to solar X-rays as well as the cosmic X-ray background.

Sample-Return Capsule (SRC) OSIRIS-REx safely returns the samples to Earth in a Stardust mission-heritage SRC (Brownlee et al. 2003). The SRC lands at the Utah Test and Training Range (UTTR), following protocols established during recovery of the Stardust SRC. The SRC recovery team follows Stardust-heritage procedures to transport the

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Fig. 8 OSIRIS-REx is reflying the successful sample-return capsule from the Stardust mission

SRC to Johnson Space Center (JSC), where the samples are removed and delivered to the dedicated OSIRIS-REx curation facility (Fig. 8).

Flight System The OSIRIS-REx flight system builds on proven Lockheed Martin experience and uses established hardware, software, technology, and processes from Stardust, Odyssey, and MRO, as well as Juno, GRAIL, and MAVEN. The flight system architecture was developed in concert with science, instruments, subsystems, mission operations, navigation, and management. The resulting construct was populated with heritage subsystems and components. The OSIRIS-REx flight system pulls from previous spacecraft designs to create a flight system that is fully capable of achieving the mission at a low level of risk. This ability to select the “best of the best” enabled the team to select heritage components and designs without over-constraining the mission. OSIRIS-REx is single-fault tolerant with block, functional, and subsystem internal redundancies with appropriate cross-strapping, autonomous fault detection, isolation, and recovery. Instrument accommodations meet all pointing, power, thermal, and data handling requirements with significant margins. The flight system design was evaluated for its ability to execute the design reference mission (DRM) within the context of launch vehicle, trajectory, communications, and ground systems.

Contamination Control and Knowledge The pristine nature of the sample is preserved using stringent cleaning protocols during fabrication and careful mission design during spacecraft operations. Any

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contamination is thoroughly documented. The OSIRIS-REx team defined pristine to mean that no foreign material introduced into the sample hampers scientific analysis of the sample. This requires that contamination sources of astrochemically relevant compounds are low and that sufficient knowledge of the low levels of contamination introduced by the flight system and sample handling can be understood and corrected for. Amino acids are a compound class of high scientific interest with low meteorite abundances (1 μg/g) and high industrial and biological backgrounds. With the exception of contamination originating from the aerogel itself and nylon bags initially used for curation, there were no contamination issues discovered during scientific investigations of the Stardust material. Analyses of Stardust foils showed a maximum amino acid contamination level of 186 ng/cm2 (sample C2092S,0), which still resulted in significant amino acid results (Elsila et al. 2009). This demonstrates that Stardust’s assembly, launch, return, and curation procedures provided sufficiently stringent contamination control procedures. The Stardust mission collected samples on aluminum foils and in aerogel, which made for much more challenging contamination control compared to cleaning the metal and Mylar surfaces inside TAGSAM. Thus, the pristine nature of the OSIRIS-REx sample will be preserved by starting with the Stardust contamination control plan and then incorporating technology improvements and applying the lessons learned from that mission, including ten lessons explicitly stated by the Stardust contamination science team (Sandford et al. 2010). In addition, the OSIRIS-REx team requires contamination levels from the high-purity aniline-free hydrazine (N2H4) used in the spacecraft propulsion system be no greater than the total carbon requirement of 180 ng/cm2. These requirements are placed on the TAGSAM surface since that can be quantitated directly and no assumptions about the properties of Bennu regolith are required. In addition to contamination control, OSIRIS-REx implements a detailed contamination knowledge plan, driven by the level-1 requirement to “Document the contamination of the sample acquired from collection, transport, curation, and distribution.” Documentation of possible sources of sample contamination throughout collection, return, and curation and stringent contamination control procedures is essential for understanding the pristine nature of samples returned by OSIRISREx. The contamination knowledge group sets the methods of implementation of the contamination control as well as performs the contamination science of studying hardware, witness material, and analogs to characterize and document the trace levels of contamination that will be present. The mission has also developed and implemented detailed contamination control plans for construction and testing of the spacecraft, recovery, and curation. The team scrutinizes materials lists for substances to archive or be wary of and provides detailed knowledge of the trace contaminants that are acceptable, monitors spacecraft contamination control, and ensures that the documentation and contamination information collected is available to the OSIRIS-REx science team and international science community. For example, the team has worked to limit the number of different organic materials used in construction and ensure that those used are carefully selected to minimize organic contamination of the sample. TAGSAM

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construction materials and witness plates exposed during flight system construction will be periodically tested and archived.

Baseline Science Mission OSIRIS-REx will usher in a new era of planetary exploration. The mission executes precise navigation to the surface of a carbonaceous asteroid, thoroughly characterizes the asteroid and the sample site, acquires a significant quantity of pristine regolith, and returns these samples safely to Earth for detailed analyses (Lauretta and OSIRIS-REx Team 2012). To ensure mission success, the OSIRIS-REx system engineering team developed a comprehensive design reference mission (DRM). The team uses the DRM to validate all top-level mission requirements and systematically flow requirements down to the flight system and ground system. The DRM schedule provides ample time to conduct and plan asteroid proximity operations and properly develop comprehensive global knowledge of Bennu prior to sampling. The OSIRIS-REx mission employs a methodical, phased approach to ensure success in meeting the mission’s science requirements. OSIRIS-REx launches in September 2016 on an Atlas V 411 launch vehicle. The spacecraft will arrive at Bennu in August 2018. Sampling is nominally scheduled to occur in 2019, but the DRM timeline provides substantial operational margin beyond this point. The departure burn from Bennu occurs between March and June 2021. On September 24, 2023, the SRC lands at the Utah Test and Training Range (UTTR). Stardustheritage procedures are followed to transport the SRC to JSC, where the samples are removed and delivered to the OSIRIS-REx curation facility. After a 6-month preliminary examination period, the mission will produce a catalog of the returned sample, allowing the worldwide community to request samples for detailed analysis.

Science Objectives Objective 1: Return and Analyze a Sample of Pristine Carbonaceous Asteroid Regolith in an Amount Sufficient to Study the Nature, History, and Distribution of Its Constituent Minerals and Organic Material Primitive asteroids are the remnant building blocks of the terrestrial planets (Bottke et al. 2002). Laboratory investigations of meteorites and interplanetary dust particles from asteroids reveal the nature of early Solar System processes responsible for planet formation (Lauretta and McSween 2006). The presence in primitive meteorites of complex organic compounds with terrestrial counterparts has led to speculation that meteorites could have seeded early Earth with prebiotic elements and molecules. However, meteorite samples are altered by the processes of ejection from their parent body and by atmospheric entry. In addition, these materials are

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very quickly contaminated, colonized, and consumed by terrestrial microbes. For example, the possible presence of extraterrestrial RNA nucleobases in the Murchison meteorite has been controversial for 30 years because of likely contamination from terrestrial DNA and RNA (Stoks and Schwartz 1979, 1982; Martins et al. 2008; Martins 2011; Callahan et al. 2011). Only by studying the organic chemistry and geochemistry of a pristine carbonaceous asteroid sample can the nature of extraterrestrial organic compounds be understood. Primordial organic compounds are preserved in the interiors of grains and freshly exposed surfaces on Bennu. However, extended exposure to the space environment modifies these compounds. These processes include micrometeorite impact and reworking, implantation of solar wind and flare particles, radiation damage and chemical effects from solar particles and cosmic rays, and sputtering erosion and deposition (Sasaki et al. 2001). Carbonaceous asteroids contain minerals and organic matter potentially modified by space weathering. However, the effect of space weathering on carbonaceous material is essentially unknown. Large carbon-based polymers may be produced. These polymers would darken asteroidal surfaces, redden the visible and near-IR spectral slope, and produce a dark and featureless spectrum such as that of Bennu. OSIRIS-REx offers the first opportunity to study the distribution of organic molecules and the effects of space weathering processes on an organic-rich body both in situ and through detailed analysis of a returned sample. After Earth return, samples are available to the worldwide scientific community, who perform precise analyses in terrestrial laboratories that cannot be duplicated by spacecraft-based instruments. Ongoing sample analysis by generations of scientists using cutting-edge tools and methods guarantees an enduring scientific treasure that only sample return can provide. Combining true exploration and laboratory-based science, OSIRIS-REx leaves a multigenerational legacy for the science community and people of the world. Just as Apollo lunar samples are still being analyzed in new and previously unpredictable ways more than 40 years after their collection, OSIRIS-REx samples will be available for the future of humankind (Fig. 9).

Objective 2: Map the Global Properties, Chemistry, and Mineralogy of a Primitive Carbonaceous Asteroid to Characterize Its Geologic and Dynamic History and Provide Context for the Returned Samples OSIRIS-REx provides insight into the geologic and dynamic history of Bennu (Lauretta et al. 2014). According to the current paradigm of asteroid dynamics, Bennu formed in the main asteroid belt, where most B-type objects currently reside (Bus and Binzel 2002; Walsh et al. 2013). Its parent body was a primitive asteroid that formed 4.5 billion years ago. A collision shattered this parent body. Bennu then migrated due to the Yarkovsky effect into a dynamic resonance capable of placing it into an Earth-crossing orbit (Delbo and Michel 2011). This history is recorded in the shape, surface texture, spectral properties, mass, rotation state, and composition of Bennu. OSIRIS-REx will thoroughly map the global properties,

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Fig. 9 Coordinated sample analysis exponentially increases science return

chemistry, and mineralogy of Bennu and develop global-scale knowledge of Bennu at a spatial resolution that provides a well-defined context for the returned samples (Fig. 10). OCAMS characterizes the shape, rotation state, and surface texture of Bennu. MapCam captures global images at a spatial resolution of 1-m per pixel of the physical dimensions and orientations of all surface geological features, including craters, boulders, grooves, faults, and regolith distribution. Bennu’s crater distribution will help determine the timing of the last major resurfacing event on the body.

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Fig. 10 OSIRIS-REx develops complete global knowledge of Bennu, which is necessary to understand its geologic history and its impact probability

Bennu has a prominent equatorial ridge, which may be a region of regolith pileup and provide evidence that Bennu was the primary object in a binary system (Bottke 2008). However, extensive ground-based characterization shows that Bennu has since lost any major companion. Furthermore, its rotation period is now far too slow for it to be actively shedding mass. The origin of the equatorial ridge on Bennu will be inferred from geologic analysis of surface morphology and mineral distribution.

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Spectral mapping of the surface of Bennu is performed using the four spectral filters (470, 550, 770, 860 nm) on MapCam. These wavelength regions characterize the broad spectral features observed on a wide variety of carbonaceous asteroids and provide direct comparison with ground-based observations. These images provide context for the high-spectral-resolution data from OVIRS and OTES and guide sample-site selection. Though the Spitzer Telescope observations the team has analyzed show no thermal-excess evidence for a dust belt around Bennu, it is possible that a few particles remain. For science and mission safety, PolyCam and MapCam will determine the orbit and nature of any particles >10 cm in the vicinity of Bennu in the Hill Sphere (the region of space where orbits are stable). OLA provides an independent means to determine shape and surface texture and provides an absolute range for all other remote-sensing data. OLA will generate global topographic maps with 1-m spatial and vertical resolution. OLA will also provide precise data of surface slopes. The synergy between OCAMS and OLA significantly enhances and accelerates the characterization of large- and small-scale topography. These surface topographic data will also constrain Bennu’s internal structure. OSIRIS-REx performs extensive global mapping of the surface spectral characteristics with comprehensive spectral coverage (0.4–50 μm) and global spatial resolution of 5 % in this wavelength range. This data set provides information on the distribution and composition of minerals and organic material across the surface of Bennu. It allows the first analysis of surface processing of carbonaceous material and guides sample-site selection, ensuring maximum science value from the samples. In addition, any spectral diversity will be used to understand how material is being displaced on the surface, providing important clues to the geological and geophysical evolution of Bennu. Radio Science will determine the mass of Bennu and estimate the mass distribution to second degree and order, with limits on the fourth degree and order distribution. Knowing the mass estimate and shape model, the team will compute the bulk density and apparent porosity of Bennu. Together, this information constrains the internal structure. Most importantly, the gravity field knowledge provides information on regolith mobility and identifies areas of significant regolith pooling.

Objective 3: Document the Texture, Morphology, Volatile Chemistry, and Spectral Properties of the Regolith at the Sampling Site In Situ at Scales Down to the Sub-centimeter The value of the sample increases enormously with the amount of knowledge captured about the site from which it was obtained. The OSIRIS-REx spacecraft

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is highly maneuverable and capable of investigating any region on Bennu at scales down to the sub-cm. The OSIRIS-REx instruments are used to characterize the spectral properties, micro-texture, and geochemistry of the regolith at the sampling site in exquisite detail. Sample-site characterization is performed over several phases of the DRM at increasing resolution. During the Orbital Phase, PolyCam is used to map up to a dozen candidate sample sites using stereo imaging with 5-cm resolution. Concurrently, OLA performs detailed topographic mapping of the entire asteroid. These data sets enable the team to assess the safety and sampling potential of each candidate site. The PI prioritizes four of these sites for detailed reconnaissance. The Reconnaissance phase consists of four 225-m altitude flyovers over the sunlit side of Bennu, out of the 1-km terminator orbit plane, for collecting data needed to assess the sampleability of up to four candidate sites, followed by two 525-m flyovers, one over each of the highest priority sites to characterize their science value. These six sorties to low altitude are separated by a period of 2 weeks back in the 1-km Safe-Home orbit to determine the orbit of the spacecraft, design and perform an orbit phasing maneuver to ensure the spacecraft departs the orbit at the right place and time to target flyover of the candidate site, and perform additional tracking to upload final maneuver adjustments to the spacecraft prior to orbit departure. Between sorties the science data is being processed, analyzed, and interpreted to select the prime and backup sites. After the prime site is selected, a methodical and incremental series of approach events is executed to safely prepare for the touch-and-go (TAG) sample collection (Berry et al. 2013; Sanchez et al. 2013). During this phase, each step in the sampling maneuver is practiced sequentially, followed by a return to SafeHome orbit. The TAG dynamics are driven by the ability of the Flight Dynamics team and the Guidance, Navigation, and Control (GN&C) subsystem to deliver the spacecraft to the ground with an accurate touchdown velocity and minimum attitude and rate errors. MapCam images are collected to provide additional verification of the trajectory and provide additional photo documentation of the sample site. OVIRS and OTES continuously acquire data during this phase. Before leaving the Rehearsal phase, newly identified surface hazards (slopes, rocks that exceed safety limits) must be analyzed before a decision to proceed with the TAG can be made. The TAG maneuver follows the transfer orbit, approach, and velocity-matching maneuvers as previously rehearsed. Following the MatchPoint maneuver, OSIRISREx approaches the surface along the vector normal to the sampling plane under reaction wheel attitude control, as OCAMS (MapCam or SamCam), OVIRS, and OTES continuously collect data to characterize the surface. The result of these extensive efforts is complete documentation of the texture, morphology, geochemistry, and spectral properties of the regolith at the sampling site, greatly enhancing the science value of the returned samples.

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Fig. 11 OSIRIS-REx provides an unprecedented level of understanding about the Yarkovsky effect – in which the thermal reemission of absorbed sunlight changes Bennu’s orbits

Objective 4: Measure the Yarkovsky Effect on a Potentially Hazardous Asteroid and Constrain the Asteroid Properties that Contribute to This Effect Bennu is a potential Earth impactor. The highest individual impact probability is 9.5  10 5 in 2,196, and the cumulative impact probability is 3.7  10 4, leading to a cumulative Palermo Scale of 1.70 (Milani et al. 2009; Chesley et al. 2014), one of the highest for any known asteroid. The primary source of uncertainty is the dynamic model of its orbital evolution. The main nongravitational orbit perturbation expected over a time span of centuries is due to the Yarkovsky effect, which results from the way the asteroid rotation affects the surface temperature distribution and therefore the anisotropic thermal reemission (Chesley et al. 2003). When thermal forces align with orbital vectors, the Yarkovsky effect can cause a steady drift in semimajor axis. OSIRIS-REx dramatically extends the time horizon for reliable position predictions for Bennu, not only by measuring spin state, surface area, albedo distribution, and thermal emission, but also by directly measuring the Yarkovsky acceleration (Fig. 11). A close approach of Bennu to Earth in September 2011 permitted the OSIRISREx team to use the Arecibo Planetary Radar System to acquire radar astrometry and detect the Yarkovsky effect. The signal-to-noise ratio in this detection was sufficient to measure the range to within one asteroid diameter. During encounter, precision tracking of the OSIRIS-REx spacecraft, in combination with modeling of the spacecraft motion relative to Bennu, will improve the signal-to-noise ratio, providing the most accurate determination of the Yarkovsky effect. This increase in position knowledge leads to better understanding of the possible threat, allowing ample time for policy makers to approve appropriate mitigation efforts. The Yarkovsky effect on Bennu accumulates quadratically with time (Milani et al. 2009), reaching approximately 200 km by the time of the OSIRIS-REx rendezvous relative to the ballistic ephemeris. The OSIRIS-REx navigation plan results in high-quality range measurements over 2 years. Radio ranging to the spacecraft fixes its position in the heliocentric frame, while the Doppler tracking,

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optical navigation, and OLA measurements constrain the position of the spacecraft with respect to Bennu. Combining the Earth- and Bennu-relative spacecraft solutions into a global fit with all data determines the location of Bennu to within 10 m. This precision exceeds that of the best ground-based asteroid radar measurements, and continuous measurements made over the course of the mission, rather than only for a few days near-Earth approach, result in an extremely precise measurement of the extent of Yarkovsky drift.

Objective 5: Characterize the Integrated Global Properties of a Primitive Carbonaceous Asteroid to Enable Direct Comparison with Ground-Based Telescopic Data of the Entire Asteroid Population The diversity of the asteroid population is reflected in both the large variation in their spectral properties and the large compositional range of meteorites. Although the silicate mineralogy of asteroids can be inferred by spectral matching between asteroids and meteorites (e.g., Hiroi et al. 2001), the detailed mineralogy of most asteroids is still unknown. This record is obscured by the fact that astronomy (telescopic measurements) and cosmochemistry (laboratory measurements) study inherently different samples. Telescopic reflectance spectra sample the top few μm of an object’s surface while meteorites represent subsurface material. OSIRISREx’s separate collection of bulk and surface material, combined with spectral characterization of Bennu, enables detailed understanding of the connection between the spectral properties of asteroid surfaces and the bulk composition and mineralogy of the returned samples. The possible parent asteroid associated with a meteorite class can be constrained with reflectance spectroscopy and is helped when a dynamic mechanism can be identified to deliver meteorite samples. Success in connecting meteorites to asteroids began with the identification of Vesta as the source of the HED meteorites (Drake 2001) and confirmed by the Dawn mission (McSween et al. 2012). However, there are several spectral classes of asteroids whose meteorite counterparts have been difficult to locate. As a result, the compositional distribution of planetary building blocks is essentially unknown. This fact is highlighted by the recovery of fragments from the F-class asteroid 2008 TC3, which shocked the meteorite world by linking this class of asteroids to the ureilite meteorites (Jenniskens et al. 2009). The spectral characteristics of the extremely dark B-class asteroids are unlike any measured meteorites, though the extremely rare and friable CM1 chondrites provide the closest spectral match (Clark et al. 2011). Only sample return allows definitive identification of the mineralogy of such complex and important asteroids and provides the first ground-truth calibration for asteroid remote-sensing data. The team will perform high-precision astrometry to refine the ephemeris of Bennu as the spacecraft approaches Bennu. MapCam will measure photometric properties, obtain a light curve, determine color indices, and characterize the phase

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function. From this data set, the team will perform the same type of reduction used with telescopic data to predict asteroid properties. During the approach to Bennu, OVIRS and OTES will acquire high-spectralresolution full-disk coverage until Bennu fills the entire field of view for each instrument. The combination of these observations, ground-based telescopic spectral measurements, and detailed spectroscopic and mineralogical characterization of the returned samples will provide ground truth for the Bennu reflectance spectrum. These results will be extrapolated to the global B-type asteroid and comet populations to estimate the distribution of volatile and organic compounds across the Solar System.

Conclusion OSIRIS-REx will characterize and return samples from Bennu, the most accessible, organic-rich body from the early Solar System. OSIRIS-REx explores the past through detailed characterization of the B-type carbonaceous asteroid Bennu. Bennu is a time capsule from the birth of our Solar System that records presolar history, the initial stages of planet formation, and the sources of prebiotic organic compounds available for the origin of life. OSIRIS-REx returns extraterrestrial samples from an extremely dark (albedo = 4.3 %), B-type carbonaceous asteroid, with extraordinary context from a thoroughly documented sample site. OSIRISREx also explores the hazards and resources in near-Earth space that are important for securing Earth’s future, since Bennu is an accessible near-Earth asteroid and potential impactor. Detailed knowledge of Bennu can be extrapolated to thousands of carbonaceous asteroids in the main belt, revealing the distribution of volatile and organic compounds across the Solar System.

Cross-References ▶ Airburst Modeling ▶ Defending Against Asteroids and Comets ▶ Directed Energy for Planetary Defense ▶ Economic Challenges of Financing Planetary Defense ▶ International Astronomical Union and the Neo Hazard ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Introduction to the Handbook of Cosmic Hazards and Planetary Defense ▶ Minor Planet Center ▶ NASA’s Asteroid Redirect Mission ▶ Nature of the Threat/Historical Occurrence ▶ NEOSHIELD: A Global Approach to Near-Earth Object Impact Threat Mitigation ▶ Planetary Defense, Global Cooperation, and World Peace

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▶ Potentially Hazardous Asteroids and Comets ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards ▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE ▶ Strategies to Prevent Radiological Damage from Debris

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Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning Harold J. Reitsema and Edward T. Lu

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mission Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mission Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

The nonprofit B612 Foundation is building a space observatory called Sentinel. Its goal is to find a much larger number of smaller-scale asteroids than previous ground-based and space-based surveys because of its improved capabilities. Sentinel will be able to detect potentially harmful asteroids that may impact Earth with sufficiently early warning to permit the deflection of the threat. The Sentinel mission will position a 0.5-m infrared telescope in an orbit around the Sun’s interior to the Earth’s orbit and will scan space in the region near the Earth’s orbit for at least 6.5 years. There are an estimated one million asteroids near the Earth that are larger than 40 m that can destroy a city-sized area if they impact the Earth, and only about 10,000 of these have been found to date since smaller-size asteroids are difficult to observe. Sentinel is designed to find over 100,000 near-Earth asteroids per year. The data collected by Sentinel will allow the orbital path of these detected objects to be determined with H.J. Reitsema (*) Reitsema Enterprises Inc., Holland, USA e-mail: [email protected]; [email protected] E.T. Lu The B612 Foundation, Mill-Valley, CA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_42

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sufficient accuracy that it will be possible to map the asteroid’s future path for up to 100 years and assess whether there is a potential for an impact with Earth. Sentinel will be built by Ball Aerospace & Technologies Corp. under an innovative contracting approach that enables substantial cost savings. Sentinel will be privately funded by the B612 Foundation with philanthropic support. Launch is planned for 2018. Keywords

Asteroid • Ball Aerospace & Technologies Corp • B612 Foundation • Capacitive Trans • Comet • Falcon 9 space mission vehicle • Deep Space Network (DSN) • Field of regard (FOR) • Hubble Space Telescope (HST) • Impedance Amplifier readout circuit • James Webb Space Telescope • Kepler Space Telescope • Keplerian orbital motion • Minor Planet Center • NASA • NASA Deep Space Network (DSN) • Near-Earth asteroids (NEA) • Near-Earth objects (NEOs) • Sentinel Space Telescope • Spaceguard Survey program • Spitzer Space Telescope • Torino hazard scale • Tunguska asteroid event • Space Act Agreement • Spitzer Space Telescope

Introduction The threat to Earth posed by asteroids has been known since at least 1963, when Gene Shoemaker of the US Geological Survey convincingly demonstrated that many impressive craters on Earth were formed by asteroid impacts. The asteroids that cause these impacts are members of a group of asteroids known as near-Earth objects (NEOs). The potentially hazardous objects are primarily asteroids but there are also a small number of comets. NEOs are asteroids that originated in the main asteroid belt between the orbits of Mars and Jupiter. These asteroid NEOs (nearEarth asteroids or NEAs) have been gravitationally or collisionally perturbed into orbits which now bring them closer to Earth. NASA initiated the Spaceguard Survey program in 1998 as noted in chapter ▶ “NEOSHIELD: A Global Approach to Near-Earth Object Impact Threat Mitigation.” The objective established at that time was to locate within 10 years at least 90 % of the near-Earth objects that are larger than 1-km diameter. As substantial progress was being made by 2003, NASA commissioned a Science Definition Team (SDT) (Stokes et al. 2003) to study the threat posed by even smaller NEOs. The SDT determined that the most efficient observations of NEOs were to be obtained in thermal infrared (~5 to ~10 μm), where they reemit sunlight absorbed on their dark surfaces. Following the SDT report, in 2005 the United States Congress gave NASA the goal of compiling a catalog complete to 90 % by 2020 of all NEOs larger than 140 m in diameter (US Congress 2005) as the next step in reducing the possibility that an impact can occur without advance warning. The Spaceguard Survey program created by NASA, together with other groundbased activities, has produced the discovery of over 10,000 NEOs. Current

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detection rates are about 1,000 NEOs per year, with the expectation that this rate could double with the maturing of the Pan-STARRS search program (Denneau 2013). From statistical analysis of discoveries, it is estimated that there are somewhat less than 1,000 NEOs with diameters greater than 1 km, of which over 90 % are known (Harris 2008). The detection rate for smaller NEOs, however, is a much greater problem. This is because these smaller asteroids are both much more numerous and much more difficult to detect because their small size makes them quite faint. There are perhaps one million NEOs larger than 40 m, the size of the object that exploded over Tunguska in Siberia in 1908 with a force of a several megaton atomic bomb. The force of that airburst flattened over 1,000 km2 of forest. The total number of NEOs within this size range is uncertain to at least a factor of two, and possibly as much as 10 (Brown et al. 2013). Thus predictions of the risk of impact by a Tunguska-like object (or worse) are also uncertain by as much as a factor of ten, but the current expectation is that Earth will experience a Tunguskalike event every 200–300 years. This is generally consistent with the Torino hazard scale. The recent fireball event near Chelyabinsk, Russia, was produced by an asteroid estimated to have had a size of 19 m and released an explosive energy equivalent to 500 kt of TNT. Multiple such events occur every century. This threat of an asteroid impact is the reason that the B612 Foundation was established. After showing the feasibility of deflection of a potential asteroid impact by either a gravity tractor (Lu and Love 2005) or a kinetic energy impactor (Hall and Ross 1997), the foundation decided in 2010 to address the problem of identifying impact risks. The detection rate of 1,000/year is wholly inadequate to address the problem, given the estimated number of potentially hazardous asteroids that might destroy a city (i.e., 40 m in size). It is very difficult to improve on this rate from the surface of the Earth because of the diurnal cycle, weather, lunar stray light, and the transmission properties of the Earth’s atmosphere which blur images and block infrared radiation. Thus, the B612 Foundation decided to develop a space observatory along the concept studied by the NASA SDT a decade ago. Since the time of the SDT report, substantial progress has been made in developing infrared astronomical technologies for space, demonstrated by NASA’s Spitzer and WISE missions (Mainzer 2011). It is now possible to implement a space infrared mission that will provide a catalog of the majority of the Earth-threatening NEOs (National Research Council 2010). The B612 Foundation is developing such a mission, raising money through private sources to build a halfmeter infrared telescope that will operate in space and detect and track over a halfmillion NEOs. This IR space telescope is named Sentinel. It will couple the heritage of these prior infrared missions with technologies from the Kepler planet-finding telescope that demonstrated a wide field-of-view telescope in deep space (i.e., not Earth orbit) with a large-format camera and substantial on-board data processing (see Fig. 1). As Ball Aerospace & Technologies Corp. developed both the Kepler mission and the Spitzer telescope, the B612 Foundation selected Ball as the contractor to build Sentinel.

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Fig. 1 The Sentinel observatory is designed for long-term operations in deep space, drawing technology and design from previous successful missions including Spitzer and Kepler. The abbreviations refer to the low-gain antenna (LGA), medium-gain antenna (MGA), and high-gain antenna (HGA) (Figure courtesy Ball Aerospace)

Mission Objectives The Sentinel mission objective is to maximize the number of NEOs for which orbits are sufficiently accurate to permit accurate prediction of future impact threats. Based on the 2003 NASA SDT report, and consistent with the George E. Brown Act, B612 has defined the top-level mission requirement to be to find 90 % of all NEOs larger than 140 m in diameter. The time required to meet that goal is dependent on models of the NEO population and its orbital characteristics, but studies have shown that excellent progress can be made toward this goal in 6.5 years, taken as the minimum mission design lifetime. Sentinel will have the capability to find much smaller asteroids than 140-m NEOs. At closer range, smaller NEOs will be recorded with the same accuracy. This will permit Sentinel to track objects that are 30 m in diameter or even smaller. Sentinel will be able to see 30-m objects that are at the Earth’s orbital distance from the Sun (a range from Sentinel of 30 million miles) and can see 140-m NEOs at a range of 70 million miles. Data processing for all discoveries will be conducted without initial knowledge of NEO size. Size will be determined only much later

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once an orbit has been determined and therefore the distance to the NEO at the time of observation. The observed brightness is corrected for distance to determine the intrinsic brightness and hence the size of the NEO. The size distribution of NEOs generally follows a power law, increasing by more than 200 % for every decrease in size of 50 %. Smaller NEOs have less surface area emitting infrared radiation. In the case of the smallest detectable NEOs, their proximity to the telescope gives them high apparent motion that smears their images and makes them less detectable. Consequently, Sentinel will discover the highest number of NEOs in a size range of 25–50 m, where Sentinel expects to find over 200,000 objects during the mission. At larger sizes, there will be fewer discoveries because of the decreasing population of objects. Sentinel will find nearly all of the roughly 1,000 objects larger than 1 km in size during the mission. The mission will also identify and catalog perhaps 40,000 asteroids larger than 140 m (>90 %) and a total of about 500,000 NEOs of all sizes. The actual population of NEOs in the 10–100-m size range is poorly known at this time as earlier noted. For this reason the above predictions are uncertain by perhaps 50 %. Thus one of the important scientific outcomes from the Sentinel mission will be a far better understanding of the population statistics for smaller NEOs. The good news might be that they are less numerous than currently projected. There is also the possibility that they are actually more numerous. The data obtained on new discoveries will be used to project the orbits forward to search for Earth impact threats. Accurate orbit prediction requires that each discovered object be followed for at least a month to give the desired accuracy. Even then, orbits will have substantial uncertainty associated with forward projections. Reduction in the predicted position uncertainty will be obtained by repeated observation from Sentinel whenever the NEO is within the field of view of the telescope and sufficiently bright to be recorded. Further orbit refinement will be achieved through follow-up observations from ground-based observatories. These observations of known objects can reach much fainter objects than can search programs. Follow-up observations from both ground and space (Sentinel and other missions such as Hubble) are important for objects whose orbits show a high potential for impact: most objects that draw attention because of moderate impact potential will be shown to come close to, but not impact, the Earth once more accurate orbits are known. The Sentinel mission is somewhat larger in scope and complexity than missions that have flown in the NASA Discovery mission line (such as Kepler). Those missions have been budgeted at roughly $650 M including launch and mission operations. The B612 Foundation will implement the Sentinel mission using a different programmatic approach than that employed for US Federal Government and NASA missions. B612 will put the selected contractor, Ball Aerospace, under a fixed-price contract with specific payment milestones and detailed performance requirements. This is an approach frequently used by commercial organizations with space-based activities such Intelsat, Inmarsat, etc. The burden of proof of mission suitability will be on Ball. The B612 Foundation has convened a review board of highly competent people that have experience on nearly every NASA deep

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space mission, both within the US government and from private industry. This Sentinel Special Review Team (SSRT) will be convened at key milestones during the mission. Thus, the Foundation will have input and advice on mission risk and progress from people with deep understanding of space mission implementation. Ball Aerospace will function as a traditional prime contractor, responsible for manufacturing and testing the observatory as well as launching it and performing mission operations. Sentinel can be launched on the Space Exploration Falcon 9, a lower-cost launch alternative for deep space missions. Mission operations, both command and control and data handling, will be performed for Ball by the University of Colorado Laboratory for Atmospheric and Space Physics (LASP). Ball has used LASP extensively in this role, but for Sentinel, LASP will also be processing the returned data into useable track information for each NEO that is discovered. This data will then be forwarded to the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics where it will be incorporated into their already large database of NEO orbits. The Foundation has established a Space Act Agreement (B612 Foundation Space Act Agreement 2012) with NASA to cooperatively conduct the Sentinel mission, with no exchange of funds. In exchange for all of the mission data for the MPC, NASA will provide assistance through use of the Deep Space Network for spacecraft communications as well as tracking information. NASA is also providing technical consultants in a NASA Technical Consulting Team that will supplement the SSRT.

Technical Characteristics Figure 2 shows the Sentinel observatory’s orbit which is interior to the Earth’s orbit so that the survey can include a large region surrounding the Earth. Sentinel can view all of the sky within a 100 half-angle cone that is centered on the anti-sun point, covering over half of the sky. This field of regard (FOR) includes over ¼ of the Earth’s orbit and is ideal for searching space near the Earth. A further advantage of an orbit interior to Earth is that the observatory will have an orbital period of only ~206 days, permitting it to lap the Earth every ~514 days and enabling observations of objects whose orbital periods are near 1 year and therefore seldom come close enough to be observed from Earth or space observatories close to Earth. Thus the interior orbit is an important design element of the Sentinel mission that provides excellent discovery performance. The final orbit for Sentinel is to be established through a gravitational encounter with Venus that slows the spacecraft and reduces its aphelion below 1 AU. The final orbit is determined by the flyby geometry, but since there are no tight requirements on the orbit, the encounter geometry is not tightly constrained. The simple requirement is that Sentinel be slowed sufficiently to result in a semimajor axis that permits the desired observing opportunities. The nominal eccentric orbit ranges from 0.6 to 0.8 AU. No propulsive maneuvers are required to establish or maintain the orbit with only trajectory correction thrusts required to establish the Venus encounter

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Fig. 2 Sentinel orbit. The Venus flyby reduces the orbital energy of Sentinel resulting in an elliptical orbit that ranges from 0.6 to 0.8 AU from the Sun (Figure courtesy Ball Aerospace)

parameters. Survey observations can begin once observatory checkout has been completed, well before the final orbit is established. NEOs are identified in images by their changing position caused by Keplerian orbital motion. While a NEO may show a streaked image in a single exposure, it is much easier to identify them by comparison of two images taken at different times, allowing the NEO to move relative to the background star field. Comparison of the two images reveals a detection of an object in one image of the pair that is not reproduced in the second because it has moved elsewhere. With crowded fields having multiple moving objects (as is expected for Sentinel), unique correlation of one observation on an object with another requires confirmation from a second image pair. Sentinel’s nominal design obtains these image pairs with 1 h of separation between them. Analysis of the expected NEO population shows that over 1 h, a typical NEO will move roughly one arc minute, easily revealing its motion but not moving so far as to increase confusion. Once a moving object has been identified on this series of four images (taken at times 0 h, 1 h, 48 h, and 49 h), data analysis can produce a vector called a track that allows the calculation of a range of potential orbits. An object is not considered to be “found” with the observation of a single track. Sentinel scans its entire FOR in an observing cycle (lasting roughly 1 month) and

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Fig. 3 Modeled completeness prediction showing that Sentinel will detect and track nearly 90 % of all NEOs larger than 140 m in diameter and will catalog 63 % of 60-m NEOs in 7 years. When combined with continuing ground-based searches, this will achieve the goals of the George E. Brown Act (Figure courtesy Ball Aerospace)

then repeats the FOR scan during the following observing cycle. An object has been “found” if Sentinel can provide a track for the object in at least two observing cycles (or if observations from ground-based observatories give a similar second observation epoch). This gives a reasonable orbit that permits the NEO to be uniquely identified whenever it is seen again. More importantly, the orbit has sufficiently small errors that the future location of the NEO can be determined to identify potential threats to Earth. An orbit derived from only two observing cycles will have uncertainties that will need to be reduced for objects whose motions will bring them close to Earth. By design, Sentinel will provide many more than the minimum two observing cycles of observations for the great majority of NEOs. With its 200 FOR, most NEOs will be observable during five successive observing cycles, and many will be seen during subsequent orbits providing observations spanning several years and leading to very good orbits with reliable predictions for roughly 100 years. The Sentinel team has developed two models for evaluating the expected performance of the observatory, one at Ball Aerospace and the other within the B612 team. These models are used in design studies that evaluate the potential of various design alternatives. The models show that Sentinel will reach the 90 % completion level on 140-m NEOs in roughly 7.5 years (Fig. 3). This number further reduces to 6.5 years when the ongoing and anticipated ground-based efforts are included in the calculation. The model is also useful for a number of other comparisons such as alternative cadences for the pairs of images that are currently baselined at 1 h and 2 days. To help with the analysis of that issue and others, the Foundation has established a Sentinel Operations and Data Architecture working group chaired by Dr. Marc Buie, the Sentinel Mission Scientist. This working group has members with deep experience in ground-based NEO

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detection and is able to identify and address many issues that arise in planning Sentinel observations. Infrared detector technology has been developed for previous space missions such as Hubble, Spitzer, and the James Webb Space Telescope, and B612 will take advantage of these efforts in developing the focal plane detector for Sentinel. While these prior astronomy missions have had very low background signals, Sentinel must address a significantly different problem. The thermal blackbody emission from NEOs in the inner solar system is strongest in the 5–10.2 μm spectral region where the NEO is bright. In this spectral range, zodiacal light, arising from dust derived from solar system formation and erosion of comets and asteroids, is the dominant source of background noise. Thus, while previous space IR detectors have focused on very low detector noise, Sentinel is working with a different, higher background signal level, design requirement. Following investigations of the Sentinel mission parameters by detector manufacturers, B612 and Ball have made the selection of a readout scheme that will perform well in the high background noise situation that Sentinel faces. Thus the Sentinel detectors will employ a Capacitive Trans-Impedance Amplifier readout circuit rather than the more common source follower readout. The detector unit cell contains a capacitor which can accumulate the expected large signal levels without saturation while maintaining its linear signal response. Also necessary is good gain stability over the 1-h period between a pair of measurements of a single star field so that any detected changes in signal level will clearly be due to object motion and not due to gain changes. A demonstration detector has been built for Sentinel that has shown good performance in important parameters including self-emission. The next step is the development of a prototype detector that will demonstrate all of the key performance requirements for the device. The Sentinel focal plane will consist of a mosaic of 16 individual infrared detectors arranged in a 2  8 array of detectors each having 1,640  1,120 pixels with 32-μm pitch. The photosensitive material is mercury cadmium telluride. This will have detection sensitivity extending to 10.2 μm. The detectors have minimal structure on three sides, permitting a close-packed array with minimum-size gaps of approximately 1 mm, giving a fill factor of 95 %. The active area is 54  294 cm, covering a field of view on the sky that is 2.5  11 . The focal plane will be cooled to 40 K to lower thermal charge generation well below the zodiacal light background. Sentinel will use an off-axis three-mirror anastigmat telescope to achieve the wide field of view with low obscuration, low emissivity, and high rejection of stray light. The telescope mirrors and structure will be made of aluminum to control cost, mass, and thermal distortion. This approach is possible with the lower optical tolerances of infrared systems relative to the familiar visible-light telescopes. The telescope includes a flat fold mirror that moves the focal plane to a readily accessible position. This design will facilitate detector integration and thermal control. The telescope line of sight is offset from the observatory symmetry axis by 40 to allow the observatory to scan the entire anti-sun hemisphere while keeping the sun within 50 of normal to the solar arrays. This arrangement will allow adequate power production to be maintained in all positions.

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Thermal control of Sentinel is very similar to the scheme successfully employed on the Spitzer Space Telescope. The heat load from the Sun is intercepted by a series of three thermal shields. The solar array provides the first layer of shielding, being populated by a combination of the required area of solar array and filled out with silvered surface to reject solar heat. Two additional shields are positioned between the back of the solar array and the telescope, each having a good view of space toward which they reject heat that they intercept. Following the Spitzer design, and using the Spitzer-calibrated thermal model, the Sentinel telescope is expected to achieve a temperature of 70 K even at 0.7 AU where the solar insolation is twice that received by Spitzer. To achieve the required 40 K for the focal plane, Sentinel will use a mechanical Stirling cycle cryocooler similar to the one built by Ball Aerospace for the Landsat Imagery mission (Bertele et al. 2012). In addition to providing 3 W of cooling at 40 K for the detectors, the cooler also will be able to provide additional cooling to the telescope. This will enhance performance margin to ensure that thermal emission from the optics is not detectable. The spacecraft for Sentinel will be based on Ball’s highly successful Kepler spacecraft bus design. While the Kepler reaction control system experienced a failure after the mission design lifetime, Sentinel will use different reaction control wheels that have demonstrated highly reliable performance on other missions. Spacecraft mechanical, thermal, power, and control systems will be very similar to Kepler’s. The largest modification to the Kepler design will come in the telecommunication area. Even though Kepler was deployed in deep space and sent data back over a range of 0.7 AU, Sentinel’s orbit will take it to a range of 1.7 AU. At this range, a more powerful transmitter is required. The Kepler-type transmitter is capable of this range but, since it will need to be operated at higher power, it will require additional qualification testing. Kepler performed on-board data co-adding and editing, a data-compression approach that will also be used on Sentinel. Six successive 30-s exposures of a given field will be co-added to achieve the 3-min integration. Intercomparison of each sub-exposure will allow on-board software to identify and reject cosmic ray signals. The co-added 3-min image will be stored in memory until the companion image of the same field of view is obtained 1 h later. At that point, the on-board computer examines both images to identify pixels that show changes that exceed the noise threshold by a factor of five (signal-to-noise ratio SNR > 5). Moving objects that are sufficiently bright will produce differences that exceed this value at both the location it had in the first image and in the second. The on-board computer will extract the 4  4 region centered on the change and copy those pixels into the telemetry memory. This approach reduces the data volume by more than a factor of 1,000 and sends all of the image data on moving objects to the ground in only 4 h of telemetry per week. Sentinel will employ the NASA Deep Space Network 34-m antennas operating in the Ka-band for this purpose. Telemetry data volume will be controlled through selection of the SNR threshold. Additional image pixels are put into telemetry for pre-planned astrometric reference stars to establish the precise pointing of the images. Sentinel will have the capability to transmit entire images for quality inspection or other engineering or scientific purposes.

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Ground operations and data processing will be performed at the Laboratory for Atmospheric and Space Physics at the University of Colorado under contract to Ball Aerospace. There, received telemetry will be reconstructed into images that will have no data (zeroes) in regions that experienced no change (SNR > 5) in the 1-h interval separating the image pair. These images will then be examined to reject spurious signals from noise spikes, residual cosmic rays, variable stars, and other sources of variability not related to moving objects. The remaining objects will be examined for potential linkages indicating motion. Such so-called tracklet linkages are considered to be preliminary and are stored for reconsideration when the second pair of images of the region is obtained 2 days later. Once the second of the 1-h pairs is available, with their associated tracklet identifications, further analysis looks for pairs of tracklets that can be linked by a Keplerian orbit. This level of linkage produces a track from which a very preliminary identification of a moving object is possible. Comparison with the database of known objects will show if this is a previously known object or a possible new discovery. New discoveries are only confirmed when this process produces a second linkage during a second observing cycle. This might occur as soon as 1 month later. Once a second track is associated with an object, the object is a confirmed discovery. These are forwarded to the Minor Planet Center at the Smithsonian Astrophysical Observatory. There they are confirmed and added to a comprehensive database of NEOs and other solar system objects.

Mission Status Sentinel is being financed through philanthropic donations to the B612 Foundation. A Program Concept and Implementation Review has been conducted and reviewed by the Sentinel Special Review Team, whose suggestions and findings have been incorporated into the program plan. B612 and Ball are preparing for the Mission Requirements Definition work that will culminate in the Sentinel System Architecture Approval review. Launch will be in 2018 for the nominal 6.5-year mission. The only consumable commodity on the spacecraft is fuel for the reaction control system. Sentinel will launch with a minimum of 10 years of fuel so that the mission can continue at least that long if desired.

Conclusion Only with Sentinel will the census of NEOs be extended to sizes small enough to fully assess the hazard to Earth from asteroid impact. The prime objective is to detect a half-million objects down to a size of less than 20 m; Sentinel will greatly increase the scientific understanding of this important population of objects. There will be much better statistics regarding how many objects exist, and the high-quality orbits that will be determined will help quantify the threat that they pose. While today the number of objects in

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the city-killer size range of 40–100 m is known with an accuracy of less than a factor of 5, Sentinel will determine the population statistics with much, much higher accuracy. Even more importantly, Sentinel will determine accurate orbits for the objects that it detects, permitting the forward propagation of their orbits and the identification of potential threats of impact on Earth. Early identification of potential threats is extremely important so that sufficient time will exist to deal with any identified risks. It will take time to get additional information on the orbit and characteristics of a NEO before any deflection efforts are initiated. Ground-based follow-up will provide better orbit determinations that will assist in assessing the impact probability. Spectroscopic observations will reveal the composition of the asteroid. Photometric studies can establish the rotation rate, shape, and pole orientation of an asteroid, which are important factors for future mitigation missions. It may also prove desirable to fly a reconnaissance mission to rendezvous with a potentially threatening NEO to obtain even better information. One attractive feature of such a mission would be the capability to determine a very precise orbit for the object, allowing an improvement in the prediction of the future location of the NEO and potentially demonstrating that the NEO will miss the Earth without deflection.

Cross-References ▶ Deep Impact and Related Missions ▶ Defending Against Asteroids and Comets ▶ European Operational Initiative on NEO Hazard Monitoring ▶ International Astronomical Union and the Neo Hazard ▶ Minor Planet Center ▶ Nature of the Threat/Historical Occurrence ▶ NEOSHIELD: A Global Approach to Near-Earth Object Impact Threat Mitigation ▶ Potentially Hazardous Asteroids and Comets ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE ▶ Water Impact Modeling

References B612 Foundation Space Act Agreement (2012) The B612 Foundation. http://b612foundation.org/ wp-content/uploads/2012/06/SAA-redacted.pdf. Retrieved 28 Dec 2013 Bertele T, Aerospace B et al (2012) Test results for a high capacity cryocooler with internal thermal storage. AIP Conf Proc 1434:154–160 Brown PG et al (2013) A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors. Nature 503:238–241

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Denneau L (2013) The Pan-STARRS moving object processing system. Pub Astr Soc Pac 125:357–395 Hall CD, Ross M (1997) Dynamics and control problems in the deflection of near-Earth objects. Adve Astrol Sci: Astrodyn 97(Part I):613–631 Harris AW (2008) What spaceguard did. Nature 453:1178–1179 Lu ET, Love SG (2005) Gravitational tractor for towing asteroids. Nature 438:177–178 Mainzer A (2011) NEOWISE observations of near-Earth objects: preliminary results. Astrophys J 743:156–172 National Research Council (2010) Defending planet Earth: near-Earth object surveys and hazard. National Academies Press, Washington, DC Stokes G et al (2003) The study to determine the feasibility of extending the search for near-Earth objects to smaller limiting diameters. NASA Office of Space Sciences, Solar System Division U.S. Congress (2005) National Aeronautics and Space Administration Authorization Act of 2005. Retrieved 28 Dec 2013, from Public Law 109–155 – 30 Dec 2005. www.gpo.gov/fdsys/pkg/ PLAW-109publ155/pdf/PLAW-109publ155.pdf

Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE A. Mainzer, J. Bauer, T. Grav, R. Cutri, J. Masiero, R. S. McMillan, C. Nugent, S. Sonnett, R. Stevenson, R. Walker, and E. Wright

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mission Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Key Findings and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Main Belt Asteroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hildas and Jovian Trojans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermophysical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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A. Mainzer (*) • J. Bauer • J. Masiero • C. Nugent • S. Sonnett • R. Stevenson JPL, Pasadena, CA, USA e-mail: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] T. Grav Planetary Science Institute, Tucson, AZ, USA e-mail: [email protected] R. Cutri California Institute of Technology, Pasadena, USA e-mail: [email protected] R.S. McMillan University of Arizona, Tucson, AZ, USA e-mail: [email protected] R. Walker Monterey Institute for Research in Astronomy, Monterey, CA, USA e-mail: [email protected] E. Wright UCLA, Los Angeles, CA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_41

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Outer Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Next-Generation NEOWISE: The Near-Earth Object Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

NASA’s Wide-field Infrared Survey Explorer (WISE) mission, designed to survey the entire sky at infrared wavelengths, has proven a valuable means of discovering and characterizing the small bodies in our solar system. Modifications to the mission’s science data processing system, collectively known as NEOWISE, have allowed new minor planets to be discovered using this spacebased infrared telescope. Using radiometric thermal models, physical properties such as diameter and albedo have been derived for more than 158,000 asteroids, including approximately 700 near-Earth objects and 160 comets. Following the conclusion of its primary mission, the WISE spacecraft was placed into hibernation in February 2011. Now renamed NEOWISE, the spacecraft was brought out of hibernation in 2013 to continue the search for near-Earth objects. Keywords

Asteroids • Comets • Impact • Infrared telescope • Main belt asteroid • Minor planet • Near-Earth object • NEOCAM • NEOWISE • PanSTARRS • Spatial resolution • Surveys • Wide-field Infrared Survey Explorer (WISE) • WISE moving object processing system (WMOPS) • Cosmic Background Explorer (CBE) • Infrared Astronomical Satellite (IRAS) • Main Belt Asteroid (MBA) • NASA Infrared Science Archive (IRSA)

Introduction Asteroids and comets have interacted with the Earth since the dawn of the solar system. Examples of collisions exist throughout history and evidence for these events can be found around the globe. Approximately four billion years ago, a massive number of asteroids and comets collided with the nascent Earth, possibly delivering much of our oceans (see, e.g., Chyba 1990). The formation of a large impact crater on the Yucatan peninsula in Mexico 65 million years ago is thought to be associated with the mass extinction of non-avian dinosaurs (Alvarez et al. 1980). Most recently on February 15, 2013, a 20 m asteroid entered the atmosphere over Chelyabinsk, Russia, bursting into pieces and causing widespread damage to persons and property. Quantifying the impact hazard posed by these objects to the Earth requires discovering and characterizing as many as possible. Significant strides have been made in this area in the last two decades. However, much work remains to be done, particularly for sub-kilometer-sized near-Earth objects (NEOs), both in terms of discovering the majority of potential impactors and determining basic physical properties such as size, albedo, composition, rotational state, etc.

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Fig. 1 The WISE flight system during the process of assembly into the launch vehicle shroud at Vandenberg Air Force Base, with protective aperture cover still installed

While spacecraft in situ missions allow for the most detailed investigations of asteroid physical properties, the expense of such missions means that only about a dozen asteroids have been visited. Terrestrial radar observations, which are capable of improving orbits and in some cases determining shapes and spin states, have observed several hundred NEOs to date. With infrared radiometry, it is possible to discover objects as well as obtain information on objects’ sizes, albedos, and thermophysical properties for a large number of minor planets.

Mission Objectives NASA’s Wide-field Infrared Survey Explorer (WISE, Fig. 1) mission obtained thermal infrared observations for more than 158,000 minor planets (Wright et al. 2010; Mainzer et al. 2011a). As a Medium Explorer mission funded by NASA’s Astrophysics Division, WISE was competitively selected and was completed on cost and on schedule. Led by Principal Investigator Dr. Edward Wright of UCLA, the WISE mission’s primary scientific objective was to map the entire sky in four infrared wavelengths (3.4, 4.6, 12, and 22 μm). Scientific goals included the discovery of extremely nearby cool stars and distant, ultraluminous infrared

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galaxies. In the 3 years since the first public data release, the mission has resulted in more than 700 peer-reviewed journal articles across a broad range of topics in astronomy and planetary science. WISE’s original science requirements were driven by the need to produce the all-sky images and source catalogs. Nevertheless, it was recognized that the mission would also be well suited for observing asteroids and comets. However, the baseline mission provided only for producing an image atlas and catalogs based on coadding all exposures collected at a given part of the sky together. While these coadded images are adequate for study of sources that do not move, minor planets are removed by outlier rejection schemes designed to eliminate cosmic rays and other transient sources. To facilitate study of small bodies in our solar system, NASA’s Planetary Science Division provided the resources to archive the individual exposures and extracted single-frame source lists and to discover new moving objects from the data in near real time. These two tasks were collectively named NEOWISE.

Technical Characteristics WISE. WISE was launched on December 14, 2009, into a 525 km 6 am/6 pm Sun-synchronous polar orbit. Formal survey operations began on January 14, 2010, following in-orbit checkout. In order to maximize survey efficiency, the telescope scanned continuously, while images were frozen onto the 4747 arcmin field of view using a small mirror moving in the opposite speed and direction of the telescope boresight. The 11-s exposure cycle allowed sufficient time for images to be collected in all four wavelengths; images were read out, while the scan mirror reset to the starting position. The survey was designed to provide significant overlaps over the entire sky by offsetting the telescope’s pointing by 10 % of a frame width each orbit, ensuring 90 % frame overlap with each successive orbit. In the in-scan direction, a frame-to-frame overlap region of 10 % allowed for accurate registration of images. All four wavelengths were imaged simultaneously through the use of three beamsplitters. This survey design allowed the mission to complete its first survey of the entire sky in all four wavelengths after 6 months. The average region of the sky received more than 12 exposures, rising to hundreds at the ecliptic poles (Fig. 2). The spacecraft always observed near 90 solar elongation. To minimize loss of sky coverage, data downlinks and momentum dumps via magnetic torque rods were executed over the ecliptic poles. As an infrared space telescope, WISE is millions of times more sensitive than an observatory operating at similar wavelengths on the ground, as ground-based telescopes must observe through the infrared background produced by selfemission and the atmosphere. WISE’s two shortest wavelengths, 3.4 and 4.6 μm, were collected using HgCdTe detectors that were cooled to 32 K during the first 8.5 months of the mission. The two longer wavelengths, 12 and 22 μm, used Si:As arrays that required cooling to 7.8 K. The telescope optics and structure were kept below 17 K to allow for background-limited sensitivity.

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Fig. 2 The WISE Sun-synchronous orbit results in continuous observing near 90 solar elongation and provides an average of 10–12 exposures over all parts of the sky. Coverage increases to hundreds of exposures near the ecliptic poles. Full sky coverage was achieved after 6 months

To achieve these temperatures, the mission employed a two-stage solid hydrogen cryostat. The cryostat exceeded its required lifetime of 7 months by 3 weeks. The first tank was depleted on August 5, 2010, causing the immediate loss of the 22 μm channel and gradually reducing the sensitivity of the 12 μm channel. On September 30, 2010, the remaining hydrogen was exhausted, and the instrument warmed to 73.5 K. The two shortest wavelengths, 3.4 and 4.6 μm, continued to operate with little change in performance. At this point, NASA approved a 4-month extension of the mission to complete a survey of the inner main belt and to continue the search for NEOs. On February 1, 2011, the mission was placed into hibernation; its solar arrays were left pointed at the Sun, but communications with it ceased. During its entire operational lifetime, the WISE spacecraft provided detections of 747 million sources extracted from more than three million images (Cutri et al. 2012). The sensitivity and spatial resolution were significantly improved over the previous generation of all-sky surveys at these wavelengths: the Cosmic Background Explorer and the Infrared Astronomical Satellite (IRAS). Despite having a smaller aperture than IRAS (40 vs. 60 cm), the WISE satellite returned images hundreds of times more sensitive at 12 and 22 μm because its four-megapixel infrared array images to be critically sampled. In contrast, IRAS had 62 pixels and consequently undersampled images at similar wavelengths, underscoring the profound impact of modern electronics on astronomy (Neugebauer et al. 1984). NEOWISE. To extract moving object candidates from the data, an algorithm known as the WISE Moving Object Processing System (WMOPS) was developed. This code was adapted from the PanSTARRS project to work with the WISE observing cadence (Kubica et al. 2007). WMOPS operates on extracted source lists, comparing them from exposure to exposure to remove stationary objects such as stars and galaxies and then linking the remaining transient detections to form position-time lists known as tracklets (Mainzer et al. 2011a). The WISE observing cadence allows a typical minor planet to be observed 10–12 times over a span of 36 h. This cadence was sufficient to allow many of the new candidates to be declared by the Minor Planet Center as “discovered.” However, to secure orbits such that objects can be recovered at the next apparition, it is necessary to obtain follow-up observations that span at least 20–30 days. A requirement was therefore levied on the NEOWISE project to deliver tracklets to

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Fig. 3 The WMOPS quality assurance (QA) process allowed for visual inspection of objects that could not be unambiguously associated with previously known minor planets. The QA system allows astronomers to reliably distinguish between real point sources (or extended objects such as 2009 WJ50, shown here and revealed to be cometary by NEOWISE) and artifacts such as latent images, cosmic rays, diffraction spikes, etc. The display shows repeated exposures at the same coordinates in different wavelengths (12 and 22 μm are shown in the top and second rows, respectively) as well as the immediately preceding exposures

the Minor Planet Center within 10 days of the midpoint of their observations on board the spacecraft. This requirement ensured that they could receive the prompt follow-up needed to avoid objects becoming lost, with orbits so uncertain that future positions cannot be predicted accurately. The WMOPS pipeline was run every 4–5 days during the prime mission, and the average lag time between observational midpoint and delivery to the MPC was 4.5 days. In order to distinguish real asteroids from spurious transients such as cosmic rays, noisy pixels, or other artifacts, WMOPS requires a minimum of five detections before a tracklet is assembled. Tracklets with observations that cannot be entirely associated with previously known objects are evaluated by scientists for validation prior to being submitted to the MPC (Fig. 3). At the beginning of the mission, WMOPS was operated with a conservative source signal-to-noise (SNR) threshold of 7 in place, while artifacts and distortion were precisely mapped. Once these calibrations were completed, the SNR threshold was successively lowered to 5, then 4.5, and finally 4. When searching for new objects, many are found at or near the survey’s detection threshold. Although increasing numbers of objects can be detected when the SNR is decreased, it becomes more difficult to distinguish between real

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objects and noise or artifacts. Moving object identification is particularly sensitive to the presence of transient artifacts such as latent images, cosmic rays, stray light, and noisy pixels. The WISE data’s artifacts were carefully and continuously monitored and flagged using the full-frame uncompressed images, allowing them to be excluded from the data. Candidate NEOs detected by WMOPS were placed on the Minor Planet Center’s NEO Confirmation Page to make them widely available for the community to follow-up. Follow-up observations were obtained by observers all over the world, including both professional and amateur astronomers. The average equivalent visual magnitude of most NEOWISE NEO candidates was V  21.5; however, as an infrared telescope, NEOWISE frequently detected extremely low-albedo NEOs with visual magnitudes as faint as V  23. Furthermore, as an all-sky space-based survey making multiple passes over the ecliptic poles, detections frequently fell at extreme declinations in both hemispheres. Follow-up was also complicated by the fact that NEOWISE detected objects regardless of lunar phase or weather, unlike ground-based observers. In spite of these observational challenges, nearly all of the NEO candidates submitted to the NEO Confirmation Page during the prime mission were followed up. Out of 135 new discoveries, only 25 candidates never received optical follow-up, but 13 of these objects had WISE observational arcs sufficient to be declared discovered even without follow-up. Of the more than 300,000 tracklets submitted to the Minor Planet Center, fewer than a dozen were rejected as spurious associations. In 2010, the NEOWISE survey submitted more observations of minor planets than all other surveys by a factor of two. An advantage of the WMOPS system is that previously known and newly discovered objects’ tracklets were constructed in an identical fashion. Furthermore, the survey’s sensitivity and pointings were well known, and as a space-based survey, weather and atmospheric seeing were not factors. Because the four WISE bands are primarily sensitive to thermal emission from asteroids, they are equally sensitive to both low and high-albedo objects. These properties made it possible to compute the observational biases and selection effects that govern the observed sample. Once these biases in orbital elements, size, and albedo were determined, it was possible to extrapolate the properties of the observed sample to the population as a whole. This debiasing work has allowed the project to estimate the numbers, orbital characteristics, and physical properties of a number of minor planet populations to date. In total, the NEOWISE project detected more than 158,000 minor planets, including >34,000 new discoveries (Fig. 4). Of these, most are main belt asteroids (MBAs). The spacecraft observed 700 NEOs, including 135 new discoveries, and 160 comets, of which 21 were discovered by NEOWISE. The project is currently engaged in mining the dataset for new detections by rerunning WMOPS with lower SNR thresholds (applied in a uniform manner over the entire survey) and by stacking all available detections of all 600,000 known minor planets. Because WISE collected an average of 10–12 detections per object, stacking frames should result in the recovery of many additional objects that fell just below the single-frame detection threshold. The NEOWISE project delivered its data products, including single-frame images and extracted source lists, on schedule to NASA’s Infrared Science Archive (IRSA),

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Fig. 4 NEOWISE detected >158,000 minor planets, mostly in the main belt (black dots). Red and green circles represent NEOs discovered and detected by NEOWISE, respectively. Yellow and cyan squares indicate comets discovered and detected by NEOWISE. The red dashed line indicates the position the WISE spacecraft was observing when the cryogen was completely exhausted and the 4-month post-cryogenic phase of the prime mission began. Planet orbits are shown in gray, with the largest orbit belonging to Jupiter

hosted at the California Institute of Technology’s Infrared Processing and Analysis Center (IPAC). All data products from the prime mission are publicly available and accessible through IRSA. During the fully cryogenic portion of the mission, the 3-band cryogenic, and post-cryogenic phases, respectively, the project delivered 9.5 billion, 3.7 billion, and 7.3 billion extracted sources taken from a total of 2.7 million exposures. The NEOWISE project also supported the development of solar system science-friendly query tools that allow users to enter an object’s name or orbital elements and search through all available images and extracted sources. These tools support the “precovery” of objects discovered by other surveys in the future (Cutri et al. 2012). In addition to providing a well-determined set of survey biases, the NEOWISE survey offered the opportunity to derive physical properties for a large number of minor planets. Because asteroid thermal emission is a weak function of albedo, infrared observations allow for the derivation of radiometric diameters. Furthermore, the WISE observational cadence of 10–12 observations spaced uniformly

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over 36 h usually resulted in reasonable coverage of each object’s rotational light curve. Comparison of radiometrically derived diameters and albedos of objects with independently derived diameters from radar observations, spacecraft visits, and stellar occultations revealed agreement to within 10 % and 25 %, respectively, for models using WISE 12 μm observations (Mainzer et al. 2011b, c). Using only the 3.4 and 4.6 μm observations available during the post-cryogenic mission phase, radiometric diameters and albedos reproduced those derived from 12 μm data to within 25 % and 40 %, respectively (Mainzer et al. 2012c; Masiero et al. 2012a). By comparison, diameters derived from visible light data alone are uncertain by factors of 2–3, and albedos cannot be computed. Prior to NEOWISE, robust physical properties were only known for several thousand minor planets, including IRAS, AKARI, radar, and ground-based infrared observations. With infrared observations of >158,000 objects, physical properties are now available for many more small bodies.

Key Findings and Results WISE data are being used at a rate of roughly one peer-reviewed journal article per day. NEOWISE data have resulted in >100 peer-reviewed journal articles since the first public data release of single-frame images and source lists in 2010 (Wright et al. 2010). Because NEOWISE represents a time-domain infrared survey, the data have been used for a wide range of topics in astronomy and planetary science, including cosmic distance ladder determinations, galactic structure, variable star studies, proper motion and parallax measurements, compact objects, and a plethora of solar system studies. NEOs. For NEOs, NEOWISE data have been used to constrain their numbers, sizes, albedos, and orbital characteristics. The sample of 429 NEOs detected by WMOPS during the fully cryogenic phase of the mission at 12 μm reveals the NEO albedo distribution to be roughly independent of size for objects ranging from more than 1 km in effective spherical diameter to 100 m (Fig. 5). This result contradicts previous findings that suggested that smaller NEOs became brighter; however, previous studies were based on optically selected samples, i.e., the objects were discovered by visible light surveys that are less sensitive to smaller, darker objects. Computing and accounting for the observational biases of the fully cryogenic sample suggest that there are 20,500  3,000 near-Earth asteroids (NEAs; nearEarth comets were not included in the study) larger than 100 m, a somewhat smaller number than prior estimates, which ranged from 36,000 to 100,000. Furthermore, the NEOWISE study concluded that the so-called Spaceguard goal of discovering >90 % of near-Earth asteroids larger than 1 km had been met. However, the study found that only 25 % of objects larger than 100 m have been discovered to date. The study was inconclusive for NEAs smaller than 100 m as only a handful were detected by WMOPS (Mainzer et al. 2011e).

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Fig. 5 The albedo distribution as a function of size for NEOs selected by WMOPS based on their 12 μm fluxes is roughly uniform (blue line), whereas the albedos for small NEOs discovered by visible light surveys and subsequently recovered from the NEOWISE data show a marked increase with decreasing size (black line)

The debiased NEO orbital element distribution showed reasonably good agreement with previous model predictions (e.g., Bottke et al. 2002). However, a notable exception was found when the sample was narrowed only to those NEOs considered potentially hazardous asteroids (PHAs; the subset of NEOs with minimum orbit intersection distances 90 % over a range of temperatures achievable via passive cooling

The mission architecture combines elements from the WISE, NEOWISE, and Spitzer missions. As with the WISE project, the science data processing center is at IPAC, and image atlases and source catalogs will be released annually through IRSA. Industrial partners include Teledyne Imaging Sensors and the Space Dynamics Laboratory, producers of the WISE payload. At present, the new detectors are undergoing detailed characterization to evaluate their performance and ensure that they are space qualified. Comparison with Sentinel. The B612 Foundation has proposed to build a very similar mission to NEOCam in 2012 named Sentinel using only private donations instead of NASA funding and project management. Like NEOCam, Sentinel proposes to use an infrared telescope with a central wavelength near 8 μm to search for NEOs. The major architectural differences between NEOCam and Sentinel are (1) orbit, (2) detectors, (3) cryogenic system, and (4) science data processing techniques. Instead of the Earth-Sun L1 Lagrange point, the B612 Foundation proposes to send Sentinel to a Venus-like orbit. The detectors they propose to use employ a different readout architecture: a capacitive transimpedance amplifier that is traditionally used in high-background applications, such as Earth science and defense, as opposed to the source follower per detector readout circuit that is standard for space-based astronomy that NEOCam uses. Because a spacecraft in Venus-trailing orbit is typically located 0.3–1.7 AU away from Earth, compared with 0.01 AU from the L1 Lagrange point, the data rate is reduced by a factor of 900–30,000. This necessitates a radically different approach to science data processing than the techniques employed by NEOWISE to detect moving objects. Lossless data compression only yields factors of 2–3

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compression, so at this distance from the Earth, lossy compression is necessary and will result in loss of sensitivity. The desire to use standard scientific data reduction techniques inherited from WISE, NEOWISE, and Spitzer that allow for accurate subtraction of instrumental and sky background signatures, along with identification of artifacts and undesirable transient sources such as cosmic rays, diffraction spikes, latent images, and other stray light partially, motivates the choice of the Earth-Sun L1 Lagrange point for NEOCam. In a survey, most new objects are discovered near the sensitivity threshold, so it is preferable to avoid any destructive data compression that reduces sensitivity. Maintaining the low temperatures necessary for natural background-limited performance for a cryogenic telescope is also more difficult at 0.7 AU from the Sun instead of 1 AU. Passive cooling is insufficient to drive the telescope structure and detectors to the necessary temperatures, so Sentinel must therefore employ mechanical cryocoolers. Finally, survey simulations show that there is no substantial benefit to a Venustrailing orbit compared to the L1 Lagrange point for objects larger than 100 m. It is most likely significantly more challenging when accounting for data compression losses.

Conclusion Asteroids and comets have interacted with the Earth since its formation and continue to pose an impact hazard. Understanding the orbital distributions and physical properties of these objects is crucial to gauge the present risk. With this in mind, the NEOWISE project and the proposed NEOCam mission seek to fill this knowledge gap through the detection and characterization of NEOs using spacebased infrared detectors. The NEOWISE project has significantly expanded the number of minor planets that have well-determined physical properties. The archiving and serving of the individual exposures from the WISE project has resulted in a significant number of scientific investigations covering a wide range of topics in planetary science and astrophysics. The total cost of the NEOWISE augmentations to the WISE science data processing pipeline, including operating the spacecraft for 4 months during the post-cryogenic mission phase, was $8.5 million, compared to the $320 million cost of designing, building, launching, and operating WISE. In the 3 years since launch, NEOWISE single-exposure images, source lists, and derived minor planet physical properties have been used in over 200 peer-reviewed publications. As with the WISE mission, the NEOWISE project delivered its data on cost and on schedule, providing a legacy for current and future solar system science. As new asteroids and comets are discovered, researchers can search the archival NEOWISE datasets for them, and the restarted NEOWISE mission is collecting new observations. By continuing to discover and characterize minor planets throughout the solar system, NEOWISE data will help to refine our understanding of how often and with what energy these bodies encounter Earth.

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Cross-References ▶ Deep Impact and Related Missions ▶ European Operational Initiative on NEO Hazard Monitoring ▶ Key Reports on Cosmic Hazards and Planetary Defense Issues and Initiatives ▶ NASA’s Asteroid Redirect Mission ▶ OSIRIS-REx Asteroid Sample-Return Mission ▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE

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Part X Ground-Based Discovery Efforts

A good deal of our knowledge about cosmic hazards comes from highly sophisticated diagnostic systems onboard scientific spacecraft that have enabled astrophysicists to detect and track asteroids and comets or determine the physical characteristics of the sun. There are also a considerable number of ground-based observatories in the United States, Europe, and around the world that are fully dedicated to determining all types of cosmic hazards and especially near Earth objects. This section provides information about the global ground observatories that provide valuable information to the scientific community to provide a deeper understanding of a range of cosmic hazards and to augment space-based discovery efforts.

European Operational Initiative on NEO Hazard Monitoring Simonetta Di Pippo and Ettore Perozzi

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The ESA SSA-NEO Segment: Federating European Assets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NEO Segment Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The NEO Coordination Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Catalogues and Databases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Visualization Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NEO Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Future Developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

An operational approach to NEO hazard monitoring has been recently developed at European level within the framework of the Space Situational Awareness program (SSA) of the European Space Agency (ESA). Through federating European assets and profiting from the expertise developed in European universities and research centers, it has been possible to start the deployment of the so-called SSA-NEO segment. This initiative aims to provide a significant contribution to the worldwide effort to the discovery and characterization of the

S. Di Pippo (*) UNOOSA – United Nations Office for Outer Space Affairs, Vienna, Austria e-mail: [email protected] E. Perozzi Deimos Space/INAF-IAPS, Madrid, Spain e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_50

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Near-Earth Object population, to the computation of the associated hazards, and to the study of the possible mitigation measures. The SSA-NEO segment is intended to work in close cooperation with and to be complemented by the other NEO-related programs of the European Commission. A major achievement in this respect has been the inauguration in May 2013 of the ESA NEO Coordination Centre located at ESRIN (Frascati, Italy), whose services and operations are discussed in detail. Keywords

AstDyS – Asteroid Dynamic Site • Asteroid hazard • Catalina observatory • CINEOS ground observatory • EARN database • ESRIN • European Commission • European Commission Horizon 2020 program • European Space Agency (ESA) • ESA NEO Coordination Centre • European Optical Ground Station at Tenerife • ESA “Wide Survey” Network • Gaia FUN-SSO (Follow-Up Network of Solar System Objects) • Impact monitoring • International Astronomical Union (IAU) • La Sagra Sky Survey • Minor Planet Center • Mitigation measures • Near-Earth Object (NEO) • NEODyS (NEO Dynamic Site) • NEOShield project Palermo Risk Scale • Pan-STARRS observatory • Priority List • Sentry system at JPL • Sky surveys • Spaceguard Central Node at INAF • Space Situational Awareness NEO segment Space Surveillance and Tracking (SST) Segment • Space Weather (SWE) Segment

Introduction The NEO (Near-Earth Object) segment of the ESA Space Situational Awareness program (Drolshagen et al. 2011) is one of the three major service components of the SSA system, together with the SST (Space Surveillance and Tracking of man-made space objects) and the SWE (Space Weather monitor and forecast) segments. The SSA program aims to raise awareness concerning the population of space objects, the space environment, and existing threats and risks. This is accomplished by the timely providing of data and services to users, customers, and stakeholders. The users of this data range from the scientific community to satellite operators, from governmental institutions for risk monitoring to space agencies, and from insurance companies to the public at large. The SSA Preparatory Phase was initially decided and funded at the ESA Council at Ministerial level (C-MIN) in 2008 for a first 4-year period in order to carry out the system studies leading to the consolidation of both the system requirements and the architectural design of all segments. At the subsequent ESA C-MIN in 2012, the SSA program has been further extended to encompass the deployment of precursor services and operational activities. The customers, users, and stakeholders of the SSA program are assumed to be: • Governments • UN and international bodies

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• • • • • • • •

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Defense sector Air traffic control agencies Insurance companies Disaster management organizations and national alert centers Space agencies Science community Schools and universities The public and the press

The SSA-NEO segment has been able to federate existing European assets, establish the NEO Coordination Centre at ESRIN, and initiate operations. Initiatives focusing on SSA-related topics have been also started under different ESA programs, EU Framework programs, and other European Commission funding schemes. From the operational point of view, it is worthwhile mentioning the contribution of the NEOShield project (http://www.neoshield.net), whose aim is to increase our knowledge on the consequences of an impact through modeling both the asteroid characteristics and the impact scenario. Preparing to perform mitigation in space by timely deflecting hazardous objects is also studied in detail in realistic cases (Harris et al. 2011), thus providing complementary information to the SSA-NEO segment.

The ESA SSA-NEO Segment: Federating European Assets The first step to be undertaken by the individual SSA segments is to survey European existing assets and assess their utilization within the program. Facilities which are potentially relevant for building up a NEO alert system should provide the following basic functionalities: • • • • • •

Databases to store and retrieve NEO dynamical and physical properties Repository of observational data Tools for orbit calculations and propagation Tools for impact risk assessment and prediction Tools for supporting NEO observations Observation capabilities

In this respect the European worldwide excellence in orbit determination and impact monitoring, as provided by the long-standing operational experience offered by the NEODyS system (Milani et al. 2000a; Chesley and Milani 1999), was recognized as a major asset for the SSA-NEO segment. It satisfies all requirements related to the identification and ranking of NEO collision risks with the Earth, the determination of the orbit state and propagation, and the computation of all sorts of ancillary information regarding NEOs such as the ephemerides of observable objects, error propagation, and virtual impactors determination. The most important output of the NEODyS system is the risk

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Fig. 1 Distribution of the recovered (above) and lost (below) objects as a function of their size in three different time spans; in red the period in which the Spaceguard Central Node priority list was available (Credits: Spaceguard Central Node)

page, where objects are listed in the order of increasing hazard, as determined by the value of their Palermo Scale (Chesley et al. 2002). The NEODyS functionalities are complemented by the Spaceguard Central Node services, devoted to prioritize NEO observations by ranking them according to their importance for impact monitoring. The so-called Priority List (Boattini et al. 1999) has demonstrated to be extremely useful for the coordination of followup observations performed by both professional and amateur astronomers (Fig. 1). Physical characterization is also essential in order to evaluate the consequences of an impact, to prepare mitigation actions, and to compute high-accuracy longterm orbital evolutions. The tiny nongravitational forces which act on small bodies can in fact sometimes make the difference in estimating the likelihood of an impact. In this respect, Europe plays also a prominent role: a large scientific community performs observation campaigns having access to a wide variety of options, form

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Fig. 2 Distribution in time of NEO discoveries showing the contribution of the various surveys. Note in 2010 the significant contribution of the WISE mission, the US infrared space observatory observing NEOs from space (http://neowise.ipac.caltech.edu/) (Credits: JPL NEO Program)

small 1-m class telescopes to the large infrastructures ruled by international consortia (e.g., ESO). These observations allow determining the composition, the shape, the rotation, and the thermal properties of individual NEOs through photometry, spectroscopy, and polarimetry. Data dissemination is under the responsibility of EARN (European Asteroid Research Node) which keeps updated lists of the available physical characteristics of known NEOs. At university/research level, Europe has developed over the years many of the basic functionalities of a NEO information system, encompassing the fundamental knowledge needed for properly addressing the asteroid hazard. This has resulted in an ever-increasing ability at European level to deal with the subtleties involved in assessing potential threats as well as increasing the efficiency of the follow-up astrometric and physical observations. As concerning NEO discovery, the US supremacy in the field is clearly shown in Fig. 2. Although European assets such as the privately owned La Sagra Sky Survey, operated by the Observatorio Astronomico de Mallorca, Spain (http://www. lasagraskysurvey.es/), the CINEOS program (Campo Imperatore Near-Earth Objects Survey, Bernardi et al. 2002), and the ESA Optical Ground Station (Koschny et al. 2011) have often led to significant discoveries, they cannot compete with the overall efficiency of US-based NEO surveys such as Catalina (http://www. lpl.arizona.edu/css/) and Pan-STARRS (Wainscoat et al. 2011). Note that in 2013 the NEO discovery rate overcame for the first time the remarkable threshold of 1,000 objects per year (see, e.g., Fig. 8).

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Within this framework and in order to provide a significant contribution to the worldwide effort in studying and preventing cosmic hazards, federating existing European assets under NEO segment coordination consists, on one side, of advanced data processing and dissemination and, on the other one, of follow-up observations, whether for astrometry or physical characterization. The latter function seems to be particularly promising since it is largely performed by the scientific community on a voluntary basis; thus SSA-NEO collaborating facilities ready to observe even upon short notice could significantly contribute to the orbit improvement of already known/recently discovered objects leading to a better evaluation of the corresponding impact probabilities. The contribution of space-based assets, and in particular of the ESA Gaia mission (http://sci.esa.int/gaia/, which foresees the issue of astrometric alerts to the Gaia FUN-SSO (Follow-Up Network of Solar System Objects), is also envisaged (Tanga and Thuillot 2013). The functionalities of an early European SSA-NEO segment federating existing sensors and systems can be summarized as follows: – – – – – – – – – – –

Orbit determination and identification Orbit propagation Impact prediction Risk page generation Prioritization of follow-up observations Astrometric follow-up observations Physical properties observations NEO physical properties database Risk analysis and warning policy Front desk daily operations Data dissemination and public outreach These core services can be ensured by the following existing assets:

• The NEODyS system at the University of Pisa, Italy (http://newton.dm.unipi.it/ neodys/) • The EARN database maintained at DLR Berlin in Germany (http://earn.dlr.de) • The Spaceguard Central Node at INAF in Italy (http://spaceguard.rm.iasf.cnr.it/ SGF/INDEX.html) • Collaborating observatories/telescopes from Switzerland, Spain, Italy, Germany, the UK, Norway, France, Romania, and Belgium • The ESA Optical Ground Station in Tenerife As it will be described in detail in the next sections, federating European assets has been successfully achieved by establishing the SSA-NEO Coordination Centre located at the ESRINESA Centre (Frascati, Italy). Precursor services have been also started for continuously monitoring the growing NEO population, assessing future orbital evolutions, and isolating objects for which more detailed observations, both physical and astrometric, are needed.

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NEO Segment Overview Federating existing European assets has the advantage of allowing ESA to quickly enter the NEO hazard monitoring activities by providing useful services and data. Yet the NEO segment has been designed as a long-term endeavor (Perozzi et al. 2011). An incremental growth in both services and facilities is foreseen, eventually encompassing also an innovative system of wide-field high-sensitivity telescopes for NEO discovery in order to reduce the gap with respect to the most successful NEO surveys. As such the final configuration of the NEO segment is composed of three major elements: • Small Bodies Data Centre: in charge of the downstream data processing (e.g., orbit determination, risk assessment, follow-up coordination) and the provision of NEO-related services (raw image archive, physical properties and fireball databases, etc.) • Collaborating observatories: dedicated mainly to astrometric follow-up observations as well as to performing unsolicited and serendipitous observations (e.g., amateurs, space telescopes, etc.) • WideSurvey: a network of optical telescopes performing an all-sky survey focused on the discovery of small-size, potentially hazardous objects. The actual implementation of this scenario depends on many factors, both technical and programmatic. The inauguration, in May 2013, of the ESA NEO Coordination Centre has confirmed ESA’s commitment in pursuing the NEO segment objectives. In its present configuration the NEOCC hosts several features and services, as described in details in the next sections, and further improvements are foreseen. During the first year of operations, the NEOCC has fully profited from its collaborating observatories in coordinating follow-up observations of peculiar objects. The first real-case event for testing the potentiality of the NEOCC was the near encounter of asteroid 2002 GT with the Earth in June 2013. The asteroid was successfully observed in detail by a network of European astronomers under NEOCC coordination. 2002 GT is a relatively large object a few hundred meters across, which made a close flyby with Earth, passing at almost 50 lunar distances on 26 June 2013. The asteroid was intended to be the future target of NASA’s EPOXI spacecraft (former Deep Impact mission: http://www.nasa.gov/mission_pages/deepimpact/main/), which was aiming at reaching the asteroid in January 2020. The 2013 near encounter was the last favorable appearance before 2020 to study the object with the aim of understanding its physical characteristics such as its diameter, rotation, and composition. By alerting and then collating observation data from various European teams, the NEOCC was able to provide a comprehensive set of results including: • Photometry and light curve data from the Observatoire de la Cote d’Azur, France • Spectroscopic data from the Osservatorio Astronomico di Padova and the University of Padua, Italy (Fig. 3)

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Fig. 3 Spectrum of asteroid 2002 GT obtained from observations performed from the Asiago Observatory (Lazzarin et al. 2013) following a NEOCC alert. The averaged spectra relative to the S, Q, and Sq taxonomic types of asteroid classification (Bus and Binzel 2002) have been superimposed, confirming that the Sq type best fits the observations

• Infrared observations from the INAF Campo Imperatore Observatory (Italy) • Astrometry measurements from the Gaia Follow-Up Network of Solar System Objects (FUN-SSO) These data together enabled a very good characterization of the asteroid surface composition and of its thermal properties, shape, and rotational period. Moreover, the analysis of the 2002 GT light curve showed that it is compatible with the presence of a satellite. Unfortunately, a few months later NASA lost contact with the EPOXI spacecraft, but the results obtained highlighted the quick response of the European astronomical community and validated the role of the NEO segment in coordinating observations and providing information on all known NEOs such as their orbits, impact risks, and close approaches to Earth. The efficiency of a European “Wide Survey” focused at discovering small (10–50 m in size) NEOs approaching the Earth using innovative “fly-eye” telescope technology was demonstrated by extensive simulations (Farnocchia et al. 2012). The aim is to ensure a daily coverage of the whole visible sky with sensors characterized by a large field of view (about 45 square degrees) and a high

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Fig. 4 Sample weekly sky coverage of present NEO surveys (Credits: Minor Planet Center)

sensitivity (reaching down to 21.5 limiting magnitude). This would represent a major improvement in terms of sky coverage as it can be deduced from comparing the diagram in Fig. 4, where the sky coverage of the present NEO survey is shown. A “Wide Survey” as such could guarantee the European competitiveness in discovering a peculiar class of objects, i.e., those very small in size (1 μm 45,919 5.62e + 3.58e + 22,241 30,162 4.98e + 6.07e + 1.97e + 8.62e + 7.00e +

12 14 12 13 14

09 09

>10 μm 45,919 4.12e + 09 1.13e + 09 22,241 30,162 4.98e + 12 1.18e + 13 1.62e + 12 2.70e + 13 4.53e + 13

>100 μm 45,919 3.84e + 08 1.17e + 08 22,241 30,162 2.33e + 12 – 2.28e + 11 1.08e + 12 3.64e + 12

>1 mm 31,139 1.53e + 4.46e + 22,241 30,162 1.39e + – – 8.00e + 1.67e + 06 08

08

07 06

>1 cm 5,827 433,466 92,677 15,790 18,410 177,914 – – – 744,084

>10 cm 5,814 14,719 2,927 5,750 – – – – – 29,210

Table 4 Sources and their contributions to ESA’s MASTER-2009 space debris model (Flegel 2010) in different size regimes for May 1, 2009 >1 m 4,174 432 63 773 – – – – – 5,442

818 H. Klinkrad

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SRM combustion residues are mainly composed of aluminum oxide and residues of motor liner material. Aluminum powder is added to most solid fuels, typically with a mass fraction of 18 %, to stabilize the combustion process and improve the motor performance. It is assumed that about 99 % thereof is continuously ejected with the exhaust stream during the main thrust phase in the form of Al2O3 dust of diameters largely within 1 μm  d  50 μm. Due to design constraints, many solid motors have nozzles protruding into the burn chamber, causing cavities around the nozzle throats. During the burn phase, trapped Al2O3, molten aluminum droplets, and parts of released thermal insulation liner material can cumulate in this pool and form slag particles which can grow to sizes of typically 0.1 mm  d  30 mm. These slag particles are released at the end of the main thrust phase, as the internal motor pressure decreases. It can be assumed that during more than 1,100 SRM firings, more than 1,000 tons of propellant were released into space of which approximately 320 tons were Al2O3 dust particles and 4 tons were slag particles formed of Al2O3, metallic aluminum, and motor liner material. Due to orbital perturbations and their different effects on μm-size dust and cm-size slag, merely 1 ton of Al2O3 dust and 3 tons of SRM slag particles are believed to be still on orbit. Apart from more than 1,000 orbit insertion burns, there were also several hundred SRM burns to deorbit objects in a controlled fashion. These deorbit burns were almost exclusively performed for Russian reconnaissance satellites at very low altitudes, and the resulting SRM combustion products had a correspondingly low orbit lifetime. However, some in situ measurements (mainly from returned space hardware) show temporal increases in small-particle impact rates due to these events. At sizes of 1 μm  d 1 cm, SRM combustion residues dominate the space debris environment (see Table 4). Apart from intact objects, fragmentation debris, and SRM residues, there are other contributors to the space debris population: (1) sodium-potassium (NaK) coolant released from 16 Russian RORSATs as they ejected their reactor cores in the 1980s, (2) multilayer insulation (MLI) material that is unintentionally released by spacecraft or rocket stages, (3) ejecta material that is released by small-particle impacts on surfaces of spacecraft and orbital stages, and (4) degradation products that are released by aging surfaces of spacecraft and orbital stages. The debris mass contribution from these sources is much less than 1 % of the overall on-orbit mass, and they are either too small in numbers (NaK, MLI) or too small in size (surface ejecta and degradation products) to constitute a significant risk for space missions. Today’s population of trackable and non-trackable objects can be reproduced by space debris environment models, such as ESA’s MASTER-2009 model (Flegel 2010). Such models consider historic launch and release events, known in-orbit fragmentations, known solid rocket motor-firing events, intentional releases of NaK coolant liquid from Buk reactors of Russian RORSAT satellites, unintentional releases of surface degradation products (MLI and paint flakes), and the generation of ejecta and spall by surface impacts. Table 4 lists the resulting debris sources and their contributions to the MASTER-2009 population at the reference epoch of May 2009 for the applicable size regime larger than 1 μm. From the risk point of view, more than 160 million particles larger than 1 mm, at typical LEO collision velocities of 10–14 km s1, can disable sensitive satellite subsystems, more than 740,000

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Fig. 6 Spatial density distribution of MASTER-2009 objects of d > 10 cm, in LEO to GEO altitudes, discriminated by sources (Flegel 2010)

particles larger than 1 cm can render a spacecraft dysfunctional, and almost 30,000 objects larger than 10 cm are likely to cause a catastrophic breakup of a satellite or orbital stage. Figure 6 shows the altitude distribution of MASTER-2009 objects larger than 10 cm in terms of resulting spatial densities (in objects/km3). The contributing debris sources at these sizes are explosion and collision fragments, intact objects, and lightweight sheets of MLI. Highest concentrations are in the LEO regime, between 750 and 900 km, with almost equal contributions from explosion fragments, collision fragments, and intact objects. In general, however, explosion fragments dominate the LEO and GEO regions, with GEO object concentrations about three orders of magnitude below the LEO maximum. When going to a 1 cm-size threshold, additional source terms come in, including NaK droplets and solid rocket motor slag, while launch and mission-related objects start playing a minor role. Figure 7 shows the individual contributions as a function of altitude. Reducing the size threshold further to 1 mm leads to the addition of ejecta particles, as shown in Fig. 8. With the decrease of the debris sizes from 10 cm to 1 mm, the enveloping curve of spatial densities tends to flatten, due to an increasing share of particles on eccentric orbits with a wider distribution over altitudes. As a consequence, the relative magnitude of the GEO concentration peak with respect to the LEO maximum reduces from 3 to less than 2 magnitudes. One cause of the increase of orbit eccentricities with decreasing object sizes lies in the area-to-mass ratio that drives solar radiation pressure and airdrag forces and is inversely proportional to the object diameter. This effect leads to a decay of small-size objects that have extended dwell times at altitudes within the denser Earth atmosphere.

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Fig. 7 Spatial density distribution of MASTER-2009 objects of d > 1 cm, in LEO to GEO altitudes, discriminated by sources (Flegel 2010)

Fig. 8 Spatial density distribution of MASTER-2009 objects of d > 1 mm, in LEO to GEO altitudes, discriminated by sources (Flegel 2010)

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Spatial object densities are an essential input to debris collision risk assessments. The statistical behavior of the orbital debris population can be well represented by the laws of kinetic gas theory. Hence, the number of collisions c encountered by an object of collision cross section Ac, moving through a stationary debris medium of uniform particle density D, at a constant relative velocity Δv, during a propagation time interval Δt is given by c ¼ Δv D Ac Δt

(1)

where F = Δv D is the impact flux (in units of m2 s1) and Φ = F Δt is the impact fluence (in units of m2). The collision probability follows a binomial law which can be well approximated by a Poisson distribution, generating the following probability Pi=n of n impacts and Pi=0 of no impact: Pi¼n ¼

cn expðcÞ 7! Pi¼0 ¼ expðcÞ n!

(2)

The probability of one or more impacts is hence the complement of no impact, given by Pin ¼ P ¼ 1  expðcÞ  c 7! P  Δv D Ac Δt

(3)

The challenging part in the evaluation of this equation is the particle flux F = Δv D. In the MASTER-2009 model 3-dimensional, time-dependent spatial object density distributions are established for a grid of spherical volume elements covering the entire Earth environment from LEO to GEO altitudes. Contributions from each member of the orbital debris population go into this distribution. For each of these objects, the velocity magnitude and direction is retained for each volume element passage. This information is later retrieved to determine relative impact velocities with respect to a target object passing through individual cells of the volume grid (Klinkrad 2006). The resulting impact flux is then determined from a summation over all volume cells that are passed by the target object, with contributions from all debris objects that passed the individual cells. When considering relative velocities between two objects on circular orbits at the same altitude, with the same orbital velocities v, but on different inclinations, then Eq. 4 yields the resulting collision velocity as a function of the impact azimuth A within the local horizontal plane (where A = 0
denotes impacts from the flight direction): Δv  2 v cos ðAÞ

(4)

Since near-circular orbits are dominant for debris of critical sizes, Eq. 4 provides a good approximation of the correlation of impact velocity with impact geometry. It also states that the maximum relative velocity can be twice the orbit velocity, for an approach from the flight direction, and that the minimum relative velocity can be close to zero, for a sideways approach from 90
. Impacts from the rear quadrants

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Table 5 Sample orbits for analyzing space debris collision flux ISS ERS-2 Globalstar GPS GTO GEO

Hp [km] 356 774 1,399 19,997 560 35,782

Ha [km] 364 789 1,401 20,003 35,786 35,790

i [deg] 51.6 98.6 52 55 7 0.1

a [km] 6,738 7,159 7,778 26,378 24,551 42,164

e [–] 0.0006 0.0010 0.0001 0.0001 0.7174 0.0001

ω [deg] 0 90 0 0 178 0

Table 6 Mean time between impacts of a given debris size for a spherical target of 1 m2 cross section, on sample orbits as defined in Table 5, for a space debris environment according to ESA’s MASTER-2009 model (Flegel 2010) Diameter ISS ERS Globalstar GPS GTO GEO

>0.1 mm 9.0 d 0.7 d 1.7 d 244.8 d 36.8 d 676.3 d

>1 mm 636 y 42.5 y 102 y 10,794 y 2,627 y 18,674 y

>1 cm 41,102 y 1,252 y 9,208 y 1.1e+ 7 y 241,546 y 6.5e+ 6 y

>10 cm 942,507 y 43,783 y 126,550 y 7.2e+ 8 y 4.4e+ 6 y 1.4e+ 8 y

can only occur for impactors that travel on eccentric orbits, during their perigee passes. Likewise, impacts from 0
can only occur if the impactor has an orbit with a “complementary inclination” of 180
minus the inclination of the target object. Only in that case can both objects be in the same orbit plane, on counter-rotating orbits, if their ascending orbit nodes are separated by 180
. For typical target orbits defined in Table 5, the mean times between impacts by orbital debris of different sizes are listed in Table 6 for a common reference cross section of 1 m2, assuming a spherical target object. In accordance with spatial densities shown in Figs. 6, 7, and 8, the highest collision risk for any of the selected sample orbits is encountered for ERS-2 on a sun-synchronous orbit of 774 km  789 km at an inclination of 98.5
. Apart from the debris concentration at this altitude, the collision frequency is also driven by the collision velocity (see Eq. 1). For ERS-2 it attains a most probable value of about 14 km s1, which is close to the maximum for two circular orbits at this altitude. Objects that could impact at such velocities are originating from the complimentary inclination band close to 81.4
(=180
 98.6
; see Figs. 3 and 4). Since all major flux contributions are from inclinations i  65
, the resulting collision velocities are mostly within 14  2 km s1 at impact azimuth angles –30
 A  +30
(see Eq. 4), with particles mainly originating from breakup events for the size regime larger than 1 cm. The situation changes for the ISS orbit. Its lower altitude goes along with a reduction of the debris flux by about one order of magnitude, and its lower inclination of 51.5
results in a gap of complementary inclination bands at 180
 51.6
= 128.4
. The populated inclination bands only start at about 100
. As a

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consequence, there are no impacts from azimuth angles –15
 A  +15
, and most probable collision velocities are at 10  1 km s1, resulting in approximately 50 % of the impact energy as compared to ERS-2. In contrast to ERS-2, slag residues from SRM firings are dominating the 1 cm debris population for ISS. They mostly reside on highly eccentric orbits of low inclinations, with perigee velocities that allow low-velocity impacts also from rear quadrants of ISS azimuth angles. When looking at a typical geostationary target orbit, then the spatial density of the debris environment as compared to the LEO peak drops by about three orders of magnitude for the 10 cm population and by about two orders of magnitude for the 1 cm population. For the GEO orbit velocity of about 3 km s1, the predicted collision velocities are in the range of 0  v  1 km s1, with a most probable value of 0.8 km s1, caused by old GEO objects that reached a maximum inclination excursion of 15
due to long-periodic orbit perturbations with a period of 53 years. Due to the low relative velocities, the impact azimuth angles are mostly at 80
. There are minor flux contributions from objects on GEO transfer orbits (GTO) and on 12 h Molniya orbits. They have apogee velocities of about 1.5 km s1, causing frontal impacts on the faster GEO objects. There are different ways to mitigate the risk and/or consequences of a collision of an operational spacecraft with a space debris object. For large-size catalog objects, the concept of conjunction event analysis and collision avoidance can be pursued. For sub-catalog debris that cannot be tracked, passive protection measures can be taken. To avoid catastrophic collisions with catalog-size objects of d 10 cm, the ISS operators perform a conjunction event screening on the basis of the US Space Surveillance Network (SSN) catalog. This screening is performed at least three times a day, for 72 hours ahead, in five steps: 1. SSN catalog-based identification of ISS approaches that fall within a 60 km radius (based on limited-accuracy orbit data in two-line element format) 2. Use of more accurate, osculating orbital elements, if the approach falls within 10 km   40 km   40 km (radial  along-track  out-of-plane) 3. Consideration of orbit uncertainties, if the approach falls within 2 km   25 km   25 km 4. Determination of collision probabilities, if the approach falls within 0.75 km   25 km   25 km 5. Decision on an evasive maneuver, if an accepted risk threshold is exceeded (e.g., 1 in 10,000) In the first 4.5 years of operation, the ISS performed seven debris avoidance maneuvers, with three of them executed by the visiting Space Shuttle. Due to improved procedures, based on more reliable orbit data, the subsequent avoidance maneuver was only 5.5 years later, executed by the attached ATV-1 on August 27, 2008, to avoid a fragment of Cosmos 2421. This fragment was one of approximately 500 cataloged objects generated during three main breakup events in early 2008, just 60 km above the ISS altitude (Johnson 2009). A year of peak ISS

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collision avoidance activity was noted between April 2011 and April 2012, when ISS performed four evasive maneuvers. Two more conjunction events would have led to a maneuver. However, due to an insufficient reaction time span for a maneuver, the crew had to retreat into the attached Soyuz vehicle, to prepare for an emergency departure in the event of a collision. As is done by NASA for the ISS, ESA has maintained a conjunction event analysis service for their operational satellites (e.g., for ERS-2, Envisat, CryoSat-2, Cluster-2, etc.). Once a day the entire TLE catalog of the US SSN is screened for close conjunctions with the accurately known ESA satellite orbits for 7 days ahead. If the predicted collision probability exceeds a level of 1 in 3,000, then more precise orbit data are obtained for the conjunctor object through the processing of radar data from tasked observations. In most cases, the more accurately know conjunctor orbit with its much reduced error dispersion leads to a maneuver suppression, even if the flyby geometry is unchanged. If, however, the collision probability remains at a level above 1 in 1,000, then a collision avoidance maneuver is initiated by the relevant project team. Envisat, launched in 2002, had to perform five avoidance maneuvers up to December 2009. Due to the Chinese Feng Yun 1C ASAT test in January 2007, and as a result of the collision between Cosmos 2251 and Iridium 33 in February 2009, the debris environment at the Envisat and ERS-2 orbit altitude significantly deteriorated. As a consequence, the overall avoidance maneuver frequency in the year 2010 increased to 9 (4 each for Envisat and ERS-2 and 1 for CryoSat-2). The risk of catastrophic collisions of Envisat with a 10 cm fragment from the Feng Yun 1C and Cosmos 2251/Iridium 33 breakup events alone increased by +58 % as compared to the rest of the US SSN catalog. The risk of a mission-terminating impact by a 1 cm class debris object even grew by +86 %, as compared with a modeled space debris population prior to these events. In total, ESA satellites performed 22 collision avoidance maneuvers between 2004 and 2012. To protect against non-trackable debris and meteoroids, the ISS has its manned modules covered by stuffed Whipple shields. For ESA’s Columbus module, for instance, they consist of a 2.5 mm bumper and a 4.8 mm back wall, separated by an 11 cm standoff distance. Between the bumper and the back wall, fabric layers of 4 mm Kevlar and 6 mm Nextel sheets are embedded as a “bulletproof vest.” The shields of the ISS manned modules can withstand impacts by objects up to 1.4 cm in size, at velocities on the order of 10 km s1. The related kinetic energy corresponds to a 1.5 ton midsize car hitting at 50 km h1 or to the energy released by an exploding hand grenade. An ISS module of 100 m2 cross section is expected to have impacts from debris objects of d 1 cm at a rate of 1 in 410 years. Meteoroid impacts are negligible in this size regime. For the same module cross section, impacts from objects of d 1 mm will occur at a rate of 1 in 6 months, with a 90 % probability that they originate from meteoroids. Whipple shields rely on impact velocities that are larger than about 6 km s1, in order to break up the impacting object into a cloud of solid, liquid, and gaseous matter that can more easily be withheld by the back wall and intermediate fabrics, due to a wider spreading and time-distributed arrival of the fragment cloud, with a resulting reduction of the pressure peak. While the volume and mass requirements of such

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shields are prohibitive for normal spacecraft, there are still ways of reducing their impact risk. The Canadian Radarsat, for instance, used lightweight Nextel fabric covers as external protection and rearrangements of sensitive spacecraft subsystems to improve the survivability of its 5-year mission by 50–87 %. This gain was achieved for a mass penalty of 0.6 % (+17 kg). In order to increase the safety of US space assets, the US Space Command is upgrading its operational surveillance network. In particular, the replacement of the UHF-based surveillance fence that extends along the 33rd parallel across the USA to an S-band system is expected to allow a catalog maintenance down to 2 cm sizes at the ISS altitude. This could increase the SSN catalog size to more than 100,000 objects. With the full orbit knowledge of these objects, one would be in a position to close the gap between avoidable and shieldable objects for ISS and hence significantly improve the on-orbit safety for manned space flight. The space debris environment at critical sizes above 10 cm has in the past been dominated by explosion fragments and by dysfunctional but intact remnants of previous missions. Collisions played a minor role until the Feng Yun 1C ASAT test in 2007 and the accidental collision between Cosmos 2251 and Iridium 33 in 2009. By 2010 these two events alone accounted for almost 40 % of the US SSN catalog. In order to curtail the growth rate of hazardous space debris, particularly in the LEO regime, the international space community has identified and adopted a set of space debris mitigation measures. The main categories of recommendations can be summarized as follows: • • • • •

Reduction of mission-related objects Prevention of on-orbit explosions (passivation) Limitation of nonexplosive release events Collision avoidance between trackable objects and operational assets Post-mission disposal of space systems

Mission-related objects (MROs) contribute 6 % to the trackable catalog population, with 72 % of these related to launch systems and 28 % related to payloads. MROs, also referred to as operational debris, are defined as objects released during nominal operations by both spacecraft and rocket bodies. This includes debris from launcher staging and payload separation (such as adapters, shrouds, and clamp bands) and objects released during spacecraft deployment and commissioning (such as parts of explosive bolts, solar array latches, and lens covers). Most of these objects are released with low relative velocities, and so they remain in close proximity to the operational orbit of the source object. The release of MROs can be limited by system design. The best method of reducing the population of MROs is not to produce the objects in the first instance. This is reflected in most debris mitigation standards through recommendations to minimize or to avoid the use of debris-generating systems (e.g., yo-yo despinners, nozzle closures of propulsion systems, protective lens covers, etc.). System design is also encouraged to ensure that released parts (e.g., antenna deployment mechanisms, protective covers, explosive bolts, ullage motors, heat shields, etc.) are retained with the primary object. This can be achieved through the use of lanyards,

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sliding or hinged covers, and special catchment devices. Moreover, materials and basic system technologies (e.g., tanks, surface materials, structures, etc.) should be selected such that they are resistant to environmental degradation (e.g., aging by radiation, atomic oxygen and microparticle impact erosion, and thermal cycling). Explosions of spacecraft and upper stages in orbit have been the major source of debris in the past, with some 250 events up to 2013, at a mean annual rate of about 5. These failures, which caused at least 4,000 cataloged fragments, might have been avoided, if onboard passivation techniques had been employed. Such procedures are a standard on many of today’s launchers, and so far there are no recorded explosions of successfully passivated orbital stages. End-of-life (EOL) passivation was first considered as a design requirement at the beginning of the 1980s. All upper stages and spacecraft which were launched before then, and which are still in orbit, continue to pose an explosion hazard (a Titan III-C Transtage launched in 1967 exploded after 27 years in orbit). Hence, there is a significant number of latent explosion sources still on orbit. Space debris mitigation standards recommend that all onboard reservoirs of stored energy (e.g., propellants, pressurants, batteries, momentum control gyros) should be permanently depleted when they are no longer required for any nominal or post-mission operations. The following passivation aspects should be considered: • Idle burn or venting of residual propellants, with valves left open • Venting of all pressure systems and/or activation of pressure relief mechanisms to avoid explosions due to external heating • Discharge of batteries, shutdown of charging lines, and maintenance of a permanent discharge state • Deactivation of range safety systems • Dissipation of energy contained in momentum control gyros Fuel depletion or “idle” burns of orbital stages may be performed such that the resulting thrust leads to a braking maneuver, leaving the stage in a reduced-lifetime orbit. The residual lifetime should be less than 25 years to be compliant with international recommendations for space debris mitigation. The class of non-breakup release events includes residues from SRM firings (slag and dust), sodium-potassium droplets that were generated during RORSAT reactor core ejections, or surface degradation products that are caused by aging paint coatings or multilayer insulations (MLI). All of these debris sources can be reduced or even suppressed in total through design measures. Collision avoidance, as another debris mitigation measure, is nowadays implemented by many space operators for their operational payloads. This concept, however, can only be applied to about 5 % of the catalog population, assuming that about 1,000 of the on-orbit payloads in 2013 were operational, of which about 80 % could be maneuvered. Hence, future collisions will most often occur between uncontrollable debris objects. To reduce the number of catastrophic collisions between large, intact, but nonoperational objects, the use of ground-based lasers

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is investigated. If a close conjunction is predicted, then a radar-guided laser beam could ablate material from one of the objects to impart a momentum that could sufficiently alter the flyby distance to a safe level. In 2013 the mean time between two catastrophic collisions in the LEO region was on the order of 5 years. One way of reducing future collision rates is through post-mission disposal measures, i.e., through mass removal of (still) active space assets. International guidelines recommend removing spacecraft and orbital stages after their mission completion, in particular from the densely populated LEO regime and from the unique GEO ring. For GEO spacecraft disposals, an orbit raise to a graveyard region at approximately 300 km above GEO is recommended. The magnitude of the altitude raised to a near-circular disposal orbit is determined by the area-to-mass ratio of the spacecraft. It is defined such that long-term orbit perturbation effects will not lead to a return of the orbit into a “GEO protected region” that extends 200 km around the GEO ring (which is at 35,786 km altitude). Table 7 shows a summary of GEO post-mission disposals over a 13-year time span. It is evident that the degree of compliance with international guidelines has gradually improved and has reached a mean level of almost 50 % by 2012 and a 64 % compliance in 2012 itself (Flohrer 2014). End-of-life mitigation measures for the “LEO protected zone” (i.e., below 2,000 km altitude) recommend an active deorbiting or a natural decay of payloads and orbital stages into a destructive reentry within 25 years after mission completion. For typical area-to-mass ratios of such objects, a timely natural decay requires an end-of-mission altitude below 600 km. Alternatively, chemical or electrical propulsion can be used to induce a direct reentry. A monopropellant hydrazine system would need about 8.8 % of the spacecraft mass for a controlled deorbit from 800 km (6.3 % for a bipropellant system). Electrical propulsion systems, due to their higher ejection velocities, can be more mass efficient by a factor of about 10. Their lower thrust levels, however, will lead to an uncontrolled reentry. An accelerated uncontrolled reentry can also be induced by thin, conductive tethers of several kilometers length that orientate themselves along the local vertical through gravity-gradient forces. As they cut through the magnetic field lines, they induce a tether current that is closed through the ambient plasma and that leads to a retarding Lorentz force, acting opposite to the direction of motion of the spacecraft, with best performance for low-inclination orbits. For a mass penalty of less than 3 %, such systems are able to reduce orbital lifetimes of Globalstar satellites (at 1,400 km and 52
inclination) from 9,000 years to less than 2 months, and they can reduce orbital lifetimes of Iridium satellites (at 780 km and 86
inclination) from 100 years to less than 8 months. Space debris mitigation guidelines, standards, and requirements have been developed by several space agencies since the early 1990s. In parallel, the knowledge on space debris sources increased, and the understanding of effective remedial actions improved. A first step to a wider, international application of debris mitigation measures was taken by the Inter-Agency Space Debris Coordination Committee (autonomous) in 2002, with the publication of their space debris mitigation guidelines

EoL disposal Left at L1 Left at L2 Left at L1/L2 Drift orbit (too low) Drift orbit (compliant) Annual total

‘99 5 1 – 4 5 15

‘00 3 1 2 2 3 11

‘01 5 1 – 6 2 14

‘02 1 1 – 5 4 11

‘03 – 1 – 7 8 16

‘04 2 1 – 5 5 13

‘05 1 1 1 5 11 19

‘06 2 1 – 7 9 19

‘07 1 – – 1 11 13

‘08 2 1 1 1 6 11

‘09 3 – – 6 12 21

‘10 1 – – 4 11 16

‘11 – – – 3 12 15

‘12 1 – – 4 9 14

Total 27 9 4 60 108 208

(15.5 %) (5.0 %) (2.2 %) (29.3 %) (48.0 %) (100 %)

Table 7 History of post-mission disposal activities of geostationary spacecraft through December 2012 (L1 = 75
E, L2 = 105
W, “too low” and “compliant” refer to the IADC orbit raising recommendation in Anonymous (2002))

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(Anonymous 2002). This document, which was first presented at the UN COPUOS Scientific and Technical Subcommittee in 2003, serves as a basis for the development of space debris mitigation principles in two directions: towards a nonbinding policy document and towards applicable implementation standards. The former route was followed by a UN COPUOS working group, while the latter direction was pursued by an Orbital Debris Coordination Working Group (ODCWG) within the Technical Committee 20 and its Sub-Committee 14 of the International Organization for Standardization (ISO TC20/SC14). To a large extent these UN and ISO working groups recruit their experts from IADC member organizations. International space debris mitigation policies and standards, based on the consensus of the IADC guidelines, could in the future facilitate and harmonize the implementation of space debris mitigation measures at a global scale. Internationally agreed standards could enforce appropriate debris mitigation measures on spacecraft operators and launch service providers through the mechanisms of conditional launch license issuance and insurance coverage, depending on the acceptance of a space debris mitigation plan by the launch authority. Fifty years after the beginning of space flight, the voluntary implementation of debris mitigation and disposal measures by many space operators has become common practice. For several launching nations, the compliance with national regulations, or with a national space law, makes debris mitigation measures even mandatory. While debris mitigation is a necessary condition to maintain an orbital environment within a tolerable risk level for space missions, long-term forecasts of the debris environment indicate that some orbit regions may still become unstable within a few decades. Figure 9 illustrates the evolution of the LEO debris population larger than 10 cm for a hypothetical case of no future launches. The case corresponds to an extreme, hypothetical mitigation scenario, with immediate deorbiting of payload(s) and insertion stage(s) after orbit injection and with no intermediate release of mission-related objects. Predictions with NASA’s LEGEND model (Liou and Johnson 2008a, b) demonstrate that even for such optimistic assumptions, the LEO environment will become unstable. Within 20 years collision fragments will start to outnumber explosion fragments, and within 70 years, an initially stabilizing effect from naturally reentering objects will be superseded, and the 10 cm population growth will follow the slope of the collision-induced fragment increase. In the course of the 200-year projection, more and more collision fragments will collide with other collision fragments. This so-called Kessler syndrome is a self-maintained collisional cascading process that is fed by the LEO mass reservoir of 2,500 tons in 2013. Its natural termination would be reached in the very far future when all LEO crossing objects are ground to subcritical sizes that can no more reach the specific impact energy threshold of 40 kJ kg1 for causing a catastrophic breakup. As a consequence, space debris mitigation is a necessary but insufficient condition to maintain a stable orbital environment. In order to sustain an acceptable debris risk level for future space missions, debris mitigation measures must be augmented by space debris environment remediation measures that actively remove mass from orbit, with priority on the LEO

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Fig. 9 Long-term prediction of the LEO debris environment of critical-size objects of d > 10 cm, discriminated by source terms, for a “no future launch” scenario according to Liou (2011)

regime (Klinkrad and Johnson 2009, 2013). The effectiveness of space debris environment remediation measures is governed by their capability to reduce the short- and long-term risk of catastrophic collisions. An initial indicator of the debris environment deterioration is the concentration of critical-size objects of 10 cm and larger that have the capability to cause catastrophic breakups. Figure 4 shows the distribution of the catalog objects in LEO. Highest concentrations are at 800  200 km, spread over inclination bands at 65  2
, 72  2
, 82  1
, and 97  3
, with an almost equal share of intact objects, explosion fragments, and collision fragments. There are a lower, secondary LEO peak at 1,400  100 km and minor local peaks for MEO navigation satellite constellations and for GEO objects, both of which are about three orders of magnitude lower. In 2013, the orbit environment consisted of almost 12,200 cataloged LEO objects, larger than 10 cm, of a total mass of almost 2,500 metric tons. The corresponding rate of catastrophic collisions was 0.19 per year, resulting in one such event every 5–6 years. About 45 % of these collisions would have a rocket body, while 55 % would have a spacecraft as their main object. As many as 22 % of all catastrophic collisions will be attributed to a single 2
 50 km bin at 86.5  0.5
inclination and 780 km altitude, covering 72 large, intact objects, most of which are spent upper stages (Tsyklon 3rd stages, each with 1.4 tons and 6.2 m2; Vostok 3rd stages, each with 1.4 tons and 10 m2; and Delta II 2nd stages, each with 0.9 tons and 12 m2; Klinkrad and Johnson 2013). These 72 objects are facing fragments from the Iridium 33/Cosmos 2251 collision and from the Chinese

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Feng Yun 1C ASAT test as the main causes of their 10 cm collision flux. A secondary maximum of catastrophic collision rates at 11 % is due to a cluster of Cosmos satellites at 82
inclination and 920 km altitude. The short-term risk to the orbital debris environment can be expressed by the product of (collision flux)  (colliding mass), where the dominant target object masses drive the number of critical-size collision fragments, which determine the short-term level of debris environment deterioration. Using the same assumptions for determining catastrophic collision rates as above, the mass-weighted short-term environment risk is governed to 61 % by rocket bodies and to 39 % by spacecraft. Approximately 28 % of the overall short-term risk is due to objects in a single bin of 2
 50 km, centered at 71  0.5
inclination and 825  20 km altitude. Most of the corresponding mass is related to Russian Zenit 2 2nd stages with dry masses of 8.2 metric tons each. Of the 20 top-ranking objects according to metric #2, 19 are Zenit 2 rocket bodies, all of which are located in the above defined bin. The long-term risk to the environment can be expressed by the product (collision flux)  (colliding mass)  (orbit lifetime of fragments). As a simplifying, conservative assumption, the same orbital lifetimes shall be considered for the target object and its resulting fragments. The resulting aggregate of the individual products of catastrophic collision rate, target mass, and target orbit lifetime, over all intact LEO objects, leads to a long-term debris environment risk indicator that is governed to 72 % by rocket bodies and to 28 % by spacecraft. Approximately 42 % of the overall long-term risk is due to the same objects that dominate the risk metric #2, stemming from a single bin of 2
 50 km, centered at 71  0.5
inclination and 825  20 km altitude. Again, most of the related mass is due to Russian Zenit 2 2nd stages with an empty weight of 8.2 metric tons each, with a cross section of 33 m2, and with orbit lifetimes on the order of 700 years. Long-term debris environment projections (Liou and Johnson 2008a, b; Bastida and Krag 2009; Liou 2011; Klinkrad and Johnson 2013), based on an extreme scenario with no future launches and 90 % success rates of LEO post-mission disposals, indicate that the current environment could lead to a net increase of the long-lived 10 cm debris population by about 30 % in the next 200 years (see Fig. 9). This result confirms the onset of collisional cascading in some LEO orbit regions, also known as the “Kessler syndrome.” In the case of continued launch activities at today’s rates, the 10 cm debris population will even grow by 60 %, fueled by 24 catastrophic collisions (Bastida and Krag 2009). These collisions will almost exclusively occur between members of the previously identified, densely populated LEO inclination bands and between orbits of low to moderate eccentricities. Further parametric studies of the long-term debris environment evolution predict that active mass removal, focusing on inclination and altitude bands with high mass concentrations in a few large objects, can reduce the number of catastrophic collisions to 14 within 200 years and lead to a stable 10 cm object population, if 5–10 removals per year are performed (Bastida and Krag 2009; Liou 2011; Klinkrad and Johnson 2013). Several research groups, with different backgrounds and application targets, have devised techniques that could be used for the removal of mass from orbit

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and hence for orbital debris environment remediation. In order to qualify as a remediation measure (as opposed to a mitigation measure), all techniques must be applicable to dysfunctional target objects. Mass removal from orbit has a technical, a financial, and a legal dimension. As of today, many of the suggested solution concepts are not yet sufficiently advanced in their technology readiness, and even the most mature concepts would incur significant costs if they were realized. Moreover, the removal of on-orbit mass that belongs to another launch authority and/or space operator requires mutual agreement on the procedure, on the cost sharing, and on possible liabilities, particularly for an uncontrolled reentry.

Conclusion Out of 16,316 objects that were contained in the US Space Surveillance Network catalog in November 2013, slightly more than 1,000 were operational spacecraft, of which roughly 80 % could be maneuvered. More than 420 of these were in the GEO ring, and more than 300 were in the LEO regime. Since LEO and GEO are of particular interest for space operators, these orbit regimes were denoted as “protected regions” by IADC and UN COPUOS. In order to safeguard a sustainable long-term usability of the LEO and GEO regions, space debris mitigation measures must be applied rigorously by all space-faring nations and supernational organizations. The necessary mitigation measures have been identified, e.g., by the 12 IADC members, and cast into international guidelines and standards, into agency-specific sets of requirements, and into national space laws. Analyses of the long-term evolution of the space debris environment indicate that such agreed mitigation measures are a necessary but insufficient condition to maintain the space object population at a stable level. Even an extreme mitigation scenario with no future launches will result in a long-term collisional cascading (the so-called Kessler syndrome) at some LEO altitudes. This runaway process is fueled by existing mass on orbit, and the only way to stabilize the environment is through active mass removal from particularly densely populated altitude and inclination bands. This is a challenging task from a technical, economical, and legal point of view that can only be successfully implemented if an international consensus is reached among space-faring nations. In the past the Scientific and Technical Subcommittee (STSC) of UN COPUOS, with guidance from autonomous members and contributions from COPUOS members, installed a working group that developed the UN COPUOS Debris Mitigation Guidelines (Anonymous 2009) in the course of a multiyear work plan. Likewise, in 2010, UN COPUOS STSC established a working group on the “sustainable use of outer space.” This initiative could be a starting point for the development of an international framework that could include space debris environment remediation as one of its main objectives. Following the publication of previous reports on “space traffic management” and “space debris mitigation,” the International Academy of Astronautics (IAA) published a report on “space debris environment remediation” in 2013 (Klinkrad

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and Johnson 2013). Its authorship, with more than 20 contributors from 11 different countries and many different disciplines, could further consolidate the basis for international deliberations on the technical, economical, and legal aspects of mass removal from critical orbit regions. Such joint initiatives could prepare the ground for a sustainable and safe use of outer space. The overarching principle of a responsible and sustainable use of space was formulated back in the 1990s by the late Joseph P. Loftus, former assistant director of NASA/JSC: “Space operations should comply with a general rule of the National Park Service: ‘What you take in you must take out’.”

Cross-References ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris

References IADC for Autonomous (2002) IADC space debris mitigation guidelines. IADC-02-01, rev.1 IADC for Autonomous (2009) UNCOPUOS space debris mitigation guidelines. A/RES/62/217, UNCOPUOS Scientific & Technical Sub-Committee Bastida B, Krag H (2009) Strategies for active removal of space debris. In: Proceedings of the 5th European conference on space debris, ESA-SP-672 Flegel S (2010) Maintenance of the ESA MASTER model, final report of ESA contract 21705/08/ D/HK Flohrer T (2014) Classification of geosynchronous orbits – issue 16. European Space Agency, GEN-DB-LOG-00126-OPS-GR, 2014 Johnson NL (2009) The International Space Station and the space debris environment 10 years on. In: Proceedings of the 5th European conference on space debris, ESA-SP-672 Klinkrad H (2006) Space debris – models and risk analysis. Springer-Praxis, Berlin Klinkrad H, Johnson NL (2009) Space debris environment remediation concepts. In: Proceedings of the 5th European conference on space debris, ESA-SP-672 Klinkrad H, Johnson NL (2013) Space debris environment remediation. International Academy of Astronautics (IAA), ISBN 978-2-917761-30-4 Liou JC (2011) An active debris removal parametric study for LEO environment remediation. Adv Space Res 47(11):1865–1876 Liou JC, Johnson NL (2008a) Instability of the present LEO satellite populations. Adv Space Res 41:1046–1053 Liou JC, Johnson NL (2008b) A sensitivity study of the effectiveness of active debris removal in LEO. Acta Astronautica 64:236–243 Oswald M, Wegener P, Stabroth S, Wiedemann C, Rosebrock J, Martin C, Klinkrad H, Vo¨rsmann P (2005) The MASTER 2005 model. In: Proceedings of the 4th European conference on space debris, ESA-SP-587

Nature of the Threat / Historical Occurrence Frederick M. Jonas

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar System Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Late Heavy Bombardment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Earth Impact History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Meteor Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mitigating the Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

The threat of a comet or meteor Earth impact exists and is evidenced by the geologic record of impacts on Earth. More recently is the well-publicized Chelyabinsk meteor airburst that occurred in Russia on February 15, 2013. Explosion was estimated to be on the order of 4–500 kt (TNT equivalent). The resulting airburst explosion resulted in numerous injuries and building damage. Chelyabinsk showed us that the threat to Earth is real. It is also natural. The evolution of the solar system began with mass lumping together, and it is still doing so today. Mass accretion. The Earth is still growing. It will continue to do so in the future. However, this natural order can be hazardous depending on the size of the impactor continuing the mass accretion process. This threat to Earth regarding potentially dangerous impactors must be mitigated. There is a growing international effort and concern, heightened by the Chelyabinsk meteor, to find, characterize, and defend against threatening solar system bodies. The good news is these efforts have begun. They must continue. F.M. Jonas (*) Amateur Cosmologist, Gallup, NM, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_71

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Keywords

Accretion • Solar nebula • TNT equivalent • Late Heavy Bombardment (LHB) • Astronomical unit (AU) • Shoemaker-Levy 9 • Earth impact data • EarthCrossing Objects (ECOs) • Near-Earth Objects (NEO) • Potential Hazard Asteroid (PHA) • NASA • NOAA

Introduction Clearly, the threat of a comet or meteor Earth impact exists as is evidenced by the geologic and recent record of impacts on Earth. Meteor (Barringer) Crater (Fig. 1) in Arizona offers visible evidence of a relatively recent impact that occurred a mere 50,000 years ago. The impactor is estimated to have been a nickel-iron meteorite about 50 m in diameter. This impact resulted in a crater about 1,200 m wide and 170 m deep. To give a broader context, such a crater would have been created from a 10-Megaton (TNT equivalent) nuclear explosion. It should be noted that 10-Megaton TNT equivalent nuclear device is in the range of the largest yield hydrogen bombs developed during the Cold War. Other evidences regarding large impacts on Earth of course include the event that may have contributed to the final demise of the dinosaurs 65 million years ago (the Chicxulub crater). Analysis of the geologic record seems to indicate that the dinosaurs may have already gone extinct by the time of this impact; regardless, this impact sealed the deal and significantly altered the Earth’s environment and weather for many years after. Finally and most recently is the Chelyabinsk meteor airburst that occurred in Russia on February 15, 2013. The latter was estimated to be on the order of 4–500 kt (TNT equivalent). The resulting airburst explosion resulted in numerous injuries and building damage evidenced by the numerous broken windows due to the air-blast shock wave. And if the scant yet convincing Earth impact record is not enough, then all we need to do to convince ourselves that impacts due to meteors and comets occur is to

Fig. 1 Meteor (Barringer) Crater in Arizona

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Fig. 2 The backside of the moon gives visible evidence of impacts across the entire surface

look to the heavens. Most notably, our closest neighbor, the moon, especially the back side, is excessively pockmarked by impacts as shown in Fig. 2. Visible eye evidence shows the scars of multiple impacts. Other airless bodies we have observed in the solar system all bear the same evidence regarding the nature of the threat due to impacts. Their surfaces are literally covered with impact craters of all sizes, preserving a record of impacts over the course of our solar system’s four-and-a-halfbillion-year history. And that history appears to be very violent. More importantly, it appears that impacts are but a natural evolution of the solar system development, growth, and maturity built on the premise of “mass accretion.” That is how the solar system is believed to have evolved, mass accreting and clumping together growing into the Sun, planets, moons, comets, and asteroids, all that we see. And, this is how the solar system will continue to evolve. The threat will remain as long as the solar system exists. It represents the natural order.

Solar System Evolution The solar system is believed to have been borne from a swirling shrinking disk of gas and dust called the solar nebula some 4.5 billion years ago. Now, thanks to the Hubble Space Telescope, there are many recorded and archived evidences of creation and transmutation of nebulas into solar disks (Fig. 3). Ultimately, out of this swirling chaotic mass is borne the solar system. It all began with the process of mass accretion which then was ultimately dominated by gravity as the clumps grew larger. As it is today. As it will continue to be.

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Fig. 3 A solar/disk around Beta Pictoris representative of our early solar system

That mass which clumps together naturally in this environment was vividly demonstrated in space by astronaut Donald Pettit onboard the International Space Station in 2004. His experiment demonstrated that matter ranging in size from 1 μm to 6 mm naturally clumps together in the microgravity environment perhaps due to electrostatic forces, but nevertheless clumps together. This process was also shown to be fast and repeatable. This presented clear evidence of the mechanism that initiated the growth of these “lumps” of matter before gravity begins to take over. The Sun, planets, and all bodies in the solar system then grew based on attracting and accreting the mass around them in the solar disk. A picture of such a solar disk around Beta Pictoris is shown in Fig. 3. This European Southern Observatory (ESO) photograph shows not only the solar disk but a planet (white dot) as well that is most likely suffering numerous impacts in its accretion process. That “accretion” process and gravitational attraction result in what we call impacts today and are occurring in Beta Pictoris as well. And, this process of accretion is never ending. The Sun, planets, and moons continue to gain mass today, albeit slowly. Recent evidence was seen by the entire world in Jupiter’s capture and resulting impacts of comet Shoemaker-Levy 9 in July 1994 (more information on this event is presented elsewhere). Accretion and impacts, with the potential for Earth impacts, will continue indefinitely which is the natural order. In order to estimate the threat, we need to understand the historical record of impacts and when they occurred. From this we can perhaps better predict the future probability of impacts here on Earth and determine if the rate of impacts with time is decreasing as we might expect. In that process, it was discovered that a significant and surprising increase in the impact record occurred some 3.9 million years, well into the solar system development some 600,000 years after the formation. That period of time has come to be called the Late Heavy Bombardment (LHB). Understanding why that occurred is important to our ability to predict and understand the nature of future impacts.

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Late Heavy Bombardment All was proceeding in an orderly “chaotic” fashion in those first few hundreds of millions of years of formation in the early solar system. The first clues that this orderly “infinitely chaotic” process was interrupted about 3.9 million years ago came from the moon. The clues seemed to indicate that during a relatively short period of time, there was a huge increase and spike in the number of surface impacts. Examinations of Apollo moon rocks showed evidence that nearly all the craters in the lunar highlands formed during a brief period of time, approximately 100 million years long. Based on their age, this appeared to be 3.9 million years ago. During this period of massive impacts, it is estimated that nearly 2,000 impacts (resurfacing 80 % of the moon’s face) were larger than the Chicxulub meteor impact that coincided with the end of the dinosaurs. The resulting crater in the Gulf of Mexico near the Yucatan Peninsula centered near the town of Chicxulub is approximately 110 miles in diameter that resulted from a meteoroid estimated to have been 6 miles in diameter. The Earth, being a bigger target than the moon, is estimated to have suffered impacts 10 times more severe covering every square inch of the Earth during this same period. That qualitative increase in the number of impacts during this period is graphically depicted in Fig. 4 and is called the Late Heavy Bombardment (LHB). Up until the evidence began to accumulate in favor of the LHB, the solar system was thought to have operated with clockwork precision once the planets were formed. There were however other clues that this picture was not as it seemed. Pluto exists in an oddball elliptical orbit that is inclined almost 12 to the solar equator. Further, it is locked in a curious resonance with Neptune, orbiting the Sun twice for every three orbits of Neptune. Uranus has been knocked on its side with its north and south poles nearly aligned with the solar system’s orbital plane, an axial tilt of nearly 98 . Saturn orbits the Sun once for every two orbits of Jupiter. And, in the Kuiper Belt, numerous rocks and frozen objects have been found with wildly

Fig. 4 The Late Heavy Bombardment (LHB)

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different orbits. Remnants of the solar system development, the Kuiper Belt is a defined region beyond the planets of the solar system starting at Neptune (30 astronomical units (AU)) out to 50 AU from the Sun. This belt consists mainly of small bodies composed of frozen volatiles and includes bodies like the planet Pluto. Emerging theories of solar system formation had planets like Neptune and Uranus forming closer to the Sun. From this evidence, it appeared that something very disruptive had happened in the early solar system. Making matters more disconcerting, discoveries of planets around other stars were showing wildly different planetary systems with Jupiter- and Neptune-like planets racing around their Sun in scorching orbits with observed orbits of other planets being wildly eccentric. The “orderly” chaos is evident in these numerous observed systems. Perhaps our view of a clockwise system was simplistically reflecting our view then of the assumed stability and infinite unchanging universe. However, the evidence was piling up in favor of the LHB. The mounting evidence showed that some type of chaotic event occurred during this time period resulting in the solar system we see today. What had happened during this time period? One way to perhaps answer such questions is to employ computational models and simulations that obey the laws of physics as we understand them. That approach bore fruit in this case. A sophisticated computational model, called the Nice Model, developed in 2004 provided results that began to shed light on these mysteries. Hal Levison (Southwest Research Institute) (Reference) and three coworkers, R. Gomes, Alessandro Morbidelli, and Kleomenis Tsiganis, were the principal developers of the Nice Model. The developers were motivated by trying to understand the orbital eccentricities of Saturn and Jupiter and how Uranus and Neptune could have formed so far from the Sun in a theorized region of space that did not support their development. The culprit behind the LHB appeared ultimately to be Jupiter. The model begins with the assumption that Neptune, Uranus, and Saturn had formed closer to the Sun in nearly circular orbits as confirmed by many other theories. The computational results of their simulation showed that as Jupiter and Saturn locked into their 2:1 resonance about 500–700 million years into the solar system development, once linked, Neptune and Uranus were hurled violently outward to their present locations. Neptune then locked into the resonance with Pluto as we see today. In about half of the simulations, Neptune and Uranus swap places. Regardless, the violent sudden motions of these giant planets and resulting gravitational disturbances throughout the solar system caused chaos in the asteroid and Kuiper Belts, extending even into the Oort cloud. Named after Dutch astronomer Jan Oort, the Oort cloud is a hypothesized spherical cloud of icy bodies 5,000 A.U. to 100,000 A.U. from the Sun. 50,000 A.U. is approximately one light year. As noted earlier, Pluto at its farthest is slightly less than 50 A.U. from the Sun. The Oort cloud is estimated to contain 100–200 billion icy bodies and is believed to be the source of long-period comets. The entire solar system felt the effects of these massive gravitational disturbances. While sending bodies in all directions, many headed towards the inner solar system. The resulting violet bombardment of the inner planets (and moon) was brief on geologic time scales, lasting an estimated 100 million years according to the

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model. Since then, we have returned to a “clockwork” solar system, and impacts have decreased with time as one might expect. However, what we have learned from this model prediction and observations of other solar systems is that the clockwork system can be disrupted with catastrophic results.

Earth Impact History The majority of impact craters on Earth have long been erased with time due to tectonic shifts, geological surface activities, wind, and rain erosion. However, there are enough remaining Earth impact traces such as the Barringer Crater in Arizona to conclude that mother Earth is quite vulnerable to impacts. We are not immune. The Earth Impact Database (http://www.passc.net/EarthImpactDatabase/) provides a list of confirmed impact craters such as Meteor Crater. It is maintained by The Planetary and Space Science Centre (PASSC) located at the University of New Brunswick (Canada). From their web page: “TheEarth Impact Database (EID)is a collection of images, publications and abstracts from around the world (compiled over the last 25 years) that provides information about confirmed impact structures for the scientific community and space enthusiasts.” And, “The Earth Impact Database (EID) comprises a list of confirmed impact structures from around the world. To date, there are 184 confirmed impact structures in the database.” The following is a review of a few of the more interesting Earth impact craters: • Suavj€arvi Crater (Fig. 5): The oldest known crater is estimated to be approximately 2.4 billion years old. Definitely formed well after the LHB. Estimated to be 16 km in diameter, it contains the Suavj€arvi lake at its center (approximately 3 km in diameter). The crater is located about 50 km north of Medvezhyegorsk in

Fig. 5 Vredefort Dome

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Fig. 6 Chesapeake Bay crater

the Republic of Karelia, Russia. Not much of the crater survives today, and it was identified principally through the resulting impact shock formations in the surrounding geology. • Vredefort Crater: The largest Earth impact crater with an estimated diameter of 160 km just edges out the Chicxulub crater at 150 km. The Vredefort crater is located in South Africa and is estimated to be just over two million years old. It is also the second oldest crater known. The town of Vredefort is located near the center of the crater. Evidence of impact (shock formations) was again noted in the surrounding geology confirming the crater as due to impact and not volcanic as originally thought. The body creating the crater is estimated to have been somewhere between 5 and 10 km in diameter. While common throughout the solar system, Vredefort is one of the few multiple-ringed impact craters on Earth. • Chesapeake Bay Crater (Fig. 6): The largest known impact crater in the United States. With a diameter of 40 km, it is the sixth largest in the world. Estimated to have occurred about 35 million years ago, the site was confirmed as an impact crater in the 1990s again based on evidence of a layer of fused glass beads (shock heating). While buried with time, the crater created a long-lasting topographic depression ultimately determining the eventual location of Chesapeake Bay. The size of the body that created the crater is estimated to have been between 3 and 5 km.

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Fig. 7 Wolfe Creek Crater

• Wolfe Creek Crater (Fig. 7): Another crater as well preserved as Barringer (Meteor) Crater. Barringer Crater is located in the desert of Arizona. This crater is also located in a desert. The lesser known Wolfe Creek Crater is located in the north-central desert of Australia. It is also the second largest rimmed crater in the world, second again to the Barringer Crater. Estimated to be about 300,000 years old, the crater is 870 m in diameter and 60 m deep. It is located 150 km south of Halls Creek in Western Australia. While most of the preceding has assumed solid impactors, we must not forget about the threat due to comets. Visible evidence of the reality of that threat was seen by the world in July 1994 with the impacts of the remnants of comet ShoemakerLevy 9 with Jupiter (more is presented elsewhere on this comet). Comet Shoemaker-Levy 9 presented to the world the first direct visible observation and proof of extraterrestrial impacts with other solar system bodies. Another highly suspected and highly controversial impact perhaps due to a comet is the Tunguska event that occurred over remote areas of Siberia in 1908. The best theories regarding this event pose an airburst at 5–10 km altitude due to either a small asteroid or comet about 60–190 m in diameter. If so, it is the largest impact on Earth in recorded history. Fragments have been found at the site that may be of meteoric origin. The blast is estimated to have been in the range of 10–15 megatons of TNT based on the level of destruction that occurred over 2,000 km2 of the forested area (over 80 million trees were estimated to have been toppled). Following the event, while unknown to most of the world at that time, glowing sunsets were reported. Natives and Russian settlers near the burst reported a bright bluish light moving across the sky, a flash, than artillery-like sounds rumbling in the distance. Those closer to the blast were knocked over by the blast wave. Seismic stations across Eurasia recorded the event, and atmospheric fluctuations were recorded in Great

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Britain. The first recorded expedition to the site was in 1921, years after the event, but the evidence for an airburst was and is overwhelming. No crater has been found. A similar well-publicized but much smaller airburst occurred in February 2013 over Chelyabinsk (Russia) resulting in numerous injuries from the air blast and resulting blast (shock) waves. Thus, whether a comet or a meteor, impacts have occurred on Earth. Being the natural order of how this solar system grew and evolved, the threat of Earth impact remains and will continue indefinitely.

Meteor Hazards In order to understand and assess the impact hazard accurately, one must be able to characterize and quantify attributes including size, distribution, and orbits of these near-Earth objects (NEOs) or those objects with orbits that regularly come close to the Earth orbit (those that intersect Earth’s orbit are called Earth-crossing objects (ECOs)). There is a significant effort by NASA and other institutions around the world, including an international effort led by the U.N. to identify and catalogue such heavenly bodies. It is a tedious skywatching activity and understood to underscore the survivability of human race as we know it and cannot be taken seriously enough. As might be expected, amateur astronomers play a huge role in this vigil. The results of this international community effort have shown to date that as expected, there exist many more small NEOs than large ones. Figure 8 is a NASA graphic showing potentially hazard asteroid (PHA) orbits numbering over 1,400 objects. We are of course interested in finding the most dangerous bigger NEOs first. It is estimated that there exist approximately 1,000 NEOs larger than 1 km in diameter and a 1,000 times that number, one million, greater than 40 m in diameter. While there may be many more comets, they are generally in orbits where they spend great distances from the Sun and are estimated to only contribute 1 % to the Earth-impact hazard. By 2013, more than 10,000 NEOs have been discovered, and as our ability to observe these objects improves, that number will only increase. Overall, it is estimated that over one million NEOs exist that could cause damage to the Earth from impact. None yet have been found that poses an immediate threat. The latest numbers, known sightings, and predicted orbits of these objects can be found at http://neo.jpl.nasa.gov. Small meteors, rocks and ice, and bits of space dust are striking the Earth daily. The Earth’s atmosphere protects us from most of these impacts creating colorful displays in the sky as “falling stars” with an occasional fireball. The Earth’s atmosphere protects us from most objects up to 40 m in diameter. Beyond that, the actual likelihood of a dangerous impact is small and much less than the risk from natural terrestrial hazards such as earthquakes or storms. Regardless, if large enough, impacting meteors or comets have the potential to end life as we know it and could perhaps lead to the extinction of the human race. Bodies with a diameter greater than 40 m and up to a kilometer in diameter entering the atmosphere can

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Fig. 8 Dangerous asteroid orbits visualized near Earth

cause severe local damage (e.g., the Tunguska event). Those 2 km in diameter and up, like the Chicxulub meteor, can result in mass extinctions and worldwide disturbances to the environment and weather. More importantly, massive impacts by objects such as the Chicxulub meteor, impacting in water, will create massive tsunamis. Wave heights created in such impacts would be hundreds of meters, compared with tens of meters for some of our recent worst tsunamis (Indian Ocean and Japan). Imagine the devastation such impacts would wreak. Most of civilization lives near the shore. Waves this immense would continue inland for significant distances. And the Earth is 70 % water. Chances of a water impact are much greater. Thus, while large impacts may be rare, the consequences can be severe. The lunar record of impacts shows that the frequency of impacts decreases with roughly the cube of the crater diameter, which in turn is related to the impactor size or diameter. It is estimated that for meteors 2 km in diameter or larger, impacts occur once every 100 million years and those 1 km in diameter every 500,000 years. The risk due to airbursts, however, may be higher than previously thought. The recent Chelyabinsk meteor, a suspect blast near the Prince Edward Islands off the coast of South Africa in 1963 (an estimated 1.1 megaton TNT equivalent blast), and the 1908 Tunguska event suggest that the risk due to incoming small space rocks is much higher than the risk assumed based on astronomical observations. Further, computer simulations of these events suggest that they are more damaging than equivalent nuclear explosions of the same yield. And, the frequency of these events is more difficult to estimate since they leave little or no impact evidence on the

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ground. Based on these recent airburst impacts, it is believed by many that the next destructive impact will be an airburst. Finally, an associated man-made risk associated with such an airburst may be that such an event is actually misinterpreted as a nuclear attack. The Chelyabinsk meteor came out of the Sun, undetected. If it had been a cloudy day, the bright explosion, blast wave, and artillery-like sounds in a different part of the world where nuclear tensions might be high might be interpreted as such. Even if on a clear day, the streaking meteor could have been seen to be an entering nuclear armed reentry vehicle. The Prince Edwards Islands blast could also be interpreted as a nuclear blast and was in fact detected by networks designed to detect nuclear blasts during the height of the Cold War. While perhaps extreme examples of playing the “what-if” game, this simply illustrates the need to better track and characterize objects near the Earth that potentially pose a hazard due to impact. Without knowing the source, the blasts themselves can be easily misinterpreted and perhaps lead to greater catastrophe. The recent update from the Nuclear Test Ban Treaty Organization’s (CTBTO) International Monitoring System (IMS) that reported it had detected 26 nuclearlevel explosions caused by asteroid air impacts from the year 2000 through early 2014, however, indicates greater frequency of asteroid impact than had been previously thought.

Mitigating the Hazard There is a growing international effort and concern, heightened by the Chelyabinsk meteor, to find, characterize, and defend against these threatening solar system bodies to include the recent formation of an International Asteroid Warning Group by the United Nations General Assembly. And, there is information now posted on the Internet concerning NEOs. Notable sites include the NASA Near-Earth Object Program site at http://neo.jpl.nasa.gov/, the NOAA Space Weather Prediction Center site at http://www.swpc.noaa.gov/, and the spaceweather.com site at http:// spaceweather.com/ (Tony Phillips, a NASA astronomer, runs the unaffiliated spaceweather.com website). Information concerning the latest on the NEO threats to Earth is presented at these sites. For example: • Information on the numbers of NEOs are presented at the NASA NEO Program site as shown in Figs. 9 and 10. It is believed that over 90 % of NEOs larger than 1 km in diameter have already been discovered (shown in red in Fig. 9). Those NEOs of course pose a significant threat to our civilization if they were to impact the Earth. Thankfully to date, there are none to worry about in the immediate future. The effort is now focused on finding 90 % of the population larger than 140 m. Figure 10 shows the numbers discovered by estimated diameter. Still a ways to go yet before we get to 40 m in diameter (where the Earth’s atmosphere takes over), but we are getting there as our observational capabilities improve. The dramatic improvement in our capabilities is graphically illustrated in Fig. 9 starting about the year 2000. Significant to this activity are the world’s amateur

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Fig. 9 Known near-Earth asteroids

Fig. 10 Known near-Earth asteroids by size

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848 Table 1 Recent and upcoming Earth-asteroid encounters (spaceweather. com). LD is lunar distance=384,401 km (0.00256 AU), the distance between the Earth and the moon

F.M. Jonas Asteroid 2013 XH17 2013 XYB 2013 XS21 2013 XT21 2013 XU21 2011 YD29 2007 SJ 2012 BX34 2006 DP14 2000 EM26 2000 EE14

Date (UT) Dec 11 Dec 11 Dec 11 Dec 11 Dec 14 Dec 28 Jan 21 Jan 28 Feb 10 Feb 18 Mar 6

Miss distance (LD) 7.1 2 0.2 1.1 6.2 6.1 18.9 9.6 6.2 8.8 64.6

Size (m) 37 50 6 15 26 24 1,900 13 730 195 1,800

astronomers who provide daily input on the numbers and orbits of these potentially threatening objects. • Daily updated information on potentially hazardous asteroids (PHAs) is presented at the spaceweather.com site. PHAs are defined as objects larger than 100 m in diameter that come within 0.05astronomical units (AU) of the Earth. The good news is that no known PHA is on a collision course with Earth, but new ones are being found all the time. As of 15 December, 2013, there are 1446 PHA encounters. Recent and upcoming Earth-asteroid encounters are listed daily as duplicated in the following table (Table 1): Finally, numerous innovative ideas are being developed throughout the world to defend the planet Earth against such catastrophic threat. The key to successfully defend Earth is to identify the threat, i.e., the heavenly body with an Earth-crossing orbit, well before it gets near the Earth orbit. After that, the threat can be mitigated by imparting an infinitesimal delta velocity so that the net momentum of body is altered ever so slightly and hence its trajectory would veer-off away from the Earth orbit. There are several proposals on imparting a delta velocity to a fast-moving asteroid; using space mirror to blow off mass from the asteroid or detonate a device in its path where the detonation product would nudge it away, run right into it hence perturbing its trajectory. More elegant solutions include the use of gravity, the great nemesis causing the problem, to work for us instead of against us. Such concepts involve using a satellite and its mass to perturb the objects orbit enough to miss Earth. Given sufficient time, this gradual tugging could be used to shape the orbit so that it comfortably misses the Earth now and into the future.

Conclusion The more warning time the better, and thus, the international effort and collaborative activities amongst the world’s astronomers, including the ever-important amateur astronomers, are crucial to making sure we identify any potential threat

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as soon as possible. As the former New York Yankee Hall of Fame (baseball) player Yogi Berra once said, “you can observe a lot by just watching.” That is just what we are doing, watching, and we are getting better at it. The solar system is not a static environment as we have seen. Disturbances to orbiting bodies can and do occur on a continuous basis, and we must be continually observing the heavens to make sure these bodies do not pose a hazard to Earth. If they do, then we must be ready to deal with and mitigate that threat. It is after all ultimately a matter of survival.

Cross-References ▶ Defending Against Asteroids and Comets ▶ Directed Energy for Planetary Defense

References Irion R (2013) It all began in chaos. Nat Geosci 224(1):42–59 Lakdavalla E (2011) Pummeling the Planets. Sky Telesc 122(2):20–27

Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris Joseph N. Pelton

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Key Concerns and Threshold Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Threshold Question Number 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Debris Removal Fund . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Next Steps Forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Economic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Legal Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bounding the Size of Space Activities in Terms of Their Economic Import . . . . . . . . . . . . . . . . . Various Space Activities and Their Economic Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Users of Different Orbits: Why They Would Pay Differing Amounts in the Fund? . . . . . . . . . The Costs of Space Situational Awareness Versus the Costs of Orbital Debris Removal . . . Key Steps Forward Concerns Orbital Debris Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feasibility of Establishing a New International Entity for Active Debris Removal . . . . . . . . . . The Value of Earth Orbit to Humanity and Future Space Commerce . . . . . . . . . . . . . . . . . . . . . . . . Micro- and Nano-satellites and Orbital Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis of Different Means and Ways for Solving the Space Debris Problem . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

The topic of cosmic hazards is most closely associated with comets and asteroids that might crash into Earth with devastating effect. The truth is that in the nearer term adverse solar events might threaten Earth with powerful coronal mass ejections that could also result in a number of disaster scenarios. When these catastrophic events are the focus, the more modest issue of orbital debris is

J.N. Pelton (*) International Association for the Advancement of Space Safety, Arlington, VA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_70

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clearly seen as far less threatening. But the truth is that orbital debris also constitutes serious hazards to future human progress and safety in many different ways. Orbital debris will have an increasing chance of disabling critical satellite infrastructure – particularly in low Earth orbit – that can jeopardize critical services and in the case of major collision escalate the buildup of orbital debris even further. Orbital debris is nothing like the threat to life on Earth of say a category 10 asteroid on the Torino Scale colliding with Earth (“the Torino Impact Hazard Scale”), yet this hazard represents a serious problem to the long-term sustainability of space operations that will only get worse unless an active program to undertake debris removal is initiated. Most of what is written about space debris focuses on their characterization in terms of size number and orbital mechanics, the space technology needed to remove debris from orbit, or relevant regulatory issues. Technical papers such as the chapter written by Dr. Heiner Klinkrad describe such aspects as the growing extent of the problem and the factors that are contributing to the rate of buildup of debris. Other chapters of a technical nature often address the very important issue of the best approaches that can be used for debris removal and remediation. Regulatory papers, such as the chapter by Dr. Ram Jakhu and Dr. Fabio Tronchetti, on the other hand, address the current “due-diligence procedures” that are aimed at preventing or minimizing the creation of new debris. They also consider the questions of liability and legal responsibility and efforts aimed to create new regulatory processes within the UN system to control debris and/or remove debris from orbit. The focus of this chapter, however, is on examining the merits of establishing national, regional, and in time perhaps universal agreements to establish economic funds or entirely new international cooperative mechanisms to oversee the removal and mitigation process. The purpose of such a new international entity or international fund would be manyfold. Such mechanisms or economic processes would create financial incentives both to prevent new debris from occurring and for the removal of existing debris. It would create a recognized international process for active debris removal that would be consistent with existing UN treaties and to which all countries would be able to respond. Such an active response would be in recognition of the incentives for active debris removal as well as penalties associated with either the creation of new debris or not supporting the removal of debris. The ability to create universally accepted new international mechanisms to undertake such tasks as active debris removal is more difficult than it was several decades ago. This is due to the ever-increasing number of nations who are now within the UN system and that now participate in COPUOS, the lack of a cohesive support for coordinated world initiatives – such as existed immediately after World War 2 – and the divergence of world economic, political, and strategic interests in outer space. This divergence of views is particularly noticeable in the outer space arena since this sector is often associated with military and strategic applications on the part of many spacefaring nations. This divergence of views suggests that any new international arrangements related to

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the active removal of orbital debris will most likely follow an evolutionary path. In short, any longer-term international consensus to address the orbital debris problem will most likely be developed slowly over time. Since the key UN space treaties were developed in the 1960s and early 1970s, no major new space conventions have been agreed since. This chapter thus discusses possible evolutionary processes – led by economic mechanisms or active mitigation and removal techniques that directly reduce the orbital debris buildup. These processes are most likely to start – at the national and regional level and ultimately transition to the global level as time goes by. This might lead to longer-term efforts to create an international mechanism or organizational mechanism to address not only the space debris problem but perhaps other space operations issues such as commercial space flight safety, space traffic management, space and improvement in the nearEarth space environment, etc. (Jakhu et al. (2011) The need for an integrated regulatory regime for aviation and space: an ICAO for space? Springer Wien, New York).

Keywords

China • Debris mitigation • Debris removal Europe • France • GEO orbit • InterAgency Space Debris Coordinating Committee (IADC) • International Telecommunication Union • Intelsat • Japan • Kessler syndrome • LEO orbit • MEO orbit • Office of Outer Space Affairs (OOSA) • Russian Federation • Space debris • Space debris mitigation • United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) • United States • Upper stage rockets

Introduction Space applications have become a very diverse and increasingly important aspect of modern global society. Over time-space applications have expanded in scope, divided into many submarkets, and have evolved into a series of many different “space actors.” These include civil governmental space agencies, defense-related space agencies, commercial launch operators, operators of various commercial spacecraft organization, and even public service space operators that are operated by both commercial and nonprofit organizations. The various governmental, defense, and commercial space markets are today quite large with all related annual space applications, expenditures, and revenues totaling perhaps $400 billion (US). The true impact of space activities is not simply a function of their economic size, however, but rather their overall impact on society. Space-related activities today relates to national security; the monitoring of possible attacks via nuclear-armed missiles; the use of space navigation to control transportation (including the takeoff and landing of aircraft); the deployment of satellites for voice, data, and television communications; and the use of satellites to forecast weather and avert the impact of hurricanes, typhoons, and other violent

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weather. There are many remote sensing operations that observe the Earth to detect natural resources, conduct fishing operations, monitor oil spills, and chart the impacts of climate change. These remote sensing have a variety of public service and commercial goals as is the case with telecommunications satellites, remote sensing, meteorological, navigation satellites, and other types of application satellites. In recent years the proliferation of orbital debris associated with space activities has raised serious questions about the sustainability of human space activities going forward. In 1980 there were just under 5,400 sizeable objects in space being tracked; by 2010 this number of large space debris objects had increased to 15, 639 and currently it is over 22,000. There is also substantial buildup of microelements too small to track (under 4 cm in diameter). There are perhaps 750,000 space objects the size of 1 cm or larger and millimeter-sized space debris now numbers in the millions. The threat of the so-called Kessler syndrome whereby space debris collides in a cascading manner to create more and more debris has now become a truly serious concern (“New Debris Tracking.” 2012). Despite the guidelines developed within the Inter-Agency Space Debris Coordinating Committee (IADC) and the UN COPUOS to limit new debris, the reality is that there is, in fact, a continuing formation of additional space debris. This continued creation space debris is due to many factors. These factors include, among others: (i) hardware degradation; (ii) collisions involving existing debris and various space objects; (iii) continued deployment of all types of satellites that by a certain percentage fail to be disposed or safely removed when they become defunct; (iv) large, medium, and small upper stage rockets that remain in orbit; and (v) explosions of pressurized tanks and batteries. Mitigation of space debris creation is a condition necessary but no longer sufficient to stabilize the orbital debris environment. Major junks, like defunct satellites and spent upper stages, are those that in a way or the other will generate in time a multitude of smaller debris. They must be therefore the primary target of active removal efforts. If the buildup of space debris is not curtailed and instead continues to increase, then all future space activities could eventually become impossible, and all future space applications, scientific missions, and space exploration could quite simply become unsustainable. When most people think about cosmic threats, they perhaps first think about threats from comets, asteroids, or powerful space weather eruptions from the sun, but orbital debris increasingly poses a risk to the continued successful operation of the world’s extensive satellite infrastructure. Uncontrolled falling space debris poses real threats to air and land safety as well.

Key Concerns and Threshold Questions There are a number of key threshold questions that world leadership must consider with regard to orbital debris and its removal from Earth orbit. Threshold Question Number 1: Can better design and engineering for spacecraft and launch vehicles plus new due-diligence procedures as developed by the

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UN COPUOS, the International Telecommunication Union (ITU), and the InterAgency Space Debris Coordinating Committee (IADC) sufficiently mitigate the spread of space debris going forward with enough effectiveness that new regulations are not needed and active removal of space debris will not be required? Response Number 1: The short answer clearly appears to be no. The truth is much more needs to be done! Despite guidelines and due diligence the rise of space debris continues to rise. Computer modeling that forecasts future amounts of space debris projects a continuing buildup of orbital space debris especially in polar and low Earth orbits that are crucial to remote sensing, meteorological, and other satellite applications. Such projections may, in fact, underestimate the threat. This is because these models may not fully take into account battery explosions, fuel tank explosions, buildup due to natural causes such as mini-meteoroids striking satellites, etc. Procedures to mitigate debris need to be made mandatory and backed by financial incentives (or penalties) to ensure compliance, plus concerted efforts made to finance active debris removal. Otherwise orbital debris buildup will continue to increase and become ever more difficult to deal with in future years. The choice is to pay now or pay much more at a later date. This applies to pollution on the Earth and it applies to pollution in space. Threshold Question Number 2: Is there a cost-effective and reliable method to ensure the effective deorbit of space debris from Earth orbit in the years ahead. Response Number 2: Again the answer is no, but progress is being made. Today the processes are generally fairly expensive and often unreliable. Current processes and technology need to be improved and/or new capabilities developed. Passive systems that can be deployed at end of life like balloon or kitelike devices can create drag to bring satellites down earlier than would otherwise be the case. Active plasma jet systems now in development seem promising as a reliable system to deorbit smaller satellites in low Earth orbit. One of the larger problems is constituted by medium Earth orbit that need large amounts of fuel to be successfully deorbited at end of life. (Typically medium Earth orbit satellites require a 40 % add-on of fuel just to deorbit at end of life.) Active removal systems for larger derelict satellites or rocket upper stages represent the largest technical challenge. Removal systems of this nature are today unproven, expensive, and in need of extensive further research and development. Threshold Question Number 3: If better processes for active removal of space debris objectives from Earth orbit could be developed, who would be authorized to undertake such deorbit operations and who can designate orbit debris as appropriate for removal from Earth orbit? Response Number 3: Today there is much discussion about the fact that no entity exists with the authority to designate satellites for removal. Even if a nation designates a “space object” as debris without maneuverability, that nation still remains liable for any damage associated with deorbit. Further, much concern is expressed that many of the processes designed to achieve removal could be considered equivalent to the deployment or use of space weaponry. The use of such processes, is argued, that could have possible military applications is thus likely to be opposed in the international community.

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The discussion should be approached by a completely different angle. The nationality of each major piece of debris currently orbiting Earth is known with absolute certainty. Therefore, the countries with major debris now in orbit should have a primary concern, and indeed responsibility, for the gradual removal of their own debris. This sounds straightforward, but, in fact, it is not. Under the current liability convention as adopted by the United Nations, it is the launching country of record that is responsible, even though commercial organizations, international consortia, or a joint effort of several space agencies or research institutes may have been the ones who designed and arranged for the launch and operation of the derelict satellites. In other words, a number of other organizations, other than the launching states, may actually been involved with improper action such as not deorbiting a satellite or not degassing a hydrazine tank in a timely manner or some other critical operation that would have lessened the debris problem (Wired 2010). Clearly a removal mission can be made cost-effective by removing in sequence a number of space debris which may belong to different countries. In such case realizing missions as international cooperation, bilateral or multilateral, can effectively address the legal concerns, while reducing procurement costs. Furthermore, the development of capture systems through international cooperation, possibly on commercial basis, would eliminate, or at least minimize, the military concern of technological advantage in a dual-use technology. This point remains as a major issue to be addressed and as such will be discussed later. The key objective still remains as to how a market for such removal services could be created and how to provide incentives for voluntary removal within such a market.

Threshold Question Number 4 A number of coordinated actions are needed to move ahead with active debris removal. Liability provisions for “space objects” may need to be updated and modified. Indeed space debris needs to be defined so that there is a widely shared understanding of what this term actually means. Different regulatory provisions with regard to launch and deorbit for low, medium, and geosynchronous orbits need to be made with regard to removal activities. Certainly it would best if such provisions could be made mandatory rather than merely voluntary. If mandatory provisions could not be devised and implemented, then perhaps these could be achieved through a system of incentives and/or financial penalties forming the enforcement process. The problem is that various types of solutions and corrective actions are today entirely hypothetical. The establishment of a “fund to support debris removal is just one approach. It may be that spacefaring nations or a spacefaring region such as Europe may chose direct action through their national space agency to remove debris and not seek to create specialized financial mechanisms such as a fund to relate removal to all types of forward-looking space activities. The United States is already paying through national taxes for advanced space situational awareness tracking capability. Although the new “S-band radar

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Space Fence” that would have cost many billions of dollars more has been cancelled due to budget cuts imposed by the so-called sequester process, its expenditures on already elaborate space- and ground-based tracking capabilities remain quite high. Thus, spacefaring nations may decide that financial mechanisms involving the commercial users of outer space and creating incentives for contractors to remove orbital debris is too complicated or unnecessary to address the orbital debris problem. This direct action approach on a governmental space agency basis would also presumably be premised on the idea that due-diligence prelaunch activities would be sufficient to ensure that future debris will be removed. At this time, however, some form of financial mechanism or direct action by national governments seems more likely than the creation of an international space debris removal entity. In the following sections the way ahead to support the removal of the space debris by various means will be discussed. One possible solution would involve the so-called space debris removal fund which would provide the financial resources for removing space debris.

Space Debris Removal Fund One of the possible solutions that could help address active space debris efforts might involve as initial step the creation of a space debris removal fund. This might be done first at a national or regional level and might occur in parallel with technical demonstrations of space debris removal capabilities. Such an economic mechanism or fund should be brought into place as soon as possible. This is simply because the problem continues to worsen. The fund (or series of national/regional funds) could be established over time in an “organic manner” with countries forming such a fund on a national basis – or perhaps for Europe as a region. This type of national, regional – and in time ultimately universal – fund would be formed by space actors for the specific purpose of addressing the space debris issue. The creation of such funds could represent a proactive “forward-looking” approach to financing a solution to the problem rather than seeking a “backward-looking” approach to addressing space debris formed in the past wherein no financing mechanism was in place. The money to capitalize this type of space debris fund would be collected prior to all launches and would capitalized in an amount equivalent to perhaps 5 % of the total cost of various space-related missions. This fund would be collected for a period of perhaps 25 years but would have a sunset provision on the premise that re-mitigation of orbital debris could perhaps be successfully accomplished over this length of time. Such a fund (or network of funds) would be formed by means of a specific assessment paid into a designated bank account (or space insurance company or some other designated entity/entities) prior to launch. This fund would apply to all those deploying spacecraft into Earth orbit or if on a national or regional basis, would apply to all launches from that country or region. Organizations launching

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satellites beyond Earth orbit would also pay into the fund but at lesser rate. After each launch there would be a partial rebate assuming it was a certified as a clean “debris-free” launch as independently verified. Such a clean launch would require that the upper stage rocket would be actively deorbited and no residual debris created. When a spacecraft reaches its end of life and is then actively deorbited or successfully placed in a graveyard orbit, there would be a further rebate. The size of the rebate for a “clean launch” and “successful disposal” would be specified at the time the fund(s) were established. The rebate formulas could be updated over time at suitable intervals. Approximately half of the payments into the fund, however, would also be retained to compensate those entities involved in removing “officially designated” debris from orbit or moving defunct space objects to a graveyard orbit. The prime purpose of the national, regional (or hopefully universal global) space debris fund would be to compensate those entities “licensed under an appropriate regulatory framework” to remove debris from Earth orbit. It is possible that small fractional part of the fund could also help fund activities related to operating systems to avoid collisions (Pelton 2012). This licensing process for entities designated to undertake orbit debris removal or collision avoidance activities might, for example, be formally assigned to the UN Office of Outer Space Affairs or in time spelled out in a new international space convention. Other entities might also be “licensed” by the UN Office of Outer Space Affairs to undertake activities associated with the prevention of space debris or space debris mediation or collision avoidance activities separate from the active removal of space debris from orbit. Such activities, however, would be limited to no more than a set percentage of the available funds – such as no more than 5 % of the total available funds after rebates were paid. Payment into this fund would “seem and feel” to satellite operators and governmental space agencies conducting space operations very much like buying launch insurance for a spacecraft mission. Indeed the fund could possibly be administered by launch insurance companies. These payments would be different in that it would only represent about a third of the cost associated with purchasing launch insurance and rebates would eventually return half of the money paid into the fund. Further, the projected end date for the fund would establish a very real goal for accomplishing “a largely space debris-free world.” The creation of this fund and the rebate payments would reverse the current incentives that actually “encourage” the increase of orbital debris. Under current space law the owners and operators of space objects not only lack an incentive to remove their space debris from orbit; they actually face substantial financial penalties if the removal process somehow adversely affects another space object and create liabilities for which they are compelled to pay (Listner 2011). The payments into the fund are considered to be modest in comparison to the costs of postponing the removal process, since the cost of removal will only spiral upward. If the Kessler syndrome stage is ultimately reached and debris continues to

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cascade out of control, the cost of active debris removal might truly soar into levels that might involve trillions of dollars (US) (“Space Junk Problem”). Payments for launch insurance operations over the last three decades have widely varied from a low of about 6 % of total mission costs to as much as 20 % of total costs. If one considers this wide range of payments for launch insurance, the threat that orbital debris represents to all future space activities, and the cost of debris removal, it can be reasonably argued that a 5 % payment into an orbital debris fund is not excessive. This seems even for reasonable when consideration is given to the process of rebates after a clean launch and a further rebate when spacecraft is deorbited. One of the issues for particular further consideration is whether there should be a minimum payment related to small or nano-satellites. It is hoped that in time there would be a new international agreement reached concerning small satellites. This might provide for one of three provisions to be made for such small satellite launches. Option one would be for a passive deorbit capability at end of life. Option two would be an active deorbit capability at end of life. Option three would be for the small satellite to fly as a multi-mission vehicle with deorbit or on board a space station with subsequent controlled return or deorbit (Jakhu and Pelton 2014). If one considers the problem of orbital debris as akin to dangerous shoals on which ships are wrecked, then the logic of a fund to remove orbital debris becomes quite clear. No one ship owner wants to pay for a lighthouse and no one space mission wants to pay for all debris removal. A collection of funds associated with all future missions that is developed in a manner so that is seems quite the same as paying for launch insurance can thus be viewed as much like all ship owners contributing to the building of a lighthouse network. Another analogy that might be even closer would be for tax payers to pay for the cost of a super fund to clean up a toxic waste site (Schons 2011). The challenge would be to get this started in a serious way so that it gains traction and coincides with the development of suitable and cost-effective technology that can achieve active debris removal. The further advantage of the fund approach is that there could be a number “licensed entities” authorized under UN guidelines and approvals to be designated to undertake the removal process. Overall it is believed that the “economic fund” mechanism could help to create all the right incentives in the following ways: (a) reward to launching entities for a clean launch; (b) a further reward to operators for removing debris properly at end of life; (c) the “sunset provision” would establish a specific goal to get the job done; and (d) the “fund approach” (or alternatively even a prize approach) would allow the competitive development of the best and most cost efficient technology. Not everyone believes that this financial mechanism would work based on skepticism of the economics. One estimate has been made that ten major deorbit of large debris elements need to be undertaken each year to have a positive impact on debris buildup. If one were to estimate that the cost of each deorbit operation would be $200 million (US), then this would require $2 billion (US) a year of revenues and that such a fund would generate less than the needed finances to be viable. Such an assumption is based on a conventional fetch-and-retrieve robotic

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operation. There are many new concepts based on “electrodynamic” operations that, if they could be proved, could carry out multiple removal operations with a single in-orbit craft. The long and short of it is that new technology driven by economic incentives would be key to making such a funded approach viable in terms of achieving its mission. What is clear at this point is that there is no agreed plan – whether a fund for debris removal, national governmental debris removal missions, or any other approach – that is a viable solution to a problem that is growing worse each year. Another large-scale event such as collision of large craft or another missile shoot down could be catastrophic in threatening long-term safe access to space. The scenario vividly portrayed in the 2013 movie “Gravity” would ultimately lead to a “space debris winter” that would seal off longer-term safe access to space for humankind.

Next Steps Forward Several countries have discussed the feasibility of direct action to demonstrate the feasibility of active debris removal. But one or two demonstration projects may help prove the viability of various techniques, but this is not sufficient to solve this problem. If the United States, France, China, Japan, or perhaps the Russian Federation, or perhaps Europe would blaze a trail by creating such a fund, this could be a key first step. This could test the viability of various provisions of how such a fund would be established, payments paid in, and generally administered. Such an initial effort could serve as a very useful test case for how this might be undertaken on a larger scale. This test case approach might also be useful in terms of addressing the liability issues, whether passive or active removal systems would somehow be supported and finally with the country or region assuming liability responsibility for any “accidents” that might occur during the removal process. The other option is for several countries – again the same countries as above – embarking on experimental missions to bring down the most dangerous space debris elements on a proof of concept basis. If several countries could join together to undertake such trial missions and prove that it could be safe and effective, this would be a very desirable step forward. The main element to stress here is that the idea of creating an orbital debris removal incentive fund and individual missions to deorbit space debris are not mutually exclusive. If well-coordinated, they could become, in time, a part of a globally agreed strategy.

Economic Considerations Currently the cost of removal of debris from orbit is very high and the technology is unproven. If an active remediation program is to be undertaken to remove space debris from certain orbits, the central issue that is clearly posed is how will the cost

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of these operations be funded and would this activity be under taken via national governments, an authorized international organization, or perhaps by commercial entities? What is clear is that there is today no established and ongoing mechanism to fund space debris removal either at the national, regional, or global level. The current situation is that one or more countries might be willing to fund a test case to prove the possibility to the viability of one or more technique. A one-off test case would certainly be of potential value, but still does not offer a longer-term solution. Establishment of an “orbital debris removal fund” to which all future launch entities would contribute has the advantage of letting all space activities (i.e., those of civil space agencies, defense-related space entities, as well as commercial entities) contribute to the cost of removal. Such a fund could also be adapted so that commercial entities might be able to participate in the removal process. The major problem is that the technology needed to accomplish such removal is yet to be demonstrated and proven and currently is seen to be very expensive. Thus, no one can accurately project how much money would need to be collected to fund active fund removal. Currently the only specific concept that might be carried out on an “economic basis” is the proposal that laser pulses might be directed toward orbital debris that is seen as a collision risk with other space objects so as to change the debris orbit sufficiently to avoid collision. This approach has the negative feature as potentially being seen as a space weapon. The suggestion has been made that the registered country for the space object concerned could be asked to control the laser pulse emissions directly themselves and thus avoid the perception that such actions represent in any way a hostile action. From an economic viewpoint such an avoidance of a space-based collision by a space debris object is currently the most cost-effective way to proceed since ground-based systems are less costly to build and operate.

Legal Concerns What legal or regulatory processes could be agreed to ensure that active or operational satellites were not intentionally – or even unintentionally – removed from the orbit? There is no effective mechanism to protect satellite operators from loss of their operational spacecraft that is foolproof or even demonstrated in practice. Nevertheless, reasonable precautions are possible. The first step is a universal machinereadable system that indicates the orbital characteristics of all trackable space objects. The Space Data Association is the first step in this direction but much more needs to be done. And if such removal of an operating space system should occur, how would the operational entity that deployed the satellite be fairly compensated? No clear-cut compensation process is currently in practice. There are nevertheless reasonable ways to proceed. A demonstration project that concentrated on removing upper stage rockets would clearly be one logical way to start to show how

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precise methods could be utilized to deorbit debris while avoiding adverse effects on currently operating space systems.

Bounding the Size of Space Activities in Terms of Their Economic Import A useful first step might be to try to calibrate the economic size and importance of space-related activities as they exist today – and to project these forward. The purpose of this exercise would be to have a reasonable “yardstick” for considering what the size of the “global fund” might be without it being overly onerous to the various participants. Contributions to the “orbital debris remediation fund” itself would be in fact indexed to only two factors: (a) the orbits that various space operators utilized and (b) the size and value of the various space missions (that presumably relate to their size and thus their potential future orbital debris risk factor). There might be a cap on “assessed value” for the very largest missions.

Various Space Activities and Their Economic Size The largest single identifiable space-related market is that of satellite communications. The annual studies by the Satellite Industry Association and the Futron Corporation put the combined satellite services revenues, satellite manufacturing, associated launch services, and ground equipment market for 2010 at just over $180 billion (US) (Futron 2012). This does not take into account insurance and regulatory/consulting costs nor does it quantify defense satellite communications systems into these figures. Another very sizable amount of space-related activities relates to satellite-based defense communications, strategic space surveillance, navigation and targeting, meteorological observation, and space weather observation. Worldwide this could add over $150 billion in annual space activities if one takes into account the programs of the United States, Europe, Japan, China, Russia, and a growing number of other spacefaring nations. There is now a great deal of commercial activities and operations related to satellite navigation that is not related to defense activities. The annual sales of consumer devices and related software for satellite navigation are estimated to be as high as $30 billion. The deployment of next-generation GPS systems, Galileo, and satellite navigation systems by Japan, China, Russia, and India has a host of commercial applications, but the shift to the guidance of aircraft (including takeoff and landing), ships at sea, and trucking and bus operations adds a whole layer of economic importance and significance to satellite navigation. The quantification of the economic importance and economic product associated with remote sensing, Earth observation, and meteorological satellites (for weather forecasting and monitoring of climate change) becomes even more difficult.

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Each year meteorological satellites lead to more accurate forecasts that save perhaps tens of thousands of lives. One cannot easily quantify the value of spotting forest fires, crop diseases, natural resources, or schools of fish. It seems quite safe to say that a synoptic figure for all types of directly quantifiable space applications that provide commercial, defense, and governmental services plus scientific missions in Earth orbit is easily equivalent to some $400 billion a year and perhaps $500 billion a year. But if one considers the indirect benefits of all space-related activities to humankind and global security and safety that the actual “value” soars into the trillions of dollars. The threshold question of relevance is whether those engaged in all forms of space activities and applications and spacecraft launches into LEO, MEO, polar, or GEO orbits could be “enrolled” in a system whereby a very small percentage of their cost of their space operational costs could be marshaled toward the active removal of space debris. Today commercial satellite operators routinely spend 15 % of their satellite mission budgets on obtaining launch insurance. The payment of something like 5 % of their total mission expenses toward a space debris mitigation and remediation fund is in many ways a very parallel concept, except that it would be much cheaper, and if these undertakings were done in an efficient way, this “sustainability of space” fund might be necessary for only a relatively short period of 20–25 years. There are obviously many practical questions that are involved here that would need to be answered over time, but for now this is just an intellectual exercise – or thought experiment.

Users of Different Orbits: Why They Would Pay Differing Amounts in the Fund? The key initial question perhaps would revolve around the fact that the most profitable satellite commercial operations (i.e., satellite communications) for the most part use the geosynchronous (or Clarke orbit) where the space debris problem is now clearly the least severe. Conversely, the satellite operations in low Earth orbit and polar orbit, where the problem of space debris is the most severe, involve the types of operations that produce the least amount of revenue per satellite and involve all sorts of what might be called “extraneous markets” such as student experimenters, researchers, and developing countries wanting to launch microsatellites, CubeSats, and other instruments that have high space debris potential but low or no commercial value. This raises a major space policy question as to whether such experiments and small satellite projects should be required to have active or passive deorbit systems or be consolidated into larger integrated packages that can actively be deorbited. Quite simply, the dilemma associated with active space debris removal is the following. Those organizations with the greatest potential to help finance space debris removal are generally not those most significantly now contributing to the

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space debris problem. Further, there is no global entity such as the United Nations or the ITU that has the current authority to “tax” satellite operators or those who launch satellites in order to apply these revenues to active space debris mitigation. In many ways the economic issues here is like the classic issue of who pays for a lighthouse from among all the owners of ships at sea. The most salient facts to be considered by the satellite communications industry and others that use the GEO orbit are the following: (i) Should the Kessler syndrome develop, it would in time seriously jeopardize the ability to launch satellites to GEO orbit; and (ii) the problem of orbital debris and possible collision between satellites in GEO orbit, as recorded in the space situational and satellite conjunction reporting of the Space Data Association (that currently reports on 60 % of the GEO orbit satellites), is worsening each year (Space Data Association 2011). In short, unless efforts are undertaken sooner rather than later, the problem of space debris and dangerous conjunction of spacecraft for GEO and LEO orbits, and indeed all Earth orbits, will continue to worsen over time. New measures are needed. The longer this remediation process is delayed, the worse the problem will become and the more expensive mitigation measures will become.

The Costs of Space Situational Awareness Versus the Costs of Orbital Debris Removal Another difficult issue is that of what is called space situational awareness and the cost of knowing about the current status of space debris. The United States and other countries spend billions of dollars to track space debris and maintain what is called “space situational awareness” as part of their missile defense programs. The United States shares the information obtained from the current US Surveillance System and likewise will share information derived from any other new capability such as the almost funded – but now cancelled – S-band radar Space Fence. This new installation would have cost at least $6 billion in capital investment. The problem is that the United States is not willing to surrender the operation of its tracking capability to an international agency because it considers the function of the facility to be vital to the protection of the US homeland from attack. The most significant thing to note here is that the cost of active debris removal and the cost of current and planned space situational awareness systems are roughly comparable (“New Debris-Tracking.” 2012). A number of satellite operators have begun sharing data concerning the orbits of their operational satellites via an organization already identified above as the Space Data Association, but at this stage this sharing of data is almost exclusively among operators who deploy satellites in GEO orbit and thus does not, to date, include any significant sharing of data in the LEO or polar orbits. The extension of the data sharing to all near-Earth orbits, and in a consistent machine-to-machine manner, is a most desirable next step forward (Space Data Association 2011) (Fig. 1).

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Fig. 1 Scale representation of orbital debris in low Earth and polar orbit (Graphics courtesy of ESA)

Key Steps Forward Concerns Orbital Debris Reduction In summary, all the users of space for commercial, strategic, governmental or even educational, research, and humanitarian purposes have a stake in being able to access space reliably and “sustainably” into the future. A variety of steps are thus needed. These include: (i) improved space situational awareness; (ii) prelaunch due diligence enforced by governments in accord with international standards that would prevent the creation of further space debris; (iii) active deorbit of spacecraft at the end of their useful life, again in accord with international standards (as noted above the further issue of improved practices concerning the deorbit of small and nano-satellites must be addressed and resolved as soon as possible); and (iv) in the absence of active space debris deorbit capabilities, passive systems that assist with debris removal represent a fall back alternative. It is believed that there is merit in the creation of national, regional, and, in time, an international fund for debris removal and mitigation. This fund could be administered by one or more international banks or launch insurance companies or any other approved international mechanism. The purpose of the fund would be to pay out to “international licensed” entities which competently remove space debris

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from orbit according to a set schedule of payments for such debris cleanup activities. A small percentage of the fund could also be used to carry out internationally sanctioned debris mitigation and remediation-related activities. It might also be used to fund activities related to changing the orbit of debris that might also immanently crash into satellites or other large debris objects. The clarification of how such a fund might work and to what activities it would apply is one of the reasons that a national or regional fund – prior to a global fund – might be a useful preliminary step. The conceptual purpose of the fund in general terms, however, would be to finance (a) the mitigation of the future buildup of space debris, (b) the active removal of the most dangerous space debris elements from Earth orbit, and (c) the movement of derelict space objects in to a graveyard orbit or a safer location for the purpose of collision avoidance.

Feasibility of Establishing a New International Entity for Active Debris Removal Many might suggest that instead of creation of a fund that a new international entity might be created to undertake this purpose and that of course is certainly an option if only it were achievable. This could be an alternative and effective solution, but the currently fragmented international conditions that relate outer space make this an unlikely solution at this time as noted below. Difficulty of Obtaining International Consensus: The UN Committee on the Peaceful Uses of Outer Space is now comprised of some 70 countries where consensus is very difficult to reach. It is possible that various space agencies of the world that have formed the Inter-Agency Space Debris Coordination Committee (IADC) might create a new entity to undertake coordinated international action in this area or the Space Data Association’s role might be expanded to take on this task, but currently no such actions are seriously pending. Other Pending Space-Related Issues that Might Require an International Space Agency: The issue of orbital debris is not the only pending international issue involving space. Other serious issues such as planetary defense, atmospheric and stratospheric pollution, the regulation of the flight of space planes and the possible need for oversight of private space platforms, and possible military uses of outer space are other pending issues that might be considered higher priorities related to international space regulation. It is not clear whether an organization such as the International Civil Aviation Organization (ICAO) or the World Meteorological Organization (WMO) might, for instance, be assigned additional international regulatory authority regarding both “Protospace” and outer space, and if this were to occur, it might be assigned responsibility for addressing such issues. At this time the International Telecommunication Union (ITU) comes the closest to having regulatory authority in this area, and currently it has not been in a position to exert much authority to control the buildup of orbital debris. Certainly it lacks the power to exert sanctions over nations responsible for the creation of new debris.

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Costs and Organizational Complexity: Creation of a new international agency, whether within the UN system or under expanded versions of the IADC or the SDA would all be costly, involves much greater organizational complexity. Certainly there would clearly be difficulty in obtain agreement to given regulatory oversight authority to any new international entity and a further difficulty in raising the funds and agreeing to the staffing of this entity to operate. Incentives to Create New and More Cost-Effective Technology for Debris Removal: Aside from the other practical and political considerations, it is also likely that a fund approach – as opposed to creating a debris removal agencies – would create an economic incentive to create new technology to remove debris more efficiently and at lower cost than conventional ideas of robotic “fetch-andretrieve” concepts that are enormously expensive. It is for the above reasons that an incremental approach to addressing orbital debris issues seems most prudent. In time a new international space regulatory agency that could be empowered to address all of the space-related issues noted above may be necessary. Indeed one might begin now to identify the various important space-related activities that an international space regulatory agency needs to address and document the nature and the importance of these needs to help work toward such an important global milestone (Jakhu et al. 2011). In the nearer term the creation of a funding mechanism to address space debris may represent a more achievable objective. It would seem to be more economically efficient to make payments – perhaps most likely collected by national governments – into a bank or insurance companyadministered-and-invoiced fund. The funds would then subsequently be to pay out to “licensed entities” after they have removed debris elements from orbit. The fund would also serve a further function of creating financial incentives for “clean launches” and for “active removal” of satellites at end of life. If the fund were established on the basis of a 5 % of mission cost (i.e., a third of normal launch insurance costs), the rebate system might work as follows. After it is certified that the launch has been “clean” and created no new orbital debris – including the upper stage rocket – the entity posting the bond to the fund would be remitted 1.5 % of the 5 % payment. If at the end of life the satellite is reentered successfully or deployed in a prescribed graveyard orbit, there would be a further 1.5 % rebate. The residual amounts as well as the interest accrued on the funds would be used to “clean up” near-Earth orbits. Licensed entities deemed qualified to remove orbital debris or place an officially designated defunct satellite in a graveyard orbit would be required to work under appropriate international regulations and safety standards. Those who undertake the removal would only be compensated after the removal had been accomplished and clearly documented as to the size, mass, and orbit of the debris element. An international bank (or perhaps several banks or launch insurance companies) could be designated to undertake the investment and disbursement of the funds. Government administrations as designated by the ITU or UN COPUOS would be responsible for collecting the funds and depositing them in the bank prior to actual launch.

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The fund would be created by a two-tiered system that includes a “performance bond payment” against actual performance in terms of not creating debris at launch and in terms of removal from orbit at end of life. This performance bond payment would in each instance be equivalent to 1.5 % of the mission cost. The performance bond would certify that the mission would not release any space debris in the process of their launch and deployment, and when verified (e.g., by onboard cameras), they would receive a certification check. There would also be a performance bond against active removal of spacecraft from orbit at end of life or redeployment to a graveyard orbit. These provisions would be specifically designated for the cases of low, polar, medium, or GEO Earth orbit. They would have to provide for sufficient propellant systems and fuel (i.e., hydrazine, bipropellant, ion engine, etc.) to guarantee return of the satellite to Earth in a controlled fashion or in the case of GEO orbit to raise the satellite at least 1,000 km above GEO orbit or move the satellite into an orbit that would intersect with the sun. The entity would be refunded 1.5 % of the bond after a successful launch creating no orbital debris. After the removal of the satellite from orbit without creating debris, another 1.5 % of the bond would be returned. The size of the performance bond would be for a set amount of the overall cost of the mission (such as 5 %). The mission cost would become part of the filing with the ITU by the responsible administration at the time of the spacecraft filing. There could also be a tiered funding of the space debris removal fund. This might set the fund charge to be 5 % of the cost of the mission if in GEO orbit, 6 % of the cost of the mission if launched into MEO orbit, and 7 % of the cost of the mission if launched into LEO or polar orbit. In the case of MEO orbit missions, if there were insufficient fuel associated with the mission to maintain station-keeping and active removal at end of life, the fee would be set at a much higher rate. This process for establishing and sustaining the fund would in effect raise the net cost of all satellite launches by about 3–4 % percent for the next 25 years (assuming that most launches were indeed clean and most end-of-life disposal operations were successful.) The funds raised should be sufficient to reduce the amount of space debris substantially within a two decade to 25-year period. The cost of paying into the fund would create large economic incentives to eliminate the formation of new space debris due to new satellite launches and also pay to remove significant elements from orbit by means of the licensed entities. There could be a mechanism to adjust the collection rates, if, for instance, the removal process turned out to be less costly than currently envisioned. Such an orbital debris removal fund concept would put economic incentives front and center. Operators and all types of space agencies would have a direct economic incentive to eliminate existing and future space debris. Those entities developing technologies and systems to remove space debris would have maximum economic incentive to actually remove existing material from orbit. Government regulators would be charged with identifying “prime targets” for removal of space debris. Launching states and space system operators would have strong incentives to create less space debris, not leave derelict space objects in orbit. Operators would likewise be financially motivated.

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The exact formula for payments into such a fund can obviously be crafted more carefully and precisely by those that might come together to negotiate the exact terms of building the funds. If the funds are first established on a national basis, there should be a “model charter” for the fund so that national and regional funds could subsequently be merged into a global or universal fund. The challenge of course would be to convince all those launching satellite systems that a 5–7 % increase in their overall costs is a wise investment against avoiding a future condition in which all space operations would be impossible – i.e., the onset of the Kessler syndrome. In this case national governments may need to be the “grown-up in the room” that first act to create the initial funds. In this regard, there is a marked similarity in these proposals to various other economic strategies to stop speeding on highways, to maintain safe naval navigation, to stop environmental littering or pending strategies, and to stop runaway climate change. In all cases one is simply creating significant economic incentives to keep everyone on their best behavior and to take needed preventive action. The universal economic fund strategy would separate the fund from a number of “licensed actors” that would be free to develop multiple technologies and systems to carry out remedial actions. Today many technical approaches are currently under consideration to address this problem. These approaches are outlined in the preceding chapter. The fund would avoid trying to pick a winner and would let a market system decide which technology or system was actually best.

The Value of Earth Orbit to Humanity and Future Space Commerce Some might argue that such a fund for removal of orbital debris is premature. Others would argue that since the problem now is largely concentrated in the low Earth and polar orbits, the fund, if created, should collect only for launches into these orbits. These short-sighted views of the problem do not account for the fact that as the debris problem grows and cascade, debris from larger debris elements will eventually endanger all space launches – even those launches of payloads beyond Earth orbit. The most important thing to focus on is that the value of all Earth orbits is tremendous. If one concedes that the value of a GEO slot is today perhaps $1–3 million per year and access to a safe LEO environment is also worth millions per year, then the combined value of “safe access to Earth orbit” is worth perhaps a billion per year and that mounting orbital debris is constantly serving to depreciate the value and usability of this global commons resource. Indeed these valuations are perhaps quite low. Fairly recently two companies, out of a total seven bidders, won the rights to use satellite orbital positions auctioned in 2011 by Anatel of Brazil. Hughes Communications will pay $95 million for two Ka and Ku slots in GEO. Star One (owned by Embratel) will pay $39 million for two slots in the X, Ku, and Ka bands (“Slim Owned.” 2011).

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The value of the GEO, MEO, and LEO orbits is by any reasonable calculation now worth billions of dollars (US) over just a 10-year period. Investing several hundred millions to clean it up for all space users seems not only logical but costeffective as well. These valuations would tend to put the annual worth of many orbital positions to be $4–10 million per year. The bottom line is that there are “costs” associated with not cleaning up Earth orbit from orbital debris, and the sooner this challenging task is undertaken, the lower the cost of removal will be and the safer access to space will be for the longer term. Economic analysis suggests that delay in the attacking serious common global problems – whether it be climate change, ozone layer depreciation, or orbital debris buildup – will only become more difficult, more technically challenging, and certainly more expensive.

Micro- and Nano-satellites and Orbital Debris One may also suggest that this approach, however, could also serve to limit the launch of microsatellites and smaller projects of developing countries. Certainly, this new system could well serve to create economic disincentives for smaller educational and research space projects and for projects of developing countries. Yet at the same time, it could also create “incentives” to consolidate their efforts within larger platforms or to fly experiments on the International Space Station or other space stations. A number of “CubeSats” can be joined together and efficiently flown as an integrated system. It is certainly the case that small or microsatellites are indeed one of the key complicating factors in the development of space debris. Small satellites, especially when launched into low Earth orbits, are currently a small amount of the orbital debris problem, and it is the largest satellites (and derelict larger space objects) that are the most significant concern. Nevertheless better ways to mitigate debris caused by small satellites need to be addressed. The three options that might be internationally agreed with regard to the deorbit of small satellites have been briefly outlined above in “Key Steps Forward” (Jakhu and Pelton 2014).

Analysis of Different Means and Ways for Solving the Space Debris Problem Regulatory Approaches: Clearly any of the various ways forward will include a regulatory component. The UN COPUOS has developed voluntary guidelines for orbital debris control and minimization in conjunction with the Inter-Agency Space Debris Coordination Committee (IADC). The Space Data Association (SDA) has contributed quasi-regulatory concepts to the control of space debris. There is a need for more than guidelines to control formation of debris and the removal of space debris has technical and economic challenges that are not likely to be solved by

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regulations alone. An international agreement on linking the granting of launch and operations licenses to a credible plan for the removal of a space system at the end of its mission, and to levy high penalties equal or higher than the cost of the system in case successful removal is not achieved, would be a key step to create a market for removal services. Technical Approaches: The current wide diversity of ideas about how to remove space debris suggests several things. It suggests that at this stage at least there is no clear “winning idea” about how this could be done. All of the technical options now available are unproven, are expensive, and also give rise to a variety of concerns. It has been proposed that the best place to start is to undertake several demonstration projects to start the removal of the largest derelict objects. This makes a great deal of sense. Nevertheless, the idea of a fund would likely create major incentives to develop newer, lower cost, and more efficient technology. Organizational Approaches: The creation of a single international agency to carry out this task gives rise to a host of concerns. These concerns include (i) high likelihood of focusing on a single technology; (ii) high overheads; and (iii) the problem of international agencies not necessarily being the best source of innovation, not likely to produce cost-effective solutions, and often can be self-sustaining even if their mission has been fulfilled. Instead a mixed government-private consortium similar to the early INTELSAT that launched international telecommunication services via satellite 50 years ago may be an interesting model to follow, in particular if transition in due time to a fully private company is pre-agreed. An even more important consideration is that there may need to be a new organization to address other such issues as space traffic management, stratospheric pollution and climate change, etc. Such a new space-related organization would need to consider these issues as well as orbital debris. In short, a synoptic overview is needed as to which existing international organization could best address these complex of issues or if a new international entity is indeed required. Economic and Incentive Prize Approaches: The best way to alter human and state behavior on a global scale today seems most often to involve the creation of clear market incentives. If there is a price to pay for NOT removing space debris and there were also strong economic incentives to create the best technology to remove debris from Earth orbit, then the likelihood of success seems to increase considerably. If there were a strict process for controlling the “licensing” of entities to remove elements from space and there were the equivalent of a major prize that would go to the entity that could develop the best and most efficient way to remove space debris, then the most rapid and effective progress might well be achieved. This would be in some ways equivalent to the “XPrize” approach to developing commercial space travel or fuel-efficient cars or low-cost ways to explore or create permanent settlements on the Moon. The international “licensing” of international entities that were “authorized” to develop the technology and then to remove space debris under guidelines developed by the UN COPUOS or a consortium of governmental space agencies (organized like the IADC) poses a number of tricky issues to be solved. But such challenges are not an impossible goal to achieve.

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Conclusion If one creates economic incentives for prevention of space debris and high penalties for its creation, this will prove to be a powerful tool to stop this growing problem. A focus on economic solutions can allow a diversity of new and more cost-effective technology to be developed. Performance bond incentives based on actual results (i.e., rebates against no new debris and payouts for deorbiting at end of life or placing satellites into graveyard orbits) should be a part of the solution. The ideas outlined in this paper are analytic and conceptual. The details of actually implementation would need to be worked out through detailed international negotiation. The basic concepts are, however, quite clear: • A new space convention that allows the right incentives and penalties for “clean launches” and system disposal at end of life and allows derelict space objects to be designated as space debris would certainly be a step forward. Such new space convention would link the granting of launch and operations licenses to credible plans for removal of space systems at the end of their mission and would levy high penalties perhaps equal or higher than the cost of the system itself in case successful removal is not achieved. Creation of a fund that would compensate “licensed entities” after they had performed debris removal would create a powerful market force to get the greatest amount of debris down in the most efficient way. This solution would let economic market forces drive technical innovation. • The fund should have a beginning and end of life with a clear objective to accomplish the “cleaning up” of Earth orbit by the time space operators would stop paying into the fund. • The funds may well start at the national or regional level and this could work out a number of problems about the funds’ efficient operation. The desire would be for the fund to eventually be “universal” among all space launching entities. A “model charter” for such a fund would facilitate the “evolution” of the funds to become universal. There should be technical, regulatory, and economic incentives for small satellites, microsatellites, and nano-sats to be combined and consolidated. These smaller missions should where practical and possible be carried out on the International Space Station or consolidated so that active disposal is possible. The three options for addressing orbital debris and small satellite proliferation as outlined above under “Key Steps Forward” should become a part of the international discussion. • Creating a “wise, effective, and strategically effective way” to license entities to perform space debris removal is one of the top challenges to this approach but this is not an impossible task. • International banks or launch insurance companies or some other entity could administer such a fund or funds. Limited new mechanisms would be necessary for proceeding in this manner and if the arrangement looked, felt, and essentially acted as if it were a new form of launch insurance, then its implementation could certainly be advanced more quickly.

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• None of the ideas provided with regard to creation of a Fund for Orbital Debris Mitigation should be considered to be opposition to or against the parallel efforts for national space agencies to undertake trial programs to undertake “fetch and retrieve” programs to deorbit major space debris elements. Such efforts should be carried out in concert with each other and not in competition. • Finally it should be noted that there are several key issues of global governance involving near Earth that are currently pending. These include (i) frequency management, interference, and future spectrum demand; (ii) stratospheric pollution and climate change; (iii) space traffic management and regulation of the use of the “Protozone” (i.e., 21–100 km in altitude); and (iv) increasing levels of orbital debris. It is really not logical or even possible to consider these issues in isolation of each other. A systematic solution to appropriate regulatory action in all of these areas is needed. In the interim if economic incentives could be created to minimize the creation of new debris and also actively move to deorbit debris elements, this would be a very positive step forward.

Cross-References ▶ Active Orbital Debris Removal and the Sustainability of Space ▶ Hazard of Orbital Debris ▶ Nature of the Threat/Historical Occurrence ▶ Regulatory Aspects Associated with Response to Cosmic Hazards

References Futron Corporation (2012) Annual assessment of satellite communications enterprise for the Satellite Industry Association. Bethesda Jakhu R, Pelton J (2014) Small satellites and their regulation. Springer Press, New York Jakhu R, Sgobba T, Dempsey P (2011) The need for an integrated regulatory regime for aviation and space: an ICAO for space? Springer Wien, New York Latin American Herald Tribune (2011) Slim-owned satellite company wins orbital slots in Brazil. www.laht.com/article.asp?CategoryId=14090&ArticleId=421247. Accessed 1 Sept 2011 Listner M (2011) Revisiting the liability convention: reflections on ROSAT, orbital space debris, and the future of space law. The Space Review, 17 Oct 2011 Pelton JN (2012) A global fund for space debris remediation: a new way forward to address the mounting space debris problem. International Space University symposium, Strasbourg, March 2012 Schons M (2011) Superfund: how one government program helps clean up toxic-waste sites. National Geographic Education. http://education.nationalgeographic.com/education/news/ superfund/?ar_a=1. Accessed 21 Jan 2011 Space junk problem is more threatening than ever—report warns. www.space.com/12801-spacejunk-threat-orbital-debris-report.html Space.com (2012) New debris-tracking ‘space fence’ passes key test. http://www.space.com/ 14867-space-fence-orbital-debris.html. Accessed 12 March 2012

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The Space Data Association (2011) Space Data Association now performs conjunction screening for more than 300 satellites. http://www.space-data.org/sda/wpcontent/uploads/downloads/ 2011/01/SDA_press_release_21_Jan_2011_RELEASED.pdf The Torino impact hazard scale. neo.jpl.nasa.gov/torino_scale.html Wired Magazine (2010) The looming space junk crisis: it’s time to take out the trash. www.wired. com/magazine/2010/05/ff_space_junk/all/1. Accessed 24 June 2014

Potentially Hazardous Asteroids and Comets Frederick M. Jonas and Firooz Allahdadi

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spaceguard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

Potentially hazardous asteroids and comets or, more generally, potentially hazardous objects (PHOs) are defined to be near-Earth asteroids or comets (nearEarth objects [NEOs]) with orbits that come close to Earth. These potentially hazardous objects have the potential to cause significant human suffering unlike anything we have encountered in our history if Earth impact with a PHO did indeed occur. The population of NEOs with a diameter larger than one (1) kilometer is estimated to be 1,000 objects. The estimated population with diameters greater than 40 m is a 1,000 times (one million) greater. Overall, it is estimated that over one million NEOs exist that could cause damage to the Earth from impact. None yet has been found that poses an immediate threat. We must continue to be vigil, and current programs watching the heavens are presented.

F.M. Jonas (*) Amateur Cosmologist, Gallup, NM, USA e-mail: [email protected] F. Allahdadi Space Science and Environmental Research, Applied Research Associates, Albuquerque, NM, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_65

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Keywords

Asteroid • Comets • Potentially Hazardous Asteroid (PHA) • Impact • Crater • Tracking • Spaceguard • Near- Earth Object (NEO) • Telescope • Survey • NEOWISE • ICE • Deep impact • Earth impact • Hazard • Observatory

Introduction Potentially hazardous asteroids and comets, or more generally, potentially hazardous objects (PHOs) are defined to be near-Earth asteroids or comets (near-Earth objects [NEOs]) with orbits that come close to Earth. These heavenly and potentially hazardous objects are big enough to cause significant regional damage in the event of an impact. Close enough has been defined as anything less than 7,500,000 km. This is defined as the minimum orbit intersection distance (MOID) with respect to Earth. This is approximately 19.5 lunar distances. Big enough is defined to be an object with a diameter of at least 100–150 m. Significant regional damages mean that for an impact on land, the result will be regional devastation to human settlements unprecedented in human history. For an ocean impact, the result would be a major tsunami that would again be unrivaled in human history. The resulting devastation to human settlements, especially those near the ocean, would be complete destruction. The point is that these potentially hazardous objects have the potential to cause significant human suffering unlike anything we have encountered in our history if Earth impact did indeed occur. Either at land or at sea, the results would be devastating. Such an impact is depicted in Fig. 1. The fact that large objects from the heavens do indeed impact Earth is visible on the Earth’s surface (Fig. 2) and is recorded in Earth’s geologic record dating back over 2.4 billion years ago. That record is contained in Suavj€arvi Crater and is currently the oldest known Earth impact. Approximately 16 km in diameter, it contains Suavj€arvi Lake at its center (approximately 3 km in diameter). The crater is located about 50 km north of Medvezhyegorsk in the Republic of Karelia, Russia. It was in fact discovered from space and photographs of the Earth’s surface. Further, that record of impact is clearly evidenced by the entire surface of the Moon and the surfaces of other moons and rocky planets in the Solar System. The Earth-Moon system is in fact postulated to be the result of a major impact that occurred between Earth and a Mars size body four and a half billion years ago. Major impacts have been postulated and linked to other major events in Earth’s history to include bringing the necessary ingredients for life, bringing our water, and perhaps causing major extinction events. Most recently, the entire world observed the impact of comet Shoemaker-Levy 9 with Jupiter in July 1994. The recorded history on the surfaces of these Solar System bodies shows impacts have happened over the entire history of the Solar System. Impacts are happening now, and impacts on Earth and other celestial bodies will continue far into the future. It is all part of the natural process of the birth and growth of solar systems. While a natural process, we no longer have to sit idly by as these impacts continue on Earth.

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Fig. 1 Hypothetical Earth impact with a potentially hazardous asteroid

Fig. 2 Meteor (Barringer) crater in Arizona gives evidence of recent impacts

We now have the technology to find and categorize these potentially hazardous objects, and perhaps the technology to do something about it if such as object is found. Regarding the hazard, the population of NEOs with a diameter larger than one (1) kilometer is estimated to be 1,000 objects. The estimated population with diameters greater than 40 m is a 1,000 times (one million) greater. While there may be many more comets, they are generally in orbits at great distances from the sun with orbital periods of tens to hundreds of years. These occasional visitors are estimated to contribute only 1 % to the impact hazard. Currently (2013), more than 10,000 NEOs have been discovered, and as our ability to observe these objects improves, that number will only increase. None yet has been found that poses an immediate threat. Overall, it is estimated that over one million NEOs exist that could cause damage to the Earth from impact (the latest numbers, known sightings and predicted orbits of these objects can be found at http://neo.jpl.nasa.gov).

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The task of identifying and tracking these objects is an ongoing effort. It simply does not stop once we complete the list (if there ever was such a thing). We must continually identify and track these objects due to the dynamic nature of the Solar System. Bodies in the Solar System are continually being perturbed, tugged, pushed, and pulled by the other bodies in the Solar System (notably Jupiter), the solar wind, thermal heating, and other effects meaning that orbits can and do change. Predicting these changes can be difficult especially for low mass bodies like asteroids and comets versus planetary larger mass bodies like Earth. While the orbital perturbations may be small overall, the change to the orbit may be just enough to be the difference between an Earth impact or a miss, thus the reason why we must be continually vigilant and prepared. Thus, the programs and efforts to continually scan the heavens and find these threats are presented next. Vitally important and crucial to all these ongoing activities is the continuous and unyielding contribution of amateur astronomers around the world. They are as sentries keeping eyes on sky on behest of us citizens of Earth, and for that, we are thankful.

Spaceguard There are a number of programs worldwide, including the amateur astronomy community, focused on identifying and categorizing PHOs. The general name for all these programs is Spaceguard. Spaceguard is the name of the early warning system created following a catastrophic asteroid impact in an Arthur C. Clarke novel, Rendezvous with Rama. The name has stuck. Most notable is the Spaceguard Foundation. The Spaceguard Foundation is a private nonprofit organization based in Frascati, Italy (http://spaceguard.rm.iasf.cnr). The organization evolved from the 1995 workshop entitled “Beginning the Spaceguard Survey” held by the Working Group on NEOs of the International Astronomical Union (IAU). The IAU consists of a collection of professional astronomers around the world with a doctorate degree or better who are active in research and/or education in Astronomy. Membership currently numbers approximately 11,000. The IAU is the internationally recognized authority for assigning designations to celestial bodies. The purpose of the Spaceguard Foundation is to study, discover, and observe NEOs and protect the Earth from possible threat of collision. There are a number of other Spaceguard-related programs around the world to include Spaceguard Croatia (Fig. 3), the Spaceguard Foundation (Germany), Japan Spaceguard Association, Spaceguard Spain, Spaceguard Australia, Spaceguard Canada, and Spaceguard UK (United Kingdom). Not meant to be an all-inclusive list, the point is that there is a collective international effort to identify any threats from the heavens. One of the key players in this activity is the United States (US) National Aeronautics and Space Administration (NASA). The NASA Near-Earth Object Program is the focus of these efforts (http://neo.jpl.nasa.gov/).

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Fig. 3 Croatia Spaceguard

NASA Near-EarthObjectProgram. The USA, through NASA, has a national effort to detect, track, and identify PHOs. In 1998, Congress charged NASA to discover 90 % of the objects with a diameter of at least 1 km or greater by the end of 2008 that might impact Earth. Once the majority of these objects were identified, and as ground-based and space-based capabilities to find PHOs improved, Congress again tasked NASA in 2005. The task then was and is now to detect and track 90 % of PHOs with diameters of 140 m or greater by 2020. Note that the Earth’s atmosphere takes care of anything up to 40–50 m in diameter so we are quickly closing the gap. The ability to achieve the goals above depends of course on observations and data. Those observations and data come from the professional and amateur astronomical community, ground-based observing sites, and space-based systems being used to detect, identify, and track these objects. For example, the assets and search programs used by NASA to perform such task include the Catalina Sky Survey, Pan-STARRS (Panoramic Survey Telescope and Rapid Response System), LINEAR (Lincoln NearEarth Asteroid Research), Spacewatch, and NEOWISE (NEO Wide-field Infrared Survey Explorer). Brief descriptions of each are as follows: • Catalina Sky Survey (CSS) (http://www.lpl.arizona.edu/css/): CSS is currently the world’s best at finding NEOs as can be seen by the Catalina contributions in Fig. 4. CSS has contributed to hundreds of NEOs discovered since its start in circa 2003/2004. In 2012, CSS discovered more than 625 NEOs. The Catalina Sky Survey is based at the University of Arizona. The CSS mission is focused on finding PHAs. CSS currently consists of three cooperating surveys: the Catalina Sky Survey (CSS), the Mt. Lemmon Survey, and the Siding Spring Survey (SSS). Operating primarily on clear nights, same night discoveries of PHAs

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Fig. 4 Near-Earth asteroid and comet discoveries continue to grow as our ability to observe increases

are possible due to the cooperative and focused efforts. Once quickly identified the orbits, then the potential hazard to Earth can be quickly determined. CSS is the only NEO survey that covers both Northern and Southern hemispheres. Primarily, three telescopes provide the observing power for CSS: 1. A 1.5 m (60 in.) f/2 telescope on the peak of Mt. Lemmon (Tucson area) 2. A 0.68 m (27 in.) f/1.8 Schmidt telescope near Mt. Bigelow (Tucson area) 3. A 0.5 m (20 in.) f/3.5 Uppsala Schmidt telescope at Siding Spring Observatory in Australia Identical thermoelectrically cooled cameras and common software are used at all three sites. Cameras are cooled to approximately 100  C resulting in a dark current of about one electron per hour. 4096  4096 pixel CCD cameras capture the data. Recently, and providing further evidence to the importance of the CSS activity, NASA provided CSS $4.1 million to upgrade and operate its telescopes through 2015. • Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) (http://pan-starrs.ifa.hawaii.edu/public/). The Pan-STARRS project’s primary purpose is to detect potentially hazardous objects in the Solar System. The project is a collaboration between the University of Hawaii Institute for Astronomy, MIT Lincoln Laboratory, Maui High Performance Computing Center, and Science Applications International Corporation. The PS1 Science Consortium funds the operation of the Pan-STARRS 1 (PS1) telescope (Fig. 5) on Mount Haleakala in Hawaii for the purposes of astronomical research. The Pan-STARRS consortium is made up of astronomers from 10 institutions from four countries including the Max Planck Society in Germany; National Central

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Fig. 5 Pan-STARRS

University in Taiwan; Edinburgh, Durham, and Queen’s Belfast Universities in the UK; and Johns Hopkins and Harvard Universities in the USA and the Las Cumbres Observatory Global Telescope Network. Ultimately, there are planned to be four telescopes. In addition to discovering potentially hazardous asteroids, Pan-STARRS is expected to detect Jupiter Trojans Kuiper belt objects; trojan asteroids of Saturn, Uranus, and Neptune; and large numbers of comets. The PS1 telescope, run by the University of Hawaii’s Institute for Astronomy, is a 1.8-m telescope on Haleakala in Maui Hawaii. It represents an innovative design for a wide-field imaging facility developed at the University of Hawaii’s Institute for Astronomy. The telescope combines relatively small mirrors with very large digital cameras. This results in an observing system that can observe the entire available sky several times each month. The cameras are the world’s largest digital cameras. The focal plane contains an almost complete 64  64 array of CCD devices, each containing approximately 600  600 pixels, for a total of about 1,400,000,000 pixels. The system systematically surveys the entire sky on a continuous basis. By seeing objects 100 times fainter than those currently observed in NEO surveys, PS1 will help finish off the Congressional mandate to find and determine orbits for threatening 1-km diameter or larger NEOs. The survey also complements efforts to map the infrared sky by the NASA WISE (Wide-field Infrared Survey Explorer) orbital telescope. The results of one survey complement and extend the other, creating a database of all objects visible from Hawaii (approximately three-quarters of the entire sky) down to apparent magnitude 24. • LINEAR (Lincoln Near-Earth Asteroid Research) (http://www.ll.mit.edu/mis sion/space/linear/). The LINEAR program is run by the MIT Lincoln Laboratory and is the result of a collaborative effort between the US Air Force, NASA, and MIT. The LINEAR program has made significant contributions to the discovery of NEOs with diameters greater than 1 km. LINEAR implements electro-optical

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Fig. 6 LINEAR test site

sensor technology developed for the US Air Force Ground-based Electro-Optical Deep Space Surveillance (GEODSS) network. These wide-field telescopes were designed to detect and track Earth-orbiting space systems. In 1996, the LINEAR program was focused on the discovery of NEOs using a single one (1)meter diameter telescope. In 1999, a second 1-m diameter telescope was brought on line. Figure 6 shows the LINEAR Experimental Test Site collocated with the GEODSS system with the two 1-m diameter telescopes. The LINEAR sensor currently is a 3.5-m Space Surveillance Telescope (SST) located on the US Army White Sands Missile Range Atom Peak in New Mexico near the Stallion Range Center. The current telescope began operation in 2013. • Spacewatch (http://spacewatch.lpl.arizona.edu/). Founded in 1980, Spacewatch ® is the name of a group located at the University of Arizona as part of the Lunar and Planetary Laboratory. The primary goal of this group is to investigate the evolution of the Solar System by studying the various populations of small objects, asteroids and comets, in the Solar System. Observations are conducted using both the Steward 0.9-m and 1.8-m telescopes located on Kitt Peak (Fig. 7). The 0.9-m telescope operates in the stare mode, while the larger 1.8-m telescope operated in the drift-scan mode until 2011 and now operates in the stare mode using a staring CCD that resulted in observing 54 % more NEOs once implemented. Some firsts for Spacewatch include: – First to routinely use CCD-scanning and survey the sky for asteroids and comets. – First to detect near-Earth asteroid (1990 SS) using a CCD in 1989. – First to discover comet (125P/1991 R2) using a CCD. – First to use automated real-time software to detect moving objects and then discover a comet (C/1992 J1) using this software. • NEOWISE (NEO Wide-field Infrared Survey Explorer). The NEOWISE project (http://neowise.ipac.caltech.edu/) is the asteroid-hunting portion of the Widefield Infrared Explorer (WISE) mission. NEOWISE (Fig. 8) is a remarkable story. A NASA developed infrared astronomical telescope (40-cm diameter), NEOWISE, was launched into low earth Sun-synchronous polar orbit in December 2009. During its first 8 months of operation, the project was

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Fig. 7 Spacewatch telescopes

Fig. 8 NEOWISE

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called WISE. The WISE mission was to map the universe in infrared light. When the telescope lost its coolant, it became NEOWISE and shifted to finding asteroids and comets in the Solar System. NEOWISE then completed its survey of the Solar System in the next 4 months and was then put into forced hibernation. NEOWISE is remarkable in that it has been recently revived by NASA in September 2013 to continue the asteroid survey. The new mission was due in part to calls for NASA to step up asteroid detection after the previously undetected Chelyabinsk meteor exploded over Russia in February 2013. Within the first 25 days of operation, NEOWISE found three new objects and detected an additional 854 objects. In December 2013, NEOWISE discovered YP139, an asteroid estimate to be about 650 m in diameter. In a highly elliptical orbit, it has the potential to come within 300,000 km of Earth, a bit greater than the EarthMoon distance. NEOWISE is currently observing and characterizing at least one NEO a day, a welcome addition back to the watch for PHAs. To date, the total NEOWISE effort has contributed to the discovery of approximately 158,000 asteroids at thermal infrared wavelengths, including approximately 700 NEOs. Overall, it has discovered approximately 34,000 new asteroids, 135 of which are NEOs, and detected more than 155 comets. Operations are planned to continue for 3 years. Thus Safeguard, both the national US efforts and international efforts, are helping to meet Congressional goals. More importantly, the world-wide effort is meeting the task of identifying all PHOs. By 2013, more than 10,000 NEOs (Fig. 9)

Fig. 9 Known near-Earth asteroids

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have been discovered, and as our ability to observe these objects improves, that number will only increase. None yet has been found that poses an immediate threat. Finally, it should be noted that although not listed above, a significant contributor to finding and tracking near-Earth objects is the US Air Force Space Surveillance Network. This network is dedicated to detecting and tracking objects in orbit about the Earth and specifically those passing over the USA. Currently tracking approximately 21,000 objects, a key part of this capability was to be provided by the upgraded Space Fence which was canceled or put on hold in 2013. Consisting of three S-band radars spatially located along the 33rd parallel (33 North Latitude), the system was designed to perform un-cued detection and tracking of orbiting objects and would have significantly expanded the number of objects being tracked in Earth orbit. Funding however has been restored, and the program is expected to start again in April, 2014.

Space Missions There are still many unknowns regarding asteroids and comets. In order to fully assess the impact hazard due to these bodies, their physical attributes including their composition, orbits, and sizes need to be identified and characterized. Telescope observations rely on brightness measurements and assumptions regarding the albedo to determine size and mass. Albedo is defined to be the ratio of the reflected radiation from the surface to the incident radiation upon it. In this case, the Sun is the source of the radiation. The resulting albedo depends on the type of surface material indicating what kind of material makes up the observed body. Further, is the asteroid or comet a compact body or a loosely aggregate of ice particles held together weakly by gravity? There are many questions such as this regarding the chemical properties, and the physical dimensions of these near-Earth bodies/objects that need to be answered before a true assessment of potential hazard due to an Earth impact can be made. The best way to reduce the uncertainties and unknowns is to visit these bodies and make the needed measurements. That is indeed occurring and essentially started with visits to Comet Halley as it visited the inner Solar System in 1985. Comet and asteroid missions were highlighted on July 4, 2005 by the NASA Deep Impact mission and first impact with a comet surface (Tempel 1). That historic and well-known impact is shown in Fig. 10. These missions will continue for the future as other interests such as mining become more feasible and interest grows in the mineral wealth of these bodies. A list of some of the notable missions and spacecraft including the NASA Deep Impact is presented in the following: • International Cometary Explorer (ICE), originally known as the International Sun/Earth Explorer 3 (ISEE-3) – NASA mission, placed in halo orbit at EarthSun Lagrangian Point L1 then later sent to Comet Giacobini-Zinner. First spacecraft to fly through a comet’s tail (1978–1997).

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Fig. 10 Deep impact with comet Tempel 1

• Vega 1/Vera 2 – Former Soviet Union (Russia) missions to Venus and Comet Halley. Vega 1 and 2 were identical. Principally designed to explore the planet Venus, took advantage of launch dates to explore Comet Halley (1983–1985). • Giotto – European Space Agency (ESA) mission to Comets Halley and GriggSkjellerup. The first spacecraft to make closeup observations of a comet (1985–1992). • Sakigake – Japanese Institute of Space and Astronautical Science (ISAS) mission to Comet Halley. Japan’s first interplanetary spacecraft and the first deep space probe to be launched by any country other than the USA or the former Soviet Union (Russia). Part of the Comet Halley exploration effort during its visit to the inner Solar System in 1986 together with Japan’s Suisei, the Soviet/ French Vega probes, the ESA Giotto, and the NASA International Cometary Explorer (1985–1995). • Suisei – Japanese ISAS flyby mission to Comet Halley. Suisei was identical in construction and shape to Sakigake, but carried a different payload (1985–1992). • NEAR (Near-Earth Asteroid Rendezvous), renamed Shoemaker – NASA mission flyby of 253 Mathilde and rendezvous with 433 Eros (1996, terminated with landing on Eros, 2001). • Deep Space 1 – NASA flyby mission to Comet Borrelly and asteroid 9969 (Braille) (1998, retired 2001). • Stardust – NASA discovery mission to collect samples from Comet P/Wild 2, comet coma sample return mission, flew by asteroid 5535 (AnneFrank).

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A mission extension culminated in February 2011 with Stardust intercepting comet Tempel 1 (1999, 12-year mission ended 2011). • Hayabusa (Muses-C) – ISAS (Japan) sample return mission to Asteroid 25143 (Itokawa). Sample return failed however did recover some material from landing on asteroid (2003, returned to Earth 2010). • Rosetta – ESA Mission to Comet 67P (Churyumov-Gerasimenko) fly and flyby of asteroids Steins and Lutetia (2004, 10-year mission). • Deep Impact – NASA flyby of Comets 9P (Tempel 1 and surface impactor) and Hartley 2. On July 4, 2005, the impactor successfully collided with comet Tempel 1 nucleus (the first mission to impact the surface of a comet). Re-designated EPOXI in 2007 with dual purpose to study extrasolar planets and comet Hartley 2 (2005, mission ended 2013).

Conclusion The key ingredient to defending Earth from any potential asteroid or comet impact is time. The more time we have to prepare, the better. The key to more time is more accurate measurements of the objects size and orbit, then accurate predictions. We are moving in the right direction with continual improvements in sensor and realtime computing technologies. We are moving in the direction to give us more time once we identify a threat. However, we must not become complacent with our technology. We must remain vigilant at all times because there are surprises. For example, the risk due to air bursts may be higher than previously thought. The recent Russian Chelyabinsk meteor (2013) combined with other similar past air burst events suggests that the risk due to incoming small space rocks is much higher than the risk assumed based on astronomical observations. Further, computer simulations of these events suggest that since they are air burst, they are more damaging than the ground impact of equivalent nuclear explosions of the same yield. Finally, the frequency of these air burst events is more difficult to estimate since they leave little or no impact evidence on the ground. Based on these recent air burst impacts, it is believed by many that the next destructive impact will be an air burst. Thus, we still have much to do to fully categorize the threat due to PHOs. Regardless, once a PHO headed towards Earth is detected, what can we do? NASA and other agencies, including efforts supported by the United Nations, are working on the potential defenses now. Versus Hollywood and the movies, we will not simply “nuke” asteroids or comets. Unless carefully done, this will only turn one projectile into many (much like Comet Shoemaker-Levy 9) and significantly increase the threat for those on the ground. There are other options including the careful application of nuclear detonations. Perhaps, the most elegant of these Earth defense approaches are those that use gravity to perturb the PHOs orbit (Fig. 11). Using either push or pull, a spacecraft of

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Fig. 11 Defending Earth begins with finding the threat

sufficient mass can be put in orbit about the PHO and use its mass (gravity) to exert a force on the target object over time. The objective is to gradually change its orbit to avoid collision with the Earth. This technique is practical only for small NEOs (tens of meters to roughly 100 m in diameter) or possibly for medium-sized objects (hundreds of meters). It would also likely require decades of warning. Of the slow push/pull techniques, the gravity tractor appears to be by far the closest to technological readiness. For the larger asteroids or comets with diameters greater than 1 km, well-placed nuclear explosions may be our only option. The key to defending Earth is time. Imminent impacts with very short warning times of hours or weeks require better discovery capabilities. These capabilities need to improve to give us more warning time. As noted, we are moving in the direction of improved observations. Further, there will be more space missions telling us what these objects are composed of and even bringing back samples to Earth. However, the task of monitoring the heavens is and will be never ending. The Solar System is a dynamic environment, ever changing, and ever in motion. Orbits can and do change over time due to this dynamic environment as noted earlier. We must be continually vigilant, but then staring at the heavens is something mankind has done from the beginning of time.

Cross-References ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Hazard of Orbital Debris

Potentially Hazardous Asteroids and Comets

▶ Nature of the Threat/Historical Occurrence ▶ OSIRIS-REx Asteroid Sample-Return Mission

References Irion R (2013) It all began in chaos. Nat Geosci 224(1):42–59 Lakdavalla E (2011) Pummeling the Planets. Sky Telesc 122(2):20–27

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Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Threat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Launch Abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nuclear Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demise of Cosmos 954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operation Morning Light (Heaps 1978) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . International Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . United Nations Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . US National Space Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cosmos 1402 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Demise of Other Russian Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . US Nuclear Launch Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kennedy Era (20 Jan 1961–22 Nov 1963) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Johnson Era (22 Nov 1963–20 Jan 1969) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nixon Era (20 Jan 1960–9 Aug 1974) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ford Era (9 Aug 1974–20 Jan 1977) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carter Era (20 Jan 1977–20 Jan 1981) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reagan (20 Jan 1981–20 Jan 1989) and Bush, Sr. (20 Jan 1989–20 Jan 1993), Eras . . . . Clinton Era (20 Jan 1993–20 Jan 2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bush, Jr. (20 Jan 2001–20 Jan 2009), and Obama (20 Jan 2009–today) Eras . . . . . . . . . . . .

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C. Botts (*) Launch Safety, Air Force Space Command, 45th Space Wing Safety Office, Patrick Air Force Base, FL, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_69

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Safety Analysis Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Program Safety Analysis Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSRP Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Final Launch Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

Discussion of the potential threats to population from accidents involving satellite payloads utilizing radioisotopes for power generation or heating. Accidents include launch aborts and on-orbit failures that subsequently lead to Earth impact and possible release of radioactive materials. Understanding risks and acceptance prior to launch and contingency operations used to mitigate impact or release. Keywords

Radiological payload • Debris impact • Launch abort • Exposure • Acceptable risk • Launch criteria • INSRP • Range safety

Introduction The threat from cosmic space objects is not the only lurking danger our planet can face. Man-made satellites abound in various orbits and exist from launch until they exit our neighborhood or decay and impact the Earth. This transitory “life” means there are ample opportunities for accidents to occur. Anomalous events can happen during the difficult initial climb from the surface, while orbiting, or during a planned entry and landing or disposal. Encountering other space objects or reaching their end of life can lead to loss of a stable orbit and unplanned entry and impact of debris. These scenarios carry increased hazards and challenges when the involved spacecraft carries radioisotope materials. The benefits of the reliable radioactive components for generating necessary heat or power must be carefully weighed against the exposure risks should an accident occur.

The Threat Launch Abort Since the discovery of rocket propulsion, there have been launch accidents. Since 1957 there have been approximately 845 orbital rocket launches from the US Air Force Eastern Range (including Cape Canaveral Air Force Station and Kennedy Space Center). Sixty-nine of these launches ended in failure leading, in most cases,

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to a suborbital trajectory and ground or ocean impact. Because a successful launch and ascent to orbit cannot be guaranteed, the Range evaluates the potential for failure and calculates the risk to the public, personnel, and assets from the three basic hazards of launch abort – debris impact, toxic effluent exposure, and distant focusing overpressure (DFO) effects.

On Orbit Once the challenge of achieving a stable orbit is met, spacecraft can enjoy a rather benign life, performing a primary task, making station keeping adjustments, and basically taking up residence at its assigned spot in space. Events that can disturb this condition include onboard system failures, encounters with other space objects, and final expenditure of critical “fuel” to defend against the interminable pull of gravity. A sufficient disturbance can lead to rapid or slow decay until the space vehicle or remaining debris encounter atmospheric entry and terminal descent toward final impact. Some satellite missions are designed for space exploration and do not maintain a standard orbit around Earth. These transfer trajectories can take advantage of gravity assist maneuvers to increase velocity and may utilize an Earth flyby. Anomalies during transit could lead to atmospheric entry and subsequent impact.

The Risk Each launch from the Eastern Range is evaluated to verify the risk is within acceptable limits. Criteria for the three standard launch abort hazards are dictated in Air Force Space Command Manual (AFSPCMAN) 91-710, Range Safety User Requirements, volume 1, Air Force Space Command Range Safety Policies and Procedures: 2.3.5. Range Safety Offices. . . .The responsibilities of the Chiefs of Safety or their designated representatives apply throughout all phases of a launch program (planning, generation, execution, and recovery) and include, but are not limited to, the following: 2.3.5.8. Determining criteria for flight termination action; assessing risks to protect the general public, launch area, and launch complex personnel and property; developing and using mathematical models to increase the effectiveness of errant vehicle control while minimizing restrictions on launch vehicle flight; establishing mission rules and criteria for flight termination action in conjunction with the Range User. 2.3.5.16. Ensuring public safety up until the time of flight at which the launch vehicle/ spacecraft achieves a sustainable orbit or escape velocity for space vehicles, or through final impact for vehicles with suborbital trajectories and can be shown to pose no statistically significant additional safety risk. 2.5.3.5. Performing risk analyses and implementing design and mission plans consistent with acceptable risk to the general public for deorbiting launch vehicles, upper stages and spacecraft.

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Fig. 1 Air force launch risk criteria

Calculated risk values are in the form of collective expectation of casualty, EC, and individual probability of casualty, PC, based on each hazard’s influence on human survivability or probability of impact, PI, for asset damage assessments. The consolidated EC risk (from debris, toxics, and DFO) to persons unassociated with launch processing activities (i.e., the general public) must be below 100 in a million (100  10 6 or 1 chance in 10,000). The Launch Decision Authority (i.e., the Space Wing Commander or designee) approves launch and under certain circumstances may accept a higher risk (usually based upon national need) according to Fig. 1. Additionally, the individual risk, PC, must be below one in a million (1  10 6). These criteria were developed early in the space program when Public Law 60, establishing the Joint Long-Range Proving Ground for guided missiles, was approved in May of 1949. In the Legislative History the need for a test range was discussed and the then undisclosed location’s ideal placement in a remote area was promoted. The following excerpt described the basic safety philosophy that led to present day risk criteria: For reasons of military security, the location of the proposed long-range guided-missile proving ground cannot now be disclosed. However, it has been ascertained that there will be no serious likelihood of hazard to persons or property, or of interference with private and commercial interests in connection with the test flying of missiles on the proposed range. The danger will be very small because every possible precaution will be taken. Means will be provided to dispose of missiles in the air, over a safe area, should they deviate too far off

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course. Normally they will fly so high as to be impossible of detection except with special instruments. From a safety standpoint they will be no more dangerous than conventional airplanes flying overhead, and from a nuisance standpoint they will be less objectionable. Most important of all, the test range will be located in a region so sparsely inhabited in the areas where there might be any danger that the hazard will be wholly negligible.

This suggestion made good sense, to be no more dangerous than an aircraft flying overhead, and studies at the time provided reasonable estimation of that aircraft risk thus establishing a benchmark for rocket flights. Launch constraints evacuate the launch pad and surrounding Flight Hazard Area on CCAFS/KSC and the immediate ocean downrange. Additional requirements prevent purposeful overflight of landmasses during the early phase of ascent. Autonomous and commanded Range Safety Systems can detect anomalous flight behavior that violates predetermined rules and appropriate action can terminate thrust or destroy the vehicle’s propellant tank integrity to control fallback and impact within acceptable risk zones. Launches of spacecraft payloads which utilize radioisotope materials require additional risk evaluation to understand the potential long-term effects of accidental exposure should a failure lead to release.

Nuclear Risk The use of radioisotope material in spacecraft is well established providing reliable heat to maintain electronics or generate electricity. Since 1961 there have been approximately 70 launches from the USA, USSR/Russia, and China of payloads which utilize radioisotope materials. Thirty-one of those originated from the USA. Ten of the 70 international payloads had failures at launch or during the mission. Table 1 provides a description of these failures and their outcomes, some speculative since they have not been registered in the United Nations Office for Outer Space Affairs Register of Space Objects (UNOOSA). Design features of spacecraft utilizing radioisotope material normally include either survivable protection or the ability to deposit the space nuclear subsystem into a longduration, safe orbit. In the case of Cosmos 954, the nuclear reactor was successfully separated from the spacecraft, but the system intended to boost it into a safe orbit failed. Failure of that mitigating device can lead to release upon reentry and land impact. The Soviet safety philosophy provides for a backup mode that disperses the reactor core designed to limit radiation dose to people living in a potentially contaminated area to less than 0.5 rem (5 mSv) during the first year after reentry (Angelo 1985). Following this accident, the reactor safing system was redesigned to improve reliability and safety.

Demise of Cosmos 954 The most intensive recovery operation to date following the reentry and impact of a man-made nuclear powered spacecraft was initiated early in December of 1977

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(Heaps 1978). Technicians at the North American Air Defense (NORAD) Space Defense Center had been monitoring the Russian Cosmos 954 Radar Ocean Reconnaissance Satellite (RORSAT) for 88 days since its launch on September 18, 1977. Known in Russia as the Upravlyaemy Sputnik Aktivny (У правляемый Спутник Table 1 Nuclear payload reentries Launch vehicle ThorAblestar

Radioisotope system 2 SNAP 9A RTGs (238Pu)

Date of impact/ burn up 04/21/ 1964

Date launched 04/21/1964

Spacecraft Transit 5B-N3 USA

05/18/1968

Nimbus B-1 USA

Thor Agena-D

1 SNAP 19B2 RTG (238Pu) PuO2 Mo Cermet

05/18/ 1968

02/23/1969

Luna Ye-8-5 USSR

Proton 8K82K

1 210Po RHU

02/23/ 1969

23 September 1969

Cosmos 300 Luna Ye-8-5 USSR

Proton 8K82K

1 210Po RHU

09/27/ 1969

10/22/1969

Proton 8K82K

1 210Po RHU

10/24/ 1969

04/11/1970

Cosmos 305 Luna Ye-8-5 USSR Apollo 13

Saturn V

04/17/ 1970

ALSEP RTG impacted in Tonga Trench, Pacific Ocean. No release detected

04/25/1973

ALSEP USA Unnamed

1 SNAP 27 RTG (238Pu) PuO2 microspheres

Tsiklon-2

Buk Reactor (235U) 1st flight of BES-5

05/07/ 1973

Launch failure led to reactor fallback into the Pacific Ocean north of Japan. Radiation was detected by US air sampling aircraft

Alternate 02/19/1969

RORSAT USSR

Impact/burnup area Atmospheric burnup over West Indian Ocean north of Madagascar Santa Barbara Channel ~5 km north of San Miguel Island. Recovered at ~90 m depth 5 months later. No detrimental effects to fuel 1st Stage engine failure caused rocket to crash 15 km from pad. Rumor is sentries downrange found source and used it as a hand warmer Failed to leave low Earth orbit due to stage 4 failure. Reenters and is destroyed by frictional heating Still attached to 4th Stage, reenters and is destroyed by frictional heating

(continued)

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Table 1 (continued)

Date launched 09/18/1977

Spacecraft Cosmos 954 RORSAT USSR

08/30/1982

Cosmos 1402 RORSAT USSR Mars 96

11/16/1996

Launch vehicle Tsiklon-2

Radioisotope system Buk Reactor (235U)

Date of impact/ burn up 01/24/ 1978

Tsiklon-2

Buk Reactor (235U)

02/07/ 1983

Proton K/D-2

4 RTGs (238Pu) PuO2 pellets

11/17/ 1996

Russia

Impact/burnup area Atmospheric breakup and impact in Northwest Territory, Canada. Major recovery effort, Operation Morning Light Atmospheric burnup over South Atlantic, east of Brazil. No release detected Atmospheric burnup over South Pacific Ocean off the coast of Chile and Bolivia. No release detected. May have impacted land

RTG radioisotope thermoelectric generator, RHU radioisotope heater unit, ALSEP Apollo Lunar Surface Experiment Package

Fig. 2 RORSAT with Buk (Бук) reactor

Активный), or US-A, this satellite was powered by a Buk (Бук) nuclear reactor utilizing 30 kg of uranium-235 (see Fig. 2). Concerns were rising as the spacecraft’s orbit showed signs of instability and ever decreasing velocity. The US Department of Energy’s Nuclear Emergency Search Team (NEST) was alerted of Cosmos 954’s

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impending reentry. Given the chaotic nature of the spacecraft’s trajectory, it was extremely difficult to predict when the final entry point would occur and where the debris would impact. Without sufficient information the risk of exposure to the radioactive materials was unknown. Impact in a high population area meant high risk of exposure and long-term effects. Ocean impact meant low concern of public exposure. Land impact in a low population area meant the risk might be manageable if the hazardous debris could be safely recovered. Throughout January of 1978 Cosmos continued to orbit erratically with each ground track moving westward. International governments were notified of the potential disaster, and by the 21st of January, reentry was narrowed to within a few days. However, an accurate impact footprint could not be completed until the debris entered the atmosphere. A consensus of aerospace engineers examining the reentry formed a solution that made the likely impact in the northern part of North America. By the night of the 23rd, the impact location was becoming more focused and the final orbits of Cosmos 954 were bringing it over the North American continent more and more frequently. At 2:00 AM on January 24 Cosmos appeared to be on its last orbit and NORAD predicted a 3:56 AM Pacific Standard Time reentry with impact at 4:17 AM. At 4:30 AM Cosmos reentered the atmosphere and in a fiery death trailed debris toward the Northwest Territories of Canada. There were few eyewitnesses on January 24 in Yellowknife, a small town situated on the western end of Great Slave Lake. Jimmy Doctor, a Dog Rib Indian observed a big flame going northeast and thought it might be a plane on fire. Marie Ruman, also of the Dog Rib tribe worked at the Canadian Broadcasting Corporation cleaning offices at night. She had arrived home early that morning and saw what she thought was a plane on fire with a flaming jet stream heading northeast. Peter Pagonis was delivering tanks of water to the military aircraft hangar at the Yellowknife airport. He noticed three bluish red UFOs streaking across the dark morning sky. The streaks trailed fiery tails and dove beyond the town in a northeasterly direction. In this early instance of nuclear powered spacecraft use, there was no pre-approved risk assessment. There certainly was an understanding that the space nuclear power reactor provided a threat. and thus, a reliable means to “dispose” of the hazard was designed into the system. But once this disposal mechanism failed to transport the reactor core to a sufficiently high orbit, the risk event was inevitable. The Soviet-designed backup system allowed for reentry burnup of the reactor core but admittedly would deliver some remaining material to impact leaving a purported low-level contamination area. Perhaps too high of a guarantee was afforded to that critical system; perhaps any remaining failure probability was acceptable to the designers and launch agency. This event would drive fundamental changes in the way the world would accept these types of launches. For this disaster, however, the mitigation had failed; only reaction, response, and recovery could be employed to lower the risk of exposure.

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The Mitigation Operation Morning Light (Heaps 1978) With the reentry and impact assured, NEST had begun to assemble the necessary manpower and equipment needed to conduct a recovery operation. On January 22 the NEST team began assembling their final members and equipment at Andrews Air Force Base in Maryland. By January 23 a small team had deployed to the Canadian Forces Base near Edmonton, 600 miles south of Yellowknife. While many breathed sighs of relief that Cosmos 954 had landed in a remote area of northern Canada, locals at Yellowknife became concerned for the nearly 47,000 people, scattered over approximately 1.5 million square miles. Certainly this population consisted of small communities of trappers and hunters, but the extent of the debris coverage was as yet unknown. The chosen headquarters for Operation Morning Light was the second floor of Hangar 5 at the Canadian Armed Forces Base at Namao north of Edmonton. Military personnel, scientists, and equipment began assembling there to determine the nature of the incident and the appropriate response. This was made especially difficult considering the time of year and the extreme temperatures ( 60  F at night) that would be faced on the Great Slave Lake. Colonel David Garland, Commander of Base Edmonton, acted as the on-scene commander of the mission directing Canadian and American personnel from Canada’s Department of National Defense and Atomic Energy Control Board and the US Department of Energy. DOE efforts were under the control of Mahlon Gates through scientific advisors and equipment managers. The Department of National Defense objective was to locate, secure, and identify risk. The Atomic Energy Control Board was to recover, store, and dispose of the hazardous materials found. Public relations were controlled through DOE representative Dave Jackson, tasked with communicating details of the accident and recovery operations to a growing crowd of media agents arriving from the USA, Japan, Australia, Europe, and, of course, Canada. Initial surveys on January 25 at high altitude detected no radiation, and the search began in earnest on the ground. Twelve aircraft flew over the predicted debris footprint (see Fig. 3) searching for indications of radiation from specialized instrumentation. On January 28 the gamma ray spectrometer flying aboard a Canadian Hercules aircraft gave the first indication that a radiation source was below in the McLeod Bay region at the northeast end of Great Slave Lake. Finding the debris that caused the reading would be the next difficult task. On that same day, Mike Mobley and John Mordhurst were traveling over the Thelon River via dog sled tracing the route of John Hornby an explorer who had died in the area in 1927. Headed to Hornby’s final camp, they came around the river bend and discovered a small, shallow, pock-marked crater, about 8 f. across, containing pieces of metal. Several charred, twisted metal tubes

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Fig. 3 Cosmos 954 debris footprint and search areas

were disconnected from a squashed canister. What looked perhaps like an abandoned snowmobile had dug into the snow and burned an irregular pattern, forming a patch of smooth black ice. Mordhurst touched the metal with his gloved hand. Other smaller pieces of metal were scattered along a path to the crater. They left after about 5 min and continued on to Hornby Point. Later, when they returned to their base camp at Warden’s Grove, rejoining their larger group, they made contact via radio with Yellowknife and reported what they had seen. That was followed with a transmission warning them to stay a thousand feet from the objects and by morning a plane picked them up and took them to Yellowknife for examination and interviews. A NEST geophysicist departed for the site just hours after the discovery was reported and suspected the metal pieces were part of the satellite’s propulsion unit. His radiation detector registered only 15 Roentgens, a hazard, but this indicated the debris was not part of the reactor core. By January 30 two large fragments and several dozen smaller pieces had been found making it possible to refine the footprint and predict the most likely areas where debris might be located. As hits were made from the airborne instrumentation, their location would be transmitted to helicopter teams who would try to locate the site and survey with handheld detectors. Debris or snow containing very small particles were deposited in bags and sealed in specially lined steel drums for transport to Namao and onward to the Whiteshell Atomic Energy Labs at Pinawa, Manitoba, for analysis. The slow progress and difficult logistics involved led to

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building an intermediary supply camp named Camp Garland on “Cosmos” Lake very near Warden’s Grove and Hornby Point in the Thelon Wildlife Sanctuary. The search continued into February with only small “pepper flake” pieces being found in the snow. Results from the Whiteshell analyses were withheld from the public which caused increased concern. On February 8 a small, flat fragment, 10 in. by 3 in., was found on the ice near McLeod Bay which had a reading of 500 roentgens per hour. Two other “hot” fragments were also located. Cosmos 954’s reactor core assembly was estimated to weigh about 117 lb (53 kg). The reactor assembly (with fuel) weighed approximately 298 lb (135 kg) (Grahn). By the end of March, searchers had accumulated 100 lb (45.4 kg) of material of which only a fraction was from the uranium core. Some of the material would have been vaporized on reentry. Since the core had been ejected, the reentry of the spacecraft would have a separate trajectory than the reactor core. Radioactive particles were being found south of the footprint meaning the wind may have dispersed the material over a larger area. In April particles of enriched uranium from the core were discovered hundreds of miles from Yellowknife as far west as Buffalo Lake and Hay River. Cleanup efforts began in the towns of Snowdrift, Pine Point, and Fort Resolution. The distribution of particles was sparse; in Snowdrift six particles were found roughly 200 f. apart. As the spring thaw began, particles would no longer be dormant on the ice surface. Summer teams, mostly Canadian Geological Survey personnel, continued the search as the US teams returned home. Camp Garland had been disbanded by the end of March since the lake ice could no longer hold the 78,000 lb Hercules aircraft. On April 3 40 fishing lodges had been searched and cleared of fallout. It was concluded that the core did not completely burn up in the atmosphere as many scientists suggested. There may have been millions of the tiny particles on the ice which sank to the lakebed when the spring thaw arrived. The data obtained during Operation Morning Light was reviewed for months after the end of the effort. An analysis by Lawrence Livermore Lab (Hanafee 1978) provided information on debris recovered much of which consisted of beryllium parts. Perhaps a more thorough examination of the potential failures and a rigorous assessment of the consequences could have revealed the need for higher reliability systems or alternative methods of preventing release of these hazardous components. Depending on pure chance that reentry might occur at such a time and location to assure impact in a less populated zone is not a recommended practice. Designing in protective devices or other reaction systems that prevent release under any failure circumstances provides a much better assurance that the benefits of radioisotope power systems are worth the risk.

Design Changes Cosmos 954 prompted design changes to the Buk reactor. The modifications would trigger the safing sequence by active command from the ground, or if the spacecraft lost pressurization or became unstable, or if reactor power anomalies occurred (Siddiqi 1999). The systems would separate as before into three components: the

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nuclear reactor with a self-contained booster rocket, the satellite’s propulsion stage, and the satellite bus. If the reactor boosting maneuver failed, a backup mechanism would trigger due to natural orbital decay. At 114–120 km altitude, the aerodynamic heating would activate ejection of the fuel core from the reactor. In 1983 this system was operated for Cosmos 1402.

International Policy United Nations Reaction Following the Cosmos 954 accident, the UN pushed for increased notification of hazardous satellite launches. In November 1978 the General Assembly authorized its existing Committee on the Peaceful Uses of Outer Space (UNCOPUOS) to establish a technical working group to evaluate space nuclear systems and their risks. Beginning as an ad hoc committee in 1958, UNCOPUOS was made a permanent body by 1959, and in 1961 requested that a public registry of launchings be maintained. The Convention on Registration of Objects Launched into Outer Space in 1974 provided that Member States declare launchings to the UN. As of 1 January 2012, 56 States have acceded or ratified, four have signed, and two international intergovernmental organizations have declared their acceptance of the rights and obligations provided for in the Registration Convention. Approximately 93.5 % of all functional space objects have been registered with the SecretaryGeneral (UNOOSA). The Scientific and Technical Subcommittee debated implications of Cosmos 954. A moratorium on launches of nuclear reactors was proposed but a consensus was not reached to support this. In 1979, the Subcommittee established a Working Group on the Use of NPS in Outer Space which deliberated use of, reentry prediction, and possible safety measures for these devices (Benko et al. 1985). Their report provided agreements including: 1. Appropriate measures for radiation protection should be derived principally from the existing, and internationally accepted, basic standards recommended by the International Commission on Radiological Protection (ICRP). These measures should be taken for protection during all phases of an orbital mission of a spacecraft with nuclear power sources: launch, parking orbit, operational orbit, or reentry. 2. The safety of radioisotope systems is being assured by designing them to contain the radioisotope for all normal and abnormal conditions. The design should ensure minimal leakage of the radioactive contents and must at least meet the limits recommended by the ICRP in all circumstances including launch accidents, reentry into the atmosphere, impact, and prolonged water immersion. 3. Reactor systems should be started and operated in orbits sufficiently high to give time for radioactive materials to decay to a safe level in space after the end of mission. In this way the dose equivalents at the time of reentry could be

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guaranteed in all circumstances to be within the limits recommended by the ICRP for non-accident conditions. If reactors are intended for use in low orbits where the radioactive materials do not have sufficient time to decay to an acceptable level, safety depends on the start of the operation in orbit, and the success of boosting nuclear power sources to a higher orbit after operation is completed. In the event of an unsuccessful boost into higher orbit, the system must in all circumstances be capable of dispersing the radioactive material so that when the material reaches the Earth, the radiological hazard conforms to the recommendations of the ICRP. They concluded that Space Nuclear Systems can be safely used provided the above considerations were addressed and the decision to use such a system should be based on technical considerations provided safety requirements can be met. In 1992, Principles Relevant to the Use of Nuclear Power Sources in Outer Space, provided 11 guidelines to ensure the safe use of space nuclear systems. Principle 3 restricted the use of nuclear systems to missions which could not otherwise be powered (e.g., solar, nonnuclear) and described general goals and specific criteria for nuclear reactors and radioisotope generators. Principle 4 ensures that a thorough and comprehensive safety assessment is conducted prior to launch and is made publicly available. Principle 5 requires notification of reentry “in a timely fashion” and Principle 6 that the launching State promptly respond to requests for further information on a reentry event. In 2007, the Subcommittee and the International Atomic Energy Agency (IAEA) agreed to jointly draft a safety framework for space nuclear systems. This Safety Framework for Nuclear Power Source Applications in Outer Space represents technical consensus of both bodies (UN and IAEA 2009). It provides guidance for governments on safety policy, requirements, and processes, justification for use of nuclear systems, launch authorization, and emergency preparedness and response. The framework describes assignment of responsibilities for safety and leadership goals in maintaining a safety culture. Technical guidance is provided for maintaining competency in nuclear safety, incorporating safety in design and development, appropriate risk assessment methods, and mitigation of accident consequences.

US National Space Policy The latest update of US National Space Policy (Pres. B. Obama 2010) reminds readers of the growing orbital debris issue and challenges departments and agencies to “strengthen measures to mitigate orbital debris.” It encourages international cooperation in identifying improvements and innovations toward space surveillance and debris monitoring capabilities as well as advances in space nuclear power to support science and exploration. To preserve “the space environment for the responsible, peaceful, and safe use of all users,” the Policy directs that the USA must:

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• Lead the continued development and adoption of international and industry standards and policies to minimize debris, such as the United Nations Space Debris Mitigation Guidelines; • Develop, maintain, and use space situational awareness (SSA) information from commercial, civil, and national security sources to detect, identify, and attribute actions in space that are contrary to responsible use and the long-term sustainability of the space environment; • Continue to follow the United States Government Orbital Debris Mitigation Standard Practices, consistent with mission requirements and cost effectiveness, in the procurement and operation of spacecraft, launch services, and the conduct of tests and experiments in space; • Pursue research and development of technologies and techniques, through the Administrator of the National Aeronautics and Space Administration (NASA) and the Secretary of Defense, to mitigate and remove on-orbit debris, reduce hazards, and increase understanding of the current and future debris environment; and • Require the head of the sponsoring department or agency to approve exceptions to the United States Government Orbital Debris Mitigation Standard Practices and notify the Secretary of State.

This focus on debris mitigation enhances the statements provided in previous editions of National Space Policy by Presidents Bush (Pres. G. H. W. Bush 1988) and Clinton (Pres. W. Clinton 1989); (Pres. W. Clinton 1996). In 1997 a US interagency working group created a set of orbital debris reporting standard practices. These were based on NASA’s standard (NASA 1996) for limiting debris and intended for government-operated or government-procured systems. Approved for implementation by all US Government agencies in February 2001 (SecDef 2001), these guidelines have been shared with international aerospace agencies to encourage adoption of similar practices. The Inter-Agency Space Debris Coordination Committee (IADC) promotes information exchange and development of space debris research and mitigation methods.

Cosmos 1402 On 23 January 1983 these policies were tested as another Russian Cosmos spacecraft failed to boost the separated nuclear reactor into a higher, safe, 400-year orbit. As designed, the reactor components were separated and burned up on reentry. Remaining particles dispersed over the South Atlantic Ocean east of Brazil.

Demise of Other Russian Reactors Of 39 RORSAT satellite launches from 1965 to 1998, 31 carried nuclear material. Of these 31, three failed to properly achieve relocation to a safe orbit and the radioisotope burned on reentry with any remaining debris or particles impacting in the ocean or, in the case of Cosmos 954, the Northwest Territory of Canada.

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US Nuclear Launch Approval Since the Space Age began with Sputnik’s debut, the USA has developed the use of space nuclear systems and the accompanying space policies to safely utilize them. In November 1957 President Eisenhower reconstituted President Truman’s little used Science Advisory Committee (United States 1986) as the President’s Science Advisory Committee (PSAC). Prompted by the launch of Sputnik, Eisenhower ushered in a new era of collaboration between President and scientists. On advice of the PSAC, he proposed to the Congress that the country’s civilian space program should be led through the existing National Advisory Committee for Aeronautics (NACA), the precursor to NASA which was later established in 1958. The National Aeronautics and Space Council (NASC) was also created in 1958 and consisted of the President, as chairman, the Secretaries of State and Defense, the NASA Administrator, the Chairman of the Atomic Energy Commission (AEC), and any additional members that the President chose to appoint. In January 1959, the advent of space nuclear power was christened when AEC officials showed a polonium thermoelectric demonstration device to President Eisenhower in the oval office! In reaction to complaints that a highly lethal item had been placed on the President’s desk, a safety evaluation was developed in a matter of days. This first Safety Evaluation Report (SER) covered handling procedures and other matters regarding the safety of RTGs and accompanied the demonstration device as it toured other foreign capitals. Criteria were developed in June 1960 at a meeting of the AEC’s Aerospace Nuclear Safety Board and included: • The isotope material should be contained and the capsule present no hazard in the event of a launch abort. • This condition should be maintained in the event of failure to reach orbit, and in addition the capsule should fall in broad ocean areas. • In the event of failure to obtain a stable orbit, or in reentry from a successful orbit for any planned time, the capsule and contents should be burned and dispersed in the upper atmosphere. By the end of 1959, the AEC had established an Aerospace Nuclear Safety Board “to analyze and project the possible effects of nuclear space devices upon the health of the peoples of the world. . .and recommend standards of safe practice for the employment of nuclear powered space devices proposed by the U.S.” (DOE 1987). In 1960, Keith Glennan, the first NASA Administrator, suggested that the AEC should begin to define the conditions for safe use of nuclear auxiliary power systems in space missions and propose safeguards which would have to be provided. In August a memorandum of understanding was signed between the AEC and NASA assigning Harold Finger as manager of a joint project office. This new AEC-NASA Nuclear Propulsion Office reported to the Director of the Division of

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Reactor Development in the AEC and to the Director of Launch Vehicle Programs in NASA. Safety concerns and the organizational effort to bring the AEC and NASA together led to new mechanisms for handling and anticipating safety problems.

Kennedy Era (20 Jan 1961–22 Nov 1963) By March 1961 a comprehensive safety analysis of the Transit spacecraft to be launched aboard a Thor-Ablestar rocket was completed. The Transit-4A spacecraft utilized a SNAP-3B radioisotope thermoelectric generator (RTG). This early RTG was one of the many Systems for Nuclear Auxiliary Power which were developed and flown. The analysis focused on potential hazards that might result if launch or reentry failures were to occur. It was shared at a joint meeting of Navy, Air Force, DoD, and AEC personnel, and responsibilities of the various agencies were defined. In May of this same year, a National Security Action Memorandum (NSAM) was issued by then President John F. Kennedy’s Special Assistant for National Security Affairs, McGeorge Bundy. NSAM-50, Official Announcements of Launching Into Space of Systems Involving Nuclear Power In Any Form, provided in three short sentences that: The President desires to reserve to himself all first official announcements covering the launching into space of systems involving nuclear power in any form. The President is especially concerned with announcements relating to the planned use of SNAP devices aboard TRANSIT satellites which are tentatively scheduled for launching in June and July of 1961. Will you please advise members of the Space Council of the President’s interest.

Seventeen years before the Cosmos 954 accident, the importance of appropriate decision authority was evident. Vice President Lyndon Johnson was made the head of the NASC per the National Aeronautics and Space Act of 1961. This Act provided that presidential approval of nuclear power system launches be coordinated by the NASC. Initially denied approval by the NASC due primarily to objections from the Department of State, the Transit 4-A launch received approval on 23 June for a scheduled launch on the 27th. Two days delayed, the first launch of a US satellite carrying radioisotope material occurred on 29 June 1961. In 1962, concerns that a single launch failure might shut down the SNAP program led the Joint Space Nuclear Propulsion Office to expand the review group (DOE 1987). NASA was invited to participate in the reviews of DoD’s Transit spacecraft. These early reviews solidified procedures for launch approval. While most assessments showed little safety risk from a launch abort accident, it was pointed out that the potential for political repercussions was great, especially if foreign territories were affected. Establishing a review group to assess safety issues required some choices in the organizational structure. An ad hoc panel representative of concerned agencies was preferred over a standing committee, since it was thought that a committee would

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require public participation, a difficult prospect given the confidential nature of the information. As early as January 1963, a model charter had been developed for a possible interagency review group, eventually dubbed the Interagency Nuclear Safety Review Panel (INSRP). On 17 April 1963, following the second Transit launch with more launches scheduled, President Kennedy signed a more definitive policy via NSAM-235, Large-Scale Scientific or Technological Experiments with Possible Adverse Environmental Effects. This policy governed conduct of “experiments that might have significant or protracted effects on the physical or biological environment” and provided the following guidelines (paraphrased): 1. The head of an agency proposing such an experiment must notify the Special Assistant to the President for Science and Technology sufficiently in advance. 2. The sponsoring agency must prepare a detailed evaluation of the importance of the experiment and possible direct or indirect effects associated with it. 3. The Special Asst. for Science and Technology reviews this evaluation to assure that the need has been properly weighed against possible adverse environmental effects. 4. The Special Asst. recommends to the President what action should be taken. He may request additional sponsoring agency studies or undertake independent study if the provided information is deemed inadequate. 5. Experiments involving significant or protracted adverse effects will not be conducted without President Kennedy’s prior approval. 6. Experiments with major national security implications require notification of the Special Asst. for National Security Affairs and Special Asst. for Science and Technology. The Special Asst. for Nat’l Security Affairs determines the procedure for review of these experiments to assure the need has been properly weighed against possible adverse environmental effects. 7. Consistent with national security and subsequent to approval, there should be early and widespread dissemination of public information explaining experiments of this type. 8. The final decision to conduct such experiments resides with the government. The National Academy of Sciences and where appropriate international scientific bodies or intergovernmental organizations may be consulted in the case of those experiments that might have effects beyond the USA. This course of action requires consultation with the Special Asst. for Science and Technology, the sponsoring agency, and the State Department. This then specified review and approval authority for launches of nuclear materials but left out any details of the required evaluation.

Johnson Era (22 Nov 1963–20 Jan 1969) On 10 April 1965, President Johnson, once again through McGeorge Bundy, revised the original NSAM-50 with a re-titled subject of Launching into Space of

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Systems Involving Nuclear Power. It reiterated that presidential approval was required for all launches of nuclear power devices into space and exempted “minor radioactive calibration and heat sources.” More specific criteria for the required evaluation were provided including probability of mission success, health and safety factors, and international political considerations. It required that the Secretary of State be consulted as to the timing of tests, that official announcements be made by the White House Press Secretary, and that the Executive Secretary of the NASC be responsible for coordinating requests for launch approval. This update directly followed the successful launch of SNAPSHOT on 3 April 1965, 1 year after the Transit 5B-N3 launch failure that caused 2 SNAP-9A RTGs to reenter and burn up over the West Indian Ocean north of Madagascar. There had been four successful launches of Transit spacecraft using RTGs prior to that event. SNAPSHOT carried the first Uranium-based space reactor power system designated SNAP-10A. After mission objectives were met, the reactor was placed in a high orbit (presently at approximately 832 miles altitude). No US reactor system has been launched since.

Nixon Era (20 Jan 1960–9 Aug 1974) Even with four more failures (five total) involving space nuclear systems (i.e., Nimbus B-1, Cosmos 300, Apollo 13, Cosmos 469) during the years from issuance of the new NSAM-50 until the end of 1977, there were no changes to this policy. Evaluations followed the prescribed process laid down by the Aerospace Safety Review Board. The Interagency Safety Review Panel (ISRP 1969) wrote in their SER that the evaluation provided “Agency Heads of NASA, AEC and DoD with a common nuclear safety basis for their recommendations regarding flight approval.” The Apollo missions that involved deployment of the Apollo Lunar Surface Experiments Package (ALSEP) in 1968, which utilized the SNAP-27 RTG, shows how the ISRP established a protocol for conducting and reporting their findings. This ISRP consisted of five discipline-oriented working groups: Range Safety, Reentry, Meteorology, Oceanography, and Biomedical. For the SNAP-27/ALSEP review, approximately 100 varied scientific and engineering specialists from a number of government agencies, laboratories, and universities brought the best available expertise to bear. Each working group produced a final report of their analyses and conclusions which were used as a basis for the SER. In July 1973, President Nixon abolished the NASC and PSAC and shifted responsibility for nuclear power source launch approval to the National Security Council (NSC).

Ford Era (9 Aug 1974–20 Jan 1977) President Ford instructed the Congress, in the first week after his inauguration in 1974, to reinstate the Science and Technology advisory function in the Executive

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Office of the President. The Office of Science and Technology Policy (OSTP) was formally established in May 1976 and given responsibility for nuclear power source launch approval (Frederick 1989).

Carter Era (20 Jan 1977–20 Jan 1981) Cosmos 954 had launched in September 1977 and began to threaten reentry by the end of November. Perhaps prompted by this pending accident, President Carter issued a new policy rescinding all previous NSAMs relating to nuclear payload launch approval. The first version of the Presidential Directive, National Security Memorandum-25 (PD/NSC-25) was signed on 14 December 1977 by the President’s National Security Advisor, Zbigniew Brzezinski. It reiterated the continued previous policy of providing the President with approval opportunity but also created limits on approval levels for radioactive source material. PD/NSC-25 established that: 9. A separate procedure will be followed for launching space nuclear systems. An environmental impact statement or a nuclear safety evaluation report, as appropriate, will be prepared. In addition, the President’s approval is required for launches of spacecraft utilizing radioactive sources con-taining more than 20 curies of material in Radiotoxicity Groups I and II and for more than 200 curies of material in Radiotoxicity Groups III and IV (as given in Table I of the NASC report of June 16, 1970 on “Nuclear Safety Review and Approval Procedures.” An ad hoc Interagency Nuclear Safety Review Panel consisting of members from the Department of Defense, Department of Energy, and National Aeronautics and Space Administration will evaluate the risks associated with the mission and prepare a Nuclear Safety Evaluation Report. The Nuclear Regulatory Commission should be requested to participate as an observer when appropriate. The head of the sponsoring agency will request the President’s approval for the flight through the Office of Science and Technology Policy. The Director is authorized to render approval for such launchings, unless he considers it advisable to forward the matter to the President for decision.

In his first year as President, Jimmy Carter faced a unique challenge dealing with the reentry of a Russian nuclear reactor. The impact of Cosmos 954 debris on Canada drove changes at the United Nations level, but did not prompt changes to US nuclear payload launch approval policy. Seventeen years would pass before PD/NSC-25 was revised.

Reagan (20 Jan 1981–20 Jan 1989) and Bush, Sr. (20 Jan 1989–20 Jan 1993), Eras During this period between 1981 and 1993, there were 20 launches of nuclear payloads with one incident involving reentry of the Cosmos 1402 spacecraft in 1983.

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Clinton Era (20 Jan 1993–20 Jan 2001) In May 1995 President Clinton’s Assistant for National Security Affairs, Anthony Lake, signed a revised PD/NSC-25 providing an update to the standard used to determine radioactivity limits associated with approval authority. This was prompted by an interagency review led by OSTP. The older NASC report of 1970, Nuclear Safety Review and Approval Procedures for Minor Radioactive Sources in Space Operations, was replaced with a more global specification in the International Atomic Energy Association’s (IAEA’s) Safety Series Number 6, Regulations for the Safe Transport of Radioactive Materials, written in 1985 and amended in 1990. Paragraph 9 changed to: 9. A separate procedure will be followed for launching nuclear systems. An environmental impact analysis or nuclear safety evaluation report, as appropriate, will be prepared. The President’s approval is required for launches of spacecraft utilizing reactors and other devices with a potential for criticality and radioactive sources containing total quantities greater than 1,000 times the A2 value listed in Table I of the International Atomic Energy Agency’s Safety Series No. 6, Regulations for the Safe Transport of Radioactive materials, 1985 Edition (as amended 1990). Launch of sources containing quantities greater than 0.1 percent of the A2 value from this table will be forecasted quarterly to the Office of Science and Technology Policy (OSTP). This report is for information and is not intended to introduce a new approval procedure. An Interagency Nuclear Safety Review Panel consisting of members from the Department of Defense, Department of Energy, National Aeronautics and Space Administration and the Environmental Protection Agency, will evaluate the risks associated with missions requiring the President’s approval and prepare a Nuclear Safety Evaluation Report. The Nuclear Regulatory Commission will participate as a technical advisor to the panel as appropriate. The head of the sponsoring agency will request the President’s approval for the flight through the Office of Science and Technology Policy. The Director is authorized to render approval for such launchings, unless he considers it advisable to forward the matter to the President for a decision.

The term “reactors” was added, likely to accent the previous accidents, and inclusion of the NRC was no longer a recommendation, but a requirement. The phrase ad hoc was removed as pertains to the INSRP and that had the potential to change their process. Ad hoc (Latin: for this) was previously applied in the initial version of PD/NSC25 to show preference to use of empanelment for a single mission or system only. This was mainly since use of a committee had connotations of requiring public inclusion in the review, a difficult prospect given the confidential or classified nature of the information at the time. Legislative rules of the Congress provide that (Sullivan 2007): All meetings for the transaction of business of standing committees or subcommittees, except the Committee on Standards of Official Conduct, must be open to the public, except when the committee or subcommittee, in open session with a majority present, determines by record vote that all or part of the remainder of the meeting on that day shall be closed to the public.

There are some advantages to a standing committee as might be applied to the INSRP. The existing ad hoc nature of the panel means that constituting membership

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for a particular mission is done through a direct empanelment action. Upon completion of review and delivery of the SER to OSTP (or following launch in some cases) the INSRP is disbanded. Given the unique disciplines needed to conduct this type of review, often under limited schedule, there are benefits to having access to a more permanent membership. Often, during hiatus, there are opportunities for testing or model development used for nuclear risk assessment. These are not easily accomplished while preparing for a mission. Additionally, the maturity of INSRP members, necessary for the requisite experience level, makes it difficult to accommodate long-term developments of space nuclear systems. An allowance for an apprenticeship in the INSRP could boost the abilities of the panel to support any increase in nuclear payload missions or advancing technologies. However, allowing for the rather sparse number of these missions can provide for long gaps between empanelment. PD/NSC-25 was revised 1 year later in May 1996, returning the phrase ad hoc to the INSRP. The apparent importance of the phrase was reinforced since this was the only revision.

Bush, Jr. (20 Jan 2001–20 Jan 2009), and Obama (20 Jan 2009–today) Eras Since 2001 there have been only five nuclear payload launches including the two Mars Exploration Rovers, Pluto New Horizons, Mars Science Laboratory, and China’s Chang’e 3 Yutu Moon Rover. They have all successfully left Earth’s orbit.

Safety Analysis Process Program Safety Analysis Process The “Program” wishing to launch a nuclear payload, for example, NASA’s Mars Science Laboratory, initiates the process years before a launch date is finalized (Ref. Fig. 4). Normally, the Program will initially work on the requirements of the National Environmental Policy Act (NEPA) since the approval of the Environmental Impact Statement (EIS) is needed early in the mission planning phase. The EIS describes accident scenarios using the best available information on spacecraft and space nuclear systems providing environmental consequences of launch or mission failures. In this early phase, a launch vehicle may not yet have been chosen due to the lengthy acquisition process. Unique aspects of candidate launch vehicles and their response to accidents must then be included in the environmental assessment. The proposed, preferred design of the nuclear power system is compared to alternative methods (e.g., solar power) explaining benefits or disadvantages of each. The affected environments are described as well as any adverse, damaging short-term or long-term effects. A response to public comments is included that addresses questions or statements derived from a review of a Draft EIS as required by NEPA.

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Fig. 4 Launch approval process

Contingency plans are also provided describing what actions would be taken in the event of an accidental release of the radioisotope. The Mars Science Laboratory EIS (NASA 2006) included the following sections and appendices: 1. Purpose and Need for the Action 2. Description and Comparison of Alternatives 2.1. Description of Proposed Action (Alternative 1) 2.1.1. Mission Description 2.1.2. Spacecraft Description 2.1.3. Rover Electrical Power 2.1.4. Spacecraft Processing 2.1.5. Representative Launch Vehicle Configurations for the MSL Mission 2.1.6. Radiological Emergency Response Planning 2.2. Description of Alternative 2 (Solar Power) 2.3. Description of the No Action Alternative (if this mission isn’t accomplished)

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4. 5. 6. 7. 8.

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2.4. Alternatives Considered But Not Evaluated Further 2.4.1. Alternative Power Sources (Other RTGs, Power Systems with Less PuO2) 2.5. Comparison of Alternatives Including the Proposed Action Description of the Affected Environment 3.1. Land, Air, Noise, Geology, Hydrology, Biology, Socioeconomics 3.2. The Global Environment Environmental Consequences List of Preparers Agencies, Organizations and Individuals Consulted Index References

Appendix A: Glossary of Terms Appendix B: Effects of Plutonium on the Environment Appendix C: Environmental Justice Analysis Appendix D: Responses to Public Review Comments Appendix E: Public Review and Comment Meetings Following submittal of the EIS to the US Environmental Protection Agency (EPA) for review, the development of a Launch Vehicle Databook begins. This documents the details of a particular launch vehicle’s characteristics, failure modes, reliability, and launch abort environments. MSL launched aboard an Atlas V 541 (5 m payload fairing, 4 augment solid rocket booster, 1 Centaur upper stage motor). The MSL Atlas V 541 Final SAR Databook had the following outline structure: 1. 2. 3. 4. 5. 6. 7. 8.

Introduction Mission Overview Launch Vehicle Description Spacecraft Description Launch Complex Description (LC-41, Cape Canaveral Air Force Station, Florida) Flight Safety System Trajectory Data Accident Probabilities 8.1. Introduction 8.2. Technical Approach 8.3. Prelaunch Accidents (Launch Processing to T-0) 8.4. Post Engine Health Check Accidents (T-0 through Earth escape) 8.5. Sensitivity and Uncertainty Analyses 9. Accident Environments 9.1. Liquid Propellant Explosions 9.2. Solid Propellant Explosions 9.3. Liquid and Solid Propellant Fires 9.4. Launch Vehicle Debris 9.5. Accidental Earth Reentry

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The data produced in Sections 8 and 9 especially are important for the development of the SAR. Section 8 applies the basic principles of Probabilistic Risk Assessment (PRA) logic models to compile and evaluate accident scenarios and sequences that lead to adverse environments being applied to the space nuclear system. All known and speculated failure modes of the launch vehicle subsystems and spacecraft are evaluated for their potential to damage the nuclear system. Each subsystem’s reliability values can be assessed by comparing to similar launch vehicle subsystems (nationally or internationally) and adjusted via Bayesian Update methodologies to provide a more accurate prediction of failures. These subsystem failures initiate the potential cascade of failures that may lead to damage of the nuclear system. Scenarios progress from a Basic Initiating Event (BIE), which may involve a single subsystem of the launch vehicle, but has the potential to subsequently affect other subsystems or directly affect the nuclear system. Event Sequence Diagrams (ESDs) visually and mathematically map the branch points along each failure scenario. At each branch a probability is assigned indicating the likelihood that one path or the other is potentially followed (Ref. Fig. 5). The assignment of branch point probabilities can be accomplished by analysis, use of empirical data, or by expert elicitation. Expert elicitation relies on individual judgment on the particular system’s failure mode to progress along one or another branch. Subjectivity in these judgments can be tempered by using multiple experts to gather a range of probabilities and selecting appropriate values. A BIE can lead to an Accident Initiating Condition (AIC) which will affect the nuclear system at varying levels of damage. The effects of the AICs are evaluated based on environmental threats such as explosive overpressure, fragment impingement, fire and thermal exposure, and impact energy. Mapping the AIC probabilities through the potential damaging effects provides an end state Accident Outcome Condition (AOC). As all accidents are mapped, an understanding of the AICs which can lead to high-risk AOCs is revealed, and mitigation techniques may be applied to reduce that risk. The probabilities assigned or calculated for these scenarios are then used as input values for the nuclear risk analysis. Section 9 details the assessment of adverse environments produced from accidents involving explosive yield of solid propellant, liquid propellant mixtures, fires involving propellants or other components, overpressure blast, and impact energy. Potential for damaging the space nuclear system from impacts of explosively propelled fragments in the near field is evaluated. Damage from accidental reentry and ground impact is also assessed. These defined environments are then applied in the nuclear risk analysis to determine the potential for release of radioisotope material and possible dispersion in the environment. Results of the nuclear risk analysis are documented in the Safety Analysis Report (SAR).

Fig. 5 Branch point probabilities and event sequence diagrams

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INSRP Process The procedure used by the INSRP (Ref. Fig. 4) follows the original AEC methodology. The “Program” initiates the process by requesting empanelment of an INSRP per PD/NSC-25 sending letters to each of the participating agencies (i.e., NASA, DoD, DOE, NRC, EPA). Each agency responds assigning an INSRP Coordinator (NASA, DoD, DOE) or Technical Advisor (NRC, EPA). Coordinators then select Chairmen of the necessary Working Groups. Traditionally, NASA has assigned Chairmen of the Reentry and Risk Integration and Uncertainty Working Groups, DoD the Launch Abort and Power Systems Working Group Chairs, and DOE the Biomedical and Environmental Effects Working Group Chairs. Each Working Group Chairman then gathers the necessary expertise to evaluate their particular technical area (Ref. Fig. 6). The Program normally introduces the INSRP to the mission shortly after completion of the EIS. The INSRP then follows the Program’s progress in developing the LV Databook, any ongoing or planned testing or analysis, results of risk modeling, and writing of the safety analysis reports. The INSRP has the opportunity to provide questions or inputs to the Program, and responses are returned to alleviate concerns or address issues. As the Program completes the Final SAR, the INSRP will produce a Safety Evaluation Report (SER) documenting their evaluation of the Program’s SAR and any related information.

Fig. 6 INSRP working groups

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The SER can evaluate alternative probabilities of accidents, and thus consequences; provide risk assessments via alternate software; or document areas of concern (e.g., inadequate conservatism, overly conservative assumptions, improved or alternative methodologies) and recommendations for evaluating uncertainties for future missions.

Final Launch Approval The Program’s FSAR and INSRP’s SER are provided to OSTP for review, requesting approval to launch the nuclear source. Addressing the risk, probabilities of occurrence, mitigation techniques, and contingency operation plans provides OSTP necessary information to make a decision or elevate the decision up to the President. Once any concerns are addressed, OSTP issues their final approval to the Program. Air Force Safety requirements dictate that once all necessary launch constraints are met (normal processes for a launch that does not involve radioisotopes), the final launch can proceed after receipt of OSTP’s approval. Contingency operations commence when the space nuclear system is integrated with the spacecraft, normally as late in the processing flow as possible. Should a prelaunch accident occur that could lead to release of the radioisotope material, the contingency operations personnel can respond accordingly to mitigate any risk. Emergency teams are on station during the final countdown and remain ready to respond until the spacecraft with its nuclear source has reached a mission phase where it cannot return to Earth. If a mission includes a later flyby of Earth, contingency teams are available during that maneuver to monitor and respond as necessary if an accident occurs.

Conclusion Careful use of space nuclear power systems is necessary in the distant realms of space exploration and applications. By understanding the risks involved and applying reliable mitigation techniques, nuclear power systems can be more safely employed.

Cross-References ▶ Hazard of Orbital Debris ▶ Nature of the Threat / Historical Occurrence ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris

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References Angelo JA (1985) Space nuclear power (original edition ed.). Orbit Book Company, Malabar Benko M, De Graaff W, Reijnen G (1985) Space law in the United Nations. Marinus Niijhoff Publishers, Dordrecht DOE (1987) Atomic power in space: a history. Office of Nuclear Energy, Washington DC Frederick S (1989) The Evolution of the Space Nuclear Safety Review Process, NASA Jet Propulsion Laboratory, Appendix A of unpublished INSRP report, Interagency Nuclear Safety Review Panel Launch Approval Process Guidelines, Oct 1994 Grahn S (nd) The US-A Program (RORSAT) and radio observations thereof. Retrieved 2 19, 2014, from Kosmos-951 & Kosmos-954, a near-disaster: http://www.svengrahn.pp.se/trackind/ RORSAT/RORSAT.html Hanafee JE (1978) Analysis of beryllium parts for Cosmos 954. Lawrence Livermore Lab for US Department of Energy, Livermore Heaps L (1978) Operation morning light, terror in our skies, the true story of Cosmos 954. Paddington Press, New York ISRP (1969) SNAP 27/ALSEP safety evaluation report NASA (2006) Final environmental impact statement for the mars science laboratory mission. Science Mission Directorate, NASA, Washington DC NASA (1996, Mar 28) Space debris mitigation standard. NASA Pres. B. Obama (2010, Jun 28) National Space Policy. Washington DC: U.S. Govt. Pres. G. H. W. Bush (1988, May 5) National Space Policy. Washington DC: U.S. Govt. Pres. W. Clinton (1989, Nov 2) National Space Policy. Washington DC: US Govt. Pres. W. Clinton (1996, Sep 14) National Space Policy. Washington DC: US Govt. SecDef (2001, Feb) US government orbital debris mitigation standard practices Siddiqi A (1999, Nov/Dec) Staring at the sea: the Soviet RORSAT and EORSAT programmes. Br Interplanet Soc 397–416 Sullivan, JV (2007, July 24) How our laws are made. Retrieved 5 Mar 2014, from The Library of Congress: http://thomas.loc.gov/home/lawsmade.toc.html UN, IAEA (2009) Safety framework for nuclear power source applications in outer space. IAEA, Austria United States (1986) The papers of the president’s science advisory committee, 1957–1961. University Publications of America UNOOSA (nd) United Nations office for outer space affairs register of space objects. Retrieved 1 Feb 2014, from http://www.oosa.unvienna.org/oosa/en/SORegister/index.html

Part XVI Future of Planetary Defense

As the nature of various types of space-related risks have become more clearly defined, and the advisability of action regarding cosmic hazards has come into clearer focus, global efforts to respond to these various types of planetary risks have grown. Today there are scores of organizations working on programs to detect and report dangers related to cosmic hazards, to coordinate the collection and sharing of data regarding these hazards, and even to create appropriate responses to reduce or minimize these dangers. Rocket scientists, orbital tracking engineers and astronomers, nuclear physicists, economists, risk management officials, space agencies, international scientific organizations, military and defense units, and experts in various international organizations and study groups are all cooperating to understand the nature of various types of cosmic hazards – including orbital debris – to devise new methodology to detect these dangers and minimize their potential negative impacts on Earth. Private initiatives such as the B612 Foundation are seeking to build and launch the infrared space telescope called Sentinel, while space agencies such as NASA have carried out their NEOWise program and are planning a new NEOCAM project to detect asteroid and comet hazards. Methods to combat the increase of orbital debris and to devise ways to remove defunct spacecraft and upper stage rockets from orbit have also increased. Ways to devise a defense against extreme solar events constitute a challenge still to be seriously addressed. This final chapter addresses various efforts to identify cosmic hazards and to defend planet Earth against these threats from outer space.

Active Orbital Debris Removal and the Sustainability of Space Joyeeta Chatterjee, Joseph N. Pelton, and Firooz Allahdadi

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Approaches to Active and Passive Debris Removal as well as Collision Avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technologies to Address Space Debris Mitigation Under Development . . . . . . . . . . . . . . . . . . . . . Passive Deorbiting Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground-Based Systems to Divert Orbits to Avoid Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground-Based Laser Systems to Trigger Deorbiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ion Beam Shepherd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrodynamic Propulsion Systems for Space Debris Removal . . . . . . . . . . . . . . . . . . . . . . . . . . Tether-Deployed Nets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Terminator Tape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Mist Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Harpoon System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Debris Cleanup Robotic Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What Is the Optimal Technology for Debris Removal? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Importance of Space Situational Awareness to Debris Minimization . . . . . . . . . . . . . . . . . . . . Current Initiatives Related to Space Debris Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phoenix Program, DARPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deutsche Orbital Servicing Mission (DEOS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orbital Express Space Operations Architecture, DARPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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J. Chatterjee (*) Institute of Air & Space Law, McGill University, Montreal, QC, Canada e-mail: [email protected]; [email protected] J.N. Pelton International Association for the Advancement of Space Safety, Arlington, VA, USA e-mail: [email protected] F. Allahdadi Space Science and Environmental Research, Applied Research Associates, Albuquerque, NM, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_75

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NASA Robotic Refueling Mission (RRM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CleanSpace One . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Infrastructure Servicing (SIS), MacDonald Dettwiler and Associates . . . . . . . . . . . . . ViviSat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrodynamic Debris Eliminator (EDDE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . International Demonstrator Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Legal and Policy Concerns Related to Active Space Debris Removal . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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In the 1980s Donald Kessler of NASA noted the continuing buildup of space debris and projected that if not mitigated, it would severely limit future safe access to space. In particular, he noted that at some stage the accumulation of orbital space debris would begin to create new debris due to collisions and that this cascading process would threaten the long-term sustainability of human activities in space, including key space applications for communications, navigation, remote sensing, and weather monitoring. This concern, which today is quite real, has become known as the Kessler syndrome. Today there are international guidelines to control the debris population by deorbiting the upper stages of launch vehicles and other preventive measures. These include the 25 year rule for active or passive deorbiting of debris and the degassing of excess fuel that can lead to explosions in space. But these guidelines are insufficient to prevent the buildup of additional debris, particularly in low earth orbit and polar orbits, where the problem is more severe. There is increasing international agreement that a process for active removal of orbital debris elements – once they are clearly defined – will become necessary to address this problem that continues to grow worse over time despite the guidelines to minimize new debris. This orbital debris problem is a difficult one for many reasons. The cost of active debris removal is very high and the appropriate technology that would be ideal for this purpose remains elusive. Nevertheless, many proposals regarding various debris mitigation methodologies are being pursued. The launch of many small satellites with many of them lacking either an active or passive deorbit capability complicates the orbital debris problem even further. In addition to the technical and prohibitive cost associated with active orbital debris mitigation, there are legal issues as well. The current space law regime has no formal definition of space debris in that all elements in space are simply known as “space objects” despite whether they are functional or not. Current legal liability provisions that place all liability with the launching State do not help to facilitate any active removal activity. In short there are no incentives to remove debris from space at this time. This chapter addresses the threats to the long-term sustainability of space posed by the continuing buildup of space debris. In particular, it addresses current efforts and plans around the world to address

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the space debris problem with active removal and mitigation techniques and possible international legal changes or agreements that might facilitate these actions. Keywords

Active orbital debris removal • Committee on the Peaceful Uses of Outer Space (COPUOS), electro-dynamic propulsion • Inter-Agency Space Debris Coordination Committee (IADC) • Liability convention • Kessler syndrome • Mitigation techniques • Outer space treaty • Robotic systems • Space weapons • Space data association • Space debris • Space object • Sustainability of space • United Nations

Introduction In the early 1980s when the problem of orbital space debris was first a subject of analysis and discussion, natural debris in the form of micrometeorites represented a much larger issue and concern. At that time spacecraft were more than a hundred times more likely to be hit by cosmic particles and interplanetary dust than humancreated debris; thus, this issue was considered only a tangential area of concern. Over time, more and more launches, explosion of fuel tanks in orbit, upper stage launch vehicles remaining in orbit, derelict spacecraft not being deorbited, and a host of other activities over the past three decades have worsened the situation dramatically. Several key events such as the collision of the Iridium and Russian Kosmos satellite and the Chinese in-orbit targeting of an out-of-service weather satellite with a missile have sharply increased orbital debris and engendered an international discussion of what can be done about the increasing accumulation of space debris and a growing cascade effect that is worsening the problem. The InterAgency Space Debris Coordination Committee (IADC) and the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) have developed voluntary guidelines that launching nations are now systematically using to prevent or lessen the buildup of new space debris. The Space Data Association (SDA) has also developed procedures to help avoid the conjunction (i.e., collision) of operational satellites by sharing of orbital data (Space Data Association). Yet even with all these measures in effect, debris population still continues to rise. Also there are a rising number of small satellite launches that also continue apace. A large number of these diminutive craft have no active capability to deorbit after their mission is completed and are thus left to naturally deorbit over time due to atmospheric drag. In addition a large number of these small crafts are not formally registered with the International Telecommunication Union as formally required under existing international regulations that apply to all ITU members. This may seem harmless for very small satellites, but if the same practice were followed along our highways, all of our roadways would be littered with debris. Today, however, the most major problem with space debris involves the very largest debris.

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International discussions on the long-term sustainability of space are thus now focused on how to actively remove the largest derelict objects from space since collision of these objects can give rise to the largest amount of new debris. There are also many other topics that are being addressed, which include (i) How can it be ensured that there is sufficient fuel to deorbit spacecraft or put them at the end of life into a “safe parking orbit” that is sometimes referred to as the “junkyard orbit”? (ii) How can it best be ensured that the upper stage of launch vehicles actually descend from orbit immediately after launch? (iii) How can truly cost-effective and reliable means be developed to remove derelict spacecraft from orbit? (iv) How can “space debris” be clearly defined under international law and how can current liability provisions be amended so there is an incentive to deorbit spacecraft that have become derelict? (v) How can active debris removal be accomplished by either active space debris mitigation vehicles or via ground-based systems (i.e., laser beam or ion beam projection) without violating bans on the deployment and use of “space weapons”? (vi) If active deorbit capacities are not available, are there appropriate ways to systematically employ “passive systems” to accelerate the deorbit process without becoming space debris themselves? (vii) Are new registration procedures needed or applicable to small satellites, given that many are not now being registered under UN procedures? (viii) Are there internationally acceptable new ways to use ground-based systems to avoid collisions? and (ix) Are there new international institutional, financial, and legal arrangements that can assist with orbital debris reduction activities that need to be implemented as a matter of priority? (Pelton 2012). Other chapters in this handbook address the nature and the causes of orbital debris buildup, as well as the financial and institutional arrangements that might be employed to encourage new solutions to the pervasive orbital debris problem. The focus of this chapter is on the means – both passive and active – that can be employed in space or on the ground to lessen the risk of orbital collision and hence lead to the decrease of the orbital debris population over time. The discussion of alternative technical means that might be employed to remove space debris from orbit will be followed by a listing of various initiatives that are underway or planned to remove debris from orbit. These projects are covered in subsequent sections. Finally, there will be a discussion on the legal issues and concerns that limit or serve to prevent the active mitigation of orbital debris under existing international laws and conventions.

Technical Approaches to Active and Passive Debris Removal as well as Collision Avoidance There is a high degree of agreement as to the need to lessen the buildup of orbital debris. Yet despite this general international consensus, it is far from clear as to what should be and even what can be done. Some believe that orbital debris are a menace and should be “entirely eliminated,” while others believe that the reasonable goal is to simply keep it largely in check as a form of homeostasis (Finkleman).

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The actual technology to be employed is another area of contention. There are a number of different ideas as to how orbital debris removal should be accomplished. One view is to use ground-based laser systems to create a pressure gradient by illuminating a large target, e.g., an upper stage rocket body, to alter its trajectory thus eliminating the risk of impending collision. Others propose the use of highpowered particle beam or laser systems to steer derelict space objects so that they would rapidly deorbit. The critics of this approach believe that such ground-based systems are, in fact, space weapons and thus cannot be used under international law. Others fear that the technology is not sufficiently mature and could lead to space collisions rather than prevent them. Then there are a wide range of possible space-based technologies that will be discussed briefly below that might be deployed once developed to bring space debris down. It is important to ensure that these space-borne debris-mitigating systems would not become debris themselves. Some techniques such as those employing robots that would latch on to an out-of-service satellite and then bring them down would work quite rapidly. Other systems that would “squirt” glueball balloons or mists to attach a tape onto derelict satellites would only hasten deorbit over time. Then there are advocates of passive systems that would at the end of life deploy a balloon or sail to create atmosphere drag to bring satellites (particularly small, low earth orbit) down at a more accelerated pace. This approach would involve putting a passive system on the satellite before launch. Some concepts such as the glueball balloon would be “stuck” on by an in-orbit maneuverable spacecraft (The Looming Space Junk Crisis). Finally, there are those that contend that none of these technologies can be used until the issues of legal liability and what constitutes a space weapon are resolved – except putting passive deorbit systems, i.e., inflating a balloon at end of life. Meanwhile, billions of dollars are being invested in radar systems in space, as well as the so-called S-band radar system (i.e., the “space fence”) just to track space debris. Currently some 22,000 space debris elements the size of a baseball or larger are being actively tracked. New radar systems will be able to track even smaller-size debris.

Technologies to Address Space Debris Mitigation Under Development Passive Deorbiting Systems A number of projects have been designed or are under development to create inflatable balloons, inflatable tube membranes (ITMs), tethers, solar sails, or deployable drag systems to accelerate the deorbiting process. Most of these are for small satellite programs in low earth orbit that do not have active thrusters to allow a controlled deorbit at end of life. Satellites that have used this type of passive deorbit technology include the NASA FASTRAC satellite with a large deployable solar sail, the Canadian-funded CANX-Drag Sail (Bonin et al. 2013), the European Union Protec 1-2015 program (“Passive Means..”), and a large number of

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university programs in the United States, Europe, and other parts of the world. These are typically designed for low earth orbit and quite small satellites. When these passive systems are deployed, the cross section that creates atmospheric drag can be significantly increased and thus accelerate the deorbit time and thus make deorbit two to three times more rapid.

Ground-Based Systems to Divert Orbits to Avoid Collisions Relatively low-powered laser systems can be used to illuminate a derelict satellite or a large debris element such as a rocket body that is projected to be on a collision course with another space body. If the collision trajectory can be predicted well in advance, then a small change in the linear momentum of the target debris either due to a change in velocity vector or mass removal (ablation) caused by laser illumination or both would prevent the collision. In this case the heat from the low-powered laser would create a small jet from the material of the satellite that would slowly push the space debris object into a new orbit (Ablative Laser Propulsion).

Ground-Based Laser Systems to Trigger Deorbiting A much high-powered laser beam could provide sufficient ablation of the satellite’s mass so as to push (i.e., momentum change principle) the satellite into a new orbit; the satellite would then lose altitude and reenter the Earth’s atmosphere (Buccino). This technique has also been suggested by the Planetary Society as a means of diverting the orbit of a threatening asteroid by sending a number of such ablative laser systems to create multiple jets from the surface of the threatening cosmic hazard.

Ion Beam Shepherd There are several techniques that might use ion beam projection systems. One of these approaches would utilize a precisely focused hypervelocity ion beam. This beam would be directed against a piece of space debris. This beam would then “shepherd” the space debris to a controlled deorbit. This approach could utilize a spacecraft-based ion beam, or with higher-powered mechanisms this could potentially be a ground-based system. This technique is being studied by the European Space Agency, NASA, and the Japanese Space Agency (JAXA) (Bombardelli et al.). A high-powered laser or particle beam system would be considered by most nations as a space weapon. A number of countries strongly object to such use of ground-based lasers or particle beam systems since they are seen as antisatellite weapons and as such are considered to be contrary to Article 4 of the Outer Space Treaty. One solution to this issue that has been recently proposed is that the country that is recorded as the launching State would be given control of the laser or particle beam ionic stream for the deorbit operation.

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Electrodynamic Propulsion Systems for Space Debris Removal This concept would utilize the Earth’s magnetic field to generate electric propulsion. This approach has the distinct advantage of not having to burn up rocket fuel to carry out its operation. These systems would use the Earth’s natural geomagnetic energy as its “fuel supply.” Two variations of this approach would be possible. The least ambitious means would be to have a conventional satellite with a chemical propellant that would maneuver in low earth orbit to simply attach tethers to satellites to help deorbit derelict space objects. This may or may not include an electric ion thrust motor with the tether to accelerate deorbit with the tether therefore being used to generate electric power. A much more ambitious technological approach has been proposed. This would be to create a large-scale electromagnetically driver device. In this case the in-orbit mechanism would seek to remove hundreds of orbital debris pieces over time (Pearson et al. 2011) and see (Hoyt).

Tether-Deployed Nets This system would deploy “nets” around smaller elements of space debris and speed up their deorbit. (This system has been called “Rustler” for “Round Up of Space Trash – Low Earth orbit Remediation.”) The so-called GRASP approach (i.e., Grapple, Retrieve, and Secure Payload) represents a relatively low technology in principle. The derelict satellite would simply be enveloped by a net that would greatly increase atmospheric drag (Hoyt).

Adhesives A less complicated version of the deployed nets would be to deploy a satellite that would be capable of shooting at close range on to the surface of the debris object what might be called very sticky adhesive balls. These balls would be composed of substances such as resins or aerogels. The precise method of extruding the adhesive has not been precisely defined at this time. Once these adhesives are attached to space debris objects, they would in time alter their debris objects so they would degrade over time (Kushner 2010).

Terminator Tape This approach attaches a so-called terminator tape to the debris element, and this would by the pull of the Earth’s gravity be deployed like a gravity gradient antenna to create the maximum drag. This approach would assist small satellites to meet the 25-year deorbit objective (Hoyt).

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Space Mist Systems The least sophisticated type system of this nature that would be for the smallest of debris elements would be a spacecraft that would shoot out “space mists” onto targeted space objects. In this case chemically propelled rockets would deploy especially equipped satellites in low earth orbit. These satellites would maneuver close to derelict space objects and then would spray gas mists, and the frozen gas mist would serve to help deorbit smaller orbital debris (Kushner 2010).

Space Harpoon System Astrium UK has proposed to develop a system that could fly in close proximity to a defunct satellite or upper stage rocket motor that had become space debris and then shoot it with a harpoon device. There would be a propulsion pack linked by a tether to the projectile. This propulsive system would then pull the targeted space debris downward so that it then burns up as it reenters the atmosphere. The harpoon system, as proposed by Astrium, will include about 30 cm long barbed spear. It would be possible to mount several harpoons and propulsive deorbiting systems on a “chaser satellite” that would advance to within 100 m of a junk object (Fishing Space Debris).

Space Debris Cleanup Robotic Systems The most commonly planned cleanup programs for space debris are robotic systems. This spacecraft would simply find and then clamp on to targeted space debris. Some systems would then just fire rockets to bring the robotic spacecraft and the debris element down in a controlled manner. Other designs would use the robotic spacecraft to deflect, using a detachable propellant motor, the space debris object and push it into a new orbit that would rapidly degrade. At the most ambitious level there have been thoughts of creating a large nuclear-powered robotically controlled “space pod.” This “space roaming spacecraft” might be able to operate over a period as long as 15 years. It would be able to propel large space debris into new orbits that would quickly degrade. This type of technology has been conceived as being able to capture and deflect a dangerous asteroid or bolide that is threatening Earth (Proceedings of the International Interdisciplinary Congress on Space Debris).

What Is the Optimal Technology for Debris Removal? Currently there is no clear-cut indication as to what can be considered the “best” or the “right” technology to undertake the task of orbital debris mitigation. In the chapter on the financial and institutional arrangements to remove space debris from orbit, there is currently a concern that if a single international agency is formed to remove

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orbital debris, it could focus on a single and perhaps ultimately the wrong technology. This could perhaps needlessly drive up the cost of this activity. This has led to thoughts that a new international fund to support the development of competitive technology to remove orbital debris should be established. This fund might even support a contest based on the XPrize model to develop such new technology.

The Importance of Space Situational Awareness to Debris Minimization Finally it is important to maintain spacecraft and debris tracking as part of an accurate space situational awareness capability. Obviously, it is not possible to remove debris unless there is a clear awareness of what orbit it is traveling in. Today the most “competent” space agencies to deal with space situational awareness and space debris removal technologies are most probably military entities. This concentration of technological expertise for tracking and active removal technologies naturally gives rise to concerns about space weapons and military uses of systems developed to remove space debris from orbit. The new S-band radar system known as the Space Fence will be able to track debris elements in low earth orbit as small as a golf ball.

Current Initiatives Related to Space Debris Mitigation This section provides a survey of current international space debris remediation initiatives around the globe undertaken both by government actors and private industry. Many governmental programs see active debris remediation and satellite servicing as parallel and overlapping activities involving robotic mission capabilities, and thus these technical capabilities are treated as if they are one and the same in this review of active programs. In fact in-orbit servicing and repair, active orbital debris repair, and strategic defense capabilities in space are all interlinked, and thus one often sees an overlap of civilian and defense activities in this area. One of the reasons that the UN Committee on the Peaceful Uses of Outer Space (COPUOS) has often not been able to make progress in this area is because of the perceived overlap of strategic, defense, and civilian space considerations in this area. The National Aeronautics and Space Administration (NASA) and the Defense Advanced Research Projects Agency (DARPA) in the United States have sponsored several conferences on space debris remediation to encourage expert dialog among the international space community (NASA and DARPA) and (Barnhart). There has also been consensus among international experts in the form of a key finding at a conference organized by the European Space Agency (ESA) in 2009 that “active space debris remediation measures will need to be devised and implemented . . . there is no alternative to protect space as a valuable resource” (“Key Findings”). In a motion for a resolution on the European Space Policy – Green Paper in 2003, the Committee on Industry, External Trade, Research, and Energy of the

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European Parliament underlined the significance “to establish the necessary international cooperation to develop in-orbit servicing” and called upon ESA “to establish a research, development and demonstration programme on in-orbit servicing as a matter of priority, given its potential strategic advantage for the European space sector” (Report on European Space Policy). In the United States, the NASA Satellite Servicing Capabilities Office was established in 2009 to inter alia, “advance the State of robotic servicing technology” and “help to enable a future U.S. industry for the servicing of satellites” (Satellite Servicing Capabilities). Further, the United States Air Force and the National Reconnaissance Office have jointly established a space protection program office to advise the military and intelligence community on the safeguarding of space assets (Singer).

Phoenix Program, DARPA The Phoenix program under the aegis of the Unites States Defense Advanced Research Projects Agency (DARPA) has the stated goal of recycling space assets – usable antennas, solar arrays, and other components – from defunct or inactive satellites in orbit. Its goal is to “develop and demonstrate technologies to cooperatively harvest and re-use valuable components from retired, nonworking satellites in GEO and demonstrate the ability to create new space systems at greatly reduced cost” (DARPA Phoenix Satellite Servicing). It aims to secure “around-theclock, globally persistent communication capability. . .by robotically removing and re-using GEO-based space apertures and antennas from de-commissioned satellites in the graveyard or disposal orbit” (DARPA Phoenix Satellite Servicing). The Phoenix program will develop miniature satellites which could be transported to the GEO region through a “piggyback” ride on a commercial satellite launch and then be used to create a new space system by robotically attaching it to the antenna of a nonfunctional cooperating satellite. It has set its first keystone mission in 2015 to “demonstrate harvesting an existing, cooperative, retired satellite aperture, by physically separating it from the host non-working satellite using on-orbit grappling tools controlled remotely from earth,” which will then be “reconfigured into a ‘new’ freeflying space system and operated independently” to boost the notion of space recycling (DARPA Phoenix Satellite Servicing). DARPA has selected Honeybee Robotics Spacecraft Mechanisms Corporation to develop new tele-robotic end-effector prototypes designed to enable a servicing satellite to dock with and manipulate communications satellites in GEO (Honeybee).

Deutsche Orbital Servicing Mission (DEOS) The German Space Agency (DLR) also has an active space servicing mission currently in the works (Wolf). When the program was announced in 2010, the stated goal for the DEOS project is to “demonstrate the availability of technology

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Fig. 1 Concept image of German DEOS active deorbit systems (Image Courtesy of DRL)

and verify procedures and techniques for rendezvous, capture, maintenance and removal of an uncontrollable satellite from its operational orbit through a demonstration mission” (Sommer and Landzettel). This project entails two satellites, the robotic retriever and the “target” for recovery. This target satellite represents a noncooperative, unstable drifting, and tumbling satellite that has to be captured by a servicing satellite for repair, refueling, or disposal (DEOS). One might question why a new target satellite would be needed when so many defunct satellites are in orbit. Unfortunately, there are legal issues yet to be resolved as who can recover, service, or dispose derelict spacecraft in orbit. This DLR German Aerospace Center project is funded by the German Federal Ministry of Economics and Technology (BMWi). The aerospace company Astrium has been selected to carry out the definition phase of this project (Astrium wins; Fig. 1).

Orbital Express Space Operations Architecture, DARPA Another DARPA project in this area is known as the Orbital Express Space Operations Architecture program. This project was designed as a 3-month mission in 2007. The stated goal of this DARPA project was to “validate the technical feasibility of robotic, autonomous on-orbit refueling and reconfiguration of satellites” (Espero) and (Hastings 2006). The program, just as in the plans for DEOS, involves the deployment of two satellites – one that is the target for servicing and the other is the robotic capturing satellite. In this case the satellite designed to be serviced is called NextSat. The name for the satellite designed for capture is NextSat while the servicing vehicle is called ASTRO. This pair of satellites has been optimized to carry out a series of experiments to demonstrate autonomous rendezvous and docking capability. It is also designed to carry out tests to achieve unassisted on-orbit refueling as well as to replace batteries and other parts that might naturally fail on an extended mission

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(Orbital Express Space Operations). A compact state-of-the-art automated guidance system known as Advanced Video Guidance Sensor (AVGS) is considered critical to the docking operations. This sensor allowed ASTRO to capture NextSat and provide refueling with difficult to manage hydrazine hypergolic propellant. The mission design includes the ability to insert a new battery as well as an additional component (Smith 2007). Clearly, the capabilities demonstrated in this mission could also be applied to active debris remediation.

NASA Robotic Refueling Mission (RRM) The Robotic Refueling Mission (RRM) represents a collaboration between the Canadian Space Agency (CSA) and NASA and as such is also relevant. This experiment was carried out at the International Space Station (ISS) to “demonstrate and test the tools, technologies, and techniques needed to robotically refuel satellites in space—especially satellites not designed to be serviced” (NASA Robotic Refueling). The critical element in this experiment was in the use of the ISS’s “Canada Arm.” This device is formally known by the more complicated name of the Special Purpose Dexterous Manipulator. This is usually referred to as simply Dextre. This robotic device has now often been used for the capture and ad hoc docking of spacecrafts such as the SpaceX Dragon capsule and the Orbital Science Cygnus vehicle. The experience with these spacecraft captures has helped to add to the knowledge associated with spacecraft servicing and capture that should assist with future active debris mitigation missions. Dextre has been key to the capture of arriving spacecraft when conventional docking was not an option (Active Debris Removal). Shuttle-based Canada Arm was utilized by the crew members of STS-49 when they had to capture and repair the stranded Intelsat-VI satellite and then reequipping it with a new kick motor so that it could be lifted from low earth orbit to geo orbit. This was a particularly difficult operation because the spinner of the spacecraft had to be slowed down to attach this large rocket motor (Flight History of Canada Arm).

CleanSpace One Swiss Space Agency and the commercial company Swiss Space Systems (S3) are actively supporting the CleanSpace One project. This project is designed to recover and deorbit a small spacecraft from low earth orbit. The plan is to develop and build the first installment of a fleet of satellites designed to deorbit space debris. This initial low-cost demonstration project planned for 2017–2018 has an estimated cost of only about 10 million Swiss francs. This project is also being carried out in cooperation with the Swiss University EPFL or Ecole Polytechnique Federale Lausanne. The plan is to eject a small “capture” satellite from a suborbital space plane being developed by Swiss Space System. The CleanSpace One spacecraft

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Fig. 2 CleanSpace One capturing a small satellite (Graphic Courtesy of Swiss Space Systems)

will be traveling in a very high velocity trajectory at the point of ejection. This will allow the spacecraft to burn sufficient fuel to go into orbit and to be in proximity to one of the two Swiss nanosatellites selected for the deorbiting mission. This small spacecraft with robotic arms would be able to capture the small satellite and then in a controlled burn safely deorbit (Orbital Cleanup Satellite; Fig. 2).

Space Infrastructure Servicing (SIS), MacDonald Dettwiler and Associates MacDonald, Dettwiler and Associates (MDA), the Canadian space company has developed its Space Infrastructure Servicing (SIS) vehicle to assist with in-orbit servicing as well as potentially a deorbiting mechanism. This spacecraft with a specially designed robotic arm is capable of performing space-based maintenance and repair tasks, refueling, and servicing of a spacecraft. It could alternatively also be used to capture and assist with the deorbiting of a defunct spacecraft or upper stage rocket (Oldham). MDA, as a result of this work, has recently been chosen to support the DARPA Phoenix program (MDA to be Key Supplier). In 2011, it had entered into an agreement with Intelsat as its anchor tenant to provide on-orbit servicing to the latter’s future generation of communications satellites. This agreement, however, has now been terminated (Space Infrastructure Servicing).

ViviSat ViviSat is a project that is jointly owned by US Space LLC and Orbital ATK. This company is offering on-orbit life extension and fleet management services but could also be utilized as means to deorbit space debris. These services would be provided by ViviSat.

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Mission Extension Vehicle (MEV) is a robotic spacecraft that would allow long-term station-keeping and attitude control for spacecraft that have exhausted their fuel or batteries but were otherwise functional. This service could also be used to relocate spacecraft in Geo orbit to alternative orbital slots. This same type satellite could also be used for the deorbiting satellites in cases where permissions had been granted and legal liability issues resolved (Vivisat) and (McGuirk).

Electrodynamic Debris Eliminator (EDDE) This project is signally different than the other active projects in that it would create a device that rather than relying on rocket fuel would utilize the Earth’s magnetic field to maneuver in low earth orbit. As envisioned by the EDDE enterprise, it would consist of wires several kilometers in length to generate electrical power with units along the wire that could manipulate space junk that the EDDE device would encounter. As currently envisioned, the EDDE device would consist of a thin cable several kilometers in length that would serve to generate electrical power as it moves through the Earth’s magnetic field. There would be devices at the end to push device into a new orbit to accelerate decay. This type of approach would be used to assist with the deorbiting of a large number of defunct satellites and upper stage vehicles – as opposed to missions that would deorbit one satellite or piece of space debris at a time – would pose a much different type of issue in terms of international legal and liability issues that would arise with this comprehensive as opposed to a “single shot” operation. A claim is made that a configuration of 12 such EDDE vehicles could remove essentially all debris elements in excess of two kilograms–or about 2,500 large units of space junk–within a 7-year time frame (EDDE).

International Demonstrator Project There are a wide range of international initiatives that have been presented and discussed within such forums as the International Astronomical Federation and the International Academy of Astronomy, the International Group of Experts on Space Debris, the International Space Debris Workshops, the Inter-Agency Space Debris Coordination Committee (especially within its working group on active debris mitigation), and the UN Committee on the Peaceful Uses of Outer Space. There have been specific proposals for an international demonstrator project that would involve a number of active space nations including Russia, Japan, Europe, the United States, and other space-faring nations. At this stage although there have been a number of proposed projects, such initiatives are still in the discussion stage (Activity on Space Debris Problem).

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Legal and Policy Concerns Related to Active Space Debris Removal The preventive measures in the form of debris mitigation taken during the last decade through voluntary nonbinding guidelines have clearly not been able to effectively address the impending catastrophic situation. The only way to ensure secure and sustained access to the long-term utilization of space is through space debris remediation in the form of active removal of debris and on-orbit satellite servicing. However, the technology involved in this endeavor gives rise to a plethora of regulatory complexities and unanswered legal questions (Liou 2011). The current regime of international space law consisting of the five United Nations Treaties and five Declarations does not contain any specific definition of what is considered space debris. The operative terminology used in these Treaties, Conventions, and Declarations is a simply “space object.” This rather vague and ill-defined term apparently, covers any tangible human or even robotic-crafted matter or instrumentality in outer space. The concern over the absence of a proper definition of this term is underlined by the fact that “the basis of liability is that the damages or injury is caused by a space object” (UN Outer Space Treaty, Art. VII and Convention on Legal Liability, Art. II-III). The definition of “space objects” is broad enough to include objects constructed or assembled in outer space under the regime of the Liability Convention. This breadth of concept is to ensure that States do not ignore or contravene the provisions of applicable Treaties, Conventions, or Declarations by constructing or assembling said space objects in outer space. Thus, it is also important to address the status of satellites whose components have been derived from functional parts of “space debris” salvaged or serviced in outer space. This is certainly pertinent given the objective of the Phoenix program to retrieve and reutilize space assets from inactive satellites by 2015, as discussed in the preceding section. The consideration as to when a space object might be considered to be space debris seems to weigh heavily on the ability of said object being capable of being commanded to move. The key phrase that is cited in this context is “the ability of the man-made instrumentality to traverse in outer space.” Hence, the lack of maneuverability or functionality of the space object is frequently seen as key to determining its status as space debris so that it can be classified as a candidate element of “space debris” that is suitable for remediation (Hurwitz 1992). The Outer Space Treaty grants jurisdiction and control over a space object to the State of registry, that is, the State on whose registry an object launched into outer space is carried. The State of registry is further required to retain its jurisdiction and control over the space object, even after the expiry of its functional phase. Hence, it is certainly deemed to be quite clear that space objects include space debris. It is interesting to note that the international definition of “ownership” of space objects is not the same as the jurisdiction and control over them. While “jurisdiction and control” can be retained “while in outer space or on a celestial body,”

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“ownership” is “not affected by their presence in outer space or on a celestial body or by their return to Earth” (Outer Space Treaty, Art. VIII and Moon Treaty). The various UN Treaties and Conventions are silent about the legal possibility of renouncing de jure jurisdiction and control by a State of a space object. This means that there is considerable legal uncertainty about the status of possible legal liabilities that apply while a State or a private entity might undertake remediation activities for a space object. Legal liability and de jure ownership of a space object remain with the State of registry even if it has lost de facto control due to a variety of technological or contractual means. Legitimate exercise of jurisdiction by a State is marked by the presence of a genuine link between itself and the object in question (Nottebohm Case). Scholarly discourse identifies registration of space objects as sufficient nexus between the State and the space object (Hobe 2012). In the absence of registration, ownership over the object can be used to determine which State could lawfully exercise jurisdiction and control. Some States are currently not registering small satellites in all instances. This is particularly true of nanosats that are released as secondary or even tertiary parts of a larger mission. The status of such space objects has never been firmly established in a specific legal action, but the lack of registration is not likely a means of escaping legal liability (Hobe 2012). It is clear that public international space law is silent about the legality of remediation when it relates to the transfer of jurisdiction and control of a space object. In the event of a remediation performed by a State or a State-licensed actor, it will be considered legitimate if the State retains de jure jurisdiction and control of that space object or obtains explicit authorization from the State of registry. Thus, no legal complications are anticipated when a State seeks to remediate its own space objects. However, when a State or State-licensed actor seeks to remediate a space object that it did not carry its registry, the question will arise whether there can be an exception to this general rule of jurisdiction and control on grounds of the public policy goal of facilitating the long-term sustainability of outer space. Although international space law does not contain explicit provisions for the transfer of registry, public international law jurisprudence coupled with contemporary State practice have circumvented such a gap through the conclusion of bilateral or multilateral agreements. Actual practice will likely clarify the situation in the coming days as actual active remediation of defunct space objects takes place in the future. The implementation of advanced technology to perform remediation activities poses a number of legal and regulatory challenges. This is the result of the fact that the current regime of international space law is silent or ambiguous on what can and cannot be done and what legal liabilities do or do not apply. The primary concerns arise from definitional issues, registration processes, jurisdiction and control of space objects, and related liability considerations. These have been extensively examined in a theoretical sense to try to determine what public international law jurisprudence developed over the years does or does not apply. Actual practice and specific legal determinations are most likely to resolve these issues. Given the lack of any major new agreements, conventions, or declarations, it seems unlikely that a new space law to clarify these issues will be forthcoming any time soon.

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Conclusion The issue of active remediation of space debris is currently one of great interest around the world for many reasons. The problem of increasing buildup of orbital debris is of great concern because new collisions of larger space debris objects can generate thousands of smaller debris pieces. Two events in the past decade have particularly accentuated concerns about the long-term sustainability of space and particularly focused attention on low earth orbits and polar orbits where the debris accumulation has become most severe. In the 1980s natural debris such as micrometeorites outnumbered man-made debris by much more than ten to one. Today the situation in low earth orbit has reversed itself. Voluntary procedures to reduce the buildup of new orbital debris, as agreed by the Inter-Agency Space Debris Coordination Committee (IADC) and the United Nations Committee on the Peaceful Uses of Outer Space have served to ameliorate the situation, but the number of debris pieces larger than a baseball currently being tracked exceed 22,000 objects. The cost of satellite-based and ground tracking systems (such as the proposed S-band radar Space Fence) that maintain space situational awareness of orbital debris and now allow maneuvering to avoid major collisions in orbit now requires investments costing billions of dollars (US). The increasing consensus is that active orbital debris removal is necessary to sustain long-term access to and effective use of space for the future. Some have suggested that just the active removal of 5 to 10 large objects a year could represent major progress to address this problem. This chapter has indicated the various types of technologies that might be deployed to assist with active and passive debris remediation technologies – both in the near and longer term. Much more research is needed to find the best, most efficient, least costly, and environmental friendly way to proceed to make the use of outer space sustainable for the long run. A number of demonstration projects are now underway and new ideas about how active debris removal might be undertaken abound. In the shorter term positive steps are possible. These include active collision avoidance techniques, sharing of data about possible conjunctions such as what the Space Data Association (SDA) is doing, and use of passive technologies to assist with the deorbit of low earth orbit satellites (particularly small satellites). These steps represent good progress. The IADC and UNCOPUOS guidelines to prevent debris from being created in the first place are clearly major steps forward. Eventually active debris removal (especially for larger defunct satellites and upper stage rocket motors) will be needed. As technical progress is made to develop the best techniques to make this possible is achieved, the legal and regulatory community needs to develop practical methods and guidelines to be followed to limit liabilities, minimize the potential for accidents, and to ensure that only defunct and unusable space objects are removed from orbit. The starting point would be a widely agreed definition of space debris. The next steps would be methods for space debris removal that are safe, reliable, and do not represent a threat to anyone’s current or future civil or defense space operations.

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Cross-References ▶ Hazard of Orbital Debris ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris

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Hastings D (2006) Studies to enable a paradigm shift in the space enterprise: atro/orbital express, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology. Online: http://www.dtic.mil/dtic/tr/fulltext/u2/a455064.pdf. Last accessed June 2014 Hobe S (2012) Environmental protection in outer space: where we stand and what is needed to make progress with regard to the problem of space debris. Indiana Journal of Law 8 Honeybee Robotics selected for DARPA Phoenix program for on-orbit satellite servicing. Online: http://www.honeybeerobotics.com/about/honeybee-news/130-darpa-phoenix-selection. Last accessed June 2014 Hoyt R, Tethers Unlimited The rustler deorbit systems. www.tethers.com/papers/Tethers_RUS TLER_Presentation.pdf. Last accessed June 2014 Hurwitz BA (1992) State liability for outer space activities in accordance with the 1972 convention on international liability for damage caused by space activities. Martinus Nijhoff, Amsterdam, Netherlands, p 23 Key findings from the 5th European conference on space debris. 2 Apr 2009. Online: European Space Agency, http://www.esa.int/esaMI/Space_Debris/SEMYN9LTYRF_0.html. Last accessed June 2014 Kushner D (2010) The future of space: orbital cleanup of cluttered space. Popular Science 60–64. http://www.popsci.com/technology/article/2010-07/cluttered-space. Last accessed 6 October 2014 Liou JC (2011) A note on active debris removal. Orbital Debris Quarterly News 15:7–8. Online: http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv15i3.pdf. Last accessed June 2014 MDA to be key supplier in satellite servicing demonstration for US Government. 18 October 2012. Online: MDA http://www.mdacorporation.com/corporate/news/pr/pr2012101801.cfm. Last accessed June 2014 (2010) NASA and DARPA sponsor international debris removal conference. Orbital Debris Quarterly News 14:1. http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf. Last accessed June 2014 NASA Robotic Refueling Mission fact sheet. Online: http://ssco.gsfc.nasa.gov/images/RRM_ Factsheet.pdf. Last accessed June 2014 Nottebohm Case, International Court of Justice ICJ reports, 1955, p 4; 22 ILR, p 349 Oldham S, Vice-President MDA (2012) What the future holds: near-term servicing plans. Presented at the NASA second international workshop on on-orbit satellite servicing, May 2012. Online: http://ssco.gsfc.nasa.gov/workshop_2012/Oldham_final_%20presentation_ 2012_workshop.pdf. Last accessed June 2014 Orbital ceanup satellite to be launched in partnership with S3. http://space.epfl.ch/page-87472-en. html. Last accessed June 2014 “Passive means to reduce the impact of space debris” Protection of European assets in and from space-2015-LEIT SPACE Protec-1 2015. 11 Dec 2013. http://ec.europa.eu/research/partici pants/portal/desktop/en/opportunities/h2020/topics/2453-protec-1-2015.html. Last accessed May 2014 Pearson J, Levin E, Carroll J (2011) Commercial space debris removal. Space Safety Magazine (1):21–22 Pelton JN (2012) The problem of space debris. In: Satellite communications. Springer Press, New York, pp 29–33 Proceedings of the international interdisciplinary congress on space debris, 7–9 May 2009. http:// www.mcgill.ca/channels/events/item/?item_id=104375. Last accessed June 2014 Report on European space policy – green paper (2003/2092(INI)), 10 Sep 2003. Online: European parliament, http://www.europarl.europa.eu/sides/getDoc.do?type=REPORT&reference=A52003-0294&language=EN#title2. Last accessed June 2014 Satellite Servicing Capabilities Office, NASA Goddard Space Flight Centre. Online: http://ssco. gsfc.nasa.gov/about.html. Last accessed June 2014

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Directed Energy for Planetary Defense Philip Lubin and Gary B. Hughes

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Concepts for Orbit Deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laser Phased Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laser Versus Mirror . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Requirements to Evaporate Asteroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Escape Speed and Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailed Thermal Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orbital Diversion via Plume Thrust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground Versus Airborne Versus Space-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pointing Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . “Stand-on” Applications: DE-STARLITE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laboratory Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standoff Approach for Efficient and Cost-Effective Impact Risk Mitigation . . . . . . . . . . . . . Other Uses for DE-STAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of Other Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

Directed energy in the form of photons plays an increasingly important role in everyday life, in areas ranging from communications to industrial machining. Recent advances in laser photonics now allow very large-scale modular and P. Lubin (*) Physics Department, University of California, Santa Barbara, CA, USA e-mail: [email protected] G.B. Hughes Statistics Department, California Polytechnic State University, San Luis Obispo, CA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_77

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scalable systems that are suitable for planetary defense. The fundamental requirements of directed energy planetary defense systems are described here, along with the current state of technological readiness. A detailed design is presented for an orbital planetary defense scheme, called DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation. DE-STAR is a modular phased array of kilowatt class laser amplifiers fed by a common seed and powered by photovoltaics. The main objective of DE-STAR is to use focused directed energy to raise the surface spot temperature of an asteroid to ~3,000 K, sufficient to vaporize all known substances. Ejection of evaporated material creates a large reaction force that alters the asteroid’s orbit. Both standoff (DE-STAR) and stand-on (DE-STARLITE) systems are discussed. The baseline standoff system is a DE-STAR 3 or 4 (1–10 km array) depending on the degree of protection desired. A DE-STAR 4 allows initial engagement beyond 1 AU with a spot temperature sufficient to completely evaporate up to 500 m diameter asteroids in 1 year. Small objects can be diverted with a DE-STAR 2 (100 m), while space debris is vaporized with a DE-STAR 1 (10 m). Modular design allows for incremental development, minimizing risk, and allowing for technological co-development. Larger arrays would be developed in stages, leading to an orbiting structure. The smaller stand-on systems (DE-STARLITE) are appropriate for targets with very long lead times to impact so that a dedicated mission can be implemented. Keywords

Asteroid impact • Directed energy • Laser phased array • Planetary defense

Introduction Recent advances in photonics make a scientific discussion of directed energy planetary defense feasible, whereas even 10 years ago it was close to science fiction. High-power lasers are capable of delivering sufficient energy density on a target to melt and vaporize any known material. Laser machining and welding are commonplace in industry, where even refractory metals are directly machined or joined with lasers. Scaling of laser technology has spurred the development of directed energy systems that are capable of delivering high energy density on distant targets. Recent developments have resulted in conversion efficiencies of electrical to photon energy of close to 50 % with powers in excess of 1 kW per (handheld) unit. Additionally, and critical for any phased-array program, such devices can be phase locked. Laser design is rapidly changing and even more efficient devices with higher power density will be available in the near future. High power density allows the contemplation of directed energy systems for largescale deployment. Inside the Earth’s atmosphere, directed energy systems are hindered by atmospheric fluctuations of the coherent beam. A directed energy system deployed above the atmosphere could project a beam through space unfettered by atmospheric interference and thus allows the design of systems that are

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essentially diffraction limited as the interplanetary medium (IPM) is extremely tenuous and does not affect the laser beam significantly. This chapter describes a feasible design for a future orbiting standoff directed energy system, which is called DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation (Lubin et al. 2013, 2014; Hughes et al. 2013). The system consists of an array of phase-locked modest power laser amplifiers. By controlling the relative phases of individual laser elements, the combined beam can be directed to a distant target. Lasers are powered by solar photovoltaics of essentially the same area as the laser array. By increasing the array size, it is possible to both reduce the spot size due to diffraction and increase the power. This dual effect allows the system to vaporize elements on the surface of asteroids at distances that are significant compared to the solar system. By raising the flux (W/m2) on the target asteroid to a sufficiently high level, direct evaporation of the asteroid occurs within the beam. This has two basic effects. First, direct evaporation of the asteroid begins, and given sufficient time, a threatening asteroid could be totally vaporized before hitting the Earth. Second, evaporation at the spot causes a back reaction on the asteroid from the vaporization plume which acts as a rocket, and thus the asteroid can be deflected to miss the Earth. This chapter explores the potential capabilities of the system for mitigating the threat of asteroid impact. Since DE-STAR is a phased array consisting of a very large number of elements, it can simultaneously be used for multiple purposes and is intrinsically a multitasking system. Figure 1 depicts an orbiting DE-STAR system simultaneously engaged in both evaporating and deflecting a large asteroid as well as powering and propelling a spacecraft. As this is a modular system, each DE-STAR is classified by the log of its linear size; thus, a DE-STAR 1 is 10 m, DE-STAR 2 is 100 m, etc. A DE-STAR 4 system will produce a reaction thrust comparable to the Shuttle Solid Rocket Booster (SRB) on the asteroid due to mass ejection and thus allow for orbital diversion of even larger asteroids, beyond several km in diameter, thus allowing for protection from every known asteroid threat. Smaller systems are also extremely useful. For example, a DE-STAR 2 (100 m size array) would be capable of diverting volatile-laden objects 100 m in diameter by initiating engagement at ~0.01–0.5 AU (AU = astronomical unit = mean distance from Earth to Sun ~1.5
1011 m). Smaller objects could be diverted on shorter notice. The phased-array configuration is capable of creating multiple beams, so a single DE-STAR of sufficient size could engage several threats simultaneously, such as a Shoemaker-Levy 9 scenario on Earth. An orbiting DE-STAR would also be capable a wide variety of other functions. Narrow bandwidth and precision beam control would aid narrow search and ephemeris refinement of objects identified with wide-field surveys. Propulsion of kinetic or nuclear tipped asteroid interceptors or other interplanetary spacecraft is possible using the “photon rail gun” mode from direct photon pressure on a spacecraft, propelling a 100 kg craft to 1 AU in 3 days and a 10,000 kg craft to 1 AU in 30 days. A DE-STAR could also provide power to ion propulsion systems, providing both a means of acceleration on the outbound leg and deceleration for orbit. Ideally two systems would provide the ability to “ping pong” spacecraft if this were needed, though this is vastly more challenging. Vaporization and deorbiting of debris in the Earth’s orbit could be

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Fig. 1 (a) Concept diagram of an orbiting DE-STAR engaged in multiple tasks including asteroid diversion, composition analysis, and long-range spacecraft power and propulsion. The system consists of an array of phase-locked lasers. By controlling the relative phases of individual laser elements, the combined beam can be directed to a distant target. Lasers are powered by a solar panel of effectively the same area as the laser array. A DE-STAR of sufficient size would be capable of vaporizing elements on the surface of asteroids. Given sufficient time, a threatening asteroid could be vaporized, deflected, or disintegrated prior to impacting Earth. The ability to direct energy onto a distant target renders DE-STAR capable of many functions. Asteroid interrogation may be possible by viewing absorption lines as the heated spot is viewed through the ejected vapor plume. Photon pressure can be used to accelerate (and decelerate) interplanetary spacecraft, among many other possibilities. (b) Visualization with relevant physical phenomenon included at a flux of about 10 MW/m2. For comparison, laboratory test setup is shown below in Fig. 24 where the bright high-temperature spot is also visible with about the same flux. The plume density is exaggerated to show ejecta. Asteroid diameter is about that of Apophis (325 m) relative to the laser beam diameter (30 m). Target is at 1 AU

accomplished with a DE-STAR 1 or 2 system. DE-STAR 3 and 4 arrays may allow standoff interrogation of asteroid composition by observing absorption lines in the blackbody spectrum of a vaporizing surface spot. There are a number of other applications as well, including downlink power via mm, microwave, or laser – the so-called Space Power System or SPS mode. The system is a standoff planetary defense system that is always ready when needed, and no dedicated mission is needed for each threat, as is the case with other proposed mitigation methods. The multipurpose aspect of the system allows it to be useful with very high “duty cycle.” The DE-STAR system is inherently modular and scalable, thus allowing a means to build and test smaller units in the lab, on the ground, and in suborbital test flights on balloons. Each module is modest in size and power and identical allowing for mass production. This is key to cost reduction. Each element uses only modest laser power, and thus the areal power density is low (0.2 kW/kg with near 40 % efficiency for the laser amplifier. Efficiency goals are comparable to current LEDs that are already about 50 % efficient. Coincidentally, on the space PV side, the power density is nearly identical at 0.1 kW/kg (ATK UltraFlex) with modest term possibilities for increasing this to 1 kW/kg. Recent work on Inverted Metamorphic Multijunction (IMM) cells promises >0.5 kW/kg. Schematic block diagram for a phased-array laser system based on individual kW-class fiber amplifiers is shown in Fig. 2. Long coherence length is critical and the existing fiber-based laser amplifiers are already good enough (depending on the mode in which they are operated), though new advances are becoming available to allow the SBS (stimulated Brillouin scattering) limit to be extended with even longer coherence lengths. With the current technology a DE-STAR 2 program could be started leading to launch and possibly a DE-STAR 3. A conservative and logical approach is possible, rapidly

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Fig. 2 (a) A system block diagram of the fiber amplifier configuration, based on the work by Vorontsov et al. (2009). Individual beams combine near the target. Here, coarse beam orientation is accomplished by moving individual fiber amplifier tips in relation to the transmitting element. Fine beam steering and beam combination at the target is accomplished by phase control. (b) Existing 1.5 kW Yb-doped fiber amplifier of the baseline design. Size is about 30
40
10 cm. Only one amplifier is required per 2 m2 of the system

building smaller and much lower cost units (DE-STAR 0 and 1), testing on the ground, and then, as technology catches up and technological and system problems arise and are solved move to larger systems, eventually leading to orbital testing and scaling up to the full defensive goal. The system is not binary in that small systems have immediate applications (e.g., DE-STAR 1 space debris) as larger systems are being developed for comet and small asteroid protection (DE-STAR 2) leading eventually to a DE-STAR 3 or 4. As a goal, studies have been performed to assess the feasibility of a system possessing the capability to evaporate, prior to impact, asteroids in the size range 150 m to 1 km, and with typical orbital closing speeds. These stated capabilities drive system requirements into the multi-km-class array size for both the diffraction limit of the optics and the power required. As a specific example, one objective might be seeking to evaporate an Apophis-class asteroid (325 m diameter) with a worst-case assumption of complete chemical binding and less than 1 year to evaporate the entire boloid, with a desired interdiction starting at 1 AU. A 10 km DE-STAR system would be capable of meeting the stated goal as shown in the calculations presented below. It is also fortuitous that the same size system required to form a small spot on the distant asteroid from the diffraction limit, assuming a wavelength near 1 μm, is also about the same size as needed to power the laser amplifiers in order to raise the flux to the evaporation point from converting sunlight that falls on the DE-STAR into electricity. At the Earth’s orbit, the “solar constant” is about 1,400 W/m2 or 1.4 (140) GW of sunlight on a 1 (10) km-sized solar array. This is sufficient to power the entire system and no additional power is needed. This also forms a very large potential for an SPS system to send excess power to the Earth. By utilizing a filled array of solar-powered phase-locked lasers, there is a near-ideal convergence of size required both to power the system and to produce the diffraction-limited beam needed to begin vaporization. Baseline calculations are developed using a 1.06 μm wavelength, to produce sufficient flux at 1 AU that will sustain evaporation, which requires greater

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than approximately 5 MW/m2 flux at target. As stated existing Yb laser fiber amplifiers at 1.06 μm wavelength have efficiencies near 40 %. Space solar PV has efficiency of about 35 % in one Sun (not concentrated) with near 50 % when concentrated. Modest efficiency improvements are assumed for both laser and PV to 70 % which is not unreasonable in the realistic time scale of a full DE-STAR 4 system. Overall conversion efficiency of sunlight to laser power of about 50 % is assumed, resulting in approximately 0.7 GW/km2 of laser power. For a 1 km system, laser power would be 0.7 GW, while a 10 km system would have laser power of 70 GW, which is more than sufficient for meeting the stated goal of surface vaporization at 1 AU of all known materials. One major advantage of a phased array is that multiple independent beams can be produced, so multiple targets or efforts can be simultaneously engaged. For reference, 70 GW is the equivalent of about 1.4 MT (megatons TNT – 1 MT ~ 4.2
1015 J) per day or about 500 MT per year of potentially deliverable energy, a significant portion of the total currently active US nuclear arsenal. Note that in the process there is also 100 GW of electrical energy produced or the equivalent of about 100 large utility nuclear reactors. This would allow a very large SPS if needed. For DE-STAR, launch mass is critical in the costing analysis, so while the required efficiency is already effectively available, the power mass density must increase significantly. Solar PV cells can be extremely thin and low areal mass through focusing with thin film mirrors on solar PV may allow the lowest densities. For example, if 10 μm thick PV could be produced (this is more of a mechanical issue as thinner films already exist on plastic), a 104 m PV array would have a mass of about 3
106 kg. The current issue for many space solar cells is the charged particle degradation which is currently met with a “cover glass” on each size of about 100 μm. If laser power density of 10 kW/kg could be reached (50
higher than current), then 70 GW of fiber lasers would be 7
106 kg. This mass does not represent the entire DE-STAR system, but the scale is not outrageous. 10 kW/kg for laser mass density over 20 years is a goal, but even the existing 0.2 kW/kg density allows up to nearly a DE-STAR 3 using existing launcher capability. For reference, the International Space Station (ISS) mass is about 0.5
106 kg with much more than this being lifted into orbit as much of it was also returned in Shuttle missions. Conservatively, it is already possible to launch few
106 kg class space mission, an example being the ISS. Either heavy lift chemical launchers would be needed to loft DE-STAR 4 modules or a bootstrap ground-based DE-STAR-driven hybrid booster would be required. The modules are being designed around the existing heavy lift fairing size allowing for a 3–4 m diameter class module. The modules can be quite thin and stacked during launch and assembled in orbit. Since the system is a phased array, the structure does not need the structural integrity of a conventional mirror but rather must be stiff enough to have vibration modes that are below the metrology servo loop bandwidth as phase control is not handled by keeping the structure stiff but rather by measuring the relative position of each element adjusting the phase shifter in each amplifier to keep the beam on the target. While the baseline design is run in a continuous fashion (CW mode), it is also possible to run the system pulsed if needed, though short pulses are more

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problematic to phase properly. Extensive simulations and some laboratory testing indicate the debris field caused by the mass ejection should not significantly interfere with the incoming laser as the ejecta density is quite low (maximum near the surface is estimated to be 102 kg/m3 and rapidly falling off due to the near isotropic ejecta emission into the space vacuum). Typical molecular ejecta speeds are 1–2 km/s. A reality check is to watch laboratory tests in one atmosphere at up to 40 MW/m2 or to view a video of a laser milling machine. The system is much like a laser-heated target in a semiconductor fabrication system. Thermal Dissipation: The average thermal load (to dissipate) of the system (independent of size) is about 500 W/m2 which is approximately that of a person (or the Earth). It is equivalent to a 300 K blackbody. The average thermal load is extremely low. The average laser power is also quite low, being about 700 W/m2 which is less than the solar “constant” on the surface of the Earth which is about 1,000 W/m2. You could literally walk in front of the system when operational and not be harmed (laser glasses are recommended however). Optical Design: The optical design of a phased array is different than that of a classic optical telescope in that the phasing to achieve constructive interference (which is what allows the image to form) is not done with mechanical alignment as it is in a mirror or lens (where every part of the mirror is essentially a part of the overall “phased array”), but rather the phasing is done by adjusting the phase at each sub-element to achieve constructive interference at the target. The design is an extremely narrow field of view system, and thus many of the constraints of a classical optical system do not apply. The array can be any shape, for example. The system is also extremely narrow bandwidth so thin film holographic grating diffractive “lenses” become viable. For simplicity the design will be roughly planar with each sub-element being either a small reflector or possibly a thin film holographic lens. The latter has been tried in some narrowband receiving mode systems, and extremely low areal densities have been achieved. This is an area where further work is needed to decide on the optimum approach. The design is a large number of identical low-power (700 W/m2) modules that lend themselves to mass production. Ultralow-mass holographic thin film large area “lenses” are particularly attractive, but SiC- or CFRP-replicated reflective optics may be suitable with refinement to lower the mass. In the current baseline, each element has a single fiber amplifier that feeds an optical element. A single 1 kW amplifier can feed a 1.5 m2 optic (mirror or lens). Coarse pointing could be accomplished using fiber tip position actuators behind the lens or mirror as appropriate. A fallback option would be to gimbal each element, though this is more complex. Fine pointing is done with electronic phase adjusters at each amplifier input. The phase is also compared at the output and between elements. The metrology of the entire structure becomes a key part of the servo system. There have been a number of orbital programs looking at extremely high-precision laser metrology over long baselines. The most extreme is the LISA gravitational wave detector that sets a metric of 20 pm resolution over 5
109 m baseline. This is vastly better than required for DE-STAR. Metrology of about 0.1 μm (λ/10) is required over 10 km for the full DE-STAR 4. Similarly the AMD-MOST program has achieved 1 nm resolution over roughly 10 m baselines

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Fig. 3 Coherent beam combining of a 2
2 laser array in Zemax. The four individual elements are shown on the left, and then when combined, the central peak is intensified and the sidelobes are suppressed. With additional elements, the peak will grow and the sidelobes will decrease. The baseline uses a filled close-packed array to minimize sidelobes and to maximize the central peak

(limited by the vacuum chamber for testing). At longer wavelengths the Event Horizon Telescope has phased locked 1.3 mm wavelength telescopes across the globe (107 m baseline) and achieved 0.1 nrad beam formation or the same as the current goal. The RadioAstron, a Russian and Earth long baseline interferometer, has produced fringes corresponding to 0.04 nrad. Note that since the optical F# is very large (~1.5
107 for a DE-STAR – 1 AU target), the asteroid is far away and hence the beam is nearly parallel at the target with a large “depth of focus” ~F#2 λ ~ 2
108 m. The F# (F number) is the ratio of L/d, where L is the target distance and d is the DE-STAR size. There are a number of challenges to the optical design and the targeting servo system that need to be explored. Asteroids are dynamic, and while motion in angle may be small relative to a viewing angle from Earth, it can still be significant. Typical asteroid moves at 10–30 km/s, and with a 30 m beam, this is 300–1,000 beam diameters per second in the worst case. The system will be moving in its orbit, the Earth is moving, etc. There are a lot of issues to be worked out. The Hubble Space Telescope has about a 35 nrad pointing stability over 24 h as an example. Better than 0.1 nrad pointing is ideally required (the current experimental beam is 0.2 nrad full-width, half max (FWHM) for a DE-STAR 4), though, as shown below in the simulations, there is some latitude in this. Optical designs have been started; Fig. 3 shows a simple 2
2 array as an example using coherent beam combining in Zemax. A far-field beam pattern simulation, based on beam propagation equations, is shown in Fig. 4.

Laser Versus Mirror In general, the DE-STAR system can be described as “laser machining” on a solar system scale. While laser machining is common in everyday life, from processing

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Fig. 4 Simulation of 1,000
1,000 array of 1 m sub-apertures. (a) 1D cut and (b) the full 2D pattern. Simulation includes the effects of uncorrelated phase noise equal to a WFE of λ/10 per element. For WFE phase noise less than about λ/6, there is little effect on the final beam pattern with the primary effect being main beam power being spread into the sidelobes (Hughes et al. 2014)

of clothes to cars, it is not common to think about systems that can machine on solar system scales. One of the first questions asked is, “why not use a mirror to form an intense spot rather than convert from sunlight to electricity to laser light?” The answer is simple. If the Sun were a point source, it would be possible to do precise

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beam formation and targeting, but the Sun is not a point source and the conservation of phase space (Liouville’s theorem) prevents beam formation without the use of a mirror about the size of the distance to the target. For an object at 1 AU, targeting with a mirror would require a reflector about the size of the solar system! Stated more precisely, the flux for a spot on the target Fsp when using a mirror of a given F# = focal length/diameter focusing a source whose surface flux is Fs will give ϵFs 4F2#
ϵ 1=4 ϵ 1=2 Fsp ¼ σT 4sp ¼ T 4s F2 ¼ F# T s ! T sp # 4 4 Fsp ¼

where Tsp is the spot temperature assuming only radiation equilibrium (no mass ejection), Ts is the source surface temperature, and ϵ is the efficiency of coupling the photons to the target. An assumption of ϵ = 1 is used for simplicity. The Sun is roughly equivalent to a 5,700 K blackbody with a surface flux of about 60 MW/m2. To achieve good efficiency for rocky materials typical of asteroids, flux at the target needs to be greater than about 10 MW/m2 which requires a mirror with an F# ~ 1 or the diameter about the same as the target distance as mentioned above. This is also one reason why bringing mirrors to an asteroid requires that mirrors also have an F# ~1 so that the mirror must be very close to the asteroid which can be very problematic for a variety of technical reasons. Comets require much lower temperature and flux to evaporate, but since the target flux drops inversely with F#2 and the spot temperature drops inversely as F#1/2, even an ice asteroid would require an F# < ~300, so standoff planetary defense against comets with mirrors is not feasible; mirrors brought to comets and asteroids with large percentages of volatile compounds are feasible if it is possible to bring the mirror to the target Laser Arrays: It is possible to analyze the case of a simple square array as an extension of a series of rectangular apertures. The circular case is very similar. More complex systems with realistic phase noise and pointing errors are analyzed in Lubin et al. (2014). For the simple case of a square array of side d and target distance L assuming only cooling by radiation transfer (the case of mass ejection is considered below), the following definitions and relations hold: d = laser array size (m) PE = electrical power (W) ϵ L = laser efficiency (wall plug) PL = laser power (W) PL ¼ ϵ L PE ðWÞ

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λ = laser wavelength (m) L = target distance (m) D = spot size (m) D = 2Lλ/d = 2F#λ = spot diameter where F# ¼ Ld ϵ B = beam power fraction in spot = beam efficiency F = flux at target (W/m2) F¼

ϵ B PL D2

eT ¼ Target Absorption coeficient ¼ 1  α at wavelength λ of laser α ¼ albedo ðreflectionÞ which includes surface and melt=vapor reflection Solving for the target parameters gives the following relations (note the scaling laws): ϵ B PL ϵ B ϵ L PE ϵ B ϵ L PE d 2 ϵ B PL d 2 ¼ ¼ ¼ D2 4L2 λ2 4L2 λ2 ð2Lλ=dÞ2 2 2 2 / PL , d , L , λ

F¼

ϵ T F ¼ σT 4 ¼ target adsorbed flux from laser ¼ radiated flux Here we assume only radiation balance and no mass ejection The real case of mass ejection dominance is discussed below  1=4 T ¼ ϵ TσF h i  1=4  d 1=2 2 1=4 T ¼ ϵ T ϵ4LB ϵ2LλP2 σE d ¼ ϵ T ϵ4σB PL Lλ / PL , d1=2 , L1=2 , λ1=2 rffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ϵ T ϵ B ϵ L PE d ϵ T ϵ B PL d ¼ L¼ 2 4σ 4σ T 2 λ T λ 1=4

/ PL , d, T 2 , λ1 1=2

PL ¼

4L2 λ2 αT 4 2 4 2 ϵ T ϵ B d2 , λ , T , d 2 /L

Solving for T and D for the general case of an arbitrary-sized array, power, and target distance gives

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T ðKÞ  8, 160ðϵ T ϵ B Þ1=4 PL ðkWÞd1=2 ðmÞL1=2 ðkmÞλ1=2 ðμÞ L where F# ¼ d DðmmÞ ¼ 2 LðkmÞλðμÞd 1 ðmÞ DðμÞ ¼ 2F# λðμÞ   1=2 LðkmÞ ¼ 66:4 ðϵ T ϵ B Þ1=2 PL ðkWÞd ðmÞT 2 103 K λ1 ðμÞ   L2 ðkmÞλ2 ðμÞT 4 103 K PL ðkWÞ ¼ 2:27
104 ϵ T ϵ B d2 ðmÞ  2 3 2 4 4 L ðkmÞλ ðμÞT 10 K PL ðkWÞ ¼ 2:27
10 ϵ T ϵ B d 2 ðm Þ 1=4

For L ¼ 1AU : DðmÞ ¼

3
105 λ ðμ Þ d ðmÞ

DE-STAR with PV Array Equal to Laser Array Size: For simplicity in designing the baseline system, the assumption is that the PV array would be the same size as the laser array. In practice this is not necessary, but it yields about the right amount of power needed to begin interdiction at 1 AU for a class 4 system. In the case of the PV array being the same size as the laser array, the previous equations can be simplified. It is possible to solve for the flux on target and equivalent radiation transfer temperature at the spot – again assuming only radiation equilibrium and no mass ejection: F¼

PL Kd 2 eP eL eB d 2 Kd4 eP eL eB ¼ ¼ D2 4L2 λ2 4L2 λ2

ep = PV conversion efficiency eT = target absorption = 1  α where α = albedo eB = the beam eff (frac in spot) eL = the laser conversion efficiency (“wall plug” efficiency) K = “solar constant” in space near Earth  1,361 W/m2 at solar minimum and about 1,362 W/m2 at solar maximum. Radiated flux is set equal to absorbed laser flux: F ¼ σT 4 ¼ eT F 1=4  4 1=4  F Kd eP eL eB d KeP eL eB 1=4 T¼ ¼ ¼ pffiffiffiffiffiffiffiffi σ σ 4L2 λ2 σ 2Lλ pffiffiffiffiffiffiffiffi d ¼ T 2LλðkeP eL eB =σ Þ1=4 L¼

1 d2  Kep eL eB eT σ 2 2T 2 λ

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Fig. 5 DE-STAR laser power, diffraction-limited beam divergence, and spot size at target engagement of 1 AU

As an example, a class 4 system has F# = Ld  1:5
107 for a target at L = 1 AU with d = 104m and achieves a spot temperature, if radiation limited, in excess of 6,000 K and delivers more than 1 MT/day equivalent. Figure 5 summarizes the above calculations for various values of array size and target distance. Coherence Length Requirements: For a phased array to work properly, the light must be coherent over a time and thus length scale sufficient for all elements to be able to interfere. The coherence length required can be calculated by determining the length difference between the various elements with the most extreme case being the conservative limit. For a planar array of size d and a target of distance L away, the path length difference between the central beam and the outermost beam is δ ~ d2/8 L = d/8 F# for the case of a target that is normal to the plane of the phased array. Moving off normal, the path length difference is δ = 1/2 d sin(θ), where θ is the angle of the target off the normal. The worst case is at right angles (θ = π/2) where δ = d/2. If there are controllable optical delay lines, then these issues are drastically mitigated, but it is preferable to have long coherence length, so delay lines are needed. For a target at L = 1 AU ~ 1.5
1011 m and a DE-STAR 4 with d = 104 m that F# is ~ 1.5
107 - > δ ~ 80 μm corresponding to a coherence time tc = δ/c ~ 0.3 ps. For the worst case of δ = d/2, the equivalent tc = δ/c ~ 17 μs. The laser coherence time must be greater than these times. The “coherence bandwidth” of the current Yb fiber

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amplifiers is intrinsically about 5–10 kHz (with corresponding coherence times tc ~ 100 μs or comfortably longer than the stated worst case. For amplifiers run at their highest power level, this “coherence bandwidth” is generally artificially broadened to about 10 GHz (100 ps) in order to overcome what is known as the stimulated Brillouin scattering (SBS) limit that limits the amplification power. This is well above the normal incidence case but allows extremely little pointing margin. For example, even a 1 pointing difference will give a path length difference of δ =1/2 d sin(θ) ~ 90 m with a corresponding coherence time tc = δ/c ~ 300 ns. When the amplifier is run at a few hundred watts versus kilowatts, the “coherence bandwidth” is about 5–10 kHz or less as above. The solution to this is to run at normal incidence (not really a good option), add path delay lines (also not a good option in general), or run the amplifiers well outside the SBS limit where the coherence time is longer. The latter is the preferred option. There is technology that has been developed that appears to allow the Yb amplifiers to run at both relatively high power and with long coherence time. This is one of the development items on the roadmap. Since volume (as opposed to mass) is not as much of an issue, there may be a trade space that can be exploited to allow for better performance. Note that the deviation of the planar array from a sphere with radius R = L is ξ = d2/8R = d2/8 L ~ 80 μm and deviation of the array plane from a classic optic with focal length f = L is ξ = d2/16f = d2/16 L ~ 40 μm. The array is indeed quite planar! Space Qualification Issues: The DE-STAR system is a complex system of both power conversion (solar to electrical to laser) and metrology, targeting among many others. Solar PV is a mature technology, and the space qualification and “rad hardening” issues are understood. The situation for fiber amplifiers needs to be addressed as a part of the roadmap. Much of this can be done on the ground in accelerator beam lines, and some early long-term space exposure will help with determining what issues, if any, are critical to address in this area. The long-term exposure to radiation is not well understood for fiber amplifiers and needs to be addressed. Rad hardening of thin film holographic lenses also needs to be addressed, as does lowering the areal mass of space PV which is often dominated by the glass used to reduce charged particle (mostly electron) damage.

System Requirements to Evaporate Asteroids It is possible to calculate the energy required to melt and vaporize the various materials that are common in S-type (Si-rich), C-type (carbon-rich), and M-type (metal-rich) asteroids. Comets are much easier to vaporize in that they do not require a high temperature to begin significant mass ejection. The gravitational binding energy of a molecule to a typical asteroid is very small and is negligible compared to the chemical binding energy. The chemical bonding energy that requires heating of the spot to high temperature can be expressed through the heat of vaporization. The heat of fusion (melting) is a small fraction of the heat of vaporization. Models have been developed to explore the thermal interaction between the laser and asteroid in three ways. The first is a simple analysis based

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on power only with a flux equivalent to about a 6,000 K blackbody. The second method uses detailed calculations of the vapor pressure versus temperature for every element and many of the estimated compounds that are thought to make up asteroids. This is a quasi 2D analysis in that it includes radiation emission and mass ejection but ignores thermal conduction. The third method uses all the calculations from the second method but uses a full 3D finite element analysis (FEA) of spherical (any shape is possible) asteroids with various thermal conductivities. All three methods give essentially the same answers, which the calculations confirm with increasingly sophisticated simulations. The final method is a laboratory test system that uses a 19-element laser array to produce a spot flux similar to that of the full DE-STAR 4 at 1 AU, namely, about 40 MW/m2, and targets “rock” samples with similar compositions to asteroids. This testing has begun and will continue over the next year to cross-check the simulations for evaporation rates, mass ejection densities, and plume thrusts among other parameters. As expected, when the flux exceeds about 2 MW/m2, most materials begin to significantly vaporize. The energy required to melt an asteroid is given by the heat of fusion and required increase in temperature to bring it to the melting point from (assumed) initial low-temperature starting point. In practice this is small compared to the heat of fusion and heat of vaporization. The typical energy per m3 is of order 1010 J to vaporize most materials. This can be seen in Figs. 6 and 7, which show models of the vapor pressure in pascals (N/m2) versus T and versus target flux for 93 elements. In addition models are shown for four common asteroid molecular compounds. Even vapor pressures of 103 Pa (0.01 atmospheres) correspond to enormous reaction forces on the asteroid and large mass ejection rates. While an asteroid of solid tungsten is not expected, it would still be possible to mitigate it. Contrary to the small iron-rich meteorites that are found on the ground, a more typical asteroid looks more like the lunar surface and has quite low thermal conductivity and is thought to be a “rubble” pile in many cases, particularly for larger (greater than a few hundred meters) asteroids. The worst case of complete chemical binding (i.e., solid) is assumed. In many cases asteroids will have significant low-temperature volatile materials that may make mitigation much easier. Asteroids are also molecular rather than atomic in species in general, but the conclusion is the same; namely, at temperatures around 2,000–3,000 K or target fluxes of 106–108 W/m2, all known materials will undergo vigorous evaporation. What is critical is to increase the spot flux to the point where evaporation becomes large. It is not sufficient to simply apply a large amount of total power; there has to be a large flux to initiate evaporation. Once the material properties of the targets are understood (Binzel et al. 2009), it is possible to design a system that is capable of evaporating them and in this process divert them due to the large plume thrust generated. Figure 8 illustrates at what distances it is possible to begin to engage targets of differing compositions. For example, a comet will begin evaporation at much lower flux than a rocky asteroid and thus engage them at much lower total power levels and hence smaller systems or at much larger distances. These simulations assume the Sun is also illuminating

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Fig. 6 (a) Melting and vaporization energy per unit volume for S-type (Si-rich) asteroids. (b) Vapor pressure versus T for virtually all elements on the periodic table (93 are modeled). (c) Vapor pressure versus target flux for the same 93 elements. The upper outlier is Mercury

the targets which accounts for the lower-temperature limit. This is approximate as it depends on the target reflectivity and orbit. The Sun does not have a significant effect except in the case of comets.

Escape Speed and Temperature It is possible to calculate the gravitational binding energy and thus the escape speed and equivalent escape temperature as follows. The equivalent temperature for escape is 1 2 3 mv ¼ GMm=R ¼ kT 2 2 vescape ¼ ð2GM=RÞ1=2

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Fig. 7 (a) Vapor pressure versus T for four common high-temperature asteroid compounds. (b) Vapor pressure versus target flux for the same found compounds. Note that at temperatures of 2,000–3,000 K or fluxes of about 10 MW/m2, the vapor pressure and hence mass ejection rates are very high

Fig. 8 (a) Spot temperature versus DE-STAR array size for various target distances from 103 to 10 AU, including average solar illumination on asteroid (sets lower limit on asteroid or comet temperature). (b) Distance to target versus array size for various spot temperatures from 300 to 6,000 K. At 300 K, icy comets become targets, while at 6,000 K (hotter than Sun), no known material survives

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Tesc ¼ 2GMm 3kR , where m is the molecular/atomic mass (kg), M is the asteroid mass (kg), R is the asteroid radius. Assume constant density ρ (kg/m3): 4 M ¼ πR3 ρ 3

4 2G πR3 ρ=R 3 rffiffiffiffiffiffiffiffiffiffiffiffi 8π Gρ ðm=sÞ vesc ¼ R 3 pffiffiffi vesc ¼ 2:36
105 ρR

1=2

vesc ¼ ð2GM=RÞ1=2 ¼

Tesc ¼

8π GρmR2 ¼ 1:35
103 ρmR2 9k

Detailed Thermal Modeling Thermal modeling is critical. Three approaches are presented here, and all yield consistent results. The basic equations are derived from energy conservation where we now also include the critical mass ejection term. Power in (laser) = power out (radiation + mass ejection) + dU dt , where U = dU asteroid internal energy and dt is effectively from conduction. In the steady state dU dt ¼ 0, Ð Pin ¼ Pout þ dU ρcvdv, where cv = specific heat (J/kg-K): dt with U = FL ¼ Laser Flux  in W=m2 Frad ¼ Radiation Flux  out W=m2 Fejecta ¼ Ejecta Flux  out W=m2 Fcond ¼ Thermal Conduction  in W=m2 P þ in ¼ Prad þ PEjecta þ Pcond   FL  Frad  FEjecta  Fcond  n^ dA ¼ 0 ð   ¼ ∇  FL  Frad  FEjecta  Fcond dv ¼ 0 Locally, FL ¼ Frad þ FEjecta þ Fcond

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Frad ¼ σT 4 n^ FEjecta ¼ Γe Hv n^ ¼ M1=2 ð2πRT Þ1=2 αe 10½AB=ðTþCÞ Hv n^

Frad ¼ σT 4

Fcond ¼ K∇T

FEjecta ¼ Γe Hv where kT is the thermal conductivity (which can be position and temperature dependent) and Γe is the mass ejection flux (kg/m2-s) and Heff is the effective heat of vaporization (J/kg) (here the heat of fusion and integrated specific heat are ð Tv Cv dT. In some cases the material will directly also included, H eff ¼ Hv þ H f þ Ta

sublimate into the vacuum. Hf is typically a small fraction of Hv so for practical purposes it is a good approximation to use Heff  Hv : Γe ¼

Mαe ðPv  Ph Þ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ M1=2 ð2πRT Þ1=2 αe ðPv  Ph Þ 2πMRT

where M = molar mass (kg/mol) Pv = vapor pressure (Pa) Ph = ambient vapor pressure (Pa) = 0 in vacuum αe = coef. of evaporation 0 α 1 Models are given for the vapor pressure for each element and compound using a semi-analytic form known as Antoine coefficients where the vapor pressure and temperature T are related by: Log Pv = AB/(T + C), where A, B, and C are the Antoine coefficients and are unique to each element and compound. These form the basis for Figs. 6 and 7. Hence, Pv ¼ 10½AB=ðTþCÞ

FEjecta ¼ M1=2 ð2πRT Þ1=2 αe 10½AB=ðTþCÞ Hv A Gaussian profile is assumed for the laser as an approximation. For a Gaussian laser of power PT,



FL ¼ PT er3 =2r2 2πσ2 where r = distance from spot center. In the approximation where the spot is small compared to the asteroid, the equation becomes FL ¼

PT r3 =2r2 e n^ 2πσ2

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In the dynamic case, it is possible to solve for transient heat flow by solving the following heat flow equation: d ðρcv T Þ ¼ 0 dT d K∇2 T þ ρcv ¼ 0 dt

∇  ðK∇T Þ þ

In the last equation, it is assumed that kT (the thermal conductivity) is independent of position and ρ, cv are time independent. In the full 3D time-dependent solution, all of the above conditions are invoked, and the equations are solved simultaneously using a 3D numeric solver (COMSOL in this case). In the 2D steady-state solutions, the thermal conductivity is assumed to be small (this is shown in 3D simulations to be a valid assumption as well as from firstprinciple calculations), and a combination of radiation and mass ejection (phase change) is used:





FL ¼ Frad þ FEjecta ¼ FT FT ¼ σT 4 þ M1=2 ð2πRT Þ1=2 10½AB=ðTþCÞ Hv Inversion is not analytically possible, so numerical inversion is used to get T(FT) which gives Pv(FT), Γe (FT), etc. In this inversion, a function fit is found for each relevant compound (to 10th N X order typically): T ¼ an ðlog FT Þn . n¼1

A Gaussian approximation to the laser profile is used (this is not critical) to get T(r), Pv(r), Γe(r), where r is the distance from the center of the spot. Since radiation goes as the fourth power of T, while the mass ejection from evaporation is exponentially in T, at low flux levels, the outward flow is completely dominated by radiation (you heat the asteroid slightly and it radiates). As the spot flux level increases (spot size shrinks or power increases or both), evaporation (mass ejection) becomes increasingly dominant, and eventually at about T ~ 2,000–3,000 K or fluxes of 106–107 W/m2, mass ejection by evaporation becomes the dominant outward power flow and (just as water boiling on a stove) the temperature  stabilizes and increasing flux only increases the rate of mass ejection with small increases in temperature. To help illustrate this, the relationship between flux and temperature in the purely radiation-dominated mode is depicted in Fig. 9. Results from the three methods are briefly summarized below: • 1D – energetics alone. Use heat of vaporization and set spot flux to T ~ 6,000 K. No radiation or conduction included.

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Fig. 9 Relationship between flux and temperature in spot in the radiation-dominated case. In reality the temperature rarely gets above 3,000 K as the power is diverted from radiation to mass ejection

• 2D – model elements and compound vapor pressure versus T. Include radiation emission. Ignore thermal conduction. • 3D – full 3D FEA. Include phase change, vapor pressure, mass ejection, radiation, and thermal conduction. 1D – Energetics Alone: The heat of vaporization of a compound is the energy (per mole or per kg) to remove it from the bulk. Removal energy is related to an effective speed and an effective temperature which are related to but somewhat different than the physical speed of ejection and the physical temperature of vaporization. To be more precise, the term evaporation refers to molecules or atoms escaping from the material (e.g., water evaporating), while boiling is the point at which the vapor pressure equals or exceeds the ambient pressure. At any nonzero temperature, there is a probability of escape from the surface, so evaporation happens at all temperatures and hence vapor pressure is a quantitative measure of the rate of evaporation. The heat of vaporization is also temperature and pressure dependent to some extent. Table 1 gives thermal properties for various materials in asteroids. Figure 9 shows a plot of vapor pressure versus T and flux. These materials have relatively high effective temperatures reflecting the fact that there is a probability distribution of energies and that the increase in vapor pressure versus T in Fig. 9 shows that the thermal probability distribution has a “tail” allowing for escape from the surface at lower temperatures that one would naively conclude from a mean analysis only. A similar analogy is the Saha equation that relates the ionization fraction versus temperature where a mean analysis would conclude that extremely high temperatures are required to ionize an atom, but in fact significant ionization occurs at much lower temperatures due to the probability distribution

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Table 1 List of thermophysical properties of common high-temperature asteroid compounds Material SiO2 Al2O3 MgO ZnS

Hf (kJ/mol) 9.0 14.2 77.4 38.0

Hv (kJ/mol) 143 293 331 320

M (g/mol) 60.1 102.0 40.3 97.5

Hv (106 J/kg) 2.38 2.87 8.21 2.46

Cv (J/kg-K) 730 930 1,030 472

Teff (104 K) 0.573 1.15 1.32 1.28

Veff (km/s) 1.54 1.69 2.87 1.57

Here Hf is the heat of fusion and Hv is the heat of vaporization. Effective ejection speed Veff = (Hv(J/kg))1/2 and Teff = (M*Hv)/3R where R = k*NA ~ 8.31

tails. If power PT from the laser impinges on the asteroid in a small enough spot to heat to above the radiation-dominated point (typically 2,000–3,000 K for “rocky” asteroids (vs. 300–500 K for comets)), it is possible to compute the evaporation flux (mass ejection rate) as: Tðv

Γe ¼ PT =Heff where H eff ¼ H v þ H f þ

Cv dT Ta

Heff is the energy required (for 1 kg) to raise the temperature to the vaporization point and to vaporize it and includes the heat of vaporization, heat of fusion and energy required to raise the temperature to the vaporization point from the ambient asteroid temperature. Tv is the temperature at which vaporization is occurring and Ta is the initial asteroid temperature. In general Cv (specific heat) is temperature T Ðv dependent. For most materials Hf  Hv and the integrated specific heat Cv dT is a Ta

small correction (ie 150 m) are largely gravitational-bound “rubble piles” and for these the maximum rotation is independent of diameter and only depends on density ρ with an angular speed ω and rotation period τ given by sffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffiffiffiffi 4 2π 3π ω¼ πGρ ¼ , τ ¼ 3 τ Gρ τ  1.19
104ρ(g/cc) 1/2s  3.3ρ 1/2h – this is independent of diameter. As an example, assuming a typical average density of 2 g/cc gives ρ = 2 ! τ = 2.3 h. There is indeed a remarkably sharp cutoff in rotation periods very close to 2 h (about 10 rotations per day) for asteroids greater than diameters of approximately 150 m. Some smaller asteroids can rotate faster as they can have a tighter binding than purely gravitational (such as an iron meteorite), but these are relatively rare and even the fastest ones can be dealt with since the mass ejection begins so quickly (type < 1 s) after the laser is turned on. As is seen in the transient thermal simulations below, the mass ejection and hence thrust begin within about 1 s for a DE-STAR 4 at 1 AU. It is largely a flux issue so that for the same flux at any distance, the mass ejection remains at this rate. This is assuming solid SiO2 which is extremely conservative. Loss is included to mimic the absorption qualities of asteroids which are very absorptive having typical reflection coefficients around 5 %. Thus a rotating asteroid with this rate (1 h) poses little problem. More interesting perhaps would be an attempt to spin up (or down) an asteroid depending on beam placement. 3D Results: Hundreds of 3D model simulations have been run, and a few salient results are apparent. Perhaps the most interesting bottom line is that starting with the simplest assumptions, namely, energetics only and conservation spot flux were borne out as being valid, but more sophisticated tools are available with which to analyze and optimize the system. 4D Simulations: For the case of dynamic targeting and rotating objects, time evolution has been added to the 3D solver (Johansson et al. 2014). Some of this is motivated by the need to understand the time evolution of the mass ejection under dynamic situations. This is partially shown in Fig. 14 (right) where the time evolution of the temperature at the center of the spot is shown. It is now possible to simulate full dynamics and apply this to the case of rotating asteroids. The same techniques can be applied to pointing jitter and “laser machining of the asteroid or other target.” Comparison of 2D and 3D Simulations: While the 3D simulations give time transient solutions and include full thermal conduction, they lack the numerical flexibility of the 2D solutions. Results of the temperature distributions for a Gaussian laser illumination are compared and found to be very close in their predictions. This builds confidence that it is possible to do both 2D and 3D simulations with high fidelity. The ultimate test will come when comparing model results with laboratory tests. Figure 15 compares the temperature distribution for a 3D model (blue) with a 2D model (black). They have nearly identical

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Fig. 14 All cases refer to SiO2 as the equivalent material. (a) Steady-state surface temperature distribution for a 100 m diameter asteroid at 1 AU with a DE-STAR 4 Gaussian beam derated to 50 GW. Spot diameter is approximately 30 m. Temperatures rise to the point of being mass ejection limited, which is about 2,600 K in the center of the spot. Solar illumination is modeled with an isotropic average of 350 W/m2. (b) Temperature distribution versus theta (angle from beam axis). High-frequency substructure is due to numerical meshing. (c) Transient time solution of temperature in the spot center (K) versus time (seconds) after the laser is turned on at t = 0. Initial temperature is 200 K. Mass ejection begins within 1 s

results in the critical center of the spot and then differ in the wings. As laboratory tests are refined, the results will feed back into the models.

Orbital Diversion via Plume Thrust In general, it is not necessary to evaporate the asteroid to avoid an impact scenario. It is sufficient to change its orbit enough to miss the Earth. The ability to stand off and divert using the plume thrust that DE-STAR generates is an extremely

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Fig. 15 Comparison of 2D and 3D models: temperature versus theta (angle from beam axis on sphere) for SiO2 with 50 GW total power and sigma = 5 m Gaussian beam illumination. Results are nearly identical in the critical central region

attractive approach. Consider the example of Apophis. It is approximately 325 m in diameter with a mass of 4
1010 kg and has an orbital speed of 30.7 km/s with a 30 h rotation. A direct hit would have a yield approaching 1 GT (gigaton TNT). This would be a bad day. The momentum is approximately p = mv ~ 1.2
1015 N-sec. If a theoretical thrust to power ratio of 1 mN/W can be achieved, then the thrust with a DE-STAR 4 would be 7
107 N. If it is possible to activate DE-STAR for 1 month, then a change in momentum of Apophis of δp ~ 1.7
1014 N-s is possible. The effect on the orbit depends on the details of when and where the interaction begins, but it is possible to estimate the deflection angle to be δθ ~ δv/v = δp/p ~0.14 radians or a δv ~ 0.14v ~ 4.2 km/s. This is enormous by standards the deflection community speaks of. A simplistic distance deflection is given by δr (miss distance) ~L δθ (L = 1 AU 1.5
1011 m) ~ 2
1010 m ~ 3,000
Earth radii. This is 50 times the Earth-Moon distance. This is obviously extremely conservative and less extreme scenarios are possible. In addition when running actual orbital trajectories as shown below the simple calculation shown above is often pessimistic and the actual orbital modification can be much larger for the same thrust since the asteroid is in a gravitational bound orbit relative to the Earth’s orbit. See section on “DE-STARLITE” for a detailed example of this. The amplification factor is typically a factor of three times the nay¨ve deflection calculation depending on the details of the asteroids orbit. Keyhole amplifications due to the earth-moon orbit are also very large. Targeting andLIDAR Mode: One of the difficulties with asteroid mitigation in general is knowing where the targets are. Generally asteroids are found by looking for them in the visible bands using their reflected sunlight or in the thermal IR using

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their heat signature or with radar. It is possible to use a DE-STAR system for active illumination of targets to aid in both their detection and orbital refinement. This is done in much the same way that a radar system works except the laser beams are much smaller, providing much finer target determination and much greater range. The general technique is sometimes referred to as Light Detection and Ranging (LIDAR). The same phased-array optical system is used for the reception of the return light, as is used for the transmission of the laser. In this case, the system is run in a gated or long-term pulsed mode. The light travel time to 1 AU is about 8 min or a round trip light travel time of 16 min. The laser could be turned on to scan potential targets and then turned off just before the photons that are scattered off the target are expected to return and switch to a receive mode. This then forms a complete LIDAR system with the same optics used for transmit and receive. The receive system could also be phased to form a full phased-array receiver or could be run in a mode where each element acts as an independent receiver with the sum of all sub-elements co-added before detection. There are advantages to this mode in both simplicity of operation and in that a much larger field of view is received eliminating scanning the field for reception. The disadvantage is the increased background from a larger field of view per sub-element. The return signal is computed for a variety of mission scenarios, as well as the equivalent mapping times for small error boxes to full sky blind surveys. Illustrated in Fig. 16 are the background levels relevant for survey times at the target illumination (the same as the mitigation) wavelength of 1 μm. The relevant backgrounds are the cosmic infrared background (CIB) and the zodiacal backgrounds, which include both scattered sunlight and thermal emission. This technique not only allows for an “in situ” and “co-aligned” determination of the target position but also gives ranging from time of flight (or phase modulation) as well as speed from measured Doppler. Here a heterodyne technique is assumed for detection, which is now feasible with at the baseline wavelength. This is another relatively new development in photonic technology. Backgrounds for Remote Targeting: In order to determine the signal to noise of the return signature, it is necessary to understand the nontargeting signal-related sources of photons. This is generically referred to as the background. There are a number of such backgrounds that are important. Going outward from the detector to the target and beyond, there are: • Dark current and “readout noise” associated with the detector. • Thermally generated photons in the optical system. It is assumed the optical system is mostly running near 300 K. • Solar system dust that both scatters sunlight and emits from its thermal signature. Dust in the solar system is typically at a temperature of about 200 K. This is generically called “zodiacal” scattering and emission, respectively, or “zodiacal light” or zodi for short. • Photon statistics noise from the laser hitting the target. This is due to both the counting statistics nature of the light and its detection and to its bosonic nature (spin 1 statistics).

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Fig. 16 Active illumination (LIDAR mode) scenarios showing photon return rate versus asteroid diameter and system parameters as well as blind survey integration time to detect target versus sky fraction searched, asteroid size, and system parameters (Riley et al. 2015)

• • • •

Scattering of sunlight from the target itself as it is illuminated by the Sun. Thermal emission of the target. Distant background stars that are in the field of view. Sunlight scattered into the field of view for targets that are near to the Sun in the field of view. This is generally only important for targets that are very

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Fig. 17 Diffuse CIB component flux versus wavelength

close to the Sun along the line of sight, though off-axis response of the optical system can be an issue as well. • The far-IR background of the universe is known as the cosmic infrared background or CIB. This is the total sum of all galaxies (both seen and unseen) in the field of view in the laser band that are NOT blocked by the target. This is relevant IF the target is smaller than the receive beam. It is not relevant to first order IF the target is larger than the receive beam (or spot at the target distance). • The cosmic background radiation or remnant radiation from the early universe. This turns out to be negligible for laser-directed energy systems. In all of these cases, the fact that the laser linewidth (bandwidth) is extremely narrow (from kHz to GHz depending on the system design) and the field of view is extremely narrow mitigates these effects which would otherwise be overwhelming for a broadband photometric band survey. Heterodyning is possible at 1 μm and will greatly aid in detection. Cosmic IR Background: The CIB was first detected by the Diffuse IR Background Explorer (DIRBE) instrument on the Cosmic Background Explorer (COBE) satellite launched in 1989. It is an extremely faint background now thought to be due to the sum of all galaxies in the universe from both the stellar (fusion) component at short wavelengths near 1 μm and from the reradiated dust component near 100 μm. On large angular scales (degrees), it is largely isotropic though at very small angular scales (arcsec), individual sources can be detected. The diffuse CIB component is shown in Fig. 17.

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Fig. 18 Zodi background flux versus wavelength

Zodiacal Light: Like the CIB, the zodiacal light has two components and both involve dust in the solar system and the Sun. The sunlight both scatters off the interplanetary dust grains giving a “streetlight in fog” effect and heats the dust grains which then reradiate in the mid- to far IR. The scattered component can be seen with the unaided eye in dark extreme latitudes and is sometimes known as the “Gegenschein” and traces the ecliptic plane. The dust grains are in rough equilibrium through heating by the Sun and cooling through their own radiation. This “background” is NOT isotropic but is highly anisotropic depending on the position and orientation of the observer in the ecliptic. This was studied in detail by the DIRBE instrument on COBE. As seen in Fig. 18, based on some of the DIRBE measurements, the brightness of both the scattered and emitted components varies dramatically with the observed line of sight relative to the ecliptic plane. In the plot the angle relative to the ecliptic plane is given by the ecliptic latitude (Elat) where Elat = 0 is looking in the plane and Elat = 90 is looking perpendicular. The situation is even more complex as the scattered and emitted components vary with the Earth’s position in its orbit around the Sun. By comparing the CIB and the zodi, it is clear that even in the best lines of sight (perpendicular to the ecliptic plane), the zodiacal light completely dominates over the CIB. For the JWST mission, the zodi light is typically the limiting factor for IR observations. When observing asteroids with active illumination (LIDAR mode), the zodi is also an important factor. However, since illumination occurs with an extremely narrow laser bandwidth, and detection occurs with an extremely matched narrow bandwidth, it is possible to largely reduce the zodi and the CIB to negligible levels. This is NOT necessarily true in broadband photometric (typically 30 % bandwidth)

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Fig. 19 Laser wavelength bandwidth in μm versus the frequency bandwidth in Hz

surveys that search for asteroids using scattered sunlight or using the thermal IR signature of the asteroid. This is one significant advantage of active illumination. The baseline laser amplifiers can be run with bandwidths between less than 100 Hz and 10+ GHz. The advantage of smaller bandwidths is the larger coherence length and stability, while the advantage of the larger bandwidth is higher power levels when in a stimulated Brillouin scattering (SBS)-limited mode. The current generation of high power density (1–3 kW) Yb fiber amplifiers uses large bandwidth (typ ~10 GHz) in order to mitigate the SBS limit by broadening the bandwidth, while the lower-power units (few hundred watts) have intrinsic bandwidths that are much less (typ ~100 Hz). There is a path forward to high power and lower bandwidth that is preferred for DE-STAR. To compare to the CIB and zodi backgrounds, Figs. 18 and 19 show the wavelength bandwidth in μm versus the frequency bandwidth in Hz. Optical Emission: Since the plan is to use the same phased-array elements used to transmit the optical emission of the laser illuminator, it is necessary to compute the optical emission rate into the detector. The optics are assumed to be at roughly 300 K for simplicity (this could be changed in some scenarios), indicating a brightness or emission rate of about 1.1
107 γ/s-m2-st-μm for unity emissivity (or for a blackbody emitter) at 1.06 μ. This is clearly an overestimate but represents a worst case. Under the assumption of a diffraction-limited system, the etendue of the optics is such that A Ω = λ2 ~ 1012 m2-st. The bandwidth of reception must also be included. Here a matched filter spectrometer is assumed (to get Doppler) with a bandwidth equal to the laser linewidth. As explained above, this is

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typically104–1010 Hz or approximately 4
1011 to 4
105 μm. The total per sub-element is thus an emission of about 4
1016 to 4
1010 γ/s again for an emissivity of 1. This is an extremely small rate compared to the return LIDAR flux (see Fig. 16). Compare the brightness of 1
107 γ/s-m2-st-μm for unity emissivity to the CIB and zodiacal light which are both much larger. For comparison, note that when looking directly at the Sun, the brightness of the solar surface is ~5
1025 γ/sm2-st-μm at 1.06 μm. Assuming a diffraction-limited system, the resulting photon rate would be about 2
103 to 2
109 for laser (receiver) bandwidths from 104 to 1010 Hz as above. This is NOT small compared to the CIB and zodi (as was the optical thermal emission), but it is still small compared to the LIDAR photon return rate for a DE-STAR 4 illuminating a 100 m asteroid at 1 AU. It does, however, point out the need to be reasonably careful in rejecting direct solar illumination in the off-axis response.

Ground Versus Airborne Versus Space-Based Systems While the baseline for DE-STAR is an orbital approach, a ground-based approach offers many obvious advantages in terms of testing and deployment, while the severe impediment of the atmospheric perturbations may be insurmountable for the foreseeable future. In all initial “roadmaps” to DE planetary defense, ground deployment for the smaller systems during test and debugging is a crucial step. The great strides made in adaptive optics for astronomy and situational awareness allow sub-arcsecond beam formation. Based on the active laser guide star programs, micro-radian beam formation is feasible from the ground. The transmission on clear days from excellent ground-based sites allows for less than 10 % transmission loss near 1 μm from ground to space. On cloudy days the transmission will be essentially zero. However, it is not the transmission which is the critical issue. It is the atmospheric turbulence or “seeing” – phase perturbations in the beam formation that is the limiting factor. One great advantage of a phasedarray approach is that every aperture element is part of an “adaptive optics system” by the very nature of the phased array. In addition, rather than mechanically adjusting the phase front across a sub-optic in a classical adaptive optic system, DE-STAR will have much higher servo phase control bandwidth. This will lead to greatly improved adaptive optics performance, the limits of which are still to be explored. The early and smaller versions of DE-STAR, such as a DE-STAR 1 (10 m aperture), can be used from the ground to explore not only system design and performance but also may allow for initial space debris mitigation. As illustrated in Fig. 5, the beam size θ (nrad) for an aperture size d (m) system is θ (nrad) ~ 2
103/d. For reference the “seeing” from an excellent ground-based mountain top site (e.g., Mauna Kea) is about 2 μrad RMS at 1 μm wavelength. Ground-based seeing is typically given in arcsecond where 1 arcsec ~5 μrad, while adaptive optics are often quotes in wavefront error (often in nm) or in milliarcsec (mas) where 1mas ~5 nrad. It is important to note that seeing is usually much more stable at night due to thermally driven perturbations during the

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day and that the “seeing” quoted for ground-based systems is for nighttime operation. With adaptive optics and decent Strehl ratios (~ > 0.5), 50 mas or 250 nrad at 1 μm wavelength is expected when using multiple active laser guide stars being planned for the next generation of ELT (extremely large telescopes) such as the TMT (Thirty Meter Telescope) among others when operated at night (of course). This (250 nrad) is approximately the beam size for a DE-STAR 1. Extremely aggressive sites, such as being above the boundary layer at Dome A, may allow even better adaptive optics and would be a possibility for small DE-STAR deployments. The extremely high-speed phase control of DE-STAR may allow even better Strehl ratios. This territory needs to be explored. For systems capable of true planetary defense (DE-STAR 3 or 4), one would need to have 100–1,000 times smaller beams, and thus ground-based deployment, while not impossible to imagine someday, is not likely to be effective with currently understood technologies for atmospheric perturbation mitigation. However, this area should be explored. In order to perform a proper analysis, the issues of weather (cloud cover, and other atmospheric distortions) and day/night seeing would have to be factored in. Daytime adaptive optics is also a complicated issue that needs further study. Airborne platforms offer the advantages of reduced atmosphere but usually severe operational constraints. Fixed wing aircraft are particularly problematic due to high-speed turbulence and airframe microphonics. Airship- and balloonborne platforms are another alternative as balloons operate at above 30 km with near-zero relative airspeed. Balloon-borne platforms are viable for the smaller DE-STAR systems for multiple uses, but one of the primary issues is power. Beamed power from the ground is one option that has been studied in some detail for other programs. One could imagine large fleets of airship- or balloon-borne platforms, but it does not seem feasible for all but the smallest systems. Space-based deployment offers many advantages with the severe disadvantage of launch cost. Much of the current focus is on ultralow areal mass systems with a goal of under 1 kg/m2 for overall areal density. With the exception of thin film holographic lenses, no current technology can meet this goal. This optical possibility is the subject of active research. The lowest launch energy solution is a LEO Sun synchronous orbit to allow constant (except for eclipses) solar illumination and a relatively constant thermal environment. More stable orbital environments such as at a Lagrange point or possibly at geosynchronous orbits are more costly to achieve and vastly more complex to service. A lunar surface deployment might be another choice but again is much more difficult logistically and much more costly to deploy but could be a future defensive position for the Earth.

Pointing Issues The pointing requirements of the DE-STAR system are one of the more difficult technical challenges. Ultimately, the requirements for achieving high flux on target drive the overall pointing and thus the sensing and servo feedback loops. Unlike a

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classic optical system, a phased array offers both advantages and challenges compared to the bulk rigid body requirements of a system like the Hubble Space Telescope. The sub-element sizes of even the largest DE-STAR units are currently baselined to be in the meter diameter class (shroud size limited). Experience with rigid body pointing from the HST and upcoming JWST as well as many other space-based telescopes can be leveraged. As mentioned, HST had a 24 h RMS of 35 nrad. If each sub-element is pointed to this level but with uncorrelated pointing errors to its neighbors (clearly there will be some cross talk), the question is “what will the overall effect be on the synthesized beam?” Simulations of these scenarios are occurring now, and this will be covered in a future optical design paper. Since the beam from a 1 m sub-element (as an example) has a beam size of approximately 2 μrad, the individual element pointing error can be much smaller than the individual element beam size. Correlated pointing errors are a much more serious issue and one where the overall feedback loop needs to feed information to correct for the final beam pointing. This is a nontrivial problem and one where significant work needs to take place for the largest systems where sub-nanoradian final beams need to be synthesized. A related effect of phase errors has been simulated extensively. Here the effect is opposite of the effect of pointing errors. For phase errors, complete correlation of the phase errors (or overall shifts) is canceled out to first order since it is the phase differences and not the absolute phase that is important. Large-scale correlated phase errors are important however. For example, a linear phase shift across the array would be equivalent to a pointing error. Again, the servo loop must correct and control the phasing to make a phased array. The effects of random phase error as might arise from phase noise in the amplifiers or high-frequency (beyond the servo bandwidth) mechanical vibrations have also been simulated. A Monte Carlo simulation is used with RMS phase errors of 103 to 1 wave (2π equivalent phase) and from 2 to 104 elements of individual sizes from 0.01 m to beyond 1 m and finds that the initial assumption of maintaining 1/10 wavefront error is a reasonable one, though 1/20 would be significantly better. Results are shown in Fig. 20. Simulation results are compared to simple Ruze theory (which is technically not appropriate due to the assumptions of correlation sizes in Ruze theory). The relationship from D’Addario (2008) is used: hI i 1  eσ0 2 þ eσ 0 ¼ Io N 2

where I0 is the flux with no phase perturbation, hIi is the expected value of flux with phase perturbations, σ0 is the RMS phase perturbation with zero-mean Gaussian distribution, and N is the number of elements. Simulation results agree extremely well with the simple Ruze exponential roll of forward gain or flux on target wherein the limit of infinite number of aperture becomes I = I0 eVar(φ), where Var(φ) is the variance of the phase per element, I is the flux on target with phase perturbations, and I0 is the flux on target with no phase perturbations.

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Fig. 20 Orbital deflection versus thrust for an Apophis-class asteroid with a diameter of 325 m and a laser on time of 15 years. Private communication K. Walsh 2014. Note the relatively small amount of thrust needed to deflect the target (2N yields about a 2 Earth radii miss)

“Stand-on” Applications: DE-STARLITE While the primary motivation for DE-STAR has been as a “standoff defense” system, it can be used in a variety of modes where much smaller systems can be used as “stand-on” systems. The use of the same system in miniature to get close to a target and then use the focused laser in the same mode but at much closer distances allows for applications where a high flux laser can be used for remote laser machine of targets in asteroid or even lunar or Martian mining as well as for asteroid deflection via the same “plume thrust” mechanism outlined above. An example of this is the DE-STARLITE mission where a small (1–1,000 kW) system is taken near to the asteroid and mass ejection is initiated. The advantage compared to a simple mirror focusing on the asteroid is that the mirror must have an F# < 2 to be effective on high-temperature rocky compounds which requires getting the mirror extremely close to the asteroid (typically 10–100 m away). The reason that the F# has to be so low, for a mirror, is that the Sun is not a point source and thus the flux on target IT (W/m2) is the flux at the surface of the Sun divided by 4 times the F#2; thus, IT = Isun/4 F#2. The flux at the surface of the Sun is about 60 MW/m2, and thus with an F# = 2 mirror, the spot flux on the target would be about 4 MW/m2 which is just barely enough to start significant evaporation of rocky materials unless there are significant volatiles present. An F# = 1 mirror would be much preferred in this case. This is the same reason that a simple mirror at the Earth will not evaporate distant asteroids unless the mirror diameter is roughly the size of the distance to the target (i.e., 1 AU mirror diameter). While using mirrors close to an asteroid is not insurmountable, the close proximity can cause severe optical pitting and dust

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Fig. 21 Artistic rendering of a deployed DE-STARLITE spacecraft deflecting an asteroid (Kosmo et al. 2014). The spacecraft is outfitted with two 15 m diameter ATK MegaFlex PV Arrays that give a total of 100 kw electrical power, a z-folded radiator deployed up and down, a laser array mounted on a gimbal at the front, and ion engines at the back. The laser array can be either a phased array or a parallel non phased array. Larger systems up to a megawatt fit within the SLS Block 1 launch vehicle

buildup on the mirror. DE-STARLITE can stand off some 1–100 km away from the target and does not require Sun-target alignment allowing much more flexible steering. DE-STARLITE can also run pulsed if needed for more flexible mission scenarios. In all of these cases, the asteroid material is converted into its own propellant offering a much more efficient and powerful thruster than an ion engine of equivalent power and needed no propellant other than the asteroid itself. Studies to date indicate that Apophis-class asteroids (325 m diameter) can be deflected with a dedicated mission using less than 100 kW of power for a mission that gives roughly a decade of active mission time on target. Since the asteroid itself is the “rocket fuel,” such a mission does not suffer from having to take up a very large fuel load as required by an approach that uses ion engines only. A combined mission with ion engines for transport of the laser to the target and use of the ion engines for station keeping looks feasible with the upcoming SLS (Space Launch System). As a specific example, the deflection of a 325 m diameter asteroid (like Apophis) is studied, assuming a DE-STARLITE stand-on mission with the laser on for 15 years with a reasonable Earth-crossing orbit. A force as small as 2 N is sufficient to cause a 2-Earth-radius miss distance. Results of an orbital propagation simulation are shown in Fig. 21. Assuming a 0.1 mN/W (optical), this implies a 20 kW laser would be sufficient. A more conservative approach would use a 100 kW-class laser. In either case this is an extremely efficient approach to the mitigation of large asteroids using lasers. One option currently being studied is to use a laser add-on to the ARM mission concept where ion engines are used to propel the spacecraft to the asteroid and the laser is used to deflect it. This hybrid approach (ion engines + laser) works extremely well. Figure 21 shows the latest design

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Fig. 22 Laser deflection time needed to achieve 2 Earth radii miss distance vs electrical power available assuming 50% amplifier efficiency and 80 micro-N/wopt coupling efficiency. Note that this is the laser on time not the warning time. The warning time needs to include a build and travel time from LEO to target. The time shown here is the time the laser is actually on. The asteroid density is assumed to be 2000 kg/m3

concept for DE-STARLITE with 100 kw of solar PV. Since the build time after warning that an impact is likely, is not trivial, a better approach would be to keep a system (or several) in LEO or GEO or another orbit ready for a threat. This greatly reduces the total time required for mitigation. In the next few figures, we show the current status of the designs for the DE-STARLITE stand-on system. As seen in Fig. 22, the total time for (laser on) deflection for even large targets like Apophis are quite small.

Laboratory Testing A laboratory test system was constructed to check calculations and simulations. The test system consisted of 19-fiber CW lasers, each of which was homogenized in an 800 μm core fiber and then reimaged to simulate active phase control. Each fiber had a diameter of about 150 μm and was fed with 2.1 W diode laser at 808 nm. The beam diverges with a NA ~ 0.2 and reconverges with a roughly 1:1 ratio to produce a spot that was about 1 mm in diameter. Fluxes up to 40 MW/m2 are achieved which is close to the target of a DE-STAR 4 at 1 AU. For reference, the surface of the Sun (assuming a 5,800 K surface) has a flux of about 60 MW/m2. When the laser is fired

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Fig. 23 (a) Cross-sectional diagram showing laser (which is 19 individual fiber-fed lasers) and the re-collimating optics. (b) Rendering showing beam expansion and imaging as well as sample holder. (c) Laser firing at a target (basalt in this case)

at a target, an extremely intense white hot spot is created that lights up the room and vaporizes every material tested. So far, tests are done outside the vacuum chamber, but vacuum tests will begin shortly. Diagnostics include IR (out to 12 μm) and visible light cameras as well as a fiber-fed optical spectrometer. Optical coupling from fiber tip to target was measured at about 90 %. Mass ejection was definitely observed (holes were punched through), but quantitative comparison to mass ejection model will be done in vacuum as the vapor pressure would have to exceed 1 atmosphere for normal evaporation. For basalt, the measured mass ejection (in 1 atm air) was 0.42 mg/s, while the theoretical maximum for this test was 2.2 mg/s. One significant issue is the complex nature of the test materials that are being evaporated. Some standard targets will be used in the vacuum tests. Air convection is also a serious issue, so it is not surprising that the measured mass ejection is less than anticipated for a variety of reasons. Plain sand from the local beach was used as a target; the sand was placed in a small crucible and the laser energy melted it into a glass ball as well as vaporized some of it. The laboratory setup and associated simulation results are shown in Figs. 23 and 24.

Standoff Approach for Efficient and Cost-Effective Impact Risk Mitigation There is a fundamental difference between DE-STAR and previously described approaches to orbit deflection. All currently described concepts are “stand-on” systems, in that assets required for orbit alteration would need to be deployed onto, or at least very near, the threatening asteroid. DE-STAR is a standoff system that would be capable of altering an asteroid or comet’s orbit from afar. Costs associated with DE-STAR development would be amortized over multiple threats

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Fig. 24 (a) 2D simulation with laboratory test parameters. Similar to Fig. 14 but set for lab testing. Plot is of expected mass ejection versus sigma (Gaussian beam) for various power levels. Measured sigma based on hole size in targets is less than 330 μm. Sample is assumed to be SiO2. (b) Picture of test system. Small camera is an 8–12 μm FLIR IR microbolometer unit. Sample is sand

and over multiple applications beyond planetary defense, since a functioning system could be used repeatedly. Asteroid 2012 DA14 (~45 m) was discovered 1 year before its close approach; could a kinetic impact mission have been attempted, had the asteroid been on a collision course? If the object that struck near Chelyabinsk had been discovered 1 year (or 1 day) before impact, could (or would) any stand-on mission be deployed to nullify the threat? A single DE-STAR system of modest size and flexibility would have been capable of eliminating the threats from both 2012 DA14 (in about a day of targeting) and the Chelyabinsk impactor in less than 1 h of targeting (assuming prior detection by

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surveillance efforts). In particular, a functioning DE-STAR would be capable of mounting very rapid responses to newly discovered objects that have no chance of being mitigated by stand-on systems. As previously stated, a single orbiting DE-STAR of sufficient size could be designed to simultaneously engage multiple approaching objects. Unlike stand-on approaches, DE-STAR could be tested and validated at every stage of development, considerably increasing confidence that the system would succeed when needed the most. Since DE-STAR would be capable of addressing other scientific goals, development costs could also be spread across multiple scientific budgets. The standoff strategy of DE-STAR has many obvious and critical advantages over stand-on schemes currently being considered for asteroid impact avoidance. It is worth the effort to explore the many issues associated with designing, developing, and deploying an orbiting DE-STAR. In this chapter, baseline system requirements and architecture are considered; cost-benefit analysis will be addressed in future work.

Other Uses for DE-STAR Summary of Other Uses DE-STAR is a standoff directed energy system and there a number of other uses that are possible. Some of these alternative uses are explored in detail. Clearly if it is possible to “laser machine” on solar system scales, this brings up some thoughtprovoking discussions. Some of the more mundane ideas are: • Space debris mitigation – a small unit (DE-STAR 1) is extremely effective against space debris. A unit attached to the ISS would be very useful in clearing out orbital debris. • A LIDAR mode for refining the orbital parameters of asteroid. DE-STAR is extremely bright and makes an excellent “flashlight” to target asteroids in order to detect and refine their positions (Riley et al. 2014). As an aid to existing efforts, active illumination can be quite useful. The narrow bandwidth allows for extremely low-background searches as well as Doppler velocity determination. • Standoff composition analysis – the bright heated spot might be used as a backlight to determine asteroid ejecta composition. An analysis is underway to see what is feasible. • Orbital capture – modifying the orbits of asteroids may allow for easier capture if desired. • Beam power to distant probes – the system can be used to beam power to very distant spacecraft. At 1 AU, the flux is 70 MW/m2 or about 50,000 times the flux of the Sun. At the edge of the solar system (30 AU), it is about 80 kW/m2. At 225 AU, the beam is about as bright as the Sun is above the Earth’s atmosphere.

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Similarly it could be used to provide power to distant outposts on Mars or the Moon or literally to machine on the lunar surface (or possibly Mars). The latter would be a complex sociological and geopolitical discussion no doubt. Spacecraft rail gun mode – while photon pressure is modest, it is constant until the beam diverges to be larger than the reflector. In a companion paper, Bible et al. (2013) discuss using this mode to propel spacecraft at mildly relativistic speeds. For example, a 100, 1,000, and 10,000 kg spacecraft with a 30 m diameter (9 kg – 10 μm thick multilayer dielectric) reflector will reach 1 AU (~Mars) in 3,10,30 days. Stopping is an issue! The 100 kg craft will be going at 0.4 % c at a 1 AU and 0.6 % c at the edge of the solar system. This is 1,800 km/s at the edge of the solar system with just a 30 m reflector. This speed is far greater than the galactic escape speed and nearly 100 times faster than the Voyager spacecraft. If a reflector could be built to intercept the beam out to the edge of the solar system (900 m diameter), the same craft would be going 2 % at the edge of the solar system and 3 % if illumination stayed on for about 2 months. It is not currently known how to build km-class reflectors that have low enough mass, though it appears feasible to make 30 m and 100 m reflectors. There is work on graphene sheets that may allow for future extremely large- and extremely low-mass reflectors that may allow for fully relativistic speeds. Future generation may build even larger DE-STAR 5 and 6 units to allow highly relativistic probes. Laser-driven launch and boosters – a high-power ground-based DE-STAR could be used for launch purposes when used as an ablation (Campbell et al. 2003) or plume thrust driver. Similarly for orbital boost from low Earth orbit (LEO) to geosynchronous Earth orbit (GEO) and beyond, a DE-STAR could be extremely useful. SPS mode – beam power to the ground via microwave or mm wave. The system would produce about 100 GW (electrical). The US consumption is about 440 GW (electrical) average (1,400 W/person – average). Interstellar beacon – DE-STAR appears brighter than the brightest nighttime star at 1,000 ly (typical distance to Kepler-discovered exoplanets). Optical search for extraterrestrial intelligence (SETI) use is being explored for both transmit and receive modes. Ultrahigh-speed IR communications – the calculated data rates for DE-STAR to long-range, even interstellar probes are enormous with Mb/s speeds back to Earth from probes at the nearest stars for relatively small spacecraft transmitters and reflectors.

Conclusion Directed energy systems represent a solution to planetary defense against asteroids and comets that threaten Earth. The same system can be used for a multitude of other purposes and thus is not a single-use system waiting for an asteroid.

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Its use in active illumination, remote composition analysis, spacecraft propulsion, space debris mitigation, and SPS (Space Power Satellite) could more than justify its cost let alone its ability to protect the Earth from catastrophe. Being modular and scalable, the DE-STAR can be built in stages as technology progresses. Small DE-STAR 0 (1 m) and DE-STAR 1 (10 m) class units can be built, tested, and even flown on suborbital platforms to test the basic concepts as small orbital versions are built. The technology is improving rapidly and already nearly “there” in terms of conversion efficiency. There are many other uses that are not discussed here for brevity. A logical progression is possible from the smaller DE-STAR ground and suborbital units to small orbital units as the technology improves and laser mass power density improves until it is possible to deploy a full-scale system such as a DE-STAR 4. As humanity becomes more technologically advanced, even larger systems can be envisioned including systems that will allow the first interstellar probes.

Acknowledgments The funding from the NASA California Space Grant NASA NNX10AT93H in support of this research is gratefully acknowledged. The assistance from the Zemax support team for the Zemax optical simulations is also appreciated.

Cross-References ▶ Comet Shoemaker-Levy 9 ▶ Deep Impact and Related Missions ▶ Directed Energy for Planetary Defense ▶ Economic Challenges of Financing Planetary Defense ▶ European Operational Initiative on NEO Hazard Monitoring ▶ Hazard of Orbital Debris ▶ Impact Risk Estimation and Assessment Scales ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Minor Planet Center ▶ NASA’s Asteroid Redirect Mission ▶ NEO Discovery and Follow-up Surveys ▶ NEOSHIELD - A Global Approach to Near-earth Object Impact ▶ OSIRIS-REx Asteroid Sample-Return Mission ▶ Planetary Defense, Global Cooperation, and World Peace ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris ▶ Potentially Hazardous Asteroids and Comets ▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning

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▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE ▶ Strategies to Prevent Radiological Damage from Debris

References Belton MJS, Morgan TH, Samarasinha NH, Yeomans DK (eds) (2004) Mitigation of hazardous comets and asteroids. Cambridge University Press, New York Bible J, Johansson I, Hughes GB, Lubin PM (2013) Relativistic propulsion using directed energy. In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VII. Proceedings of SPIE, vol 8876, 887605 Binzel RP, Rivkin AS, Thomas CA, Vernazza P, Burbine TH, DeMeo FE, Bus SJ, Tokunaga AT, Birlan M (2009) Spectral properties and composition of potentially hazardous asteroid (99942) Apophis. Icarus 200:480–485 Campbell JW, Phipps C, Smalley L, Reilly J, Boccio D (2003) The impact imperative: laser ablation for deflecting asteroids, meteoroids, and comets from impacting the earth. In: BEAMED ENERGY PROPULSION: first international symposium on beamed energy propulsion 664(1), AIP Publishing, Melville, pp 509–522 Colombo C, Vasile M, Radice G (2009) Semi-analytical solution for the optimal low-thrust deflection of near-earth objects. J Guid Control Dyn 32(3):796–809 Conway BA (2004) Optimal interception and deflection of Earth-approaching asteroids using low-thrust electric propulsion. In: Belton MJS, Morgan TH, Samarasinha N, Yeomans DK (eds) Mitigation of hazardous comets and asteroids. Cambridge University Press, New York, pp 292–312 Cuartielles JPS et al (2007) A multi-criteria assessment of deflection methods for dangerous NEOs. In: New trends in astrodynamics and applications III. AIP conference proceedings 886(1), American Institute of Physics/Springer, New York, pp 317–336 D’Addario LR (2008) Combining loss of a transmitting array due to phase errors. IPN Progress Report 42-175, Nov 2008 Delbo` M, Cellino A, Tedesco EF (2007) Albedo and size determination of potentially hazardous asteroids: (99942) Apophis. Icarus 188:266–270 Fan TY (2005) Laser beam combining for high-power, high-radiance sources. IEEE J Sel Top Quantum Electron 11:567 Gibbings MA, Hopkins JM, Burns D, Vasile M (2011) On testing laser ablation processes for asteroid deflection, 2011 IAA planetary defense conference, Bucharest Gritzner C, Kahle R (2004) Mitigation technologies and their requirements. In: Belton MJS et al (eds) Mitigation of hazardous comets and asteroids, vol 1. Cambridge University Press, New York, p 167 Harris AW (1998) A thermal model for near-Earth asteroids. Icarus 131:291–301 Hughes GB, Lubin P, Bible J, Bublitz J, Arriola J, Motta C, Suen J, Johansson I, Riley J, Sarvian N, Wu J, Milich A, Oleson M, Pryor M (2013) DE-STAR: phased-array laser technology for planetary defense and other scientific purposes (Keynote Paper). In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VII. Proceedings of SPIE, vol 8876, 88760J Hughes GB, Lubin P, Griswold J, Bozinni D, O’Neill H, Meinhold P, Suen J, Bible J, Riley J, Johansson I, Pryor M, Kangas M (2014) Optical modeling for a laser phasedarray directed energy system (Invited Paper). In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VIII. Proceedings of SPIE, vol 9226

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Hyland DC, Altwaijry HA, Ge S, Margulieux R, Doyle J, Sandberg J, Young B, Bai X, Lopez J, Satak N (2010) A permanently-acting NEA damage mitigation technique via the Yarkovsky effect. Cosm Res 48(5):430–436 Johansson I, Tsareva T, Griswold J, Lubin P, Hughes GB, O’Neill H, Meinhold P, Suen J, Zhang Q, Riley J, Walsh K, Mellis C, Brashears T, Bollag J, Matthew S, Bible J (2014) Effects of asteroid rotation on directed energy deflection. In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VIII. Proceedings of SPIE, vol 9226 Kahle R, Hahn G, K€uhrt E (2006) Optimal deflection of NEOs en route of collision with the Earth. Icarus 182(2):482–488 Koenig JD, Chyba CF (2007) Impact deflection of potentially hazardous asteroids using current launch vehicles. Sci Glob Secur 15(1):57–83 Kosmo K, Pryor M, Lubin P, Hughes GB, O’Neill H, Meinhold P, Suen JC, Riley J, Griswold J, Cook BV, Johansson IE, Zhang Q, Walsh K, Melis C, Kangas M, Bible J, Motta, Brashears, T., Mathew S, Bollag J (2014) DE-STARLITE – a practical planetary defense mission. In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VIII. Proceedings of SPIE, vol 9226 Lu ET, Love SG (2005) A gravitational tractor for towing asteroids. arXiv preprint astro-ph/ 0509595 Lubin P, Hughes GB, Bible J, Bublitz J, Arriola J, Motta C, Suen J, Johansson I, Riley J, Sarvian N, Clayton-Warwick D, Wu J, Milich A, Oleson M, Pryor M, Krogan P, Kangas M (2013) Directed energy planetary defense (Plenary Paper). In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VII. Proceedings of SPIE, vol 8876, 887602 Lubin P, Hughes GB, Bible J, Bublitz J, Arriola J, Motta C, Suen J, Johansson I, Riley J, Sarvian N, Clayton-Warwick D, Wu J, Milich A, Oleson M, Pryor M, Krogen P, Kangas M, O’Neill H (2014) Toward directed energy planetary defense. Opt Eng 53(2):025103-1–025103-18. doi:10.1117/1.OE.53.2.025103 Maddock C, Cuartielles JPS, Vasile M, Radice G (2007) Comparison of single and multispacecraft configurations for NEA deflection by solar sublimation. In: AIP conference proceedings, vol 886. AIP Publishing, Melville, p 303 McInnes CR (2004) Deflection of near-Earth asteroids by kinetic energy impacts from retrograde orbits. Planet Space Sci 52(7):587–590 Melosh HJ, Ryan EV (1997) Asteroids: shattered but not dispersed. Icarus 129(2):562–564 Morrison D, Harris AW, Sommer G, Chapman CR, Carusi A (2002) Dealing with the impact hazard. In: Bottke W et al (eds) Asteroids III. University of Arizona Press, Tucson, pp 739–754 Mueller M (2007) Surface properties of asteroids from mid-infrared observations and thermophysical modeling. arXiv preprint arXiv:1208.3993 Mueller M, Harris AW, Fitzsimmons A (1989) Size, albedo, and taxonomic type of potential spacecraft target Asteroid (10302) 1989 ML. Icarus 187:611–615 Olds J, Charania A, Schaffer MG (2007) Multiple mass drivers as an option for asteroid deflection missions. In: 2007 Planetary defense conference, Washington, DC, Paper, pp S3–S7 Riley J, Lubin P, Hughes GB, O’Neill H, Meinhold P, Suen J, Bible J, Johansson I, Griswold J, Cook B (2015) Directed energy active illumination for near-Earth object detection. J Astron Telescopes Instrum Syst (accepted) Schweickart R, Chapman C, Durda D, Hut P (2006) Threat mitigation: the gravity tractor. arXiv preprint physics/0608157 Vasile M, Maddock CA (2010) On the deflection of asteroids with mirrors. Celestial Mech Dyn Astron 107(1):265–284

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Vorontsov MA, Weyrauch T, Beresnev LA, Carhart GW, Liu L, Aschenback K (2009) Adaptive array of phase-locked fiber collimators: analysis and experimental demonstration. IEEE J Sel Top Quantum Electron 15:269 Walker R, Izzo D, de Negueruela C, Summerer L, Ayre M, Vasile M (2005) Concepts for nearEarth asteroid deflection using spacecraft with advanced nuclear and solar electric propulsion systems. J Br Interplanet Soc 58(7–8):268–278 Warner BD, Harris AW, Pravec P (2009) The asteroid lightcurve database. Icarus 202:134–146 Wie B (2007) Hovering control of a solar sail gravity tractor spacecraft for asteroid deflection. In: Proceedings of the 17th AAS/AIAA space flight mechanics meeting, AAS, Washington, DC, vol 7, p 145

Economic Challenges of Financing Planetary Defense Henry R. Hertzfeld and Pierre-Alain Schieb

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measuring the Probability of Risks and Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Funding Mechanisms for a NEO Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Evaluating Possible Methods of Governance and Financing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Is It All Worth Worrying About? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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This chapter examines analyses that have been used to assess various types of large-scale economic risks that could apply to the global economy and attempts by such groups as the World Economic Forum to examine what the impact of various types of “Black Swan” catastrophes might be. In particular it indicates why economic systems are generally not well equipped to address major global disasters with worldwide impact that also have a very low probability of occurrence. In light of economic scarcity, conflicting political priorities, and a number of other factors, there is currently little likelihood that a systematic economic response mechanism or a global disaster response fund will be created H.R. Hertzfeld (*) Space Policy Institute, Elliott School of International Affairs, The George Washington University, Washington, DC, USA e-mail: [email protected] P.-A. Schieb NEOMA Business School, Reims, France Consultant to the OECD, Paris, France e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_80

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within the United Nations system or any other global institution. The general conclusion reached is that the evolution of new types of space technologies that might be developed for other purposes such as space debris removal, on-orbit servicing, etc. – may represent the most logical way forward. Keywords

Economics • Finance • Risk • Risk analysis • Disasters • Funding • Catastrophe • Resilience

Introduction Economic activity tends to work best within a well-established regulatory regime where values, markets, and financial incentives and risks are well known. Accurate and current information about economic conditions also supports economic efficiency. A major cosmic event such as a massive hit by an asteroid or a coronal mass ejection from the sun of epic proportion that could destroy a massive amount of global infrastructure is almost the worst possible case for developing a systematic and efficient economic response to such a catastrophe. These types of events have an extremely low probability of occurring, but they do have potentially huge socioeconomic consequences. Creating an economic fund in advance for the purpose of responding to such a low-probability event via a conventional-type insurance or risk-management scheme is unlikely for a number of reasons that will be explored in this chapter. First of all, fund raising – for whatever purpose – is always difficult. Whether it is for charitable purposes, business ventures, or government programs, there are numerous challenges to obtaining the necessary funds. The economics of funding is basically quite simple: investors want a low-risk, short-term payback. Money has time value – the longer it takes to obtain a return, the larger that return must be to overcome the lost opportunities that inevitably will be present. And, the larger the up-front investment is, the more difficult the hurdles are to funding. For purposes of this chapter, the focus will be on the worst possible scenario – a very large asteroid crashing into the Earth and having an impact that affects all life on Earth. Other scenarios concerning space objects doing terrestrial damage are more analogous to the “typical” types of natural disasters that occur very frequently on Earth – volcanic eruptions, earthquakes, hurricanes, etc. The effects of these incidents are localized, and there is an extensive literature available on managing and recovering from these types of risks. In virtually all cases, the regions and nations involved are resilient and recover, sometimes quite quickly, from these damages. And, sometimes the results from an economic perspective may even (but not always) be quite positive over time where the rebuilding effort creates new jobs and infrastructure and consequently revitalizes a region that was in decline. Space technologies can help in predicting, identifying, and characterizing damages as well as in the planning and organizing of a recovery. International

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organizations and international cooperative efforts also are helpful, particularly in responding to regional disasters. But, the more challenging question, for which there is no definitive answer, is how collectively human beings and space technology can be mobilized to identify and possibly even prevent a catastrophic disaster that could affect the entire Earth. Most studies of this problem focus on the first step – identifying and monitoring space for potentially hazardous Near-Earth Objects (NEOs). That process is relatively inexpensive and is closely coupled with other space-monitoring programs. These programs are funded for other purposes – safety of operations in space, identification of potential resources and other uses of various celestial bodies or orbits, and security/national defense. The challenge for funding is to address the eventual issue of defending our planet from a catastrophic impact originating from space, which is a global effort with unknown risks and costs.

Measuring the Probability of Risks and Losses The list below of Asteroid Fast Facts prepared by the NASA Jet Propulsion Laboratory describes the types and sizes of asteroids that could cause potential harm to Earth (NASA Fast Facts). Note that the risks are very low for a catastrophic occurrence (NASA Jet Propulsion Laboratory). Asteroid Fast Facts (Source: NASA, Jet Propulsion Laboratory) Size and Frequency • Every day, Earth is bombarded with more than 100 tons of dust and sandsized particles • About once a year, an automobile-sized asteroid hits Earth’s atmosphere, creates an impressive fireball, and burns up before reaching the surface. • Every 2,000 years or so, a meteoroid the size of a football field hits Earth and causes significant damage to the area. • Finally, only once every few million years, an object large enough to threaten Earth’s civilization comes along. • Impact craters on Earth, the moon, and other planetary bodies are evidence of these occurrences. • Space ricks smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth’s atmosphere and cause little or no damage. • If a rocky meteoroid larger than 25 meters but smaller than one kilometer (a little more than ½ mile) were to hit Earth, it would likely cause local damage to the impact area. • We believe anything larger than one to two kilometers (one kilometer is a little more than one-half mile) could have worldwide effects. At 5.4 kilometers in diameter, the largest known potentially hazardous asteroid is Toutatis. • By comparison, asteroids that populate the main asteroid belt between Mars and Jupiter, and pose no threat to Earth, can be as big as 940 kilometers (about 583 miles) across.

Figure 1 compares four cases. Only the one shaded dark red is of a major concern for humanity as a whole. All the others are, as mentioned above, manageable and society and property are relatively resilient over time. Current space-monitoring systems can be improved and will help provide regions and localities with advance warning disaster relief efforts.

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Small NEO with no impact

Large NEO, impact small (occurs in remote area or “near miss”)

Resilience: none needed Total Cost: zero to very low Funding for R&D: No new funds— included with other monitoring programs

Resilience: fast--minor disruptions Total Cost: affordable by nation(s) Funding for R&D: Very large, same as for one with major impact

Probability: high

Probability: low

Small NEO, impact major but localized

Large NEO, major impact on all humanity

Resilience: major issue locally, but manageable nationally Total Cost: large but “affordable” to nation(s) Funding for R&D: Moderate to large depending on global interest

Resilience: Not resilient Total Cost: Very high; global, not recoverable Funding for R&D: Very large with significant risk—attempts at protection may fail

Probability: moderate

Probability: very low

Fig. 1 Probability of a catastrophic loss

However, focusing only on major space weather events or asteroid risks is misleading. The real question is where does this activity fit in relation to the multitude of other risks facing the Earth and humanity. The World Economic Forum each year publishes a chart comparing the likelihood of major threats occurring with the impact of these risks, and the most recent is reproduced below (World Economic Forum 2014) (Fig. 2). There are several possible explanations of the recent flurry of interest in the risks of damage from asteroids. The first is the Feb. 15, 2013, event where an asteroid measuring about 14 m in width detonated in the skies over the Russian city of Chelyabinsk, causing millions of dollars of damage and injuring 1,500 people. As dramatic and disruptive to the region that this was, it was no threat to humanity in general or to the planet. However, with today’s speed of communications, instant and ubiquitous distribution of photographs and video, and other media coverage, people everywhere were aware of what previously would have been a footnote in most newspapers appearing days after the event. Second, relatively recent documentation of previous asteroid impacts on Earth has led to the realization that this is not an uncommon phenomenon and that serious damage has been done in the past. Coupled with an increasing world population, increasing concentrations of people in urban areas, and increasing property values in some areas vulnerable to natural disasters (coastal property, hillsides prone to mudslides, etc.), the economic damage from all natural disasters has also increased over time. (This has been balanced by better forecasting of natural events, which has led to better mitigation techniques and resilience but nonetheless increased perception of risk.)

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The global risks landscape

Fiscal crises Climate change Water crises Unemployment and underemployment

5.0 Biodiversity loss and ecosystem collapse

Critical information infrastructure breakdown

Failure of financial mechanism or institution

Political and social instability Weapons of mass destruction

Extreme weather events

Cyber attacks

Income disparity

Global governance failure Pandemic

average 4.56

Natural catastrophes

Food crises

Antibiotic-resistant bacteria

Liquidity crises

4.5 State collapse

Terrorist attack Oil price shock

Data fraud/theft Man-made environmental catastrophes Interstate conflict

Economic and resource nationalization Corruption Failure of critical infrastructure 4.0

Impact

Chronic diseases

Decline of importance of US dollar

Mismanaged urbanization

Organized crime and illicit trade 3.5

4.5

4.0

Likelihood

4.31 average

5.0

5.5 plotted area

Fig. 2 World Economic Forum Global Risks

Third, space technology and capabilities are expanding rapidly. Our ability to monitor space and observe activity in space has increased dramatically, partly from better technology and partly as a result of the recent concerns about human-created space debris and its possible detrimental effects on active satellites. Furthermore, with the advent of possible multiple types of in-space activities such as satellite servicing, resource extraction, and debris removal (all with possible commercial as well as public value), the monitoring of asteroids from both the perspective of danger and a source of valuable materials has increased. Fourth, some of those in-orbit future capabilities may also be applicable to allow the development of techniques to move asteroids that are threatening the Earth to orbits that will safely avoid the planet. (However, it must be noted that with any human-created technology, especially untested ones, there also could be an increased probability of errors and mistakes that could actually increase risks of damage instead of decreasing them.)

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Fifth, the increasing dependence of terrestrial economies on space assets and satellite applications such as communications and navigation has added attention to the protection of those assets for the continuity and effective operation of many Earth-based economic activities. And, finally, with these motivational drivers, the space-monitoring efforts of the past decade have detected previously unknown asteroids that have the potential of an impact on Earth. Although the actual probability of an impact with Earth has not changed over thousands of years, our knowledge has. And with that knowledge, the perceived risks are now considered to be higher, even if the probability of a major strike is still quite low. Figure 2 shows one compilation of risk likelihood and potential impact produced by the World Economic Global Forum. It is significant that space-based risks are not separately identified in this chart. However, space catastrophes may affect global infrastructure and space systems may be able to help mitigate the impacts of natural disasters.

Costs A US National Academy of Sciences review of hazards and mitigation strategies for NEOs included an analysis of estimated costs for eight different programs ranging from telescopes for monitoring space to several types of proposals for mitigating the danger from NEOs (US National Academy of Sciences). The range of estimates was, on the lower end for telescopes, $90 million to almost $2 billion. On the upper end, for deflection or destruction of NEOs, the costs ranged from $1.7 billion to over $3.5 billion. These figures are the ones calculated in the study that the estimators reported at the 95 % confidence level (there were lower total costs at lower statistical confidence thresholds). It should be also noted that these costs were calculated in 2010$ US, and when and if the government programs associated with those cost estimates were to be funded, they would have to be adjusted upward to account for inflation. It is also noted that in the past cost estimating models typically understate the actual costs by 30–50 %. And if these efforts to monitor and mitigate large NEO impacts are a global effort involving many nations, international cooperative programs may result in lower expenditures for each nation participating, but in a total cost that is greater than what would be needed if a single nation funded and managed the projects. Finally, the costs do not include any risks of accidents, mistakes, or unforeseen damages in space or on Earth from these activities. Although these additional factors may be minimal for equipment in space used in monitoring efforts since those technologies are well proven and similar to many types of existing satellites, they could be very significant for moving NEOs to different orbits or destroying a NEO, neither of which has ever been done or tested to date. NASA’s Planetary Science Research Program currently does have a $40 million budget for the identification and characterization of objects in the solar system that

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pose threats to Earth or offer resources for human exploration. It is noteworthy that this line item has been doubled in FY 2014 from the prior year’s budget but is projected to remain flat at $40 million in the future (NASA 2014). In the United States, the Space Situational Awareness efforts are led by the Department of Defense. The total annual costs of the satellites, launches, ground equipment, and other supporting and associated equipment and personnel are unknown, partly due to security classification and partly due to the reality that these systems serve more than one purpose and the costs are difficult to allocate to specific goals. However, manufacturing and launching sophisticated tracking satellites can easily cost upward of $500 million each, and the future S-Band Space Fence facility will cost billions of dollars (US). Therefore, it is not unreasonable to estimate that well over $1 billion per year of the DOD budget is dedicated, directly or indirectly, to the types of monitoring of space that detects and analyzes the trajectories and risks associated with space debris, missile launches, and NEOs. NASA missions such as NEOWISE, the proposed NEOCAM, and other activities involve additional major expenditures. Expenditures of lesser amounts for monitoring space also are made by other nations, and there are also multimillion initiatives by other organizations such as the B612 Foundation that are planning to implement the Sentinel infrared space telescope project. Clearly, even accounting for these large expenditures, all nations are still in the infancy of having a full knowledge of celestial bodies and NEOs that could threaten the Earth. And, even if that information were available, technologies for predicting the trajectories and true risk to Earth of any of these objects are still under development and not perfected. The conclusion is fairly obvious that even though very significant annual funding is being devoted to direct and indirect surveillance of space, it is currently insufficient for purposes of accurately detecting and predicting the dangers to Earth of a catastrophic incident. It is also unknown if human beings will ever be able to predict such an event with enough advance notice to mitigate the impact, although more research and development, monitoring, and other actions should improve on current knowledge. NASA and other nations have also spent billions of dollars to learn more about the sun, solar flares, and coronal mass ejections, but in this area preventive actions are at an even more rudimentary level of development.

Funding Mechanisms for a NEO Program A program designed to identify and move NEOs so they will not have an impact on Earth would have to:• Be a long-term commitment, possibly spanning decades • Be coordinated with other ongoing space R&D efforts • Involve many nations, either directly or indirectly • Overcome associated issues of national security and classified technology and information

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Any nation undertaking a program of this sort would experience difficulties in developing justifications for a long-term budget commitment. In the United States, for example, budgets are determined annually. Any commitment to any given year’s funding is subject to many economic and political factors, all of which may change from year to year. As witnessed over the years by many programs (Shuttle, International Space Station, expendable launch vehicle development, human exploration), there have been multiple changes, program cancellations, and budget reductions, even for the most beneficial and important programs. Similar fluctuations occur in other nations, although the specific triggers and methods of approving budgets vary considerably among different governments. Planetary defense presents a particularly difficult challenge; one so large that it is likely that there will never be funds raised at a sufficient level for a dedicated government program, international program, or business venture for this purpose unless there is a clear and imminent threat to a nation or to Earth. The latter is unlikely, as the probability of life as we know it on Earth being destroyed by a NearEarth Object (NEO) is extremely low. In fact, the probability has remained the same over thousands of years. Just because there was recently massive press coverage of a “near miss” over Russia in 2013 of a NEO that was not large enough to do anything more than severe local damage does not warrant a panic response, nor does it signify an increased probability of a catastrophic event. Recent data collected from nuclear detection monitoring systems has confirmed that impacts from asteroids are up to ten times more frequent than previously thought to be the case. Disasters that affect a region or a nation may not be insignificant or minor. Lives are lost, property is damaged, and a nation’s economic growth may be harmed. Recovering from a major earthquake, tsunami, volcanic eruption, or even an industrial accident can be lengthy and painful. However, these incidents are localized and the resiliency of human beings has been quite remarkable over time. Space activity and space technology is, however, changing and advancing. In the very near future, there will be both government and private ventures that will make use of space with new capabilities that include building platforms, servicing space assets, and extracting resources from other celestial bodies. Associated with those activities is an increasing need to monitor assets and orbits, assess the dangers to assets from space debris, and protect any human lives that are on space platforms such as the International Space Station (ISS). The technologies developed for monitoring and for performing these activities may also greatly contribute to our knowledge of NEOs and to our ability to protect the Earth. In short, the financing for planetary protection will continue to be largely indirect – it will progress from the technology and uses of space that will have direct near-term government and commercial paybacks. This chapter will address those developments. One of the most important considerations in any program designed to operate in the high-risk/long-payback space environment is funding. Access to space is risky and expensive, particularly for new and untried or unproven technologies and applications. Working in space is even more difficult – if it weren’t, there would today be many more types of in-orbit activities happening. Addressing risks to

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Earth from Near-Earth Objects is something that is clearly still in a research and development stage. We still do not know how to “save” the Earth from a major NEO catastrophe or extreme solar events. There is no guarantee that any national or any multinational program to accomplish this task is: 1. 2. 3. 4.

Needed in the near-term horizon Technologically sound Affordable Could not be accomplished without increased risks and possibly liability

The newly established United Nations International Asteroid Warning Network and the Space Mission Planning Advisory Group will undoubtedly have to address such issues. The ability to carry out a NEO program is currently limited to only a very few nations that have the technology, experience, and launch capabilities. Yet the location of a possible NEO incident could be anywhere on Earth. The immediate destruction would be local but the damage over time could be spread over the entire globe. Who benefits, who loses, and who pays are all critical questions that cannot be definitively and directly answered today. Although the purpose of this chapter is to review the issues related to funding a program directed toward NEOs and extreme cosmic hazards, funding is really a derivative issue. The key question of whether we should or should not seriously begin a planetary defense effort is addressed elsewhere in this book. Funding issues will be addressed in two ways – evaluating risk-management issues and summarizing analogies to the handling of other global catastrophic-type events. These issues are compounded when other considerations are added to the mix. In particular, planetary defense is a global threat – if a meteor or asteroid is determined to threaten the Earth, as mentioned above, the exact location may be unknown and indeterminate until the threat is upon us and it is too late to act. From a financing perspective, this exacerbates the risks since no one government in any one nation is likely to find the money to save another nation. Thus, unknown risks, unknown timing of an occurrence, unknown locations, unknown costs, unknown technologies needed, and unknown probabilities of success make for a very difficult case for any government (or anyone else) to defend current budget proposal or actual expenditures. Clearly, the usual economic investment criteria of risk, return on investment, and opportunity costs cannot be applied to this problem. Similarly, standard economic methodologies such as benefit cost analysis, internal rates of return, and decision analysis cannot be quantified in this case. One may ask, what is, then, the point of even analyzing the funding issues for this problem? The answers vary. First, there will not be any planetary defense if our society can’t find a way to fund it. Second, a look at other analogous high-risk/ low-probability threats may provide insights into finding ways to begin allocating funds to this issue. Third, a clear awareness of this huge problem and the international aspects of it may provide a new way of viewing and organizing resources designed to address both this and other global issues that are well documented but

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difficult to amass international support and mechanisms to alleviate or at least lower future risks. Solutions are unlikely, but awareness and planning for the future are possible and deserve attention.

Evaluating Possible Methods of Governance and Financing There is no international organization that governs space, nor is there likely to be one. For specific purposes, nations have joined collectively to share information, monitor world situations, and develop the means to cooperate on both political and economic matters. The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), the UNISPACE Conferences, and the Inter-Agency Space Debris Coordination Committee (IADC) and the newly formed International Asteroid Warning Network (IAWN) and the United Nations Space Missions Planning Advisory Group (SMPAG) are today the closest approximation of worldwide space coordination. Hypothetically, if scientists today made a prediction that a very large NEO was headed toward a devastating collision with Earth in 5 years, there is no doubt that those nations with the resources to help prevent that from happening would find a way to go to work on the problem. But, if those same scientists predicted that the NEO would land harmlessly in the ocean, the result might be different. Or, if the prediction was that it would hit the Earth in midtown Manhattan, there likely would be a major effort on the part of the United States to prevent that, but it is unknown how much other nations would contribute to that before the incident occurred. (After the fact, it is well demonstrated that nations most often offer to help in the recovery.) Spacefaring nations have joined forces on some issues. The UN Disaster Charter is an example where nations have formed an agreement to share and exchange remote sensing information without charges after a major natural or other disaster. This information is invaluable in helping to organize and mobilize a recovery mission. Even in the commercial world, companies that operate satellites in the geostationary orbit have recognized the need to share information about their satellite location and possible debris threats. They have recently formed a private company (the Satellite Data Association chartered in the Isle of Man) that collects the corporate data, assesses the vulnerability of satellites, and issues warnings and recommendations to help prevent collisions in space. Governments have also joined in this recent effort, illustrating that a threat of significant economic loss coupled with collective interest in preventing future losses can be funded and managed. It is conceivable that a joint effort requiring little new funding or technology to share information on what is known about NEOs and to monitor their movements could build on these models of international cooperation. Scientists and space agencies routinely share these types of data, and an existing organization, either under the United Nations or another international entity, could fill this need.

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But the possibility of similar international cooperative efforts for managing NEO threats requires a very different approach. There is no specific economic asset at risk, the technology to move or deflect NEOs is both undeveloped and has embedded in the R&D that will need to be performed significant issues with the sharing of sensitive information, and the funding would require very large contributions.

Is It All Worth Worrying About? Fear, risk, and governmental action are the subjects of many interesting academic analyses. For example, an article from the Harvard University Law Review (Sunstein and Zeckhauser 2008) highlights the points this chapter is emphasizing. To quote from their conclusions: . . .when risks are vivid, people are likely to be insensitive to the probability of harm, particularly when their emotions are activated. If terrible outcomes are easy to visualize, large scale changes in thought and behavior are to be expected, even if the statistical risks are dramatically lower than those associated with many activities where the stakes are equivalent but do not raise public concern. This claim about action bias helps explain public overreaction to certain highly publicized, low-probability risks, including those posed by sniper attacks, abandoned hazardous waste dumps, anthrax, and perhaps terrorism more generally. With financial crises, as late 2008 made tragically clear, fears and anxieties, and the action bias they induce, may dramatically magnify both the likelihood and size of a severe adverse outcome. It follows that government regulation, affected as it is by the public demand for law, is likely to stumble on the challenge of low probability harms as well. The government should not swiftly capitulate if the public is demonstrating action bias and showing an excessive response to a risk whose expected value is quite modest. A critical component of government response should be information and education. But if public fear remains high, the government should determine which measures can reduce most cost effectively, almost in the spirit of looking for the best “fear placebo.” Valued attributes for such measures will be high visibility, low cost, and perceived effectiveness. Reducing fear offers two major benefits: (1) Fear itself imposes significant costs. (2) Both private and public responses in the face of fearsome risks are likely to be far from rational. These observations lead to the difficult questions of how to monetize and reduce public fear. The answers lie well beyond the current topic.

In a similar vein, the extract below from the Global Economic Forum Report discusses similar types of reactions from major catastrophes and specifically mentions the asteroid threats to humanity. An Emerging Spectrum of Catastrophic Risks: Existential Threats ({originally} Contributed by the Global Agenda Council on Catastrophic Risks) Throughout history, humanity has been all too familiar with catastrophes affecting life and livelihoods on a major scale: earthquakes, floods, drought, tsunamis, cyclones and so on. Increasingly, however, the new risks coming into focus are more complex, more uncertain and potentially exponentially more consequential. These are existential risks – those that could either annihilate intelligent life or permanently and drastically curtail it potential.

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Natural disasters could conceivably trigger existential risks in combination with new technologies – a possibility suggested by the March 2011 tsunami that caused a meltdown at the Fukushima nuclear power plant in Japan. There is also the theoretical potential for “error or terror” in emerging sciences, such as nanotechnology or synthetic biology: within a few decades, for example, it may become as feasible to create real viruses in a home laboratory as it now is to create computer viruses on a home computer. Among other existential risks is the possibility that breakthroughs in artificial intelligence could move rapidly in unexpected directions; the spread of antibiotic-resistant bacteria could dramatically set back modern medicine; solar super-storms could devastate vital information and communications technology networks; climate change could tip into a self-reinforcing, runaway phase of rising temperatures; a meteorite could hit a denselypopulated area or an asteroid could strike the earth. Although these threats sound forbidding, there areways to prevent most of them, or at least to mitigate their impacts. While research and innovation can provide new approaches, established institutions can also play an important role. For example, in October 2013 the UN General Assembly approved the creation of an International Asteroid Warning Group. It is important for the public and private sectors to work together to address existential risks. The private sector has experience and expertise to offer in the realms of strategic planning, organizational design, institutional adaptation, research, scientific investigation and technological innovation. However, effective public-private collaboration will require vision, strategy and commitment to more extensive, consistent and systematic approaches at the country, regional and international levels. This, in turn, requires an appreciation that existential risks exist not only in the realism of science fiction but also in reality. Note: Existential risks as defined by Nick Bostrom of Oxford University.

It is not, therefore, surprising that a number of analyses of similar low-probability/high-consequence disasters result in recommendations that call for monitoring and increased research and development. That R&D would be oriented toward both better monitoring and mitigation aimed at reducing the threat itself, but it would also extend to methods for a recovery from such a disaster. Examples are found in the Organization for Economic Cooperation and Development’s report on systemic risks (OECD), the National Academy of Sciences report on NEOs (US National Academy of Sciences), and the UN Office for Disaster Risk Reduction (UN Office for Disaster Risk Reduction, UNISDR). The United Nations report lists five categories that it tracks where nations have increased their programs to deal with potential disasters of all sorts. The categories are governance and institutional arrangements, risk identification and early warning, knowledge and education, underlying risk, and preparedness and response (UNSIDR). A disaster of the magnitude discussed in this report is assumed to be inevitable and avoiding it is not an option. The monitoring and mitigation efforts, ones that have the greatest potential to alleviate public fear, are emphasized. The literature on NEOs is slightly different. The engineering- and sciencedominated space agencies are more focused on programs to avoid a NEO hitting the Earth than they are on disaster mitigation and recovery. Balancing that, the few studies that have been done by international organizations such as the UN and the OECD focus more on the near-term responses – monitoring and prediction technologies. The US National Academy of Sciences report on NEOs mentioned above covers both aspects – monitoring and preventing a NEO impact – but its

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clear recommendations are near term and realistic, improving the detection and prediction. Finally, one of the fears underlying the large asteroid hitting the earth is the evidence that such an event led to the extinction of the dinosaurs. The analogy is that the same type of event could have similar effects on human beings. A very new study has developed a theory from scientific evidence that the asteroid’s effect on the climate of the Earth during the reign of the dinosaurs was only one event in a series of other preceding natural events that created a “perfect storm,” and the combination of climate changes and the NEO impact in Mexico acting together led to the demise of the dinosaurs (Ghosh 2014). If future research confirms this theory, there is a reasonable probability that even the “global catastrophe” of a NEO event may not have as severe an impact upon human beings as feared and that the Earth and its inhabitants are resilient and could survive.

Conclusion In summary, for the foreseeable future, humanity will likely have to bear the risk and uncertainty associated with a highly improbable NEO catastrophe or an extreme solar weather event that might threaten widespread or even global mass extinction. Such an event would, of course, threaten not only humanity but many other species as well. Funding and programs that are specifically directed toward avoiding such an occurrence are unlikely to be forthcoming in the near term. Major international funding initiatives will likely depend on numerous factors that include technological breakthroughs in detection, new space servicing and robotics, and a political and macroeconomic environment that is amenable to global agreements for an international defense fund. However, as with other types of natural disaster potentials, there are many ongoing indirect R&D programs, technologies, and mechanisms that are currently funded which will increase our understanding of NEOs, help alleviate excessive fear of the unknown, and contribute to the ability to monitor and predict possible impacts on Earth. These along with the continued technological developments for in-space activities extending lifetime of satellites, removing human-created debris in space, on-orbit space servicing, and new space technologies that might be deployed to use valuable space-based natural resources may also be directly applicable to protecting the Earth from experiencing the worst-case scenario of a devastating threat to human beings.

Cross-References ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ Regulatory Aspects Associated with Response to Cosmic Hazards ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards

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References B612 Foundation, Sentinal, Data Sheet, http://sentinelmission.org/sentinel-mission/sentinel-datasheet/ (accessed 12/16/14). Ghosh P (2014) ‘Bad luck’ ensured that asteroid impact wiped out dinosaurs. BBC News, 28 July 2014. Accessed at: http://www.bbc.com/news/science-environment-28488044 Kliesen KL (1994) The economics of natural disasters, The Regional Economist, St. Louis Federal Reserve Bank, April 1994. https://www.stlouisfed.org/publications/re/articles/?id=1880. Accessed 30 July 2014 NASA Jet Propulsion Lab. http://www.jpl.nasa.gov/asteroidwatch/fastfacts.cfm. Accessed 31 July 2014 NASA, Asteroid fast facts. Jet Propulsion Laboratory, Pasadena. http://www.jpl.nasa.gov/ asteroidwatch/fastfacts.cfm. Accessed 31 July 2014 NASA (2014) FY2015 President’s Budget Summary Request. National Aeronautics and Space Administration, Washington, DC, p PS-2 Natural disasters: counting the cost of calamities|The economist. http://www.economist.com/ node/21542755/print (accessed 12/16/2014) Sunstein CR, Zeckhauser R, (2008) Overreaction to fearsome risks, Harvard University Law School Program on risk regulation, research paper no. 08–17, Dec 2008 UNISDR (2013) From shared risk to shared value – the business case for disaster risk reduction. Global assessment report on disaster risk reduction. United Nations Office for Disaster Risk Reduction (UNISDR), Geneva US National Academies of Science (2010) Defending planet earth: near-earth object surveys and hazard mitigation strategies. National Academy Press, Washington, DC World Economic Forum (2014) Global risks 2014, 9th edn. World Economic Forum, Geneva

International Cooperation and Collaboration in Planetary Defense Efforts Joseph N. Pelton

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Agency Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . United States and NASA, NOAA, DHS, DoD, and the NSF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . European Union and European Space Agency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CNES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DLR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . JAXA-ISAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROSCOSMOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Space Agency Efforts to Address Cosmic Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . University, Research Institute, and Ground Observatory Coordination . . . . . . . . . . . . . . . . . . . . . . WGNEO of the IAU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The B612 Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Planetary Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Action Team-14 Effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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This chapter seeks to highlight the various activities that are now ongoing around the world in the planetary defense arena – broadly defined. This chapter also seeks to address key problems and challenges related to future planetary defense and how emerging patterns of collaboration in these areas are evolving in a positive way. In some cases entirely new models of cooperation across a

J.N. Pelton (*) International Association for the Advancement of Space Safety, Arlington, VA, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_74

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number of diverse technical fields are emerging. Some of these levels of cooperation involve colleges, universities, foundations, and research institutes. Other collaborative links involve corporations, governmental agencies, and even concerned nongovernmental organizations and foundations such as the Association of Space Explorers (ASE), the Safeguard Foundation, and the B612 Foundation. The United Nations has also begun to build effective new collaborative programs. These UN programs are addressed in a separate chapter. In short, much, much more remains to be done, but serious new efforts to collaborate in this daunting field are indeed underway. In addition to reviewing patterns of international cooperation, this chapter also examines some of the national and regional programs of countries that are most active in this area. Keywords

Action Team-14 (AT-14) • Association of Space Explorers (ASE) • Asteroid • B612 Foundation Sentinel Project • Canadian Space Agency • Canadian Office of Critical Infrastructure Protection • Chinese National Space Agency (CNSA) • Coronal mass ejection • DLR • European Space Agency • ESA Near-Earth Object Coordination Centre • European Union • Global space observatories • Inter-Agency Space Debris Committee • International Academy of Astronautics Conferences on Planetary Defense • International Astronomical Union (IAU) • Japanese Space Agency (JAXA) • Jet Propulsion Lab (JPL) Sentry Risk Table • Meteoroid • Minor Planet Center • NASA • National Science Foundation • NEOShield • NEOWISE • Near-Earth Object Dynamic Site (NEODyS) system • The Planetary Society • Panel on Asteroid Threat Minimization (PATM) • Russian Space Agency (Roscosmos) • Safeguard Foundation • Solar flare • Solar max • Solar observatories • Space debris • Space situational awareness • UN Committee on the Peaceful Uses of Outer Space • UN Working Group on Near-Earth Objects • US Department of Homeland Security • Wide-Field Infrared Survey Explorer (WISE)

Introduction There are a great many institutions around the world that are currently addressing the issue of cosmic hazards and planetary defense. At the international level, there is one organization, the Near-Earth Object Dynamic Site (NEODyS) system in Pisa, Italy (with a mirror site in Spain), that monitors and provides worldwide alerts with regard to potentially hazardous near-Earth objects. This system provided an alert with regard to the TC3 asteroid that resulted in an airburst over Sudan in 2008. Yet the air burst explosion of the 17 m meteorite over Siberia caught the world by surprise. The NEODyS system, the United Nations Near-Earth Committee and the Minor Planet Center, and the Safeguard Foundation provide useful services, but their focus is on NEOs and not other types of cosmic threats that could also create major damage and loss of life. The Safeguard Foundation is a joint effort of the

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United States, the European Union, Japan, and other countries. This nonprofit foundation was created to coordinate NEO detection and studies. It is currently located at the European Space Agency’s (ESA’s) Centre for Earth Observation (ESRIN) in Frascati, Italy, and this foundation works in close cooperation with NEODyS and the Minor Planet Center and also links to the United Nations NEO Committee. All of these activities represent progress toward international cooperative action (“Defending Planet Earth”). Yet, what is truly needed is a global cosmic hazards and planetary defense system that can help provide well in advance effectively communicated global warning of specific cosmic threats as well as serve as a hub to carry out research and test program to achieve an effective planetary defense. The degree of international cooperation and collaboration in the various areas of cosmic threats continues to grow and expand around the world. There are several complicating factors that make collaboration and cooperation in these areas difficult. First of all there are so many different types of actors in this field. Thus, one finds research institutes, colleges and universities, foundations, space agencies, and other affected governmental agencies in many diverse areas that are involved. These governmental agencies cover such areas as homeland defense, emergency management, economic development, transportation, environmental protection, energy, national defense, and related scientific and space research. In addition there are also private corporations, a number of regional and international agencies (both intergovernmental and nongovernmental), and of course the relevant United Nations entities. It is difficult for so many disparate groups to find the means and methods to share data and engage in cooperative programs and, of course, to find the necessary levels of funding. Secondly there are a sizable number of cosmic hazards which need to be taken seriously and addressed by a wide diversity of protective measures. Near-Earth objects and potentially hazardous asteroids and comets receive perhaps the greatest amount of attention. Yet a variety of hazards from solar and cosmic radiation and coronal mass ejections, changes in the Earth’s natural protective systems such as its geomagnetosphere and atmosphere, and other threats such as orbital space debris represent very serious concerns in terms of dangers to human life, air traffic, as well as credible threats to critical infrastructure on which a world of some seven billion people now depend. Each of these types of threat involve different types of scientific research and involve different types of technologies and observational equipment (on the ground and in space) to address these issues. Protective measures and defensive actions are likewise widely different. In short collaborative actions related to cosmic hazards involves finding ways to get many different types of players around the world to share data and work effectively together. It also involves a perhaps even larger challenge of finding ways for research scientists and engineers who work in many different fields (astronomy, celestial mechanics, radiation, nuclear physics, atmospheric sciences, radar systems, satellite systems engineering, chemical and electronic propulsion systems, computer modeling, etc.) to find effective ways to share knowledge and develop effective planetary defense systems and technology across these very diverse areas of technical expertise. The truth of the matter is that a concerted effort on the scale of the

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Manhattan Project or the Apollo Program is likely needed to take on true planetary defense in a meaningful way. Unfortunately the political will to devote such a huge amount of resources is not there, because the perceived level of threat is simply not there. Currently activities such as the Safeguard Foundation, the Minor Planet Center, NEOShield, NEODyS system, etc. represent an expenditure level at the level of tens of millions of dollars – not tens of billions. And even if there was a clear recognition of a massive threat, the ability to marshal all of the resources needed to accomplish the many acts of economic and technical coordination on a global scale is clearly lacking. Another chapter addresses the leadership and global cooperative challenges that planetary defense, but the clear conclusion is that neither the political will nor dedicated high-level leadership is now present. The first obvious step is to explore what cooperative processes are now underway and to develop preliminary strategies to build meaningful relationships that can make true planetary defense feasible in future years. The starting point for effective regional and international cooperation and collaboration in the area of planetary defense is to have a clear understanding of what cosmic hazards are concerned and what is meant by planetary defense. Unfortunately neither of these clear definitions now exists. Substantial risks to plant and animal life, humans, and critical infrastructure can originate from near-Earth objects (i.e., potentially hazardous asteroids, comets, bolides, and meteors) and from solar flares and coronal mass ejections, cosmic radiation, antimatter/matter collisions, and space debris now threatens vital infrastructure. A deterioration of Earth’s natural protective shielding systems such as the geomagnetosphere and the atmosphere must be considered a key part of planetary risk assessment and protection. Global radiation management measures will increasingly be recognized as a part of planetary defense as the seriousness of climate change becomes clear in coming decades. All of these risks need to be considered in a holistic way and relevant data and information shared as widely as possible through systems that have proved effective in such areas as weather forecasting and other forms of disaster prediction and recovery. All legitimate agencies and entities (both private and public) conducting research, collecting data, or working on protective or recovery systems should be integrated into systematic information sharing arrangements. Steps that have already been taken such as the creation of the Minor Planet Center; the Near-Earth Object Dynamic Site (NEODyS) System in Pisa, Italy; the Safeguard Foundation, the JPL Sentry Risk Table, the ESRIN Near-Earth Object Coordination Centre; the Inter-Agency Space Debris Coordination (IADC) Committee; the various solar observatories around the world; the NOAA Online Solar Weather Dashboard; the IAA Conferences on Planetary Defense; the United Nations COPUOS Working Group on Near-Earth Objects, the NEOShield Project of the European Union; and other initiatives reported on and discussed in this chapter and elsewhere in the handbook are important efforts to be commended and their efforts are documented in this handbook. Nevertheless, the current system of collaboration needs to be strengthened and improved in a number of ways. The space agencies need to do more, and national

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Fig. 1 NASA hazardous asteroid map with Earth orbit shown in bright white (Graphic courtesy of NASA)

governments (especially those with active space programs) also need to extend their research and discovery programs to detect space hazards as well as their efforts to mount improved measures to provide for planetary defense. The most important first step that needs to be done is to put the various types of risks into some sort of systematic process as to their nature, relative likelihood of doing damage to human life and infrastructure, as well as to plant and animal life. The good news is that there has been substantial progress in this regard. If one takes the example of near-Earth objects that are a potential threat to humans, we can chart this progress in fairly straight-forward terms. The number of known potentially hazardous near-Earth asteroids with traceable orbits that could constitute major threats to life on Earth as of the end of September 2013 was 10,232 (JPL 2012). Figure 1 depicts the map as produced by NASA that charts the orbits of the “top 1400” asteroids that could collide with Earth (“NASA Reveals. . .”). In 1898 the first near-Earth object was detected with an orbit that could be considered threatening to Earth. This NEO is known as 433 Eros. In the next hundred years, i.e., from 1898 to 1998, only about 500 additional NEO were detected. Since that time, however, additional emphasis has been given to these NEO-detection efforts through ground observations and space-based infrared telescope efforts. There is even now in place a congressionally enacted mandate (i.e., under the so-called George Brown Act) to set a deadline for NASA to detect all Near-Earth Asteroids 1 km or more in diameter. Thus, the current NEA discovery rate is about 1,000 per year (NEO Coordination Centre). Out of the 10,000 discoveries, roughly 10 % are larger than 1 km in size, while the vast majority of NEAs are smaller than that, with the number of objects of a

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given size quickly increasing as the size decreases. It is thought that perhaps 90 % of all NEOs that are 1 km or more in size have been detected. Although this is clear progress, one should be aware that NEOs in the range of 140 m up to 1 km in size can have very considerable damage whether in an airburst, land impact, or water impact mode. The fact that all of this detection data is recorded with the Minor Planet Center and is systematically available to the world community represents great progress. The further fact that the Torino Scale has been globally accepted as a useful measure to help calibrate the impact damage of various-sized NEOs and their likely impact with Earth is also a key step forward. The parallel acceptance of the so-called Palermo Scale that assigns to detected NEOs the probability of their impacting Earth represents a further positive step in terms of global cooperation. Despite this progress, much more needs to be done. We now see private initiatives such as those of the Planetary Society and the B612 Foundation to assist with the detection and recording process. We see quite helpful efforts to coordinate efforts of universities in various countries to study how to mitigate or prevent the threat of detected NEOS from actually impacting Earth. One such effort is that spearheaded and funded – albeit at modest level – by the European Union, known as NEOShield. This program is coordinated by DLR, the German Space Agency that provides the funds to universities and research institutes to study how to prevent major damage and life-threatening events from NEOs. But this is but only one type of space threat. There are both naturally occurring space dangers as well as man-made dangers to space infrastructure and these dangers now number over a dozen. These include collisions involving asteroids, comets, and bolides, solar flares, coronal mass ejections, cosmic radiation, biological hazards from space, antimatter collisions, orbital space debris, electromagnetic pulses from space (that could be caused by a nuclear explosion in space), solar radiation and micrometeoroids that damage critical satellite infrastructure, and possible collapse or deterioration of natural Earth-protective systems such as the geomagnetosphere, the upper stratosphere, and ozone layer. What is needed and what is now lacking is an effective global process to address all of these forms of space-related risks; assess their threat level; undertake detection, measurement, and recording of relevant data; and carry out research to see out, minimize, mitigate, or eliminate these threats that could result in the loss of life at the level of millions to billions of people; create major harms to animals, plant life, and vital crops;, and create economic and infrastructure losses that could run in the many trillions of dollars (US). The first place for this to start would be in coordinative actions among the world’s space agencies.

Space Agency Coordination Today there are a dozen spacefaring nations with the ability to launch satellites into orbit. Beyond these countries with launch capabilities, there are some 50 countries with active space research or space applications agencies or commissions. At the annual International Astronautical Congress, many of these national and regional

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space agencies plus organizations such as EUMETSAT, the International Space University, etc. hold coordination meetings and exchange information. Beyond these rather space-focused nations, there are now some 90 nations that participate as members of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). Virtually every country and territory in the world actively utilizes space for telecommunications, remote sensing, meteorological forecasting, and space navigation. In short there is a wide spectrum of countries that range from intensive space activities and major space research, exploration, and applications programs with large annual budgets down to those that only use space facilities for services. It would seem reasonable for space agency coordination with regard to cosmic hazards and planetary defense to start by building on the positive experience of the established Inter-Agency Space Debris Coordination (IADC) committee that includes a critical mass of space agencies with the depth of resources and technical expertise to assist with this demanding field. The current IADC member agencies include the following: • • • • • • • • • • • •

ASI (Agenzia Spaziale Italiana) CNES (Centre National d’Etudes Spatiales) CNSA (China National Space Administration) CSA (Canadian Space Agency) DLR (German Aerospace Center) ESA (European Space Agency) ISRO (Indian Space Research Organisation) JAXA (Japan Aerospace Exploration Agency) NASA (National Aeronautics and Space Administration) NSAU (National Space Agency of Ukraine) ROSCOSMOS (Russian Federal Space Agency) UK Space (UK Space Agency)

Indeed the positive experience that has come from the IADC is clearly part of the inspiration for the formation of the so-called Action Team-14 that includes the 14 countries and their space agencies that agreed coming out of UNISPACE III to work together to coordinate the tracking of asteroids and comets and to explore means to deflect potentially hazards near-Earth objects from impact with our planet. The IADC as currently organized includes a Steering Group plus four Working Groups. These Working Groups include (i) Working Group 1 on Measurements, (ii) Working Group 2 on Environment and Database, (iii) Working Group 3 on Protection, and (iv) Working Group 4 on Mitigation. The IADC has been an effective international coordination process and has worked very effectively to develop orbital debris mitigation guidelines and has worked very effectively with the UN Committee on the Peaceful Uses of Outer Space (COPUOS) to provide key technical and scientific information (Pelton 2012). The AT-14 is indeed structured in a similar manner to work in such areas as (i) detection and measurements; (ii) collaborative space research and investigation

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programs; (iii) theory and analysis; (iv) strategies and capabilities for threat detection, reduction, and mitigation; and (v) public awareness and education. The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) has also already established Working Groups of its Scientific and Technical Subcommittee that are relevant to this international coordination process. These are the Working Groups on Space Debris Mitigation (established in 2004), on Sustainability of Space (established in 2012), and on Near-Earth Objects (established in 2007) (United Nations Office of Outer Space Affairs 2013). The chapters later in this handbook, especially the one related to the work of the United Nations as provided by Sergio Camacho-Lara, report on the status of the UN COPUOS efforts and especially on the Working Group on Near-Earth Objects. It is clearly important for the space agencies’ coordinative efforts to develop specific methods of data exchange and systematic information collection and to help initiate joint space missions to be undertaken by specific spacecraft. The work as carried out by Action Team-14, the Association of Space Explorers, the Planetary Society, the B612 Foundation, the Safeguard Foundation, the Minor Planet Center, and others with technical space expertise can be undertaken in such a way so as not to duplicate the “global space policy” development process undertaken by the UN COPUOS. Perhaps most importantly this interagency committee might help to begin actual efforts to mitigate and reduce a variety of space hazards including not only with regard to near-Earth objects but also concerning radiation- and solarrelated concerns. Perhaps it is useful to provide analogy here with regard to defining the respective roles of the Inter-Agency Space Committee and the UN policy concerns. It is likely that the work of the UN COPUOS will develop new broad space policy for the “overall forest” in this technically complex area. The interagency’s coordinative efforts, among the various space agencies, would be to develop detailed and specific collaborative space-related efforts at the level of “the trees, branches, and leaves” which would carry out the broad policies. In short the UN COPUOS efforts would involve process and procedure. The space agencies would carry out the research programs, launch the spacecraft programs, and perhaps even carry out steps to divert the orbits of threatening asteroids and comets or seek ways to divert the most dangerous ionic bombardments of the sun’s coronal mass ejections or better shield the Earth from solar radiation.

United States and NASA, NOAA, DHS, DoD, and the NSF Currently the United States, NASA, and NOAA, in partnership with a number of academic and independent research programs, carry out the most ambitious space threat inventorying, data collection, and threat mitigation programs. NASA is charged by the US Congress to create a complete inventory of large near-Earth objects. NASA was first charged to identify all NEOs of 1 km or more in size by 2008. Subsequently under the George Brown Jr. Near-Earth Object Survey mandate NASA was charged with identifying 90 % of all potentially hazardous objects that

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were 140 m in diameter or larger. NASA is required to prepare a formal report entitled the Near-Earth Object Search Report each year. Unfortunately this inventory is behind schedule and not complete. This activity has been largely carried out in space with the NEOWISE Space Infrared Survey (WISE is an acronym standing for the Wide-Field Infrared Survey Explorer). The NEOWISE project that was inactive for the last nearly 3 years was reactivated for another 2.5 years of NEO detection as of September 1, 2013 (“NASA Spacecraft Reactivated. . .”). To extend the capabilities for space-based infrared imaging to detect hazardous NEOs, the B612 Foundation is proposing to build and launch a highly capable Sentinel infrared telescope that could complete an inventory for smaller potentially hazardous NEOs and provide improved warning capabilities. NASA is also now working on defining a new IR telescope called NEOCAM that would also aid in identifying NEO threats. Of course not all NEOs are detected by space-based systems. There are many efforts underway using ground-based observatories. The Lincoln Near-Earth Asteroid Research (LINEAR), Near-Earth Asteroid Tracking (NEAT), Spacewatch, Lowell Observatory Near-Earth Object Search (LONEOS), Catalina Sky Survey, and the Harvard, Smithsonian Astronomical Observatory are among the US-based observatories that collect and inventory information on NEOs as well as on solar activity. In addition, the Minor Planet Center, located at the Harvard-Smithsonian Observatory, collects data from US sources, but from all over the world to create a complete inventory of data related to observed NEO threats. While NASA activities related to NEOS, including activities at JPL and the Minor Planet Center (which is 90 % funded by NASA), represent the prime US governmental agency actor with regard to asteroid and potential hazardous NEO detection, there are many other governmental agencies that play and active role with regard to cosmic threats. The National Oceanic and Atmospheric Administration (NOAA) provides warnings – a near-real-time dashboard display – with regard to space weather and solar flare and coronal mass ejections. The Department of Homeland Security that is responsible for civil defense and the National Response Framework has a potential major role to play in the case of a major threat and need for mass evacuation, but it has limited capabilities and guidelines deployed with regard to cosmic threats. This indeed is the case around the world. The Torino Scale helps to explain the potential threat level of NEOs based on their size, and the Palermo Scale assigns a threat level based on known objects of NEOs, but most civil defense agencies around the world lack clear procedures of what to do in case of detected threats due to NEOs, solar flares, coronal mass ejections, or other types of cosmic threats. The National Research Council report has also identified other agencies such as the Department of Defense, the National Science Foundation, as well as the Department of Agriculture. The US Department of Defense, which maintains the so-called space fence using S-band radar to carry out space situational awareness and has responsibility for the deployment of nuclear weapons that might be required for deflecting the orbits of hazardous NEOs, obviously has international capabilities in addition to national responsibilities. Other governmental units that were identified in the report included the Environmental Protection Agency, the Department of Health and Human Services,

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Department of Transportation, and even the Department of Agriculture as having some form of role in responding to cosmic threats. The bottom line is that the United States, nor virtually all other countries, has clearly developed an actionable plans to address various types of cosmic threats that may be possible. The NEO survey as mandated by George Brown Jr. Act would seem to provide some level of reassurance as to being well protected against NEO impacts, but the recent discovery of a nearly 3 km asteroid in retrograde orbit after NASA’s survey of larger NEOs was thought to be essentially complete and serves as a reminder that much more still needs to be done. It is the contention of the B612 Foundation that only with the deployment of an especially designed infrared telescope optimally designed for potentially hazardous NEOs can hope to detect all serious threats on a comprehensive basis.

European Union and European Space Agency After the United States, it is the European Union and the European Space Agency that have devoted the most resources to the study of cosmic hazards and planetary defense. The Near-Earth Object Dynamic Site (NEODyS) system is a service sponsored by ESA operated in Italy and Spain. The most valuable service provided by NEODyS is the projection of all asteroid, meteoroid, and comet impacts with all of the planets in the solar system through the year 2100. This facility which is primarily supported by faculty from universities in Pisa and Rome with backup support from faculty in Spain uses specially developed computer software to calculate orbits from data supplied from the Minor Planet Center and other sources. Many believe that the most important feature of the NEODyS system is the so-called Risk Page that provides information for all NEOs with probabilities of hitting the Earth that are greater of 10 11 and from now until 2100. This Risk Page provides information on objects that are divided into five categories sorted into “Special,” “Observable,” “Possible Recovery for Observation,” “Lost,” and “Small.” Each object recorded in the “Risk Table” has its own so-called Impactor Table (IT). This table shows information such as size, type of orbit, albedo, thermal qualities, and calculated likelihood of impact that would be useful in assessing the level of risk of Earth impact. The center also served as the focus point for scientific studies needed to improve NEO warning services and provide near-real-time data to European and international customers (The Near-Earth Orbit Dynamic Site (NEODyS)). Closely associated with Near-Earth Object Dynamic Site is the ESA-sponsored Space Situational Awareness-Near-Earth Orbit Coordination Centre which is operated by the Space Dynamics Services S.r.l. (SpaceDys) under a contract with Elecnor Deimos, Spain, on behalf of the Agency’s Space Situational Awareness Programme Office. It serves as the central access point to a network of European NEO data sources and information providers being established under ESA’s Space Situational Awareness (SSA) Programme.

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The center supports experts in the field to carry out space situational awareness and detection and monitoring of near-Earth objects. The objective of the center is to create a cooperative federation of new and existing European assets, systems, and sensors to support an increasingly capable future NEO system. It supports the integration and initial operation of ESA’s NEO information distribution network. The network within the federation will supply information to scientific bodies, international organizations, and decision-makers (ESA Space Situational Awareness-NEO Centre). ESA has also launched infrared space telescopes to help chart the heavens and to detect near-Earth objects. The first of these missions was the ESA Infrared Space Observatory (ISO) mission which was launched in 1995 and remained active collecting data through 1998, and data from this mission was archived and analyzed through 2006 (The ISO Infrared Space Observatory). In May 2009 ESA launched the largest infrared telescope ever, the 3.5 m mirror system that was designed primarily to map the universe but with the additional capability to detect near-Earth objects. This highly capable Herschel Space Observatory has almost depleted its helium coolant and thus is nearing the end of its life. It might be repurposed as was the case with the NASA WISE (Wide-Field Infrared Survey Explorer) to target NEOs in the last stages of its operation (ESA “Herschel Space Observatory”; NASA “NEOWISE”). The European Union has sought to take a step beyond the collection of NEO impact risk data and to consider what types of countermeasures might be possible. This EU initiative called NEOShield is coordinated by the German Space Agency DLR. Currently this effort is funded at a modest level of about 4 million Euros. The NEOShield activity promotes relevant research at European universities to study the nature and composition of NEOs such as asteroids, bolides, and meteoroids (and even comets such as 3552 Don Quixote) and to consider means and methods by which their orbits, if detected as being on a collision course with Earth, might be deflected (“NEOShield”).

CNES France is one of the major funders of the European Space Agency and thus helps fund the abovementioned activities. France has some research capabilities with regard to asteroid threats and has maintained certain capabilities to following the orbits of so-called co-orbiting asteroids, meteoroids, and comets (“Co-orbital Asteroid Leaves Earth’s Orbit”). The French Space Agency CNES has actually paid a more active role with regard to other types of cosmic threats. Thus, CNES played a key role in developing experiments (in cooperation with NASA and ESA) of the SOHO satellite to explore the nature of solar flares and coronal mass ejections. It has been a key participant in the multi-satellite Swarm research satellite program to understand the nature of the Earth’s protective magnetosphere with launch of the Swarm satellites in late 2013. It has also participated in the earlier Oersted and Champ research satellite programs that have sought to explore changes

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to the Earth’s magnetic field and to discover a better understand in changes to the Earth’s ozone layer (Champ, Oersted, and Swarm Satellite Research Programs).

DLR The German Space Agency has for some years played a key role in asteroid and near-Earth orbit survey activities. DLR and its Institute of Planetary Research has been assigned the key role of coordinating research efforts associated with the NEOShield effort that is funded by the European Union cited earlier. Using EU funding, DLR works with universities and research institutes to undertake efforts to describe the composition of asteroids and to consider viable ways to divert threatening NEOs from Earth impact. These partners are listed below: • • • • • • • • •

DLR Institute of Planetary Research The Paris Observatory The Open University of the UK The Fraunhofer Institute for High-Speed Dynamics/Ernst Mach Institute (EMI) Queen’s University of Belfast Astrium Deimos Space SETI Institute, Carl Sagan Center Russian Federal Space Agency (Roscosmos)/Central Research Institute of Machine Building (TsNllMash) • Surrey Space Center, Ltd./University of Surrey NEOShield was established in January 2012 under DLR direction with these 13 partners from research institutions and industry that are largely from Europe but with Russian and US participation. The first 4 years of activity began with 4 million Euros of funding from the EU plus 1.8 million in funding from the research partners. The objective is to investigate on a joint basis the prevention of impacts by asteroids and comets. The investigations will include the impact of a space probe with the asteroids to deflect them from their threatening courses, the use of longterm gravitational effects using adjacent probes, and other methods. Another German effort is the so-called Asiago DLR Asteroid Survey (ADAS). ADAS is a dedicated program to search for and follow-up on the orbits of asteroids and comets using ground-based observatories. This activity utilizes the 67/92 Schmidt telescope in Asiago/Padua, Italy, as well as the DLR Institute of Space Sensor Technology and Planetary Exploration in Berlin, Germany. This activity places a special focus on the discovery of NEO. It represents a part of the International Astronomical Union’s efforts under its Working Group on NEO and is also supported by the Spaceguard Foundation (Asiago DLR Asteroid Survey (ADAS)). In addition to the ADAS activities, there is a parallel effort called the Uppsala Astronomical Observatory-DLR Asteroid Survey (UDAS) as well as the

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DLR-Archenhold NEO Precovery Survey (DANEOPS). Each of these efforts uses ground-based astronomical observatories to detect NEO asteroids (Daneops Home Page).

JAXA-ISAS The Japanese Aerospace eXploration Agency (JAXA) was formed in 2003 by the combination of the NASDA (the National Space Development Agency of Japan) with the Institute of Space and Astronautical Science (ISAS) and the National Aerospace Laboratory (NAL). ISAS as a part of JAXA continues to be focused on planetary and space research including solar phenomena, cosmic radiation, and asteroids and near-Earth objects (NEOs). JAXA has been active in several programs to learn more about cosmic hazards. On May 9, 2003, the Hayabusa satellite mission was launched with the objective of the goal of collecting samples from a small asteroid near Earth that is name 25143 Itokawa. The Hayabusa satellite (that translated to Peregrine falcon in English) successfully landed on this small asteroid and gather samples in the fall of 2005. Hayabusa returned to Earth orbit and then released a small capsule that was able to return to Earth as of June 13, 2010, as pictured below. This was the first capture and return of a sample from an asteroid ever accomplished as is depicted in the graphic in Fig. 2 (JAXA “Hayabusa Project”). JAXA has also been quite active in the field of infrared telescope missions to map the skies and to assist in the identification of NEOs. JAXA infrared telescope missions have included the IRTS telescope (in 1995) and the Akari mission (in 2006). A planned infrared telescope mission for 2015 named SPICA is also planned with the possibility of contributed instruments from NASA and ESA. In addition JAXA provided support to ESA with regard to its ESA Infrared Space Observatory (ISO) mission that was carried out in the 1990s (JAXA “ISO Mission..”). Finally Japan has been quite active in the area of solar research. Japan’s solar astronomy started in the early 1980s with the launch of the Hinotori (ASTRO-A) x-ray mission. The next launch, also an ISAS mission was the so-called Hinode satellite (also known as the Solar-B) spacecraft. Next came the follow-on which was a joint Japan/US/UK mission with the Japanese name of Yohkoh but the international designation of this satellite is known as Solar-A. This spacecraft was launched on 23 September 2006. A Solar-C mission that would be a joint Japanese (JAXA), US (NASA), and European (ESA) project is contemplated for 2018 (Solar C Working Group).

ROSCOSMOS Russia and in particular the Russian Federal Space Agency (Roscosmos) has been active in various aspects of solar research, cosmic radiation hazards, and near-Earth object (NEO) research for many decades. In its recent future space research projects

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Fig. 2 Hayabusa satellite releasing the capsule with samples from Asteroid 25143 Itokawa (Graphic courtesy of JAXA)

ROSCOSMOS has developed over a quarter of a billion dollars (US) to a total of ten solar and Sun-Earth research projects. Not only is Roscosmos an active member of the NEOShield research consortium, but it has contributed very innovative ideas to the process. The latest idea is to capture nearby smaller asteroids and tow them to locations so that they could collide with an incoming dangerous asteroid so as to deflect the orbit so as to protect Earth from impact. This so-called “space billiards” concept has been examined in computer modeling analysis and shown to be a possibly viable protective strategy (Eremenko 2013).

Other Space Agency Efforts to Address Cosmic Hazards There are a great number of additional space agency efforts that are directed toward detecting potentially hazardous near-Earth objects (NEOs) or to monitor space weather and cosmic radiation. A large number of space agencies around the world, for instance, operate ground-based observatories that report sightings of NEOs that are discovered and report these to the Minor Planet Center, the ESA-sponsored Space Situational Awareness-NEO Coordination Centre, etc. Many of the space agency observatories of China, India, Brazil, Israel, Pakistan, South Africa, etc. have active programs to observe solar events, space weather, and

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cosmic radiation that are shared with the global space community at scientific conferences and through processes of the International Astronomical Union. Some of these space agencies have even begun space-based efforts in this regard. The Canadian Space Agency (CSA) in partnership with the Defence Research and Development Canada (DRDC) has sponsored the design and launch of the NEOSSat (Near-Earth Object Surveillance Satellite). This satellite now in an 800 km high orbit with a 100 min periodicity is searching in the infrared spectra for previously undetected NEOs. This satellite was built by Microsat Systems Canada and launched in February 2013. This small $15 million suitcase-sized satellite is the first space telescope developed by Canada to search for asteroids. In partnership with the India Space Research Organization, this small satellite was one of seven satellites launched on the Indian Polar Satellite Launch Vehicle-C20 (PSLV-C20) rocket (“Indian Space Launch to Deploy Canadian Satellite”).

University, Research Institute, and Ground Observatory Coordination Perhaps more than a thousand universities, research institutes, and ground observatories constitute a part of the global resources that are available around the world to monitor and identify potentially hazardous NEOs. These research efforts also contribute useful information with regard to solar events, cosmic radiation, comets, asteroids, bolides, meteoroids, and cosmic hazards. There are sophisticated processes by which observations and findings from these institutions can be widely shared. Most national space agencies have cooperative arrangements with national universities and often provide research grants or have research contracts with national research universities. The earlier section with regard to the German Space Agency (DLR) and the European Space Agency indicated just some of those types of programs. In Europe there are not only many national arrangements but regional programs as well. Three international types of coordinative programs with regard to cosmic hazards and planetary defense are of particular note. These are the Working Group on NEOs of the International Astronomical Union (IAU), the B612 Foundation that is sponsoring the Sentinel space telescope and other initiatives with regard to potentially hazardous asteroids, and the Planetary Society that also plays an important role in this field.

WGNEO of the IAU The Executive Committee of the IAU, shortly after its May 2010 meeting, formally proposed to reactivate its Working Group on Near Earth Objects. The charge that was provided for the WGNEO was to investigate and formulate requirements for an international ground- and space-based NEO survey, to detect, track, and characterize, through the use of optical, infrared, and radar sensing, the location of 90 % of all NEOs with a diameter greater than 40 m. It was also proposed to establish a permanent International NEO Early Warning System. The IAU has continued since that time to

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work toward this objective in cooperation with the United Nations Committee on the Peaceful Uses of Outer Space (UN COPUOS) and the International Council for Science (ICSU). The IAU also continues to play a key role in this arena by its sponsorship at the Minor Planet Center, at the Harvard-Smithsonian Astronomical Observatory that is the universal location for all reported detections of NEOs. As of the February 2013 meeting of the UN Committee on the Peaceful Uses of Outer Space (COPUOS), the IAU presented a formal report of its current concerns about NEOs. This report stated: It is clear that, in order to be prepared for NEO impacts, the world needs a permanent international NEO Early Warning System, combining all efforts of ground-based NEO surveys and space-based NEO surveys. The UN COPUOS STSC Action Team 14 is working on protocols to coordinate this important issue. (“Statement by the IAU to the 50th Session of the UN COPUOS”)

In light of the need for the UN COPUOS which now includes some 90 international members, to achieve consensus, the ability to agree and implement such a NEO Early Warning System will take time. In the meantime the IAU Minor Planet Center represents the closest approximation of such a system. The problem is not so much on the detection of potentially hazardous NEOs, but a process to decide what to do against potential threats and how to communicate warnings effectively to the world community. As noted in the IAUs, most recent report, a near-Earth asteroid of about 45 m in diameter flew inside the Earth’s geosynchronous orbit at about 5 miles per second (7.8 km/s) on February 15, 2013. This potentially destructive NEO had the power of thousands of atomic bombs of the Hiroshima size and could have done tremendous damage and was detected only 1 year before its flyby. As noted earlier, the Russian Space Agency Roscosmos actually proposed in 2009 sending up a mission to crash into 99942 Apophis a PHA that has a diameter of some 325 m and thus capable of considerable lethal damage if it should hit a city or trigger a tidal wave near a major inhabited coastline.

The B612 Foundation The B612 project, a reference to the mythical asteroid of “The Little Prince” children’s book, originated from a workshop on asteroid organized at the NASA Houston Johnson Space Center on October 20, 2001. The nonprofit nongovernmental organization was officially established a year later. Although the original discussions at the workshop in 2001 focused prevention techniques such as a nuclear power spacecraft to tug a threatening asteroid into a harmless orbit, the B612 Foundation has developed new goals. These goals are the early detection of hazardous NEOs. The prime objective at this time is to deploy the so-called Sentinel infrared telescope spacecraft in a Venus-like orbit to provide an early warning capability. This spacecraft is designed in partnership with Ball Aerospace. This high-resolution telescope is designed to detect comets and

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asteroids of 140 m (or less) diameter and early enough that deflection missions could be successfully mounted. The cost of this spacecraft with a projected 6.5 year lifetime, a 50 cm telescope aperture, 95 gigabytes of memory, and 2 kW of power that is designed for launch on a Falcon 9 launcher would involve a total mission cost of nearly $400 million. It is thus the most ambitious private space initiative for space exploration ever attempted. The fact that this spacecraft has no backup and a limited lifetime of less than 7 years – driven by loss of coolant for the IR telescope – is a major element of risk concern (“The B612 Foundation”).

The Planetary Society The Planetary Society that was founded in 1989 was initially spearheaded by the noted astronomer Carl Sagan and his colleagues Bruce Murray and Louis Friedman. The Planetary Society that is a worldwide alliance of scientists and space enthusiast is closely aligned with the B612 Foundation, the International Astronomical Union, and the International Astronautical Federation. The goals of the Planetary Society are wide and far-reaching. These goals include hunting for Earth-like planets, searching for life in the universe, advocating for science funding, and Science, Technology, Engineering, and Mathematics (STEM) education. It does strongly support the search for dangerous asteroids by its members and the efforts of B612 Foundation and the IAU. The Planetary Society can accurately claim to be the largest and most influential public space organization around the world with a global membership. Among the Planetary Society’s many activities are the Shoemaker awards to support asteroid tracking and identification. These grants provide funding to support the efforts of amateur observers as well as trained observers in developing countries and even professional astronomers to chart near-Earth objects. These efforts seek to identify previously unknown NEOs and especially to flag those that might potentially collide with Earth.

The Action Team-14 Effort The Action Team-14 efforts are coordinated through the UN Office of Outer Space Affairs (OOSA). This initiative was undertaken as one of the outcomes of the UNISPACE Conference III. The 14 member countries, subsequent members, as well as regional groups are as follows: National Members Australia, Brazil, China, the Czech Republic, Finland, German, Iran, Japan, Kazakhstan, Lebanon, Malaysia, Nigeria, Pakistan, Poland, Russian Federation, Saudi Arabia, Syrian Arab Republic, United Kingdom, and the United States Organization Members Association of Space Explorers (ASE), European Space Agency (ESA), Committee of Space Research (CoSpar), International Astronomical Union (IAU), National

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Space Society, Space Generation Advisory Council, European Space Science Committee, European Science Foundation, and the Spaceguard Foundation. The way the Action Team-14 is now configured is that it has efforts in the following areas: • • • • • •

NEO detection and characterization Orbit determination and cataloguing Consequence determination In situ characterization Mitigation Policy

The broad spectrum of participants in this AT-14 effort helps to ensure that if there is agreement with regard to mitigation and policy within this unit, that broader consensus within COPUOS can also likely be achieved. These and other initiatives and their programs are discussed in greater detail elsewhere in the handbook.

Conclusion What should be clear from this chapter is that there not only are many activities around the world to track and identify NEOs of various types but also efforts to develop systematic early warning and mitigation systems as advocated by the IAU to the UN Committee on the Peaceful Uses of Outer Space. Part of this ongoing process will be to put in place a more systematic way of assessing relative levels of risk and prioritization of effort consistent with the best understanding of overall levels of risk, immanence of occurrence, and interdisciplinary tools and instrumentation to study various forms of cosmic hazards. Perhaps even more important is to also recognize the need for greater coordination of effort with regard to space weather, cosmic hazards, solar flares, and coronal mass ejections as well as changes in the Earth’s natural protection systems in terms of its geomagnetosphere and the ozone layer in the upper atmosphere. While the efforts to track and defend against NEOs is being addressed by a well-coordinated group of national, regional, and international units, the same sophistication of effort is lacking with regard to radiation and ionic dangers related to highly threatening and potentially destructive space weather.

Cross-References ▶ Defending Against Asteroids and Comets ▶ Directed Energy for Planetary Defense ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense

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▶ NEOSHIELD - A Global Approach to Near-earth Object Impact Threat Mitigation ▶ Planetary Defense, Global Cooperation, and World Peace ▶ Potentially Hazardous Asteroids and Comets ▶ Regulatory Aspects Associated with Response to Man-Made Cosmic Hazards ▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning

References Asiago DLR Asteroid Survey (ADAS). http://dipastro.pd.astro.it/planets/adas/ Champ, Oersted, and Swarm Satellite Research Programs. http://www.cnes.fr/web/CNES-en/ 5922-swarm.php Co-orbital asteroid leaves earth’s orbit leaves earth’s orbit. http://www.cnes.fr/web/CNES-en/ 5259-co-orbital-asteroid-leaves-earths-orbit.php Daneops Home Page. http://earn.dlr.de/daneops/. 10 Jul 2013 Defending planet earth: near-earth object surveys and hazard mitigation strategies, section 7: National and International Coordination. http://www.nap.edu/openbook.php?record_id= 12842&page=92 Eremenko A (2013) Russians propose space billiards for planetary defense. http://en.rian.ru/ analysis/20130531/181439126.html. 31 May 2013 ESA Space Situational Awareness-NEO Centre. http://www.esa.int/Our_Activities/Operations/ Space_Situational_Awareness/About_SSA-NEO_Coordination_Centre http://www.cnes.fr/web/CNES-en/1394-champ.php and http://www.cnes.fr/web/CNES-en/1452oersted.php Indian space launch to deploy Canadian satellite. http://www.redorbit.com/news/space/ 1112790403/india-rocket-launch-polar-satellite-launch-vehicle-c20-canada-satellite-022513/. Apr 2013 JAXA (2012) The Hayabusa Project. http://jaxa.jp. Jul 2012 JAXA. ISO mission. http://en.Japan_Aerospace_Exploration_Agency Jet Propulsion Lab (JPL) (2012) Near earth object program. neo.jpl.nasa.gov./faq/. Dec 2012 NASA. NEOWISE. http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Chron&StartYear= 2010&EndYear=2019&MCode=WISE NASA spacecraft reactivated to hunt for asteroids. http://rt.com/news/nasa-hazardous-asteroidmap-575/. 16 Aug 2013 NEOShield Preparing to protect the planet. http://www.neoshield.net/en/index.htm NEO Coordination Centre (2013) http://neo.ssa.esa.int/. 13 Oct 2013 Pelton JN (2012) Orbital debris and other space hazards. Springer Press, New York, p 32 Solar C Working Group. http://hinode.nao.ac.jp/SOLAR-C/index_e.html. Apr 2004 The Herschel Space Observatory—The largest infrared space telescope. http://www.space.com/ 20120-herschel-space-telescope-mission-ending.html. 10 Nov 2013 The ISO Infrared Space Observatory. http://iso.esac.esa.int/ The Near Earth Orbit Dynamic Site (NEODyS). http://newton.dm.unipi.it/neodys/ UAO-DLR Asteroid Survey. http://earn.dlr.de/udas. Apr 2013 United Nations Office of Outer Space Affairs (2013) Working group on near-earth objects. http:// www.oosa.unvienna.org/oosa/en/COPUOS/stsc/wgneo/index.html. Apr 2013

International Legal Consideration of Cosmic Hazards and Planetary Defense Fabio Tronchetti

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Positive Contribution of Current International Law for a Planetary Defense . . . . . . . . . . . . Key Gaps in International Law Relating to Planetary Defense Initiatives . . . . . . . . . . . . . . . Duty to Intervene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Need for Authorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unilateral Planetary Defense Initiative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Participation by Private Entities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of Weapons, Including Nuclear Weapons, in a Planetary Defense Mission . . . . . . . . . Liability Issues Related to a Planetary Defense Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Organizational Framework for a Planetary Defense Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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The relevance and importance of law for the issue of planetary defense are, and should be seen as, instruments facilitating international cooperation for avoiding legal risks should they arise while carrying out planetary defense operations. Currently, there is a significant absence of a specific legal and regulatory framework governing planetary defense since the international community has for the most part not addressed this matter seriously in the past. There is one important exception in the form of the University of Nebraska study commissioned by the Secure World Foundation (Legal Aspects of NEO Threat Response). In short, there is little legal literature on this issue as the space law F. Tronchetti (*) School of Law, Harbin Institute of Technology, Harbin, Heilongjiang, People’s Republic of China School of Law, University of Mississippi, Oxford, MS, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_79

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community has not yet conducted extensive research in this regard. The situation may be expected to change as the threats from cosmic hazards become more known broadly and processes within the United Nations and the Committee on the Peaceful Uses of Outer Space continue to work in this area particularly through the Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA). This chapter briefly addresses and highlighted the need for clarifying the main legal issues relevant to planetary defense; i.e., the authority and duty to intervene, the responsibility to undertake planetary defense initiatives, as well as possible liability for damage or injury caused during such operations. It will also identify the challenges to existing international legal rules and suggest possible amendments thereto for undertaking planetary defense. Legal issues related to international response to cosmic disasters will also be briefly addressed. International space law, as provided for in the United Nations (UN) space treaties and in a number of General Assembly resolutions, lacks specific as well as binding provisions dealing with the protection of the Earth from natural cosmic hazards. Nevertheless recent actions by the UN General Assembly have led to new efforts in these areas. This has been seen in the creation in 2010 and 2010 of UN COPUOS Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA). This has even more recently seen in the actions of the UN General Assembly to activate the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG) (“International asteroid warning network: first meeting of the steering committee” http://www.minorplanetcenter.net/IAWN/ and “SMPAG: summary of the first meeting” http://blogs.esa.int/rocketscience/2014/02/12/smpag-sum mary-of-the-first-meeting/comment-page-1/). The prime objective of this analysis is to examine what recent activities have been undertaken by the United Nations General Assembly, the UN Committee on the Peaceful Uses of Outer Space (UN COPUOS), and the UN Committee on Defense Analysis to develop legal or regulatory mechanisms concerning cosmic hazards and planetary defense. The parallel part of this analysis is to consider where principles of public international law can aid in the future development of relevant regulatory or legal concepts to address the major issues presented by cosmic threats. Keywords

Action group-14 • Inter-Agency Space Debris Coordination Committee • International Asteroid Warning Network (IAWN) • International Astronomical Union • Liability Convention • Minor Planet Center • Outer Space Treaty • Principles of public international law • Registration committee • Space Mission Planning Advisory Group (SMPAG) • United Nations • UN Committee on Defense Analysis • UN Committee on the Peaceful Uses of Outer Space (UN COPUOS) • Working Group on Near-Earth Objects (WGNEO) • Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA)

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Introduction The fact that efforts to address cosmic hazards took some time to occur is not surprising. The space treaties were formulated when the primary goal of their drafters was not to address hypothetical threats coming from outer space but to lay down basic rules enabling all States to participate in the exploration and use of outer space and prevent outer space from becoming an area of conflict. In the decades that followed, attention was paid to more urgent issues, such as the legal questions related to remote sensing from space, direct broadcasting with satellites, and the use of nuclear power sources. In order to fill in the gaps that international space law presents in relation to the organization of planetary defense the way forward appears to be two fold. On one hand various initiatives were being carried out through the United Nations, such as the UN General Assembly, the Committee on the Peaceful Uses of Outer Space, the Action Group 14, the COPUOS Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA), the International Asteroid Warning Network (IAWN), the Space Mission Planning Advisory Group, and even the UN Committee on Defense Analysis. The other part of the process is to consider ways that it is possible to rely on principles of public international law that might be invoked in the case of planetary defense or in cases involving a response to an international cosmic disaster such as international peace-keeping operation. The relevance and applicability of public international law to outer space activities is clearly spelled out in Article III of the Outer Space Treaty, and this can also help define a practical way forward. Principles such as the right to national defense and intergenerational equity come particularly into play. Thus Article III of the UN Charter (UN Charter) can assist both in understanding a coordinated international effort related to space hazards and methods to proceed with regard to planetary defense (Outer Space Treaty). For the purpose of this analysis, notions like the right to act in self-defense, the responsibility to protect, and the intergenerational equity remain of particular significance in mounting a response to a cosmic hazard. While self-defense is a right attributed to States under Art. 51 of the United Nations Charter, the responsibility to protect and the concept of intergenerational equity are not strictly legal rights and/or obligations but norms of international law which are currently strongly emerging in connection with gross human rights violations and environmental protection. It is important, however, to point out that the application of these principles to a natural cosmic threat is not an automatic process, as normally they are utilized in different contexts and to pursue different goals, most notably on a nation to nation basis. Recently, the international community has started acknowledging the danger that natural space objects, particularly near-Earth objects (NEO), pose and taking concrete step to address it. The COPUOS Working Group on the Long-Term Sustainability of Outer Space Activities has recognized not only the threat of space debris and near-Earth objects but has also recognized space weather and other cosmic hazards. This has been reflected in the formation of expert groups to consider these dangers from space. The initiatives undertaken within the United

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Nations have focused on the technical aspects of cosmic hazard prevention and mitigation, rather than addressing legal problems. Most recently the Legal Subcommittee of COPUOS has also begun to consider the legal and regulatory matters as well. Nongovernmental organizations such as the Security World Foundation have also contributed to the discussion and preliminary considerations of legal issues that are involved. Even though international space law does not include measures dedicated to the organization and implementation of planetary defense initiatives, this does not amount to saying that it is irrelevant for that purpose. Actually quite the reverse is true. Instead, existing international space treaties and conventions may very well contribute to setting up similar initiatives, which, in any case, must be consistent with the basic international space law principles (Outer Space Treaty; Registration Convention; Rescue Convention, Liability Convention, Charter of the United Nations).

Positive Contribution of Current International Law for a Planetary Defense From the discussions currently taking place within the Technical and Scientific Subcommittee of the UN Committee on the Peaceful Uses of Outer Space (UN COPUOS), it appears that States view international cooperation as the foundation for any action aimed at responding to the threat posed by a natural cosmic hazard. This means that in the most likely scenario any such action will not be carried out by a State unilaterally but rather by a group of willing countries as shown in the diagram below. This approach is consistent with the fundamental principles of international space law, which can be seen as actually favoring similar multilateral initiatives. Indeed, the importance of promoting and enabling international cooperation is emphasized in the UN space treaties on multiple occasions. Additionally, the legality of an international action for a planetary defense is, at least indirectly, supported by the words of Article I, paragraph 1, of the Outer Space Treaty, which stipulates that “the exploration and use of outer space. . . shall be carried out for the benefit and in the interests of all countries. . . and shall be the province of all mankind” (Outer Space Treaty). This provision is broadly understood to signify that the exploration and use of outer space shall not be the “private business” of a single State but that all countries should directly or indirectly benefit from any such activity in outer space (Hobe (2009)). In the event of a collective action for planetary defense, it is clear that such an action would not be intended to benefit and protect only the States taking part in it but all countries or, better, humankind as a whole (International Cooperation). The Outer Space Treaty also contains provisions that are relevant for the preparation and the implementation of an international initiative for planetary defense. For example, on one side it requires State Parties to undertake appropriate international consultations before proceeding with a space activity or experiment

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that may cause harmful interference with the activities of other States, and, on the other side, it demands them to guarantee, to the greatest extent feasible, transparency about their operations in space (Outer Space Treaty, art. IX and XI). Thus, the States involved in a planetary defense initiative must timely inform other States about the dangers that it may pose and guarantee an adequate level of transparency over their activities. Such duties would be even more pressing if the initiative would be undertaken on a unilateral basis. Importantly, no State can be forced to undertake or cooperate in an international action for planetary defense. States are free to determine when to participate in international cooperation and under which conditions. This idea is clearly affirmed in the 1996 Space Benefits Declaration. In particular Principle two states: “States are free to determine all aspects of their participation in International cooperation in the exploration and use of outer space on an equitable and mutually acceptable basis. Contractual terms in such cooperative ventures should be fair and reasonable and they should be in full compliance with the legitimate rights and interests of the parties concerned as, for example, with intellectual property rights” (Declaration on International Cooperation).

Key Gaps in International Law Relating to Planetary Defense Initiatives Despite providing a basic contribution toward organizing a planetary defense, international space law leaves numerous and fundamental questions related to the preparation, implementation, and consequences of such an action open. Some of these questions are briefly discussed below:

Duty to Intervene A preliminary but important issue is whether or not States have a duty to intervene in the event of a natural cosmic hazard threatening the Earth (Legal Aspects of NEO Threat Response). Essentially, the question is if in the presence of reliable data confirming the danger posed by a natural cosmic body and of effective means to avoid its collision with the Earth, are States to be considered under the obligation to take action? The answer currently is that no explicit obligation exists. Under present general international law and international space treaties and conventions, no legal requirement exists. This, however, does not amount to say that States do not have a right to intervene or even have a “moral” responsibility to do so. Eventually, an effective duty to take action might be agreed upon at a later stage. International space law contains provisions that, in principle, can be used to support a right to intervene in case of a natural cosmic threat. For example, the Outer Space Treaty calls for mutual assistance, for “conduct by States of their activities (. . .) with due regard to the corresponding interests of other States,” and for space activities “to avoid (. . .) adverse changes in the environment of the Earth”

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(Outer Space Treaty, art. XI). These provisions encourage States to take actions, to the greatest extent possible, for the collective good rather than in the interest of a single State. Nevertheless, due to their abstract nature and lack of concrete standards of behavior, they cannot be seen as imposing on technologically advanced States a collective duty to protect the Earth in the event of a natural cosmic threat. Significantly, in the context of disaster prevention and mitigation, a practice has emerged according to which States possessing advanced (remote sensing) satellite capabilities voluntarily make their resources available to less advanced States to warn them about upcoming natural dangers and to help coordinating post-disaster rescue operations. Such a practice, which has its origin in the UN Remote Sensing Principles (Principles Relating to Remote Sensing), has found concrete implementation within the International Charter on Space and Major Disasters. The Charter is an instrument that has been put in place to encourage cooperation in the use of space facilities to support the management of crisis arising out of natural and man-made disasters (International Charter on Space). Parties to the Charter are not States, but space agencies and space system operators. From a legal standpoint, the Charter is not a legally binding per se, but it is an instrument to which Parties participate on a voluntary basis without exchange of funds among them. Although the Charter is not directly legally binding on States, one should always keep in mind that space agencies are governmental agencies and, as a consequence, their activities are coordinated with and are financed by the respective governments. Thus, the success of the Charter that has now been activated hundreds of times shows that States, operating through their space agencies, may fruitfully cooperate in using their space-related resources to achieve common goals, rather than pursuing mere individual ones. From this perspective the Charter represents a significant precedent for States willing to take collective action to protect the Earth from a natural cosmic disaster (International Charter on Space; Legal Aspects of NEO Threat Response). General international law, while containing principles that may provide a legal foundation for an international action for planetary defense, does not establish a clear-cut obligation to do so. In this respect, one could think of the so-called responsibility to protect, a concept which has emerged in connection with human right protection. Accordingly, in view of gross violation of human rights in a State’s territory and of the incapacity of the government of that State to halt it, the international community may have the responsibility to intervene. This responsibility, it has been submitted, may include a “responsibility to react,” a “responsibility to prevent,” and a “responsibility to rebuild” as well as an evaluation of the costs and benefits of intervention versus nonintervention (Legal Aspects of NEO Threat Response). There are, nevertheless, issues related to the possible application of a “responsibility to protect” in relation to a planetary defense initiative. Firstly, it is doubtable whether such a “responsibility” constitutes a rule of international law. Secondly, it is unclear whether it establishes an “obligation” to take action. Thirdly, it raises questions of violation of territorial sovereignty of the State in which the intervention takes place. Fourthly, a “responsibility to protect” should be seen as a

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collective responsibility and should be implemented through collective security arrangements established under the UN Charter, i.e., within the General Assembly or the Security Council. Thus, no single State could likely validly unilaterally claim the responsibility to protect (The Responsibility to Protect). For the above reasons, it seems problematic to rely too much on the “responsibility to protect” principle to justify a planetary defense. However, if one wants to proceed in this direction despite these reservations, the following two preconditions should be, arguably, present: (a) the threat should be detected and detectable, and it should be presumably agreed upon to be of sufficient severity; (b) acceptance of the idea that while a State is primarily responsible to protect fundamental human rights of their respective populations, including the right to life, in case such a State would be unable to provide protection against a major natural cosmic threat, the international community should be attributed a secondary obligation to do so. Every State has the right to defend its citizens against, essentially, any threat provided that its actions are consistent with relevant international obligations and do not cause disproportionate harms to other States. The UN Charter recognizes the right of States to act in self-defense and the possibility to exercise this right both individually or collectively (Charter oftheUnited Nations). The UN Charter limits its applicability to the need to respond to an armed attack by another State. As in the case of a natural cosmic threat, the element of an “armed attack” would be missing, the right to act in self-defense to counteract a natural cosmic threat could be debatable. However, if one accepts a broader understanding of the concept of self-defense, which includes the right of a State to take actions to protect its citizens without threatening the territorial sovereignty of another State, there would be room to argue that the right of self-defense could be used to sustain the legality of a planetary defense initiative. Nevertheless, recognizing the right to act in (global) self-defense to protect the Earth from a cosmic hazard does not equate to say that there is a duty for States to do so. Theoretically, a duty to act would exist if it were enshrined in a rule of customary nature; nevertheless, a similar rule is far from being present at the present stage. It could also be possible to support the argument that States have a responsibility to take action for a planetary defense initiative based on the concept of intergenerational equity. Such a concept has become an integral component of international law dealing with environmental protection, resource utilization, and socioeconomic development. In short, it calls States to take into account the rights of present and future generation in relation to the use of resources and the preservation of the environment. The concept of intergenerational equity, which has found expression, for example, in the 1972 Stockholm Declaration and in a number of other subsequent documents (The Stockholm Declaration) and in the UN Agenda 21 (Agenda 21 of 1992 UN Conference), does not have mandatory nature and its implementation is left to the will of and coordination among States. Considering the devastating effects that the impact of a NEO would have on Earth and its long-lasting negative impact on mankind, the concept of intergeneration equity, thus, provides an additional element to support a collective response to such a cosmic threat.

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Need for Authorization Another relevant question is whether an international action for planetary defense would require authorization, and, if so, who would be the entity entitled to grant it. Before addressing this question, one should keep in mind that such an international action would be undertaken on behalf of mankind and, most likely, would also include the use of weapons. Mankind does not exist as an independent legal subject under international law; therefore, States could not be directly authorized to carry out a planetary defense initiative by mankind or by a body representing it. One could argue that the United Nations represents mankind, because nearly all States are members in it. However, this does not automatically makes it a “representative” of mankind as a whole and is not a sufficient reason per se to claim that States should obtain a permission before carrying out a planetary defense response. The need for obtaining a UN mandate could be derived from the envisaged recourse to armed force in the context of this response. One of the main goals of the United Nations and, in particular, of the UN Security Council is to maintain international peace and security. In the presence of a threat to them, the Security Council may decide measures not involving the use of armed force as well as armed measures. These measures are officially authorized by means of a dedicated Security Council Resolution. Authorization by the Security Council is a condition sine qua non for the use of force under the UN Charter system (Charter of the United Nations, Chapters VI and VII). A natural cosmic hazard could be viewed to constitute, at least indirectly, a threat to international peace and security, due to the potential devastating consequences that it could have upon impact on the Earth’s surface. If such interpretation of the expression “threat to international peace and security” is accepted, there would be room to argue that an international initiative to respond to a natural cosmic threat should be authorized by the Security Council, especially if it would include the use of armed force. Such an approach would have the advantage of utilizing practices and procedures already existing within the United Nations. One, however, should always be aware that an authorization by the Security Council is automatic, as some of its permanent members (i.e., China, France, the Russian Federation, the UK, and the USA) could veto it. Presumably since all countries could be a direct or indirect risk, this would not be the case.

Unilateral Planetary Defense Initiative In principle, the existing law does not prevent a State to organize and undertake a planetary defense initiative on a unilateral basis. However, it seems unlikely that a State might follow this path, due to the high costs and risks involved. It is realistic to imagine that a State might decide to act on its own if: (a) it is technically capable to do so and (b) no other State is willing to join it. This might be particularly the case if the area expected to be directly affected by the impact of the natural cosmic hazard

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would be exclusively in its national territory. The logic of countries choosing to or not to participate on such a basis would remain questionable since most major cosmic hazards, despite the area of impact, would eventually have worldwide consequences. The question is whether such a unilateral action would require an authorization from the UN Security Council. Under the UN Charter, a State is entitled to act in self-defense until the Security Council intervenes (Charter of the United Nations, art 51). Thus, if one accepts the idea that a planetary defense initiative constitutes an act of self-defense, it could be argued that a State need not wait for the approval of the Security Council before proceeding with its individual initiative. However, this argument could be counteracted by pointing out that, as a consequence of the danger that this initiative would pose to operational space objects (i.e., satellites) and to the space environment, a State should obtain authorization from the Security Council prior to the commencement of operations. Such an authorization would provide a legal basis for the use of military force in space and would constitute a valid instrument to ensure that the authorized State complies with international obligations and does not intentionally endanger or disrupt other States’ space assets. Additionally, such a State would have to address liability issues for damage caused in the context of its unilateral planetary defense initiative. Indeed, there would be room to claim that, irrespective of the humanitarian character of the initiative, the State that undertakes it on a unilateral basis would assume full responsibility and liability for any damage it may cause.

Participation by Private Entities Another relevant point is whether or not private entities should be allowed to participate in a planetary defense initiative (Legal Aspects of NEO Threat Response). States could indeed consider drawing the private sector into this context of this initiative due to its high costs; at the same time, private entities could view their involvement as a potentially profitable and beneficial opportunity. Any involvement of the private sector should be limited by the understanding that a planetary defense mission is a public (government) affair, the primary goal of which is humanitarian. Obviously, much will depend on the role that private entities will effectively play that could range from merely being involved in the manufacturing process to be a partner in a public-private partnership or even to act as a stand-alone profit-generating venture. The more the entity will act independently and for profit-related purposes, the more there will be a need for an authorization and control by a State. These considerations would also apply in the event that a private entity or nongovernmental agency was asked to participate in a recovery operation in an instance where the government in the jurisdiction was not able to request aid due to damages. Under international space law, private entities may carry out space activities as long as they do so under the umbrella of an “appropriate State,” which authorizes

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and continuously supervises these activities (Outer Space Treaty, art. VI). The appropriate State is internationally responsible for the authorized private space activities and is obliged to ensure, inter alia, their compliance with international obligations. Such a State might also face liability claims for damage occurring in the course of the authorized and supervised activities of the private companies or nongovernmental organization.

Use of Weapons, Including Nuclear Weapons, in a Planetary Defense Mission A planetary defense initiative most likely will encompass recourse to physical force in space (a kinetic vector impacting the NEO), perhaps also nuclear force. It is worth exploring the legality of similar plans in the light of general international law and the specific international space law regime. Currently, a specific and comprehensive legal regime governing the use of force in outer space does not exist, and relevant rules had to be drawn from different instruments. The Outer Space Treaty only prohibits the placing and orbiting of nuclear weapons and weapons of mass destruction in outer space (Tronchetti (2011)). This provision is generally understood to mean that, in principle, the placing of conventional weapons in outer space is not forbidden (Schrogl and Neumann (2009)). As far as the use of conventional weapons is concerned, international law and, in particular, the Charter of the United Nations established a general prohibition on the threat or use of force against the territorial integrity and political independence of any State, or in any other manner inconsistent with the purposes of the United Nations (Charter of the UN, art. 2(4)). The UN Charter lays down two exceptions to this prohibition: a) the right to use force in self-defense and b) the use of force authorized by the UN Security Council. Thus, States are forbidden from using force, specifically conventional weapons, in outer space to threaten or harm the territorial sovereignty or properties (i.e., space objects) of other States, unless this constitutes the exercise of the right of self-defense or it is expressly permitted by the Security Council. This is, of course, relevant in the context of a planetary defense mission. Indeed, provided that the use of force falls within one of the two exceptions described above, there does not seem to be any specific legal obstacle to using conventional weapons during such a mission (Legal Aspects of NEO Threat Response). The only prohibition that would seem to exist would be to place weapons on the surface of the Moon with the purpose of firing them at an incoming cosmic threat, as the Outer Space Treaty and, in particular, the Moon Agreement fully demilitarize the Earth’s natural satellite (Outer Space Treatyand Moon Treaty). The situation is more complicated if one considers recourse to nuclear weapons to avert a natural cosmic threat (Legal Aspects of NEO Threat Response). On one side, it is quite possible that a nuclear device would not only encounter a NEO threat and at the same time affect the surrounding environment, possibly including

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the Earth’s environment, and orbiting space debris objects. On the other side, international space law does not deal with the possibility to use nuclear weapons in space. In this respect, while Article IV of the Outer Space Treaty prohibits the placing in outer space of nuclear weapons, it is silent about the option to recur to these weapons as an ultima ratio in extreme circumstances. If one looks outside of the limited circle of the specific space law instruments, some useful elements can be obtained. For example, the Nuclear Test Ban Treaties forbid any nuclear explosion in outer space. However, this should not be interpreted as banning any use of nuclear weapons if unequivocally necessary to protect mankind from an “extraordinary” danger, such as a NEO (Legal Aspects of NEO Threats). In any case States would always have the option to withdraw from these treaties if national security reasons would dictate so. Overall, it is unquestionable that the legality of the threat or use of nuclear weapons, even in an extreme circumstance of self-defense, is still currently debatable under present international law (Legality of the Threat). Therefore, even if one constructs the use of nuclear weapons as a last-resort option, it is advisable that States define clear parameters related to the use of these weapons prior to the start of the planetary defense mission.

Liability Issues Related to a Planetary Defense Mission Liability considerations are crucial with respect to the preparation and implementation of a planetary defense mission. It is foreseeable that in the course of such a mission, damage to third-party space objects and, possibly, to the Earth’s environment may occur. Arguably, damage may happen in three cases: (a) the lack of an action, (b) action undertaken successfully, and (c) action not completely successful (Legal Aspects of NEO Threat Response). As far as case “a” is concerned, as previously described, under current international law there is no obligation for States to take action to respond to a NEO threat. As a consequence, States cannot be held responsible as well as liable for the damage that may result from their lack of intervention, for example, for the damage resulting from the impact of a NEO on the Earth’s surface. An established principle of international law provides that a State committing an internationally wrongful act is under the obligation to make reparation for such an act. As there is no duty to act in case of a NEO menace, States would not commit an internationally wrongful act by deciding not to intervene. Thus, the States that theoretically possess the technological ability to act could not be forced to compensate the damage that a NEO collision with the Earth may cause. With regard to cases “b” and “c,” one should first ascertain the relevance of the 1972 Liability Convention, which is the primary legal instrument regulating liability for damage arising in the context of outer space activities. The Convention deals with the damage caused by space objects either on Earth, i.e., on the ground, or to an aircraft in flight, or in outer space. The first category of damage is governed by a regime of absolute liability, the latter by a fault-based liability scheme. Inter alia,

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the Convention declares that “a space object includes components parts of a space object as well as its launch vehicle and parts thereof” (Liability Convention). Undoubtedly, damage might occur during the launching phase of a mission aimed at responding to a cosmic threat. As this situation would not be different from any other case of damage happening during the launching of a space object, the Liability Convention would be fully relevant in such an event (provided, of course, that those damages are of international nature). A different scenario could be envisioned in relation to damage occurring in outer space. Assuming that a planetary defense initiative would be undertaken using a kinetic impactor, it is conceivable that, as a consequence of the collision between the impactor and the NEO, pieces of the latter would be released in the void outer space and would hit space objects belonging to States not involved in the initiative. In such a circumstance, the Liability Convention would most likely not be applicable to compensate the damage caused to those objects. First of all, the Convention deals with (physical) damage caused by a space object; as NEOs as such, clearly, are not space object, any damage that they may cause falls outside of the scope of the Convention. Secondly, the Convention covers indirect damage only when the primary damage derives from a collision between two space objects. However, in our case, as the collision would involve a space object (the kinetic impactor) and a NEO (which is not a space object), indirect damage to active orbiting space objects would not be compensable under the Convention. Thirdly, as described above, a fault liability regime applies to damage in outer space. Thus, even if one would argue that indirect damage resulting from the planetary defense mission should be coverable, the claimant States (or private entities) would still have to prove that the operators of the mission have committed fault and that a causal link between the fault and damage exists (Liability Convention). Conversely, one could argue that damage to a third State’s space objects would have not occurred if a planetary defense action had not been undertaken (Legal Aspects of NEO Threat Response): thus, the operators of the action should be held accountable for them. Furthermore, it could be claimed that such damage should still be viewed as “damage caused by that space object,” leading, therefore, to the liability of the launching State(s) of the planetary defense response mission, mostly because the object causing the collision, i.e., the kinetic impactor, is a space object. Additionally, Article IV of the Liability Convention provides that, in the event of an impact between two space objects resulting in a damage to a third party, if the collision was the consequence of the fault, the launching State(s) would be liable for the damage caused to such third party (Legal Aspects of NEO Threats). Similarly, if the collision between the kinetic impact and the NEO was characterized by the fault of the launching State(s), such State(s) could be deemed liable for the secondary damage caused to the space objects of a third State. Nevertheless, there is room to claim that, because a planetary defense mission would presumably be undertaken jointly by a group of States with the ultimate goal of saving mankind (or parts thereof) from a devastating impact (and not with the intention of harming third States and/or their properties), these States should be exempted from liability for damage that they may cause. Indeed, taking into

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account their bona fide effort, States not involved in the planetary defense mission should consider the waiving of any liability claim against the operators carrying out such a mission. A similar approach is already in place within the context of the International Charter on Space and Major Disaster where “no legal action will be taken against the parties in the event of bodily injury, damage or financial loss arising from the execution or non-execution of activities, services or supplies arising out of the Charter” (International Charter on Space and Major Disasters, art. 5 (4)). Furthermore, numerous States incorporate at national level the so-called “Good Samaritan” principle, according to which person who injures another in imminent danger while attempting to aid him (as long as not under an obligation to do so) is not to be charged with contributory negligence and/or liabilities unless the rescue attempt is an unreasonable one or the rescuer acts unreasonably in performing the attempted rescue (Legal Aspects of NEO Threat Response). Notably, the practice of waiver of liability is not uncommon in the context of space activities, particularly in connection with those presenting a high level of risk. For example, States taking part in the management and operation of the International Space Station have accepted to reciprocally waive liability claims with the exclusion of those resulting from criminal acts and willful misconduct (1998Intergovernmental Agreement on the Civil International Space Station). In any event, there is little doubt that a global acceptance to waive liability claims against the States taking part in a planetary defense mission would represent as a further incentive for those States to actually undertake such a mission. However, liability should not be waived when damage would be the consequence of: (a) fault and (b) a disproportionate use of force. The former is a classic reason to exclude liability waivers. In the context of a response to a NEO threat, fault could be conceivable in case of an unjustifiable wrong maneuver (i.e., a man-made mistake not caused by a technical failure) or an unannounced change of the mission plan which would result in a failure and damage to third states. The latter refers to the unnecessary use of powerful devices, such as nuclear weapons, during a planetary defense mission. A similar scenario could occur when, despite being in the presence of data demonstrating that recourse to nuclear weapons is not needed, States would anyhow decide to make recourse to such weapons and such a choice would lead to several collateral damages in outer space and, possibly, also on Earth. To end on a note of realism, a nation under direct threat of extinction would likely act and then sort out any legal issues or claim after the planetary threat had been averted. Clearly resolving these liability issues in advance would be the preferred solution.

Organizational Framework for a Planetary Defense Mission Another relevant question is how a planetary defense mission could be structured from an organizational point of view, in particular in terms of decision-making procedures and relation among the States involved in it.

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Fig. 1 Diagram of initial concepts being considered by the IAWN and SMPAG (Conceptual Representation Developed by Dr. Sergio Camacho-Lara of Action Group 14)

In principle, such a mission should be, at least in some manner, open to all, not only to those States capable of making a significant and effective contribution. Such an element should be considered essential in order to give a State the right to participate in the decision-making process. Importantly, this process should be structured in a way to attribute to the States most directly involved in the preparation and implementation of the planetary defense mission a stronger possibility to influence it. A similar approach is already in use within the context of the International Seabed Authority and largely resembles the way the Security Council of the UN is structured. The process outlined in Fig. 1 would have the UN Committee on the Peaceful Uses of Outer Space with about 80 members from around the world acting as a key enabler of action. Other chapters in this handbook suggest that the Secretary-General should be authorized to dispatch UN peace-keeping forces to respond to global cosmic disasters. Clearly the General Assembly and COPUOS in coordination with the newly created IAWN and the SMPAG will all play a role. As noted above the UN Security Council will undoubtedly have some role to play as well. Clearly a future international treaty or convention on this subject should clarify the best and most efficient organizational framework that could be deployed under various types of planetary threats. States taking part in a planetary defense action should be willing to accept the risks that such an action encompass and, consequently, waive liability claims (i.e., cross-waiver of liability) among each other for damage arising in the context of this action (Legal Aspects of NEO Threat Response). Furthermore, these States should, to the greatest possible extent, share costs, be guided by the principles of transparency and mutual cooperation and agree on the procedure to be followed for the settlement of disputes. With respect to the latter point, States could set up a dedicated dispute settlement procedure or make reference to already available possibilities, such as recourse to the International Court of Justice or arbitration under the Permanent Court of Arbitration (PCA) (Optional Rules for Arbitration of Disputes Relating to Outer Space).

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Conclusion If a planetary defense system is planned, it should be international in nature and scope. The setting up of these arrangements will likely be led by technological and economically advanced States that will play a major role. Naturally and logically, this system should be governed by international law. The above analysis has demonstrated that current international law, including space law, does not provide a comprehensive legal framework dealing with the prevention and mitigation of natural cosmic threats as well as recovery activities. Clearly numerous issues remain open for discussion. More importantly, it poses numerous legal and organizational challenges related to a planetary defense. These issues include the possibility of liability and illegality in the use of (nuclear) force. In the absence of a uniform and legally binding regime, there will be uncertainty, diverging interpretations, and, potentially, conflicts among the States involved in such a response. It would, thus, be advisable that States, particularly those that intend to take part in a planetary defense, should develop a dedicated legal framework to govern the preparation, implementation, and aftermath of a response to a natural cosmic threat. More specific details, such as setting up a comprehensive structure, decisionmaking processes, emergency response plans, technical and human resources for monitoring, and research about risks posed by near-Earth objects, space debris, adverse space weather, dispute settlement, the transparency of operations, etc., could be left to a later date. Ultimately these should be covered in an international treaty on some type of convention. Ultimately it might be realized that the issue of climate change is, in fact, a type of cosmic hazard and closely linked to severe space weather conditions, and in this respect, the issues of planetary defense and environmental controls, as related to climate change, may be considered in this broader context. More importantly, these proposed arrangements must have clauses incorporating cross-waiver of the liability and permission to use (nuclear) force, if it becomes necessary, as well as other provisions amending those treaties that might be seen as legal barriers in the creation of a planetary defense system. Other elements to be considered for inclusion are the arrangements for disaster response in the event governments experiencing a cosmic disaster in the case of a major catastrophe are not in a position to request relief and whether UN peace-keeping forces should be deplored in such instances. The international regulatory framework must strike a fair balance between the interest of mankind in its survival, the acceptance of the main positions of States taking an active part in planetary defense initiatives, and the meaningful participation of private companies and nongovernmental organizations. It is also recommended that the Working Group on Near-Earth Objects established by the Technical and Scientific Subcommittee of the COPUOS as well as the Long-Term Sustainability of Outer Space Activities (LTSSA) established by the full COPUOS body should become more active and seek extensive and interdisciplinary input from nongovernmental organizations,

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governmental bodies, international institutions (like IADC, IAWN, SMPAG, IAU), academics, and the private sector. To date most of the legal analysis with regard to cosmic hazards has focused on Near Earth Objects (NEOs), but in future years solar and other cosmic hazards will likely receive much more attention. Acknowledgment The author of thischapter wishes to thank Dr. Joseph Pelton and Mr. KuanWei (David) Chen for reviewing its earlier draft. Their comments significantly enhanced the quality of this section. Undoubtedly, the author remains exclusively responsible for the text of the section and any errors or omissions it may contain. – Fabio Tronchetti

Cross-References ▶ Directed Energy for Planetary Defense ▶ Economic Challenges of Financing Planetary Defense ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Major Gaps in International Planetary Defense Systems: Operation and Execution ▶ Planetary Defense, Global Cooperation, and World Peace ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards

References Declaration on International Cooperation in the Exploration and Use of Outer Space for the Benefit and in the Interest of all States, Taking into Particular Account the Needs of Developing Countries, UNGA Res 51/122, UN Doc A/RES/51/122 (13 Dec 1996) Draft Articles on Responsibility of States for Internationally Wrongful Acts (2001) of the International Law Commission, art. 31. http://legal.un.org/ilc/texts/instruments/english/draft %20articles/9_6_2001.pdf. May 2014 Hobe S (2009) Article I. In: Hobe S, Schmidt-Tedd B, Schrogl KU (eds) Cologne commentary on space law, vol 1. Carl Heymanns Verlag, Cologne, pp 25–44 Intergovernmental Agreement (1998) the Agreement among the Government of Canada, Governments of Member States of the European Space Agency, the Government of Japan, the Government of the Russian Federation, and the Government of the United States of America concerning Cooperation on the Civil International Space Station (also known as the Intergovernmental Agreement), Washington, done 29 January 1998, entered into force 27 March 2001; TIAS No. 12927; Cm. 4552; Space Law – Basic Legal Documents, D.II.4, art. 17 International cooperation in the peaceful uses of outer space, UNGA Res 68/75, UN Doc A/RES/ 68/75 (2013), para 8. UNCOPUOS, Report of the Scientific and Technical Subcommittee on its fiftieth session, held in Vienna from 11 to 22 February 2013, UN Doc A/AC.105/1038, particularly Annex II “Legality of the Threat or Use of Nuclear Weapons”, Advisory Opinion (1996) International Court of Justice. Rep 226 Liability Convention – Convention on international liability for damage caused by space objects (hereafter Liability Convention), London/Moscow/Washington, done 29 March 1972, entered into force 1 September 1972; 961 UNTS 187; TIAS 7762; 24 UST 2389; UKTS 1974 No. 16; Cmnd. 5068; ATS 1975 No. 5; 10 ILM 965 (1971)

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International Charter on Space and Major Disasters, Signed on 20 Oct 2000, online at: International charter on space and major disasters http://www.disasterscharter.org/web/charter/char ter. Last accessed May 2014 Permanent Court of Arbitration (PCA) Optional rules for arbitration of disputes relating to outer space (effective 6 Dec 2011), http://pca-cpa.org/shownews.asp?ac=view&pag_id=1261& nws_id=323. Last accessed May 2014 Principles Relating to Remote Sensing of the Earth from Outer Space, UN Resolution 41/65, 3 December 1986, Principle X Registration Convention – Convention on Registration of Objects Launched into Outer Space (hereafter Registration Convention), New York, done 14 January 1975, entered into force 15 September 1976; 1023 UNTS 15; TIAS 8480; 28 UST 695; UKTS 1978 No. 70; Cmnd. 6256; ATS 1986 No. 5; 14 ILM 43 (1975) Rescue Agreement – Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space,London/Moscow/Washington, done 22 April 1968, entered into force 3 December 1968; 672 UNTS 119; TIAS 6599; 19 UST 7570; UKTS 1969 No. 56; Cmnd. 3786; ATS 1986 No. 8; 7 ILM 151 (1968) Schrogl KU, Neumann J (2009) Article IV. In: Hobe S, Schmidt-Tedd B, Schrogl KU (eds) Cologne commentary on space law, vol 1. Carl Heymanns Verlag, Cologne, pp 75–76 The Declaration of the United Nations Conference on the Human Environment, adopted on 16 June 1972, by the United Nations Conference on the Human Environment, Principles 2, 4 The Outer Space Treaty – Treaty on principles governing the activities of States in the exploration and use of outer space, including the moon and other Celestial bodies London/Moscow/Washington, done 27 January 1967, entered into force 10 October 1967; 610 UNTS 205; TIAS 6347; 18 UST 2410; UKTS 1968 No. 10; Cmnd. 3198; ATS 1967 No. 24; 6 ILM 386 (1967) “The Responsibility to Protect”, Report of the International Commission on Intervention and State Sovereignty (ICISS), December 2001, } 2.29. http://www.iciss.ca/pdf/Commission-Report. pdf. Last accessed May 2014 The Stockholm Declaration. The Declaration of the United Nations Conference on the Human Environment, adopted on 16 June, 1972, by the United Nations Conference on the Human Environment, Principles 2, 4 Tronchetti F (2011) Preventing the weaponization of outer space: is a Chinese-European-Russian common approach possible? Space Policy 27:81–82 United Nations Conference on Environment and Development (UNCED) (1992) Agenda 21 voluntary action plan on sustainable development. http://www.unep.org/Documents.Multilingual/ Default.asp?documentid=52. Last accessed May 2014 United Nations Conference on Environment and Development (UNCED). Agenda 21 http://www. unep.org/Documents.Multilingual/Default.asp?documentid=52. Last accessed May 2014 von der Dunk F, rapporteur for the study (2010) Legal aspects of NEO threat response and related institutional issues http://www.swfound.org/media/40426/legal_aspects_neo_response_institu tional_issues_final_report.pdf. Last accessed May 2014

Major Gaps in International Planetary Defense Systems: Operation and Execution Michael Potter

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detecting Cosmic Risks Is Just the Start of What Needs to Be Done . . . . . . . . . . . . . . . . . . . . . . . Creating a Planetary Defense Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A New Set of Priorities of Space Agencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Risk of Cosmic Hazards Is Larger than Popularly Known . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Need for Urgent Action Must Be Recognized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A Planetary Defense Model Based on Multilateral Peacekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

The current focus related to planetary defense concentrates on detecting cosmic hazards. However, the largest gap in planetary defense is the organization of an appropriate response revolving around operations, command, and control and execution of a planetary defense mission against all threats to the world today. This need for a global response capability applies whether this involves an asteroid, a comet, or a coronal mass ejection or some other threat. There is a need for clear management and control structures that are built on a framework that is based on multilateral enforcement and peacekeeping conventions. Some action has recently been initiated within the United Nations framework via the Committee on the Peaceful Uses of Outer Space at the behest of the General Assembly. But this is really an initial step that must be considered as inadequate in terms of implementing a truly full-scale global response to a major and

M. Potter (*) International Institute of Space Commerce, Douglas, Isle of Man e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_81

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potentially devastating event with a potentially global impact. Without such framework it is not possible to begin to properly plan for operationalizing planetary defense. Keywords

Asteroid • Global cooperation • Space hazard • International cooperation • Multilateral • Near-Earth object • Peacekeeping • Practical models • Structures • International relations

Introduction Most experts spend a significant amount of time trying to identify the various cosmic hazards that exist. Thus they bring attention first to the larger existential issue of space threats and secondly to the challenge of building systems of detection and early warning of space hazards. Certainly there is a sequential logic to emphasizing public awareness and support, and there is absolutely a requirement for the development and deployment of detection and alert infrastructure or even a plan for one. It is also logical to argue that beyond detection and beyond alert, the greatest gap in planetary defense, at this moment, is that there is no effective planetary defense infrastructure. It is important to note that the asteroid 2012 DA14, with the potential impact power of 1,000 atomic bombs, that missed the Earth (on the same day that the completely unrelated and undetected Chelyabinsk meteor hit Russia) was detected by an amateur astronomer http://www.nasa.gov/content/goddard/around-theworld-in-4-days-nasa-tracks-chelyabinsk-meteor-plume/#.Uw-IWPldVUc. Assuming that humanity can indeed make substantial progress on the space hazard detection and warning front in the coming years, the next critical question is what is the next step from an operational and execution point of view? In the near-to-medium term, there are two realistic response scenarios – a response that is effectively dominated by a single country or region, or a response that is truly multinational in substance. In order to be truly effective in the longer term, the multinational capability, backed by an agreed international framework, is essential.

Detecting Cosmic Risks Is Just the Start of What Needs to Be Done If one views the common dilemma that many national leaders confront, it is not unusual to be presented with two options, with both being bad options but hopefully with one option being slightly less worse than the other.

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In the case of actively confronting a planetary hazard, the first challenge would likely be assessing relative probabilities of risks. How likely would the hazard affect the planet? What sort of danger does it present? How many lives are at stake? What sort of economic impact and dislocation might it cause? How much will it cost to mount a defense, and what are some of the consequences from mounting a defensive mission? Will the action from the defensive measure adversely affect one nation or population more than another? Is there a possibility that a defensive action can create more future hazards? Could mounting a mission to target a smaller more immediate threat make it difficult to respond to a larger less immediate threat? Assuming that a leadership team can satisfy themselves on the above issues, it is still clear that a response mission dominated by a national or regional player will still involve a great deal of international communications and cooperation. Nevertheless, ignoring the scientific and technical challenges for a moment, simply from a mission command and control point of view, the operation would very much resemble a space agency mission or require something akin to a military tactical operation.

Creating a Planetary Defense Capability A planetary defense mission is extremely complex due to its international leadership and integration implications, including design, development and testing, and the scale of its operational execution requirements, not to mention funding. These represent huge challenges in today’s political environment. Additionally there is the issue of the dual-use technologies that are interconnected to planetary defense. The same technologies that can protect the planet can also provide offensive military capabilities. This “dual use” aspect of military systems for humanitarian and civilian purposes can be observed in a variety of ways today. In the area of orbit debris response, high-powered laser systems that might divert a space-based collision could also be a potential space weapon. The systems to track orbital debris and maintain space situational awareness are also designed to track missile strikes. The systems that are used to track asteroids, observe extreme solar weather events, monitor terrestrial storm systems, and so on may be operated by defense agencies to support military operations. Under the limits of current national political realities and budgetary allocations, one must try to imagine and assess what the scale of space hazards might be and what resources are needed to face these hazards. This risk assessment process would include an attempt to bind the magnitude of the cost and the scope of complexity of a planetary defense effort and the potential size of a recovery response. The larger the scale and complexity, the greater the need to stimulate a more robust and unified international response to a true “black swan” event. In the area of multilateral peacekeeping, it is not necessarily the scale of the actual task that drives internationalism but often the political complexities and political sensitivities of a particular region or mission. While international

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peacekeeping, for example, may broaden international participation, such multinational effort may be less efficient in terms of command and control than if carried out by a single nation which might be entrusted with carrying out the same sort of activities. Internationalism, almost by definition, carries more administrative and leadership overheads and costs than a do-it-alone approach would have entailed. Often with mega-science and technology projects, when the lofty project mission and vision statements are stripped away, we often see them strongly influenced by the development of a national industrial base. A large and complex industrial base, while arguably required to support national missions and future state goals, can often be translated into the need for industry subsidies and institutional inefficiencies (One hundred year starship study). One must always trade off efficiencies in order to obtain multinational support and participation. One of the key questions that will impact the scope of a global response to a space hazard, or a possible massive response effort, will revolve around the size of the hazard and the amount of time that we on Earth have to respond to the hazard – either before, in the case of an asteroid or comet threat, or perhaps after, in the case of a recovery from a massive and damaging extreme solar event. The larger the hazard and the greater the period of time for preparation and prevention or for a massive recovery effort, the greater will be the need for orchestrated and institutionalized global participation to respond to the particular space hazard. Alternatively stated, the smaller a specific hazard, involving a shorter time horizon, that might be effectively dealt with by one or two players, the more likely there will be an efficient unilateral or limited multilateral response. In such instances there is likely no global participation and response accomplished outside an international institutional structure. Often multinational mega-science projects seem to revolve more around job creation and the building of indigenous industrial capabilities, rather than executing the original intended goal of the project itself. National political and economic concerns often trump almost everything else including longer-term goals such as coping with climate change or planetary defense. Currently no nation has a powerful, focused national space strategic plane development that is being undertaken for the purpose of making humanity a multi-planetary species. Likewise developing commercial space plane systems is not being undertaken as part of a robust planetary defense.

A New Set of Priorities of Space Agencies Space agencies need to update their strategic plans in several regards. The first change would be to explicitly identify the identification of cosmic hazards and to undertake planetary defense against such hazards as a primary goal. The second change would be to seek to integrate planetary defense efforts and technology development within the context of its other longer-term programmatic goals and objectives.

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In fact, the longer-term goal of developing the technologies and systems needed to become a multi-planetary species is a logical plan B in case we fail at plan A in defending our planet. Depending on the particular planetary threat to be faced, money may not be the most significant issue. Planetary defense is not so much a technical issue, as it is a matter of national and international political prioritization and the allocation of funding among alternative programs. Recently, NASA launched two initiatives. One program is the so-called 100-Year Starship and the other is the “Fragile Oasis” program. Fragile Oasis is inspired by the increasing awareness of the fragility of our planet, when viewing the Earth from outer space – the so-called overview effect (100-Year Starship). The 100-Year Starship project is an initiative which challenges thinkers and policymakers to strategize the key issues that would be involved with running a multigenerational project to launch a starship that could reach beyond the Milky Way galaxy. If the two initiatives were, for instance, viewed in the longer-term context of planetary defense and preservation of the human race, these two initiatives would seem to dovetail nicely together. Both program initiatives address the logical conclusion of an ultimate planetary defense strategy. As many astrophysicists such as Stephen Hawking have said, we must leave the cradle of the Earth sometime if only for the purpose of not putting all of the eggs of humanity into one basket. The goal of becoming a multi-planetary species is thus ultimately not about industrial expansion or space technology development but the preservation of humanity and the ultimate planetary defense.

The Risk of Cosmic Hazards Is Larger than Popularly Known A recent report from the World Economic Forum in Davos (2014), Switzerland, from one of its committees – in this case one related to space activities – stated the risks to the world economy posed by cosmic hazards in this fashion: “Catastrophic risks from space are low-likelihood but high impact events. Extreme space weather, for example, could harm satellites, disrupt pipelines and telecommunications networks, and collapse electric grids. Large objects impacting Earth could cause even greater regional or global damage” (“Bringing Space”). This report notes the possibility of great damage but minimizes the danger by characterizing the risks as being of “low likelihood.” Such reassuring assessments, however, conveniently ignore a lot of evidence. A reanalysis of historical astronomical observations from Mexico suggests that the Earth narrowly avoided a “near-extinction event” just over a hundred years ago. There is considerable evidence that a billion-ton comet may have missed Earth by only a few hundred kilometers as recently as 1883. Each fragment was bigger than the asteroid or round comet thought to have hit Tunguska, Russia, in 1908 that created great damage to the region. (This day. . .) Analysis of the 1883 photographic evidence suggests that had the 1883 comet hit Earth, it would have been the equivalent of 3,275 Tunguska events occurring in the span of 2 days. This could

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Fig. 1 A fragmenting comet that nearly missed Earth in 1883 would have looked similar to this Hubble image of the SchwassmannWachmann 3 Comet

indeed have been an event so devastating that many species, including humans, may not have survived (Hubert Foy 2013) (Fig. 1). In 2012, there was a coronal mass ejection from the sun that largely headed away from the Earth, but if this event had occurred just a week later, it would have been comparable to the Carrington event, and it may have wiped out much of our space infrastructure and perhaps much of our global electrical and telecommunication grids. In addition the world population, urban concentration, and dependence on electric power system, modern transportation, and space systems have grown exponentially in the last century, and this means our vulnerability level has actually soared without it being that obvious.

The Need for Urgent Action Must Be Recognized Planetary defense should be viewed both as morally right and technically feasible by the entire world community. For those who are not interested in defending the planet, they should recognize the extent of the risk and the dangers of the lack of foresight and inaction. The words of former US president George H. Bush (1991) at the opening of the US Holocaust Museum are in this regard remarkably apt: Here we will learn that each of us bears responsibility for our actions and for our failure to act. Here we will learn that we must intervene when we see evil arise. Here we will learn more about the moral compass by which we navigate our lives and by which countries will navigate the future. (George H. Bush)

The context of President George H. Bush’s words was quite different, but the lesson is vividly clear. There is a price for inaction. There is a need for an active program to create a global framework for planetary defense against all types of

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cosmic perils. Unless there is an effort to create an active defense initiative, there could well come a time where there is a need to build memorial parks, to honor the millions that were condemned to death through a lack of comprehension and inaction.

A Planetary Defense Model Based on Multilateral Peacekeeping Operational action plans should be developed for response when a space hazard is discovered. Demonstration test missions should be designed and flown to demonstrate and validate the most promising defense options for planetary hazards. The current UN Committee on the Peaceful Uses of Outer Space (COPUOS) efforts to develop a framework for international decisions and coordinated actions are a worthwhile first step. Even so there remains serious doubt as to whether such a framework would be sufficient or truly adequate to a true global crisis. Ultimately there is a need for a much more commanding model. This is for a framework that creates a mechanism for multilateral enforcement and global peacekeeping mechanisms. The strength of multilateral peacekeeping is that the objective is usually humanitarian, with a tremendous focus on political and legal legitimacy and immediate positive impact. The weakness of multilateral peacekeeping generally revolves around: – – – –

Mission creep Exit strategy Discipline and professional conduct of one’s own troops The frailties, complexities, and dangers of dealing with competing local religious, tribal, warlord, and other constituencies – A serious study of how to apply the model of multilateral peacekeeping to a global response to either an imminent cosmic hazard and planetary defense or recovery from a cosmic hazard needs to consider these factors. This means both an assessment of the weaknesses and what the appropriate corrective actions might be could be applied.

Conclusion Chapter VII of the Charter of the United Nations provides the framework within which the Security Council may take enforcement action. It allows the Council to “determine the existence of any threat to the peace, breach of the peace, or act of aggression” and to make recommendations or to resort to nonmilitary and military action to “maintain or restore international peace and security.” For over half of a century, the United States has utilized the Chapter VII military sanctions under UN authorization. Desert Shield/Desert Storm in the early 1990s represented only the second American initiative, one which was provided a UN license for the use of force without restricting the manner in which the US-led

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coalition was to “secure Iraq’s immediate and unconditional withdrawal of its forces from Kuwait.” While required to provide periodic updates to the UN Headquarters, the coalition was allowed full planning and operational freedom to use “all necessary means” to execute the mission. This may indeed be the most efficient and effective model and framework for organizing a mission to defend against cosmic hazards. In addition the UN should declare that all people should be able to lead their lives free from fear of preventable space hazards. This should become a fundamental human right. Those who undertake efforts to protect humanity from space hazards ought to be able to do so free of the threat of legal liabilities and concerns relating to compensation under the auspices of a sort of cosmic “Good Samaritan” legal standard. These concepts need to be further developed and incorporated into the existing legislation and conventions – perhaps those related to space liability. An obvious data point in terms of both international space activities and cost is the International Space Station (ISS). By the time the ISS is decommissioned in the coming years, between $150 billion and $200 billion dollars will have been spent in a fully cost-loaded analysis. Compared to the International Space Station, planetary defense needs to be viewed as a low-cost global insurance policy. The B612 Foundation has pioneered the use of the nonprofit model for the detection of near-Earth objects. The Sentinel Project is a remarkable example of what can be accomplished by international cooperation within the constructs of a nongovernmental organization. In fact, developing a plan for a global grassroots planetary defense initiative can accomplish a great deal in a very efficient and cost-effective manner. Initiatives such as “open source” hardware and software development can be an important factor in helping to save our “fragile oasis.” In the global computer technology ecosystem, hundreds of billions of dollars have been saved through open-source initiatives. With clear management and control structures built on the framework that we have previously seen with existing multilateral enforcement and peacekeeping conventions, we can close the largest piece of the planetary defense gap. Such integrated systems and international frameworks can ensure that humanity has a fighting chance of defending all life forms here on planet Earth. Note: Portions of this chapter are protected under the Creative Commons, Attribution, Non Commercial (CC BY-NC) license, 2014. Published with permission of Michael Potter.

Cross-References ▶ Active Orbital Debris Removal and the Sustainability of Space ▶ Directed Energy for Planetary Defense ▶ Economic Challenges of Financing Planetary Defense ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense

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▶ Planetary Defense, Global Cooperation, and World Peace ▶ Regulatory Aspects Associated with Response to Cosmic Hazards ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards

References Around the world in four days: NASA tracks Chelyabinsk meteor plume. http://www.nasa.gov/ content/goddard/around-the-world-in-4-days-nasa-tracks-chelyabinsk-meteor-plume/#.UwIWPldVUc Bringing space down to Earth. World economic forum annual meeting, Jan 2014, Davos Bush GH (1991) Remarks on the occasion of the dedication of the Holocaust Museum. Washington, DC Foy H (2013) Re-Analysis of 1883 observations suggest that a billion-ton comet buzzed Earth. Space Saf Mag. http://www.spacesafetymagazine.com/2013/01/02/reanalysis-observationsrecorded-1883-zacatecas-mexico-suggest-fragments-billion-ton-comet-close-earth/ One hundred year starship study. NASA. http://100yearstarshipstudy.com/ This date in science: the explosion. http://earthsky.org/space/what-is-the-tunguska-explosion

Planetary Defense, Global Cooperation and World Peace Michael K. Simpson

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Political Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pathways for Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Progress Through Consensus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Work Ahead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

Out of a growing sense of shared vulnerability on a planet whose cosmic environment is recently better known and seemingly less benign than it once appeared, an international response to the cosmic hazards posed by some nearEarth objects and other significant space phenomena has begun to take shape. Although asteroid strikes are far from the only or even most likely threats posed by Earth’s cosmic neighborhood, they have a tangible character that makes them easy to visualize by many people, and they could, in a worst-case scenario, lead to apocalyptic consequences. Thus, among the many very real hazards covered in this handbook, the threat of asteroid impacts is one that has inspired sufficient study and political action to have brought two new institutions into being with the mission of protecting not just a few select countries but the entire planet. Seeking to draw some insights for the problems remaining to be addressed from the progress made in the area of defense against NEOs and to a certain extent other major space hazards, this chapter looks at the political environment and pathways for cooperation that have led to this progress. Lastly, it looks at some M.K. Simpson (*) Secure World Foundation, Broomfield, CO, USA e-mail: [email protected]; [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_82

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of the work remaining to be done to ensure that institutions that have been designed on paper could actually someday meet the challenge of delivering protective measures including something as dramatic as deflecting a massive space rock bound for an unwelcome rendezvous with Earth. Keywords

Asteroid • Global cooperation • Outer Space Treaty (OST) • Transparency • Liability • Association of Space Explorers Panel on Asteroid Threat Mitigation (PATM) • Inter-Agency Space Debris Coordination Committee (IADC) • Space Data Association (SDA) • Disaster Charter • Group on Earth Observation (GEO) • UN Committee on the Peaceful Uses of Outer Space (UN COPUOS) • International Code of Conduct for Outer Space Activity (ICoC) • Group of Governmental Experts on Outer Space Transparency and Confidence Building Measures (GGE) • International Asteroid Warning Network (IAWN) • Space Mission Planning Advisory Group (SMPAG) • Action Team-14 (AT-14) • UNISPACE III

Introduction As many chapters in this volume have pointed out, humankind has made some considerable progress in its ability to identify many cosmic hazards including asteroids and comets that present a possible risk of collision with Earth. We have even advanced some creative ideas about how asteroids in particular, detected early enough, might be deflected sufficiently for them to pass us by harmlessly. Until very recently, however, progress has been much less substantial on the critical questions of how we would decide to act at all and who would take that decision. In some ways this is hardly surprising. Much of human history has focused most attention on decisions about how to defend oneself from other groups of humans perceived to be hostile or potentially so. Throughout this long social evolution, humankind has developed a distinct preference for maximizing the autonomy of its decision making and preserving independence and freedom of action in the face of outside threats whether real or imagined. This period of history has also been characterized until very recently by a tacit acceptance of the fact that human beings could not act effectively to prevent a threat posed by cosmic hazards. Such action was in the hands of either God or random fortune. In the last 50 years, things have changed rapidly. First humankind proved its ability to reach space with rocket propulsion and to orbit objects it had created. Then it demonstrated the ability to go to the Moon, to the inner planets, to more distant planets, and even to much smaller targets like asteroids and comets. Along the way humanity perfected space navigation, developed great skill in rendezvous, and honed its capacity for space surveillance. By the early twenty-first century, it was no longer possible to argue credibly that humankind had no possibility of conceiving and executing a mission capable of affecting the course of an asteroid. Although a similar statement about most comets, especially those with orbits highly

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inclined relative to that of Earth, may yet be impossible to make, asteroids represent the vast majority of space objects with a significant chance of striking the Earth. Thus, we entered the new century in a technical environment in which deflection of an Earth-bound asteroid, however difficult or costly, was understood to be possible. Ironically, this good news left us with a political problem and several ethical dilemmas. The problem was rooted in the reality that although an inbound asteroid threatened the entire planet due to “nuclear winter” effects and uncertainty about the actual point of impact, there were very few countries that actually possessed the technical and financial means to mount a deflection mission. Since none of these countries had agreements that could be construed to cover shared decision making with each other let alone other countries that might be affected, the default option would have been an independent action, probably conducted under the usual cloak of military secrecy and viewed with intense suspicion by other space-capable and non-space-capable countries around the world. As one expands the implications of this scenario, we could quickly reach a point where the greatest threat posed by an incoming asteroid of “city-killer” size was how nervous countries reacted to each other’s independent and politically opaque preparations to intervene. Ethically, the challenges related to the inevitable reality that to deflect an asteroid bearing down on the Earth, one would often have to temporarily make some parts of the Earth’s surface more at risk as the asteroid was nudged to a trajectory that eventually would cause it to miss the planet altogether. Since many non-spacecapable countries were likely to occupy those parts of the surface, independent, opaque action would be likely to leave them very anxious, if not enraged. A second moral issue is equally disturbing. What if the technically advanced nations were each individually to determine that an asteroid of significant size was on a collision course with Earth but presented zero likelihood of significantly impacting them and then chose to do nothing but “take the hit”? The effect of these independent decisions would then be to open the possibility that the eventual collision devastated some part of the world with no capability of protecting itself. Preventable deaths and material devastation would not have been avoided. To a large extent, this chapter is about how these political and ethical issues have been confronted, the progress that has been made, and the work remaining to be done. It presents an interesting story of international and cooperative initiative. Unlike some of the world news we confront these days, it also provides some reasonable grounds for optimism.

The Political Environment Understanding the relationship of any space activity to global cooperation and world peace requires understanding the unique political characteristics of the cosmos. Space is universal high ground. Navigating through it necessarily puts an object above every sovereign state on Earth and as such arouses the concern of every military leader charged with protecting national territory. No military planners have ever wanted to see anyone, especially a potential adversary, occupy a

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position higher than their own, even briefly. Yet objects orbiting Earth can routinely pass over head at regular intervals. The situation looked even scarier in the mid-1960s as the Soviet Union and the United States raced each other to the Moon. Then, the stakes were not limited to occasional overflights by satellites; they included the possibility that the victor in the Moon race might also gain permanent control of the high ground of Earth’s natural satellite on which military bases and powerful weapons could be placed. With neither the United States nor the Soviet Union absolutely confident that it would get to the Moon first, and with many states that were not in the race fearful that the victor might try to lay territorial claim to it much as Balboa had once claimed all lands bordering the Pacific Ocean in the name of the Spanish Crown, the conditions were right for the first of the five space treaties to be negotiated. The result of that first negotiation was the Outer Space Treaty (OST) of 1967 (UN Treaties 2008, pp. 3–8). In a somewhat revolutionary act, it secured the agreement of its parties to forsake for all time any claim of sovereignty over a celestial body beyond Earth. In so doing it created a legal and political environment that was unprecedented and simultaneously gave birth to the inevitable need for cooperation in resolving any conflicting objectives in space activity. There is no attempt here to make this a definitive synopsis of all the legal tenets and principles that might impact a mission to intercept and deflect an asteroid or otherwise undertake an active mission to protect Earth from a threat from space, but some ideas are so central to understanding the context in which peaceful cooperation in such an endeavor could be carried out that they are worth mentioning. The Outer Space Treaty conferred full responsibility for any activities carried out in space on nation-states (Article VI). It established the “principle of cooperation and mutual assistance” as a guiding principle and incorporated “due regard to the corresponding interests of all other States Parties to the Treaty” as an obligation (Article IX). The treaty also came down squarely on the side of transparency in a way that would establish a useful foundation under the efforts 40 years later to broaden the international base of information available to track near-Earth objects passing near to Earth: In order to promote international cooperation in the peaceful exploration and use of outer space, States Parties to the Treaty conducting activities in outer space, including the Moon and other celestial bodies, agree to inform the Secretary-General of the United Nations as well as the public and the international scientific community, to the greatest extent feasible and practicable, of the nature, conduct, locations and results of such activities. On receiving the said information, the Secretary-General of the United Nations should be prepared to disseminate it immediately and effectively. Article XI

Consistent with its Cold War origins, the Outer Space Treaty also revealed one of the great phobias that, having survived the end of the Cold War, would inevitably impact discussions about how to respond to an asteroid threat: States Parties to the Treaty undertake not to place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner. Article IV

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Political discussions of asteroid response always seem to include arguments for and against the use of nuclear devices. Opinions can range from those who resist any use of them whatsoever to those who argue that to use anything else is to place the planet needlessly at risk. As more and more creative solutions for altering an asteroids trajectory have been advanced, the debate gets increasingly interesting. It certainly will not be resolved here. Nonetheless it is impossible to understand the intensity of some countries’ reactions to any asteroid response option that defaults to independent action by nuclear capable countries without being aware of how deeply rooted in some quarters is opposition to the use of nuclear devices even in apparent defense of the planet. It is also worth noting that although the OST also bans “any other kinds of weapons of mass destruction” from space, no objections to the proposed use of kinetic impactors massive enough to deflect asteroids (and therefore large enough to cause considerable terrestrial damage) have surfaced. Other options such as focused beam systems that are now proposed were not developed at the time that the OST was negotiated. Ultimately concern about restricting the nuclear option would play a role in creation of the first international, cooperative institutions charged with responding to an eventual asteroid threat. Before leaving the discussion of the effect of space treaties on the political environment in which countries would confront decisions to respond to an Earthbound asteroid, it is useful to know that two of these treaties specifically address the issue of liability and that that liability is essentially unlimited. Especially under the Liability Convention of 1972, a country launching a mission to intercept and deflect an asteroid could find itself completely liable for any resulting damage no matter how catastrophic: A launching State shall be absolutely liable to pay compensation for damage caused by its space object on the surface of the Earth or to aircraft in flight. Article II

No doubt a lot of ink would flow to create the legal briefs necessary to determine whether a bungled deflection mission that leads to a catastrophic impact on Earth would constitute damage caused by a space object, but even if a country acting independently did avoid legal liability for such a catastrophe, the political liability would be enormous. This alone would provide an incentive to find a structure for cooperative, multilateral response. Beyond the legal agreements, the political environment of asteroid response includes strong concerns about the weaponization of space. Every technology powerful enough to change the course of an asteroid has some military potential. Any sensor network good enough to look for objects large enough to inflict significant damage on Earth has the potential to gather military intelligence. Some of the earliest discussions of the need for coordinated, cooperative response to potentially hazardous objects addressed this concern and came quickly to recognize that only processes that were largely open and transparent would avoid facing crippling opposition from countries who suspected that asteroid response was merely an excuse for developing high-tech tools for powerful military systems. Inevitably skepticism and suspicion also arose out of the large differences in size and substantial asymmetry of national space capabilities. Although several

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countries could claim the ability to launch large missions to intercept an asteroid, the relative experience of those countries in rendezvousing with fast moving objects far from Earth differed widely. Furthermore, distribution of detection capability was very uneven, with only the United States having funded a significant program dedicated to finding potentially hazardous asteroids of 140 m diameter or bigger. The inclusion of near-Earth objects as one of the three focus areas of ESA’s Space Situational Awareness initiative and the possibility of adding the International Scientific Optical Network (ISON) headed by Russia to the pantheon of NEO detection capabilities hold the promise of expanded capacity going forward. The Sentinel infrared telescope proposed by the B612 Foundation, a nongovernmental organization based in the United States, would dramatically enhance detection capabilities if it can be successfully funded. Although most countries might have been very glad to leave the expense of asteroid detection to others, they were not immune to worries that countries with detection capabilities might sound a false alarm for political purposes or to provide cover for a weapons development program. To some people such fears may seem irrational, but they can be expected where great differences in power are present. More importantly for our purposes, they are present in the current political environment confronted by those trying to deliver on the promise of a cooperative global response to a threatening NEO. As noted in the introduction, some countries also worried that space-capable states might simply choose to do nothing if their tracking of an incoming asteroid indicated that their own territory faced little or no risk. When the Association of Space Explorers Panel on Asteroid Threat Mitigation (PATM) was meeting regularly between 2005 and 2008, one of the countries eager to host it was Costa Rica, which lay directly under the path of danger then predicted for a possible impact from the recently discovered asteroid, Apophis. One of the questions posed more than once during the session held there concerned how small states could be certain that larger ones would act to protect their interests in cases where the larger ones appeared to be at less risk. With this political environment of skepticism, suspicion, and anxiety, any broadly accepted solution would need to make use of every pathway for cooperation available. Fortunately there were many to choose from.

Pathways for Cooperation Despite the competitive and military roots of much space activity, it has proven to be a fertile ground for acts of cooperation and collaboration. Early work on the four broadly adopted space treaties, especially the Astronaut Treaty, reflected an understanding that space was a special place where the need for synergy could easily overwhelm the desire for independence. The International Space Station Intergovernmental Agreement (IGA) particularly reflects this cooperative bias, bonding 15 countries into a team that has built and managed one of the most complex human-made structures ever created. Given that key players include the United States, Russia, Japan, France, Germany, Italy, and Canada, various combinations of

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which have been at war with each other in recent history, the cooperative governance of the ISS is particularly noteworthy. There are other interesting examples of cooperative activity emerging from space activity. The Inter-Agency Space Debris Coordination Committee (IADC) joins 12 space agencies in an effort to identify cooperative opportunities for mitigating space debris (IADC TOR, pp. 7–8). The Space Data Association (SDA) links 18 members and participants in a cooperative effort to avoid satellite collisions through improved conjunction analysis, the Disaster Charter (Charter On Cooperation To Achieve The Coordinated Use Of Space Facilities In The Event Of Natural Or Technological Disasters). This latter agreement has institutionalized cooperation in the use of space facilities and data to respond rapidly and effectively to the management of disaster situations and the delivery of relief to victims (Disaster Charter, Article 2). Lastly, drawn from a population of examples that really is quite large, there is the Group on Earth Observations (GEO) founded in 2002 with the task of coordinating the integration of independent national systems of Earth observations into a “system of systems.” Under this concept the many sources of Earth observation data including that supplied by satellites could be made more useful to the goals of economic development, Earth research, disaster recovery, and terrestrial applications. The tradition of cooperation in dealing with the use and benefits of space activity is thus pretty firmly rooted in contemporary practice. This too is part of the political environment confronted by those seeking to address cosmic hazards cooperatively and is part of the political culture of several key political institutions that played important roles during the effort to create a structure for cooperation to meet the global threat posed by potentially hazardous asteroids. As Sergio Camacho’s chapter on the UN System has shown, cooperative, international engagement on the peaceful uses of outer space has roots almost as deep as the space age itself. Although the ultimate authority of UN action in this domain comes from its Charter and the action of the UN General Assembly (UNGA), the heavy lifting has mostly fallen to the UN Committee on the Peaceful Uses of Outer Space (UN COPUOS) and its two subcommittees, Legal (LSC) and Scientific and Technical (STSC). These bodies would play a critical role in the effort to build institutions equal to the task of confronting an asteroid threat internationally. During the 5 years from 2008 to 2013 that the UN System worked to build those institutions, there were two other major political processes under way that also strengthened the spirit of openness and cooperative intent that they would require to succeed. One was the broadening debate over the possible creation of an International Code of Conduct for Outer Space Activity (ICoC), and the other was the Group of Governmental Experts on Outer Space Transparency and Confidence Building Measures (GGE). Notwithstanding a focus on the anthropogenic threats of space activity that left no room to consider cosmic hazards, these organizations would provide a backdrop of cooperative possibility that would allow discussions of protection from cosmic hazards of all types and very specifically asteroid defense to proceed with optimism.

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Although hobbled by an awkward start that left some countries worried about the intent of the initiative, the effort to negotiate an ICoC for outer space activities steadily gained political ground as it broadened the base of input and listened carefully to the concerns of the early skeptics. Although not directly connected to the process of developing institutions to meet cosmic threats, the lessons of the ICoC discussion seemed to be well learned by those trying to mitigate threats to Earth from space hazards. Every effort was made to include all countries with an interest in the process, and countries that might otherwise have seen the issue as unimportant made the effort to stay in touch with the discussions, decision points, and arguments. This breadth of attention would have a very important impact on the institutional solutions that ultimately emerged. The role of the GGE was important but more subtle. For one thing this was the second GGE to tackle the challenge of improving transparency and building confidence in outer space activities. The first had delivered its report to the United Nations in 1993, and the mere fact that a second was needed 20 years later leads some to conclude that the first had not had the impact desired. In fact a close reading of the recommendations emerging from the 1993 GGE report shows that it was on track toward several innovations and developments that were to improve information flow and cooperation in the years that followed (GGE 1993, pp. 84–89). Particularly with respect to improvements in data sharing concerning potential collision between satellites and improved sharing of Earth observation data in connection with disaster mitigation and economic development, much progress was made on the 1993 recommendations in the two decades following the report. Thus, by the time the second GGE on space TCBMs convened in 2011, its focus on the importance of transparency and confidence building to the sustainability of any long-term political cooperation in space activity resonated perfectly with the need for cooperation in the face of a PHA. Perhaps even more importantly, as it reached consensus on a report to the UNGA in 2013, it demonstrated not only that cooperation was possible between great space powers that had not always agreed on key matters of policy in recent times but also that that agreement could extend more broadly to include other countries whose abilities, capacities, and experiences with space activity extended over a very wide range. All of this cooperative karma in the background would prove useful, because no matter how well drafted the working document developed by the PATM might have been, once submitted to UN COPUOS, it needed to achieve political consensus to move from an object of discussion to a basis for action.

Progress Through Consensus Ultimately, what emerged from the discussions and debates at UN COPUOS was a recommendation that two institutions be endorsed for the purpose of advancing an international response to future asteroid threats. The first is the International Asteroid Warning Network (IAWN) that would gather and share asteroid data from around the world and provide assessments from an international team of

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experts. This maximizes data acquisition while also assuring users of the data that it is credible and not subject to political spin. The second institution is the Space Mission Planning Advisory Group (SMPAG) that would combine many of the world’s space agencies into an expert team able to advise UN COPUOS on actions that should be endorsed and taken in concert to avert or mitigate impact. Much has already been said about the critical role of the UN system in building the political foundations for international response to an asteroid threat. There was a dynamic interaction in that process that bears review, however, if we want to understand the full role of cooperation in peacefully advancing planetary defense. One important challenge confronted by a consensus-based system like that practiced by UN COPUOS is overcoming the political inertia present at the beginning of nearly every policy-making discussion. UN COPUOS has overcome this inertia with an elaborate network of working groups and action teams that can do enough initial work on an issue area to permit developing momentum slowly enough for others to get on board comfortably along the way. With an issue as complex and multifaceted as planetary defense, however, the inertia is increased by political anxieties over military implications, information sharing, power asymmetries, and technical complexities. In the case of asteroid defense, it proved useful to have a working document produced outside the system by civil society and then presented as a point of departure to those whose task would be to create a politically viable proposal from it. It also proved useful that the coordinator of the input from civil society was an international group whose expertise and credibility were unassailable, the Association of Space Explorers (ASE). Representing the international community of people who have been among the early pioneers in human space flight and admitting only those who have flown in space, ASE came to the discussion of asteroid defense with a combination of technical expertise and the experience of having gazed at the fragility of Earth from above its atmosphere. ASE shared with the Secure World Foundation (SWF), one of their principal funders and like ASE an official observer at UN COPUOS, the belief that humanity knew more about how to detect and deflect asteroids than it knew about how to make a decision to do either. Acting on this belief, ASE created a Panel on Asteroid Threat Mitigation (PATM) and invited experts from many countries and disciplines to join in the search for a politically acceptable, technically well-grounded, and operationally effective means of coordinating a global response to what would inevitably be a global threat were a large asteroid to be found tracking on a collision course with Earth. Working on the project from 2005 to 2008, the PATM produced a thoughtful document with enough solid, practical suggestions for Action Team-14 (AT-14) of UN COPUOS to use it as the foundation of the hard political thinking and institution building necessary to bring the IAWN and SMPAG into existence (Asteroid Threats). AT-14 was itself a part of the UN COPUOS response to the Third United Nations Conference on the Exploration and Peaceful Uses of Outer Space. Created in 2001, this action team reflects the desire of UN COPUOS to pursue concrete opportunities for implementing the Conference’s many declarations, one of which

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dealt very directly with near-Earth objects and the potential risk they posed to the planet (UNISPACE III, p. 3): To improve the international coordination of activities related to near-Earth objects, harmonizing the worldwide efforts directed at identification, follow-up observation and orbit prediction, while at the same time giving consideration to developing a common strategy that would include future activities related to near-Earth objects

While the other international, cooperative initiatives cited here have been important for the background of cooperative practice, they provided during the discussion of building a structure for cooperation in the face of asteroid threats here the UNISPACE III declarations indicated a clear sense that NEOs and their potential threat to Earth were a matter that deserved international attention. The work would prove difficult, but at least now UN COPUOS had assigned the task to a body that would take it very seriously indeed and the principle that collective UN action against a cosmic threat was possible would have a tangible example. AT-14 had therefore been at its work for nearly 8 years when it received the PATM report in 2009, and over the next 3 years, the action team carefully shaped it into a document that could not only muster political consensus but could also meet the criteria of technical grounding and effective operation. Along the way the three institutions recommended by PATM were re-crafted into two, and the role of the Security Council that PATM had assumed would be at the center of response was reassigned to UN COPUOS itself. In some ways this reassignment reflected the triumph of the cooperative ideal in this endeavor since it demonstrated a desire to make use of an agency that understood the technical issues, that did not have a tradition of great power veto, and that broadly included the large number of countries whose interest in space was sufficient for them to join willingly in the pursuit of planetary defense against a threat from space. As the world moves now from conceiving and launching institutions designed to protect it against asteroid threats toward the detailed work of establishing terms of reference, operational procedures, and patterns of work that can fulfill its mission, there is some reason to believe that we have proven a model for cooperative global response that may address other cosmic threats as well. Coronal mass ejections, solar flares, and increased cosmic radiation in the wake of a reduced terrestrial magnetic field and improved methods of addressing orbital debris are now next in line. Since these hazards can threaten the world’s electronic grids and cause and threaten significant damage on Earth’s surface, this is a very good thing. Hopefully these may all lend themselves to solutions developed out of a similar blend of cooperative tradition and the proven efficacy of collaborative solutions.

The Work Ahead It is not always the devil who lurks in the details. Sometimes long-sought angels and helpful sprites can be concealed there as well. For IAWN and SMPAG, the quest for those angels and sprites will pass through the development of terms of

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reference, operating procedures, and habits of communication. The experience of the ISS and its IGA will help as will lessons learned from the IADC and even the nongovernmental SDC. There will be more countries involved in this process, however, and so we can expect there will be more lessons learned and more input to assess along the way. We can also expect the volume of data to increase as well as the IAWN extends its sources to more and more countries, and those countries become ever better at gathering information. If the B612 foundation proves successful in funding, launching, and operating its Sentinel mission, the data growth could prove exponential. That data is certain to reveal many more potentially hazardous objects than anyone would have predicted just a few decades ago as it gives us the ability to detect smaller objects and those spending a large portion of their orbital period inside Earth’s orbit where the Sun’s glare currently shields them from view. It may also generate the ability to intervene against objects as small as the one that exploded over Chelyabinsk in February 2013, an object far too small to be detected by current means, but one large enough to have caused significant damage and injury in a city that it effectively missed by over 100 km. On the one hand, this will be good news, but it will also greatly increase the theater of operations confronted by the recently created institutions and likely increase the number of countries who find themselves eager to be involved in the process of assessment and planning. It will also greatly increase the challenge of communication faced by the new institutions. A working group convened in Boulder, Colorado, in 2011 concluded that although manageable, there were many challenges to communicating about near-Earth objects and the dangers they represented (NEO Communications, pp. 18–21 and 28–29). Here, too, the challenge will be to cooperate sufficiently to ensure that messages are received accurately irrespective of the culture or language of the recipient. This is a good example of the wisdom that a cooperative and global response to a cosmic threat does not mean that all aspects of the response will be uniform or homogeneous. Synergy thrives on difference and we can expect a great deal of difference in the way people react to cosmic hazards. Of course, not everyone welcomes this level of international diversity. There will almost certainly be advocates for a return to national independence and supposed freedom of action. Although no one doubts that major space powers could eventually act alone in the face of a serious asteroid threat to their territory and any demonstrated reluctance to act on the part of the new institutions, complete independence of action is now clearly understood as a myth and probably always should have been. No independent action taken apart from broad international consensus could ever have been launched against an asteroid without creating enough anxiety in other states to bring about a political situation perhaps more dangerous than the asteroid threat, itself. At least now, pre-consultation, transparency of information, and an international exchange of concerns are largely guaranteed. Knowing whether that will be sufficient to coalesce into an international response may just have to wait for the detection of a space rock that has Earth undeniably in its cross hairs.

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Conclusion Although Earth-threatening situations have often been the subject of mythology, until recently science confined its planetwide, apocalyptic scenarios to the distant future or to those situations where humans spoiled their environment through war or environmental pollution. As we learn more about our cosmic environment, science has revealed other threats where the danger can confront us in real time and the origins clearly lie beyond the realm of human causation. Faced with a real and external threat to which they did not respond, however, people could still bear the responsibility for any eventual catastrophe, because they would bear the burden of inaction. Given the state of technology available to humankind, we no longer have the luxury of shrugging in helplessness after some future piece of space rock, perhaps no bigger than the Tunguska object of 1908, lays waste to a large part of the human community. With a significant number of the world’s countries engaged through the IAWN in the search for hazardous space objects and SMPAG representing a cooperative structure in place to facilitate synergy of action rather than response at cross purposes, excuses for inaction are rapidly evaporating. The same will likely also become true for threats that appear less tangible like those resulting from solar flares or radiation storms. As communication becomes more democratized and the flow of information across political lines less easy to control, threats that genuinely put the whole planet at risk will increasingly be recognized as such and widely known. People and their sovereigns will clamor to be informed of the risk’s magnitude and involved in developing patterns of response. The result is likely to be more global cooperation and more examples of the power of a world at peace to act effectively in its own defense.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Comet Shoemaker-Levy 9 ▶ Directed Energy for Planetary Defense ▶ European Operational Initiative on NEO Hazard Monitoring ▶ Impact Risk Estimation and Assessment Scales ▶ International Astronomical Union and the Neo Hazard ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ Minor Planet Center ▶ NEOSHIELD - A Global Approach to Near-earth Object Impact Threat Mitigation ▶ Potentially Hazardous Asteroids and Comets

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▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning ▶ United Nation Activities

References Asteroid Threats Association of space explorers, asteroid threats: a call for global response, (Houston, Texas USA: 2008). Text available at. http://www.space-explorers.org/committees/ NEO/docs/ATACGR.pdf. Accessed on 4 Mar 2014 Disaster Charter Charter on cooperation to achieve the coordinated use of space facilities in the event of natural or technological disasters Rev.3 (25/4/2000).2. Text at. http://www. disasterscharter.org/web/charter/charter. Accessed on 4 Mar 2014 GGE (1993) United Nations General Assembly, prevention of an arms race in outer space, study on the application of confidence-building measures in outer space, A/48/305, 15 October 1993, 144 pp IADC TOR Inter-Agency Space Debris Coordination Committee, terms of reference for the InterAgency Space Debris Coordination Committee (IADC)” IADC-93-01 (rev.11.2, public version), Status: July 11, 2011. Index to text at. http://www.iadc-online.org/index.cgi?item= docs_pub. Accessed on 4 Mar 2014 NEO Communications Secure World Foundation, near earth object media/risk communications working group report, (Broomfield, CO: June 2012) in cooperation with the Association of Space Explorers UN Treaties (2008) Office for Outer Space Affairs, United Nations treaties and principles on outer space, United Nations, New York, Reference: ST/SPACE/11/REV.2 UNISPACE III United Nations general assembly, report of Third United Nations Conference on the exploration and peaceful uses of outer space (Vienna, 19–30 July 1999), A/conf.184/6, 157 pp

Regulatory Aspects Associated with Response to Man-Made Cosmic Hazards Ram S. Jakhu

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contamination of the Earth-Space Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Release of Organic and Biological Bacteria (i.e., Issue of Planetary Protection) . . . . . . . . Radiation Released by Nuclear Reactors (i.e., Nuclear Power Sources-NPS) . . . . . . . . . . . Radiation Resulting from Nuclear Tests and the Use of Nuclear Weapons . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

The risks posed by man-made cosmic hazards include pollution in outer space and on Earth primarily caused by artificial space debris and the contamination of the Earth-space environment and celestial bodies created by the release of organic and biological bacteria, radiation released by nuclear reactors used to provide electric power for space objects, and radiation resulting from the use of nuclear weapons or their tests. In general, current international law (including space law) does not provide a satisfactory and binding legal framework to address all the risks posed by these hazards. Nevertheless, the international community has adopted some non-binding regulatory mechanisms to regulate and control these risks. This chapter briefly describes and points out the strengths and weaknesses of these mechanisms. Finally, some recommendations are made with respect to the future actions the international community ought to take in order to avoid or at least minimize the risks posed by man-made cosmic hazards. Clearly there are also a number of legal and regulatory issues related to natural R.S. Jakhu (*) Faculty of Law, Institute of Air and Space Law, McGill University, Montreal, Canada e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_64

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cosmic hazards such as Near-Earth Objects and hazardous solar events, but these issues are addressed in the earlier chapter by Fabio Tronchetti. Keywords

Space debris • Inter-Agency Space Debris Coordination Committee (IADC) • Planetary protection • Nuclear power sources • Nuclear weapons tests • Space debris mitigation guidelines • Active debris removal • Committee on Space Research (COSPAR) • International Atomic Energy Agency (IAEA) • NASA • Liability convention • Outer space treaty • Registration convention • Comprehensive Nuclear Test-Ban Treaty • Partial Test-Ban Treaty • United Nations • United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS)

Introduction Cosmic hazards, both natural and man-made, may present various kinds of risks to mankind. Depending on the severity of the hazard, the danger could range from catastrophic disasters to the destruction of property and possibly cause injury to humans on Earth. While to a large extent natural cosmic hazards cannot be avoided, their legal and regulatory considerations essentially relate to the development and employment of planetary defense. On the other hand, man-made hazards result from human activities in outer space and can be avoided to a good extent; thus, the role of the law in this regard is to strive for their prevention, mitigation, and regulation of the risks posed by them. The legal and regulatory issues related to natural cosmic hazards are different from those of man-made. This chapter addresses the risks posed by man-made cosmic hazards, which include (1) the physical and/or radiological pollution in outer space and on Earth primarily caused by artificial space debris and (2) the contamination of the Earth-space environment and celestial bodies created by (i) the release of organic and biological bacteria (i.e., issue of planetary protection), (ii) radiation released by nuclear reactors used to provide electric power for space objects (i.e., nuclear power sources-NPS), and (iii) radiation resulting from the use of nuclear weapons or their tests. Such risks are much more known, current, and prevalent. In general, current international space law does not provide a satisfactory and binding legal framework to address all the risks posed by these hazards. The five main UN space treaties do not address specifically these issues (Outer Space Treaty1967; Rescue Agreement 1968; Liability Convention 1972; Registration Convention1975; Moon Agreement 1979), though two other treaties that deal with nuclear tests are also relevant (Partial Test Ban Treaty1963; Comprehensive Nuclear Test Ban 1996). Nevertheless, the international community has adopted some regulatory mechanisms (mainly non-binding recommendations in the form of guidelines) to regulate and control these risks. These have been fairly well discussed in legal literature, and this chapter briefly describes and points out the strengths and weaknesses of these mechanisms.

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Space Debris The risks posed by space debris are real, serious, and expanding as the amount of space debris grows due to increasing number of space activities and space actors. Debris is an intensifying hazard to multibillion dollars’ worth operational satellites of all space-faring nations as well as a serious risk to humans, property, and the environment on Earth (UNCOPUOS 2011). The main causes of the generation of space debris are dispersion of pieces of launcher or satellite-related metal pieces, unintended accidents (breakup of large pieces), and intentional destruction of space objects (ASAT tests). According to several authoritative studies, the presence of space debris has reached the “tipping point” (Hildreth and Arnold 2014). Currently, there is no binding international treaty that specifically and effectively governs the prevention, mitigation, disposal, or removal of man-made space debris. After discussions since 1994, the international community has adopted some space debris-related international guidelines, e.g., the 2002 and 2007 Inter-Agency Space Debris Coordinating Committee (IADC) Guidelines and the 2007 United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS) Space Debris Mitigation Guidelines, which are essentially based on the IADC Guidelines and have been endorsed by UN General Assembly. While these instruments are non-binding in nature, their value should not be ignored since several space-faring States have been incorporating their provisions in their respective national space legislation in order to make them applicable to satellite operators falling under their jurisdiction (Austrian Federal Law on Space Activities 2011, Section 5). Briefly, all space-faring States are encouraged to apply the UNCOPUOS Guidelines to their mission planning and the operation of newly designed spacecraft and orbital stages in order to avoid accidental breakups, limit the probability of accidental collision in orbit, and limit the release of debris during normal operations (UNCOPUOS Guidelines, Section 3). For these purposes, the Guidelines recommend: (a) The depletion of onboard sources of stored energy (b) The avoidance of the intentional destruction of any on-orbit spacecraft and launch vehicle orbital stages or other harmful activities (c) The removal of dead spacecraft and launch vehicles in the low Earth orbit (LEO) from orbit in a controlled fashion to avoid their long-term presence in the LEO region (d) Leaving the dead geosynchronous Earth orbit (GEO) space objects in an orbit above the GEO region such that they could not interfere with, or return to, the GEO region (UNCOPUOS Guidelines, Section 3) There are several limitations in the UNCOPUOS Guidelines. As noted above, they are not legally binding under international law; thus, they do not create legal obligations for States to comply with them (UNCOPUOS Guidelines, Section 3). They are general recommendations to be implemented on a voluntary basis by

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States primarily through national legislation, regulations, and/or policy directives, subject to the unilaterally determined government decisions, which are normally based on balancing policy goals, economic considerations, and national security interests. Consequently, such national implementation may be limited in scope and would lack international uniformity and consistency. Under current international space law, the generation of space debris is not per se illegal, except the intentional creation of debris to interfere with the peaceful use and exploration of outer space by other States (Outer Space Treaty, Articles VI, VII and IX). The Guidelines maintain the status quo and do not outlaw a space debris creation activity and do not impose sanctions on the violators. More importantly, the UNCOPUOS Guidelines are not designed as a comprehensive approach for the space debris problem and particularly do not deal with the reduction of the debris currently in space (e.g., remediation). It is believed that even if no new space object is launched, due to the “cascade effect” (or Kessler Syndrome), the number of objects will keep expanding, making the risks increasingly worse and consequently the use of outer space unsustainable (UNCOPUOS 2012). Therefore, it is imperative to make efforts not only for the prevention and mitigation but also the remediation of existing space debris. The relevance and importance of law in this regard are not only to govern the rights and obligation of States with respect to generation and mitigation of space debris but also to facilitate the undertaking of remedial (space debris removal) efforts. However, active debris removal (ADR) operations will run into several legal hurdles (UNCOPUOS 2012). Under the current international space law, only the State of registration is entitled to have jurisdiction and control over its registered space object (Outer Space Treaty, Article VIII). A State, or its licensed company, can legally remove (a) a dead satellite over which it has jurisdiction and control and (b) a foreign space object but with the prior permission from the State of registration of that object (UNCOPUOS 2012). In addition, if such a foreign space object carries American technology, its removal will be further subject to prior approval of the United States Department of State pursuant to the US International Traffic in Arms Regulations (ITAR, }123.1). One also needs to keep in mind several serious and sensitive strategic and military implications of ADR operations because debris removal technology is similar, or closely connected, to antisatellite (ASAT) weapon capability (UNCOPUOS 2012). The UNCOPUOS (and IADC) Guidelines define space debris “as all man-made objects, including fragments and elements thereof, in Earth orbit or re-entering the atmosphere, that are non-functional” (UNCOPUOS Guidelines). Therefore, if a space object is nonfunctional, it is a space debris. Nevertheless, this description is insufficient not only for ADR purposes but also for the application of the some international space treaties and agreements because nonfunctional objects still have legal inferences. For example, under the Liability Convention, a launching State remains liable for damage or injury caused by its nonfunctional object (i.e., space debris). In this regard, one may note that the Soviet Union paid compensation to Canada for the damage caused by the Soviet nonfunctional satellite, COSMOS 954, when it fell back to Earth in 1978 and spread radioactive debris in the northern

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parts of Canada (Canada’s Claim from Soviet Union 1978). Legally speaking, space debris cannot be considered “space junk” or “space waste” abandoned by its launching State because such a State cannot unilaterally change the international legal status of the space object, and the law of salvage, as applicable in maritime affairs, is not valid for space operations (UNCOPUOS 2012). Moreover, such a technical definition in the non-binding Guidelines cannot fill-in the lacunae or requirement of an internationally binding definition of space debris. Such a legal lacunae pose challenges to the exercise of the freedom of exploration and use of outer space (Outer Space Treaty, Article I), the identification of the launching State (particularly, of small pieces of debris), proof of fault of the launching State for damage caused in space by space debris, etc. (Liability Convention, Article III). In essence, it is doubtful that the above-discussed Guidelines are an adequate tool to provide legal protection against a serious and rapidly expanding man-made cosmic hazard created by space debris.

Contamination of the Earth-Space Environment Release of Organic and Biological Bacteria (i.e., Issue of Planetary Protection) Regular human visits to, and continued presence in, outer space, including celestial bodies, are inevitable. Their frequency and number can be projected to grow, particularly because of the expected emergence of human space travel (space tourism) within a few years and the ongoing race for space exploration among the United States, Russia, Europe, Japan, China, and India. Consequently, there is a possibility of contamination with the introduction of Earthly organic and biological bacteria to the environment of the outer space and celestial bodies (known as “outward contamination”). Similarly, the Earth and its environment could also be polluted with bacteria of space origin so far unknown on Earth (known as “backward contamination”). The issue of pollution of planets (including Earth) and outer space has been addressed extensively by the global scientific community. The Committee on Space Research (COSPAR), the world’s leading scientific nongovernmental space research body under the International Council for Science, has been advocating for sufficient and effective measures to protect planets and outer space from harmful contaminants (i.e., “planetary protection”). According to NASA, the term “planetary protection” means “the practice of protecting solar system bodies (i.e., planets, moons, comets, and asteroids) from contamination by Earth life, and protecting Earth from possible life forms that may be returned from other solar system bodies” (NASA Office of Planetary Protection). In this regard, the law has been mainly confined to a broad and general principle included in Article IX of the Outer Space Treaty, under which States Parties have undertaken to “pursue studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination

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and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose.” There is no mechanism in the Treaty for the elaboration and implementation of this principle. That task has been performed, to some extent, by COSPAR that has adopted its planetary protection policy (COSPAR Planetary Protection Policy). Noting Article IX of the Outer Space Treaty, COSPAR promulgated this policy “to avoid organic-constituent and biological contamination in space exploration, and to provide accepted guidelines in this area to guide compliance with the wording of this UN Space Treaty” (COSPAR Planetary Protection Policy, Preamble). The policy posits to protect other life in the solar system, if it exists, and to protect “the Earth from the potential hazard posed by extraterrestrial matter carried by a spacecraft returning from another planet” (COSPAR Planetary Protection Policy). Therefore, some controls on contamination from certain space missions must be imposed. For this purpose, the policy divides target bodies or missions into five categories and recommends protection requirements and procedures for each mission and target body depending on the need and nature of the protection required (COSPAR Planetary Protection Policy). The COSPAR members are required to provide information to COSPAR, based on some critical factors indicated, about the procedures and computations used for planetary protection for each exploration mission of the solar system. The policy is a reference for space-faring nations as an international planetary protection standard on procedures, which ought to be implemented by them through their respective national policy and regulatory mechanisms. Pursuant to its international obligation under Article IX of the Outer Space Treaty, in the USA, NASA has enacted its own planetary protection policy. It is important to note that pursuant to the NASA Act of 1958 (NASA Act), NASA is authorized to make, promulgate, and issue policies, regulatory directives, and regulations governing the manner of its operations and the exercise of the powers vested in it by law. For example, in 1999, NASA promulgated its Biological Contamination Control for Outbound and Inbound Planetary Spacecraft (NASA NPD 8020.7G), which was revalidated on 17 May 2013. Compliance with this directive is mandatory and it applies to NASA missions and to NASA contractors, where specified by contract. It is required to be applied to: all space flight missions, robotic and human, which may intentionally or unintentionally carry Earth organisms and organic constituents to the planets or other solar system bodies, and any mission employing spacecraft which are intended to return to Earth and/or its biosphere from extraterrestrial targets of exploration. (NASA NPD 8020.7G)

The NASA Planetary Protection Policy itself is detailed in several documents that include (1) Planetary Protection Provisions for Robotic Extraterrestrial Missions, (2) Biological Contamination Control for Outbound and Inbound Planetary Spacecraft, (3) Handbook for the Microbial Examination of Space Hardware, and (4) Curation of Extraterrestrial Materials (NASA Planetary Protection documents). All these documents and handbooks are applicable to NASA missions.

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In short, there is an interesting regulatory process for achieving protection from cosmic hazard caused by possible contamination of the Earth, planets, and outer space. There exists under Article IX of the Outer Space Treaty a general and broad internationally binding obligation that has been transformed into an international policy, adopted through a nongovernmental scientific body, and that is being implemented through national mandatory compliance mechanisms. This practice is considered to be successful so far, though its adequacy might be challenged in the future. It is believed that the USA is in the lead in this regard, but it is not clear if its practice is being followed to the same extent by other space-faring States. Moreover, the US regulatory practice is limited to NASA (governmental) missions only, and its application to the private sector missions, which are expected to increase, is questionable. On the international level, there is no international treaty, except the Outer Space Treaty as mentioned above, that could be considered directly applicable to the issues of both the outward and backward contamination of the Earth, planets, and outer space. However, Paul B. Larsen advocates for the application of the precautionary principle to the activities on the Moon (Larsen 2006), as expressed in Principle 15 of the 1992 Rio de Janeiro Declaration (UN 1992). Principle 15 of this Declaration specifies: In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.

Increased human activities on the Moon, ranging from tourism to colonization and mining, provide rationale to consider applying this precautionary principle to the Moon prior to the environmental degradation of the celestial body. However, it is doubtful if this principle has become a part of customary international law for it to be considered applicable to the Moon. It can thus be safely said that the current international law and policy on planetary protection is inadequate to meet the challenges of the near future.

Radiation Released by Nuclear Reactors (i.e., Nuclear Power Sources-NPS) The use of nuclear energy (power) is highly risky due to the intentional creation, or possible accidental release, of highly dangerous radiation. However, for some space missions, it is believed that the use of nuclear power sources (NPS) is “particularly suited or even essential owing to their compactness, long life and other attributes” (Nuclear Power Sources Principles, Preamble). Such accidents do happen. Tommaso Sgobba, the Executive Director of the International Association for the Advancement of Space Safety (IAASS), has complied in an unpublished paper the following chronology of nuclear space accidents:

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(a) United States: SNAP 9-A, April 1964: Launched aboard a Department of Defense weather satellite that failed to reach orbit. Reactor, as designed, released radioactive contents in upper atmosphere during reentry and then burned. Remnants struck the Indian Ocean. A total of 2.1 lb of plutonium-238 vaporized in atmosphere and spread worldwide. (b) United States: SNAP 19, May 1968: Meteorological satellite. Nuclear fuel, 4.2 lb of uranium-238, stayed intact and was recovered off Southern California coast and reused. (c) Soviet/Russian: COSMOS 305, January 1969: Soviet unmanned lunar rover lost rocket power and stayed in orbit, dispersing radiation in upper atmosphere. (d) Soviet/Russian: Soviet lunar probe, fall 1969: Unmanned lunar probe burned up and created detectable amounts of radioactivity in the upper atmosphere. Any surviving debris from incident presumed to be on the ocean floor. (e) United States: Apollo 13, 1970: Nuclear material, 8.3 lb of plutonium-238, inside lunar module when it was jettisoned before return to Earth. Now at the bottom of South Pacific Ocean near New Zealand. Sampling so far shows no radiation leak. (f) Soviet/Russian: RORSAT, April 1973: Soviet satellite launch failed; reactor fell into Pacific Ocean north of Japan. Radiation detected. (g) Soviet/Russian: COSMOS 954, January 1978: Launch failed; 68 lb of uranium-235 survived fall through the atmosphere and spread over a wide area of Canada’s Northwest Territories. Canadian-US teams cleaned up; no detectable contamination found. (h) Soviet/Russian: COSMOS 1402, 1982: Failed launch; reactor core separated from spacecraft and fell to Earth separately in February 1983, leaving radioactive trail in atmosphere and landing in South Atlantic Ocean. Not known if any radioactive debris reached the Earth’s surface or ocean. (i) Soviet/Russian: COSMOS 1900, April 1988: Soviet radar reconnaissance satellite failed to separate and boost the reactor core into a storage orbit, but backup system managed to push it into orbit some 50 miles below its intended altitude. (j) Soviet/Russian: COSMOS 1402, February 1993: Crashed into the South Atlantic carrying 68 lb of uranium-235. (k) Soviet/Russian: MARS96, November 1996: Disintegrated over Chile or Bolivia, possibly spreading its payload of nearly a half pound of plutonium. On the proposal of Canada, after the crashing of the COSMOS 954 on Canadian soil, the international community has addressed the issue of the risks posed by the use of NPS. In 1992, the UN General Assembly adopted a resolution, which underlines that the use of nuclear power sources in outer space should “be based on a thorough safety assessment, including probabilistic risk analysis” and be “reducing the risk of accidental exposure of the public to harmful radiation or radioactive material”

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(Nuclear Power Sources Principles, Preamble). The resolution contains a set of principles, goals, and guidelines to ensure the safe use of nuclear power sources in outer space, particularly for the generation of electric power on board space objects for non-propulsive purposes. In brief, the principles included in this resolution specify that the States using NPS for their space objects should endeavor to protect individuals, populations, and the biosphere against radiological hazards and outer space from significant contamination. Nuclear reactors may be operated: (a) On interplanetary missions (b) In sufficiently high orbits (According to Principle 2(b) of the Nuclear Power Sources Principles, the sufficiently high orbit is one in which the orbital lifetime is long enough to allow for a sufficient decay of the fission products to approximately the activity of the actinides. The sufficiently high orbit must be such that the risks to existing and future outer space missions and of collision with other space objects are kept to a minimum) (c) In low Earth orbits if they are stored in sufficiently high orbits after the operational part of their mission (Nuclear Power Sources Principles, Principle 3(2)(a)(iii)) Prior to the launch of an object with NPS, its launching State must ensure that a thorough and comprehensive safety assessment is conducted (Nuclear Power Sources Principles, Principle 4(1)). Any State launching a space object with NPS must in a timely fashion inform the international community on how States may obtain results of the safety assessment prior to each launch and in the event this space object is malfunctioning with a risk of reentry of radioactive materials to the Earth and the radiological risk of nuclear power source(s). After reentry of a space object, and its components, with NPS into the Earth’s atmosphere, the launching State is obliged to promptly offer and, if requested by the affected State, provide the necessary assistance to eliminate actual and possible harmful effects (Nuclear Power Sources Principles, Principle 7(2)(a)). It is interesting to note that, particularly taking into account the special needs of developing countries, it is not only the launching State of the spacecraft with NPS but also all other States and international organizations with appropriate technical capabilities are obliged to provide necessary assistance upon request by an affected State (Nuclear Power Sources Principles, Principle 7). The launching State is internationally responsible and could be held liable if its space object equipped with NPS causes damage. The launching State is liable to pay compensation under the Liability Convention and the compensation must include reimbursement of the expenses for search, recovery, and cleanup operations (Nuclear Power Sources Principles, Principle 9(3)). In addition to the UNCOPUOS, the International Atomic Energy Agency (IAEA), which was created in 1957 to promote the use of atomic energy for peaceful purposes, has made some important efforts in drafting technical standards

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to ensure the safety of NPS. In 1996, it prepared a Safety Series Document on Emergency Planning and Preparedness for Nuclear Powered Satellite Re-Entry (IAEA Document on Nuclear Powered Satellite Re-Entry 1996). Prompted by the COSMOS 954 accident, IAEA designed this Safety Practice: to provide a general and comprehensive overview of the management of incidents or emergencies that may be created when nuclear power sources employed in space systems accidentally re-enter the earth’s atmosphere and impact on its surface. (IAEA Document on Nuclear Powered Satellite Re-Entry 1996)

This fairly detailed and highly technical document is expected to help governmental organizations that are responsible to plan for potential radiological emergencies and to serve as a valuable reference for quick action. Recently, in collaboration with the UNCOPUOS Scientific and Technical Subcommittee, the IAEA published the Safety Framework for Nuclear Power Source Applications in Outer Space (IAEA Safety Framework for Nuclear Power Source Applications 2009). This publication, which “is not legally binding under international law,” has been designed to provide “high-level guidance that addresses unique nuclear safety considerations for relevant launch operation and end-of-service mission phases of space NPS applications” (IAEA Safety Framework for Nuclear Power Source Applications 2009, Preface). As a part of a UN Resolution, the principles on NPS are per se non-binding, but their mandatory language (“shall”) seems to make them more authoritative. They have been supplemented by recommended technical standards and emergency procedures promulgated by the IAEA (a neutral international organization). This regulatory approach is considered to be sufficient and appropriate for ensuring safety and protection against cosmic hazard resulting from the use of nuclear reactors in space. So far, the State practice shows that they have been consistently complied with. For example, the USA notified the UN about the launch of Cassini, the spacecraft powered by 33 kg of plutonium (UN 1997). This joint endeavor of NASA, the European Space Agency, and the Italian Space Agency was launched to study Saturn and its magnetic and radiation environment. However, so far the States using NPS for their space missions have been limited to two or three. A list of the nuclear powered space missions of various States has been compiled by Global Network against Weapons & Nuclear Power in Space (Nuclear Powered Space Missions). The increase in the number of space exploration activities and space actors, especially the private companies, may pose challenge to the effective implementation of these principles. Principle 11 of the Resolution requires the UNCOPUOS to discuss the revision of the principles on NPS. For several years, the Committee has been discussing this issue. During the 2013 meeting of the Scientific and Technical Subcommittee of the UNCOPUOS, some States expressed the need for the continuous implementation of the abovementioned Safety Framework for Nuclear Power Source Applications in Outer Space. However, others expressed that this Framework is “not adequate to meet the challenges posed by the use of nuclear power sources in outer space” and underlined the need for “the regulation of the use of nuclear power sources in outer space, due consideration should be given to relevant norms of international law” (UNCOPUOS 2013b, paragraphs 171–172). Similarly, during the 2013 meeting of

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Legal Subcommittee of the UNCOPUOS, some States expressed “that it was necessary not only to codify international law [related to NPS], but also to strengthen it and to review international instruments such as the Principles Relevant to the Use of Nuclear Power Sources in Outer Space” (UNCOPUOS 2013a, paragraphs 101–102). The debate continues, without any agreement on the type of regulation of NPS in outer space.

Radiation Resulting from Nuclear Tests and the Use of Nuclear Weapons Between 1958 and 1962, both the USA and the Soviet Union carried out several nuclear tests in the upper atmosphere and in outer space to an altitude of 540 km (Johnston 2009). Devastating effects of radiation caused by such tests became known quickly. As early as 1959, “radioactive deposits were found in wheat and milk in the northern United States” (John F. Kennedy Library and Museum). More importantly, “the nature and effects of fallout increased, and as it became apparent that no region was untouched by radioactive debris, the issue of continued nuclear tests drew widened and intensified public attention. Apprehension was expressed about the possibility of a cumulative contamination of the environment and of resultant genetic damage” (US Bureau of Arms Control). After extensive negotiations, the Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water was adopted and signed on 5 August 1963 (Partial Test Ban Treaty). States Parties to the Treaty proclaimed “their principal aim [for] the speediest possible achievement of an agreement on general and complete disarmament [. . .] and [to] eliminate the incentive to the production and testing of all kinds of weapons, including nuclear weapons.” States also sought “to achieve the discontinuance of all test explosions of nuclear weapons for all time, determined to continue negotiations to this end, and desiring to put an end to the contamination of man’s environment by radioactive substances” (Partial Test Ban Treaty, Preamble). This brief Treaty prohibits nuclear weapons tests “or any other nuclear explosion” in the atmosphere, in outer space, and under water, except underground (Partial Test Ban Treaty, Article I(1)(a)). Moreover, the Treaty prohibits underground nuclear explosions if they cause “radioactive debris to be present outside the territorial limits of the State under whose jurisdiction or control” the explosions were conducted (Partial Test Ban Treaty, Article 1(1)(b)). In addition, the States have undertaken to “refrain from causing, encouraging, or in any way participating in, the carrying out of any nuclear weapon test explosion, or any other nuclear explosion, anywhere which would take place in any of the environments described, or have the effect” spreading radioactive debris outside the territorial limits of the State carrying such tests (Partial Test Ban Treaty, Article I(2)). As of June 2014, there are 126 States Parties to this Treaty, while 10 other States have signed it. The Treaty is hailed as a successful agreement as no prohibited nuclear test has been carried since its conclusion. However, its weakness must also not be overlooked. Nuclear weapon States, like China, France, and North Korea, are not Parties to the

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Treaty. By giving 3 months advance notice, a State Party may withdraw from the Treaty, citing that extraordinary events related to the subject matter of this Treaty have jeopardized its “supreme interests” (Partial Test Ban Treaty, Article IV). The Comprehensive Nuclear Test Ban Treaty, which was adopted in 1995 by the UN General Assembly to fill the lacunae of the Partial Test Ban Treaty, has not yet come into force due to the unwillingness of major States, irrespective of the fact that it has already been ratified by 162 States and signed by other 24 States (Comprehensive Nuclear Test-Ban Treaty 1996). More importantly, the commitment of States Parties to the principal aim of the speediest possible achievement of an agreement on the general and complete disarmament and desire to put an end to the contamination of Earth and space environment by radioactive substances still remain unfulfilled after 50 years of the conclusion of the Partial Test Ban Treaty. The use of nuclear and other weapons of mass destruction (WMDs) in outer space or on celestial bodies will cause harmful radiation and contamination of the environment. Tough there is no internationally agreed upon definition of WMD, the Commission for Conventional Armaments in 1948 did attempt to define them as including: atomic explosive weapons, radio-active material weapons, lethal chemical and biological weapons and any weapons developed in the future which have characteristics comparable in destructive effect to those of the atomic bomb or the other weapons mentioned above. (UNGA 1979, paragraph 1)

Thus, WMDs are generally understood to include biological, chemical, radiological, nuclear, or other weapons that have the capacity to indiscriminately cause injury and death on a massive scale and to bring significant destruction to property and environment (Britannica Encyclopaedia). In order to avoid this risk, the placement of such weapons “in orbit around the earth” has been prohibited (Outer Space Treaty, Article IV; Moon Agreement, Article 3). In addition, such weapons must also not be installed on celestial bodies or stationed in outer space in any other manner. Moreover, the Moon and other celestial bodies must be used exclusively for peaceful purposes, and the testing of any type of weapons on celestial bodies is forbidden (Moon Agreement, Article 3(4)). However, it is the placement, installation, and stationing of WMDs that are prohibited, but not their use, which possibly can be made. In the Legality of the Threat or Use of Nuclear Weapons Advisory Opinion, the International Court of Justice did not reach a conclusive decision whether or not the use of nuclear weapons by a State is lawful, particularly when its very survival is at stake (ICJ 1996). Moreover, these prohibitions do not apply to (a) fractional orbital bombardment systems and antiballistic missile systems that may carry WMD but do not complete an orbit around the Earth and (b) antisatellite systems. Therefore, irrespective of these legal controls, cosmic hazards in the form of nuclear radiation and contamination of outer space and celestial bodies remain largely unregulated.

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Conclusion Man-made cosmic hazards are becoming very serious, particularly due to the risks posed by rapidly increasing space debris. Their prevention and mitigation sought by the IADC and UNCOPUOS Guidelines are important first steps, but will certainly not be sufficient in the near future. They must be supplemented by active debris removal (and possibly on-orbit servicing satellites) for which the private companies must be encouraged and facilitated with an internationally binding framework that takes care of several hurdles posed by existing international law and politics. Included in this framework should be provisions related to the clarification of: (a) The responsibility and liability of the launching State for events and damage involving the removal of space debris (b) The jurisdiction and control over objects to be removed or serviced (c) The application of national technology export control regulations (d) Assurance regarding exclusive peaceful nature of active removal operations (e) Cross-waver of liability for damage caused during the course of ADR operations (f) International means for the settlement of debris-related disputes These and several other serious international legal issues ought to be resolved through internationally binding instruments, and it is believed that non-binding resolutions or codes for this purpose will not be sufficient. Regarding man-made cosmic hazards in the form of radiological contamination caused by humans, the international regulatory framework created for the use of NPS seems to have been working satisfactorily. Continuous input and support of the international scientific community (particularly the IAEA) should keep the governance of this issue well on track. It is perceived that the number of players and space missions using NPS in the future will remain small. However, the ongoing deliberations on NPS in the UNCOPUOS (and in both of its subcommittees) can be expected to take care of new developments that will emerge in this field in the near future. Consequently, perhaps, at present, there is no pressing reason for transforming the 1992 UN Resolution on NPS into a binding treaty. However, on the other hand, the case of radiological contamination possibly caused by nuclear weapon tests can become severe, especially because some of the major nuclear weapon States are not parties to the Partial Test Ban Treaty. In this regard, the ratification of the Comprehensive Test Ban Treaty, particularly by these States, becomes critical. These, and other States, should be encouraged to join the 162 States that have already ratified the Treaty in order to bring it into force, not only for enhancing international peace and security but also for protecting mankind from serious cosmic hazard caused by dangerous radiological contamination, which would adversely affect all States.

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Acknowledgement The author wishes to acknowledge with sincere gratitude the help provided by Mr. Kuan-Wei (David) Chen and Dr. Joseph Pelton in reviewing and providing valuable comments on the earlier draft of this chapter that improved the quality of the chapter. As always and notwithstanding this invaluable help, the author remains exclusively responsible for any errors contained in this chapter: Ram S. Jakhu.

Cross-References ▶ Economic Challenges of Financing Planetary Defense ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Major Gaps in International Planetary Defense Systems: Operation and Execution ▶ Planetary Defense, Global Cooperation, and World Peace ▶ Regulatory Aspects Associated with Response to Cosmic Hazards ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards

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Settlement of claim between Canada and the Union of Soviet Socialist Republics for damage caused by cosmos, Canadian Department of External Affairs Communique No. 27, Released on 2 April 1981 UN (1992) Report of the United Conference on Environment and Development, Rio de Janeiro, 3–14 June 1992, Annex I, “Rio Declaration on Environment and Development”, UN Doc A/CONF.151/26 (vol I) UN (1997) Note verbale dated 2 June 1997 from the Permanent Mission of the United States of America to the United Nations (Vienna) addressed to the Secretary-General, UN doc A/AC.105/677 (4 June 1997) UNCOPUOS (2007) Space debris mitigation guidelines. Online UN Office of Outer Space Affairs: http://www.unoosa.org/pdf/bst/COPUOS_SPACE_DEBRIS_MITIGATION_GUIDELINES. pdf. Last accessed 10 July 2014 UNCOPUOS (2011) Scientific and Technical Subcommittee Forty-eighth session, Towards longterm Sustainability of Space Activities: Overcoming the Challenges of Space Debris A Report of the International Interdisciplinary Congress on Space Debris, UN Doc A/AC.105/C.1/2011/ CRP.14 (11 February 2011) UNCOPUOS (2012) Scientific and Technical Subcommittee Forty-ninth session. Active debris removal – an essential mechanism for ensuring the safety and sustainability of outer space: a report of the international interdisciplinary congress on space debris remediation and on-orbit satellite servicing, UN doc A/AC.105/C.1/2012/CRP.16 (27 January 2012) UNCOPUOS (2013a) Fifty-sixth session, Report of the Legal Subcommittee on its fifty-second session, held in Vienna from 8 to 19 April 2013, UN doc A/AC.105/1045 (23 April 2013) UNCOPUOS (2013b) Fifty-sixth session, Report of the Scientific and Technical Subcommittee on its fiftieth session; held in Vienna from 11 to 22 February 2013, UN doc A/AC.105/1038 (7 March 2013) UNGA (1979) Conclusion of an international convention prohibiting the development, production, stockpiling and use of radiological weapons, UN Doc. A/RES/34/87A (11 December 1979) US, Licenses for the Export of Defense Articles, 22 Code of Federal Regulations }123.1 US Bureau of Arms Control, Verification and Compliance, Treaty banning nuclear weapon tests in the atmosphere, in outer space and under water. Online US State Department: http://www.state. gov/t/isn/4797.htm. Last accessed 10 July 2014

Risk Management and Insurance Industry Perspective on Cosmic Hazards Scott Ross

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cosmic Hazards: Identified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NEO Occurrences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar flares and coronal mass ejections (CME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Flare and CME Occurrences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orbital Debris Occurrences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Worldwide Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Insurance Market . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Private Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Public Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hybrid Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Derivative Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Market Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solar Flares: Lloyd’s Realistic Disaster Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Liability Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Liability Occurrences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Outer Space Treaty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Liability Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Intergovernmental Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ultrahazardous Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Price-Anderson Act . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Commercial Space Launch Act . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spaceflight Participant Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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S. Ross (*) Global Aerospace, Inc., Parsippany, NJ, USA e-mail: [email protected] # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_78

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Near-Earth Object Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tunguska Event Over New York City . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biological Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract “A good rule of thumb is to assume that everything matters.” Richard Thaler

Quantifying risk is a survival mechanism innate to the human race. From the days cavemen built shelters to protect themselves from the elements, the goal has been to mitigate risk. In modern society, insurance, which spreads risk among many to protect the few who have losses, is the backbone of risk mitigation. The hazards addressed are those thought to have the highest probability of causing bodily injury or property damage. Fire, flood, hurricane, and earthquake are common perils covered by insurance. Cosmic hazards including meteors, coronal mass ejections, solar flares, and orbital debris-related accidents are rare events. Individuals, corporations, governments, and insurance companies do not believe the risk is relevant to them so they do not address it. Even the well-publicized recent meteor event over Chelyabinsk, Russia, causing $30 million in damages and wounding over 1,600 people certainly will not change this (Borenstein S, Russian meteor in chelyabinsk may mean space rocks pose bigger risk than we thought. Huff Post, Science. http://www.huffingtonpost.com/2013/11/06/russia-meteor-chelya binsk-space-rocks-risk-studies_n_4227270.html. Accessed Sept 2014, 2013). While cosmic hazards are off the radar, it does not mean that insurance is not available to cover the damage caused by them. The effects of cosmic hazards are similar to natural catastrophes and covered by insurance in the same way. Insurance policies are written covering all risks of loss with no specific exclusions for cosmic hazards. So, by default insurance companies are covering cosmic hazards. However, if the frequency or severity of hazards does reach consciousness, then insurers will limit coverage, charge a premium for it, or exclude it all together.

Keywords

Asteroid • Carrington event • Catastrophic bond • Commercial Space Launch Act (CSLA) • Comet • Coronal mass ejection (CME) • Halloween storm • Insurance-linked security • Kessler syndrome • Montreal event • Near-earth object (NEO) • Price-Anderson act • Reinsurance • Solar flare • Space debris • Ultrahazardous insurance

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Introduction “Risk comes from not knowing what you’re doing.” Warren Buffet

The earth is spinning and orbiting the sun as it has since its creation. Earth is not alone and is constantly in harm’s way of activities on the sun, comets, asteroids, orbital debris, and unknown biological contagions. History has shown that near-earth objects have caused devastation to all living things on earth. Cosmic hazards from a risk management perspective follow the same process as all other risks. The exposures are analyzed on the basis of frequency and severity. Risk mitigation options are weighed as whether to retain, avoid, reduce, or transfer the risk through the use of insurance. If available, insurance is proven to be the best risk mitigation tool. It is beneficial to society by promoting safety prior to occurrences, indemnifying insureds, and kick starting local economies after catastrophes have struck. While large catastrophic events from cosmic hazards are rare, the possibility exists. Like natural catastrophes in recent decades, the losses they can cause will increase in the future due to worldwide population growth, increase in urbanization, and concentration of exposures in coastal areas. Today earth is home to well over seven billion people, double of what it was in 1970. By 2024, the population will likely reach 8 billion, and the United Nations projects it will reach 10–12 billion by the end of the century (UN 2012). Property values will continue to rise as well. As of 2012, in the United States, there is $65 trillion in insured property and $11 trillion of that is located in coastal counties (AIR 2013). As sophisticated as modern insurance companies are with actuarial models, history proves over and over that no one can accurately predict the future. Insurance has its limits and large catastrophes can lead them to fail. This not only affects the stockholders of the company but places a large burden on policy holders, local economies, and the government. This chapter is written from a US perspective. International treaties and worldwide insurance market figures are universal in scope, while more specific regulations are US centric such as CSLA and flood insurance. Similar regimes to those discussed are in place around the world, and it is recognized they may be more advantageous than the US versions.

Cosmic Hazards: Identified The initial step in the risk management process is to identify the risks. Cosmic hazards include anything outside the earth’s atmosphere that can cause harm to people or property. There are four categories of cosmic hazards based on the damage they each cause and as such the insurance that applies. Near-earth objects

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can damage satellites but the greatest concern is the catastrophic potential they can cause on the ground. Solar hazards can be very detrimental to satellites in orbit but could be devastating to the earth’s electrical grids as well. Orbital debris is primarily seen in terms of probability of occurrence as a concern for satellites in orbit. Biological hazards are a concern for all people on earth. Near-earth objects (NEO) include comets, asteroids, meteors, meteorites, and bolides that can cause damage to the earth by impact or explosion resulting in any combination of wind, fire, earthquake, or flood. These are covered perils under standard homeowners and commercial general liability insurance policies. Earthquake coverage is not standard but it can be purchased. Flood coverage is excluded from traditional insurance and in the United States must be purchased from the government-run National Flood Insurance Program (NFIP). A quick mention of the descriptions of NEO may be helpful. Most objects directed toward the earth will burn up in the earth’s atmosphere depending on size and velocity of the object. These are referred to as meteors. Objects that are larger than meteors and explode once hitting our atmosphere are referred to as bolides. Objects that penetrate the atmosphere and strike the ground or oceans are meteorites. Asteroids orbit the sun and can be very large up to 1,000 km across and travel at very high speeds. Comets come from the farthest reaches of the solar system and have the highest velocity. The amount of damage caused by a near-earth object event can vary depending on many factors. The location of the event on the earth could mean the difference between no damage and a catastrophic event. As over 70 % of the planet is covered by water or ice, this would reduce exposure to people and property unless the force is great enough to create a tidal wave or tsunami. The Tunguska, Russia, event of 1908 was over land but in an uninhabited area so the only damage was to trees. Had such an event occurred over a large city, the outcome would have been much different. Such a scenario is described later. The power of a NEO occurrence depends on size, composition, velocity, and the angle at which it hits the atmosphere. Three levels of criticality can be discussed as to what is an insurable event. The first would be objects that burn up in the atmosphere or impact the ground or water with minimal damage. The maximum damage may be thought of as to a small area such as a single house. This is not a large concern to the insurance industry due to the low severity and low frequency of an occurrence. The second level is an area where insurance applies and encompasses objects that explode in the atmosphere or impact an area that can cause significant economic damage. Chelyabinsk is considered to be a 100-year event and would fall in the low end of this level. Tunguska incident of 1908 would be on the upper end of this level. The third level of damage would be a climate-altering event that would cause global destruction that would leave insurance to be inconsequential. Such an event would involve a 1 km or larger-diameter meteor. A meteorite this size could cause worldwide catastrophic climate change wiping out life and vegetation such as the K-T mass extinction event that occurred 65 years ago.

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NEO Occurrences • In Chelyabinsk, Russia, in 2013, a 17–19 m diameter meteor exploded over the city injuring over 1,600 people with estimated losses of over $30 million. This is an insurable event. • In Tunguska, Russia, in 1908, large air burst of a 50 m diameter comet or asteroid over Central Siberia. Trees were leveled over 2,000 km square. The area was uninhabited and remote with only trees damaged. • In Yucatan Peninsula (Chicxulub), 65 million years ago, a 5–6 km diameter asteroid caused huge tidal waves and severe worldwide climate change and led to the extinction of 70 % of all species on earth.

Solar flares and coronal mass ejections (CME) arise from eruptions of high-energy radiation and ions from the sun’s surface. Flares are associated with sunspots and they may or may not be accompanied by coronal mass ejections. When a flare occurs, plasma accelerates energy almost to the speed of light. This plasma of energy is highly charged radiation and can damage satellites and electric grids on earth. Coronal mass ejections contain billions or even trillions of tons of ions that can trigger a natural electromagnetic pulse (EMP). Damage to electric grids can cause widespread blackouts. As society becomes more dependent on electrical devices for communication and navigation (GPS), the loss of power grids or satellites becomes more detrimental. The space insurance market insures damage to insured satellites. The coverage is all risk and does not exclude damage from solar activity. Government satellites such as those in the Global Positioning System are not insured. As to the risks on the ground, standard homeowner’s policies exclude electrical outage caused away from the home so they are left in the dark. But, business interruption insurance or contingent business interruption for companies would provide coverage. Should there be a prolonged widespread electrical outage, it would be very costly for the insurance industry indeed. There are ways to improve the infrastructure of electrical grids so they are better protected from geomagnetic storms. Transformers and transmission lines can be better constructed with insulation against the elements. The use of capacitors and heavy-duty circuit breakers designed to shut off and stop the spread of highly charged currents could reduce the spread of the loss of the grid and blackouts. The 1989 Canadian event could have propagated to a much larger portion of the United States had it not been for a few dozen capacitors. Thus, most of the damage in the United States was largely contained to the Chicago area.

Solar Flare and CME Occurrences • Halloween Storm, 2003. Solar activity started in mid-October and lasted almost 5 weeks. The most powerful x-ray flare CME event recorded since satellites

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started measuring them in the 1970s occurred on November 4, 2003, and took only 19 h to reach earth from the sun. The storm caused power outages in Sweden, caused astronauts on the International Space Station to take cover, and damaged satellites. Twenty-eight satellites were damaged and two were destroyed. The Japanese Midori 2 satellite was one of the satellites destroyed and it was valued at $570 million (Satellite Digest 2003). Because it was a government-funded satellite, there was minimal insurance. • Montreal Event, Canada, 1989. The Canadian Hydro-Quebec power grid was brought down in two minutes by the strongest geomagnetic storm ever measured in recent times. Six million people lost power. The economic cost was $12.7 billion (ABC 2013). • Carrington Event, 1859. Carrington was a solar astronomer who recorded huge sunspots on the sun. The CME associated with the sunspots traveled to earth in 17 h. The solar eruption started fires in telegraph offices. Auroras were bright enough to read by. This event was before the era of satellites so there was no damage to be caused there. A similar storm today could cause more than $2 trillion to electrical infrastructure (Ferris 2012). Orbital debris is also called space junk. It is the debris field circling the earth created by man from sending objects into space since Sputnik in 1957. As of 2014, some 22,000 pieces of debris larger than 5 cm are being tracked. There are another 300,000 pieces about the size of a marble with a substantial amount of kinetic energy. The highest density of debris resides in the lower earth orbits (LEO) – about 45 % of the 6 t of debris in the earth orbit (NASA Orbital Debris Program Office 2014). A theory posited as the Kessler syndrome states that if the debris becomes dense enough, collisions between objects could cascade with each collision generating orbital debris, which increases the likelihood of further collisions. The damage we are most concerned about is that to orbiting objects in space that are operational including commercial and military satellites, the ISS, and the deorbit of any of this debris. Insurance is available for satellites in orbit. As regards bodily injury or property damage to those on the ground, insurance would be available concerning health, life, or property, but there could be liability on behalf of the “owner” or launching state of the object that caused a loss to a third party. The deorbit of large debris can be detrimental to people and property on earth. Large objects can include space stations or satellites that have reached the end of their useful life. Just as the deorbit of Skylab and Mir were of concern, the eventual deorbit of the ISS will be greater still. Deorbit events of such space stations, satellites, or spent rocket stages have been and are insurable for liability to third parties.

Orbital Debris Occurrences • Satellite collision, February 10, 2009. Iridium 33 and Cosmos 2251 collided at altitude of 789 km. Iridium was an operational communications satellite, while

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the Cosmos was deactivated as past end of life. Neither satellite was insured. In March 2011, the ISS made an avoidance maneuver due to debris from this collision. Chinese anti-satellite missile test, January 11, 2007. A Chinese weather satellite, FY-1C, at an altitude of 865 km was intentionally destroyed by a Chinese missile. This was the largest recorded creation of orbital debris in history with 150,000 debris particles, of which over 2,500 are large enough for active tracking. Space Shuttle Columbia, February 1, 2003. Seven astronauts were killed when the shuttle disintegrated. Over 80,000 pieces were recovered which were spread over 72,500 square km of Texas and Louisiana. Analysis by the US Federal Aviation Administration (FAA) estimated that there was on the order of a 1 % probability that an aircraft could have been hit by the falling debris. Mir Russian Space Station, March 23, 2001. Above the Pacific Ocean near Fiji, the 130,000 kg station broke into 1,500 fragments. Skylab US Space Station, July 11, 1979. The 70,000 kg station fell into the Indian Ocean and parts of Western Australia.

Biological hazards could be introduced to our planet from anything that reenters our atmosphere from space. This could apply to astronauts or any material from moons, planets, asteroids, or other celestial objects. The concern is bodily injury caused by a contagious agent that could reach epidemic or pandemic scale. Dangers from the cosmos causing sickness or death to people would be covered by health and life insurance. The insurance implications are reviewed later in the chapter.

Insurance “The first step in the risk management process is to acknowledge the reality of risk. Denial is a common tactic that substitutes deliberate ignorance for thoughtful planning.” Charles Tremper

Modern insurance started as fire insurance to protect property in response to the 1666 Great Fire of London. The general principle of insurance is to pool the exposures of the many to pay for the misfortunes of a few. Insurance is a contract to pay should a covered event occur. Today there is an insurance market available for almost any risk that is viewed as measurable and not catastrophic for a price. Every organization must manage its risk including insurance companies. Insurance companies not only have a responsibility to society to provide coverage but as corporations to their stockholders as well. How do insurers evaluate the unique exposures of cosmic hazards? Insurance companies require that a group of exposures have the following characteristics in order to qualify as an insurable risk (Baranoff et al. 2014): 1. Large number of similar exposure units. Insurance operates through the pooling of risks, and the larger the number of similar risks insured, the more predictable

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the losses. Insurance companies can debate how large that number must be in order to make the risk predictable. Life insurance risk is very predictable as the number of units is very large. Space insurance that may have only 30 satellites launched a year on various launch vehicles is very unpredictable. How one qualifies a one in 100 year meteor event is more difficult. Definite loss. The loss needs to be identifiable as to when it happens, where, and with a known cause. Meteor strikes would meet these criteria, but orbital debris damage to a satellite or a contagious biological hazard affecting a large number of people may not. Fortuitous or accidental loss. The loss must be outside the control of the insured. There must be an element of uncertainty as to the occurrence of risk or the time of the occurrence. Large loss. The insured must view the insurance to be of value based on the size of a loss. Losses that would not have any large financial effect on the insured would not be worth paying a premium to protect. Affordable premium. If the cost to insure is greater than the cost to the insured to retain the risk, then it makes little sense to purchase insurance. Cosmic hazards are not currently directly addressed by insurance. Should a market develop, it may be expected that due to the large catastrophic nature, a large premium would be charged. Calculable loss. The probability of the loss must be calculable, and the amount of the insurance payout must be well understood as to the value when a claim is made. A nuclear event could affect millions of people, but the standards for nuclear power stations require the probability of a major radioactive release be below 1 in 10,000. A tsunami hitting the United States could be devastating, but estimates suggest it would occur once every thousands of years. Lastly, the chance of a large meteorite hitting a large city is currently thought to have the probability of perhaps being less than 1 in a million per year. Recent data from the nuclear monitoring system indicates that meteor strikes are more common than previously thought and the growth of urban centers to cover much more land will likely alter these assessments. Limited risk of catastrophic losses. Insurable losses must have a low probability of affecting all insureds at once. Insurers must be able to spread their risk in order not to risk bankruptcy. Using the example of earthquake, hurricane, or flood insurance, the insurers limit their exposure in specific geographic areas to protect themselves should there be a large event. Reinsurance is a mechanism for insurance companies to further spread their risk and is available to all lines of insurance including aerospace and space markets.

Worldwide Insurance Worldwide insurance premiums in 2012 including life and nonlife were $4.61 trillion. Nonlife insurance includes accident, health, and property casualty insurance.

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Table 1 Largest buyers of insurance by country Top ten countries by life and nonlife direct premiums written, 2012 Country Population Premium (US$mn) United States 316,668,567 $1,270,884 Japan 127,253,075 $654,112 United Kingdom 63,395,574 $311,418 China 1,349,585,838 $245,511 France 65,951,611 $242,459 Germany 81,147,265 $231,908 Italy 61,482,297 $144,218 South Korea 48,955,203 $139,296 Canada 34,568,211 $122,532 The Netherlands 16,805,037 $100,342 Total 2,165,812,678 $3,462,680

% premium 27.55 14.18 6.75 5.32 5.26 5.03 3.13 3.02 2.66 2.18 75.08

Source: 2014 International insurance fact book (Swiss Re, sigma, No. 3/2013)

Life insurance was $2.62 trillion and nonlife $1.99 trillion (Insurance Information Institute (iii) 2014). In looking at the largest buyers of insurance, the top 10 countries represent 75 % of the world insurance premiums while only 30 % of the population. See Table 1. The United States and Japan alone purchase 42 % of the premium while representing only 6.25 % of the world population. This disproportion leaves areas of the world with large populations with much lower levels of insurance (Insurance Information Institute (iii) 2014). Looking at the largest countries by population and the amount of insurance they purchase, it can be seen that cumulatively they represent 58 % of the world population. See Table 2. When the United States and Japan, who are the largest buyers of insurance, are removed from these figures, it is noted eight of the largest countries in the world representing 52 % of the world population purchase just 9.5 % of the worldwide insurance (Insurance Information Institute (iii) 2014a). Insurance has a positive effect on society. Countries with lower per capita income must overcome larger economic losses from natural catastrophes than wealthier countries. By having adequate insurance, the effects of a catastrophe can be mitigated. Insurance provides incentives for people to reduce risk in order to reduce premiums. Insurers will require mandatory safety measures such as improved building codes that can save lives. Insurance pays losses promptly which can limit business interruption expense and help the local economy rebound. Poor countries bear the brunt of the damage. In 2013 two natural catastrophes had vastly different effects on local economies. Typhoon Haiyan in the Philippines caused $10 billion in total losses and 6,000 fatalities. Only 7 % of the losses were insured and the balance will burden the government for years. In contrast, Germany had hailstorms causing $4.8 billion in damage while 80 % of the losses were insured which had little effect on the economy. It is a compounded problem for poor

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Table 2 Largest countries and insurance premiums Ten most populated countries (July 2013) Life and nonlife direct premiums written, 2012 % of world Country Population population China 1,349,585,838 19.00 India 1,220,800,359 17.20 United States 316,668,567 4.46 Indonesia 251,160,124 3.54 Brazil 201,009,622 2.83 Pakistan 193,238,868 2.72 Nigeria 174,507,539 2.46 Bangladesh 163,654,860 2.30 Russia 142,500,482 2.00 Japan 127,253,075 1.79 Total 4,140,379,334 58.32

Premium (US$mn) $245,511 $66,441 $1,270,884 $15,509 $82,267 $1,559 $1,828 $1,044 $26,027 $654,112 $2,365,182

% of world premium 5.32 1.44 27.55 0.34 1.78 0.03 0.04 0.02 0.56 14.18 51.26

Source: 2014 International insurance fact book (Swiss Re, sigma, No. 3/2013)

countries because they not only do not purchase insurance but also unable to put safety measures in place to mitigate the losses when a catastrophe occurs (Munich 2014).

Insurance Market Insurance can be available from the private sector and government, and today there are new derivatives that can be used to access increased amounts of insurance. While coverage can be found for almost any risk, costs can be prohibitive and capacity can be an issue for certain lines of insurance. There is no specific coverage for meteorites, bolides, or even biological exposures. These cosmic hazards are treated in the same way natural catastrophes are by insurance. So a description of many lines of insurance is worth mention be it private, public, hybrid, or derivative.

Private Insurance Private insurance is what we think of as traditional insurance. It includes incorporated companies insuring life, health, and property casualty insurance. Property casualty insurance covers commercial general liability including business interruption, automobile, homeowners, marine, aviation, and space. Cosmic hazards are not excluded from any of these lines of insurance. Life and health coverages, with few exceptions, pay regardless of the cause of the loss. There are standard exclusions for

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flood and earthquake. Flood insurance can be purchased in the United States from the National Flood Insurance Program (NFIP) (see below). Earthquake coverage is available but is not often purchased except in susceptible areas.

Public Insurance Governments step in to provide insurance when it is unavailable or perceived to be cost prohibitive in the private sector. In the United States, the National Flood Insurance Program (NFIP) was created in 1968. There is no coverage for flood under standard homeowner, renters, or commercial property policies. Coverage is available from NFIP and some private insurers. The program was able to cover its losses until 2005 when Katrina required the program to borrow $16.8 billion from the treasury to cover the huge number of claims (GAO 2008). The program has been unable to charge adequate rates to cover losses which once again happened with the occurrence of super storm Sandy. There are no exclusions in the coverage for flood or tsunami caused by meteorites.

Hybrid Insurance Hybrid insurance is a combination of private and public programs. Nuclear facility insurance promulgated under the Price-Anderson Act and commercial launch liability insurance organized under the Commercial Space Launch Act (CSLA) in the United States are described later. These examples combine a layer of private insurance with excess layers of coverage provided by the government. Both programs came into effect to address the unavailability of insurance at the high limits of liability required to address what could be catastrophic events caused by ultrahazardous activities. Both programs were able to attract needed capacity and have been very successful. Similar programs have been developed in France and other countries.

Derivative Insurance Derivative insurance was started in the 1990s using insurance-linked securities (ILS) via catastrophe bonds. This was in response to the view that after hurricane Andrew and the Northridge earthquake, natural catastrophe exposures have grown. Because of population growth, rising real estate values, and development in coastal areas, the world is exposed to higher losses. In the United States, over 68 million people live in coastal areas susceptible to hurricanes, and 80 % of Californians live near active earthquake faults (GAO 2002). ILS provides a new way for insurance and reinsurance companies to spread their risk to new risk takers. The increased capacity prevents insurers from having to limit coverage or raise premiums. The catastrophe bond market by the end of 2013 has grown to $20.3 billion. Insurance or reinsurance companies to bundle risks and attract new capital have

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always sponsored catastrophe bonds. The Metropolitan Transportation Authority in New York (MTA) in response to a reduction in available insurance after super storm Sandy completed a $200 million storm surge catastrophe bond offering. This was the first cat bond tied solely to storm surge and the first cat bond sponsored by a public entity that was not an insurance company (Mayer Brown 2013). Natural catastrophes will continue to generate higher losses in the future so new capacity of any kind is beneficial to the strength of the insurance market as a whole.

Space Insurance Space insurance covers the value of a satellite during launch and on-orbit operations until end of life. Commercial satellite owners or anyone who wants to protect their financial interest in a satellite purchases insurance. Government and science satellites such as GPS or weather satellites are typically not insured as they are public assets even though insurance could be available. Coverage includes the cost of the satellite, the launch, and insurance. Should a satellite become unusable, the reimbursement of each of these costs would be required to fully indemnify the satellite owner. Insurance is typically purchased in annual increments. The most exposed phase is the launch followed by the commissioning period, the time from final release from the launch vehicle until solar arrays deploy and it is fully operational. Satellite insurance is all-risk coverage with only a small set of exclusions. Due to the inaccessibility of space when a loss occurs, it may not be possible to find the cause of loss so all-risk coverage is the best approach. Exclusions cannot be enforced if the cause of loss is unknown. In part the standard exclusions include war, anti-satellite device, confiscation, nuclear reaction or radioactive contamination (except radiation naturally occurring in space), electromagnetic or radio frequency interference, willful acts of named insured, loss of revenue, and consequential damages. Insurance pays for any loss not excluded. The space insurance market currently insures approximately 205 satellites in orbit valued at $26 billion. On average there are about 30 insured satellites launched a year. The total space insurance market premium is currently about $750 million a year. Just two large satellite failures a year can wipe out an entire year’s premium (Global Aerospace 2014). Any increases in the frequency or severity of orbital debris, solar flares, launch vehicle failures, or generic product defects could lead to a capacity crunch. Insurance companies would take note and for their own survival would have to exclude coverage for such events or limit their exposure completely by exiting the space insurance market.

Space Market Capacity The capacity of a market is the amount of coverage it can provide if each insurer provides its maximum line of insurance. A space insurance policy is backed by

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multiple insurers each taking a quota-share amount of the value of the satellite. They may in turn resell the premium to yet other insurers. This process is known as reinsurance. In today’s market, the maximum sum insured that can be covered is around $600 million. So, if a satellite owner wants to insure their satellite for $700 million, they will find only $600 million will be available. Capacity can quickly become an issue when values exceed market capacity. Dual payloads on a single launch vehicle can exceed the capacity. As private industry gets more involved with space tourism or manned transports, they will look to insure their assets. The value of such spacecraft will likely exceed space market capacity and the search for new capacity will begin. Traditional property casualty markets will be looked to for capacity, but because this is property insurance and not liability, ILS or governmental options for additional capacity will not be available. The space insurance market is a subset of the overall aviation insurance market that includes airlines, aerospace manufacturers, general aviation, and war coverage. Space is just 15 % of the aviation market (Aon 2014). The aviation market worldwide is just a quarter of a percent of the world’s property casualty market. If space capacity is to increase, the effort will be to bring in non-aviation markets.

Solar Flares: Lloyd’s Realistic Disaster Scenarios Cosmic hazards pose risks to satellites in orbit while not of great concern during launch or deorbit. If orbital debris is large enough to be tracked or a solar event spotted soon enough, there may be time for loss mitigation. Satellites can be turned away from the oncoming debris or be placed in safe mode in case of a solar storm. Even the ISS has taken evasive action when debris has been detected in its path. These mitigation techniques are very limited and spacecraft remains at the mercy of the hostile space environment. Solar flares and CME can damage a large number of satellites simultaneously, which could overwhelm the space insurance market. Lloyd’s of London has established Realistic Disaster Scenarios (RDS), which address underwriters’ risk. This is a risk management procedure based on possible catastrophic events for the insurance company to test how robust their portfolio is. Due to the catastrophic nature of a solar flare event, a RDS addresses it. The proton flare RDS reads in part as follows: For the purposes of this RDS, it should be assumed that either a single anomalous large proton flare or a number of flares in quick succession results in a loss to all satellites in synchronous orbit. All live exposures in this orbit will be affected by the proton flare. Managing agents should assume a 5 % insurance loss to all affected policies. (Lloyds 2014)

In answer to this, if 95 % of the $26 billion in insured satellites are GEO and there is a 5 % insurance loss to the GEO satellites, the loss is $1.2 billion. This is a rough overview of the RDS and this amount would represent a full market loss. Because the scenario is based on a 5 % loss of every risk, there is no differentiation on a specific portfolio. Underwriters may want to make further review as an actual

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event would likely damage some satellites more than others in which different underwriters would have different results based on the satellites they participate on and how large of a quota-share line they take on each.

Space Liability Insurance Third-party liability insurance is available for satellite launches for the launch provider, for owners of satellites in orbit, or owners when a deorbit event takes place like a space station or large satellite that may cause damage on earth. Product liability insurance is also available for components of launch vehicles or satellites. The insurance covers bodily injury as well as property damage. Bodily injury to astronauts has never been a focus as they have always been the responsibility of the launching state. But, in the not too distant future, considerations must be made for bodily injury to spaceflight participants, the FAA nomenclature for space tourists. Cosmic hazards do not affect space liability insurance except as regards orbital debris. The exposure comes when a satellite has exceeded its operational life and it becomes another piece of orbital debris. The owner of the satellite will have a liability exposure as long as the satellite remains in orbit. In-orbit liability for satellites that are no longer operational is rarely purchased. Upper stages of launch vehicles can also create orbital debris. While launch liability is primarily focused on the losses that can be caused on earth, there can be this exposure in orbit. The space insurance market addressing satellites is very specialized and underwriters are knowledgeable about space and rocket science. Liability underwriters, on the other hand, may be found in the broader aviation market that addresses products liability or other aviation liabilities. Launch liability for US providers has always resided in the comprehensive product liability policy. The market capacity for liability is based on sub-limiting exposure by each market rather than the amount of worldwide capacity, as is the case for the space markets. Limits are based on appetite of insurers as well as dictated by laws in each country or international treaties. Governmental regimes and treaties are stated below. Launch liability primarily addressing bodily injury and property damage on earth has limits of liability based on the governing laws of the launching state. In the United States, it is based on the maximum probable loss under CSLA, and that limit varies depending on size of launch vehicle and location of launch but does not exceed $500 million. $500 million per occurrence is currently the maximum available limit for launch liability worldwide (CSLA 1984). In-orbit satellite liability covers damage to third party to satellites and space stations including inhabitants in orbit or on earth in the event of a deorbit. The limits purchased are at the option on the owner but may be dictated by the launching state. Required limits are usually $100 million or less. Property damage to satellites can be endorsed to product liability policies to cover component parts of launch vehicles or satellites. Currently, this coverage is limited by underwriters to $250 million for any one satellite.

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Space Liability Occurrences • Space Shuttle Columbia, 2003. Seven astronauts were lost on Space Shuttle Columbia when it exploded over Texas. Wreckage debris spread over 100 miles from which NASA collected 45,000 pieces. NASA issued claim forms to anyone wanting to make a bodily injury or property damage claim arising from the fallen debris. Few claims were made (Manikowski 2005). • Delta II 1997 launch failure damaged a few buildings and destroyed and damaged cars for which claims were made. • Space Shuttle Challenger, 1986. Seven astronauts died and product liability claims were paid by Morton Thiokol and the Federal Government. Apollo I, 1967. Three fatalities generated product liability claims against North American Rockwell. Space liability arises from treaties and regulations and significant ones are reviewed below. The most significant concept that is incorporated in the relevant legislations is that of cross waiver of liability. In an effort to reduce third-party claims, each party agrees not to make claims against the other while participating in the specific space activity. Additionally, the cross waivers flow down to related parties including contractors, subcontractors, and customers.

The Outer Space Treaty The United Nations Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies came into force in October 1967. The Outer Space Treaty provides the basic framework on international space law, including the following principles: • States shall be responsible for national space activities whether carried out by governmental or non-governmental entities. • States shall be liable for damage caused by their space objects. • States shall avoid harmful contamination of space and celestial bodies (UN 1967).

The Liability Convention The United Nations Convention on International Liability for Damage Caused by Space Objects of 1972 provides that a launching state shall be absolutely liable to pay compensation for damage caused by its space objects on the surface of the earth or to aircraft and liable for damage due to its faults in space. The convention also provides for procedures for the settlement of claims for damages. The problem with placing all liability on the launching state has created a variety of problems

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with the rise of commercial space activities and the transfer of ownership of spacecraft (UN 1972).

The Intergovernmental Agreement The International Space Station Intergovernmental Agreement (1998), or IGA, is the treaty signed by the partners (Canada, Europe, Japan, Russia, and the United States) involved in the space station. The framework dictates that each of the partner countries shall be responsible for their nationals and the portions of the ISS they provide. The IGA recognizes the Liability Convention of 1972 and establishes cross waivers of liability between the partners, and each partner shall implement the cross waivers with any contractors or subcontractors (IGA 1998).

Ultrahazardous Insurance When in their infancy in the United States, the commercial launch and commercial nuclear industries faced the same issue of how to promote the privatization of an ultrahazardous activity. Insurance was just not available in the amounts required should an accident occur due to the large catastrophic nature.

The Price-Anderson Act The Price-Anderson Act became law in 1957, and its purpose was to ensure the availability of a large pool of funds to compensate the public in the event of a nuclear or radiological accident regardless of who is liable. The purpose of including this law is it provided the framework for CSLA. Also, it demonstrates needed cooperation between the private sector and government to address inadequate market capacity for liability limits of insurance. Coverage applied to a facility on an omnibus basis in that the same coverage provided to the owner/licensee is extended to anyone having exposure for design, construction, or operation of the facility. Three tiers of protection were put in place as stated below (Price-Anderson 1957): 1. Insurance with a limit of $375 million paid for by each facility and insured by a pool of 60 companies (American Nuclear Insurers). 2. Self-insurance that is a fund each facility contributes to and currently amounts to $12.6 billion. This is a mutual insurance where each facility is partnering with the others to create a pool of funds. 3. Congressional mandate. To date the ANI has paid out $151 million with $70 million of that related to the 1979 Three Mile Island accident and $65 million claims to the Department of

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Energy (NEI 2014). Outside the United States, the costliest nuclear accident was in Kiev, Ukraine, at Chernobyl in 1986 that cost $6.7 billion and killed 4,056 people. This excludes the meltdown in 2011 at Fukushima, Japan, which although a major nuclear accident did not directly kill people due to nuclear exposure. The payout from this event continues to produce major payout of claims (Insurance Information Institute (iii) 2014).

The Commercial Space Launch Act The Commercial Space Launch Act of 1984 (CSLA) was modeled after the PriceAnderson Act. The purpose of CSLA was to encourage commercial space launches by the private sector. Private companies required assurances from the government that they would be protected should catastrophe strike (CSLA 1984). The Federal Aviation Administration Office of Commercial Space Transportation (AST) licenses each launch provider. There are three tiers to the program: 1. Insurance. The launch provider is the licensee and they apply to FAA/AST for a launch license. The FAA calculates a maximum probable loss (MPL) based on the type of launch vehicle, the launch location, and the mission. The licensee must purchase insurance up to the amount of the MPL up to a maximum of $500 million ($100 million for government property). Importantly, cross waivers are to be in place for the government, contractors, subcontractors, and customers of the launch provider with a flow down requirement. 2. The second layer of CSLA provides that by congressional appropriation of funds up to $1.5 billion in 1984 dollars (As of 2012, the inflation adjusted amount $2.7 billion). 3. The third tier of coverage reverts back to the launch provider. Outside the United States, similar insurance structures have been implemented to protect the private launch industry. Most countries have used CSLA as a model but often improve on it. Russia, France, China, and Japan require insurance for the first tier but it is typically $300 million or less, and the second tier of government indemnification has no upper limit so there exists no third tier exposing once again the launch provider. The laws in these countries also do not contain a sunset clause as is the case in the United States. The presence of a sunset clause that could end the program leaves the future uncertain for launch providers and makes them less inclined to invest.

Spaceflight Participant Exposure Bodily injury to humans in space is now limited to travel on the Soyuz (post shuttle), International Space Station (ISS), and Chinese programs. Soon it appears the exposure shall increase with the onset of space tourism, a replacement shuttle,

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and projects underway to travel back to the moon and even Mars. While the IGA and the Space Treaties discussed address a legal framework for the ISS, the United States has yet to solidify a structure for space tourism. Initially, space tourism will be suborbital parabolic flights that will not reach orbit. The launch vehicles for spaceflight participants are new and have yet to accumulate proven performance. There is little to compare it with but one could look at the space shuttle experience as a guide. The Challenger and Columbia disasters represented the two failures over 135 shuttle missions and 14 astronauts perished of 848 (NASA 2014). It could be argued that the private sector will not be as disciplined as NASA and the failure rate could be greater than one failure every 68 missions or one in every 60 spaceflight participants is killed.

Near-Earth Object Insurance A near-earth object collides with the earth. The damage caused depends on many factors including size, composition, trajectory, speed, and most importantly point of impact. There is a 30 % chance it will hit land and perhaps a very small chance that a large meteorite would directly hit a large city. Damage from the smallest scale to the largest manageable catastrophe would trigger insurance coverage. An unmanageable event would be a catastrophe so large that damages would exceed the resources of insurance companies and they would default on coverage. What is the point that insurers would be unable to respond to a super catastrophe is hard to say. Depending on the insurance company, each will have very different concentrations of risk to specific geographic areas and their size of reserves will vary. The largest natural catastrophe to date based on total losses would be the 2011 earthquake/tsunami in Japan which had 15,840 fatalities, $210 billion in overall losses of which $40 billion of the losses were insured (Munich Re 2013a, b). The second largest overall loss would be the combined losses of hurricanes Katrina, Rita, and Wilma in 2005 which had overall losses of $176 billion of which $120 billion was insured losses (IAIS 2012). The amount of losses will be significantly larger in affluent areas of the world because of the value of the property and the ability and interest in purchasing insurance. As noted before, the United States and Japan account for 42 % of worldwide insurance premiums. While total losses in other areas of the world may have larger numbers of fatalities or larger overall losses, it is the more affluent that will have the highest insured losses. Table 3 shows the distribution of losses in respective continents over a 32-year period. For the period overall losses totaled $3.8 trillion worldwide with 37 % of them in North America. However, North America had 64 % of worldwide insured losses. Thus, all countries other than North America had 63 % of the overall losses or $2.25 trillion and of that amount only $344 billion was insured losses. The disproportion is staggering (NatCatSERVICE 2013).

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Tunguska Event Over New York City On June 30, 1908, a comet or asteroid exploded over the Tunguska River, a remote area in Russia. The event leveled 80 million trees over an area of 2,000 km2. The object is estimated to have been 50 m in diameter and the explosion was equivalent to a 10 megaton TNT explosion. Fortunately, the Tunguska airburst was in a remote area so the only damage was to trees. But, what if that event had occurred over a major city? In 2009 Risk Management Solutions did a study of what the effect of the Tunguska event would be if it were to occur over the center of Manhattan. The study estimated property losses to be $1.19 trillion, fatalities of 3.2 million, and injuries to 3.76 million people (Mignan 2009). The RMS study did not estimate what the insured loss amount would be for this scenario but it would be significant. For discussions sake very rough assumptions can perhaps be made to arrive at an insured loss figure. By referring to Table 3 in North America, it is found that insured losses are 44.3 % of the overall losses. Applying that to this scenario gives us $527 billion in insured property losses. This is over four times that of the Katrina, Rita, and Wilma hurricanes combined. Insurance companies would be distressed and some would fail. The state of New York and the Federal Government would need to provide a staggering amount of additional funding. This would be the largest loss in modern history. As devastating as this would be to the US infrastructure and financial resources would be in place to help it recover. If this event happened in Delhi, India, with a population of 25 million, the fatalities would be much higher and financial burden would be placed on the government as they purchase little insurance on a per capita basis. In terms of people and infrastructure loss, the largest potential loss would be if the impact covered the Tokyo and Yokohama metropolitan area.

Table 3 Worldwide distribution of natural catastrophes fatalities and losses Natural catastrophes worldwide 1980–2012

Continent North America South America Europe Africa Asia Australia/Oceania Total

Fatalities 290,000 50,000 150,000 610,000 1,180,000 5,900 2,300,000

% 12 2 7 27 52 1

Source: NatCatSERVICE, January 2013

Overall losses (US$mn) $1,400,000 $100,000 $500,000 $45,000 $1,600,000 $105,000 $3,800,000

% 37 3 15 1 41 3

Insured losses (US$mn) $620,000 $10,000 $160,000 $2,100 $130,000 $42,000 $970,000

% 64 1 16 1 14 5

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Year 1918 1957 1968 1900 2001 1889

Event Influenza pandemic Influenza pandemic Influenza pandemic Hurricane 9/11 terrorist attack Dam burst in rain

Location Nationwide Nationwide Nationwide Galveston, TX DC, NY, PA Johnstown, PA

Fatalities 500,000 70,000 40,000 6,000 3,031 2,209

Source: Risk management solutions: catastrophe, injury, and insurance

Biological Hazards Since the first time man traveled above our atmosphere, there has been concern with the unknown biological hazards that might be brought back to earth. It would appear these fears are unfounded, as nothing involving exploration to date has caused an issue. But, man will continue to travel further and bring back more objects of interest so there is no way of knowing what extraterrestrial contaminants exist. The exposure to humans from an insurance perspective can be equated to the exposure of an influenza pandemic. The losses would be from sickness and fatalities. Life, health, and worker’s compensation insurance would pay the losses. RMS did a study on what would cause the greatest losses as regards fatalities and injuries. The perils of most concern were earthquake, terrorist attack, industrial accident, and influenza pandemic. It was the influenza pandemic that generated the highest number of fatalities. Of the largest fatal events to have occurred in the United States, the top three are from influenza pandemic. See Table 4 (RMS 2004). The RMS pandemic scenario was based on nationwide spread only in the United States. The scenario describes the outbreak of a standard strain of human flu with a mortality rate of 0.5 %. The scenario results in 10,000,000 illnesses with 200,000 fatalities costing the industry a total of $39.9 billion. This size of a loss would be manageable by the insurance industry but put a strain on the economy, as so many people would be out of work. But, the fear would be that an extraterrestrial strain would have a higher mortality rate, and unlike this study the view would be a global one not just the United States. A more lethal flu strain such as avian strain A (H5N1) has a 30 % mortality rate or the Ebola virus has up to a 90 % mortality rate. This would be devastating worldwide.

Conclusion One can only speculate about the catastrophic losses that can possibly come from cosmic hazards. Clearly the impacts and the nature of the catastrophe would be widely different depending on asteroid or comet impact, extreme solar events,

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orbital hazards, or biological infections from space. It seems clear that private insurance could not provide anywhere near complete and comprehensive coverage and that governmental assistance must be the prime element of a recovery process. As shown by the above statistics, the degree of insurance and “insurability” varies widely around the world. This makes it quite difficult to create any type of comprehensive multinational approach to insurance related to cosmic hazards. The strong conclusion that emerges from this analysis is that preventive actions to protect against cosmic hazards would seem to be the wisest way to invest resources. It has been noted by the president of the B612 that the Sentinel Infrared Telescope that could provide a hundred-year warning system for asteroids down to 30 m in size could be built and deployed for the cost of building a modern urban overpass system. Investment in million-dollar warning systems against cosmic hazards versus trying to insure against trillion-dollar cosmic hazard events would seem a wise overall strategy.

Cross-References ▶ Economic Challenges of Financing Planetary Defense ▶ Hazard of Orbital Debris ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ Regulatory Aspects Associated with Response to Cosmic Hazards

References AIR Worldwide Corporation (2013) The coastline at risk: 2013 update of the estimated insured value of U.S. coastal properties. http://www.air-worldwide.com/Facet-Search/Search-Results/. Accessed Sept 2014 Aircraft Builders Council, Inc. (2013) Space weather forecast: blackouts with a chance of business interruption. Property casualty 360 http://www.iwpubs.com/CustomPages/CAPreview.asp?p= 16%26ispreview=1%26articleid=114221%26editionid=21214%26memberid=0%26letterid= 40401788%26_g=890F66C1819146C6A7C1395C90B8979D%26_s=DF5B351A. Accessed Sept 2014 Aon Risk Solutions Global Broking Centre, Aviation (2014) The airport casualty market overview. ACI-NA Annual risk management conference by John C. Geisen. http://www.aci-na.org/sites/ default/files/gs1_-airport_casualty_market_update_john_geisen.pdf. Accessed Sept 2014 Baranoff E, Brockett PL, Kahane Y (2014) Risk management for enterprises and individuals, v. 1.0. Flat World Education, Inc. http://catalog.flatworldknowledge.com/bookhub/1?e= baranoff-ch06_s03. Accessed Sept 2014 Commercial Space Launch Act (1984) Public law 98–575, 98th congress. 98 STAT. 3055. https:// www.govtrack.us/congress/bills/98/hr3942/text. Accessed Sept 2014 Ferris T (2012) Sun struck, the space-weather forecast for the next few years: solar storms, with a chance of catastrophic blackouts on Earth. Are we prepared? Natl Geogr 221(6):36–53 Global Aerospace Underwriting Managers, Inc (2014) Company data in response to Lloyd’s realistic disaster scenarios, scenario specification January 2014, 19. Satellite Risks 19.1

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Insurance Information Institute (iii) (2014a) 2014 International insurance fact book world life and nonlife insurance premiums. Premium source: swiss Re, sigma, No. 3/2013. Population source: U.S. Central Intelligence Agency. http://www.iii.org/publications/insurance-fact-book-2014. Accessed Sept 2014 Insurance Information Institute (iii) (2014b) 2014 International insurance fact book 20 costliest nuclear disasters, source: Benjamin K. Sovacool, contesting the future of nuclear power: a critical global assessment of atomic energy. World Scientific, London, 2011 International Association of Insurance Supervisors (IAIS) (2012) Global insurance market report (GIMAR), 2012 edition. http://www.iaisweb.org/Global-Insurance-Market-Report-GIMAR962. Accessed Sept 2014 International Space Station Intergovernmental Agreement (1998) http://www.esa.int/Our_ Activities/Human_Spaceflight/International_Space_Station/International_Space_Station_ legal_framework. Accessed Sept 2014 Lloyds (2014) Realistic disaster scenarios, scenario specifications. EM 102V1.0 http://www. lloyds.com/%7E/media/Files/The%20Market/Tools%20and%20resources/Exposure%20man agement/2%20%20RDS%20%20Scenario%20Specification%20%20January%202014. pdf. Accessed Sept 2014 Manikowski P (2005) The columbia space shuttle tragedy: third-party liability implications for the insurance of space losses. Risk Manage Insur Rev 8(1):141–150 Mignan A (2009) Comet and asteroid risk: an analysis of the 1908 tunguska event, RMS special report. Risk Management Solutions, Inc. http://www.collectionspace.it/WEB-DOCUMENTI/ 1908_Tunguska_Event.pdf. Accessed Sept 2014 Munich Re (2013a) Significant natural catastrophes 1980–2012, 10 costliest events worldwide ordered by overall losses. http://mrphillipsibgeog.wikispaces.com/file/view/ NatCatSERVICE_significant_eco_en.pdf. Accessed Sept 2014 Munich Re (2013b) NatCatSERVICE Geophysical events worldwide 1980–2012. http://www. munichre.com/en/reinsurance/business/non-life/natcatservice/annual-statistics/index.html. Accessed Sept 2014 Munich Re (2014) TOPICS GEO Natural catastrophes 2013 analyses, assessments, positions. http://www.munichreamerica.com/site/mram/get/documents_E236640509/mram/assetpool.mr_ america/PDFs/3_Publications/Topics_Geo_2013_us.pdf. Accessed Sept 2014 NASA (2014) Space shuttle, mission information. http://www.nasa.gov/mission_pages/shuttle/ shuttlemissions/index.html. Accessed Sept 2014 NASA Orbital Debris Program Office (2014) http://orbitaldebris.jsc.nasa.gov. Accessed Sept 2014 Nuclear Energy Institute (2014) Price-anderson act provides effective liability insurance for nuclear power plants at no cost to the public, fact sheet. http://www.nei.org/MasterDocument-Folder/Backgrounders/Fact-Sheets/Insurance-Price-Anderson-Act-Provides-EffectiveLi. Accessed Sept 2014 Price-Anderson Act (1957) 42 U.S. code 2210 – Indemnification and limitation of liability. http:// www.law.cornell.edu/uscode/text/42/2210. Accessed Sept 2014 Risk Management Solutions, Inc (2004) Catastrophe, injury, and insurance: the impact of catastrophes on workers compensation, life, and health insurance. http://static.rms.com/email/docu ments/liferisks/reports/catastrophe-injury-and-insurance.pdf. Accessed Sept 2014 Satellite News Digest (2003) Midori II (ADEOS II). http://www.sat-index.co.uk/failures/index. html?http://www.sat-index.co.uk/failures/midori2.html. Accessed Sept 2014 The Mayer Brown Global Insurance Group (2013) Trends and developments in mergers & acquisitions, corporate finance, insurance-linked securities, and regulatory matters. Global Insurance Industry Year in Review 2013. http://www.mayerbrown.com/Global-InsuranceIndustry-Year-in-Review-2013/. Accessed Sept 2014 United Nations Convention on International Liability for Damage Caused by Space Objects (1972) http://www.oosa.unvienna.org/oosa/SpaceLaw/liability.html. Accessed Sept 2014

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United Nations Office for Outer Space Affairs (1967) Treaty on principles governing the activities of states in the exploration and use of outer space, including the Moon and other celestial bodies. http://www.unoosa.org/oosa/SpaceLaw/outerspt.html. Accessed Sept 2014 United Nations, Department of Economic and Social Affairs (2012) WORLD: total population. http://esa.un.org/unpd/ppp/Figures-Output/Population/PPP_Total-Population.htm. Accessed Sept 2014 United States General Accounting Office (2002) Testimony before the subcommittee on oversight and investigations, committee on financial services, house of representatives. By David M. D’Agostino. http://www.gao.gov/assets/110/109634.pdf. Accessed Sept 2014 United States Government Accountability Office (2008) FEMA’s rate-setting process warrants attention. GAO-09-12. http://www.gao.gov/assets/290/283035.pdf. Accessed Sept 2014

Glossary of Key Terms, Concepts, and Acronyms

ACE Advanced Composition Explorer (ACE) spacecraft by NASA ACRIMSAT ACRIM stands for Active Cavity Radiometry Irradiance Monitor. This is a mission to study solar total irradiance. The various ACRIM packages demonstrated via measurements in a number of experimental satellites over time that the Sun’s irradiance does indeed vary over time by about 1 %. Since the variation is so small it took a number of years to confirm this quite small change in the Sun’s total energy emissions. Action Team-14 This is a United Nations sanctioned group of nations and regional organizations that is tasked with coordinating the detection of potentially hazardous near-Earth Objects (NEOs). This group was created as a consequence of the UNISPACE III conference where the need for additional global coordinative action to detect NEOs and to address how they could the threat they present could be mitigated. Active Debris Removal/Orbital Debris Mitigation Processes to remove orbital debris from orbit that are particularly focused on removing larger debris elements and on low earth orbit and polar orbits used for remote sensing and meteorological forecasting. AD Accretion disk. This is a part of the “architecture” of a so-called active galactic nuclei and its perceived process for generating cosmic radiation. AGN Active galactic nuclei. This is considered to be one of the sources of cosmic radiation. Air Bursting Impact Model Model predicting the results of an asteroid or meteoroid bursting in the atmosphere on its descent into the Earth’s atmosphere. Air Force Research Laboratory A part of the US Air Force that engages in scientific research. Albedo A term that refers to reflectivity of an object. Alpha particles An alpha particle consists of two protons and two neutrons. They are thus the equivalent of a helium nucleus. These occur in radioactive decay, but also make up some 10–12 % of cosmic rays. Amor Orbit These are a type of asteroid orbit that is larger than the Earth’s orbit but do not now intersect, even though their orbit is still very close to Earth’s orbit (i.e., less than 1.03 AU). These represent some 32 % of known NEOs.

# Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7

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Anti-matter Positive charged positrons that are the inverse of electrons. These particles emit a large amount of energy when they come into contact with matter. Apollo Orbit This is the type of asteroid orbit that crosses the Earth’s orbit twice in a solar orbit, but the asteroid’s orbit is greater in size than the Earth’s orbit. This represents about 62 % of all asteroids. Apophis Asteroid An asteroid that is about 330 m in size and will orbit near the Earth twice in coming years with the 2032 close encounter judged to be the most potentially dangerous. ARS Acute radiation syndrome. This is the general medical term to describe radiation poisoning or radiation sickness. ASE Association of Space Explorers. Its membership include astronauts from around the world who cooperate on issues of concern related to space activities and exploration. Association of Space Explorers This is the official group of astronauts and cosmonauts that work together on space related issues including planetary defense. AstDyS Asteroid Dynamic Site that was developed at the University of Pisa. Asteroid Large space rocks that are largely concentrated in the asteroid belt between Mars and Jupiter but also orbit the Sun and a number of these are in orbits that intersect with the Earth’s orbit and thus present a potential hazard of collision with our planet. Very small rocks of this nature are known as meteoroids and larger meteoroids are characterized by the French term “bolide.” Asteroids Asteroids that are trapped in resonance orbits by the gravity field of Jupiter and intersect Earth orbit. Astronaut Rescue Treaty See Rescue Treaty Astronomical Unit A distance equivalent to the orbital distance of the Earth from the Sun or 149,598,000 km or 93 million miles. Aten Orbit This is the type of asteroid orbit that crosses the Earth’s orbit twice in a solar orbit but the asteroid’s orbit is lesser in size than the Earth’s orbit. This represents about 6 % of all known NEOs. B612 Foundation A not-for-profit foundation that is devoted to identifying potentially hazardous asteroids and meteoroids and most notably is seeking to design, build, launch, and operate the Sentinel infrared telescope that has the potential to identify all NEOs of 140 m or more in diameter. Barringer Meteor Crater An impact site in Arizona where an asteroid landed some 50,000 years ago. Beta particles Solitary electrons or positrons that represent about 1 % of the make-up of cosmic rays. Bolides Exceptional large meteoroids that are lesser in size than full-scale asteroids. Canadian Office of Critical Infrastructure Protection This office is responsible along with the Canadian Space Agency (CSA) with responding to the threat of a catastrophic event precipitated by NEOs colliding with Earth. Carrington Event The most powerful known CME event ever experienced on Earth. This occurred in 1859.

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CAST Circolo Astrofili Talmassons observatory of Italy involved in the identification of asteroids and comets. Catalina Catalina Sky Survey Observatory operated by the University of Arizona. CBE Cosmic Background Explorer CCR Cloud Cover Radiometer CERN European Center for Nuclear Research in Switzerland. Home of the large scale Hadron nuclear accelerator. Chandra X-Ray Telescope Space telescope that views the skies in the X-ray bandwidth that reveals stars and power sources not identifiable in the visible light wave band. Chelyabinsk air burst asteroid event This event that occurred in February 2013 was estimated to have the TNT equivalence of 400–500 kt of explosive power. CINEOS A ground observatory in Italy that is part of the NEO Coordination Centre in Europe. CLUSTER I and CLUSTER II This is a four satellite cluster of satellites that represented a space mission of collaboration between ESA and NASA. The object of this mission was to study the Earth’s magnetosphere over the course of an entire 11-year solar cycle. The cluster in this mission was composed of four identical spacecraft flying in a geometrically structured tetrahedral formation. The Cluster II mission was a replacement for the original four Cluster spacecraft which were lost in the Ariane 5 launch failure in 1996. The four Cluster II spacecraft were successfully launched in pairs in July and August 2000 onboard two different Soyuz–Fregat rockets. The mission has been extended until December 2014 to ensure data that completely covered the entire 11-year solar cycle. The Chinese National Space Administration/ESA Double Star mission also operated together with Double Star Cluster II from 2004 to 2007. CME Coronal mass ejection. These are mass expulsions from the Sun’s corona in the form of very high velocity ions that travel at millions of kilometers per hour. These are often in conjunction with solar flares of electromagnetic radiation in the form of very high energy X-rays and gamma rays. CNES The French Space Agency. Centre national d’e´tudes spatiales or in English the National Center for Space Studies. CNSA Chinese National Space Administration Comet impact Comets travel at higher speeds than asteroids because of their much different types of orbits. The observation of the Shoemaker-Levy comet impact on the surface of Jupiter highlighted the concerns about the great danger that a comet impact on Earth would constitute. Comets Bodies that originate in the so-called Oort cloud just beyond the edge of the solar system and make a highly elliptical orbit of the Sun sometimes with a period as long as a thousand of years. COPUOS The United Nations Committee on the Peaceful Uses of Outer Space. COPUOS WGNEO The United Nations Committee on the Peaceful Uses of Outer Space Working Group on Near Earth Objects.

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COPUOS WGSS The United Nations Committee on the Peaceful Uses of Outer Space Working Group on the Sustainability of Space. Coriolis Satellite Coriolis is an Air Force Space Test Program and Space Naval Warfare Systems Command. The satellite contains an Solar Mass Ejector Imager (SMEI) which is an all-sky camera that continuously observes coronal mass ejections (CMEs) in order to seek to make predictions of geomagnetic disturbance by means of these observations. It also includes the unrelated WINDSAT instrumentation. This is a Conical Microwave Imager Sounder (CMIS) that allows the measurement of ocean wind speeds and direction. Corona The extensions of the Sun from the external surface. It is from this region that coronal mass ejections occur. Until the space age it was not well understood how far out into space this external part of the Sun extended. The masks on space-based coronagraphs showed that the corona extended out many thousands of kilometers. Coronagraph A device designed to study the corona of the Sun by masking the main body of the Sun. Coronal mass ejections These are massive bursts of solar wind. They are thought to occur when magnetic fields snap apart and release a massive burst of ions out into space traveling at millions of kilometers per hour. These coronal mass ejections (CME) typically occur more frequently during Solar Max. These CME events are often associated with other forms of solar activity, most notably solar flares. The precise causal relationship between the two phenomena has not been established. See Solar Flare. COSPAR Committee on Space Research is one of the international coordinative bodies for science. It was set up under the structure of the International Council of Scientific Unions that is now known simply as the International Council for Science. Both COSPAR and the ICSU are non-governmental organizations. COSTR The Collaborative Solar-Terrestrial Research Program. COSTR defines the NASA contributions to the GEOTAIL, SOHO, and Cluster missions. CSA The Canadian Space Agency Deep Impact Mission A NASA project to study the composition of comet 9P/Tempel that was repurposed to become the EXPOXI mission. Directed Energy or Directed Energy Beam This refers to various types of directed energy systems that transmit energy over a distance and does not involve launching of an aimed projectile but rather just utilizes focused energy. This directed energy can include sonic beams, or mass at the atomic level, but most typically refers to focused electromagnetic energy. This can include radio frequencies (such as microwave or millimeter wave) and high powered lasers and masers. Disaster Charter This is formally known as the International Charter on Space and Major Disasters. This Charter is an instrument that has been put in place to encourage cooperation in the use of space facilities to support the management of crisis arising out of natural and man-made disasters. It has now been invoked in a wide range of disasters around the world.

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DLR The German Aerospace Center. Officially it is the Deutsches Zentrum f€ur Luft- und Raumfahrt e.V. Double Star Mission A joint Chinese/ESA mission to study the solar cycle that operated from 2004 to 2007 in conjunction with the Cluster II mission. EARN Near-Earth Asteroid Research Node EC European Commission ECAs Earth-crossing asteroids ECCs Earth-crossing comets ECOs Earth-crossing objects Electrodynamic propulsion Propulsion that uses tethers moving through the Earth’s magnetic field to generate electricity and thus to power electronic thrusters in space. EMP Electromagnetic pulse ESA European Space Agency ESRIN European Space Research Institute in Italy. EUV Extreme ultraviolet radiation EV Electron volt. Note: MEV represents mega electron volt, GEV represents giga electron volt, and TEV represents tera electron volt. That is a million, billion, and a trillion EV, respectively. EXPOXI The EPOXI and Deep Impact Mission: The Deep Impact space probe was launched by NASA on January 12, 2005. It was designed to study the interior composition of the comet 9P/Tempel, by releasing an impactor into the comet which was accomplished in July 2005. The impact excavated debris from the interior of the nucleus, allowing photographs of the impact crater. The photographs showed the comet to be more dusty and less icy than had been expected. After this successful accomplishment the spacecraft was repurposed to become the EPOXI mission to study extra solar planets that successfully flew by comet Hartley 2 in November 2010 but experimenters have now lost contact with this satellite. See NEXT experiment. FITS Flexible Image Transport System used to exchange images among observatory sites. FST Fermi Space Telescope Fuel Depletion Guideline for Satellites Guideline for all satellite operators seeking that they remove excess fuel that might lead to an explosion that produces additional orbital debris. FUN-SSO Follow-Up Network of Solar System Objects Gamma ray burst (GRB) This is a high energy solar flare and represents a sudden burst of gamma radiation release from the Sun. Gamma ray detector This is an instrument designed to record and calibrate gamma ray emissions from the Sun and particular gamma ray bursts. Gamma rays Represent extremely high energy radiation. These photons have energy levels as high as 1010 eV or even higher. These rays can occur as the result of radioactivity, lightning strikes, novae, and other cosmic sources. Unlike misnamed alpha rays and beta rays, which are in fact extremely

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high energy ions, gamma rays are, in effect, super photon radiation with wavelengths even smaller than X-rays and at higher frequencies and smaller wavelengths. GCR Galactic cosmic radiation GEO also GSO Geosynchronous orbit or geostationary orbit. This is sometimes referred to as the Clarke orbit in honor of Arthur C. Clarke. It is an orbit that is a tenth of the way to the Moon or 35,840 km or 22, 230 miles above the Earth’s surface. A satellite in this orbit at a velocity to maintain orbit exactly matches the rotation of the Earth with respect to the Sun. Geomagnetosphere This is the magnetosphere that is generated from the Earth’s magnetic poles. This shapes the Van Allen Belts and is key to the protection of the world against solar flares, coronal mass ejections, and cosmic radiation. George Brown Jr. Near-Earth Object Survey Act An act passed by the US Congress in 2005 that led to NASA being tasked with location of all NEO asteroids that are of a size of 140 m in diameter and reporting to Congress each year as to progress that has been achieved toward achieving this goal. GEOTAIL GEOTAIL is a collaborative mission of Japan and the USA and specifically included JAXA/ISAS (Institute of Space and Astronautical Science) and NASA (National Aeronautics and Space Administration). GEOTAIL was designed to explore the “tail” of the Earth’s geomagnetosphere. This is a part of the program ISTP (International Solar-Terrestrial Physics). The spacecraft was built and integrated by ISAS and the launch was provided by NASA. GEOTAIL represents start of the Collaborative Solar-Terrestrial Research Program (COSTR). COSTR includes the GEOTAIL, SOHO, and Cluster missions. GGS Global Geospace Science. See WIND Solar Research Satellite. GIC Geomagnetically induced current GOME Global Ozone Monitoring Experiment Gravity Tractor This is a theoretical type of spacecraft that could conceivably be used to divert the orbit of a potentially hazardous asteroid and be able to do so without coming into physical contact with it. It would only use its gravitational field to change the orbit of the PHA over a sustained period of time. This type of gravity tractor spacecraft could either hover near the object to divert its path, or orbit it by directing its exhaust perpendicular to the plane of the orbit of the target NEO that was considered a threat. Hayabusa Mission This was a satellite developed by JAXA, the Japanese Space Agency to capture a small sample from a small near-Earth asteroid named 25143 Itokawa so that this material could be returned to the ground by capsule for scientific analysis. Helio Physics Research Scientific research to understand the physics related to the operation of the Sun and its cyclical processes. Helios A and B These are also known as Helios 1 and 2. They were probes placed into heliocentric orbits by NASA to study the Sun’s irradiation and physical processes.

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Helioscope A device used to study the Sun that blocks out the Sun’s brightest radiation so that the Sun’s corona and heliosphere can be observed. Heliosphere The vast area effected by solar weather that extends out 100 AU from the Sun in all areas. HgCdTe Detectors Mercury cadmium telluride detectors that are used in infrared telescopes. Hierarchical Clustering Methods (HCM) A mathematical processing method used to analyze and characterize families of asteroids with similar orbits such as the Nysa, Polana, and other families of asteroids. Hilda and Trojan asteroids Asteroids that are trapped in resonance orbits by the gravity field of Jupiter and intersect Earth orbit. Hinode Satellite This satellite is also known as Solar-B. It is a joint Japanese (JAXA), UK, and US (NASA) experimental satellite. It is a follow-up to the Yohkoh Satellite. Mission for solar research to study space weather and solar flares. Hungaria Asteroid A very common type asteroid that circles the Sun in the range of 1.75–2.00 AU. HV Hyper velocity. HV is referred to the velocity of orbital objects traveling at a speed in excess of roughly 2 km/s. HVI Hyper velocity impact refers to a laboratory experimental approach where the dynamic of an impulsive interaction occurring between a spaceborne structure and debris or the collisions of space objects are simulated. Two stage or single stage gas gun is used to accelerate projectiles to hyper velocity before impacting a designated target at the end of the gun barrel. HZE particles High Z-energy nuclei particles emitted from the Sun that include all emissions that are heavier than helium nuclei. IAA International Academy of Astronautics IAASS International Association for the Advancement of Space Safety. IADC Inter-Agency Space Debris Committee. This a committee of many of the world’s space agencies that has worked with the UN COPUOS to develop guidelines to minimize space debris. IAU International Astronomical Union IAWN International Asteroid Warning Network. This is a global network for sharing information on NEOs approved by the UN General Assembly. ICTSW Interprogramme Coordination Team on Space Weather IDASS Intelligence Data Analysis System for Spacecraft IDPAG Impact Disaster Planning Advisory Group as approved by the UN General Assembly. IEO: Inter Earth Objects orbits These types of orbits for IEO asteroids circle the Sun entirely inside of the Earth’s orbit but are still close to our orbit (i.e., 0.093 AUs). These are very rare and only six of these types of IEOs are known to exist. IMAGE Imager for Magnetospause-to-Aurora Global Exploration. The IMAGE spacecraft was launched in 2000 and operated until 2005. IMAGE was the first satellite mission dedicated to imaging the Earth’s magnetosphere. This region

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contains extremely tenuous plasmas of both solar and terrestrial origin. These plasmas are invisible to standard astronomical observing techniques. It is populated by ions and noxious gases that prior to IMAGE were partially and sketchily “observed” by means of charged particle detectors, magnetometers, and electric field instruments lifted by high altitude balloons. IMAGE was thus able to produce the first comprehensive global images of the plasma populations in the inner magnetosphere. IMP Interplanetary Monitoring Platform was a NASA magnetospheric research program with eight satellites in the series. IMP-8, the last of the series, launched in 1973, was instrumented for interplanetary, magneto-tail, and magnetospheric boundary studies of cosmic rays, energetic solar particles, plasma, and electric and magnetic fields. The objectives of the mission were to provide solar wind parameters as input for magnetospheric studies and as a 1-AU baseline for deep space studies, and to continue solar cycle variation studies with a single set of well-calibrated and understood instruments. INAF Istituto Nazionale di Astrofisica or the National Institute for Astrophysics of Italy INSRP Interagency Nuclear Safety Panel International Academy of Astronautics Conferences on Planetary Defense The largest international conference organized to explore cosmic hazards and to consider means to undertake planetary defense against such hazards. It is sponsored by the International Academy of Astronautics and many other entities. IPAC Infrared Processing and Analysis Center (IPAC) at the California Institute of Technology (see IRSA). IPCC Intergovernmental Panel on Climate Change IPN Inter Planetary Network IRAS Infrared Astronomical Satellite IRSA Infrared Science Archive (IRSA) that is hosted at the California Institute of Technology’s Infrared Processing and Analysis Center (IPAC). All data products from NASA infrared tracking missions are publicly available and accessible through IRSA. ISRO The Indian Space Research Organization ISS International Space Station ISSE International Sun-Earth Explorer ISTP The International Solar-Terrestrial Physics Program ISTP International Solar-Terrestrial Physics JAXA The Japanese Aerospace eXploration Agency JPL Jet Propulsion Laboratory JPSS Joint Polar Satellite System Kessler Syndrome This is the condition predicted in the 1980s by Donald Kessler of NASA where there would be a runaway cascade of orbital debris. This prediction was not initially viewed with serious concern, but today the possibility of this syndrome is viewed with increasing concern especially since the

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collision of satellites and other major activities have led to major increases in large traceable debris items. Keyhole Effect The gravitational anomaly whereby the Sun diverts orbital path of an asteroid or meteoroid in a significant way when traveling near the solar surface. LCH Laser Clearing House, US Department of Defense Monitoring Site located in Cheyenne Mountain in Colorado Springs, Colorado. LCH provides windows for conducting laser test so they do not illuminate functional satellites. The entire catalogue of space objects including the space debris is maintained by US Strategic Command (USSTRATCOM) in collaborations with Joint Space Operation Center (JSpOC). LEO Low earth orbit. It is in this orbit and particularly Sun synchronous polar orbit that there is the greatest congestion of space debris. Liability Convention This is formally known as the Convention on International Liability for Damage Caused by Space Objects that was agreed by the General Assembly in 1971 and entered into force in 1972. Libyan Desert Glass Widely distributed glass found in the Libyan Desert that is thought to have been created some 26 million years ago as the result of a massive asteroid impact that was equivalent to a massive thermonuclear blast. LINEAR Lincoln Near-Earth Asteroid Research. This is one of the ground based observatories devoted to finding asteroids and determining their orbital parameters. It is operated by Lincoln Labs at MIT and is funded by NASA and the US Air Force. LONEOS The Lowell Observatory Near Earth Object Search LRO Lunar Reconnaissance Orbiter (LRO) which is a cosmic ray telescope. Mass extinctions These are events related to climate change, asteroid collisions, or other cataclysmic occurrences that result in a third or more of all species of animal and plant life being wiped out. There have been five such events in human history. The most recent of these was the so-called K-T event some 65 million years ago that killed off the dinosaurs when a 5 km asteroid hit Earth. MEO Medium earth orbit Meteoroid and micro-meteoroid This is a small space rock to miniscule space “pebble” that can be characterized as a meteorite (larger element) or if very small a micro-meteorite. There are “clouds of meteoroids” that follow well known orbits in “streams” that are typically left-over elements of comets that when they encounter the Earth’s atmosphere burn up and create so-called meteor showers as they light up. These include the Geminids, the Quadrantids, the Perseids, and the Leonids. Millennium Ecosystem Assessment This is a report developed under the auspices of the United Nations and the Millennium Assessment Board that involved the input of over 1,300 international experts and it assess the world’s ecosystem and threats to it including NEOs. Minor Planet Center This is the global central registry for all asteroids and meteoroids found at various ground observatories that are scanning the skies for potentially hazardous objects that have not been previously identified. This is

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operated under the auspices of the Harvard-Smithsonian facilities in Boston, Massachusetts. It is responsible for detecting nearly 2,500 NEOs and some 280 comets. MIT Haystack Observatory This is a radio-astronomy monitoring site that investigates the formation of galaxies and creation of the universe. MIT Linear Observation Center Lincoln Near Earth Asteroid Research (LINEAR) is an MIT Lincoln Laboratory program funded by the United States Air Force and NASA. The goal of LINEAR is to demonstrate the application of technology originally developed for the surveillance of Earth orbiting satellites, to the problem of detecting and cataloging near-Earth asteroids – also referred to as near-Earth Objects (NEOs) – that threaten the Earth. MOID Minimum orbit intersection distance Montreal Declaration This is the declaration that came from the Manfred Lachs Conference on Global Space Governance in late May and Early June 2014 that call for a new initiative to find improved means of global space governance in light of the many new space applications as well as concerns about cosmic space hazards that present themselves to an evolving twenty-first century world. Montreal Protocol The 1987 Protocol signed in Montreal that sets forth the sets that nations should take to phase out chemicals that lead to the depletion of the ozone layer such as CFC gases. Moon Treaty or Moon Agreement This is formally known as the Agreement Governing the Activities of States on the Moon and Other Celestial Bodies. This is an international treaty that was intended to turn jurisdiction of all celestial bodies (including the orbits around such bodies) over to the international community. Thus, all activities involving the Moon and other celestial bodies would under the Agreement would conform to international law, including the United Nations Charter. Unfortunately this is largely considered a “failed treaty” in that none of the space faring nations have ratified this agreement and that only some 15 countries have agreed to the Agreement. MPC Minor Planet Center located at the Smithsonian Astrophysical Observatory (SAO) in Cambridge, Massachusetts, in collaboration with Harvard University MSSS Maui Space Surveillance Site. This 3.6 m, 75 metric tons Advanced Optical Observation System is located on top of the Haleakala mountain in Maui. NASA National Aeronautics and Space Administration NASA Sentry Risk Table This is a map of 400 near-earth objects that NASA maintains. Only one of these is a “green” on the Torino Impact Hazard Scale which is only a “1” on the scale of ten risk assessment charge. The rest are rated “0” or in the no hazard white zone. National Reconnaissance Office (NRO) The part of the US Department of Defense that carries out satellite-based and other forms of reconnaissance. Navy Research Laboratory (NRL) The part of the US Navy that engages in scientific research. NEA Near-earth asteroid NEAT Near-Earth Asteroid Tracking. This operation consists to two autonomous tracking operations. One is carried out at the Maui Space Surveillance Site

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(NEAT/MSSS) and the other at the Palomar Observatory known as NEAT/ Palomar. NEC Near-earth comet NEO Near-earth object NEO Characterization It is important not only to detect a NEO and determine its orbit but also to characterize its composition as a dense rock or perhaps a porous element. NEO Orbit Determination Once a NEO is detected it is important to determine its orbit and whether it can be classified as an Aten, Amor, Apollo, or IEO and thus be able to determine the likelihood of the asteroid impacting Earth. NEO Shield This is a European Space Agency funded project to study how to divert asteroids and meteoroids in their orbits so as not to hit Earth or otherwise minimize their threat. NEO WISE Program that used the Wide-range Infrared Surveyor Explorer (WISE) telescope to detect near-earth objects at the end of life for the WISE telescope. Currently, NASA plans to replace this facility with the NEOCAM infrared telescope that will have greatly expanded capability. NEOCam Near-Earth Object Camera is a proposed mission by NASA to detect NEOs with much greater precision than previous NASA missions and could work in tandem with the Sentinel infrared telescope to detect potentially dangerous NEOs. NEOCC Near-Earth Object Coordination Centre. This is part of the European Space Agency effort to address potentially hazardous NEOs. NEODyS Near-Earth Object Dynamic Site located in Italy. NEXT New Exploration of Tempel 1 (or NExT). This is part of the Deep Impact EXPOXI mission. NOAA National Oceanic and Atmospheric Administration of the USA. NOAA Solar Weather Dashboard An Internet based display that shows key solar weather characteristics in near real time. Observatories There are large number of observatories around the world that are heavily engaged in the effort to locate and determine the orbits of NEOS as well as help characterize their composition. Observatory Codes The Minor Planet Center maintains codes for all sites that carry out observation of minor planets and indicates their location by a parallax constant for each such site including professional and amateur observatories. OGS Optical Ground Station at Tenerife, Spain, that assists in European Space Situational Awareness. OMPS Ozone Mapping Profiler Suite (OMPS) OOSA Office of Outer Space Affairs. This is the UN Agency that supports the work of the UN Committee on the Peaceful Uses of Outer Space. Orbital debris Defunct satellites, upper stage rockets, and other “waste” items in Earth’s orbit that is now continuing to grow due to collisions of existing debris

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despite voluntary UN COPUOS guidelines to minimize the creation of new debris. OSIRIS-Rex This is an Asteroid Sample Return project undertaken by NASA with the University of Arizona personnel serving as the principal investigators. OSO Orbiting Solar Observatory (OSO) satellites OST The Outer Space Treaty adopted in 1966. Its full name is the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies. The Outer Space Treaty was considered by the Legal Subcommittee in 1966 and agreement was reached in the General Assembly in the same year as resolution 2222 (XXI). The treaty was largely based on the Declaration of Legal Principles Governing the Activities of States in the Exploration and Use of Outer Space that had been previously adopted earlier in the UN debates. Palermo Scale This is a logarithmic scale that is applied to NEOs to assess their threat level in terms of their likelihood of hitting earth. The scale ranges from 2 to 0 (i.e., minimal threat) and from 0 to +2 (increasingly large threat). Pan-STARRS Panoramic Survey Telescope and Rapid Response System observatory that includes a number of observing capabilities and located in Hawaii, but has a number of participating members in this global consortium from around the world (see WMOPS). PATM Panel on Asteroid Threat Minimization that was created by the Association of Space Explorers. PHA Potentially hazardous asteroids PHO Potentially hazardous object Phocaea Asteroid A common type asteroid that is located in the main region of the asteroid belt in the range of 2.25–2.50 asteroid astronomical units. Photosphere This refers to the outer surface of the Sun which is larger and not well defined area. The official definition of a star’s photosphere as an astronomical object is the depth of a star’s outer shell from which light is radiated. Planetary Defense This is concept of creating a globally unified process and capability to defend earth against cosmic threats that include comets, NEOs in the form of potentially hazardous asteroids, extreme solar weather, and other possible future threats from space such as biological infections from space, etc. The United Nations General Assembly action in 2013 to create the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG) as well as the COPUOS working group on sustainability represent important first steps in this direction. POES Polar Orbiting Environmental Satellite POLAR This is a NASA experimental satellite that was launched in 1996 in a highly elliptical orbit to study the Earth’s magnetosphere. Polar Cap Absorption (PCA) Event This is when a major solar storm is diverted toward the Earth’s polar regions by its magnetosphere and major radiation is absorbed in the polar region.

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QA Quality assurance Radiation Radiation refers to the energy emission in the electro-magnetic spectrum, and in the context of cosmic hazards the focus is on the very high end of the electro-magnetic spectrum at the very smallest frequencies and power levels characterized as X-rays and gamma radiation. Radiation protection Radiation whether from cosmic sources or radio-active materials can cause damage to all forms of life. Some form of protective shielding is needed to prevent damage against radiation sickness, cancer, and genetic damage. Acute radiation can cause radiation sickness with immediate effect. Radiation at low levels can cause chronic effects and also cause genetic mutation. The Earth’s protective systems generally provide a reasonable level of protection from acute radiation, but certain areas such as under the so-called ozone holes require additional protection. Rail Gun This is the concept of an electrically-powered electromagnetic projectile launcher system. Such a launching system would be comprised of a pair of parallel conducting rails equipped with some sort of a sliding armature that can be accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail. Very rapid accelerations have been achieved in tests. This technology is still at a very early development system for the purposes of unmanned launching systems or as a weapons system. The explosive force of such systems as currently conceived would represent too rapid an acceleration for human launching capabilities. Registration Convention This is formally known as the Convention on the Registration of Objects Launched into Outer Space. The Registration Convention provides that the launching State should furnish to the United Nations, as soon as practicable, the following information concerning each space object: (i) Name of launching State; (ii) An appropriate designator of the space object or its registration number; (iii) Date and territory or location of launch; (iv) Basic orbital parameters, including nodal period (the time between two successive northbound crossings of the equator, usually in minutes), inclination (inclination of the orbit, polar orbit is 90 and equatorial orbit is 0 ); apogee (highest altitude above the Earth’s surface, in kilometers), and perigee (lowest altitude above the Earth’s surface, in kilometers); and (v) General function of the space object. Rescue Treaty This is formally known as the Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space. It is an international agreement setting forth rights and obligations of states concerning the rescue of persons in space and the return of space objects. The Agreement was created on 19 December 1967 by a consensus vote in the United Nations General Assembly (Resolution 2345 (XXII)). It came into force on 3 December 1968. RHESSI This stands for Reuven Ramaty High Energy Solar Spectroscopic Imager. This is a small scale Explorer mission with a primary goal of exploring the basic physics of particle acceleration and sudden energy release in solar flares. This is achieved through imaging spectroscopy that covers both X-rays

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and higher energy gamma-rays. This satellite also captured extremely high energy releases from cosmic distances as well as from the Sun. RosCosmos The Russian Space Agency SAGE Satellite Aerosol and Gas Experiments SBUV Solar Backscatter Ultra Violet sensors on NOAA Satellite SCN Spaceguard Central Node SCR Solar corpuscular radiation SDO Solar Dynamics Observatory SECCHI Sun Earth Connection Coronal and Heliospheric Investigation. This represents five different experimental packages to observe the Sun’s corona and heliosphere. Sentinel Infrared Telescope This is a project of the B612 Foundation to create a new space capability to detect NEOs more completely and down to a diameter of 17 m as well as with greater advance warning. SEP Solar energetic particles Shoemaker-Levy Comet A collection of comets that crashed into Jupiter with enormous force that helped to understand in greater detail what the impact would be if a comet were to crash into Earth. Si:As Arsenic doped silicon. Chemical compound. Skylab This was the first space station and it was the site for many of the early solar observation experiments. Sloan Digital Sky Survey An extensive catalogue of asteroids and other objects of the solar system. The data from the NEOWise Program and this survey data have now been combined into a single data base. SMEI Solar Mass Ejection Imager SMM Solar Maximum Mission SMPAG Space Missions Planning Advisory Group as approved by the UN General Assembly. SNR Signal-to-noise ratio SOHO Solar and Heliospheric Observatory is a joint project of the European Space Agency and the USA (NASA). This satellite was designed and built by European contractors and launched on a US Atlas IIS rocket in 1995. It has provided a great deal of information about the Sun’s physics during its nearly 20 years of operation. Solar A See Yohkoh solar research satellite. Solar B See Hinode solar research satellite. Solar corona This is the outer edge of the Sun from which coronal mass ejections occur. Solar flares These are very high energy emissions of radiation in the form of X-rays and gamma rays that occur especially during the Solar Max phase of the Sun’s 11-year cycle between Solar Max and Solar Minimum. A coronal mass ejection may or may not occur in conjunction with solar flare. The solar flare occurs at the speed of light while the CME, composed of ions, travels at a lesser speed, but still at millions of kilometers per hour (see Fig. 1.8).

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Solar Max/Solar Minimum The Sun’s nuclear processes are still a subject of intense study. It is known that on an 11-year cycle that solar flares and coronal mass ejections fluctuate from Solar Max to a Solar Minimum and then back again. Coronal mass ejections are 15–20 times more frequent during Solar Max as opposed to Solar Minimum and the Sun’s magnetic poles also reverse on the 11-year cycle. There are also longer term variations in the Sun’s activities and intensity that are also being studied. The exact reasons for these variations are not known. Solar Wind This is the name given to “normal” particle emissions from the Sun’s corona that occur on an ongoing basis. This solar wind is much less energetic than the explosive releases known as coronal mass ejections (which see). Solwind (P-78-1) This early experimental solar research satellite used the same spacecraft platform as the Orbiting Solar Observatory (OSO) and was launched in 1979. It is of historical interest to note that it was shot down in an anti-ballistic missile test of the ASM-135 anti-satellite rocket system test in 1985 after this satellite had failed. SOR Starfire Optical Range located on Kirtland Air Force Base in Albuquerque, New Mexico. SOR has a 3.5 m telescope with adaptive optics quite capable of tracking LEO objects. Also provides angular dependent scatterometry capability for anchoring optical signature predictive methods. Space Data Association This is a group of satellite operators that has started a technical consortium to share data regarding the location of their in-orbit satellites and particularly to alert each other as to potential conjunctions. This predominantly involves satellite operators in Geo orbit, but is now beginning to cover satellites in other orbits. This group is incorporated on the Isle of Man. Space debris Space objects that are no longer of utility that are of many diverse sources such as upper stage rockets, defunct satellites, items that have been discarded in space, debris elements that have been created by random collisions in space, etc. Although space objects are a precise legal term defined in United Nations space treaties, there is no formally agreed definition for space debris. Space object Any object launched or now existing in space. Space radiation The very high energy X-rays and gamma rays that bombard Earth from cosmic sources (i.e., the Sun and the rest of the universe). This also includes “cosmic radiation” from the stars that actually includes both highly energetic electromagnetic radiation as well as high energy ions that are actually particles. Space Situational Awareness The ability to track the orbits of elements in space accurately over time. The US Space Command currently maintains the largest and most sophisticated tracking network for this purpose that includes the “Sband radar capability” known as the Space Fence. Spacewatch This is the name of a group at the University of Arizona’s Lunar and Planetary Laboratory located at Kitts Peak, Arizona, near Tucson. The primary goal of Spacewatch is to examine and identify the various populations of small objects in the solar system. This allows this research group to examine the likely

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patterns of evolution of the solar system as well as to detect potential NEO hazards. Space Weapon The Outer Space Treaty states that “States shall not place nuclear weapons or other weapons of mass destruction in orbit or on celestial bodies or station them in outer space in any other manner.” In addition this treaty referred to the use of space for peaceful purposes. In addition in 2000, the United Nations General Assembly voted on a resolution called the “Prevention of Outer Space Arms Race.” It was adopted by a recorded vote of 163 in favor to none against, with three abstentions. Despite these various actions within the United Nations there is no clear definition of exactly what is a space weapon. Space Weather This refers to all of the radiation and ionic bombardment that comes to earth from solar flares, coronal mass ejections, and cosmic radiation and can pose a threat to life and human infrastructure in its most energetic forms. Space Weather: The Earth’s Van Allen Belts, the geomagnetosphere, and the Earth’s atmosphere (particularly the ozone layer on top of the stratosphere) all serve to shield plant and animal life forms against this cosmic bombardment. Spaceguard Program of NASA A 1992 US Congressional study produced what was called the “Spaceguard Survey Report.” This report led to a mandate that NASA locate 90 % of near-earth objects that are 1 km or greater in diameter within the next ten years. This is sometimes referred to the Spaceguard Goal. Subsequently in 2005 Congress passed the George Brown Act that set a new goal of identifying all NEOs of 140 m or greater in diameter and to provide an annual report to Congress as to progress achieved against this goal. Currently NASA is well behind this goal as it has become clear that far more asteroids that are NEOs of this size actually exist than had been previously thought. The Sentinel project appears the best prospect to move forward toward this goal, particularly since the end of life of the WISE infrared telescope and no replacement currently available. SPE Solar Proton Event SRT Sentry Risk Table that is created and maintained by JPL. SSA Space Situational Awareness SST Spitzer Space Telescope SST Space Surveillance Telescope Stand-Off Space Mission A sufficiently powerful directed energy-beam system that can impact the orbit of an asteroid or orbital debris element at a distance. Stand-On Space Mission A mission involving maneuvering to be in close proximity to a space object. This would involve such missions as positioning a directed-energy beam or laser system close by an asteroid to divert its orbit. STEREO Solar TErrestrial RElations Observatory (STEREO) is the third mission in NASA’s Solar Terrestrial Probes program (STP). The mission, launched in October 2006, has provided a unique and revolutionary view of the Sun-Earth System. This two satellite project provides a “stereoscopic view” of solar events. Sun Spots These are dark areas that form on the Sun’s outer surface indicating turbulence and often precursors to solar storms.

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Sustainability of Space In recent years as concerns about orbital debris and extreme solar weather has increased, the UN Committee on the Peaceful Uses of Outer Space has created a Working Group on Sustainability to undertake research and international collaboration to see how long term sustainable access to space can be systematically attained. The Planetary Society This is a membership not-for-profit society that is devoted to the study of space and to develop systems to study and explore the cosmos as well as limit space hazards. The Spaceguard Foundation (SGF) is a private organization based in Italy. Its purpose is to study, discover, and observe near-Earth Objects (NEO). This foundation which is non-profit and non-political also seeks to protect the Earth from the possible threat of a NEO collision. The Yarkovsky Effect This effect was first suggested in 1902 by Professor Yarkovsky. The concept is that radiation from the Sun and the heating of one side of an asteroid or meteoroid would serve to slow its velocity and change its orbit. TOMS Total Ozone Mapping Spectrometer (TOMS) Torino Impact Hazard Scale A scale for assessing the potential hazard level for asteroids or comets based on their size and probability of impact adopted at the Unispace Conference in Turin, Italy. TRACE Transition Region and Coronal Explorer satellite. This is an experimental solar research satellite that seeks to explore the region of the Sun’s outer surface that makes the sudden transition from a few thousand degrees centigrade to millions of degree centigrade and to understand the physics of this tremendously large temperature gradation. Tractor beam A tractor beam is a device with the ability to attract one object to another from a distance. The term was coined by E. E. Smith in his novel Spacehounds of IPC (1931). This concept was popularized on the Star Trek series. Serious scientific efforts to create a “tractor beam” utilizing laser technology has been pursed since the 1990s and now accomplished at the microscopic level. The concept of a repussive beam that can repel object always is also known as a “pressor” beam or “repulsor” beam. TSI Total solar irradiance. Over a period of years the solar irradiation varies by about 1 %. This was demonstrated over a period of over 20 years by three different ACRIM subsystems on three different satellites. Tunguska event The 1908 asteroid explosion, which occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, on June 30. This was an air burst event that occurred at an altitude of 5–10 km (3–6 mi). There are widely different estimates as to the size of the asteroid that suggest its diameter might has been as small as 60 m or as large as 190 m. Twenty-Five Year Rule This is a “rule” developed by NASA that seeks satellite operators to remove a satellite from orbit within 25 years from the date that satellite operations cease.

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UARS Upper Atmosphere Research Satellite Ultraviolet radiation UV radiation that is more energetic and of a higher frequency than visible light. Ulysses Spacecraft Ulysses is a decommissioned robotic space probe whose primary mission was to orbit the Sun and study it at all latitudes. It was launched in 1990, and it studied the Sun in 1994/1995 and then once more in 2000/2001. UN COPUOS United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). UN OOSA United Nations Office of Outer Space Affairs. UN or UNO United Nations or United Nations Organization UN Working Group on Near Earth Objects This a working group of COPUOS that is investigating the threat of near-earth objects and possible protective approaches to Earth against potentially hazardous NEOs. UNEP United Nations Environmental Programme UNISPACE The name of the United Nations Space Conferences. There have been a total of three such international conferences. All of these were held in Vienna, Austria, where COPUOS is headquartered. UV Ultraviolet radiation. This is the energetic electro-magnetic radiation above the visible light range that can under prolonged exposure create genetic mutation and lead to skin cancer. Van Allen Belts These are two defined belts of intense radiation and ionic particles that are held in place by the Earth’s magnetic fields. These belts of radiation were discovered by a Geiger counter device included by Dr. James Van Allen on the Explorer I satellite that was the first artificial satellite launched by the USA in 1958. For a short period of time the presence of a “third belt” was witnessed briefly during 2012. This suggests that there is more transience in the nature of the Van Allen Belts than have been previously thought. Van Allen Storm Probes These are two experimental satellites launched by NASA to study the nature of the Van Allen Belts, their ability to protect Earth from solar storms, and the possibility that changes in the Van Allen Belts and their protective nature are occurring over time. VLA Very Large Array, the large Radio Astronomy station located in Socorow, New Mexico, USA. Water Impact Modeling Modeling that seeks to predict the results of an asteroid or meteoroid hitting the water on its descent to Earth. WGNEO Working Group on Near Earth Objects (WGNEO) of the Science and Technology Committee of the IAU. WIND WIND is a spin stabilized spacecraft launched by NASA in November 1, 1994, and placed in a halo orbit around the L1 Lagrange point, about 20 Earth radii upstream of the Sun to observe the unperturbed solar wind that is about to impact the geomagnetosphere.

Glossary of Key Terms, Concepts, and Acronyms

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WISE Wide-range Infrared Surveyor Explorer by NASA that is now out of service. In the last years of operation it was devoted to finding NEOs and it became the NEOWise activity. WMOPS WISE Moving Object Processing System (see WISE). World Meteorological Organization The United Nations specialized agency that is involved with global coordination of meteorological phenomena as well as space weather monitoring and hazards detection. X-rays Highly energetic radiation that is more energetic and with higher frequencies than ultraviolet radiation, but less energetic and with lower frequencies than gamma radiation. X-rays can be artificially generated for medical and other purposes but come naturally from the Sun and cosmic sources. Yohkoh Satellite This satellite was also known as Solar-A. This was the solar research satellite that was a joint project of Japan, the UK, and the USA. Its mission was to study X-ray and cosmic ray emissions from the Sun and to examine solar flares and solar weather. This mission experienced spacecraft failure in December 2001. This led to the follow-up activity known as Hinode (or Solar-B) (see Hinode). Zulu Time This is the time commonly known as Greenwich Mean Time (GMT) or the time at zero Meridian.