Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats 9783319095752

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Effects of Reduced Gravity Aaron Harrinarine Persad

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . About Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gravity on Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clarifying Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of Near Weightlessness on Physical Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluid Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiphase Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Boiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface Tension Effects and Negligible Buoyancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of Near Weightlessness on Life Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Closing Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

The acceleration due to Earth’s gravity is called a 1 g environment. Humans are well adapted to living in 1 g since, through observations and experiences, they have developed an innate intuition of how the natural world behaves. For example, it is known that liquids will settle to the bottom of their containers, that objects thrown will follow a parabolic path as they fall toward the ground, and that the flame of a birthday candle will burn with familiar color and shape. A.H. Persad (*) Astronauts for Hire, Houston, TX, USA Thermodynamics and Kinetics Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, Canada e-mail: [email protected]; [email protected] # Her Majesty the Queen in Right of Canada 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_5-1

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However, the near-weightless environment can affect both physical and life processes and cause them to behave in seemingly counterintuitive fashions. This chapter focuses on near weightlessness and its effect on the behavior of several physical and life processes that are important to life support systems in spacecraft and habitats. Physical processes that will be discussed include fluid configurations, thermodynamic stability, aggregation, surface tension, and thermocapillary flow. Life sciences discussions will include human physiology, locomotion and perception, and plant biology.

Introduction This chapter begins with an overview of gravity in general, followed by a brief description of Earth’s gravitational field. With this context, the chapter proceeds with a closer look at life support systems. Investigations are made of the effects of reduced gravity from the perspective of physical and life sciences. At the end of this chapter, the reader will have an appreciation of the synergy required between physical and life systems to tackle the challenges of implementing life support systems in reduced gravity.

About Gravity It may be surprising to know that there is no scientific explanation of gravity (Brooks 2009). Theories exist to describe how gravity behaves and how it affects physical matter and light, but the fundamental source of gravity remains a mystery. No attempt will be made here to solve the mystery of gravity. Instead, the focus in this section is to define gravity within the context of this chapter. Gravity is an observable, natural event where all things are attracted to one another, regardless of their size or of the distance between them. In 1687, Sir Isaac Newton hypothesized that the gravitation force of attraction between two bodies was proportional to the product of their masses and inversely proportional to the square of the distance between them: F¼G

m1 m2 , d2

(1)

where F is force of attraction, m1 and m2 are the masses of the two objects, d is the distance between the objects, and G is an empirical proportionality constant known as the gravitational constant. The earliest measurement of the value of G was made in 1798 by Henry Cavendish. The standard value of G as given by the National Institute of Standards and Technology (NIST) is 6.67384  1011 m3 kg1 s2, but recent studies have raised questions about the accuracy of this value (Gibney 2014; Anderson et al. 2015).

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In a majority of cases, Newton’s law of gravity works well in describing celestial motions and most of one’s everyday observations of gravity. However, for massive objects, or for objects that move near the speed of light, Newton’s law fails. Instead of describing the effects of gravitation as an attractive force, Albert Einstein in 1915 attributed gravitation to the curvature of space and time. Einstein’s general theory of relativity has proven to be more accurate than Newton’s law, for example, in describing the orbit of Mercury around the Sun. However, in the nonrelativistic limit, Einstein’s general theory of relativity simplifies to Newton’s law. With this brief overview of gravity, the next section takes a closer look at the Earth’s gravitational environment.

Gravity on Earth For the purposes of this section, Newton’s gravitation law is taken as sufficient to describe the attractive force that Earth’s gravitational field exerts on objects. An object in Earth’s gravitation field will accelerate toward the Earth due to the field’s strength. The acceleration due to Earth’s gravity depends on several factors such as time, the spatial distribution of the planet’s material composition, elevation, latitude, and the shape of the planet. When the Earth is approximated as spherical, the standard value of Earth’s gravity at the surface of the planet is taken as 9.80665 m s2 (symbolically, this gravity value is represented as 1 g). Under these assumptions, Newton’s gravitation law in Eq. 1 simplifies to: !

!

F g ¼ mg :

(2)

The symbol ! in Eq. 2 – indicates that the parameter is a vector: it has both ! magnitude and direction components. In radial coordinates, g is directed toward the center of the Earth, whereas in Cartesian coordinates, it is directed downward. By contrast, the mass of the object, denoted by m in Eq. 2, is a scalar since it has no ! ! dependence on direction. The magnitude of F g , denoted as F g , is known as the ! weight of an object. Note from Eq. 2 that F g ¼ 0 does not necessarily imply that m = 0.

!

In Eq. 2, F g indicates the force that Earth’s gravity exerts on an object with a mass of m. As the object falls toward the Earth, it will eventually encounter a surface, such as a tabletop, and stop falling. A free body diagram (FBD) is helpful in illustrating what is meant by saying that the Earth’s gravity is 1 g. Note that in Fig. 1, the object !

is exerting a force of F g directed downward on the tabletop, whereas the tabletop !

!

!

exerts an equal and upward normal force of F N on the object (where F N ¼  F g and the upward force is indicated by the negative sign). Thus, the net force acting on the  !  ! object is F g þ  F g ¼ 0 and the object remains stationary. However, if the

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Fig. 1 Free body diagrams of objects in free fall or at rest on a tabletop

!

tabletop were suddenly removed, the net force acting on the object would be F g, and the object would continue to fall toward the Earth’s surface, only stopping once it landed on the ground, and the Earth’s surface exerted an equal and opposite force to the weight of the object. In both cases, whether or not the object was falling, the object was always subjected to the Earth’s gravity of 1 g. Thus, the 1 g of gravity “felt” on Earth is actually a result of the ground (or chair, or bed, etc.) pushing back against the object’s weight; if there were nothing to push against the object, it would experience free fall.

Clarifying Terminology Strictly speaking “gravity” has the units of acceleration. However, the term gravity is sometimes used to describe a force. Therefore, one must be careful in one’s understanding of the word “gravity” when it is used in the phrase “reduced gravity.” Consider the following example: astronauts on the International Space Station (ISS) will often talk about what it is like to float inside the station and live in zero gravity. Numerous press releases from space agencies also use the term “zero gravity,” and some even state that everything in the space station floats because there is no gravity up there. From the perspective of a scientist, the claim that there is “zero gravity” in space is false; the Moon orbits the Earth because of gravity; and the Earth is held in orbit around the Sun because of gravity. If there really were “zero gravity” in space, then the space station would not stay in orbit around the Earth; instead, it would vanish into deep space. The term “zero gravity” or “zero-g” only makes sense in the context of a force; there is no force pushing back (no opposing force) to stop the space station and the astronauts from falling around the Earth. In fact, a better term to use would be “free fall” or “weightlessness” since these terms do not incorrectly imply that the acceleration due to Earth’s gravity is zero.

Effects of Reduced Gravity

5 ISS - mean height in km

418 416 414 412 410 408 406 404 402 400 398

© Heavens-Above.com

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Fig. 2 The International Space Station has to be periodically re-boosted since its orbit decays from friction when in low Earth orbit (Peat 2015)

However, a scientist may still raise issue about using the terms “free fall” or “weightlessness” since these terms imply that space is a perfect vacuum. In reality, space is filled with micrometeorites and nano-sized dust particles that produce resistance or drag to spacecraft and other objects. The drag created by these particles in space is the reason why the space station’s orbit gradually decays and must be periodically re-boosted, as indicated in Fig. 2. For this reason (see chapter “▶ The Microgravity Environment”), some have used the term “microgravity” (106 g or μg) to more accurately describe the environment on spacecraft, since achieving a 0 g environment would not be possible. However, the term “microgravity” again confuses acceleration and forces. Thus, more appropriate terms to use to describe the space environment are “near free fall” or “near weightlessness.” The term “reduced gravity” is defined as an environment where the gravitational field is less than that of the Earth, for example, on the Moon, on Mars, on asteroids, or in deep space. The term “near weightlessness” is used in this chapter to describe the space environment that is predominantly in Earth’s gravitational field (Fig. 3). The remainder of this chapter will focus on the effects of the near-weightless environment.

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Fig. 3 There is gravity in space. Objects as high as 400 km above the Earth’s surface are well within the pull of the Earth’s gravitational field and experience 86% of the surface’s 1 g acceleration (Wikimedia Commons 2009)

Effects of Near Weightlessness on Physical Processes It may not be immediately clear what role physical sciences has to play in building a life support system for space. However, consider that a life support system must have a reservoir of water and that water must be transported from the reservoir through tubes to an outlet, and there may be air bubbles entrapped in the tubes affecting the flow of water to the outlet. In this simple example alone, a scientist must use thermodynamics to predict how the water behaves in the storage container, and an engineer must use multiphase fluid dynamics and physics to understand the flow of a water-air mixture in the tubes. This section takes a closer look at these and other physical science processes.

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Fig. 4 Glass cylinders of similar radii (approximately 30 mm), but different heights. Both contain similar amounts of pure water. At room temperature on the ground, the bulk liquid and vapor phases are stable and separated by a single, flat liquid-vapor interface

Fluid Stability Life support systems in space require that fluids such as water, liquid oxygen, and liquid ammonia be stored in reservoirs (see chapters “▶ Potable Water Supply” and “▶ Essentials of Life Support Systems: Water”). These reservoirs can be flexible or rigid and are typically closed to the environment. The fluids can be removed or added to the reservoirs through valves and tubes. If the stored fluid is volatile, both its vapor and liquid phases may exist simultaneously in the reservoir. On the ground, the reader knows that liquid water in a closed bottle will always be at the bottom of the bottle and the water vapor will be on top, with a single liquid-vapor interface between the two phases (Fig. 4). Furthermore, the reader knows that the singleinterface configuration is stable; if one were to shake (perturb) the water bottle so that the liquid and vapor phases sloshed and mixed, one would expect the liquid to eventually settle back down to the bottom. Thus, on the ground, the single-interface configuration is the stable configuration for the closed water liquid-vapor system. This makes it relatively easy for a life support system engineer to know where to place tubes to draw out the liquid water when on the ground. However, in near weightlessness, where should the engineer place the tubes to draw out liquid water from the reservoir? What if the engineer only wanted to draw out water vapor? To answer these fundamental questions, the engineer needs to know the stable configuration of the fluid held in the reservoir. Consider the two glass cylinders shown in Fig. 4 which are partially filled with water and on the ground (note that “on the ground” is a phrase used to indicate being in 1 g environment). The cylinders have similar diameters, but different heights. There is approximately the same amount of liquid water in each cylinder, and both have the

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single-interface configuration. Figure 5 indicates some possible configurations of the water in the cylinders when in near weightlessness; it may be challenging to intuitively identify which will be the final configuration of the water in each cylinder. Using thermodynamics, the stable equilibrium configuration of the water in each cylinder can be predicted. The details of the theory may be found elsewhere (Sasges et al. 1996; Ward et al. 2000), but the important result is that the temperature, amount of fluid present in the container, and contact angle of the liquid with the container’s wall are the factors that determine the equilibrium configuration. The water in the tall cylinder in Fig. 4 is predicted to take on the “double-interface configuration” shown in Fig. 5, whereas the water in the smaller cylinder in Fig. 4 is predicted to transition to the “bubble configuration” indicated in Fig. 5. In 1997, a series of water cylinder systems were flown on the Space Shuttle mission STS-87 to test the thermodynamic prediction that the confined water in the taller cylinder would transition to the double-interface configuration (Ward et al. 2000). As illustrated in Fig. 6, the experimental observations agreed with the predictions.

Multiphase Flow Another important aspect of any space life support system is the recycling of water (see chapters “▶ Potable Water Supply,” “▶ Essentials of Life Support Systems: Water,” “▶ Methods of Water Management,” “▶ Methods of Water Recovery,” and “▶ Water Quality Monitoring”). Currently, the Water Recovery System (WRS) on the ISS (see Fig. 7) is able to recycle up to 93% of the liquids it processes (NASA 2012). The efficiency of the WRS is sufficient to support the ISS crew of six, but only when complemented with periodic resupply shipments of water from the Earth. In deep space or on distant planetary habitats, there will be much less capability to resupply crew with consumables such as water from Earth. Water recycling systems in those distant habitats would have to approach 100% efficiency. The influent wastewater through the WRS may contain solid particulates and gases, producing multiphase flows in tubes (see chapters “▶ Manned Spaceflight Waste Management,” “▶ Essentials of Life Support Systems: Waste Management,” and “▶ Waste Management”). On the ground, engineers would expect that heavy solids collect at the bottom of the tube, while the lighter gases flow at the top of the tube. This aids in separating the phases. However, as the velocity of the flow increases, the flow patterns change, as indicated in Fig. 8 for the flow of a liquidgas system. In near weightlessness, the number of flow patterns is simplified since the density difference between the liquid and gas will not cause the “lighter” gas to stay above the liquid. As indicated in Fig. 9, the three main flow regimes in near weightlessness are bubbly, slug, and annular (McQuillen et al. 2003). A fundamental understanding of how fluids flow in pipes of different sizes, shapes, and junctions will be important to the design of any life support system.

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H c

b

θ Liquid

Vapor

θ

Vapor 2L

Rc

θ h

c

Single-Interface Configuration

c

Double- Interface Configuration

Liquid Vapor

Vapor

Rd

Rb

Liquid

Vapor Liquid θ

Vapor

θ

Bridge Configuration

Droplet Configuration

Bubble Configuration θ

Rsb

Rsd Liquid Vapor

Liquid

Sessile Droplet Configuration

Vapor

θ

Sessile Bubble Configuration

Fig. 5 In free fall, a single-component (water), vapor-liquid system confined to an isothermal, closed axisymmetric cylindrical vessel may reach any one of a number of possible stable equilibrium configurations shown (Sasges et al. 1996)

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Fig. 6 The predicted configuration of water in a glass cylinder in near weightlessness is shown to agree closely with observations made on the Space Shuttle mission STS-87 (Ward et al. 2000)

Fig. 7 The Water Recovery System is used onboard the International Space Station to convert wastewater into potable water, thereby conserving resources (NASA 2012)

Boiling In the WRS, water is recycled through a distillation process (NASA 2012). The reader may already be familiar with water distillation on the ground: a pool of wastewater is first boiled and turned into steam; the steam rises and leaves heavier impurities behind the pool; the steam is cooled and recondensed back into a storage container as clean water. This process is analogous to the Earth’s hydrological cycle, Fig. 10. However, in the near-weightless environment, the process of distillation is complicated by several factors.

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Fig. 8 The flow regime map for an air-water mixture flowing horizontally through a circular tube with a diameter of 5.1 cm. The flow types are illustrated in the cross-section images (Brennen 2008)

Fig. 9 Gas-liquid mixtures have different flow patterns in near weightlessness than they do on the ground. Note that the slug flow on the ground becomes plug flow in near weightlessness (McQuillen et al. 2003)

One complication comes from boiling. On the ground, as water boils, vapor bubbles form on the surface of the container, grow to a critical size, detach from the surface, and rise to the water-air surface. In near weightlessness, the vapor bubbles do not rise, but instead continue to grow in size and cause a phenomenon called dry-out: the vapor bubbles prevent liquid from reaching the hot container wall. It is more difficult for heat to travel through gases than through liquids. Consequently, in near weightlessness, the large vapor bubbles actually impede the boiling

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Fig. 10 Earth’s natural hydrological cycle uses energy from the Sun to recycle and purify water (National Weather Service 2010)

process. This is illustrated in Fig. 11 where the heat flux is shown to be less in the near-weightless environment compared to on the ground. Another complication is that, in near weightlessness, steam does not rise away from the impurities in the wastewater. To force the separation of steam from impurities, the distiller must be spun to create a localized acceleration field (NASA 2008). In this artificial acceleration field, the denser impurities collect at the walls, while the lighter steam stays near the axis of rotation. The steam is then pumped through a filter system and condensed into clean water. Water purification systems by boiling, distillation, and sedimentation are relatively straightforward to implement on the ground. However, in the near-weightless environment of space, artificial localized acceleration fields are needed in order for these processes to be of use in life support systems.

Surface Tension Effects and Negligible Buoyancy Surface tension is a material property that is important at interfaces. Many effects of surface tension are clearly visible on Earth. It is this property that causes water to have droplet shapes when it rains and to form beads on a wet spider’s web or at the

Effects of Reduced Gravity 35 30 Wall Heat Flux (W/cm2)

Fig. 11 The boiling curves for different amounts of subcooling are shown. The effect of subcooling on the ground (1 g) and in a 1.7 g environment (high-g) is small. However, in near weightlessness (μg), larger superheats result in larger areas of dry-out which reduces the critical heat flux (Kim 2003)

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Tb ulk=20°C, ug Tb ulk=30°C, ug Tb ulk=40°C, ug Tb ulk=50°C, ug Tb ulk=20°C, 1g Tb ulk=30°C, 1g Tb ulk=40°C, 1g Tb ulk-20°C, high-g Tb ulk-30°C, high-g Tb ulk-40°C, high-g Tb ulk-50°C, high-g

15 10 5 0

10

20 30 Wall Superheat (°C)

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tip of wet leaves (Shanahan 2011). At the water-air interface, the water molecules are more strongly attracted to each other than to the air molecules. As a result, there is a net inward force at the liquid-air interface, which is called the surface tension. For “ordinary” liquids, surface tension decreases with an increase in temperature (Shanahan and Sefiane 2014). On the ground, surface tension effects in physical systems are often masked. For example, as a coffee droplet dries (evaporates), it leaves behind a deposition pattern or ring stain (Deegan et al. 1997). Evaporation cools the surface of the coffee droplet resulting in temperature differences across the droplet (Fang and Ward 1999). The cool liquid near the droplet’s surface is heavier than the lighter (and warmer) liquid below. As a result the cool liquid sinks, while the warmer liquid rises to the surface. This process is called buoyancy-driven convection (Duan and Ward 2005a). This convection results in a circulation inside the coffee drop as it dries (Hu and Larson 2006) and the direction of the circulation determines type of coffee stain left behind. Furthermore, as noted earlier in this section, the surface tension also changes with temperature. The colder liquid would have a greater surface tension than the warmer liquid in the coffee droplet. As a result the cold liquid would pull the warmer liquid, also resulting in a flow called thermocapillary convection. Surprisingly, thermocapillary convection has been found to transport as much as 95% of the energy required to evaporate a liquid (Ghasemi and Ward 2010). Thermocapillary convection also plays an important role in determining the type of ring stain that will form (Hu and Larson 2006). However, on the ground, it is almost impossible to separate thermocapillary convection from buoyancy-driven convection (except Duan and Ward 2005a, b for water and heavy water since each has a maximum density

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Fig. 12 In near weightlessness, surface tension forces dominate and can cause liquids to “climb” sharp corners in a phenomenon known as capillary rise (Weislogel et al. 2011)

property), and some researchers have even mistakenly ignored thermocapillary convection completely. By contrast, in near weightlessness, buoyancy-driven convection becomes negligible, and surface tension effects dominate. As a result, simple tasks such as drinking become more challenging in space since surface tension tends to keep liquids in their container. Astronauts have typically had to drink from sealed pouches and relied on straws to suck liquid out. However, in near weightlessness, surface tension effects such as capillarity can be exploited to passively pull liquids out of their containers. Figure 12 provides a demonstration of surface tension effects and capillarity in near weightlessness relevant to life support systems (Weislogel et al. 2011): a liquid is enclosed in a cylindrical container with a vertical vane that can be rotated to produce V-shaped wall. As the angle of the V decreases (left to right, Fig. 12), the liquid “rises” up the wall more. This phenomenon has been used to develop a space coffee cup, shown in Fig. 13, that will allow astronauts to drink in a manner comparable to how it is done on the ground, without needing straws. Similarly, by tweaking the geometry of the container and making use of the surface tension properties of liquids, it may be possible to develop life support systems that move fluids passively, without the need for electricity to power mechanical parts (Weislogel and Graf 2015).

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Fig. 13 Patented 3D printed cups make use of capillary phenomena to give astronauts the ability to drink without using straws (Weislogel and Graf 2015)

Aggregation Filtering is another important aspect of space life support systems. Filters are used to remove particulates from the air that may otherwise cause irritation to the crews’ eyes and lungs (Love et al. 2014); filters are also used to passively separate solids and liquids in the WRS. On the ground, millimeter- and submillimeter-sized particles such as salt, sugar, and coffee tend to remain as individual particles. However, in the near-weightless environment, these same materials show strong cohesion (i.e., will only disperse with rigorous shaking) on the time scale of a few seconds (see Fig. 14) resulting in colloidal aggregation. There are two main pathways in colloidal aggregation. One is the transport of particles toward the aggregate, the other is the sticking of particles at the aggregate surface. The former pathway is called diffusion-limited aggregation, while the latter pathway is called reaction-limited aggregation (Veen et al. 2012). Aggregation may also result from electrostatic forces. Aggregation introduces another level of complexity in designing life support systems since they can clog filters and impede air flow and fluid circulation.

Effects of Near Weightlessness on Life Processes Life, so far as known, is designed (and perhaps even optimized) for Earth’s 1 g environment. This section takes a general, high-level look at how humans and plants react to the near-weightless environment and the implications that may exist for space life support systems.

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Fig. 14 In a near-weightless environment, salt (NaCl) crystals between 0.5 and 1.0 mm in size aggregate within seconds after having been rigorously shaken in a ziplock bag. The images show the salt immediately after rigorous shaking (a) and a few seconds later (b) (Love et al. 2014)

Humans On the ground, blood would tend to pool in the legs of a person standing upright. This would lead to an uneven distribution of blood volume with the head having the least amount of blood. However, a healthy body naturally produces a greater pressure at the legs, forcing the blood upward, resulting in a more uniform distribution of blood volume throughout the height of a person. A typical person will have between 5 and 6 l of blood in their body, which accounts for approximately 7% of their mass. In a healthy person’s circulatory system, the heart will pump the entire volume of blood around the body in approximately 1 min. The pumping of the heart forces blood through arteries and creates a maximum pressure called the systolic pressure. When the heart is at rest between beats, the blood pressure is a minimum, called the diastolic pressure. In a healthy person, systolic and diastolic pressures are approximately 120 and 80 mmHg, respectively. High or low blood pressures can be indicators of adverse health effects.

Balance and Equilibrium The vestibular system provides a person with a sense of body position and balance, or equilibrium, on the ground. The vestibular system also helps to keep one’s eyes fixed on a moving target. Among other parts, otolithic organs in the inner ear have important roles in vestibular system. Otoliths are flat crystals that cover sensitive hair bundles. When the head is tilted, the otoliths cause the hair bundles to bend and send signals to the brain to indicate the degree of the tilt (Tona and Taura 2014). In the near-weightless environment, the otoliths do not respond to head tilting, but head tilting is detected by other parts of the vestibular system, such as the semicircular canals (Clement and Wood 2014). As a result of the conflicting signals sent to the brain, an astronaut may experience motion sickness, dizziness, and imprecise movements. However, the discomforts typically last no more than a few days since the brain is able to adapt to changes in the vestibular system.

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Fig. 15 The body’s blood volume regulation mechanism produces different effects in response to a person standing upright (a), lying down in the supine position (b), or being in near weightlessness (c) (Diedrich et al. 2007)

Cardiovascular Effects and Vision Impairment When a person is suddenly brought into the near-weightless environment, blood no longer has the tendency to pool in the legs. In fact, the body’s natural physiology that had counteracted the blood-pooling phenomena on the ground now becomes responsible for pushing blood volume from the legs to the upper body, creating the appearance of astronauts having skinny “bird legs.” This results in an uneven distribution of blood volume in the body, with an excess of blood pooling in the chest cavity and head (see Fig. 15), often leading to astronauts having puffy faces in space (Diedrich et al. 2007). Other fluids migrate to the head, such as spinal fluids, and increase the intracranial pressure (the pressure of fluids pushing against the interior of the skull). An increase in the intracranial pressure can pinch the optic nerve or push against the eyeball causing deformities that can lead to vision impairment (see Fig. 16) (Marshall-Bowman et al. 2013; Nelson et al. 2014). Muscle Atrophy The shift of the bodily fluids to the upper body when in near weightlessness can trigger the body’s hemostasis to believe that there is an excess production in blood volume. The heart has to work harder to pump the blood that pools in the chest (Norsk et al. 2015). As a result, the body reduces its production of blood, and the blood volume decreases by approximately 22%. The reduced blood volume lowers the cardiac output required by the heart to circulate the blood around the body; the

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Fig. 16 In near weightlessness, astronauts may suffer from intracranial pressure vision impairment. On the ground (a), the eyeball appears round (dashed line). In near weightlessness (b), the eyeball is flattened (dashed line), and there is swelling of the optic nerve sheath (arrows) (MarshallBowman et al. 2013)

heart works less and loses muscle mass, a phenomenon known as atrophy (Diedrich et al. 2007). Other parts of the body suffer muscle atrophy in near weightlessness, especially the legs (see chapter “▶ Minimizing Muscle Atrophy”). The calf muscles will atrophy by approximately 13% in mass, resulting in a 32% reduction in peak power (Bagley et al. 2012). The loss of muscle mass and power increases the rate of fatigue of astronauts as they perform tasks.

Bone Loss Similarly, the body’s skeleton is also affected by the near-weightless environment (see chapter “▶ Maintaining Crew Bone Density”). The lack of mechanical loading and compression on the bones results in bone loss or osteoporosis (Arfat et al. 2014). Bones are composed of organic elements such as collagen that are interwoven with inorganic components such as calcium minerals. In a simplistic sense, bone is built by specialized cells called osteoblasts and broken down by osteoclast cells. At any given moment, a person’s bones are constantly being remodeled by both cell types. Thus, bone is a dynamic tissue, and a reduction of mechanical loading on bones results in a net loss of bone mass at a rate of 1–2% per month, called spaceflight osteopenia, by the routine turnover of the bone matrix (Drudi and Grenon 2014). Gene Expression Exactly how the body “knows” that it is in a near-weightless environment remains a mystery. Ultimately, near weightlessness will affect gene expression pathways that govern every aspect of the body’s composition: muscle, bone, nervous system, cardiovascular cycles, etc. It is important to identify what types of signaling

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Fig. 17 In near weightlessness, pressure suits will be important to help stimulate mechanoperception receptors in the body and slow down or even prevent muscle atrophy and osteoporosis. One such suit, shown here, is being developed at King’s College London (Wood 2014)

pathways are responsible for the physiological changes to the body in order to develop appropriate countermeasures in life support systems. For example, skeletal muscle and bone loss in near weightlessness are triggered by a mechano-signal transduction pathways (Hughes-Fulford 2002; Chopard et al. 2009). This means that life support systems should rely on mechano-perception countermeasures such as exercise (Dailey et al. 2014) and pressure suits (see Fig. 17) instead of high-protein and high-calcium diets to counter tissue loss in the near-weightless environment (Hackney and English 2014; Smith et al. 2014).

Perception The near-weightless environment also affects a person’s five basic senses. The brain is conditioned on the ground to interpret sensory information with respect to life on the ground. However, this conditioning can lead to misleading perceptions of our environment. Consider the two images in Fig. 18. Commander Chris Hadfield is easily recognized in the upright photo. Even in the upside-down photo, one can see that he is still the same person. However, by holding the page upside down, it is easily seen that there is certainly something wrong with the photo! Similarly, people have become accustomed to sunrises and sunsets: the lack of a typical day-night cycle in near weightlessness will affect sleep patterns, appetite and nutrient intake, stamina, and motivation. Implications for Life Support Systems The above discussions raise important questions about space life support systems. Consider astronauts sent on a deep space mission or to an isolated asteroid. Should

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Fig. 18 On the left image, it is easy to recognize retired Canadian astronaut, Colonel Chris Hadfield. On the right is a rotated image of Hadfield that appears normal. But if you rotate page, something is clearly wrong with Hadfield! Edited image from NASA (2011)

life support systems emulate conditions on Earth such as artificial day-night cycles? How long should a day be? Will it be necessary for astronauts to maintain the same muscle mass and bone density that they did on Earth or will a new standard of health have to be defined? Will astronauts need the same amount of nutrition intake as they did on Earth? These and many other questions are currently being investigated by the space community.

Plants Plants are important components in space life support systems (see section “▶ Long Duration Mission Life Support: Bioregenerative Life Support Systems”). Plants provide food to crew and animals, fuel, and medicine (Cohu et al. 2014). They also convert poisonous carbon dioxide gas into breathable oxygen required for crew health, and help control relative humidity and crew comfort. Moreover, gardening provides the crew with mental relaxation and boosts morale (Haeuplik-Meusburger et al. 2014). A variety of plant specimens, colors, and shapes also help to break the geometric monotony of a spacecraft. On the ground, plants typically grow relative to the pull of gravity: roots extend downward into the ground, and stalks grow upward toward the sunlight. Plants must also overcome gravity’s pull to draw nutrients and water from their roots to their uppermost parts. Specialized plant cells called statocytes located in the root tips are responsible for sensing the plant’s orientation in a gravitational field (Hoson and

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Fig. 19 Photos of cucumber seedlings grown in a 1 g acceleration field and initially positioned horizontally (a, d, g) or vertically (b, e, h). In all cases, the roots grow “downward.” In near weightlessness (c, f, i), the roots show randomness in their growth direction, but appear comparable to those grown in 1 g (Takahashi et al. 2015)

Wakabayashi 2015). The statocytes contain dense starch granules that sediment to indicate which way is up (or down) (Okamura et al. 2014). However, in the near-weightless environment, the starch does not sediment meaning that plants would not have a “gravity sensing” mechanism. Surprisingly, plants were found to grow just fine on the ISS (Takahashi et al. 2015); there was some randomness to the growth direction of the roots (see Fig. 19), but generally the roots remained in the growth media, while the leaves extended toward artificial light sources (Kordyum 2014). Thus, while statocytes are affected in near weightlessness, plants appear to have other mechanisms that help them to grow and survive in near weightlessness.

Closing Remarks This chapter briefly reviewed the meaning of gravity and the effects of near weightlessness on life support systems. There is gravity in space: it keeps the Earth in orbit around the Sun. Astronauts in spacecraft that orbit the Earth experience near weightlessness since there is no “ground” to stop them from falling. In near weightlessness, there is no differentiation between light and heavy materials. This makes processes needed for space life support systems more difficult to implement,

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such as separating gases from liquids. Buoyancy-driven convection becomes negligible in near weightlessness, and surface tension forces dominate, opening the possibility of designing fluid transport systems with no moving parts. Small particles have the ability to aggregate into larger clusters that could clog air filters. Humans will require special suits to stimulate the body’s mechanoreceptors to reduce muscle atrophy and bone loss. Other life support systems, such as greenhouses and gardening, have the added benefit of providing space crew with therapeutic relaxation. Both physical and life processes are affected by the near-weightless environment, and a synergetic approach will be needed to design and build effective space life support systems.

Cross-References ▶ Atmosphere Regeneration, Overview Biological Experiments in Space: ESA Biological Experiments in Space: NASA Biological Experiments in Space: Russia Biosuit ▶ Carbon Dioxide Reduction, Overview Characteristics of a Vacuum ▶ Effects of Space on Biological Plant Processes: Gravity ▶ Essentials of Life Support Systems: Humidity Control ▶ Essentials of Life Support Systems: Temperature Control ▶ Essentials of Life Support Systems: Waste Management ▶ Essentials of Life Support Systems: Water ▶ Hydroponics, Aeroponics and Zeoponics ▶ Life Support Systems of the International Space Station ▶ Maintaining Crew Bone Density ▶ Manned Spaceflight Waste Management ▶ Methods of Water Management, Overview ▶ Methods of Water Recovery ▶ Minimizing Muscle Atrophy ▶ Plant Physiology ▶ Potable Water Supply ▶ The Microgravity Environment ▶ Waste Management, Overview ▶ Water Recovery

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Brennen CE (2008) Flow patterns (Chapter M7). Lecture slides in PDF format. Brooks M (2009) Gravity: seven unanswered questions about nature’s most familiar force. New Sci 202:28 Chopard A, Hillock S, Jasmin BJ (2009) Molecular events and signalling pathways involved in skeletal muscle disuse-induced atrophy and the impact of countermeasures. J Cell Mol Med 13:3032–3050 Clement G, Wood SJ (2014) Rocking or rolling – perception of ambiguous motion after returning from space. PLoS ONE 9:e111107 Cohu CM, Lombardi E, Adams WW III, Demmig-Adams B (2014) Increased nutritional quality of plants for long-duration spaceflight missions through choice of plant variety and manipulation of growth conditions. Acta Astronaut 94:799–806 Dailey CM, Reinholtz C, Russomano T, Schuette M, Baptista R, Cambraia R (2014) Resistance exercise machine within lower body negative pressure for counteracting effects of microgravity. Gravit Space Res 2:94–107 Deegan RD, Bakajin O, Dupont TF, Huber G, Nagel SR, Witten TA (1997) Capillary flow as the cause of ring stains from dried liquid drops. Nature 389:827–829 Diedrich A, Paranjape SY, Robertson D (2007) Plasma and blood volume in space. Am J Med Sci 334:80–86 Drudi L, Grenon SM (2014) Women’s health in spaceflight. Aviat Space Environ Med 85:645–652 Duan F, Ward CA (2005a) Surface excess properties from energy transport measurements during water evaporation. Phys Rev E 72:056302 Duan F, Ward CA (2005b) Surface-thermal capacity of D2O from measurements made during steady-state evaporation. Phys Rev E 72:056304 Fang G, Ward CA (1999) Temperature measured close to the interface of an evaporating liquid. Phys Rev E 59:417–428 Ghasemi H, Ward CA (2010) Energy transport by thermocapillary convection during sessile- waterdroplet evaporation. Phys Rev Lett 105:136102 Gibney E (2014) Rivals join forces to nail down Big G. Nature 514:150–151 Hackney KJ, English KL (2014) Protein and essential amino acids to protect musculoskeletal health during spaceflight: evidence of a paradox? Life 4:295–317 Haeuplik-Meusburger S, Paterson C, Schubert D, Zabel P (2014) Greenhouses and their humanizing synergies. Acta Astronaut 96:138–150 Hoson T, Wakabayashi K (2015) Role of the plant cell wall in gravity resistance. Phytochemistry 112:84–90 Hu H, Larson RG (2006) Marangoni effect reverses coffee-ring depositions. J Phys Chem B 110:7090–7094 Hughes-Fulford M (2002) The role of signaling pathways in osteoblast gravity perception. J Gravit Physiol 9:P257–P260 Kim J (2003) Review of reduced gravity boiling heat transfer: US research. J Jpn Soc Microgravity Appl 20:264–271 Kordyum EL (2014) Plant cell gravis sensitivity and adaptation to microgravity. Plant Biol 16:79–90 Love SG, Pettit DR, Messenger SR (2014) Particle aggregation in microgravity: informal experiments on the International Space Station. Meteorit Planet Sci 49:732–739 Marshall-Bowman K, Barratt MR, Gibson CR (2013) Ophthalmic changes and increased intracranial pressure associated with long duration spaceflight: an emerging understanding. Acta Astronaut 87:77–87 McQuillen J, Rovito S, Jenkins D (2003) Two-phase flow in a microgravity environment. http:// microgravity.grc.nasa.gov/6712/2phase_flow/ 2phase.html. Page last accessed June 2015 NASA (2008) Recycling water is not just for earth anymore. http://www.nasa.gov/mission_pages/ station/behindscenes/waterrecycler.html. Page last accessed June 2015b NASA (2011) International Space Station imagery. http://spaceflight.nasa.gov/gallery/images/sta tion/crew-34/html/jsc2011e203354.html. Page last accessed June 2015c

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NASA (2012) Water: a chemical solution. http://www.nasa.gov/mission_pages/station/research/ benefits/Water_prt.htm. Page last accessed June 2015a National Weather Service (2010) The hydrologic cycle. http://www.srh.noaa.gov/jetstream/atmos/ hydro.htm. Page last accessed June 2015 Nelson ES, Mulugeta L, Myers JG (2014) Microgravity-induced fluid shift and ophthalmic changes. Life 4:621–665 Norsk P, Asmar A, Damgaard M, Christensen NJ (2015) Fluid shifts, vasodilatation and ambulatory blood pressure reduction during long duration spaceflight. J Physiol 593:573–584 Okamura M, Hirose T, Hashida Y, Ohsugi R, Aoki N (2014) Suppression of starch synthesis in rice stems splays tiller angle due to gravitropic insensitivity but does not affect yield. Funct Plant Biol 42:31–41 Peat C (2015) Height of the ISS. http://www. heavens-above.com/IssHeight.aspx. Page last accessed June 2015 Sasges MR, Ward CA, Azuma H, Yoshihara S (1996) Equilibrium fluid configurations in low gravity. J Appl Phys 79:8770–8782 Shanahan MER (2011) On the behavior of dew drops. Langmuir 27:14919–14922 Shanahan MER, Sefiane K (2014) Recalcitrant bubbles. Sci Rep 4:4727 Smith SM, Abrams SA, Davis-Street JE, Heer M, O’Brien KO, Wastney ME, Zwart SR (2014) Fifty years of human space travel: implications for bone and calcium research. Annu Rev Nutr 34:377–400 Takahashi H, Higashibata A, Fujii N, Miyazawa Y, Kamata G, Kobayashi H (2015) Dynamism of auxin efflux facilitators, CsPINs, responsible for gravity-regulated growth and development in cucumber (CsPINs) – 05.13.15. http://www.nasa.gov/mission_pages/station/research/experi ments/831.html. Page last accessed June 2015 Tona Y, Taura A (2014) Chapter 8: Otolith. In: Regenerative medicine for the inner ear. Springer, Japan, pp 67–74 Veen SJ, Antoniuk O, Weber B, Potenza MAC, Mazzoni S, Schall P, Wegdam GH (2012) Colloidal aggregation in microgravity by critical Casimir forces. Phys Rev Lett 109:248302 Ward CA, Rahimi P, Sasges MR, Stanga D (2000) Contact angle hysteresis generated by the residual gravitation field of the space shuttle. J Chem Phys 112(16):7195–7202 Weislogel MM, Graf J (2015) Capillary effects of drinking in the microgravity environment (capillary beverage) – 05.20.15. http://www.nasa.gov/mission_pages/station/research/experi ments/2029.html#overview. Page last accessed June 2015 Weislogel M, Robinson J, Warren L (2011) The advantage of laboratory time in space. https://blogs. nasa.gov/ISS_Science_Blog/2011/05/13/post_ 1305139790514/. Page last accessed June 2015 Wikimedia Commons (2009) Earth G force. http: //commons.wikimedia.org/wiki/File:Earth-Gforce.png. Page last accessed June 2015 Wood A (2014) King’s College London develops skinsuit to prevent muscle and bone loss in space. http://www.gizmag.com/kings-college-muscle-saving-skinsuit/31259/. Page last accessed June 2015

Characteristics of the Martian Surface David F. Wassell

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orbital and General Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cryosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Volcanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cratering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chemical-Mineralogical Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

This chapter is a general, very basic overview of the characteristics of the surface of Mars. This includes the radiation environment and insolation; characteristics of the atmosphere; dust; magnetism; surface features including volcanism, cratering, and other features; the presence and form of water; and surface mineralogy and chemical makeup. This is at times interpreted in terms of how these features may affect life support on the surface.

D.F. Wassell (*) Operations, Saskpower BDPS (Boundary Dam Power Station), Estevan, SK, Canada Astronauts4Hire, Houston, TX, USA e-mail: [email protected]; [email protected] # Her Majesty the Queen in Right of Canada 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_18-1

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Introduction Mars has captured the imagination of humanity since before written records and has played a part in various mythologies and religions worldwide. The name for this naked-eye visible planet is associated with war or fire in various languages, due to its reddish hue. After the Apollo program, Mars was looked at as the next major destination for the world’s space agencies. However, initial studies (e.g., the Space Exploration Initiative) assumed the development of new heavy lift launch vehicles designed to launch massive manned spacecraft, carrying with them all the comforts of modern society including every consumable required for the entire return trip. The program’s cost at that time (the 90-Day Study) was found to be US$450 billion, equivalent to US$805 billion in 2015. This is akin to the Franklin expedition, where the British admiralty outfitted the Erebus and Terror (interestingly, named along the same lines as the two primary natural satellites of Mars) with the latest in ocean going technology and comfort. In the end, the Franklin exhibition not only failed to navigate the northwest passage through northern Canadian waters, but it ended in disaster. Ultimately this was at least in part because they failed to use local resources; instead they attempted to bring their home with them. Successful mapping of the Canadian arctic, as well as mapping and eventual settlement of large swaths of Western Canada (by people of European descent, First Nations history is clearly different), relied primarily on small groups using mostly local resources, often in the employ of the two competing fur trading companies (the Hudson’s Bay Company and the North West Company). This pattern of successful use of local resources is seen in the settlement of Iceland, the United States, and societies around the world. The recognition of the success of small groups living off of local resources eventually resulted in an understanding of the value of in situ resource utilization (ISRU) (Zubrin et al. 2011). This understanding has led to a flurry of research on how a mission to Mars might use local resources to provide a greater return for a smaller initial cost, and eventually settlement of the red planet. For this to be successful requires a clear understanding of what local resources, and dangers, exist (Badescu 2009) (Carr 2007). This chapter attempts to provide the beginnings of this understanding by presenting an overview of the radiation environment, temperature, atmospheric conditions, and geological and chemical makeup at the surface of Mars.

Orbital and General Parameters The orbit of Mars is significantly more eccentric than that of Earth, with a perihelion of 206.7 million km and aphelion of 249.2 million km. Because of this eccentricity of Mars’ orbit, the seasons are of unequal length, resulting in spring in the northern hemisphere being the longest season, and autumn in the northern hemisphere the shortest. The Martian (tropical) year is about 668.6 local days, with each day being 24 h, 39 min, 35 s. Mars’ axial tilt is 25.19 , similar to Earth (23.4 ). There have been a number of suggested calendars, such as the Darian calendar and Robinson calendar; however, currently the Martian “date” is based on the angle of the line between

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Mars and the sun relative to the position at the northern hemisphere spring equinox (solar longitude, Ls).

Structure Mars is considerably smaller than Earth, with a mass of 6.419  1023 (about 11% the mass of Earth), density of 3.94 g
cm 3, and radius of 3393.4 km (Lide 1991–1992). Surface area is 144.4 million km2. Gravity at the surface is 0.376 g, corresponding to an acceleration of 3.711 m
s 2. Internally Mars is thought to contain a largely liquid core, thus lacking the ability to generate a global magnetic field.

Magnetic Fields Although Mars lacks a global magnetic field, there are a number of magnetic anomalies. These are thought to be fossilized remnants of an early global magnetic field, although the reason these magnetic anomalies occur mostly in the southern hemisphere remains somewhat controversial, with some models suggesting it’s due to a massive impact that is thought to have also produced the northern plains. The magnetic field strength of the strongest anomalies is less than 650 nT at 200 km (Purucker et al. 2000), two orders of magnitude weaker than Earth’s. However, this remains powerful enough, and extends high enough into space, to generate aurora. Additionally, it appears as though there is some local protection from radiation at the surface due to these magnetic anomalies.

Radiation Environment Irradiance Mars is 1.5 AU from the sun. Because of the inverse square law, this distance results in an irradiance of about 600 W
m 2 at the top of atmosphere. However, as on Earth, sunlight is reflected, blocked, and otherwise prevented from reaching the surface. At the equator, this causes the irradiance to range between about 50 W
m 2 and 200 W
m 2, with much of the variation due to dust storms (Levine et al. 1977). This is not much less than irradiance on Earth in central Canada and through central Europe, areas where photovoltaic cells are often in use. Small amount of atmospheric dust can also be responsible for diffusion of sunlight, which provides advantage for some types of solar cells. Surface Temperature Temperature at the surface ranges from 133  C to 27  C, with an average of 63  C ( 55  C is sometimes quoted). This, of course, depends on latitude and season. At the poles, temperature is maintained at around the freezing point of carbon dioxide ( 123  C) until the CO2 sublimates back into the atmosphere. At the equator, the temperature range is from 103  C to 15  C, whereas at latitude 30 S the range is from 116  C to 24  C. These are approximations; however, the suite

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of landers and THEMIS (Thermal Emission Imaging System, a thermal imager on the Mars Odyssey orbiter) shows this pattern to be reasonably accurate. Due to the orbital eccentricity and axial tilt, the southern hemisphere reaches a higher surface temperature during the southern summer than the northern hemisphere during the northern summer. Interestingly, surface temperatures appear to be a few degrees higher than in the late 1970s when the Viking program landers recorded temperatures on Mars. Beneath the surface, the geothermal gradient has been estimated to be ~10 K
km 1 for compacted regolith and 6.4 K
km 1 for permafrost/ice.

Radiation Hazards Recent results from the rover Curiosity have revealed that the average radiation exposure on the surface of Mars, including galactic cosmic radiation (GCR), solar energetic particles (SEP), and geological radiation, with no shielding, averages 0.665 millisieverts per day at a latitude of 4.5 south and about 4 km below the average equatorial altitude (the “datum”). This corresponds to an annual dose of about 243 mSv, or about 24 rem (Hassler et al. 2014). The simple expediency of using two meters of regolith as shielding material results in an annual dose of 1.5 rem per year. Assuming an average of ten hours per day in a shielded habitat, an annual dose of about 14 rem or less can be achieved. For comparison, in the most radioactive inhabited place on Earth (Ramsar, Iran), some residents are exposed to up to 26 rem per year (chronically about 13 rem/year) with no observable ill effects (Ghiassi-nejad et al. 2002). In fact, this population shows an elevated resistance to acute radiation compared to other populations. In addition, it is likely that life on Earth evolved at a time when the background radiation may have been up to an order of magnitude higher (Karam and Leslie 1996). This suggests that radiation dose on the surface of Mars, with some mitigation efforts, may not be as much of an issue as previously feared (Fig. 1).

Atmosphere As a result of the low gravity and the lack of a global magnetic field, most of the atmosphere of Mars has been slowly lost to space over time. This has resulted in a thin atmosphere exerting an average surface pressure of about 0.6 kPa, with a range of 0.03 kPa at the top of Olympus Mons, to 1.16 kPa at the bottom of Hellas Planitia. This varies by season; in the southern winter, about 25% of the atmosphere condenses out as solid carbon dioxide on the southern polar cap, reducing overall pressure, and then subliming back into the atmosphere during southern summer. During northern winter, only about 10–15% of the atmosphere condenses out on the northern polar cap. Atmospheric composition is primarily carbon dioxide (95.32%), nitrogen (2.7%), and argon (1.6%). Remaining gasses include oxygen (0.13%), carbon monoxide (0.07%), and water (0.03%). Despite the paucity of water in the atmosphere, it does form water ice clouds between 10 and 30 kilometers above the surface. These clouds result in a second temperature peak just after local midnight due to absorption of outgoing thermal radiation, heating the middle atmosphere.

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Fig. 1 Estimated cosmic ray environment from the 2001 Mars Odyssey mission (Image courtesy of NASA/Jet Propulsion Laboratory/JSC. From http://photojournal.jpl.nasa.gov/catalog/PIA03480, free use directly stated)

Researchers on the Phoenix mission observed snowfall from these ice clouds in 2008. The structure of the atmosphere is somewhat simpler than Earth’s partly due to the lack of ozone heating in the upper atmosphere of Mars. Temperature steadily declines with elevation for the first approx. 50 km (the troposphere) due to exchange of heat with the ground. From 50 km to 110 km, temperature is largely controlled by radiative emission/absorption to about 130  C. Above the mesopause, temperature begins to increase due to UV absorption in the upper atmosphere. Dust can play an important role in the vertical temperature profile by suppressing temperature variation. Mars is prone to both localized and global dust storms, which can increase optical depth dramatically. These dust storms are most common during southern spring and summer, when localized temperature variations are at their largest. Dust devils are quite common and have been recorded on the surface and from orbiters.

Cryosphere Mars was once thought to be a completely desiccated world with no available water. Recent understanding, based on data from both orbiters and landers, is that it contains a vast store of water in various forms in a variety of locations. Neutron spectrometer data (for hydrogen) has been collected for the entire surface of Mars, resulting in a global map of water resources (Fig. 2). Although it is clear that much of the water exists as water ice in permafrost in the high latitudes of the northern hemisphere, some of the mid-latitude water is likely bound as water of crystallization in sulfate salts and trapped in phyllosilicates (clay).

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Fig. 2 Global water map of Mars based on neutron spectrometer data (Image courtesy of NASA/ JPL-Caltech. From http://photojournal.jpl.nasa.gov/catalog/PIA04907, free use directly stated)

Outflow channels, layered sediments, delta fans, clays and other water-modified minerals, and a variety of other features are indications that there were once oceans or lakes on Mars, as well as significant glaciation. Currently, besides the neutron data, there are snowfall and frost, ice directly uncovered by the Phoenix lander, as well as active gully formation and other signs of large water stores. Cryosphere thickness depends on thermal conductivity, salinity, temperature, and other factors, resulting in estimates ranging from 2.3 km to 11 km for the thickness at the equator. There may also be a hydrosphere under the cryosphere, as the temperature increases at depth.

Volcanism Mars is famously home to the largest known volcano in the solar system, Olympus Mons. Like the main Hawaiian volcanoes, this is a shield volcano. Located at 18.65 N, 226.2 E, the shield is over 600 km wide and rises 21 km above the datum. The peak has six nested caldera up to 3.2 km deep and up to 80 km across. Because of the shallow angle of ascent, the short horizon on Mars (3 km), and the sheer size of the volcano, the entire thing can’t be seen from the surface. Besides its size, another unusual feature is the presence of a cliff encircling the base of the shield. The cliff height ranges from zero (where later flows conceal it) to 8 km high. Beyond the cliff is a 2 km deep moat-like depression extending annularly, likely due

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to surface depression caused by the weight of the structure. Cratering on some lava flows indicate an age of 115 to 10 million years, suggesting the possibility the volcano may still be geologically active. Immediately southeast of Olympus Mons is the Tharsis province, containing three large shield volcanos and a number of smaller volcanic features. The three primary Tharsis Montes include Arsia, Pavonis, and Ascraeus Mons, originating at 8.35 S, 120.09 E, and extending in a line to Ascraeus to the northeast. The Elysium volcanic province lies to the west of Tharsis by several thousand kilometers and is centered on Elysium Mons at 25.02 N 147.21 E. Some of the features in this province, particularly around Cerberus Fossae, are interpreted as being formed by water flowing over the surface (e.g., Athabasca Valles). Other volcanic regions are known as well, including Arabia Terra, and, in the south, the highland paterae near the Hellas crater.

Cratering Like most planetary surfaces, the Martian surface is peppered with craters of various sizes. Cratering rates are known, so the age of a surface can be estimated by counting the number of craters and noting crater overlaps. On Mars, this leads to the conclusion that the northern plains are considerably younger than the southern highlands, known as the global dichotomy. The objects generating craters bring with them a variety of materials to the surface, resulting in local sources of metals or volatiles. In addition, the impact heat may result in melting at the surface and localized differentiation, resulting in small ore bodies.

Other Features There are a multitude of canyons, valleys, channels, and gullies on the surface, the most obvious being the Valles Marineris group that extends from the Tharsis bulge to Margaritifer Terrace. These are thought to have been created largely by faulting, but outflow channels, sulfate-rich mineral layers, and sediment layers indicate that they contained lakes at one time. Numerous channels of both fluvial and lava origins exist, and seasonal gullies appear on the sides of several craters. Lava tubes are thought to exist in several areas; there are several holes or pits on imagery from orbiters that appear to be skylight openings to caves in otherwise featureless surfaces.

Dust Dust is a ubiquitous material, due to long-term weathering by the thin atmosphere and possibly by water weathering during warmer epochs in Mars’ past. A comparison of soil and dust samples from Spirit, Opportunity, and Curiosity (from the Alpha Particle X-ray Spectrometer, APXS) shows that the dust is chemically similar across

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the planet. It is, in fact, not dissimilar to fly ash from bituminous or subbituminous coal-fired power plants, suggesting a similar toxicity. Grain size is thought to be about 3 μm, putting it in the PM10 category (those particles that are between 2.5 and 10 μm in size). Regulatory agencies limit PM10 exposure to between 50 μg
m 3 and 150 μg
m 3 of air per day, depending on the country, due to the negative respiratory health effects of particles in this size range.

Chemical-Mineralogical Composition Common silicates on the surface include olivine (rich in magnesium and iron), pyroxenes (both calcium rich and magnesium rich), and plagioclase feldspars (sodium and calcium rich) (Bell 2008). These tend to be spatially separated, suggesting that these are not modified, but reflect an underlying difference in source magma chemistry. There are suggestions of high diversity of igneous materials, although at much smaller volumes than the abovementioned basalts. Mineral modification on a global scale appears to be largely physical, with limited chemical weathering evident. However, there are localized regions where it is clear that aqueous weathering has occurred. This has generated a range of phyllosilicates including montmorillonite and other smectites during an early wetter, pH neutral to alkaline era. Later volcanic eruptions would have covered large portions of the clays and released SO2 and HCl, resulting in sulfuric acid formation and hydrochloric acid condensation, at least on the local scale. Sulfate deposits, including calcium sulfate, have been found in several places on Mars, as well as rocks that appear to have been modified by acid fog (sulfuric acid readily forms fogs). Carbonates are largely absent on Mars; however, small amounts have been detected in the dust, possibly due to in situ formation of iron/calcium carbonates after condensation of thin water films on the dust particles. Chlorides are less abundant, but could be expected to be part of the later acidic aqueous environment. Low levels of perchlorate salts have been found at both the Phoenix site and the Curiosity site, suggesting that these salts are widespread. Although iron is the main source of the color of Mars, the coloration is not due to ore-body levels of enrichment. However, large amounts of high hematite (50–60%) concretions (“blueberries”) have been found by the Opportunity science team. Because Mars has differentiated, it is likely that various ore bodies exist as well. Mars shows varied surface characteristics, many of which have potential impacts on future life support system design. Potentially toxic dust, radiation, low temperatures, and low atmospheric pressure are challenges. However, the presence of water, a carbon source for polymer synthesis, passive radiation shielding, reasonable sunlight levels, and potential metal sources offer resources that may offset these challenges.

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Cross-References ▶ Characteristics of the Lunar Surface ▶ Earth’s Atmosphere ▶ Martian Atmosphere ▶ Martian Environment, Overview ▶ Radiation on the Moon and Mars, Overview

References Badescu V (2009) Mars: prospective energy and material resources. Springer Science & Business Media, Berlin Bell J (ed) (2008) The martian surface. Cambridge UniversityPress, New York Carr MH (2007) The surface of Mars. Cambridge University Press, New York Ghiassi-nejad M, Mortazavi SMJ et al (2002) Very high background radiation areas of Ramsar, Iran: preliminary biological studies. Health Physics 82(1):87–93 Hassler DM, Zeitlin C et al (2014) Mars’ surface radiation environment measured with the Mars science laboratory’s curiosity rover. Science 343(6169) Karam PA, Leslie SA (1996) The evolution of the earth’s background radiation level over geologic time. In Proceedings: IRPA9: 1996 international congress on radiation protection. Berger, Austria, Vol. 2, pp 238–240 Levine JS, Kraemer DR et al (1977) Solar radiation incident on Mars and the outer planets: latitudinal, seasonal, and atmospheric effects. Icarus 31(1):136–145 Lide DR (1991–1992) CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data. Special student edition. CRC Press, Boca Raton Purucker M, Ravat D et al (2000) An altitude-normalized magnetic map of Mars and its interpretation. Geophysical Research Letters 27(16):2449–2452 Zubrin R, Wagner R et al (2011) The case for Mars: the plan to settle the red planet and why we must. Free Press, New York

Recent American Life Support Systems: Skylab, Spacelab, and the Shuttle Davide Sivolella

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Skylab Environmental Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Space Shuttle Environmental Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Spacelab Environmental Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Abstract

Skylab, Space Shuttle, and Spacelab are each a successful program of the NASA post-moon landing era of the late 1960s and early 1970s. Though different in size and mission objectives, their life support systems shared similar features such as active and passive thermal control systems, atmosphere revitalization systems, waste management, water supply, and breathable air pressure and composition control.

Introduction While the US space program of the 1960s was dominated by the goal of stepping foot on the Moon, several NASA centers and aerospace firms across the country kept studying the feasibility of delivering a permanent outpost in low Earth orbit in which men could live for extended periods of time conducting scientific observations, experiments, and biomedical studies of human adaptation to microgravity. On May D. Sivolella (*) UK Civil Aviation Industry, London, UK Hemel Hempstead, UK e-mail: [email protected] # Springer International Publishing AG 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_42-1

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14, 1975, NASA launched its first space station. Called Skylab, it was a converted Saturn V third stage stripped of all propulsion-related systems. While the large hydrogen tank was converted in a two-compartment habitation and working area, the smaller oxygen tank at the bottom of the stage becomes the disposal volume for all the trash produced on board and for this reason was called the waste or trash tank. With such an arrangement, the third stage was denominated the orbital workshop (OWS). Outside it was shrouded in a thin meteoroid shield and provided the structural mounting for two large winglike solar arrays for the generation of electric power. Connected to the workshop was the airlock module (AM) that provided an airlock for extravehicular activities, along with the main systems for communication and data transmittal, environmental and thermal control systems, and the electric power control system. It also served as a link between the workshop and the multidocking adapter (MDA), a module that provided a principal and a backup docking port for the Apollo capsules visiting the outpost. In addition it housed experiments and the controls of the Apollo Telescope Mount (ATM). This was a large cylinder housing four telescopes for Sun observations as well as the control moment gyros for primary attitude control and four solar array wings. Skylab operations consisted in three long periods of manned occupancy spaced out by uninhabited intervals where the outpost was controlled remotely (Belew and Stuhlinger 1973) (Fig. 1). Designed and built through the 1970s, the Space Shuttle served the needs of the American space program for 30 years accomplishing a variety of complex missions that might well compete with the accomplishments of the Apollo program. The Space Shuttle was a winged flying machine, taking off as a rocket and returning as a glider. The center fuselage housed a 60 ft long by 12 ft in diameter cargo bay where most of the payload for the mission was stored along with equipment for several onboard subsystems. The cargo bay was protected by two 60 ft long payload bay doors, which stayed closed during atmospheric flight in order to provide an aerodynamic and protective fairing. On orbit, they were opened to expose the mission payload. The aft fuselage contained the vertical stabilizer plus rudder and the housing for the three main engines along with additional subsystems. The forward fuselage contained the crew compartment divided in three levels: the upper flight deck for atmospheric and orbital flying/piloting activities, a middeck for carrying out scientific activities and living functions, and a lower deck housing onboard subsystem equipment (Shuttle Crew Operation Manual 2008). Built by the European Space Agency in the late 1970s, Spacelab becomes a frequently flown payload during the Space Shuttle program before the International Space Station become operative. Spacelab was a 23 ft long and 13 ft in diameter cylindrical module placed on the rear of the Space Shuttle cargo bay and connected to the cabin crew with a tunnel. Its pressurized environment created a short-sleeve environment within which astronauts could carry out long research missions working on a multitude of experiments covering life science, materials, and fluid physics just to name a few. Several aluminum truss and panel structures called racks were lined on the laboratory walls, housing either equipment for onboard subsystems or experiments (National Space Transportation System Reference Vol 1 1988) (Fig. 2).

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Fig. 1 Skylab configuration (Copyright NASA)

Skylab Environmental Control System While the international space station is periodically visited by a fleet of resupply vehicles for her crews and onboard systems, Skylab was sent in orbit with all the consumables (fuel, food, oxygen, etc.) that it would need to healthily sustain the crews of the three planned stays. As such, its environmental control system was of the so-called open-cycle type in which the consumables were neither reclaimed for use nor replenished. The heart and lungs of the system were contained within the airlock module. On its external truss structure, six tanks of oxygen and nitrogen stored the necessary gases for atmospheric air composition and regulation within all habitable areas of the outpost. During manned operations, the astronauts breathed a mixture of 76% oxygen and 26% nitrogen at a total atmospheric pressure of 5.0  0.2 psi and with an oxygen partial pressure (PPO2) of 3.6 + 0.3 psi. This means the astronauts breathed the same amount of oxygen they would normally inhale on Earth, despite the much lower onboard atmospheric pressure. PPO2 served as the basis for the two-gas control system to automatically regulate the cabin air

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Fig. 2 Artist’s representation of Spacelab within the Space Shuttle cargo bay (Copyright NASA)

atmosphere and pressure. If it was lower than 3.6 psi, oxygen would be added to the cabin. If it was higher than the upper range, nitrogen would be drawn instead. The system was designed to be “fail-safe,” as pure oxygen would be supplied to maintain total pressure in case of electrical power or PPO2 sensor failure. Pressure relief valves in the orbital workshop would protect the hull if the total pressure exceeded 6.0 psi (MSFC Skylab Orbital Workshop Vol 1 1974). From the airlock module, a supply duct delivered conditioned air into a mixing chamber located in the forward compartment of the orbital workshop. Three distribution ducts departing from the chamber routed the air to a plenum between the lower habitation compartment floor and the oxygen tank. Flow within each duct was maintained by a four-fan cluster. Air filled uniformly the plenum, and diffusers on the floor allowed the air to disperse into the habitation area circulating it back to the airlock module for conditioning. However a portion of the air would be drawn into the mixing chamber through screens covering five of its sides, to be directed again into the plenum (MSFC Skylab Orbital Workshop Vol 1 1974). Within the airlock module, the air underwent a series of conditioning and purifying processes. Humidity was controlled by means of heat exchangers and molecular sieves that removed the moisture and condensed and stored it in the waste tank. Two molecular sieve systems were present on board, each containing one charcoal filter and two CO2 scrubbers. The former had nine pounds of activated charcoal used to remove odors and trace contaminants and had to be manually replaced once exhausted. The latter were beds of zeolite operating alternatively on a reversible absorption/desorption cycle. During an absorption cycle, one of the two beds would scrub the air for 15 min. Subsequently it entered the desorb cycle in which it was warmed up from 360 to 410 F and exposed to the vacuum of space to expel the absorbed CO2 overboard. In the meanwhile the other bed started an absorption cycle for the next 15 min (MSFC Skylab Airlock Module Vol 1 1974).

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Air temperature and thermal control of the inhabited parts of Skylab were achieved by means of active and passive systems. Cabin air temperature was actively controlled by one heat exchanger in the airlock module and by convective heaters in the three distribution ducts in the orbital workshop. Radiant heaters would provide thermal control during periods of unmanned flight to keep food and other supplies at a minimum temperature. The airlock module runs also an active cooling system consisting of two separate, redundant loops in which cooling fluid flowed through cold plates and heat exchangers to collect the heat produced onboard. While each loop was able to dissipate all the anticipated heat waste during periods of manned tenure, both loops were run simultaneously. During periods of unmanned flight, only one loop would be kept running with the second in stand-by ready to take over when a failure developed in the other loop. The gathered heat was rejected into space by 11 radiators mounted on the airlock module and on the multi-docking adapter. During intense heat peak periods, the radiators would receive a boost from the thermal capacitor module installed on the external truss structure of the airlock module. The module contained two thermal capacitors filled with tridecane wax within an insulated enclosure to provide a phase change heat sink. On orbit the capacitors were designed to be normally frozen or “charged.” As the capacitor received the coolant fluid exiting the radiators, if the outlet coolant temperature exceeded the wax melting point, the wax would melt taking away further heat from the coolant. Passive temperature control systems consisted of using coatings with different emissivity on the inside and outside of the inhabited parts of Skylab to regulate the radiant thermal energy exchange with the external environment. The external meteoroid shield was painted with black and white coatings with a pattern designed to absorb sufficient solar energy to meet the astronaut comfort temperature criteria with the convective heaters on (MSFC Skylab Airlock Module Vol 1 1974). The outboard forward dome of the workshop was covered with high-performance insulation (HPI) blankets made of multiple layers of low-emissivity insulation to provide a high thermal resistance between the exterior surface of the dome and its external environment. Two heat-pipe loops were installed inside the workshop to provide high thermal conductance paths to allow heat to be transferred readily from hot to cold areas to raise their temperature. In fact, it was necessary to maintain all areas at a minimum temperature of 55 F during habitation to avoid condensation and growth of bacteria (MSFC Skylab Orbital Workshop Vol 1 1974). During ascent, the meteoroid shield was lost and with it a fundamental passive temperature control system. As soon as Skylab arrived in orbit, temperatures raised quickly and well past the acceptable internal temperature range. In few days and with the help of thermal analysis, a parasol was built and shipped to the outpost with the first visiting crew. Once onboard, they deployed the parasol through an internal scientific airlock within the workshop facing Skylab’s Sun side. It had a segmented central pole with four telescopic spring-loaded rods that were meant to give it a rectangular shape. Despite it did not deploy fully, it nevertheless reduced the temperature inside the workshop to acceptable levels that allowed the continuation

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of the mission. The next visiting crew installed a second and bigger sunshade to provide additional protection. Throughout the life of Skylab, the active thermal control system performed as expected meeting all design requirements. The reduction of the orbital workshop passive thermal protection resulted in higher heat inputs from the external environment and therefore neither the radiant heaters nor the ventilation duct heaters were used (MSFC Skylab Orbital Workshop Vol 1 1974). Ten 600-pound capacity stainless steel tanks in the workshop held all of Skylab’s water reservoir. Identified as one to ten, each tank was assigned to a specific water network and for which only one tank at a time was used following a predetermined sequence. Each tank was a self-contained unit, in which stored pressurized nitrogen squeezed inwards a sealed metal bellow. The water was pushed out of the container into Teflon lines hoses and routed through the appropriate network. Water was provided to the wardroom water network for meal and drinks preparations, to the waste management compartment for personal hygiene, and to the urine system flush water network. An eleventh tank provided a portable contingency water container, with a capacity of 26 pounds, to be used in the event of a water network failure and for the wardroom water network. Purity of the water in each tank was periodically monitored, and if necessary iodine would be injected through an injection port to act as biocide (MSFC Skylab Orbital Workshop Vol 3 1974). Skylab was the first spacecraft to afford a toilet system worth its name. One area of the lower habitation compartment included a roomy waste management compartment where the astronauts could relief themselves. Each crew member was assigned a urine drawer in which there was a hose with a receiver similar to the relief tube used on board military aircraft. During micturition, airflow would draw the liquid toward a centrifugal separator where it was removed from air. While the air would be passed through a hydrophobic filter and odor control filter and blown back into the compartment, the urine was pumped into a 4-l storage bag connected to the separator. Every 24 h, each storage bag would be removed from its drawer and replaced with a new one, a sample would be taken and frozen for examination on the ground, and all bags would be stowed in a trash disposal bag. Also in the fecal collector apparatus, which sported a commode an astronaut could sit on, a sustained airflow was used to draw the feces into a bag. The air would then pass through the same filters used by the urine drawers and returned to the compartment. After each defecation, the fecal bag was removed, replaced with a new one, vacuum dried, and stowed in another trash disposal bag (MSFC Skylab Orbital Workshop Vol 3 1974). Trash disposal bags were used to store all dry and wet waste and refuse collected daily. They were then deposited into the trash tank by means of the trash disposal airlock assembly, built into the former oxygen tank dome and extending through the floor into the habitation area. The waste tank was maintained below the triple point pressure of water by a non-propulsive vent system so that liquids entering the tank would immediately freeze. The waste tank afforded a means for disposal of materials without contaminating the external optics of Skylab or imposing a significant demand on the attitude control system (MSFC Skylab Orbital Workshop Vol 3 1974).

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Space Shuttle Environmental Control System The space shuttle’s environmental control system was designed to provide pressure control, atmospheric revitalization, active thermal control, and water supply. Two pressure control systems kept the cabin atmosphere at a total pressure of 14.7 psi with a composition of 20% oxygen and 80% nitrogen with each system drawing gases from one liquid oxygen tank and two gaseous nitrogen tanks installed beneath the payload bay. To avoid a too low or a too high concentration of oxygen, the oxygen partial pressure (PPO2) was maintained between 2.95 and 3.45 psi. To compensate for the inevitable air leaks that would develop overtime, the so-called O2/N2 manifold system regulated the amount of gases present in the cabin. If the PPO2 fell below its lower limit, oxygen would be added as soon as the total pressure fell below 14.7 psi. If the PPO2 exceeded its upper limit, nitrogen would be added instead once the sensed total pressure was less than 14.7 psi. In the event of rapid loss of air, an emergency control valve forced a flow of gas to prevent the total pressure falling below 8 psi. To protect the structural integrity of the cabin, two positive relief valves ensured that, in case of failure of the total pressure regulator, the pressure would not increase above the safe limits by venting air into the payload bay. Likewise, two negative pressure relief valves would let air to flow in the cabin if the external pressure exceeded by 0.2 psi the internal one (Space Shuttle Operations Contract Environmental Control and Life Support System 2006). The atmosphere revitalization system conditioned the air to provide a breathable mixture devoid of noxious gases and contaminants and at a comfortable temperature. Installed beneath the middeck floor, the apparatus drew the cabin air through a duct forcing the airflow to pass first through a trap for debris removal and subsequently through a lithium hydroxide canister where the CO2 was removed along with acidic contaminants. The air was then exposed to active charcoal to remove odors and contaminants and thus cooled passing through a heat exchanger where excessive heat was transferred to the water loop of the thermal control system. Cabin air temperature control was regulated, either automatically or manually, with a bypass valve placed upstream of the heat exchanger. The valve would limit the amount of air to be cooled down through the heat exchanger. The now cold air was drawn into one of two humidity separators where a rotating drum would centrifuge the air to extract its water content to be then stored in the wastewater tank. Subsequently the cooled and dry air was further purified by the ambient temperature catalytic oxidizer, which removed carbon monoxide generated by the crew and the outgassing of nonmetallic materials in the cabin. Finally, the cold airflow and the one that bypassed the heat exchanger merged together into the supply duct that fed the conditioned air into the environment through diffusers located throughout the cabin. The avionics equipment and the inertial measurement units were cooled by a closed ventilation loop, resembling the atmosphere revitalization system but containing only a heat exchanger to cool the air through the compartment. Cold plates were also provided for extraction of thermal energy from high heat-load-generating equipment. Water was chosen as cooling liquid for cold plates and air heat exchangers as it is not toxic and any leak into the cabin would not have harmed the crew. After having extracted

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Cabin Temperature: 65 to 80 F Humidity: 30 to 75 percent Oxygen partial pressure: 2.29 psia to 3.45 psia

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Fig. 3 Space Shuttle atmosphere revitalization system (Shuttle Crew Operation Manual 2008)

the heat from the cabin, the water loop exited the crew compartment to transfer its thermal load to the Freon loops of the active thermal control system by passing through the so-called Freon/water interchanger located into the payload bay. Based on the amount of heat collected, some of the water would bypass the interchanger in order to maintain the water temperature within preset limits. Two water loops run side by side though they were not operated simultaneously for extended periods of time as they would have collected so much heat that the Freon loops would not be able to dissipate (Space Shuttle Operations Contract Environmental Control and Life Support System 2006) (Fig. 3). The two Freon loops were part of the active thermal control system and provided a way to safely reject into space the heat generated within the crew compartment and by the subsystems and payloads within the cargo bay. Upon heat collection, each loop routed the Freon to one of the radiator assemblies. Each assembly consisted of four radiator panels attached to the inside of each payload pay door. Based on mission requirements, the two most forward panels could be hinged upwards to expand the exposed surface to space and increase heat rejection. The radiators on the left side serviced Freon loop 1, while those on the right side serviced Freon loop 2. For both loops, coolant flowed in series from panel to panel and in parallel within each panel through an array of tubes connected by an inlet and outlet connector manifold. The so-called RAD/BYPASS valve regulated the amount of Freon circulating within the radiators or outside, based on the heat rejection demand of the moment. In the RAD position, it allowed Freon to flow into the radiators, while in BYPASS it bypassed the radiators, preventing them from being used for cooling

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(Space Shuttle Operations Contract Environmental Control and Life Support System 2006). With the payload bay doors closed, the Freon loops would continue to collect heat, but the radiators could not be used. For this reason, alternative heat dissipation devices were designed. While on the launch pad or on the runway post landing, the vehicle was connected to an external cooling line that passed through the onboard ground support equipment heat exchanger where the Freon would release its thermal load and cool down. During ascent, up to solid rocket booster separation, some 2 min after liftoff, the Freon loops would collect the heat, and its thermal inertia was enough to limit the temperature increase so that no active means of heat rejection were required. Post booster separation, the outside pressure had reached an almost vacuum level, and the water flash evaporator system placed in the aft fuselage kicked in. It was composed of two identical evaporators known as the high-load evaporator and the topping evaporator. The only major difference was that the former had larger spray water nozzles for a greater cooling capacity. Each was a cylindrical shell similar in size to an office wastebasket and had dual water spray nozzles at one end and a steam exhaust duct at the other end. The shell consisted of two separated finned packages, one for each Freon loop. The hot Freon flowed around the finned shell as water from the supply system was sprayed onto the shell by the nozzles. The water would immediately vaporize, thereby cooling the Freon. To work properly, the spray chamber had to be maintained at a saturation pressure low enough for the water to evaporate at a temperature below the desired Freon outlet temperature. Since the maximum desired Freon outlet temperature was 40 F, the chamber pressure had to be maintained below 0.1 psi. This also allowed the water to instantly evaporate on coming into contact with the hot chamber walls, preventing flooding and subsequent freezing to cause the device to fail. For this reason the water flash evaporator could be used only above an altitude of 140,000 ft. If necessary it could also be used in flight to supplement the radiators. Before reentry the radiators were cold soaked for 1 h, meaning that the Freon was allowed to stay longer on the radiators, cooling down. Once the payload bay doors were closed, the radiators with the cold Freon were bypassed and the remaining Freon kept circulating through the loops cooled down by the water flash evaporator. Below 175,000 ft the cold fluid trapped into the radiators was allowed into the loops, and below 100,000 ft it becomes the primary source of cooling as the flash evaporators had lost their effectivity. If, before reaching the runway, the cold-soaked Freon had reached the temperature of 40 F, an ammonia evaporation system was used. It worked in the same fashion of the flash evaporator but used ammonia as it is the most efficient evaporant after water, having a later heat of vaporization about half that of water. Once on the ground, the ammonia evaporator would keep rejecting the onboard heat up to when the ground support equipment heat exchanger was hooked up again to take over (Space Shuttle Operations Contract Environmental Control and Life Support System 2006) (Fig. 4). Drinkable water and water for the flash evaporator was produced onboard as by-product of the chemical reactions undergoing into the three fuel cells of the electric power system. In fact, the decision of generating electricity using oxygenhydrogen fuel cells derived from the advantage of saving weight by not carrying all

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Fig. 4 Space Shuttle environmental control system principal elements (Shuttle Crew Operation Manual 2008)

the water necessary for the mission. The water supply system consisted of four tanks pressurized with gaseous nitrogen drawn from the tanks of the atmosphere pressure control system. Each tank was named after a letter of the alphabet starting from A. Tank A was the first to be filled, and as it was used by the crew for meal preparation and personal hygiene, it was sterilized prior to launch. As the fuel cells produced water rich in hydrogen, a matrix of palladium tubes provided for up to 85% of dehydrogenation. The water was further purified by flowing through a microbial filter and then directed to tank A. Once tank A was full, a check valve would divert the water into tank B. Once tank B was full, the process would repeat with tank C and D. Once all tanks were full, they would be emptied by dumping water overboard starting the filling cycle again. Water dumps were a regular housekeeping activity carried out by the crew each day. Later on the program, also tank B was selected to store potable water to provide redundancy. During missions to the international space station, water from this tank would be collected into portable water bags and transferred to the astronauts of the outpost reducing the amount of water supply delivered from the ground. A fifth isolated water tank was used by the wastewater system in which humidity condensate and crew liquid waste (urine) were stored in a sanitary manner until it could be dumped overboard through a dedicated line. The normal procedure was to dump this tank when its content reached 80% (Space Shuttle Operations Contract Environmental Control and Life Support System 2006). The Space Shuttle continued the tradition started with Skylab of providing a waste collector system similar to that used on Earth. The system served either sex

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and included an integrated commode and a urinal. The commode was used in the style of a conventional toilet and consisted in a contoured seat in hard plastic material that provided proper positioning and sealing in order to minimize air leakage. The fecal matter was sucked into a container via a 4-inch opening in the seat, with the suction action provided by air drawn through small holes beneath the seat at a rate of 30 cubic feet per minute. The waste was deposited into a porous bag liner, while the air passed through a hydrophobic material to prevent free liquid and bacteria from leaving the storage container. It then passed through an odor/bacteria filter before being fed back into the cabin. The urinal was a funnel with a hose. Once again airflow sucked the urine into a fan separator where centrifugal forces separated the two fluids. While the urine was sent to the wastewater tank, the separated air was filtered and returned into the cabin (Shuttle Crew Operation Manual 2008). The Space Shuttle was originally designed for flights lasting 10 days with a crew of seven. However, it was soon realized that, if flights could last longer, much more could be accomplished. This was in particular the case for Spacelab missions which were always fully packed with experiments and highly demanding in onboard resources. In the early 1990s, mission durations were greatly extended, thanks to the addition of the extended duration orbiter kit. Developed by Rockwell, the main and largest component of the kit was a pallet mounted on the rear of the cargo bay, containing four additional sets of liquid hydrogen and oxygen tanks. With them, mission duration repeatedly surpassed the 2 weeks. The kit also introduced an improved waste management system that was more comfortable and more sanitary than its predecessor and had unlimited capacity. As lithium hydroxide canisters had to be replaced twice a day, a 2-week flight would have required an impractical amount of canisters with consequent weight penalty. For this reason, the canisters were replaced by a regenerable carbon dioxide removal system in which the CO2 was removed by flowing cabin air through one of two identical solid amine resin beds. While one bed was absorbing CO2, the other bed was being regenerated by thermal treatment and vacuum venting. Given the lack of vacuum during ascent and reentry, lithium canisters were used during these flight phases (Sivolella 2013) (Fig. 5).

Spacelab Environmental Control System While the original plan called for Spacelab to provide its own atmosphere, it was soon realized that the Shuttle would be able to carry enough oxygen to provide air for the additional habitation volume. However, Spacelab did bring its own storage of gaseous nitrogen that was used by its atmospheric revitalization system to maintain the same atmosphere composition and pressure of the Shuttle crew cabin (Lord 1987). Airflow from the shuttle crew compartment was drawn into the Spacelab cabin with a fan installed in an air duct running the full length of the connecting tunnel. While in the duct, the airflow passed through a scrubber for carbon monoxide removal. Once in the Spacelab, the air was continuously processed through lithium hydroxide canisters for CO2 removal, through a scrubber for odor and contaminant

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Fig. 5 The extended duration orbiter kit pallet installed on the rear of a Space Shuttle (Copyright NASA)

extraction and through a condenser for moisture control. Whenever the PPO2 or the atmosphere total pressure fell outside the set range, Spacelab’s own atmosphere revitalization system would draw either oxygen from the Shuttle or nitrogen from its own tank to make up for the gases lost. Part of the Spacelab cabin air was also drawn into a second loop where it was cooled down with a water heat exchanger and then supplied to the rack avionics and experiment cooling. As experiments would change from mission to mission and would be operated at different settings or mode throughout a mission, the incoming rack cooling airflow could be easily regulated to account for variable heat loads (National Space Transportation System Reference Vol 1 1988). Spacelab subsystems were instead cooled by cold plates, as it was soon determined that air cooling would not be adequate to provide a precise temperature control. Spacelab cabin temperature control was maintained by an active thermal control system consisting of a water loop that gathered heat from the air through an air heat exchanger and that run through the subsystem cold plate-mounted equipment. The loop would then run through the Shuttle payload heat exchanger to transfer the collected heat to the Shuttle Freon loops. While the thermal control system would run only during orbital flight, if necessary, it could be operated in a degraded mode during ascent and reentry if some experiment required cooling. Thermal blankets plastered the outside surface of the laboratory as a passive

Spacelab Orbiter Interface

H2O

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Fig. 6 Simplified block diagram of Spacelab environmental control system (Lord 1987)

Orbiter Payload Heat Exchanger

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Pressure Regulator

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means of insulation from the flow of thermal energy to or from the surrounding environment (National Space Transportation System Reference Vol 1 1988) (Fig. 6).

References Belew LF, Stuhlinger E (1973) Skylab: a guidebook. NASA, Washington, DC Lord DR (1987) Spacelab an international success story. NASA, Washington, DC MSFC Skylab Airlock Module Vol 1 (1974) NASA MSFC Skylab Orbital Workshop Vol 1 (1974) NASA MSFC Skylab Orbital Workshop Vol 3 (1974) NASA National Space Transportation System Reference Vol 1 (1988) NASA Shuttle Crew Operation Manual (2008) United Space Alliance, LLC Sivolella D (2013) To orbit and back again: how the space shuttle flew in space. Springer, New York Space Shuttle Operations Contract Environmental Control and Life Support System (2006) United Space Alliance, LLC

Life Support Systems of the International Space Station Davide Sivolella

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Maintain Pressurized Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Maintain a Breathable Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Maintain Atmosphere Temperature and Humidity Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Fire Suppression and Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Regenerative Environmental Control and Life Support System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Abstract

The International Space Station is a collection of different pressurized modules and structural components provided by all the world major space agencies. The station is split in a Russian and a US segment, and each provides its own environmental control system aimed at creating and maintaining a safe comfortable living environment for the astronauts. The station relies on a stream of supplies sent from Earth to replenish consumables such as oxygen and water. However, within the US segment, a regenerative environmental control system has been installed, thanks to which wastewater and carbon dioxide are reclaimed to produce potable water and oxygen. This has resulted in a 65% of savings in resupplies reducing the overall cost of maintenance of the outpost.

D. Sivolella (*) UK Civil Aviation Industry, Hemel Hempstead, UK e-mail: [email protected] # Springer International Publishing AG 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_43-1

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Introduction The International Space Station (ISS) is the largest construction project ever carried out in space. It is also a unique international partnership of all the world major space agencies in which each institution has provided at least one building block. The Russian space agency has provided the service module, the functional cargo block (FGB) module, the docking compartment “Pirs,” the mini-research module 1 “Rassvet,” and the mini-research module 2 “Poisk.” Together they form what is called the Russian segment. NASA has provided the Node 1 “Unity,” the US laboratory “Destiny,” the joint airlock “Quest” for extravehicular activities, and a long truss structure called the “backbone” that supports four large sets of solar arrays for power generation and two large radiators for thermal control. The European Space Agency has provided the Node 2 “Harmony,” the Node 3 “Tranquility,” the research facility Columbus, and the observation deck called Cupola. The Italian Space Agency has provided the permanent multipurpose module “Leonardo.” The Japanese Aerospace Exploration Agency has provided the Kibo laboratory comprised of two pressurized modules and one external platform for experiments in the vacuum of space. The Canadian Space Agency has provided the sophisticated robotic arm Canadarm 2, instrumental during assembly and for periodic maintenance. All together these modules are referred to as the US segment of the station. Both the Russian and the US segments provide a pressurized comfortable shortsleeve environment where the astronauts can live and work. This is made possible by the station’s environmental control system designed to maintain a pressurized and breathable atmosphere, to maintain temperature and humidity levels, to detect and suppress fire, and to provide and recycle water resources. Although connected together, the Russian and US segments create their own living environment in different ways with their own equipment (Fig. 1).

Maintain Pressurized Atmosphere Astronauts onboard the International Space Station breathe a mixture of 21% oxygen, 78% nitrogen, and 1% carbon dioxide at a total pressure of 14.7 psi and oxygen partial pressure (PPO2) ranging 2.83–3.59 psi. Oxygen and nitrogen are regularly supplied by Russian Progress capsules and manually released by the crew into the Russian segment. Typically a Progress vehicle carries twelve tanks manifolded together in two groups of six, one for the oxygen and the other for the nitrogen. Once inside the Russian segments, forced ventilation through ducts carries and distributes the air to all of the other modules (Wieland 1998). The Russian segment has also the responsibility of being the main place for generating oxygen. This is accomplished primarily with the Elektron oxygen generator situated in the service module. The generator uses an electrolysis process where water is dissociated into its two components. While hydrogen is vented overboard, oxygen is discharged into the service module. Oxygen is also produced by the two solid oxygen generators Vika, installed on the service module which

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Fig. 1 ISS configuration 2014 (Copyright NASA)

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release oxygen by burning canisters of solid lithium perchlorate (International Space Station Familiarization Training Manual 2004). The US segment provides a backup capability for oxygen and nitrogen release, in the form of two tanks for each gas, installed on the outside of the airlock module. Due to their location, these tanks can only be replaced via extravehicular activity. Each tank connects to the internal supply, and distribution lines of the US segment and gases are released upon command issued by the pressure control assembly. The assembly has the tasks of monitoring the total atmosphere pressure, introducing oxygen and nitrogen, and providing a venting and overpressure relief capability. Three assemblies are currently install onboard, one in the US lab, one in the airlock module, and one in Node 3. The assembly is composed of two subassemblies, the pressure control panel and the vent and relief assembly. The pressure control panel works in concert with the major constituent analyzer of the atmosphere revitalization system. The pressure control panel measures the atmosphere total pressure and, if it senses it is under the established limits, releases nitrogen monitoring every second the total pressure up to when it has been restored to nominal values. The major constituent analyzer measures the PPO2, and based on the sensed value, commands are sent to the pressure control panel to release oxygen. The vent and relief assembly provides protection against overpressure in any of the US segment modules venting overboard via a nonpropulsive nozzle. Should an out-of-control fire or extremely toxic atmosphere develop, the assembly will provide for a much rapid overboard venting than that afforded by the positive pressure relief and controlled depressurization capabilities of each module. When the facing hatches of two adjacent modules are closed, between them there is a volume called vestibule. During assembly, several space shuttle missions brought important supplies using the so-called multipurpose logistic modules. Built by the Italian space industry, they were pressurized cylinders berthed to one of the available ports on the nodes. Before leaving the station, the module was unberthed and relocated on the space shuttle cargo bay. Prior to that however, the vestibule had to be vented to vacuum; otherwise the air inside it would have seriously damaged both modules. Vestibule depressurization was accomplished via a vestibule access port connected to the vent and relief assembly. To save on oxygen and nitrogen resources, when the airlock module is depressurized for extravehicular activities, its atmosphere is pumped back into Node 1 via a one-way depress pump (International Space Station Environmental Control and Life Support System 2001). As far as monitoring of composition and atmospheric pressure within the Russian segment is concerned, this is taken care of by means of several stand-alone pressure sensors distributed in each module. Based on the readings, oxygen or nitrogen are manually or automatically released into the cabin from the Progress capsule. One important feature of the environmental control system of the US segment is that it can provide a source of vacuum and overboard venting of waste gases for experiments, on condition that they are carried out inside a vacuum-qualified chamber to prevent loss of cabin pressure (International Space Station Familiarization Training Manual 2004).

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Maintain a Breathable Atmosphere Maintaining a breathable atmosphere boils down to three major functions: carbon dioxide removal, trace contaminant control, and major atmospheric constituent monitoring. All of these functions are performed within both the Russian and US segment, using different apparatus. For instance, the Russian segment performs carbon dioxide removal by means of the Vozdukh system. It consists of a set of sorbent beds that adsorb the carbon dioxide and then release it to space by exposure to vacuum (International Space Station Familiarization Training Manual 2004). The US segment instead uses the carbon dioxide removal assembly, where a series of desiccant and adsorbent (molecular sieves) beds are used to selectively remove water vapor and carbon dioxide from the cabin and vent it overboard. The assembly operates on a 5-h cycle that consists of two 144-min half-cycles. Each cycle is characterized by a different set of beds used within the assembly. During each cycle the air has to be first dried passing through one of two desiccant beds packed with two layers of zeolite 13X surrounding a layer of silica gel. The airflow is then cooled down to get rid of the heat gained during desiccation and made to pass through one of two beds of zeolite 5A where the carbon dioxide is adsorbed. The air is now passed through the second desiccant bed, used during the previous half-cycle, and for this reason rich in water. The air gains humidity again, drying the bed and it is finally returned into the cabin. In the meantime, the adsorbing bed used on the previous half-cycles is being exposed to vacuum to expel the collected carbon dioxide. Before starting the vacuum exposure, the bed is depressurized and the air pumped back into the cabin, in order to minimize loss of cabin air. To accelerate the process, the bed is warmed up by two heaters. However if the station is flying on the night side of its orbit, the heaters are not turned on to save on power (International Space Station Environmental Control and Life Support System 2001). As the name implies, trace contaminant control aims at removing numerous contaminants that disperse into the station atmosphere as a result of material off-gassing, crew metabolism, leaks, spills, and so on. Within the US segment, the trace contaminant control subassembly monitors up to 216 different potential contaminants either organic or inorganic and maintains them within acceptable limits. Within the subassembly, the air is made to pass through an activated charcoal bed for removal of most of the high molecular weight contaminants, including a variety of compounds containing sulfur, nitrogen, and halogens. Most of the air is then warmed up to 400 C prior to enter the catalytic oxidizer assembly where organic compounds are oxidized to carbon dioxide and water and inorganic ones are converted into acidic gases such as hydrogen chloride, hydrogen fluoride, and sulfur dioxide. Exiting the catalytic bed, the air is cooled down and circulated through a lithium hydroxide canister bed to remove any acid by-products produced by the oxidation process. The air now joins the stream of air that did not pass through the catalytic assembly and returns into the cabin (International Space Station Environmental Control and Life Support System 2001). While the Russian segment has not trace contaminant capabilities, it does have several gas analyzers in each module measuring quantities of oxygen, water, hydrogen, carbon dioxide, and monoxide. In the US segment, air composition is monitored

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by the major constituent analyzer. The analyzer is serviced by the lines of the sample delivery system, which allows to draw a sample of air from each module. Before taking a sample, the lines are purged to make sure that the air being analyzed is effectively representative of the module being under analysis. Duration of the purging depends on the length of the line connecting the analyzer to the module. Once in the analyzer, only a very small part of the sample is allowed inside the mass spectrometer, while the rest is returned into the cabin. The air is then warmed up to ensure there is not liquid water. Knowing the total atmosphere pressure, the mass spectrometer determines the percentages and partial pressure of oxygen, nitrogen, hydrogen, water, methane, and carbon dioxide. The results are then fed into the telemetry for downlink and on the appropriate onboard monitoring software for environmental control. The carbon dioxide removal assembly, the trace contaminant control subassembly, and the major constituent analyzer are all housed on a single rack, referred to as the atmosphere revitalization rack. At the moment two such racks are available, one in the US lab and the other in Node 3 (International Space Station Environmental Control and Life Support System 2001).

Maintain Atmosphere Temperature and Humidity Level Along with air cabin pressure and composition, temperature and humidity control are two other parameters to monitor and regulate to ensure the astronauts can live and work within a continuous comfortable short-sleeve environment. In the service module of the Russian segment, two so-called Russian air conditioners provide two air cooling and circulation loops to both the service module and the FGB. While both conditioners could be run simultaneously, normally only one is active at a time. Temperature is maintained within a range of 18–28 C, and a dehumidifier keeps humidity at a level ranging 30–70% with the condensate collected and sent to the condensate water processor for oxygen reclamation. Dust collectors and filters with their associated fan assemblies provide removal of bacteria and airborne particulate from the air (International Space Station Familiarization Training Manual 2004). Within all major modules of the US segment, air from the open module atmosphere is drawn into filters placed on standoffs along the floor of the module, for purification from bacteria and particles. The filters are connected to the two legs of the ducting that transports the air to one of two common cabin air assemblies (port and starboard side) where part of the air is passed through a condensing heat exchanger. The heat exchanger not only cools down the air but also dries it removing the condensate. Since the condensate is carried along with a small portion of air, it is immediately sent through a water separator, where a centrifuge separates the mixture with the air being routed to the ducting exiting the heat exchanger and the water to the water recovery and management subsystems. Air exiting the heat exchanger recombines with the stream that bypassed the heat exchanger and that therefore is still warm and humid. The cold and dry airflow is now routed to the two legs of the return ducting where supply diffusers placed on the “ceiling” of the module vent the

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air into the cabin. In each return ducting leg, there are a condensing heat exchanger liquid sensor and two outlet temperature sensors. The liquid sensor allows to detect any possible leakage of water from the heat exchanger. The temperature sensors instead monitor the temperature of the air exiting the cabin air assembly. These sensors are not used for controlling the working of the cabin air assembly, but rather to provide a feedback on its performances. Temperature of the airflow is automatically controlled by software based on the readings obtained by two inlet temperature sensors placed upstream of the cabin air assembly. The software regulates the opening and closing of a temperature control and checks valve placed just downstream of the heat exchanger. Based on the position of the valve, only part of the air is drawn into the heat exchanger while the rest bypasses it. In nominal situations only one common cabin air assembly is working with the other being isolated by the supply crossover damper valve. If necessary, the crew can manually operate the valve so that both cabin air assemblies can operate at the same time (International Space Station Environmental Control and Life Support System 2001). The temperature and humidity control systems of the US lab and Node 3 also interact with their atmospheric revitalization rack. A stream of air extracted downstream of the heat exchanger is sent to the carbon dioxide removal assembly, while another stream drawn upstream of the common cabin air assembly is delivered to the trace contaminant control subassembly. The two streams are then sent back to the module ducting just upstream of the portside cabin air assembly. This allows for increase in air purification. The common cabin air assembly in the airlock module is used only when the air lock is closed for astronaut campout activity in preparation for a sortie outside the station. In this way the cabin air assembly is subjected to less wear and tear of its components. Node 1 does not have a cabin air assembly but rather only a cabin air fan used to draw the module air through four filters and redistribution back into the module via four overhead diffusers. For this reason, Node 1 does not perform any temperature and humidity control on its atmosphere. Cupola has not any means of controlling the temperature and humidity of its atmosphere. This function is provided by Node 3 to which it is attached (International Space Station Environmental Control and Life Support System 2001). Not only it is important to maintain the air temperature and humidity at the desired values, but it is also essential to maintain uniformity of temperature and proper mixing of atmosphere components across all modules. This requirement is fulfilled by the intermodule ventilation assembly, a series of fans and ducting that moves the air from one module to other. The ducting system within the Russian and US segments differs rather profoundly. The Russian modules use flexible dragthrough-type and hard-plumbed ducts running through the connecting hatches and do not have isolation valves. This solution has the clear disadvantage that in case a module has to be isolated due to an emergency condition such as fire or rapid depressurization, precious time will be wasted in manually disconnecting the ducts in order close the hatches. The FGB module releases air into the Node 1 module and from there fans route air to the rest of the station, by means of hard ducts built into the interface between modules running outside of the hatches (International Space Station Familiarization Training Manual 2004). Each module either side of an

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interface has a valve connected to the ducting of the intermodule ventilation ducting. Air is drawn through a grille assembly being driven by a fan within the ducting. At both ends of the fan, two silencers attenuate fan noise. The air is then delivered into the adjacent module through a diffuser assembly comprised of a grid and a removable debris screen. Both the air lock and Cupola modules receive air from the node they are attached to and return air through their open hatch. In case of the air lock, air exchange is blocked when the air lock needs to be closed for preparation of extravehicular activities. From Node 1, air is also returned to the Russian segment through the open hatches. Compared to the Russian intermodule ventilation ducting, the system used by the US segment has the advantage of providing a quick means of sealing a module should a fire develop. In this case, not only the hatches can be closed without removing any ducting, but the ventilation valves would be automatically commanded closed and the fans shut down preventing any circulation of air into the affected module so that no additional oxygen is added to the fire nor smoke or contaminants are spread to the other modules. It is worth adding that in the Russian segment, the ventilation ducting does not have any isolation valve (International Space Station Environmental Control and Life Support System 2001). Another means of air circulation is provided by the avionics air assembly, available for racks whose equipment or payload is not mounted on coldplates. Four inlet ducting gather air from the volume of the rack and channel it through a heat exchanger where air is cooled and returned into the rack. The assembly does not provide any means of humidity control. In the FGB module, air is instead circulated behind all equipment and payload (International Space Station Environmental Control and Life Support System 2001).

Fire Suppression and Detection Along with rapid depressurization, fire is one of the most dreaded situations onboard a spacecraft. To initiate a fire, it is necessary to have all the three elements of the so-called triangle of fire: an ignition source, a fuel source, and oxygen. Equipment and payloads inside the habitable area of the station are built with materials that either do not burn under the expected range of environmental conditions or are “selfextinguishing.” Along with careful material selection, every module is fitted with several means for fire detection and suppression (Wieland 1998). On each module, fire detection is provided by smoke detectors that sample the air within the open cabin and in each rack or instrumentation panel and determine the amount of smoke using the light obscuration principle. Detectors are placed strategically across the volume of the module near the airflows put in motion by the temperature and humidity control system, near areas of oxygen buildup, near areas where materials do not meet the required flammability requirements, and inside racks that have electrically powered equipment or experiments. This will assure a prompt detection of any incipient fire (International Space Station Environmental Control and Life Support System 2001).

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Once a fire has been detected, the station caution and warning alarm immediately issue audible and visual indications of the emergency. Power and air circulation within the affected module are automatically shut down to minimize any addition of ignition and oxygen sources, while the astronauts manually suppress the fire using portable fire extinguishers. While the Russian fire extinguishers use water-based substances, those available in the US segment use carbon dioxide as their extinguishing agent. For this reason, the US fire extinguishers cannot be used in the Russian modules as they would overtax the Vozdukh system in removing the carbon dioxide from the air. Likewise, Russian fire extinguishers cannot be used in the US segment due to shock hazards caused by the conductivity of water and the higher equipment voltage than in the Russian segment (International Space Station Environmental Control and Life Support System 2001). Several portable breathable apparatus are also available and normally located next to the fire extinguishers. They are comprised of a mask and portable oxygen bottle that provides gaseous oxygen for an average of 15 min, depending on how hard the person is breathing. Past that time, the astronaut has to plug the apparatus into one of several special ports located in each module of the US segment directly connected to the station oxygen distribution system. In alternative, a new oxygen bottle can be used. Once the oxygen bottle is exhausted, it needs to be returned to Earth for a recharge. In the Russian modules, the astronauts can use gas masks that provide between 20 and 140 min of supplemental oxygen, again based on the person breathing. Once a mask is exhausted, another one has to be donned. Portable breathing apparatus and gas masks afford the astronaut protection from harmful smoke and from the carbon dioxide discharged with the fire extinguishers. They can also be used in case of spills of toxic substances or decompression (International Space Station Familiarization Training Manual 2004).

Regenerative Environmental Control and Life Support System Since the beginning, the International Space Station has relied on a regular stream of visiting vehicles to receive supplies for its systems and crew. This includes procurements of oxygen, nitrogen, and water largely used by the environmental control system. To reduce as much as possible dependence from Earth and cut on station operation costs, a regenerative environmental control and life support system has been installed in the US segment. The system is composed of the water recovery system and the oxygen generator system (Bagdigian and Cloud 2005). The water recovery system consists of the urine processor assembly and the water processor assembly. The urine assembly uses a distillation process to recover water from the astronauts’ urine. This is collected in the waste and hygiene compartment, the official name of the toilet system for the US segment. To maintain chemical and microbial control of the urine and hardware, the urine is treated with chemicals and flush water and then delivered to the wastewater storage tank assembly of the urine processor assembly. When a sufficient quantity of urine has been collected in the tank, a process cycle is automatically initiated with the liquid sent to the urine

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processor. Here a distillation process is used to recover water from the urine. The process occurs within a rotating distillation assembly that compensates for the absence of gravity, aiding in the separation of liquids and contaminants. The distilled liquid is then pumped into the water processor assembly wastewater tank where it is combined with the condensate gathered by the humidity condenser of the common cabin air assemblies of each module. The wastewater tank includes a bellows that pushes the water into a separator where gas is removed from the liquid. Before being returned to the cabin air, this gas is passed through a separator filter (SF) where odorcausing contaminants are removed. In the meantime, the water is pumped through a particulate filter and two multifiltration beds where inorganic and nonvolatile organic contaminants are removed. The water then enters a catalytic reactor, where low molecular weight organics are oxidized at elevated temperature and in an oxygenrich environment over a catalyst. Another gas separator removes excess oxygen and gaseous oxidation by-products from the processed water and returns them to the cabin air. Purity of the water is checked by electrical conductivity sensors. In fact, the conductivity of water is increased by the presence of typical contaminants. While unacceptable water is reprocessed, good water is passed through an ion exchange bed to remove any left dissolved products of oxidation, and iodine is added for residual microbial control. These rigorous treatment processes create water that meets stringent purity standards for human consumption. The purified water is then stored in the water storage tank prior to being delivered to the potable water network where it can be used by the crew for meal preparation, beverages, and personal hygiene. Hardware for the water recovery system is installed across two racks, denominated as rack #1 and rack #2, within Node 3. The whole of rack #1 and part of rack #2 contain the water processor assembly, while the remaining volume of rack #2 houses the urine processor assembly (Bagdigian and Cloud 2005). The generated potable water is also used by the oxygen generation system, whose hardware is packaged within the so-called rack #3 in Node 3. The heart of the system is the oxygen generation assembly in which water is broken apart by electrolysis to yield oxygen and hydrogen. While the oxygen is delivered into the cabin as breathable air, the hydrogen is delivered to the carbon dioxide reduction assembly housed in rack #3 as well. In the reduction assembly, a Sabatier reactor makes hydrogen and carbon dioxide collected by the Node 3 atmospheric revitalization rack which react together at elevated temperature and pressure in the presence of a catalyst to produce methane and water. While methane is vented overboard, the water is sent to the water processor assembly further reducing the amount of water to be resupplied to the station from the ground. The oxygen generator can provide up to nine kilograms of oxygen per day if run in continuous mode or up to 5.5 kg per day during cyclic operation. The regenerative environmental control and life support system has proved to be of great benefit to station operations reducing the amount of water that needs to be delivered to the station by about 65%, that is to say about 2850 liters per year. In addition it allows a continual presence of six member crews as well as it provides a testing ground of full regenerative environmental control life support systems needed for spacecraft venturing into deep space and for which it will not be possible to rely on supply from the ground (Bagdigian and Cloud 2005) (Figs. 2 and 3).

Fig. 2 Racks of the US Regenerative Environmental Control and Life Support System (Copyright NASA)

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Fig. 3 US Regenerative Environmental Control and Life Support System diagram (Copyright NASA)

Potable Hand Shower Water Wash/ Dispenser Shaving

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References Bagdigian RM, Cloud D (2005) Status of the international space station regenerative ECLSS water recovery and oxygen generation systems. NASA Marshall Space Flight Center, Hamilton Sundstrand Space Systems International Inc. International Space Station Environmental Control and Life Support System (2001) NASA International Space Station Familiarization Training Manual (2004) NASA Wieland PO (1998) Living together in space: the design and operation of the life support systems on the international space station. NASA, Linthicum Heights

Essentials of Life Support Systems: Carbon Dioxide Scrubbing David F. Wassell

Abstract

This chapter focuses on carbon dioxide scrubbing technologies. The basic chemistry and physics of carbon dioxide are reviewed with reference to biological and geological consequences. Industrial carbon dioxide scrubbing technologies are introduced, followed by a discussion of past and current spacecraft CO2 scrubbing technologies and how they relate to the industrial applications. Finally, a brief overview of potential future scrubbing technologies is presented.

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Biology and Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Health and Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Industrial Carbon Dioxide Scrubbing Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Life Support Systems Carbon Dioxide Scrubbing Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Potential Future Carbon Dioxide Scrubbing Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Introduction Life support systems must be designed to provide healthy air under extreme environments. In sealed systems, there are a variety of contaminants that, if not controlled, will build up to dangerous levels. Some of these are off-gassed by materials of construction, while the remainder are metabolites released by organisms within D.F. Wassell (*) Operations, SaskPower BDPS (Boundary Dam Power Station), Estevan, SK, Canada Astronauts4Hire, Houston, TX, USA e-mail: [email protected]; [email protected] # Her Majesty the Queen in Right of Canada 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_50-1

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the sealed environment. In terms of life support systems for spacecraft, there are published guidelines for allowable concentrations of many contaminants, referred to as “Spacecraft Maximum Allowable Concentrations” (SMAC) (NASA 1999). One of the primary metabolites of concern in spacecraft and non-terrestrial habitats (as well as submarines, mine shelters, and other sealed environments) is carbon dioxide (CO2). This chapter will review the chemistry and physics of the carbon dioxide molecule and its production, excretion, and biological effects. The host of commercial carbon dioxide scrubbing technologies will be surveyed with a view toward adaptation to life support systems. Historical spacecraft CO2 scrubbing technologies will be reviewed and compared. Finally, some of the research into potential future life support systems, including regenerative technologies, will be presented.

Chemistry Carbon dioxide is the fully oxidized form of carbon and is therefore chemically stable in oxygenated environments (as would be found in manned spacecraft). As the IUPAC name indicates, it consists of one central carbon atom with two oxygen atoms chemically bound by double bonds. Structurally CO2 is a linear molecule with D1h symmetry, resulting in relatively weak interactions with electromagnetic radiation due to its lack of a permanent dipole (Fig. 1). Although carbon dioxide is relatively inert, it is an acid gas (a Lewis acid with latent Brønsted acidity). As such, it will react with water to form carbonic acid in solution: Scheme 1 Synthesis of Carbonic Acid CO2 þH2 O Ð H2 CO3

Fig. 1 Carbon dioxide

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Fig. 2 Phase diagram of carbon dioxide (Ben Finney and Mark Jacobs)

This is the basis for several of the chemical absorption technologies discussed later in the chapter. Physical absorption technologies generally rely on its Lewis acidity to form weak, nonbonding interactions. Spectroscopically carbon dioxide has a relatively simple spectrum in both the Raman region (1340 cm1) and infrared (IR) region (667 cm1 and 2349 cm1). There is no absorption in the UV or visible regions. Because 13C has a spin ½ nucleus, carbon dioxide is nuclear magnetic resonance (NMR) active. Despite the paucity of spectroscopic activity, in gas samples, there are few interfering species. This means that simple IR sensors, when properly calibrated, may be used to determine carbon dioxide concentration in air samples. Carbon dioxide is unusual in that it has a readily accessible liquid and supercritical phase (Fig. 2): This allows additional separation technologies based on cryogenic separation.

Biology and Geology The atmosphere of the early earth is thought to have consisted largely of carbon dioxide and nitrogen (Kasting 1993). Although much of the carbon dioxide was slowly removed from the atmosphere by dolomite formation via the carbonatesilicate cycle, the advent of a prokaryote with the ability to use water as an electron donor (cyanobacteria) resulted in the consumption of carbon dioxide and production of oxygen. Ultimately this results in the production of carbohydrates following the simplified reaction scheme:

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Scheme 2 Synthesis of Glucose hν

6 CO2 þ 6 H2 O ! C6 H12 O6 þ 6 O2 As atmospheric oxygen built up, species arose that could use oxygen to metabolize the available carbohydrate material. This effectively results in the reverse of the above reaction, liberating energy for metabolic use and resulting in waste carbon dioxide and water. Scheme 3 Oxidation of Glucose C6 H12 O6 þ6 O2 ! 6 CO2 þ6 H2 O þ ΔG The heat of combustion of glucose is 2805 kJ/mol (NIST thermochemical database), resulting in 15.6 kJ of energy available from 1 g of glucose. Under physiological conditions, the energy available from carbohydrates is reported to be 17.22 kJg1 (Eckart 1996; Bender 1997). For a standard daily 2400 calorie diet, this results in a carbon dioxide production of approximately 0.86 kg. NASA design criteria for life support systems assumes 1 kg of carbon dioxide generated per person per day (Perry and LeVan 2002). As noted, the release of energy from the consumption of simple carbohydrates (and, by extension, other foods) is associated with the production of waste carbon dioxide (as well as water and heat). The CO2 generated enters the bloodstream mostly as bicarbonate ion (after catalytic conversion in the red blood cells), although some is maintained as carbamates linked to nitrogen sites on proteins, and the remainder (about 5%) exists as free CO2 (Britannica 2015). The lungs behave as a gas-liquid exchange membrane; when blood flows through capillaries on one side of the alveolar membrane, free carbon dioxide transfers across the membrane into the air side of the membrane. This depletes the free CO2 in the blood and shifts the bicarbonate-CO2 equilibrium toward CO2 production which replenishes free carbon dioxide in the blood. This entire process depends on a carbon dioxide partial pressure differential across the membrane.

Health and Safety Carbon dioxide is a colorless and odorless gas with no known toxic effects outside of asphyxiation. There has been an intense interest in the atmospheric concentration and health effects of carbon dioxide for at least 150 years, resulting in a great deal of air analysis quite early (Smith 1868). Occupational health exposure limits are 5000 ppm for the time-weighted average (TWA) and 30,000 ppm for the shortterm exposure limit (STEL) (CCOHS 2013). The NASA limits are somewhat different, at 13000 ppm for short-term exposure and 7000 ppm for chronic exposure (NASA 1999). As noted above, high concentrations of carbon dioxide in the air suppress gas exchange through the lungs’ membranes. Partial pressure of CO2 in the body is 40–45 mm Hg (5.3–6 kPa); this means that little gas exchange can occur

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Fig. 3 Carbon dioxide scrubbing technologies (Taken from Anderson et al. submitted) aPSA = pressure swing adsorption; bTSA= temperature swing adsorption

above around 55,000 ppm. The requirement for gas exchange sets an upper limit to survivable levels of carbon dioxide, although impairment occurs well below that limit. The lowest level of carbon dioxide recorded to cause death is 9% (90,000 ppm); acute health effects are observed at levels above about 1% (10,000 ppm) (Law et al. 2010).

Industrial Carbon Dioxide Scrubbing Technology Acid gas scrubbing is a common industrial technology in use for the purification of natural gas (Ebenezer 2005; Anderson et al. 2015). Recently, this technology has also been adapted for the removal of carbon dioxide from flue gas (such as at the Boundary Dam Power Station in Saskatchewan). Currently the use of aqueous amine solutions remains the most popular method for the removal of carbon dioxide from gas streams; however there are several other technologies that may be of use as well (Ebenezer 2005, Fig. 3).

Physical Absorbers The Rectisol ® process utilizes methanol at low temperature to take advantage of the high solubility of carbon dioxide at low temperature. Methanol is an industrial chemical available in large volumes, does not foam, and is noncorrosive, but the system is complex and requires refrigeration in most climates. Selexol is a Union Carbide solvent consisting of the dimethyl ether of propylene glycol, CH3–O–CH3–[CH2–O–CH2]n–CH3–O–CH3, where n is between 3 and 9. In this case the solvent will strip all acid gasses and water, requiring only air stripping for

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regeneration. However, it is a nonspecific absorber and is much more efficient at high pressure. Propylene carbonate is the heart of the Fluor™ process, which has high carbon dioxide solubility at ambient temperatures, a low freezing point, and simple operation. Less well known are solvents like Morphysorb ®, which relies on a mixture of N-formyl-morpholine and N-acetyl-morpholine and has similar advantages and disadvantages as the Fluor™ process. All the physical absorbers are very polar, nonreactive solvents that form weak interactions with carbon dioxide with no chemical reaction. They are generally easy to regenerate, but absorb much less carbon dioxide on a molar or volume basis than chemical absorbers. As physical absorbers, these solvents all obey Henry’s law, which can be written as: Equation 1 Henry’s Constant kH ¼

csol cgas

Chemical Absorbers As an acid gas, carbon dioxide will react with a range of basic species. Thus, hydroxides, carbonates, and amines will all react with carbon dioxide and are all in use in industry for that purpose. In the case of primary and secondary amines, carbon dioxide can react with carbonic acid as below, or can react directly with the basic nitrogen to form carbamates: Scheme 4 Carbon Dioxide Reaction with Dialkylamine Generating Carbamates R2 NH þ CO2 ! R2 NCO2 H The tertiary amines only react with carbonic acid to form the quaternized alkylammonium salt with bicarbonate anion. Ammonia reacts in the same manner to form ammonium bicarbonate. Scheme 5 Carbon Dioxide, in the form of Carbonic Acid, Reaction with Trialkylamine Generating Ammonium Bicarbonates R3 N þ H2 CO3 ! R3 NHþ CO3 H As with the tertiary amines, in all other cases, carbon dioxide first reacts with water to form carbonic acid, which in turn reacts with the base to form carbonates or bicarbonates. The Benfield process requires the use of an aqueous solution of potassium carbonate; reaction with carbonic acid generates potassium bicarbonate. This process is simple and relies on readily available chemicals. However, precipitation of the carbonates and bicarbonates is an issue. The CORAL process relies on the use of amino acids in aqueous solution. These react in a similar manner as tertiary amines to form bicarbonate salts. In addition to these systems, simple hydroxides react directly

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with carbon dioxide to form carbonates. Because all of these are chemical reactions, Henry’s constant is not obeyed and reactions follow their individual thermodynamics and kinetics.

Membrane Absorbers The Cynara-Natco membranes are cellulose acetate membranes used as a separating media. Gas separation across polymeric membranes depends on molecular size, shape, and interaction. For natural gas applications, carbon dioxide is the molecule that most easily passes across the membrane; however, this may not be the case for other applications. Solid Support/Adsorption Processes In this case, the solid adsorbent interacts either as a physical adsorbent or chemical absorbent. These include iron or zinc oxides (FexOy, ZnO) or zeolite adsorbents (molecular sieves). These are microporous structures (hence very high surface area) that selectively retain carbon dioxide and then release it under low pressure conditions (pressure swing), high-temperature conditions (temperature swing), or a combination of the two (pressure-temperature swing). Cryogenic This is a low temperature distillation technology, but is generally restricted to concentrated CO2 sources (>90%). It is quite energy intensive and is typically used as a method of purifying carbon dioxide for sale. Hybrid These systems consist of combinations of the previously described technologies. This can include membrane contactors with a countercurrent chemical or physical solvent flow on the shell side, membranes generated from polymeric forms of chemical solvents, or resin bead coated with chemical absorbers (either physically adsorbed into the beads or chemically bonded to a base polymer). These are generally considered to be too new for commercial application at this time, but many are in commercial trial at the small pilot plant scale. However, some of these technologies are of particular interest for microgravity applications. As an example, resin technologies that immobilize a chemical absorber on a solid support allow high capacity solvents to be used in low gravity circumstances.

Life Support Systems Carbon Dioxide Scrubbing Technologies Historical Spacecraft Systems The initial human spacecraft, Vostok and Mercury, both relied on the reaction of carbon dioxide with an alkali metal hydroxide. In the case of Mercury, two parallel lithium hydroxide containers were used, with airflow through one. This generates lithium carbonate, which is discarded when the LiOH is completely reacted. Lithium hydroxide can be regenerated by thermal degradation of lithium carbonate under

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vacuum and reaction of the lithium oxide with water; however, this is a very hightemperature process and regeneration is not performed in spacecraft. The Vostok carbon dioxide removal system operated somewhat differently. Here, potassium superoxide is reacted with atmospheric water to generate oxygen and potassium hydroxide; the potassium hydroxide then reacts with carbon dioxide to produce potassium carbonate. Similar to the lithium hydroxide technology, the canisters are discarded. These first two spacecraft set the template for most of those that followed. Voskhod relied on the same design as Vostok, and the follow-up Soyuz relied on the same design with additional capacity provided by lithium hydroxide as did Salyut. Gemini, Apollo, and Shuttle all relied on the same type of design as Mercury. Although the simple hydroxide absorbers suffice for short-term jaunts into space, continually manned space stations cannot rely on disposable carbon dioxide absorbers. Skylab relied on regenerable Zeolites for carbon dioxide absorption. Desorption occurs with the application of heat and vacuum, which was dumped overboard. The Kvant-2 module of Mir relied on a similar system, the Vozdukh carbon dioxide removal system. ISS relies on several systems, including Vozdukh, Carbon Dioxide Removal Assembly (CDRA, the US system that also relies on Zeolites), MetOx (regenerable metal oxide absorbers, based on silver oxide), and backup lithium hydroxide canisters. Recently, the captured carbon dioxide in the ISS has been transferred to a Sabatier reactor, where it is reacted with hydrogen (from wastewater electrolysis to produce oxygen in the Oxygen Generating System, OGS) to produce high-purity water and methane (Perry and LeVan 2002) (Eckart 1996). In summary, to date, carbon dioxide removal in manned spacecraft has relied on two basic technologies: 1. Carbonate formation by reaction with lithium hydroxide (LiOH), potassium superoxide and water (KO2), and silver oxide and water (Ag2O, also known as MetOx). 2. Zeolite physical absorbers. Note that carbon dioxide is thought to adsorb on basic sites within the Zeolite pores. The Zeolite absorbers and the MetOx metal oxide absorbers are regenerable under relatively mild conditions and are both PTSA (pressure-temperature swing absorber) systems, relying on increased temperature and reduced pressure to regenerate.

Comparison with Industrial Carbon Dioxide Scrubbing In industry, carbon dioxide scrubbing is primarily associated with natural gas production. Natural gas is, in reality, a mixture of several gasses, primarily methane with several higher alkanes associated with it, along with water, carbon dioxide, hydrogen sulfide, and traces of other gasses. The higher alkanes condense out of natural gas when it is cooled; therefore these are referred to as condensates. These are typically sold separately to various markets (i.e., propane and butane are sold as separate products). Water is typically removed with glycol. Carbon dioxide is

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normally removed by contact with an aqueous amine solution, often monoethanolamine (MEA), N-methyldiethanolamine (MDEA), or variants. The Benfield process, utilizing carbonates, is quite often used. In addition to the chemical processes, membrane technology is also used for carbon dioxide separation from commercial natural gas wells. Here, it is used in situations where a small footprint is required, but efficiency is rather low, so membrane technology is often used to remove the bulk of carbon dioxide where the concentration of the gas is high. In contrast, life support systems for spacecraft use none of these well-known technologies. There are several reasons for this. The two primary reasons are related to the nature of orbital flight. Although the amine process and the Benfield process are both mature technologies, both rely on countercurrent absorber towers that depend on gravity to produce the downward flow. In addition, the amine absorbers release some of the amine into the exhaust. When used on earth, the released amine disperses and degrades without health or environmental effects. However, in a closed atmosphere, the amine would very quickly build up to potentially dangerous levels. This would likely cause health issues and overload the trace contaminant absorber or both. Notably, all spacecraft life support systems rely on simpler, solid-phase carbon dioxide absorbers. This reduces the chance of absorber release into the cabin air. The primary disadvantages of these systems are that they are less efficient than industrial carbon dioxide scrubbers and most currently in use are not regenerable. This has led to a search for new carbon dioxide scrubbing technology for spacecraft and non-terrestrial life support systems.

Potential Future Carbon Dioxide Scrubbing Technologies Because of the problems associated with orbitals flight as noted above, physicalchemical carbon dioxide scrubbing technologies rely on solid-phase absorbers. Therefore, technological development efforts have focused on adapting solventbased industrial carbon dioxide absorbers to the microgravity environment. Two basic methods can be followed to achieve this: chemically tethering the active species to a solid support or physically adsorbing the solvent into a porous solid support. As expected, these methods show different advantages and disadvantages. Tethered solvents are stable and unlikely to desorb into the cabin air, but the activity is potentially altered and these are more complex and costly to manufacture (Nalette et al. 2005). Physically adsorbed solvents are simple and cheap to manufacture and can be produced on a wide variety of support materials, but have some risk of desorption into the air stream. Over the long term, larger habitats, particularly those on bodies with significant gravitational fields (e.g., The moon and Mars), are expected to have a large proportion of carbon dioxide scrubbing provided by bioregenerative life support systems with physical-chemical systems serving as an emergency backup. Research in this area is significantly behind that of industrial systems and currently remains academic curiosities. However, terrestrial life depends exclusively on algae and plants to remove carbon dioxide and generate

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oxygen. Some interesting research has been performed with Chlorella cultivars in the past; more recent research involving higher plants have occurred as well (Eckart 1996) (Darlington et al. 2001). Research involving plant responses to microgravity continue to this day on the ISS, although here the primary interest appears to be providing more variety to the crews’ diet rather than a serious attempt at a bioregenerative life support system.

Cross-References ▶ Bioregenerative Life Support Systems, Overview ▶ Current Life Support Systems of the 2000s: Orion, Dragon ▶ Early American Life Support Systems: Mercury, Gemini and Apollo ▶ Life Support Systems of the International Space Station ▶ Methods of Carbon Dioxide Removal ▶ Physico-Chemical Life Support System, Overview ▶ Recent American Life Support Systems: Skylab, Spacelab and the Shuttle ▶ Russian Life Support Systems of the 1970s and 1980s: Salyut and Mir ▶ Russian Life Support Systems: Vostok, Voskhod and Soyuz

References Anderson K, Atkins MP et al (2015) Carbon dioxide uptake from natural gas by binary ionic liquid–water mixtures. Green Chem 17:4340–4354 Bender DA (1997) Introduction to nutrition and metabolism, 4th edn. Taylor & Francis, London Britannica, E. (2015). Human respiratory system. Retrieved 22 Feb 2015, from http://www.britannica. com/EBchecked/topic/499530/human-respiratory-system/66153/Transport-of-carbon-dioxide CCOHS (2013). Carbon dioxide. Retrieved Feb 22 2015, from http://www.ccohs.ca/oshanswers/ chemicals/chem_profiles/carbon_dioxide.html Darlington AB, Dat JF et al (2001) The biofiltration of indoor air: air flux and temperature influences the removal of toluene, ethylbenzene, and xylene. Environ Sci Technol 35 (1):240–246 Ebenezer SA (2005) Removal of carbon dioxide from natural gas for LNG production. Norwegian University of Science and Technology, Norway Eckart P (1996) Spaceflight life support and biospherics. Microcosm Press, Torrance Kasting J (1993) Earth’s early atmosphere. Science 259(5097):920–926 Law J, Watkins S and Alexander D (2010) In-flight carbon dioxide exposures and related symptoms: association, susceptibility, and operational implications, NASA/TP-2010-216126 Nalette T, Reiss J et al (2005) Development of an Amine-based system for combined carbon dioxide, humidity, and trace contaminant control. In: 35th international conference on environmental systems. NASA, Rome NASA/JSC (1999). Toxicology Group, “Spacecraft Maximum Allowable Concentrations for Airborne Contaminants,” JSC 20584 Perry JL, LeVan MD (2002) Air Purification in closed environments: overview of spacecraft systems. In: Nuclear biological chemical defense collective protection conference; 29–31 Oct 2002, Orlando Smith, R. A. (1868). Memoirs and proceedings of the Manchester Literary & Philosophical Society, vol 3. London, pp 28–56

NASA Extreme Environment Mission Operations (NEEMO): Fields of Life Support Research Jamie Guined

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aquarius Reef Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Life Support Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Human Performance and Physiology Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exercise Countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biomedical Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operational Readiness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Health and Telemedicine Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bacterial and Microbial Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Human Factors and Habitability Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extravehicular Activity and Task Performance Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

To prepare astronauts for the extreme environment of space, NASA uses analog environments on Earth to simulate many of the challenges they will encounter during life off-planet. One of the most extreme environments known to mankind is the ocean. NEEMO, an acronym for NASA Extreme Environment Mission Operations, is an analog space exploration training program used to prepare astronauts, scientists, engineers, and a variety of mission support personnel for long-duration space flight missions. The NEEMO missions are conducted at Aquarius Reef Base, the world’s only operational undersea laboratory, located 3.5 miles off the coast of Key Largo, Florida, on the Conch Reef at a depth of roughly 62 ft. NASA, an acronym for National Aeronautics and Space Agency,

J. Guined (*) SeaSpace Exploration & Research Society Inc, Houston, TX, USA e-mail: [email protected] # Springer International Publishing AG 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_165-1

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implemented the NEEMO program in 2001 and, as of 2015, has conducted 20 space analog missions ranging in duration from 7 to 18 days. The NEEMO program has provided NASA with a realistic, extreme environment that has been used to develop tools and protocols for use in space flight, to conduct space life science and engineering research, and to perform hardware evaluations on candidate space flight hardware and systems.

Introduction Since the dawn of space exploration, governments have used space analog environments and simulations as a way to conduct meaningful and relevant environment research and to prepare and train astronauts and cosmonauts for the rigors of living in the extreme environment of space.

Aquarius Reef Base The Aquarius undersea laboratory (also referred to as Aquarius Reef Base and the Aquarius habitat) was built in 1986 and put into operations in the US Virgin Islands in 1988. After Hurricane Hugo and a total of 13 missions, Aquarius was relocated to Wilmington, North Carolina, for refurbishment at the University of North Carolina Wilmington’s National Underwater Research Center (NURC). After its refurbishment in 1992, it was once again relocated, this time to its current location in the Florida Keys’ National Marine Sanctuary 3.5 miles off the coast of Key Largo, Florida, on the Conch Reef at a depth of 62 ft. The Aquarius system is comprised of three distinct parts – a life support buoy (LSB), a base living, and working space for a crew of six, which is a steel pressure vessel that is 9 feet in diameter by 43 ft long and can support undersea operations at a depth of up to 120 ft. The internal operating environment of Aquarius is at ambient pressure, meaning that the internal atmospheric pressure is equal to that of the surrounding water pressure.

Life Support Research As NASA prepares for long-duration exploration-class missions, such as to the Moon or Mars, risks and gaps in knowledge continue to be identified by the NASA Human Research Program (HRP) to help direct the agency’s research objectives. Due to obvious limitations with conducting research on the International Space Station (ISS) (e.g., crew time, cost, small sample size, long lead time), NASA developed a robust analog research program for the purpose of conducting research

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in a relevant environment while simultaneously helping to prepare astronauts for life off-planet by simulating many of the same challenges associated with space exploration through the use of these Earth-based analogs. Fields of life support research conducted during the NASA NEEMO missions spans several different disciplines. NEEMO crews have conducted research in the areas of human physiology, human factors and habitability, health and human performance, medicine (including telemedicine, or remote medicine), communications, and extravehicular activity (EVA) task performance, among others.

Human Performance and Physiology Research Since the inception of the NASA NEEMO analog research program, a focused research interest has been in the areas of human performance and physiology, as evidenced by the list of NEEMO life sciences research conducted to date (Table 1). Studies in these areas have focused on several parameters that are key factors in maintaining the health and safety of the crew, including sleep quality, physical activity, physiologic monitoring, exercise countermeasures, operational readiness, risk for decompression sickness (DCS), and nutrition.

Exercise Countermeasures The confined space of the Aquarius habitat offers a valuable test environment for candidate compact exercise countermeasure hardware that could be installed on “exploration-class” spacecraft such as the NASA Orion capsule. Exercise countermeasures are used to prevent/minimize the deleterious effects of space flight on human physiology. In general, the physiologic changes accompanying long-duration space flight include changes to the cardiovascular, musculoskeletal, neurovestibular, neurological, and pulmonary systems. The major physiological changes include, but are not limited to, bone demineralization, muscle atrophy with accompanied deficits in muscle strength, endurance, and cross-sectional area, neurovestibular impairments, neuromuscular insufficiencies, vision changes, and cardiovascular and pulmonary deconditioning. Analog environment evaluation, such as provided by NEEMO, is instrumental in the maturation of technologies and protocols before advancing them to flight-ready status. For instance, crewmembers of NEEMO 6 conducted an evaluation of a candidate exercise device dubbed the Constant Force Resistive Exercise Unit (CFREU) and also conducted a feasibility assessment for using stretching as an on-orbit countermeasure by performing the prescribed stretches in a neutrally buoyant environment (as a microgravity analog) (Life Sciences Data Archive at NASA Johnson Space Center 2015). Both investigations yielded valuable data for the research teams that could then be used to further improve the hardware and stretching protocol, correct design faults, and address limitations of both countermeasures.

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Table 1 List of life sciences experiment payloads for the NASA NEEMO program, missions 1–18 Life science research of the NASA NEEMO project Experiment payload Actigraphy: a tool for monitoring sleep and activity in an isolated environment (Aquarius) A scheduling and planning tool in NEEMO 14 – a simulated space environment Antimicrobial technology evaluation Analog validation study of team measures Assessing the impact of communication delay on performance: an examination of autonomous operations utilizing analog environments Bacterial detection: correlation of an automated real-time system operated in situ with comprehensive characterization in the laboratory Cardiac adapted sleep parameter electrocardiogram recorder Clinical nutritional assessment Constant Force Resistive Exercise Unit Evaluation Crew scheduling tools (SPIFe) Evaluation of muscle stretching protocol during neutral buoyancy Evaluation of portable ultrasound in remote environments Evaluation of space therapeutics assessment recorder and the automated neuropsychological assessment metric readiness evaluation system on the palm PDA platform: a device for real-time monitoring of drug effectiveness Evaluation of the VitalSense wireless physiological monitoring system Habitability assessment: habitat utilization analysis from human factor perspective Habitability ground and analog testing Human factors and habitability assessment tool Immune function changes during a space flight analog 12-day undersea mission Influence of center of gravity on human performance in partial gravity Latent viral shedding in small isolated groups Magic window system: habitability and recreational applications of innovative imagery systems Advanced extravehicular activity and exploration activity study to assess human performance responses in partial gravity environments Operational evaluation of in-suit Doppler Otoacoustic Hearing Assessment Oxidative damage during a 12-day saturation dive Physiologic monitoring Portable bone quality assessment device Readiness to perform in a space analog environment Sensorimotor assessment and rehabilitation in parabolic flight Smart healthcare: LifeGuard wireless physiological monitor Smart healthcare: wireless sensor networks

NEEMO mission(s) NEEMO 5 NEEMO 14 NEEMO 6 NEEMO 14 NEEMO 15, 16 NEEMO 5 NEEMO 14 NEEMO 5 NEEMO 6 NEEMO 14 NEEMO 6 NEEMO 5 NEEMO 3, 4, 5

NEEMO 6 NEEMO 1–5 NEEMO 18 NEEMO 1–5 NEEMO 12, 13, 14 NEEMO 14 NEEMO 4, 5 NEEMO 5 NEEMO 14 NEEMO 5 NEEMO 4, 5 NEEMO 12, 13, 14 NEEMO 5 NEEMO 6 NEEMO 9, 12 NEEMO 18 NEEMO 6 NEEMO 6 (continued)

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Table 1 (continued) Life science research of the NASA NEEMO project Experiment payload Vigilance, stress, and sleep/wake measures and low autonomy study in NEEMO 13 – a simulated space environment Wireless tracking locator Wound healing

NEEMO mission(s) NEEMO 13 NEEMO 6 NEEMO 5

Biomedical Monitoring NEEMO has also proven to be a relevant test bed for conducting evaluations of candidate biomedical monitoring devices that are used for monitoring a variety of physiologic parameters during exercise countermeasures, periodic fitness evaluations, and extravehicular activity. Biomedical monitoring devices are used in all phases of a space mission and for a number of mission tasks and are used to collect both operational and research data. For instance, these devices are used to assess performance factors including sleep quality, physiological responses to exercise and task performance, and stress response.

Operational Readiness Several tools have been developed to help crewmembers assess their level of “readiness” to perform under varying operational scenarios. The high-fidelity isolated, extreme environment of NEEMO missions affords researchers and mission trainers with a perfect opportunity to use these tools in an actual mission setting. As noted by NASA Astronaut Scott Kelly, Commander of NEEMO 4, “Aquarius wasn’t a simulation. It was a real mission. . .” (Space Center Roundup 2002). Crews on NEEMO missions 9, 12, and 13 conducted a suite of self-evaluations, including a 3-min Psychomotor Vigilance Test (PVT) (Fig. 1 below), salivary cortisol assessment, and sleep-wake pattern monitoring, to assess potential impairments to crewmember performance and operational readiness (Dinges 2007).

Health and Telemedicine Research As mankind continues to venture further and further away from the relatively familiar environment of Low Earth Orbit (LEO), crews will become ever more autonomous with a need for enhanced self-reliance. The value of an analog environment for developing hardware, technology, and operational protocols, such as the one provided by the Aquarius habitat for the NEEMO missions, cannot be understated. For manned missions, especially missions to other planetary bodies in the solar system, the primary concern for mission planners is the health and safety of the

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Fig. 1 NASA astronauts practice simulated space maneuvers on the ocean floor during NASA Extreme Environment Mission Operations (NEEMO) 16 in 2012. They took a 3-min Psychomotor Vigilance Task (PVT) test to help refine the test’s algorithm for use in orbit (Image credit: NASA)

crew. While all astronauts and cosmonauts receive basic training in certain aspects of medicine, the ability to diagnose and provide advanced healthcare is limited unless the crewmember is also a medical professional, and even then, there are other limitations such as access to surgical tools and diagnostic equipment. All spacefaring nations recognize these limitations and are working on the development of technological innovations to address many of these. One such innovation is the use of portable ultrasound devices for minimally invasive medical diagnosis capability. NEEMO 5 crewmembers conducted a simulated medical event that required a trained crewmember to manipulate the ultrasound probe, with guided instructions provided by the attending crew surgeon via remote monitoring, so as to facilitate the surgeon’s diagnosis of the “patient” crewmember’s simulated condition (Logan et al. 2003). Real-time, and near real-time, monitoring capability for crews has been an operational medical standard since Yuri Gagarin became the first human in space in 1961. Biomedical engineers, flight surgeons, and other medical operations support personnel rely on accurate and reliable biomedical monitoring capability for safeguarding crew health throughout all mission phases. The NEEMO missions, in particular, have been instrumental in the technological maturation for several of the advancements in remote medicine capability for space exploration. For instance, NEEMO 5 conducted evaluations of in-suit Doppler technology for assessing prevention of and risk for decompression sickness.

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Decompression sickness (DCS), while primarily associated with diving, can also occur during space flight extravehicular activity. Decompression sickness (also known as “the bends”) is the result of inadequate decompression after exposure to increased pressure and is most commonly referred to as the formation of nitrogen bubbles in the body’s fluids and tissues. The prevention of DCS is of particular concern for long-duration crews where treatment is either greatly constrained or not feasible. NEEMO Program Manager, Bill Todd, said it best: “Aquarius, with its physical and psychological isolation on the floor of the Atlantic, will provide the real stresses needed to validate telemedicine in an extreme environment” (NASA, Behind the Scenes, NEEMO 7).

Bacterial and Microbial Growth The size and similarity of the Aquarius habitat to International Space Station (ISS) modules also make it an ideal analog environment for conducting bacterial and microbial research. Bacterial and microbial growth in confined space environments where air circulation and ventilation may be constrained and humidity levels may be high, such as in the Aquarius habitat and on the ISS, could pose a threat to crew health and safety. NEEMO crews have analyzed in situ bacterial growth using an automated, real-time analyzer and have tested the efficacy of silver-ion technology in the prevention of microbial growth and contamination. A combination of preventative technology coupled with real-time analysis capability is ideal for long-duration exploration missions where ground support may be limited or nonexistent.

Human Factors and Habitability Research In the design of habitats and spacecraft, especially human-rated spacecraft, human factors and habitability are of paramount importance. Habitability assessments have the potential to yield very valuable information for designers, engineers, and mission planners, providing information related to the physical environment, work/rest schedules, crew behaviors and interactions, habitat traffic patterns, and impact of habitat layout on human performance (Thaxton 2014). Habitability and human factors research on the ground conducted during simulations in mock-up habitats and spacecraft are an important step in the design process for flight-ready vehicles. NEEMO crews have provided invaluable information, including many “lessons learned” for human factors and habitability teams through the conduct of two major habitability assessments of the Aquarius habitat during NEEMO missions 1–5 and 18 (Whitmore and Blume 2003). While the space and undersea environments are analogous, there are environment-specific differences for each type of mission that impact associated habitability considerations. Despite these differences, the development of human factors and habitability assessment tools will prove useful for both types of mission environments.

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Extravehicular Activity and Task Performance Research Future exploration-class missions to an asteroid, the Moon, and Mars will require crewmembers to perform at potentially high and demanding levels during extravehicular activity (EVA) and surface task activities. A review of energy expenditure data from NASA missions indicates that an astronaut can expend as many as 238 kilocalories per hour (kcal/hr) during EVA in 0 g, further compounded by a reduction in performance efficiency resulting from increased work demands to overcompensate for suit pressurization. NEEMO has proven to be a valuable “proving ground” for the development of new EVA communications protocols, tools, and task performance analyses for improving crew performance and efficiency during EVA. Case in point, the NEEMO 15 crew participated in a simulated asteroid mission, with a primary objective of learning how to explore the surface of an asteroid using anchoring concepts and techniques for safely traversing the low-tono gravity environment of an asteroid (NASA Facts 2011). The crew also simulated a communications delay (50 s) to assess the impact(s) of delayed communication on behavioral health and crew performance. Crewmembers assigned to exploration missions will also be expected to conduct surface sampling and specimen collection, two tasks that are also used by marine biologists conducting coral reef research (Fig. 2). The location of the Aquarius habitat on the Conch Reef makes it ideal for learning and practicing various data collection and sampling techniques and providing information that can then be used

Fig. 2 With the famous Key Largo coral in the foreground, weightless Aquanauts use an extravehicular activity (EVA) boom prototype to translate across the seafloor, simulating translation across the surface of an asteroid (Image credit: NASA)

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to develop and refine sample and collection protocols to be used on another planetary surface. Another important consideration related to crew performance during EVA is suit design and mobility. The undersea environment provides a unique opportunity for EVA suit designers to assess changes in suit configuration parameters, such as center of gravity, on crew performance. Likewise, through the use of suit weighting, mission planners and researchers are also able to simulate Moon and Mars gravity conditions during “spacewalks” outside the Aquarius habitat. Researchers from NASA Johnson Space Center conducted a study to analyze the effects of different center of gravity configurations on a variety of performance parameters collected as subjects and performed a standardized task battery in the Neutral Buoyancy Laboratory and during an EVA at the Aquarius habitat (Jadwick et al. 2008).

Summary For the purposes of studying the effects of space exploration on man and machine, nothing beats conducting the research in the actual environment of space; however, the cost of space travel makes that difficult. The use of space analog environments and habitats here on Earth are, therefore, extremely valuable for learning how to live and work in the extreme environment of space. As of 2015, there are multiple organizations across the world that have analog habitat research capability, the vast majority of which are terrestrial habitats. The Aquarius habitat, where all of the NASA Extreme Environment Mission Operations (NEEMO) missions take place, is the world’s only operational undersea laboratory, making it a truly unique and valuable resource Williams-Byrd et al. (2011). NASA recognized the value and relevance of the underwater environment as a useful training ground for learning to live and work in space early on, conducting some of their earliest analog research in pools. Because of the isolated, confined, and extreme environment of the Aquarius habitat, the NASA NEEMO missions are unparalleled in their fidelity. Referring to Aquarius, Monika Schultz, expeditionary training manager in the Astronaut Office at the NASA Johnson Space Center, said “. . .it really is the best analog for a true mission” (Space Center Roundup 2002).

References Behind the Scenes: NASA Extreme Environment Mission Operations (n.d.) In: Behind the scenes. Retrieved 4 Aug 2015, from National Aeronautics and Space Administration website: http:// spaceflight.nasa.gov/shuttle/support/training/neemo/neemo7/ Dinges D (2007) Vigilance, stress, and sleep/wake measures and low autonomy study in NEEMO 13 – A simulated space environment. In: Life sciences data archive at NASA johnson space center. Retrieved 4 Aug 2015, from National Aeronautics and Space Administration website: https://lsda.jsc.nasa.gov/scripts/experiment/exper.aspx?exp_index=2109 From the Sea to the Stars: The NEEMO Project (2002) Space center roundup 2:6–8

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Life Sciences Data Archive at NASA Johnson Space Center [NASA Extreme Environment Mission Operations (NEEMO) Project] (2015) In: Life sciences data archive at NASA Johnson Space Center. Retrieved 4 Aug 2015, from National Aeronautics and Space Administration website: https://lsda.jsc.nasa.gov/docs/research/research_detail.aspx?experiment_type_code=22& researchtype= Logan J, Clark J, Sargsyan A (2003) Evaluation of portable ultrasound in extreme environments –NEEMO. In: Life sciences data archive at NASA Johnson Space Center. Retrieved 4 Aug 2015, from National Aeronautics and Space Administration website: https://lsda.jsc.nasa.gov/ scripts/experiment/exper.aspx?exp_index=1066 Thaxton S (2014) Habitability ground and analog testing. In: Life sciences data archive at NASA Johnson Space Center. Retrieved 4 Aug, 2015, from National Aeronautics and Space Administration website: https://lsda.jsc.nasa.gov/scripts/experiment/exper.aspx?exp_index=11330 Whitmore M, Blume J (2003) Habitability assessment: habitat utilization analysis from human factors perspective. In Life sciences data archive at NASA Johnson Space Center. Retrieved 4 Aug 2015, from National Aeronautics and Space Administration website: https://lsda.jsc.nasa. gov/scripts/experiment/exper.aspx?exp_index=1099 https://www.nasa.gov/pdf/594588main_FS-2011-10-051-JSC%20NEEMO.pdf Williams-Byrd J, Reeves JD, Herrmann N (eds) (2011) NASA analog missions: Paving the way for space exploration. National Aeronautics and Space Administration, Hampton

Life Support Systems for Manned Mars Missions, Overview Thais Russomano

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of a Hostile Environment on an Earth-Adapted Physiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Potent Problem of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Psychological Stress of Being Far from Home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Advent of Advanced Life Support Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Closing the Loop on Regenerative Life Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculating the Ins and Outs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bioregeneration as a Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In Situ Resource Use: An Important Addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Making Fiction a Reality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abstract

A manned journey to Mars has long since been the subject of science fiction and fantasy, but continued advances in technology have opened up the possibility. The lengthy distance to the planet, together with its hostile environment present dangers to the health and well-being of space-travelers and huge logistical difficulties in terms of adequate resource provision to sustain a crew for a return journey and time on the planet surface. Advanced life support systems have continued to adapt and develop since the flight of Russian cosmonaut Yuri Gagarin in 1961 and the NASA led Mercury, Gemini, and Apollo missions, T. Russomano (*) Microgravity Centre, The Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil International Space Medicine Consortium Inc., Washington DC, USA Centre of Human and Aerospace Physiological Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, UK e-mail: [email protected] # Springer International Publishing AG 2017 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_188-2

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which required open-loop, disposable systems of short duration only. Arrival of the Space Shuttle program and International Space Station led to a shift in specifications, with emphasis on reusability and long-term use. This ongoing process has resulted in a complex life support system capable of sustaining a six-astronaut crew for several months. Key technologies, such as oxygen generation and water recovery systems, have reduced the need for the costly resupply of some materials to the orbiting space station, but replenishment of consumables, propellant, and maintenance equipment continues. Frequent resupply is an unfeasible option for a long-duration deep-space mission, meaning a bioregenerative life support system will be essential. Research continues in this field, with one example being the European Space Agency managed MELiSSA (Micro-Ecological Life Support System Alternative) project. Further advances in a system providing the essentials for human survival in a Mars environment, together with technology for the use of the natural in-situ resources of the planet, will undoubtedly open up exploration of this new frontier in the coming decades.

Introduction A manned space journey to Mars, the fourth planet in our Solar System, will not be an easy task to accomplish, being fraught with difficulties. The huge void of space that separates Mars from planet Earth varies greatly depending on the orbits of the two planets, ranging from 34.8 million miles at its closest to 249 million miles at its furthest, with the average distance being 140 million miles. Travelling from Earth to Mars requires more than a simple “point and shoot” launch of a spacecraft, but will involve planning a trajectory that takes account of the huge distance and the differing orbits of the two planets. Calculations using the Hohmann transfer orbit, which sets the optimum elliptical orbit needed to rendezvous a spacecraft with Mars using the least amount of fuel, have indicated a travel time of between 6 to 9 months, depending on rocket velocity and the proximity of the planets (Seedhouse 2009). Such lengthy flight duration will require a vast amount of propellant in order to leave Earth’s gravity, reach Mars, and still have the possibility of returning home again. In addition to the weight of propellant, however, consideration must be given to the consumables that will be needed to sustain a crew for the return journey, as well as the time spent on the planet surface, and this in itself will be a significant factor. It is estimated that the consumables required for a crew of just six astronauts for a return space mission to Mars will range from 100 to 200 metric tons, though it is more likely to be nearer the higher figure. This enormous amount of weight would require a series of heavy-lift launch vehicles to guarantee the necessary life support systems and supplies would be accessible to the crew. Therefore, it is vitally important that the correct balance is achieved between keeping the payload weight down to a minimum, while at the same time ensuring all essential life support provision is available, given that resupply from Earth or an early return to Earth are not feasible

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options. In order to achieve this, it will be vitally important that the life support systems adopted for such a journey to Mars and for the time spent on the planet surface be as self-sufficient as possible; to this end, it will be essential that the design of the life support systems be as regenerative as possible, operating to a high degree as a closed-loop system (MacElroy et al. 1992).

Effects of a Hostile Environment on an Earth-Adapted Physiology The distance between the two planets is not the only difficulty. Assuming the success of the first stage of the mission and the safe arrival of the astronauts onto Martian soil, they will be faced with an entirely new and hostile environment to which mankind is not yet adapted. The planet Mars is smaller and less dense than the Earth, which creates a lower gravitational force, called hypogravity. Its thin atmosphere is rich in carbon dioxide (95%) that is a toxic gas for humans, its atmospheric pressure is very low in comparison to Earth, and the Martian surface temperature ranges from 140  C at the coldest polar caps to 35  C during the equatorial summer (Russomano et al. 2008). It can therefore be seen that the mission as a whole will submit the space travelers to extreme conditions and environments; our experiences to-date with space travel and Low-Earth-Orbit (LEO) space stations has already demonstrated the detrimental physiological and psychological consequences of this exposure. Human anatomy and physiology have been shaped by Earth’s gravitational force over millions of years. When this force is reduced or removed, such as in the microgravity of space, it is known that all body systems are affected. Bones that are no longer required to support the weight of the body begin to lose their mass continuously, particularly so in the lower limbs. Skeletal muscles that are not needed to counteract the effects of gravity suffer a large degree of atrophy. The immune system appears to become less active in microgravity, and the cardiovascular system adapts to the space environment by redistributing blood and fluids from the lower to the upper body, while decreasing the plasma volume and heart size. It has been seen during space missions that astronauts also present a reduction in the number of red blood cells, called space anemia. The vestibular or balance system that is designed to keep our visual world stable and keep us from falling suffers from the moment of insertion into microgravity, causing a condition called space motion sickness, which is known to affect 70% of astronauts in the first 72 h of a space mission (Barratt and Pool 2008; Russomano et al. 2008; Seedhouse 2009).

The Potent Problem of Radiation A major consideration having serious consequences on astronaut health is the effects of space radiation and the degree to which they will be exposed during a round-trip to Mars and time spent on the planet surface. Radiation can be defined as a form of energy that is emitted or transmitted in the form of rays, electromagnetic waves,

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and/or particles. It can be divided into: visible light (radiation that can be seen), infrared radiation (radiation that can be felt), and radiation such as x-rays and gamma rays, which are not visible and can only be observed directly or indirectly with special equipment. LEO space missions, such as on the International Space Station (ISS), have shown that crew members are most likely to be exposed to high doses of radiation during solar particle events, also called solar flares. On these occasions, extremely high energy radiation is emitted in a short period of time. Most of this radiation is prevented from reaching the surface of Earth and having consequent effects on living organisms or even the astronauts on LEO missions by our planet’s magnetosphere. NASA data has shown that radiation exposure for astronauts aboard the ISS is typically equivalent to an annualized rate of 20 to 40 rems (200–400 mSv). The average dose-equivalent rate observed on a previous Space Shuttle mission was 3.9 μSv/h, with the highest rate at 96 μSv/h, which occurred while the Shuttle was in the South Atlantic Anomaly region of Earth’s magnetic field (1 Sv = 1000 mSv = 1000,000 μSv). When removed from the protection of this magnetosphere, as during an interplanetary trip, both spacecraft and astronauts will no longer be shielded from this radiation and will be exposed to Galactic Cosmic Rays (GCR). This radiation is composed of high charge and energy particles – high atomic mass nuclei, which have the ability to penetrate several centimeters of body tissue. NASA considers that a round trip to Mars of about 1 year would expose the space crew to a total of 600 mSv. Consideration will need to be given to means of creating greater shielding for spacecraft headed to Mars or alternatively shortening the travel time in order to minimize harmful exposure. Current propulsion systems are unlikely to reduce the journey length and, therefore, improved or alternative means of shielding the space crew are more likely to be considered. Ideas currently being suggested and investigated include: shields which rely on magnetic (or electric) fields to deflect energetic particles; balancing the need for a shield strong enough to deflect GCR particles while remaining weak enough so as to not harm the astronauts; artificially induced hibernation, a state known as torpor, of crew members for the journey whereby their metabolisms would remain at an extremely slow rate; and lining the spacecraft shell with food and water supplies and stored human excrement, as proposed by the Inspiration Mars Foundation plan to send a two-person crew in an orbit to Mars and back over a 501 day nonstop journey. Although seemingly coming from the realms of science fiction, radiation shielding is a serious concern for the health of a space crew to Mars, both for the time en route and once landed on Martian soil (Seedhouse 2009; Rask et al. 2012). In order to minimize radiation exposure on the planet surface, the time the astronauts spend outside their spacesuit and the distance they travel between their habitats will need to be limited in order to decrease the chances of damage to their health. If the astronauts stay on the surface of the planet while they wait for realignment to make the journey back to Earth, it is estimated they will be exposed to an additional 400 mSv, since the thin atmosphere of Mars is not strong enough to shield them from most cosmic radiation. Therefore, the total radiation exposure that the space crew will be subject to, including the journey and time spent on the planet, is estimated to be 1000 mSv (Barratt and Pool 2008; Rask et al. 2012).

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The Psychological Stress of Being Far from Home The psychological effects of being completely detached from Earth in a long-term deep space mission are more difficult to fully predict as such an unparalleled situation cannot be truly simulated on the ground. The Mars-500 psychosocial isolation experiment involving an international crew of six volunteers, which concluded in November 2011, attempted to mimic the conditions of a return trip to Mars. The group were isolated for 520 days within a spacecraft mock-up located at the Russian Academy of Sciences’ Institute of Biomedical Problems in Moscow, Russia. However, although isolated and “locked away” from the world, it was impossible to truly recreate the psychological pressures that would be caused by being millions of miles away from Earth and feeling at constant risk – after all, only a door stood between the Mars-500 crew and safety. Nonetheless, it is known from anecdotal reports and research that astronauts during space missions experience moments of monotony and are affected by stressors, such as those caused by being confined and isolated, while also contending with problems related to the lack of privacy resulting from the restricted space provided by a spacecraft environment (Russomano et al. 2008; Vakoch 2011). These factors must all be taken into account when contemplating the design and content of an appropriate life support system for a manned Mars mission. The planet on which we live has a natural life support system that has sustained us for thousands of years, providing everything needed for the continuance of life. It delivers more than simple biological requirements, such as the water we drink and fertile land on which to grow food; it has an ozone layer that offers protection from the Sun’s UV radiation; it has gas, coal, and oil that provides us with power; and natural resources from which we create homes and commodities, among other things. None of these natural conditions will be found in the hostile environs of outer space or Mars. These must be artificially recreated in a system that will supply air, water, and food to the astronauts, and deal with all body and environmental waste products, while maintaining a living and working setting with the correct temperature and pressure that will also provide shielding from radiation. Such an all-encompassing life support system for a manned trip to the red planet will need to consider the two main phases of the operation: the interplanetary mission (the outward and return journey from Mars) and the time spent on the planet surface (Seedhouse 2009; Shkedi 2009; Rask et al. 2012).

The Advent of Advanced Life Support Systems The advent of advanced life support (ALS) systems were required following mankind’s first venture into space with the flight of Russian cosmonaut Yuri Gagarin in April 1961, closely followed by US astronauts Alan Shephard and John Glenn in May 1961 and February 1962, respectively, as part of the Mercury program. The proceeding 50 plus years have seen advances in the environment and life support systems found in spacecraft. The life support systems for the first three American

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space programs, Mercury, Gemini, and Apollo, were all primarily open-loop systems; they were for short-duration use and designed to be discarded, which allowed for a much simpler system than found nowadays. The 100% oxygen atmosphere for the crew was provided by either high pressure or cryogenic storage tanks, while the expelled CO2 was removed by lithium hydroxide in replaceable canisters (NASA 2015). The earlier Mercury and Gemini missions stored water in tanks, while the fuel cells of the Apollo spacecraft provided water as a by-product of electricity production. No reuse of waste products, such as urine and waste water, took place, with these being collected and vented overboard or stored for return to Earth. The arrival of the Space Shuttle program began a shift in the required specifications for life support systems. These spacecraft were designed to be reusable and, therefore, the life support system also needed to be improved and reused, although still dependent on disposable consumables. Currently, the best example of a very complex system that has the capability of sustaining a 6-astronaut crew, living and working in space for several months at a time, is the life support system to be found on the orbiting ISS – the Environmental Control and Life Support System (ECLSS) (NASA 2015). The ECLSS was designed to perform several crucial functions for the survival of the space crew and has included further advances in life support technologies. It monitors, controls, and maintains an adequate environment for the crew, monitoring and controlling partial pressure of gases (nitrogen, oxygen, carbon dioxide, methane, hydrogen, and water vapor), cabin temperature, humidity, and pressure. It also provides breathable oxygen for human metabolism, achieved through a process of electrolysis of water, removes the carbon dioxide produced and expelled by crew members, and filters microorganisms from the cabin air. In addition the ECLSS provides a source of potable water used for crew consumption, food preparation, and hygiene. This life support system has developed over a period of years with the addition of certain key technologies, including the addition of an oxygen generation (2006) and water recovery (2008) system, and the Sabatier reactor (2010), all of which have transformed the life support to a partially closed-loop physicochemical system. This is estimated to have reduced the annual resupply requirements to the ISS by 10,000 kg. Nonetheless, the need for replenishment of consumables, propellant, and maintenance equipment continues, an unfeasible operation for a longduration deep-space mission, and therefore, the loop must be further closed before a journey to Mars is possible (Shkedi 2009; NASA 2015).

Closing the Loop on Regenerative Life Support Any mission to Mars will require regenerative life support technologies and the use of in-situ resources to maximize self-sufficiency and reduce the need for provision and resupply of consumables. The six main elements needed for such an undertaking, according to the NASA Advanced Life Support Document, are: air provision, storage, and control; biomass production leading to food transformation, processing, and storage; habitat environmental thermal control of temperature and humidity; all waste collection, sterilization, storage, and reclamation, where appropriate; and

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waste water recovery, processing, storage, and purification for crew consumption. The sheer weight of transporting all these items during the journey and the logistics of safely storing and/or producing them in an extraterrestrial environment are of great concern to space agencies and the space industry. A key issue for the planning of any mission will always be the number of crew members assigned to an interplanetary space mission as this number will be an essential part of the algorithm used to calculate essential resources. Researchers have been considering the number of astronaut crew to go as between four and six space travelers. This number is seen as vital information by many scientists as it will dictate the quantity needed of each life support element defined by ALS. Therefore, the first step for an interplanetary mission is to create an inventory of consumables that will be necessary for a successful return trip to Mars, considering the journeys and planet-based time and any recycling or regeneration techniques and methods that will be available (MacElroy et al. 1992; Rapp 2006; Barratt and Pool 2008).

Calculating the Ins and Outs Each ALS element has to be carefully quantified per-crewmember-per-day and then multiplied by the total number of astronauts. It is equally important to tabulate the amount of waste per each type, which can range from disposable (paper, clothing, food waste) to organic materials produced by the astronauts (feces, urine, expelled carbon dioxide). It is estimated, for example, that each crew member will consume 0.617 kg of food, 3.91 kg of water, and 0.84 kg of oxygen every day of a mission, while the daily production of waste will be around 5.4 kg, including liquids, solids, and carbon dioxide). These calculations will provide the needed amount of ALS elements to be transported for a space mission, especially a long-term one, and also reflect the scale of the waste produced, which must be managed, processed, and regenerated where possible. On the ISS much waste is dealt with by storing for return to Earth or by dumping it overboard. Other solutions to the waste issue have been studied and proposed over the years. Some researchers have considered exposing the waste to high temperatures and pressures, in a process called pyrolysis, to generate useful by-products. However, such a method has the need for large amounts of power, which is an important limitation when considering a remote, confined, and isolated environment, such as found on a spacecraft (Rapp 2006). In a simplistic way, humans are main consumers of oxygen and biomass and major producers of carbon dioxide and waste. This process needs to be built upon to utilize the waste products and regenerate wherever possible useful resources. For example, human waste products could be used directly by plants (nutrients and carbon dioxide) or fermented by microorganisms into minerals and other nutrients, which in turn could serve as resource for plant growth (Rapp 2006). A major part of the solution would be the development of sophisticated technologies that could be applied to the recycling and transformation of some of these elements that will be essential for an adequate life support system for space crew

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during an interplanetary mission. In other words, these fundamental elements should be provided in a regenerative form and not as consumables. If all or at least some could be reliably recycled or regenerated, it would add to crew resources and safety, and ultimately to the potential longevity and success of the mission. A trip to Mars must begin with the minimal needed amount of food, water, and biological material, such as plant seeds and microbial cultures, dried or cryopreserved, for recycling and generation of new edible biomass in order to establish a self-sustainable ecosystem. In addition, focus must be given to creating a regenerative system that is of longduration and as self-sustaining as possible; failure-free functioning with the minimal need for spare parts and expendables will be essential. A life support system with a very high recovery percentage for resources will be of less benefit if it has a poor reliability rate, and therefore, the right balance must be found between the two, i.e., a system with a recovery percentage of 99% and reliability of 90% is less preferable than a system with a recovery rate of only 90% but reliability of 99% (Rapp 2006; Seedhouse 2009; Shkedi 2009).

Bioregeneration as a Solution The research for development of a life support system suited to a Mars mission is already well under way. Consideration must be given to the resources taken to the planet, as well as the potential for utilization of the natural resources to be found on the planet itself. A bioregenerative life support system (BLSS) will ideally perform all of the basic functions required by a life support system in a manner involving natural regenerative processes that produce basic life support consumables, including atmosphere revitalization, water and organic waste recycling, and food production. Current examples of research in this field include the European Space Agency managed MELiSSA (Micro-Ecological Life Support System Alternative) project, initiated in 1989; a collaborative research involving numerous European, Canadian, and other research institutions, such as the University Autonoma of Barcelona, University of Guelph, University of Ghent, and University of Clermont Ferrand; the Controlled Environmental Life Support System (CELSS) program, initiated in 1978 by NASA; and the prototype Lunar Greenhouse (LGH) project involving the University of Arizona, USA, backed by NASA funding, and the University of Naples Federico II, Italy with the help of ESA funding, among others (MacElroy et al. 1992; Rapp 2006; Shkedi 2009; NASA 2015). Looking at one of these systems in more detail provides the basic concept of the closed loop that is created, with the astronaut crew at the center of a process that mimics an ecosystem concept to take waste products and air pollutants and pass them through several steps until converted back to usable water, oxygen, and food products. The MELLiSA Loop (ESA 2015) comprises of the interconnection of four distinct compartments, with the last being split into two sections (Fig. 1): Compartment 1- Liquefying, Compartment 2- Photoheterotrophic, Compartment 3- Nitrifying, Compartment 4- Algae and Higher Plants. The Loop begins with the collection

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Fig. 1 Diagram of the MELiSSA Loop (Micro-ecological Life Support System Alternative), a European Space Agency collaborative project. Image: ESA

of waste products in Compartment 1 where they are anaerobically transformed (at high temperature, 55  C) into more usable forms, such as carbon dioxide, hydrogen, ammonia, volatile fatty acids, and minerals, through microbial degradation using thermophilic fermentative bacteria. Compartment 2 eliminates the liquid waste products of Compartment 1, primarily the volatile fatty acid, as well as carbon dioxide and hydrogen, through photoheterotrophic organisms. Compartment 3 converts the ammonia from wastes into nitrates that can be used as a source of nitrogen for higher plants and more easily used by autotrophic algae/bacteria. Finally, Compartment 4 is split into two sections: algae compartment colonized by the cyanobacteria Arthrospira platensis and a Higher Plant compartment, both essential for the production of oxygen, water, and food. However, the simplistic nature of this description does not take account of the as yet unknown implications of operating such a system in an environment of reduced gravity and potentially increased radiation exposure. Further research is required to test the effects of spaceflight-

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related stress on the bacterial strains used in the process, and consideration needs to be given to the genetic evolution that is possible during long-term culturing. Furthermore, the composition of waste products may well be affected and changed over time by residence in a Martian environment, leading to altered bacterial responses and changes in the ecological cycle.

In Situ Resource Use: An Important Addition The surface of the planet of Mars is known to be very different from that of Earth, and although it does not offer the same abundance of accessible resources that has sustained mankind, it does have natural resources that could be utilized to assist long-term settlement. The use of in situ resources will make the establishment of extraterrestrial exploration more financially viable by minimizing the materials carried from Earth and by developing advanced, autonomous devices to make best use of these available in situ resources (Rapp 2006). On-site production of life support consumables could not only extend mission duration but also have the potential to provide scientific returns. An important aspect will be the ability of astronauts to deal with the toxic atmosphere of the planet and find ways to extract in situ from its useful resources. The Martian soil contains oxygen in its rocks, as confirmed by drill samples taken by NASA’s Curiosity robotic rover, which landed in the Gale Crater on Mars on 6 August 2012. It is, however, a difficult process to remove this gas from the soil of the planet and a more likely alternative will be to take advantage of the atmosphere of Mars that is very rich in carbon dioxide – a potential source of carbon and oxygen. The atmospheric pressure on the planet is around 100 times less than found on Earth, with the average pressure on Earth being 29.92 inches of mercury as opposed to an average of 0.224 inches of mercury on Mars. This will require the air to be first compressed by a factor of 100 or more to then be processed. A reducing agent such as hydrogen will be needed to separate the carbon from the oxygen in the carbon dioxide, in effect producing CH4 and O2 when reacting with the CO2. This process, however, will not be simple as hydrogen is a rare gas on Mars (Rapp 2006). A possible solution could be to mine the surface of Mars to retrieve any available water. Although no surface water is present, it is known that subsurface ice exists beneath the planet polar caps and surfaces, and this could be used to supply water for crew needs, while also being used to enable the atmosphere to be compressed to create carbon, hydrogen, and oxygen (Seedhouse 2009).

Making Fiction a Reality In summary, our survival depends on the provision of three basic commodities – air, water and food, preferably in quantities that enable our physiology to thrive. Whether we find ourselves on the Earth, the Moon, or millions of miles away on Mars, these needs are the same and must be met on a daily basis. The explorer

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instinct in mankind originally drove us to leave the comfort and safety of our homes and communities, to sail across vast oceans and face new challenges in unknown lands. This same instinct has made us look up to the stars in the dark night skies and wonder what lies beyond. Within our solar system, Mars is considered the most Earth-like planet, although in reality the environment on Mars is far more hostile than ours due to important differences in temperature, atmospheric pressure, and gravity. Nonetheless, it is to the “red planet” that we have dreamed of traveling, in literature from such books as Journey to Mars by Gustavus W. Pope in 1894 and The Martian Chronicles by Ray Bradbury in 1950, and in numerous films, such as Abbott and Costello Go To Mars in 1953 and Robinson Crusoe on Mars in 1964, to name but a few (Lamont 1953; Haskin 1964; Pope 2008; Bradbury 2012). Travelling to Mars is no longer solely in the realms of science fiction; several initiatives have been proposed in the last 50 years, both manned and nonmanned, and valuable knowledge has already been gained from the Mars exploration rovers that have successfully landed on the planet surface. A manned voyage to Mars and time spent on the planet surface is still an enormous challenge, despite the ongoing research. Many obstacles have yet to be overcome, including the continued development of closed-loop regenerative life support systems to ensure astronaut survival and a means to avoid excess radiation exposure; however, we are nearer to achieving the goal of a manned-mission to Mars than at any other time in our history, and continued scientific advances will undoubtedly open up exploration of this new frontier (MacElroy 1992).

Cross-References ▶ Classification and Overview of Spacecraft Life Support Systems ▶ Designing a Closed Ecological Life Support System for Plants, Overview ▶ Examples of and Rationale for Bioregenerative Life Support Systems ▶ Future Life Support Systems, Overview ▶ Human Habitability Considerations, Overview ▶ Life Support Systems of the International Space Station ▶ Micro-Ecological Life Support Alternative (MELISSA), Overview ▶ Mission Duration and Location: Effects on Mass and Cost ▶ Short and Long Duration Mission Human Factors Requirements

References Barratt MR, Pool SL (eds) (2008) Principles of clinical medicine for space flight. Springer, New York Bradbury R (2012) The martian chronicles. Simon & Schuster, New York ESA - MELiSSA Loop (Microecological Life Support System Alternative) http://www.esa.int/ spaceinimages/Images/2009/07/Melissa_loop_diagram. Accessed 6 Apr 2015 Haskin B, dir (1964) Robinson Crusoe on Mars. Perfs. Paul Mantee, Victor Lundin. Aubrey Schenck Productions

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Lamont C, dir (1953) Abbott and Costello Go To Mars. Perfs. Bud Abbott, Lou Costello. Universal Int. Pictures MacElroy RD, Kliss M, Straight C (1992) Life support systems for Mars transit. Adv Space Res 12 (5):159–166 NASA International Space Station, Environmental Control and Life Support System. http://www. nasa.gov/sites/default/files/104840main_eclss.pdf. Accessed 6 Apr 2015 Pope GW (2008) Journey to Mars. Wildside Press, USA Rapp D (2006) Mars Life Support System. International Journal of Mars Science and Exploration, Mars 2, 72–82, 2006 Rask J, Vercoutere W, Navarro BJ, Krause A (2012) NASA space faring: the radiation challenge introduction and module 1: radiation educator guide. BiblioGov, USA Russomano T, Dalmarco G, Falcão FP (2008) Synthesis lectures on biomedical engineering #18 the effects of hypergravity and microgravity on biomedical experiments. Morgan & Claypool Publishers, Connecticut v. 1. 70p Seedhouse E (2009) Martian outpost: the challenges of establishing a human settlement on Mars. Springer Praxis Books, New York Shkedi BD (2009) Lessons learned from the International Space Station (ISS) Environmental Control and Life Support System (ECLSS) water subsystem. SAE Int J Aerosp 1(1):78–83 Vakoch DA (ed) (2011) Psychology of space exploration. NASA History Series SP-2011- 4411, Washington, DC

Space Suits and Life Support: Basic Concepts of IVA vs. EVA Theodore Southern and Nikolay Moiseev

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Space Suit Basic Concepts and Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Space Suit Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Life Support Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Space Suit Operating Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Space Suit Layers and Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Human Respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Space Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Abstract

This chapter provides an introduction into the basic architecture, operational constraints, and design considerations of the space suit life support system. An outline of requirements based on environmental and physiological considerations is discussed.

Introduction A space suit is the literal interface between man and machine during space flight. The space suit is both a tailored garment and an engineered pressure vessel, needing to be flexible and impervious to damage. They combine the design constraints of two conflicting categories: human factors and space systems engineering. This chapter attempts to delineate some basic concepts and requirements of the space suit and its T. Southern (*) • N. Moiseev Final Frontier Design, Brooklyn, NY, USA e-mail: ted@finalfrontierdesign.com; nik@finalfrontierdesign.com # Springer International Publishing AG 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_202-1

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life support. As with all systems, there are exceptions to every rule; the layout and architecture presented here is to be considered representative only, not absolute. Space suits are properly categorized by NASA as “crew systems.” In the framework of space systems, the space suit is a subsystem of the life support system of the spacecraft or is part and parcel with the life support system as a self sufficient vehicle, a “spaceship for one.” Space suits can be broadly categorized into two types: 1. IVA: Suits for use inside the vehicle during mission critical stages including launch, entry, docking, and engine burn, called intra-vehicular activity (IVA) or launch-entry-abort (LEA) suits. 2. EVA: Suits used outside the vehicle for spacewalks, either in microgravity or on a planetary surface, called extra-vehicular activity (EVA) suits. The required life support for each of these types of suits varies significantly, as does their general design and layout. All of these elements are dictated by the goal or purpose of the mission.

Space Suit Basic Concepts and Requirements The IVA suit is normally not fully pressurized and is generally only used as a redundant emergency back up to the vehicle’s pressurized cabin. IVA suits generally plug into the spacecraft via umbilicals, with breathing air, oxygen, cooling, biomedical sensors, telemetry, and communications all handled by the craft. Redundant on-suit air systems are occasionally included on IVA suits, useful for only a short period of time. The IVA suit is generally operated with an open loop life support system, venting to the atmosphere. The EVA suit, on the other hand, operates nominally under pressure in a hostile environment outside the vehicle. Internal suit pressures are generally higher than IVA suits. Modern EVA systems carry a personal life support system (PLSS) including all essentials for breathing, comms, biomed, cooling, telemetry, and even propulsion. As a point of comparison, NASA paid approximately $240,000 (Jenkins 2012) for their shuttle IVA suit, the advanced crew escape system (ACES) suit, while they paid in excess of $10 m for their shuttle EVA suit, the extra-vehicular mobility unit (EMU) (Figs. 1 and 2). One major driving factor in life support design between IVA vs. EVA suits is the expected metabolic rate of the user. During IVA, the astronaut can expect a relatively low metabolic rate; IVA activity generally is limited to seated operation of systems involving switch and joystick operations. EVA operations by definition are more metabolically intensive, with rates in the range of 3.5–5 Met (1250–1750 Btu/h). (Harris 2001) EVA operations by necessity involve translation, either in microgravity or nonterrestrial gravity, and heavy physical activity including equipment connections, stowage, and even satellite capture. The metabolic rate is increased with any activity inside a space suit, because of the required torque of suit mobility. The increase in human metabolic output puts further pressure on the life support system to maintain a comfortable environment for the human. As heat and waste products

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Fig. 1 David Clark Company’s advanced crew escape system (ACES) – IVA suit

increase inside the suit with rising human activity levels, systems must work harder to maintain a comfortable and safe environment (Table 1).

Space Suit Architecture Most space suits we know of are full pressure suits, essentially gas bubbles surrounding a human. A full pressure suit covers the entire body with an even amount gas pressure. While effective, full pressure suits require very complex pressure garments and enclosures, with significant cost and mass issues. Some high altitude suits, especially for military jets, use so-called “partial pressure” suits, which incorporate a sealed neck dam and helmet, to provide the head with required pressurization, along with a very tight fitting garment around the torso and limbs to provide temporary pressurization of the body. Range of motion in partial pressure suits is very restricted while pressurized and requires significant

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Fig. 2 ILC Dover’s extravehicular mobility unit (EMU) – EVA space suit

sizing to operate well. Partial pressure suits are only used for very short amounts of time during an emergency and thus are dubbed “get-me-down” suits. Because of the limited nature of partial pressure suit’s protection, they are generally limited to altitudes below 90,000 ft. The partial pressure suit exerts so-called “mechanical counter pressure” or MCP on the body, rather than pressure from enclosed gas. Future suit designs may well include MCP technology on the body, providing a much closer fitting pressurized layer with significantly less risk of puncture. Upgrades in materials, compression techniques, and mobility strategies could enable much more mobile and effective layouts than full pressure suits. Current MCP suits are in development but have never been used in space flight.

Life Support Architecture Short-term operations in a space suit pressure garment do not always require complex life support systems. Often the decision for IVA suited scenarios under 2–3 h is to use open loop life support, which vents pressure outflow from the suit directly to the surrounding atmosphere. An air source, either a blower or pressurized

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Table 1 Space suit types compared, based on average historical missions, Russian and American Life support configuration Weight Operating pressure G loads Mobility requirements Timeframe Cooling

Intra vehicular activity (IVA) On vehicle, open loop (in majority space ships) 20–30 pounds Nominally +0.2 psi (vent pressure), emergency +3.7 psi (USA) to +5.8 psi (Russia) +5 Gz to 0 G Limited, for pilot operation and escape Less than 2 h pressurized (in common case) Air flow (liquid cooling garment optional)

Metabolic rates Suit layers required

Relatively lower

Vehicle interfaces Equipment interfaces Price

Seat, ejection system, pilot controls, screens, hatches Parachutes, rescue kits, rafts, radio, water landing equipment $$

Cooling, pressure, and flame protective

Fig. 3 Diagram of a typical open loop life support system. (1) Pressurized tank (O2). (2) First stage pressure regulator. (3) Automatic emergency control valve. (4) Cabin air fan. (5) Space suit enclosure. (6) Space suit pressure regulator

Extra vehicular activity (EVA) On suit, closed loop Between 200 and 300 pounds Nominally full pressure, +4.3 psi (USA) to +5.8 psi (Russia) 0 G – Moon and Mars G Very extensive, including translation and heavy work Maximum 9 h pressurized Liquid cooling garment, via sublimator Higher Cooling, pressure, micrometeoroid, thermal, flame and debris, tear Hatches, translation bars, boot clips, hatches EVA tools, tethers $$$$$$

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tank, provides air to the suit, via a series of regulators and valves to control safe flow; the air circulates through the helmet and suit and is vented through a regulator. The system is very similar to a standard SCUBA setup (Fig. 3).

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Fig. 4 Diagram of typical closed loop life support system. (1) Space suit enclosure. (2) Ventilation gas blower. (3) CO2 removal cartridge. (4) Secondary pressure regulator. (5) Pressurized tank. (O2). (6) Control valve. (7) Primary pressure regulator. (8) Sublimator. (9) Water cooling pump. (10) Water flow regulator. (11) Liquid cooling garment. (12) Ventilation gas outflow port

However, during longer operations in a space suit, and where consumables are critical, a closed loop life support system is used, which is often carried on the body. The closed loop system carried on the back of an astronaut is often referred to as the personal (or portable or primary) life support system (PLSS). This system is generally very complex and includes redundant equipment, including fans, water, gas, cleaning, and power consumables, communications equipment, biometrics, and lighting; only a few specialty items such as the sublimator are nonredundant. A closed loop system recycles the pressure outflow from the suit, scrubbing it for odor, vapor, contamination, and CO2 before reflowing. A closed loop suit will often use a sublimator as heat exchanger for cooling, which is often integrated with its liquid cooling garment (LCG) system. The PLSS is designed to be recharged or changed out by onboard vehicle systems and supplies, to purge waste and repressurize oxygen (or change the O2 tank), refill water, and recharge batteries. The limited size and volume of the PLSS demands the minimization of every component and the optimization of placement for functionality. The PLSS adds significant weight to the overall suit assembly and is often more than 100 pounds. Fig. 4 shows a typical closed loop life support system schematic, without redundant items called out.

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Space Suit Operating Pressure At sea level, the Earth’s atmosphere measures as approximately +14.7 psia; it has several different gases, including primarily oxygen (about 21%) and nitrogen (about 78%). The percentage of pressure of a particular gas is referred to as its partial pressure. However, every space suit that has been used in space has operated with pure oxygen internally at pressures much lower than sea level. This is, in part, to keep the internal pressure as low as possible, to aid in mobility of the suit and reduce the effort required for joint flexion. Higher differential pressures by definition restrict movement and increase torque of the space suit. The human body requires a minimum of +3 psid partial pressure of oxygen for respiration. This is a high risk feature of the space suit, as pressurized pure oxygen. Most spacecraft operate at much higher pressures than space suits, and in a mixed gas environment with both oxygen and nitrogen, closer to or equal with sea level conditions. When transitioning from a mixed gas environment to a pure oxygen environment, it is necessary for the astronaut that pure nitrogen is dissolved in their bloodstream slowly to avoid decompression sickness (DCS). The time period required for the astronaut to pure nitrogen is called the “prebreathe penalty.” A higher internal suit pressure will reduce the risk of DCS. To avoid the prebreathe penalty, an ideal suit pressure of +8 PSI is required on the International Space Station (ISS). Pressurization requirements of a space suit involve a complex series of compromises. Currently, the American extra-vehicular mobility unit (EMU) pressurizes to a nominal +4.3 psid of pure oxygen, while the ACES operates at +3.5 psid (Thomas and McMann 2012). Both the Russian IVA suit, the Sokol, and the EVA suit, the Orlan D and M series, have a +5.8 psid operating pressure (Abramov and Skoog 2003).

Space Suit Layers and Environmental Conditions Space suits have a number of layers to meet the requirements of their potential operating environment in addition to their pressure garment. Internally to the pressure garment, a LCG, biomedical monitoring equipment, communications headsets and microphones, and a sweat wicking comfort layer are worn. These components must be compatible with a pure oxygen environment, with special consideration for electronics shielding to prevent electrical sparks. External to the pressure garment, multiple insulating and reflecting layers, micrometeoroid protection layers, tear and puncture protection layers, and flame resistant layers are incorporated, depending on the environment. IVA suits only require limited outer garments, while EVA suit has multilayered outer garment. During EVA the astronaut is exposed to considerable radiation from the sun, including visible spectrum, ultraviolet, and more energetic high energy particles,

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depending on their position in space. Sun radiation can heat up surfaces of vehicles and the suit to +250  F in direct sunlight, and for this reason several layers of spaced, reflective, aluminized mylar are used for thermal protection. Visors with a special metallic coating are used to protect the astronaut’s eyes from the intense unfiltered rays of the Sun. Special care is taken to avoid EVA during solar storms, as space suits do not have any specific protection from high energy ionizing radiation. In low Earth orbit (LEO), the Earth’s magnetic field protects the astronaut from ionizing radiation, but as humans venture beyond LEO high energy radiation will have to be considered more seriously during EVA.

Human Respiration During human respiration, CO2, water vapor, heat, and other wastes are produced, which need to be removed from inside the suit to effectively support human survival. CO2 is removed from the suit enclosure through carefully designed air flow. Helmet CO2 washout is critical, as inadequate or poorly designed helmet airflow will cause CO2 pockets which can endanger the astronaut. In addition, the visor can quickly fog because of water vapor produced during exhalation and the cooling of the surface in space. For this reason, helmet airflow is directed over the face and visor via a spray bar or other carefully engineered channel system. While O2 is introduced in the helmet, gas is removed below the helmet, often in the chest, to direct general airflow down and out of the helmet. In an open loop system, the CO2 and water vapor are simply vented out of the enclosure. In a closed loop system, the CO2 is scrubbed from the ventilation gas; most commonly lithium hydroxide canisters are used for CO2 scrubbing, although these are consumable and must be replaced after use or restored. Water vapor is then removed during the course of cooling of the ventilation gas, as it is cooled in a heat exchanger and collected through capillary membrane. Some water vapor is necessary inside the suit for human comfort, reduction of fire risk, and electrostatic discharge. Finally, odor is scrubbed using charcoal filter. Even at rest, the human body is exothermic and produces excess heat. Because a space suit entirely encloses the body, some sort of cooling is required in any scenario. The most basic version of a cooling system is a series of tubes that direct vent airflow over the body and limbs. This requires a high airflow rate but is significantly less complicated and bulky than its alternative, the liquid cooling garment (LCG) (Fig. 5). The LCG is designed for high metabolic rate activity, with water flowing in tubes over the skin of the astronaut. Water is much more effective for thermal transfer than air. In general an LCG is required for EVA, long duration depressurization, and other high-metabolic rate scenarios. Cooling in open space is often achieved using a sublimation device, which can only operate in a vacuum. The sublimation plate utilizes micropores in a metal plate, which instantly sublimate water ice into water vapor, in turn cooling the metal plate, the water, and ventilation gas flowing inside of it. A space suit’s flow rate defines the

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Fig. 5 NASA’s EMU LCG

required gas flow and water flow for astronaut cooling and circulation for safe operations.

Space Systems Any system designed for space travel must be built for complex and hostile environment of space, with well understood materials, assembly processes, and physical characteristics. This is especially true for human rated systems. Redundancy, engineering standards, defined materials, best manufacturing practices, and an understanding of the environment are required for appropriate design of the system. During launch, astronauts in space suits are subject in increased G forces, vibration, noise, and potentially an ejection or rapid egress. IVA space suits must integrate well into space craft seats, restraint systems, and must not add discomfort to

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launch conditions. In addition, adequate mobility, tactility, and comfort are required for vehicle interface during launch and operations. In space, EVA suits must protect their user in much the same way as a spacecraft, shielding the astronaut from micrometeoroids, thermal radiation, and extreme temperatures, in addition to the near vacuum of space. In orbit, micrometeoroids can impact an object traveling as quickly as 36,000 mph. In LEO, thermal fluctuation can range from 220  F in the shade of the Earth to +250  F in direct sunlight. Contaminations from vehicle cooling and waste systems, hypergolic thrusters, and dust (for planetary and asteroid missions) are real factors in EVA. The pure oxygen environment of a space suit internally and the high vacuum of space externally require a researched understanding of the materials used for construction, for their interaction with pure oxygen and potential to off gas toxic/ nontoxic substances on exposure to a vacuum. Corrosion resistance and electrical galvanization must be considered in materials selection as well. During the reentry and landing stages of a mission, the astronaut is subject to similar forces as launch, including increased G forces, vibration, noise, and potentially an ejection or rapid egress. The actual landing can be very violent, especially during a capsule and parachute landing, which require a mated space suit – seat system with shock absorption capabilities during impact. If the astronaut has been in microgravity for a long period of time the body will take time to readjust to Earth gravity, and special countermeasures including recombinant seating and anti-g pants are required for a safe transition. Post landing, it is possible that the astronaut may need to survive without aid for several hours. Potable water, first aid, radios and beacons, and other survival kits should be provided based on potential landing scenarios. Further, considerations for water landing must be considered, as a space suit can quickly fill with water when submerged. All of these considerations must be factored into design of the system; at the same time, very low quantities of the final product (the space suit) are ever produced. This requires customized, one-off components that can be especially difficult to characterize and produce repeatably. All components must be reliably tracked and labeled for traceable assemblies. Commercial off-the-shelf parts can rarely fulfill the requirements of space certification but offer an alluring alternative to individual one offs for every piece of this complex assembly. These factors help to explain the very high cost of space suits in general and the massive effort required to fly and maintain them.

Cross-References ▶ Human Factors Requirements ▶ Protecting Crew from Decompression Sickness

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References Abramov IP, Skoog AI (2003) Russian space suits. Springer, New York Harris GL (2001) The origins and technology of the advanced extravehicular space suit. American Astronautical Society, San Diego Jenkins DR (2012) Dressing for altitude. NASA, Washington, DC Thomas KS, McMann JH (2012) U.S. space uits, 2nd edn. Springer, New York

Life Support Systems for Russian IVA/EVA Space Suits Nikolay Moiseev

Abstract

This chapter presents the history, basic data, and design features for every generation of Russian Life Support Systems (LSS) for space suits. The chapter starts with a short description of pre-space-era LSS development, from which the first space systems evolved. For every space craft, an original space suit with a customized LSS was developed. The milestones of the Russian space program are Vostok, Voskhod, Luna, Soyuz, Buran, and various space stations including the Salyut family, Mir, and the International Space Station (ISS). Key elements of the basic LSS were used with improvements in a few projects.

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Suit’s LSS Development: Pre-Space Era . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gagarin IVA Space Suit. Vostok LSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Leonov’s Space Suit. Berkut EVA LSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yastreb EVA Space Suit, 1969. Regenerative EVA LSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kretchet EVA Space Suit for Lunar Missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strizh Space Suit. Buran IVA Space Suit with Regenerative LSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sokol IVA Space Suit for Soyuz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orlan EVA Space Suit Family. LEO and Space Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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N. Moiseev (*) Final Frontier Design, Brooklyn, NY, USA e-mail: nik@finalfrontierdesign.com # Springer International Publishing AG 2016 E. Seedhouse, D. Shaler (eds.), Handbook of Life Support Systems for Spacecraft and Extraterrestrial Habitats, DOI 10.1007/978-3-319-09575-2_208-1

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Introduction The need for space suits in human space flight was predicted by Konstantin Tsiolkovsky (Russia) in the beginning of the twentieth century. The development of Russian full pressure suits for high altitude flights started before World War II, as in the United States. The lessons of the pre-space-flight era were used for the development of the first space suit for Low Earth Orbit (LEO) flight and their LSS. The evolution of LSS moved to from simple systems to complicated systems with longer operating life and higher performance. This article describes the main features of Russian LSS for the key Russian space programs. The diagrams of LSS were simplified for educational purposes.

Space Suit’s LSS Development: Pre-Space Era Full pressure suits for aviators, used for high altitude flights, preceded proper space suits. The first full pressure aviation suit was built in Soviet Russia in 1931 (Abramov and Skoog 2003). Before World War II, about 15 pressure suits were designed in Russia, with some of them used in high altitude flights. The pre-space era Russian pressure suits were designed for an operating pressure of 4.3 psid (30 kPa), with limited mobility. LSS for these early pressure suits had an air ventilation system and an oxygen supply system. The first regenerative or closed loop LSS was built in 1937, using a chemical absorbent for the removal of CO2 from the ventilation flow. This regenerative LSS was used in high altitude aircrafts and for high altitude parachute jumping. With the beginning of World War II, design work on pressure suits stopped. Space suit development continued after 1946 with the war’s resolution. Since 1953, all Russian space suits and LSS were designed and built at the Zvezda Company, in Tomilino town, in the Moscow Region. Before space era, 18 models of full pressure suits were designed and tested between 1952 and 1959 for high altitude flights on jet planes and stratospheric balloon flights. This experience was used later for development of space suit for Gagarin’s flight (Fig. 1).

Fig. 1 Pre-space era full pressure suits. Photos are from the Zvezda museum

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Table 1 Vostok IVA space suit Year Function LSS type Operating Pressure Duration if no pressure in cabin Ventilation flow from LSS

1961–1963 IVA Open loop 3.9–4.35 psid (27–30 kPa) 5h 1.77–5.3 scfm (50–150 l/min)

This early LSS provided ventilation air for the full pressure suit in nominal flight conditions, and an oxygen supply in case of emergency. All ventilation flow was removed from the suit through a pressure valve and vented to the atmosphere. This type of LSS is known as open loop system. Zvezda developed “mask suits,” meaning the pilot is wearing an oxygen mask inside the helmet. The oxygen mask saves oxygen but requires a bigger sized helmet. In comparison maskless suits have proven to be more viable, because they provide better hygienic comfort for the pilot, although they require more oxygen flow. Space suit developments with LSS for real space flight started at Zvezda in 1959. The experience of pre-space era development and testing of high altitude suits was critical for the reliability of space suit design and for the certification process. Test facilities, test procedures, and LSS components were established and improved in the pre-space-flight era. (Table 1)

Gagarin IVA Space Suit. Vostok LSS The space suit and LSS for the Vostok spacecraft was developed to ensure safety for the astronaut in an emergency loss of cabin pressure and for rescue in case of a water landing. The open loop LSS provided air and oxygen for up to 5 h in a depressurized cabin. The components of the LSS were placed partially on the ejection seat in the landing capsule and partially in the service module. The LSS provided ventilation to the suit and removed heat, sweat, CO2, and other gas waste from human respiration. One fan fed the helmet and a second brought cooling air across the enclosure of the suit. The relief valve on the neck portion of the helmet released excess air from the space suit when the helmet was closed (Fig. 2). If the cabin pressure is decreased below 10.59 psia (73 kPa), the LSS automatically supplies additional air from cylinders to the suit (Fig. 4, #2). Air from the suit is vented to the cabin. If leakage is too great, and the cabin pressure drops to 60 kPa or below, the helmet visor should be closed, either automatically or manually. The helmet had pyrotechnic actuators that activated and closed the visor if a signal from the pressure sensor was activated. The SK-1 space suit had a united connector to onboard LSS (Fig. 3). The united connector attached to the seat in one click and connected the suit with LSS, ventilation system, oxygen supply, communication, and biometric data collector system.

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Fig. 2 Gagarin’s space suit overview left, pressure relief valve right Fig. 3 Vostok LSS united connector

Oxygen flow to the helmet automatically started when the visor was closed. The ventilation flow in the suit was a mixture of nitrogen and oxygen; with pure oxygen supplied to the helmet, the partial pressure of oxygen in the space suit increased. If the pressure in the cabin fell to 4.35 psia (30 kPa), the ventilation fan switched off, and positive pressure was established in the suit at approximately 3.92–4.35 psid (27–30 kPa). The partial pressure of the oxygen in the Vostok suit did not exceed 45%. The Vostok LSS contained a rubber bag in an aluminum housing that acted as a breathing reservoir to decrease respiratory resistance when a deep inhalation of air happened. The standard profile of Vostok flights included ejection from spacecraft at an altitude of 23,000 feet (7 km) and a landing of the cosmonaut via parachute. After

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Fig. 4 Vostok LSS diagram. (1) Primary Oxygen tank. (2) Air tanks. (3) Primary regulator. (4) Shut off valve. (5) Redundant Oxygen cylinder. (6) Breathing reservoir. (7) Breathing valve. (8) Space suit enclosure. (9) United connector. (10) One liter oxygen cylinder. (11) Vostok ejection seat. (12) Fans. (13) Pressure Reducer. (14) Vostok service module

Fig. 5 Berkut EVA Space Suit with LSS. Back view (right) and Umbilicals (left)

ejection, oxygen from a 1 l cylinder on the hip of the suit flowed to the helmet. This suit had a compact LSS for the descent phase, with a parachute. The system had oxygen cylinder (Fig. 4, #10) that provided flow to the helmet for up to 30 min. When oxygen from the 1 l cylinder was depleted, a signal from the cylinder’s sensor activated a mechanism on the helmet to open the helmet’s visor (Fig. 5).

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Table 2 Voskhod-2 EVA Space suit Year Function LSS type Primary Operating Pressure Secondary Operating Pressure Backpack Weight with LSS EVA duration in free space Duration in vacuum Ventilation flow from LSS Ventilation from onboard LSS

1965 IVA/EVA, universal Open loop 5.8 psi (40 kPa) 3.8 psid (26.4 kPa) 47.4 lb. (21.5 kg) 12 min 22 min 0.565–0.706 scfm(16–20 l/min) 5.3 scfm (150 l/min)

Leonov’s Space Suit. Berkut EVA LSS The goal of the first EVA in history was to show that cosmonauts could work in space (Table 2). The concept of the first EVA from the Voskhod-2 spacecraft included an inflatable airlock. The Berkut (Golden Eagle) was a universal space suit and served as IVA and EVA suit. An airlock was attached to the side of the capsule and inflated before EVA; the airlock was jettisoned after EVA. The operating pressure of the Berkut suit was 5.8 psi (40 kPa). To prevent decompression sickness, a relatively high operating pressure was used. The pressure regulator allowed a reduced pressure mode of 3.8 psid (26.4 kPa) to increase suit mobility, if needed. The backpack with a Personal Life Support System (PLSS) was secured on the back of the suit with a belt system. Oxygen was stored in three 2 l volume cylinders, each at 3191 psi (22 MPa) pressure. All oxygen flowed through the helmet and then into the suit, across the arms and feet via a tubing system. All flow was released into open space through a pressure regulator on the left side of the chest. The Berkut LSS had three modes of oxygen supply: airlock pressurization/depressurization, nominal flow, and emergency supply. The airlock’s pressurization/depressurization mode had an oxygen flow rate of 0.883–1.059 scfm (25–30 l/min). Nominal flow during EVA had a rate of 0.565–0.706 scfm (16–20 l/min) Abramov et al. (1984). The emergency supply mode had a flow of 1.059 scfm (30 l/min). The emergency valve automatically turned on emergency oxygen when the suit’s pressure was reduced below 3.48 psi (24 kPa). Redundant oxygen was provided via an umbilical from the onboard LSS, if some failure happened. The suit’s umbilical consisted of a steel cable, an emergency oxygen supply hose, a biomedical data transmitter cable, and a communication cable. During the world’s first EVA, Alexey Leonov had an elongation problem with the suit during entry to the airlock. He reduced pressure in the space suit with the pressure regulator to the emergency supply pressure of 3.83 psi (26.4 kPa) and completed entry to the airlock. A second cosmonaut was waiting in the Voskhod-2 cabin, wearing the same space suit with an identical LSS. He was ready to depressurize the cabin and help Leonov, if needed (Figs. 6 and 7).

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Fig. 6 Berkut LSS Diagram. (1) Helmet manifold. (2) Pressure relief valve. (3) Pressure regulator. (4) Oxygen supply mode switches. (5) Backpack. (6) Oxygen cylinders. (7) Pressure sensor. (8) Secondary regulator. (9) Primary regulator. (10) Nominal oxygen supply from airlock LSS. (11) Oxygen disconnects. (12) Emergency oxygen supply from airlock LSS. (13) LSS inlet. (14). Ventilation hoses

Yastreb EVA Space Suit, 1969. Regenerative EVA LSS The Russian EVA space suit Yastreb (Hawk) was developed for early Soyuz flights (Table 3). This space suit allowed EVA from the Soyuz orbital module. The goal of the EVA was crew exchange between two spacecrafts. The crew launched in Soyuz 5, transferred from Soyuz 5 to Soyuz 4 on orbit through open space, and then landed in Soyuz 4. The EVA lasted 37 min. It is still the only exchange of crew between vehicles in the history of human space flights. The Yastreb was only an EVA suit, without IVA functionality. Cosmonauts were without space suits during launch and landing. They put on the suit with the assistance of the other crewmember in the orbital module of the Soyuz before EVA. The Yastreb was only used during the Soyuz 4 and Soyuz 5 flights. Design and development of this new EVA system started at Zvezda in 1966. Inputs from Alexey Leonov’s EVA were used for the development of an upgraded space suit and LSS. Yastreb had a unique placement of LSS on the space suit on the knees. During intensive testing in zero-g flights onboard of a Tu-104 flying laboratory, it was found to be necessary to reposition the backpack. The pack with the LSS was placed on the front of the legs to ease access through the small Soyuz hatch,

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Fig. 7 Yastreb EVA Space Suit with LSS pack on the knees

Table 3 Yastreb EVA space suit Year Function LSS type Primary Operating Pressure Secondary Operating Pressure Backpack Weight with LSS LSS supported duration Ventilation from LSS

1969 EVA Close loop, regenerative 5.8 psi (40 kPa) 3.8 psid (26.4 kPa) 69.45 lb. (31.5 kg) 2.5 h 8.83–10.59 scfm (250–300 l/min)

which had a diameter of only 2400 (600 mm) Abramov et al. (1984). Ten space suits with LSS were manufactured for the test program including for the vacuum chamber test, thermal vacuum tests, and zero-g flights. The goal of the project was a closed loop LSS for EVA. The oxygen flow was circulated in a closed loop, cooled, dried, and cleaned in the knee pack. The regenerative LSS that was developed for Yastreb saved volume and mass compared to an open loop design. Open loop LSS is only for a short duration EVA. The LSS was mounted in a pressurized box. It was the first LSS for EVA in a pressurized container. Pressurized backpacks were used for all further Russian EVA projects; American LSS are generally open to the vacuum. The shell of the container provides protection of sensitive LSS components from the harsh space environment.

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Fig. 8 Yastreb close loop LSS Diagram. (1) Oxygen valve. (2) Pressure reducer. (3) Primary oxygen cylinder. (4) Fan. (5) CO2 removal cartridge. (6) Vapor heat exchanger. (7) Redundant oxygen cylinder. (8) Pressure reducer. (9) United disconnect. (10) Oxygen switch off. (11) Helmet manifold

Fireproof and spark free electrical equipment were developed for use in pure oxygen. An environmental CO2 sensor system was designed to monitor the atmosphere in the suit. The newly developed cartridge cleaned the ventilation flow from CO2, CO, and other contaminants that the human lungs and body produced. Hydrated lithium hydroxide (LiOH) was selected to absorb CO2. According to the results of a research study, LiOH provides the best ratio of absorption to mass rate generation and the lowest heat production during absorption of CO2. A centrifugal fan for the LSS was certified for pure oxygen and high humidity conditions. A commutatorless fire proof motor was used for the pure oxygen atmosphere of the suit (Fig. 8). The helmet manifold is bar for distribution of ventilation flow inside of helmet’s visor. The manifold placed on the top of visor and had a hose on the side of helmet connected to ventilation system of the suit on the neck ring. A unique feature of the Yastreb suit was the ventilation suit as a separate layer. The suit had hoses for vent flow to the wrists and feet area, to direct and spread the flow. The vent suit provided cooling of the body with ventilation from LSS with a very high level of the flow during EVA. The cosmonaut put on the vent suit and then donned the space suit. The vent suit connected to the space suit inside, before closing the entry, and disconnected from the space suit after the EVA mission. An overall view the ventilation suit is shown on Fig. 9.

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Fig. 9 Ventilation Suit of Yastreb EVA Space Suit

The outer protective garment, or Thermal Micrometeoroid Garment (TMG), minimizes heat flow into and out of the pressure suit. The LSS provides thermal control during EVA with special components. An evaporating heat exchanger was used in the Yastreb kneepack for heat transfer from the space suit into space. The exchanger evaporated water vapor to space and cooled air inside the space suit. Reliable separation of water and vapor and the prevention of freezing in the vacuum were solved with the porous body design. Approximately 78% of the water was lost to open space in the evaporation process. The challenge for Zvezda was bottling oxygen at 6.092 psi (42 MPa). High pressure in an oxygen cylinder corresponds not only to the cylinders but to all hardware including valves, pressure reducers, and charging equipment. Designs and equipment were certified for this pressure. After the Soyuz 5 flight, this level of pressure for oxygen was used for all further Russian EVA projects. This high pressure saves weight and volume of the LSS but has strong requirements for design, equipment, and personnel training and handling. Yastreb’s LSS had a redundant oxygen cylinder and a redundancy of the ventilation system. If the primary fan of the ventilation system failed, the injector would provide ventilation flow to the space suit.

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Table 4 Moon EVA space suit Year Function LSS type Primary Operating Pressure Secondary Operating Pressure Space suit Weight with LSS Estimated Weight of LSS EVA duration Ventilation flow from LSS Ventilation from onboard LSS

1961–1972 EVA Closed loop 5.8 psi (40 kPa) 3.8 psid (26.4 kPa) 233.7 lb. (106 kg) 156.53 lb. (71 kg) 10 h 0.565–0.706 scfm(16–20 l/min) 5.3 scfm (150 l/min)

Fig. 10 Krechet Moon Space Suit with LSS in backpack front view (right) and side view (left)

Kretchet EVA Space Suit for Lunar Missions Zvezda started the initial development of a Lunar space suit in 1961 (Table 4). The project of a space suit for Soviet manned Lunar mission was named Krechet (Gyrfalcon). The major design change of the suit was the LSS in a backpack that served as a hatch for entry to the suit. The LSS was mounted in the backpack and had controls in the chest pack. A semi-rigid space suit design with rear entry was later used for all Russian EVA space suits. The NASA next generation suit will also be a rear entry space suit (Fig. 10).

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Fig. 11 Krechet LSS in backpack

The Krechet LSS is shown in Fig. 11. The largest box, in the center of the backpack, is the CO2 and contamination removal cartridge. The oxygen cylinder has a fiberglass with epoxy resin wrapping. New components for the Krechet LSS were developed at Zvezda in the 1960’s: a sublimator and a moisture collector from ventilation gas made from a porous metal. These components, with upgrades, are still used in the Russian EVA LSS. The sublimator is a metal cylinder heat exchanging device, in which water ice evaporates on exposure to the vacuum creating cooling, and water from the Liquid Cooling Garment (LCG) and vent gases are cooled. Evaporation of solid phase of water, called sublimation, is the most effective cooling process. A special water tank supplies water to the device during EVA. The LSS in an EVA space suit evaporates about 2–3 l of water into open space during each EVA. The sublimator is placed in the backpack with an exposed face and a hole in the outer cover and works in high vacuum condition only (Figs. 12 and 13). The Krechet LSS used a LCG to cool the astronaut’s body. The LCG is a leotard from elastic tricot garment with tubes. Water in the tubes circulates with a pump in backpack. All Krechet LSS components have been tested for operating life, cycling, reliability, and in vacuum and in thermal chambers.

Strizh Space Suit. Buran IVA Space Suit with Regenerative LSS The Strizh (Swift) space suit with an original combined open/closed loop LSS was designed for the Buran winged spacecraft (Table 5). In a nominal flight condition, the helmet was open and the suit was ventilated with cabin air. If the cabin loses

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Fig. 12 Sublimator’s opening on the backpack

Fig. 13 LCG Diagram. (1) Inlet water connector. (2) Outlet connector. (3) Elastic tricot fabric. (4) Tubing (CREDIT http://rushkolnik. ru/docs/28/index-1450274. html)

pressure, the helmet closes and the LSS worked in the closed loop configuration. The Buran required a very long runway only in Kazakhstan, meaning the space suit could have been under pressure for up to 12 h to reach the required runway. The LSS provided ventilation, oxygen, contamination control, cooling, and moisture removal for two suited crew members. In case of 4 crew members, two

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Table 5 Buran IVA space suit Year Function LSS type Primary Operating Pressure Secondary Operating Pressure Life Support LSS Feature Ventilation flow from LSS

1981–1991 IVA Open loop/closed loop 5.8 psid (40 kPa) 3.9 psid (27 kPa) 12 h 1 system for 2 crew members Total 10.6 scfm (300 l/min) (5.3 scfm (150 l/min) for each crewmember)

Fig. 14 Strizh space suits

LSS would be used. When the helmet was closed and the space suit pressurized, the gas circulate in a closed system, passing through a CO2 cartridge, a moisture absorber, and a heat exchanger for cooling. The gas enriched with oxygen came back to the space suit. A specific feature of the Strizh suit is an umbilical with a diameter 1½ in. (38 mm). The large diameter of hose and specially developed disconnects were used to reduce flow resistance of the closed loop ventilation system (Fig. 14). Because of the long duration of flight in a space suit under pressure, the Strizh had a waste management diaper consisting of 5 layers of thick and soft cotton material for absorption of urine and its smell. A drinking water supply system was included to the suit as well. Two Strizh suits with a LSS were flown onboard of Buran in its only flight in 1988. It was an unmanned flight, and dummies with sensors were placed in space suits. A lot of tests were conducted with the LSS and space suits for Buran. In 1990, 18 days of man evaluation testing were run in a vacuum chamber, which included 12 h under pressure and a series of emergency modes. Also, 5 high altitude

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Fig. 15 Strizh PLSS diagram. (1) Nominal ventilation. (2) Emergency ventilation. (3) Ejection seat O2 cylinder. (4) cylinder. (5) Pressure reducers. (6) Shut off valve. (7) Injector. (8) Disconnect. (9) Air from cabin. (10) Cabin air blower. (11) Heat exchanger. (12) CO2 removal cartridge. (13) LSS disconnects. (14) Space suit disconnect. (15) Ventilation system

ejection tests were conducted with dummies in suits at an altitude of 114,829–131,234 feet (35–40 km) and a speed of Mach 3.2–4.1. An additional oxygen supply unit with valves was included for the post ejection phase (Fig. 15).

Sokol IVA Space Suit for Soyuz The first flights of the new Soyuz spacecrafts were without space suits (Table 6). However, the flight of Soyuz 11 to the Salyut-1 space station had a tragic ending. Three cosmonauts perished due to depressurization of the cabin during reentry. After Soyuz 11, the space suit became a required personal survival garment for cosmonauts in case of cabin depressurization during launch, reentry, and abort modes. Due to the weight limitation, a lightweight full pressure suit with an open loop LSS designed for 2 h of operation was chosen. The aviation full pressure suit Sokol (Falcon) was first adapted to space flight with the name Sokol-K: K for kosmos, or space in Russian. Sokol-K was used between 1973 and 1981. It was ventilated by cabin air with LSS fans. If the cabin depressurized and dropped down below 8.7 psi (60 kPa), the helmet should be closed manually. 40% oxygen gas was supplied to the helmet and the fans of the ventilation system stopped. The gas left the suit through a pressure regulator. The regulator maintained pressure in the suit of 5.8 psi (40 kPa).

16 Table 6 Sokol IVA space suit

N. Moiseev Year Function LSS type Primary Operating Pressure Secondary Operating Pressure LSS Weight Primary Life Support Emergency flow from LSS Nominal flow from LSS

1973–current time IVA Open loop 5.8 psi (40 kPa) 3.9 psid (27 kPa) 198.4 lb. (90 kg) 2h 0.706 scfm (20 l/min) 5.3 scfm (150 l/min)

Fig. 16 Sokol KV-2 Space Suit (author of the chapter Nikolay Moiseev is in the suit)

A new version of the Sokol, KV-2, was developed with a few modifications made to increase comfort, and it has been used in Soyuz spacecrafts since 1980 (Fig. 16). The Sokol KV-2 space suit has a pressure regulator (Fig. 17, #8) on the chest. The regulator has big handle to operate with gloved hand under pressure. The key component of the regulator is a brass aneroid that serves as a control unit and keeps a certain pressure in the suit. The valve of regulator will close if absolute pressure falls lower than 5.8 psia (40 kPa). The pressure regulator supports 2 pressure levels: primary operating pressure 5.8 psid (40 kPa) and secondary 3.9 psid (27 kPa). The lower pressure level is possible after some desaturation; the space suit under lower pressure has better mobility. The pressure regulator also serves as pressure relief valve, opening if pressure in the suit exceeds 6.67 psi (46 kPa). The astronauts undergo extensive training in Sokol space suits before space flight. Training includes suited 2 h under operating pressure in a high altitude vacuum chamber. A special ventilation box is used to ventilate space suits while the crew members travel to the launch pad. The ventilation box includes a battery, fan, and ice box for air cooling if needed. Sometimes weather conditions on the Russian spaceports require heating and not cooling. The LSS diagram shows the combination of ventilation fans for nominal flight conditions and oxygen cylinders for emergency conditions.

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Fig. 17 Sokol KV- 2 LSS diagram. (1) Oxygen cylinders. (2) Pressure reducers. (3) Valve. (4) Shut off valve. (5) To other space suits. (6) Oxygen disconnect. (7) Air disconnect. (8) Pressure regulator. (9) Ventilation system. (10) Air manifold. (11) Oxygen manifold. (12) Ventilation soles. (13) Cabin blowers

Orlan EVA Space Suit Family. LEO and Space Stations Russian EVA space suits for various space stations have evolved over the years (Tables 7 and 8). Each generation of LSS and space suits for EVA have upgraded the EVA system, increasing operational life, reliability, mobility, and duration. Six generations of the Orlan, or Eagle, space suit family are presented in Table 1. All Orlan space suits are semirigid with a rear entry. The LSS is in a backpack and the control units of the LSS are on the chest of the hard upper torso. Almost all components of the LSS are in a pressurized volume in the backpack for protection from the harsh space environment. A primary oxygen cylinder can be found attached to the bottom of the backpack. Layout and packaging of the LSS in the backpack is challenging, and the primary oxygen cylinder is placed outside for easy replacement. All ventilation, oxygen supply, and water cooling tubes are inside the space suit. The astronaut connects only two disconnects, the LCG and communication cap, when donning the suit. The LCG is part of the Thermal Control System (TCS). The TCS includes a heat exchanger or sublimator, water pumps (primary and redundant), a water storage tank, filters, a sensor system, a thermal regulator, an air bubble

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Table 7 Orlan EVA space suits Year Function LSS type Primary operating pressure Secondary operating pressure Backpack weight with LSS EVA duration Ventilation flow from LSS

1977–current time, with 7 generations EVA Closed loop 5.8 psi (40 kPa) 3.9 psid (27 kPa)

No secondary pressure since 2005

132.3–165.3 lb. (60–75 kg) See table 0.565–0.706 scfm (16–20 l/ min)

Table 8 Orlan space suit generations Space suit name Orlan-D Orlan-DM Orlan-DMA Orlan M Orlan-MK Orlan-MKS a

Space station Salyut – 6 Salyut – 7 Salyut – 7 Mir Mir Mir ISS a ISS ISS

Years of operations 1977–1979 1982–1984 1985–1986 1986–1988 1988–1997 1997–2000 2001–2007 2008–2015 2016 –. . .

max EVAs (per suit) 3 6 9 12 12 15 20 (TBD)

LSS operation, h 4 4 4 5 6 7 8 8

International Space Station (ISS)

remover device, and a LCG. The astronaut manually adjusts the regulator on the chest to control the cooling temperature. With the Orlan-MKS, the suit will have an automatic climate control system (Fig. 18). The LSS of the Orlan family suit usually has three levels of redundancy. One failure of any item does not lead to abort of an EVA. For example, the TCS has two pumps. If the primary pump stops working for any reason, the second pump will start to work. If the second one fails, the astronaut will increase ventilation flow for cooling and he/she will return to the airlock. The Orlan has two oxygen cylinders – primary and redundant. They are similar. The volume of each cylinder is 1 l and the pressure is 6.092 psi (42 MPa). The ventilation system has two fans and an O2 injector. If both fans fail, the injector will provide circulation of ventilation gas with the help of the high pressure from the O2 cylinder. Cosmonauts must dry the space suit after each EVA and replace the primary oxygen cylinder, refill the water tank, charge the battery, and replace the filters and the CO2 cartridge. The first Orlan EVA suits (Orlan –D and DM) were connected to the station’s onboard LSS by an umbilical cable. The cable supplied power to the suit, supported

Life Support Systems for Russian IVA/EVA Space Suits

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Fig. 18 Orlan-D(DM) EVA space suit with LSS controls on the chest. (1) Space suit enclosure. (2) LSS umbilical connector. (3) Backpack closing handle. (4) Tether. (5) Emergency oxygen supply valve. (6) Sun visor. (7) LSS backpack. (8) Shoulder bearing. (9) Chestpack. (10) Pressure level regulator. (11) Pressure gauge. (12) Glove. (13) Waist restraint. (14) Communication and electrical umbilical (CREDIT http:// rushkolnik.ru/docs/28/index1,450,274.html)

communications, and transmitted telemetry data. The Orlan-DMA suit had an umbilical only for emergency, although it has never been used. The letter “A” in the title means “autonomous.” The most intensive improvements of the Orlan LSS were made for the Orlan-M. There was a new LCG from elastic tricot and smaller diameter tubes, a back-up pump, a modified fan, and a CO2 cartridge with increased capacity of absorption. Diapers and a drinking water bag were included in the suit. The Orlan-M suit is connected to an onboard LSS system in the airlock of Mir before and after EVA, during depressurization and pressurization airlock operations. The airlock LSS has oxygen cylinders, a heat exchanger, CO2 cartridges, an electrical umbilical, and water pumps. The autonomous time of the suit was increased when onboard LSS is used. The LSS for ISS has some further modifications. The current LSS onboard of ISS provides: – – – –

Oxygen for prebreathing from a specialized onboard storage system Maintenance equipment to check leakage, Dedicated water cooling system, Power supply, communications, and telemetry transfer.

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N. Moiseev

Fig. 19 Orlan LSS diagram

The ISS onboard LSS does not have a CO2 removal cartridge any more, mandating the increased capacity of the suit’s cartridge. Drying of the suit after EVA is provided by the suit’s fan. The onboard LSS meets the requirements of the Russian segment and ISS’s common airlock and features connections for both the EMU and the Orlan suits (Fig. 19).

References Abramov I, Severin G et al (1984) Pressure suits and systems for work in open space. Mashinostroyenie, Moscow Abramov I, Skoog I (2003) Russian spacesuits. Springer-Praxis Books, Chichester