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Research on the International Space Station

If the life of the ISS is extended, a more robust program of science, human research and technology development would significantly increase the return on investment from the Station and better prepare for human exploration beyond low-Earth orbit.

—Augustine Committee Final Report (Seeking a Human Spaceflight Program Worthy of a Great Nation), October 2009

The International Space Station (ISS) is an engineering marvel that is a testimony to human ingenuity and a sterling example of international cooperation for the purpose of conducting unique research in space. As the only existing and available platform of its kind, it is essential that its presence and dedication to research for the life and physical sciences be fully utilized in the decade ahead. Before the 2010 budget announcement, NASA’s research plan for ISS utilization was expected to focus on objectives required for lunar and Mars missions in support of Constellation timelines, and ISS participation by the United States was expected to end in 2016. There is now a de-emphasis on lunar missions along with the extension of the ISS mission to 2020. The change in focus strengthens rather than weakens the need for a permanent research laboratory in microgravity devoted to scientific research in space focused on both fundamental questions and questions posed in response to the envisioned needs of future space missions.

In accordance with the charge (see the appendix) for this interim report, this chapter identifies some of the broad research areas that represent near-term opportunities for ISS research. However, it should be understood that flight research is generally part of a continuum of research that extends from laboratories and analog environments on the ground, through other low-gravity platforms as needed and available, and eventually into extended-duration flight. Like any process of scientific discovery this process is iterative, and further cycles of integrated ground-based and flight research are likely to be warranted as understanding of the system under study evolves. Separating out a portion of the research continuum that would benefit from relatively near-term access to the ISS was therefore a significant challenge for the committee, which asks that readers keep the following in mind.

  • While the ISS is a key and unique component of research infrastructure that will need to be utilized by a life and physical sciences program, it is only one component of a robust program. Other platforms and elements of research infrastructure will be important, including those that are ground based.

  • Because of the limited amount of research time that will be available on the ISS even with an extended lifetime, most of the research that will be flown on the ISS will need to be supported by a very strong ground-based program to be scientifically credible.

  • The research discussed here includes both enabling research (associated with the development of new knowledge that could be applied to exploration mission needs) and enabled research (associated with the development of new knowledge that can be obtained only by using the unique microgravity environment of space).

The research discussed below is divided into general fields of life and physical sciences that are amenable to study on the ISS. These fields are not presented in any priority order.



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3 Research on the International Space Station If the life of the ISS is extended, a more robust program of science, human research and technology development would significantly increase the return on investment from the Station and better prepare for human exploration beyond low-Earth orbit. —Augustine Committee Final Report (Seeking a Human Spaceflight Program Worthy of a Great Nation), October 2009 The International Space Station (ISS) is an engineering marvel that is a testimony to human ingenuity and a sterling example of international cooperation for the purpose of conducting unique research in space. As the only existing and available platform of its kind, it is essential that its presence and dedication to research for the life and physical sciences be fully utilized in the decade ahead. Before the 2010 budget announcement, NASA’s research plan for ISS utilization was expected to focus on objectives required for lunar and Mars missions in support of Constellation timelines, and ISS participation by the United States was expected to end in 2016. There is now a de-emphasis on lunar missions along with the extension of the ISS mission to 2020. The change in focus strengthens rather than weakens the need for a permanent research laboratory in microgravity devoted to scientific research in space focused on both fundamental questions and questions posed in response to the envisioned needs of future space missions. In accordance with the charge (see the appendix) for this interim report, this chapter identifies some of the broad research areas that represent near-term opportunities for ISS research. However, it should be understood that flight research is generally part of a continuum of research that extends from laboratories and analog environments on the ground, through other low-gravity platforms as needed and available, and eventually into extended-duration flight. Like any process of scientific discovery this process is iterative, and further cycles of integrated ground-based and flight research are likely to be warranted as understanding of the system under study evolves. Separating out a portion of the research continuum that would benefit from relatively near-term access to the ISS was therefore a significant challenge for the committee, which asks that readers keep the following in mind. • While the ISS is a key and unique component of research infrastructure that will need to be utilized by a life and physical sciences program, it is only one component of a robust program. Other platforms and elements of research infrastructure will be important, including those that are ground based. • Because of the limited amount of research time that will be available on the ISS even with an extended lifetime, most of the research that will be flown on the ISS will need to be supported by a very strong ground-based program to be scientifically credible. • The research discussed here includes both enabling research (associated with the development of new knowledge that could be applied to exploration mission needs) and enabled research (associated with the development of new knowledge that can be obtained only by using the unique microgravity environment of space). The research discussed below is divided into general fields of life and physical sciences that are amenable to study on the ISS. These fields are not presented in any priority order. 19

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PLANT AND MICROBIAL RESEARCH Plant and microbial research on the ISS fulfills two major goals: (1) to increase basic knowledge of how these organisms sense and respond to their environment, especially gravity-related phenomena, and (2) to provide the underpinning for enabling sustained human habitation in space. There has not been a comprehensive program dedicated to analyzing microbial populations and responses to spaceflight. This represents a critical gap in our knowledge because microbial populations play significant roles in positive and negative aspects of human health and in the degradation of their environment through, for example, food spoilage and biofouling of equipment. At present there is little information on how long-term contact with the combination of factors imposed during spaceflight, such as chronic exposure to cosmic radiation and altered physical parameters associated with microgravity such as reduced convection, could lead to changes in microbial populations or provide sufficient selective pressures to drive microbial evolutionary processes. Also, the degree to which such changes reflect physiological responses to the spaceflight environment versus genomic changes remains undefined. Continued access to the ISS coupled to the technological maturity, low cost, and speed of genomic analyses, plus the rapid generation time of microbes, makes monitoring of the evolution of microbial genomic changes induced by extended growth in space a highly feasible short-term goal. Since samples could be taken from the surfaces of the ISS and the crew on board and returned for analysis on the ground, the on-orbit portion of this research could largely be accomplished using the already-existing microbial air and surface sampler kits. This research would allow a comprehensive analysis of microbial population changes in response to the factors present in the spaceflight environment that impact the rates of reproduction or survival of microbes, using both experimentally established populations and samples of microbes colonizing the surfaces and the crew of the ISS. In contrast, a series of experiments on the ISS with a focus on plants has provided an initial, limited characterization of plant responses ranging from the developmental and molecular changes elicited by spaceflight to changes in photosynthesis, phototropism, and gravisensing in this environment.1,2 One aim of this research has been to acquire basic knowledge to enable the use of plants for long- term life support in extraterrestrial habitats by capitalizing on plants’ ability to provide fresh food and to aid in the recycling of air, water, and waste products. Establishing the robust elements of such a bioregenerative life support system, which will likely incorporate a combination of biological systems and physico-chemical technologies, requires extended research now that carefully integrates ground- and ISS- based work. Levels and quality of light, atmospheric composition, nutrient levels, and availability of water are all critical elements shaping plant growth in space, where each needs to be optimized in a rigorously tested technology platform designed to maximize plant performance during spaceflight. Although such a research program will be enabled by access to the unique environment of the ISS, it is fundamentally aimed at enabling the long-term human presence in space. Developing a sustained research program combining ground- and ISS-based design and validation of components will be critical to establishing the dynamic integrated intramural and extramural research community necessary to support this area. Food plants will be a cornerstone of this effort because they alone can synthesize nutritious, edible biomass from carbon dioxide (CO2), inorganic nutrients, and water while revitalizing the atmosphere using the energy of light. However, microbial reactors will likewise require attention to ensure that they can reliably and efficiently process the solid, liquid, and gaseous wastes of habitation. The ISS provides a key enabling resource for beginning to test the efficacy of each component of a long- 1 C. Wolverton and J.Z. Kiss, An update on plant space biology, Gravitational and Space Biology 22(2):13-20, 2009. 2 C.A. Evans, J.A. Robinson, J. Tate-Brown, T. Thumm, J. Crespo-Riche, D. Baumann, and J. Rhatigan, International Space Station Science Research Accomplishments during the Assembly Years: An Analysis of Results from 2000-2008, NASA/TP-2009-213146–Revision A, NASA, Washington, D.C., 2009. 20

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term life support system in the spaceflight environment, with the long-term goal of facilitating translation from basic research to reliable, applied systems. Inextricably linked to such a program oriented toward the development of bioregenerative life support technology is the need for research into the fundamental mechanisms behind plant and microbial responses to spaceflight. Despite identification of a range of molecular components linked to gravity perception in plants, currently still unknown are the precise molecular identities of the receptors that translate the physical force of gravity to cellular signal(s) and the immediate signals generated by this sensory system and the associated response components. Similarly, understanding how the often extreme environments of spaceflight⎯ranging from high ethylene levels in the local air to lack of surface gas exchange due to the absence of convection in microgravity⎯affect microbial and plant growth is a key gap in current knowledge. Research addressing these questions will contribute to advances in basic understanding of how plants and microbes perceive and respond to the many stimuli present in space. In addition, it will provide essential insight into how these organisms might be selected or engineered, or how their growth environment might be manipulated so as to better tailor them to support a safe, sustained human presence in space. Such a research program studying the sensing and responses of plants and microbes to individual components of the spaceflight environment such as altered gravity, radiation, and atmospheric composition, and to the integrated effects of these multiple factors, will need to combine a robust ground-based program with ISS-based experimentation. Existing ISS facilities, such as the European Modular Cultivation System, should allow rapid implementation of initial elements of microbial and plant research programs. Extended access to the ISS is essential for the success of these programs because it is currently the sole facility available to test plant and microbial responses in the complex, unique environments presented by spaceflight and especially to test these responses against the background of microgravity. It is also important to note that new analytical approaches developed over the past decade have redefined understanding of biology in terrestrial settings at the molecular, developmental, and cellular levels. The study of spaceflight biology is poised to take advantage of this new knowledge and the techniques such as genomics, transcriptomics, proteomics, and metabolomics that have enabled it. It is clear that the recent massive strides in genome sequencing, for example, could revolutionize the design of experiments that can be conducted in space by allowing scientists to answer fundamental questions about the role of gravity in transcriptional regulation in biological systems. In the near term, these analyses can be accomplished by sample return and analysis on the ground. However in order to maximize scientific return via on-orbit analyses, and so minimize the currently major limitation of sample return needed for subsequent analysis, a technology development program could be initiated to take advantage of these recently developed, systems-level analytical technologies for investigations associated with the ISS. Such on-orbit analyses would enable research with a wide range of biological specimens, greatly facilitating, for example, the continuous monitoring of microbial genomes described above. The requisite technology development program will need to be initiated in the near-term if such tools are to become available while the ISS is in operation. It will also need to apply modern cell and molecular approaches and integrate a vigorous spaceflight and ground-based research program aimed at assessing the feasibility of implementation and the subsequent development of automated technology to allow these kinds of state- of-the-art molecular analyses on orbit. The resulting extensive data sets will provide the basis for analysis by large numbers of researchers and interdisciplinary teams, thus adding significant value to the limited and costly access to the ISS. 21

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BEHAVIOR AND MENTAL HEALTH RESEARCH The Augustine Committee Final Report3 pointed to the fact that future astronauts will face three unique stressors: (1) prolonged exposure to solar and galactic radiation; (2) prolonged periods of exposure to microgravity; and (3) confinement in close, relatively austere quarters along with a small number of other crewmembers with whom the astronaut will have to live and work effectively for many months, with limited contact with family and friends. All of these stressors are present in the ISS environment, although the level of radiation is likely to be lower there than on a space mission because the ISS flies under the Van Allen belts, which provide some protection against charged particle radiation. Accordingly, ISS research studies could profitably determine mission-specific effects of these and other relevant stressors, alone and in combination, on astronauts’ general psychological and physical well-being and their ability to perform mission-related tasks. In addition, the ISS platform provides an ideal laboratory for developing techniques to predict and/or monitor the psychological and behavioral status of astronauts, and to develop and test interventions to prevent and/or treat adverse behavioral responses during extended space missions. There are three key program areas for behavioral mental health research on the ISS: 1. Individual and group functioning. Studies are needed to assess how psychological well-being impacts astronaut effectiveness and accomplishment of mission goals. Similar issues pertain to team cohesiveness and effectiveness, increased crewmember autonomy, and crew-groundcrew interactions. For instance, there is accumulating evidence that longer-duration missions are associated with unusual psychological morbidity (symptoms of fatigue and exhaustion, weakness, and emotional lability and irritability, as well as difficulties in concentrating). Careful characterization of such symptoms as well as development of effective interventions is crucial for longer-term missions. Clearly, this is a research area that can best be addressed with continued study on the ISS. 2. Cognitive functioning. Because space is a hostile and unforgiving environment, even small errors in judgment or coordination can produce potentially catastrophic effects. To the extent possible, it is important that the cognitive capacity of astronauts be monitored using “embedded” measures—e.g., reaction time when working at a computer monitor or efficiency in operating a robotic arm—typical mission-related duties from which data could be culled to determine the individual astronaut’s cognitive status, thereby reducing the need for more extensive cognitive testing. Future cognitive tests would need to be validated against specific, mission-relevant tasks. 3. Sleep. NASA has a long history of recognizing the importance of sleep and circadian rhythms in crew health and performance. This emphasis on sleep has been appropriate, since it is clear that adequate sleep is necessary for normal cognitive functioning and that individuals are poor at recognizing the extent of their decreased cognitive performance in the face of sleep loss. Studies are needed to measure the extent to which sleep plays a role in maintaining mental, physical, and cognitive resilience during space missions—and the extent to which sleep-enhancing interventions reverse stress-related symptoms and restore and sustain mental resilience. The ISS offers a unique platform for this type of research. Whereas analog environments can advance knowledge in these areas, they are limited in terms of the duration of exposure, the crowdedness of the living situation, the implacable hostility of the isolated and confined environment, and loneliness juxtaposed with an excess of face-to-face crew interaction. Similarly, analog environments are limited in terms of their ability to provide crews with characteristics comparable to those likely for crews on the ISS. More fundamentally however, such analog environments are limited in terms of their ability to mimic long-term low gravity and constantly fluctuating circadian rhythms. Finally, the ISS also offers a 3 Review of U.S. Human Spaceflight Plans Committee, Seeking a Human Spaceflight Program Worthy of a Great Nation, Final Report, 2009, available at http://www.nasa.gov/pdf/396093main_HSF_Cmte_FinalReport.pdf. 22

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platform for facility design and habitability so that issues of crowdedness versus isolation can be optimally addressed. The facilities needed to advance behavioral and mental health research on the ISS are relatively modest. The most crucial “facility” needed on the ISS to advance this field is the will and commitment to exploration of the effects of extended space missions on all aspects of human functioning. As summarized elsewhere in this report, there are substantial problems with translational research efforts in space. The major reason for having an ISS is to provide a research platform. One of the key pieces of “apparatus” on this platform is its human “cargo”; yet, there have been long-standing problems with obtaining research cooperation from astronauts as well as accessing data from prior missions. In terms of other facilities needed, the equipment needs for this research area are generally modest in terms of size or mass. Sleep- monitoring equipment, for instance, has become dramatically smaller in terms of its “footprint.” Most of the other behavior and mental health research topics are facilitated by virtue of a strong communications link between the ISS and Earth—a link that can be used for communicating important diagnostic information as well as providing therapeutic links with Earth. HUMAN AND ANIMAL BIOLOGY The National Aeronautics and Space Administration Act of 2005, e.g., Article 3 of Section 305,4 directs the United States to have a national laboratory aboard the ISS to conduct animal and human space- directed research; hence the extension of the availability of the ISS to 2020 and beyond provides a platform to fulfill two major goals: (1) to increase both basic and translational knowledge of animals and humans on a variety of systems that are adversely affected by a microgravity environment and (2) to develop potential countermeasures to alleviate these deficiencies in physiological homeostasis. A large body of previous research on both animals and humans has clearly established that microgravity and equivalent ground-based analogs induce deficits/alterations in cardiovascular homeostasis, bone mass and strength, muscle mass, strength and endurance, sensorimotor function, thermoregulation, and immune function. As a result, many gaps in knowledge have been defined across these systems that need to be explored to maintain the necessary functional homeostasis when humans are faced with altered gravitation on future missions. Although this section identifies some of the key research issues (most of which have been identified previously by NASA and in earlier studies), the large number of affected physiological systems precludes even a brief discussion of every system in this interim report. The committee’s final report will contain an extensive discussion of questions in animal and human biology. The ISS provides the only opportunity to carry out both fundamental and translational research on organ and systemic function in the absence of the gravity variable. Moreover it provides the optimal environment to establish key countermeasures toward maintaining homeostasis across various organ systems and to initiate interventions that cannot be effectively duplicated by studies using ground-based analogs. The ISS provides the only opportunity to probe fundamental questions about the role of gravity in developmental biology by examining how animals grow, develop, mature, and age over a large portion of their life span without the influences of gravity. The ISS provides the only means to study, without the stimulus of gravity, these fundamental questions by (1) raising multiple generations of living mammals in space and (2) utilizing transgenic animal models (e.g., overexpression and/or knock-down of transcription factors and altered gene function, including the evolving field of epigenetics) to understand gene regulation of fundamental cell processes. Ethically and practically, these types of experiments cannot be conducted on humans. Equally important is the opportunity to obtain key functional physiological measurements in microgravity that have been unobtainable in previous science missions. This unique 4 National Aeronautics and Space Administration Authorization Act of 2005, Public Law 109-15, 119 Stat. 2895, December 30, 2005.  23

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knowledge can be gained only via the inclusion of animal studies on the ISS. To carry out these novel animal experiments, an animal facility capable of housing rodents5 is necessary to conduct current and future generational experiments that are essential to accomplishing these goals. Equipment-sharing agreements with international partners will be necessary for the successful completion of any centrifugation studies using rodents. In summary, the establishment of a rodent habitat on the ISS is a critical need. As noted above, exposure to microgravity leads to homeostatic deficits across the key systems necessary for the maintenance of health, fitness, and performance. To date, however, none of the exercise countermeasure strategies have been successful in maintaining cardiovascular fitness, muscle mass, strength or endurance, and sensorimotor function, as well as bone mass and strength. For example, recent findings for ISS astronauts who have been in space for 6 months or longer and performing the recommended exercise countermeasures indicated that the countermeasures were unable to prevent the loss of muscle mass or the decrement in muscle performance.6 Normal function of these systems is necessary for maintaining crew performance capability on return to Earth or entry into other gravitational environments. The ISS is the critical laboratory for conducting studies on countermeasures because this platform creates the capability for supporting long-term exposure in microgravity while testing whether a given countermeasure has the capability for maintaining normal function for long durations in microgravity. Success in maintaining approximately normal homeostasis on the ISS would benefit astronauts traveling to all currently proposed destinations (the Moon, asteroids, Mars, Lagrange points) with their different gravities. Hence, both basic and applied research is needed to integrate information on (1) the responsible mechanisms impacting structural and functional deficits and (2) the translational effectiveness of countermeasures for correcting them. For example, it is envisioned that integrated research teams will be assembled to simultaneously study the interactions between the skeletal muscle, bone, and sensorimotor systems and/or linkage between cardiovascular, sensorimotor, and skeletal muscle systems, as examples of crosscutting thematic research projects. Other studies could integrate pharmacological and mechanical stress investigating maintenance of bone homeostasis. The key is that multiple systems and paradigms would be investigated. Hence, a program is needed to test the effectiveness of (1) a variety of devices and (2) potential integrated exercise regimens, especially those that can impact multiple systems. It appears that mechanical loads during countermeasures have not been appropriate to provide 1-g-like loading. Studies to test appropriate countermeasures are urgently needed. Emerging pharmacological interventions to prevent bone and muscle loss also need to be explored. These kinds of integrative studies can also lead to insights in several divergent areas that have not been explored extensively in the microgravity environment of the ISS. These include but are not limited to bone formation versus resorption processes; fracture repair; reduction of the risk factors for renal stones; net protein balance and contractile protein turnover in skeletal muscle; substrate and organism energy turnover capacity during exercise; the prevalence of cardiac atrophy; head-ward fluid shifts and visual acuity; the mismatch in functional integration of sensorimotor circuits; the verification of the hypothesis that vestibular dysfunction is the cause of motion sickness; the alteration of Starling forces in the microgravity environment; the deposition of different sized aerosols in lung tissue; altered thermoregulation during extravehicular activity (EVA); alterations in female reproductive function and human spermatogenesis; and T-cell activation in astronauts prior to and following re-entry as a result of spaceflight. In summary, a strong rationale exists for evolving new directions in NASA’s approach to human and animal research. Studies on human countermeasures with new approaches to loading and pharmacological interventions in the context of thematic studies need to be considered, and animal studies can provide new insights concerning the mechanism of organ system alterations. Thus, the ISS has great 5 Rats and mice are the key model systems used by scientists to understand how gravity affects physiological processes in humans. 6 S. Trappe, D. Costill, C. Gallagher, A. Creer, et al., Exercise in space: Human skeletal muscle after 6 months aboard the International Space Station, Journal of Applied Physiology 106:1159-1168, 2009. 24

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potential to provide new knowledge of the effects of gravity and of its absence on human and animal systems and to test countermeasures for these effects. FUNDAMENTAL PHYSICAL SCIENCE The goals of the fundamental physical sciences are (1) to explore the laws governing matter, space, and time and (2) to discover and understand the organizing principles of complex systems from which structure and dynamics emerge. To achieve these goals, fundamental physical sciences researchers have a well-established need for access to space. Specifically, use of the ISS for this research can support achieving groundbreaking results, and in fact the fundamental physical sciences community has had significant experience with space-based research that has produced some high-impact results aboard the ISS. This community has included some of the best scientists of our time—several Nobel laureates as well as principal investigators who have become leading national science policy makers. At present the highest-priority areas for a pioneering, next-generation ISS program are (1) soft condensed matter physics and complex fluids, (2) precision measurement of fundamental forces and symmetries, (3) quantum gases, and (4) condensed matter and critical phenomena. Fundamental physical science research in space is unique in that it is almost entirely “enabled by” exploration, although in the long term this work may enable NASA’s exploration mission through the development of new materials and energy sources, time and frequency standards for navigation, and technologies that help humans adapt to the hostile conditions in space. Soft Condensed Matter and Complex Fluids Soft condensed matter and complex fluids are materials with multiple levels of structure. Key systems for study include colloids, polymer and colloidal gels, foams, emulsions, soap solutions, and so on because of the gradients that are formed in their properties under gravity. The ISS provides a unique opportunity to remove these gradients and study long-time dynamics free from gravitational interference. Very similar issues exist for complex and dusty plasmas, where density and morphology are height dependent under gravity. Similarly, in granular materials, stress chains and yield properties are height dependent and sensitive to the magnitude of gravity. NASA realized the importance of microgravity research to this field from its infancy, and some of the most significant discoveries were reported at NASA meetings, including highly cited papers coauthored with astronauts. Looking ahead, one example of highly relevant research is the experimentally tested, constitutive equations that describe the strain- strain rate relationships for granular materials under reduced gravity. (It is noteworthy that the Mars Rover “Spirit” has been stuck in the martian soil, a granular material, since May.) In terms of broader impact, along with the fundamental importance of complex fluids/soft materials, their manipulation is a ubiquitous part of the food, chemical, petroleum, cosmetics, pharmaceutical, and plastics industries. Precision Measurements of Fundamental Forces and Symmetries. The ISS offers unique conditions to address important questions about the fundamental laws of nature. In particular, the ISS can support high-precision measurements that probe understanding of gravity as well as theories of high-energy physics in ways that are not practical on Earth. Consider some examples: (1) Atomic-physics-based tests of the equivalence principle can probe whether different kinds of matter interact with gravity in the same way. If a violation of this principle is observed, it could offer understanding of dark energy and evidence for quantization of gravity, some of the most important ideas of our time. (2) Since the time of Einstein, physicists have been seeking an “ultimate theory” that ties together gravity, particle physics, and quantum physics. Recently it has been realized that such a theory might involve violations of very fundamental symmetries (e.g., Lorentz symmetry—the idea that the fundamental laws of nature are the same in any inertial reference frame). ISS-based experiments could 25

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provide a several-orders-of-magnitude improvement in our search for such violations. A typical experiment might consist of clock comparisons, in which two or more high-stability, ISS-based clocks are simultaneously operated and their timing compared and correlated with position and velocity in gravity. Quantum Gases When the temperature of a gas is decreased the quantum, wavelike properties of the constituent atoms or molecules can dominate the behavior of the gas, and remarkable cooperative behavior can emerge. For many gases this can represent the formation of a novel state of matter known as a Bose- Einstein condensate (BEC). A closely related state of a solid is the superconductor, and for a fluid it is the superfluid. In 2001, then NASA-supported fundamental physical scientist Wolfgang Ketterle shared the Nobel Prize in physics for realizing a BEC in his laboratory. The key to creating a BEC is to cool the gas to within nanokelvin temperatures above absolute zero. The lowest achievable temperature is currently limited by the effects of gravity; however, on board the ISS BEC temperatures on the order of a picokelvin (0.000000000001 degrees above absolute zero) should be achievable. A remarkable range of different physical phenomena can then be investigated. If the particles of the quantum gas are “fermions” (particles are classified as either “bosons” or “fermions”), then another class of physics can be investigated. Cold fermion research could address wide-ranging problems such as the unresolved mechanism of superconductivity in high-temperature superconductors. Overall, experiments with quantum gases on the ISS will allow the study of matter in regimes not achievable on Earth. This research will also support new futuristic devices such as the atom laser—a bright source of coherent matter waves analogous to coherent light waves of the familiar laser. Such devices form a basis for next-generation technologies and quantum sensors. An exciting example is the atom interferometer, which has already been tested as a rotation sensor and which can be used for the measurement of fundamental quantities such as the photon momentum and the local force of gravity. As rotational sensors for inertial navigation, these devices rival the best gyroscopes available and are potentially important for space navigation applications. Condensed Matter and Critical Phenomena One of the great scientific successes enabled by the microgravity environment over the past two decades concerns better understanding the nature of materials at a very special transition known as a critical point. At this critical point the distinction between the liquid and vapor phases disappears, creating a fog-like critical state that fluctuates wildly. Many other important materials, including superfluids, magnetic materials, and colloids, undergo similar transitions so that work on one system affects understanding of many different systems of recognized scientific and technological interest. Already, a new series of ISS-based experiments have been conceived and designed that will elucidate fundamentally new effects that can be observed when a system near its critical point is driven away from equilibrium, both in the bulk and near boundaries such as a container wall. Fundamental Physical Science Facilities and Opportunities In addition to having a track record of successful spaceflight experiments, the fundamental physical sciences community has already developed a portfolio of projects to a level of advanced flight readiness. With renewed NASA support and continued, successful peer review, these projects provide an opportunity to obtain a well-defined, rapid science return from the ISS national laboratory. In general ISS-based fundamental physical science experiments are not facility oriented, with one exception⎯the Low-Temperature Microgravity Physics Facility (LTMPF). A facility designed to attach to the ISS, LTMPF is engineered to support experiments on critical phenomena and precision measurement experiments as discussed above. It is approximately 70 percent complete, and once finished, it will enable deployment of the flight-ready experiments aboard the ISS. 26

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APPLIED PHYSICAL SCIENCES AND TRANSLATIONAL RESEARCH Applied physical sciences research on the ISS will accomplish two major goals: (1) to provide a foundation for the development of systems and technologies enabling human and robotic space exploration and (2) to enhance understanding of phenomena enabled by the reduced-gravity environment on the ISS. NASA’s future exploration missions will include long-duration, microgravity and partial gravity conditions as well as extreme thermal and radiation environments. Research on the ISS directed toward the first goal will contribute to the development of power generation and energy storage systems; space propulsion systems; systems for EVA; life support systems; fire prevention, mitigation, and recovery systems; materials production and storage; in situ resource utilization (ISRU); and habitat construction and maintenance. Research on the ISS directed toward the second goal could lead to new and fundamental discoveries that would advance exploration and also have beneficial terrestrial applications. Applied and Translational Research on the ISS That Will Enable Exploration Power generation and energy storage systems for NASA’s future missions will require power at a level ranging from a few watts (for microsatellites) to tens of kilowatts and perhaps megawatts. For low power requirements, systems based on technologies such as thermionics and thermoelectrics are preferred. For higher power, i.e., kilowatts per kilogram, Sterling, Brayton, and Rankine cycle technologies are more suitable. NASA’s power generation, storage, and heat rejection technology requirements in the coming decades will be driven by applications such as near-Earth science platforms, lunar and planetary surface missions, and deep-space exploration probes. Increasing the efficiency and lifetime of power generation and energy storage systems will reduce costs by reducing mass and redundancy. All of these systems will benefit from research, prototyping, and testing on the ISS. Power generation systems include photovoltaic, solar thermal power, and nuclear power systems. For space power generation applications, concentrating solar-thermal power systems have the highest kilowatts-per-kilogram capability. In low gravity, such systems can be lightweight, self-erecting gossamer structures supplying both primary and secondary power. Research conducted on the ISS on materials and structures can enable higher-efficiency systems. The ISS also provides a platform for research on environmental effects on solar arrays, such as the effects of plasma arcing, radiation damage, and micrometeroid impact. For energy storage, regenerative fuel cells and lithium-ion and other advanced battery technologies face major development issues in the quest to provide safe, reliable, affordable, long- life solutions to NASA’s future energy storage needs. Since such systems are integral to major ISS systems, the ISS is an excellent developmental platform. Key advantages of power systems based on the Rankine cycle are higher power and small component size because two-phase-flow and heat-transfer coefficients are much larger than those for gas in non-two-phase systems. Two-phase technology is intrinsic to power systems based on the Rankine cycle, as well as to the thermal management, storage, and handling of cryogenics and other liquids in life support and thermal control systems. Unfortunately, little is known at present about the behavior of two- phase flows and associated heat transfer in a reduced-gravity environment. To enable the design of systems utilizing two-phase technology, it is critical that microgravity research in this area be given very high priority for experiments on the ISS while being supported by a relevant ground-based program. Experimental studies of multiphase flow and heat transfer on the ISS will provide scaling of phenomena with respect to gravity, data for validation of analytical/numerical simulation models, and development of design tools for heat exchangers based on two-phase flow. Experiments on the ISS on pool boiling; forced flow boiling including phase separation and flow stability in single and multiple channels; closure relations for interfacial and wall heat; mass and momentum transfer; condensation; and capillary-driven flows would provide significant knowledge for validating computer models and designing systems. A deeper understanding of two-phase flows would impact a host of important technologies, from those for cryogenic fluid handling to nuclear and other high-power sources of energy. 27

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The major design goals for any space-bound thermal management system in power generation and electronic cooling are performance, cost, physical size, and reliability. Earth-based system processes involving phase change and/or multiple phase flow have been shown to have the highest heat transfer coefficient. Testing on the ISS of a complete system including boilers, phase separators, condensers, and radiators would allow meaningful correlations and validations to be made among the Earth-based and reduced-gravity thermal management systems. Such a system testing under microgravity will allow the study of interactions among components and provide data for validation of system-level simulation tools. A deeper understanding of capillary flow in, for example, plant nutrient transport can aid in the design of technologies for water-processing systems and fluids handling in propellant storage depots. Finally, the Microgravity Science Glovebox and the Fluids Integrated Rack are valuable facilities available on the ISS. It would be useful to consider the utility of developing a multipurpose, multiuser facility on the ISS for multiphase flow research. Such a facility would also act as a catalyst for bringing together national and international researchers to address the challenge in a cost-effective and comprehensive manner. The merits of single-purpose experiment packages would need to be weighed in such an assessment as well. To support NASA’s exploration missions, an evolutionary space transportation architecture is needed for science discovery and technology demonstration. These space propulsion systems will support the large human and cargo missions envisioned as well as pico-spacecraft that capitalize on advances in micro- and nanotechnologies. Advances in propulsion performance (specific impulse, efficiency, thrust to weight, propellant bulk density), reliability, thermal management, power generation and handling, and propellant storage and handling are key drivers to dramatically reduce mass, cost, and mission risk. The ISS provides unique opportunities for research in a number of these areas. The reduced-gravity environment on the ISS provides opportunities for research on cryogenic two-phase fluid management, propellant transfer, engine starts, flame stability, and active thermal control of injectors and combustors. In addition, the ISS can benefit non-cryogenic (Earth-storable) propulsion systems by providing research opportunities for mixing or separation, and tribology under reduced- gravity. Research conducted on the ISS on physical phenomena involved in heat exchangers, thermal control, Stirling and Brayton cycles, lightweight and high-temperature thermal structures, propellant transfer and management, and liquid metal or noble gas storage under reduced gravity will provide the opportunity for fundamental advances for solar electric, nuclear thermal, and nuclear electric propulsion options. Indeed, the ISS can be an ideal laboratory providing an infrastructure and space environment for the development and demonstration of these non-chemical propulsion options that have a potential to reduce the duration of trips to Mars. In addition, the emerging technology for inflatable and low-mass aerobraking for re-entry systems can benefit from small free-flyer aerothermochemistry experiments conducted from the ISS. Using inflatable structures in re-entry systems to transport laboratory specimens and products from the ISS to Earth can provide opportunities to characterize for prototype return systems such items as vibration and deceleration loads, minimum thermal protection, and costs for a range of cargo types, and to gain operational experience. Currently, the transport of such items is limited to the return capsules or the remaining and available shuttle flights, and so such a system might be useful for more timely return of samples for analyses. Creation of propellant depots in space that are supplied from propellant sources on Earth (and eventually the Moon) will dramatically improve the architecture and economics of exploration activities beyond low Earth orbit. Supply depots in Earth orbit can utilize a wide range of new-era commercial launch systems. Key science issues that need to be understood to make such depots a reality can be advanced with research on the ISS on cryogenic fluid management, including zero boil-off working fluids, propellant storage, two-phase flows, contact line motion on a solid surface, adhesion forces under low temperatures, and fluid transfer. For EVA, the ISS environment is ideal for testing and qualifying a wide range of spacesuit mobility and performance innovations, such as joint torque minimization, suit comfort and trauma/injury countermeasures, thermal control, and radiation protection. In addition, EVA innovations in areas such as more efficient power, communication, avionics, and informatics systems can be tested for endurance 28

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during extended ISS missions. The ISS is also the ideal platform to investigate plasma interactions with astronauts during EVAs in proximity to space structures that have high-power, high-voltage solar arrays. Research could be performed to address dust and micrometeorite interactions with spacesuits. Life support systems (LSS)⎯for pressure control; atmosphere revitalization: removal of carbon dioxide, water vapor, and trace contaminants; temperature and humidity control; and waste collection⎯ are integral to spacecraft habitats, rovers, and EVA. ISS laboratories provide a microgravity environment and facilities to characterize and test such LSS functions as heat and mass transfer in porous media and monitoring to identify major atmosphere constituents and trace contaminants. Innovative approaches can be evaluated to perform closed-loop air revitalization with CO2 removal, recovery, and reduction; oxygen generation via electrolysis with high-pressure capability; improved sorbents and catalysts for trace contaminant control; and atmosphere particulate control and monitoring. Experiments on the ISS can be conducted to study dust accumulation, particle deposition in lungs, and especially electrostatic effects. Many of these approaches remain undeveloped because of poor understanding of multiphase and capillary flow (for example, for passive solid separation technologies) in reduced-gravity environments. Fire safety is critical to enabling human exploration of space because fires can have devastating consequences, including loss of life and loss of vehicle or habitat integrity. Historically, fire research has been treated as a subset of combustion research. Basic and applied combustion research using ground- based facilities and in the ISS (Combustion Integrated Rack) have made significant advances that support fire safety research. This research includes characterization of particulates and toxic gases, smoldering, ignition, extinction, and flame spread. Nevertheless, the timely attainment of fire safety substantially depends on an adequate and comprehensive strategy that does not necessarily require a full understanding of the underlying principles of combustion, but is based more on phenomenological models and empirical correlations. As a result, the research and development (R&D) needs for fire safety for human exploration of space relate more to the understanding of how the different components together deliver an adequate fire safety strategy. The critical components are (1) a material’s response to fires, (2) fire detection, (3) fire suppression, and (4) recovery from fire (and explosions). The limited facilities, size constraints, and manpower limitations on the ISS restrict progress on the main areas of fire safety research necessary for application to space exploration. Thus, the use of ground-based facilities is particularly critical for a comprehensive fire safety program and will be detailed in the committee’s final report. The link between ISRU on the Moon, Mars, and small bodies (asteroids or planetary moons) and the ISS is indirect. Research aimed at better understanding multiphase fluid flow on the ISS will be helpful for the design of systems for handling fluids in reduced-gravity environments. Also, research aimed at developing a capability for transferring propellant in space could play a part in a future lunar or Mars ISRU-based propellant production and utilization scenario. Research in the ISS relevant to excavation and material transport would also help in situ resource utilization in reduced-gravity environments. Research activities that could be conducted on the ISS that will be beneficial, even critical, for any future planetary surface exploration involve materials and structural dynamics (self-deploying, inflatable, composite materials), as well as radiation protection systems. Testing on the ISS would benefit continuing development of food preparation, delivery, and storage systems, health maintenance equipment, radiation protection systems and materials, robotic systems, and human-machine interface systems. Applied Research That Is Enabled by the ISS Research enabled by the unique microgravity environment and facilities on the ISS can also address unexplored phenomena that have beneficial implications for exploration systems as well as many terrestrial technologies. Gravity can mask the effects of many important fluid flow phenomena. Areas that can provide new and important insights via experiments on the ISS include flows driven by gradients of surface tension caused by temperature and concentration, solid-liquid adhesion forces, interfacial forces involving 29

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shear and pressure forces, electric fields, magnetic fields, acoustic fields, and acceleration. Other examples are spreading, stability, and rupture of ultrathin liquid films. Much can be learned by considering granular materials at reduced-gravity. Key aspects concern effects such as particle clustering, self-assembly, and dissipation; the study of electrostatic effects and interstitial fluids; and the impact of having multiple particle sizes and/or shapes. In the area of materials synthesis and processing, a microgravity environment can shed new light on the nucleation process because liquids can be suspended and solidified without a container, thus removing the effects of walls, as well as convection due to compositional inhomogeneities that accompany the formation of nuclei. Thus it is possible to study the formation of stable and metastable phases from undercooled melts, the formation of glasses, the relationship between liquid structure and the resulting crystal structure, and the thermophysical properties of deeply undercooled liquids. Understanding the processes leading to the production of materials composed of phases with much different densities, such as metallic and ceramic foams, can be improved by research on the ISS. On Earth, during crystal growth the density differences between crystals and the parent fluid or vapor—as well as the temperature and composition dependence of the density of the parent phase and variations in the surface tension of a liquid-vapor—lead to convection. This convection results in nonuniform compositions as well as defects in the resulting crystal. The microgravity environment allows these crystal growth phenomena to be studied without the confounding effects of gravitationally induced convection. The Materials Science Research Rack (MSRR) available on the ISS is a very valuable asset. Gravitationally induced convection or sedimentation makes it very difficult to study the physics that underlie processes such as dendritic and cellular solidification, liquid phase sintering, and phase separation. The effects of interactions between individual dendrites or cells on their spatial distribution and morphology, the evolution of dendrite morphology during transient heating or cooling, and the effects of noise and initial conditions on the resulting patterns remain unclear. The interactions between dendrites are particularly important in setting the properties of a solid-liquid mixture found in castings, called the mushy zone. Fluid flow within mushy zones can become unstable during solidification, resulting in deleterious casting defects. The nature of this instability and the properties of the mushy zone need further investigation. Studies of combustion in a reduced-gravity environment would lead to a greater understanding of terrestrial combustion. On Earth, energy release, fluid dynamics, and gravity-induced buoyancy interact in a nonlinear fashion. By varying or eliminating the effects of gravity, researchers can extract fundamental data that are important for understanding combustion systems. Such data include parameters such as chemical reaction rates, diffusion coefficients, and radiation coefficients that strongly influence ignition, propagation, and extinction of combustion waves. It is very rare, on Earth and in space, for an area, cabin, or room to be uniformly filled with a stoichiometric, homogeneous mix of fuel and oxidizer. Unfortunately, very little is known about the behavior of flames propagating through reactivity gradients. Reactivity gradients are important for all stages of a fire or explosion from ignition and propagation through to extinction. Reduced-gravity environments can be used to learn more about flame ignition, propagation, and extinction in reactivity gradients. It is now speculated that gaseous flammability limits might not exist at all, or that a diffusive or hydrodynamic mechanism may cause extinction, or that flame balls or flame strings are themselves the limiting structure. Most combustors and unwanted fires involve diffusion flames. There remain significant gaps in the understanding of these flames, such as those associated with chemical kinetics, transport, radiation, soot formation, pollutant emissions, flame stability, and extinction. All of these areas will benefit from experiments performed on the ISS. 30