3

Science Progress Toward the Goals and Priorities of the 2011 Space Life and Physical Sciences Decadal Survey

In this chapter, the committee has assessed the progress made in the respective science disciplines against the priorities identified in the 2011 space life and physical sciences decadal survey.¹ This assessment occurred within the context of the overall advancement of space life and physical sciences and against the backdrop of advancement in related fields outside of the space sciences. This assessment also drew upon a wide-ranging discussion of the high-priority recommendations from the decadal survey and incorporated presentations from NASA and CASIS (Center for the Advancement of Science in Space) and from the literature so that the conclusions would encompass programmatic and science considerations. For each of the discipline sections below, the committee utilized data from the literature and the many presentations to the committee in order to assess progress made on the highest-priority research recommendations summarized in Chapter 13 of the decadal survey. These assessments also informed the development of Findings 2-1 through 2-4 in Chapter 2. Areas for improvement in the respective science disciplines, together with the impact of those areas on the selection of the highest-priority recommendations, are discussed in Chapters 4 and 5. Note that the length of the discipline sections in this chaper and in Chapter 4 generally reflects the degree to which progress could be easily summarized across several related topics within that discipline. Growth in opportunities provided by new tools (such as omics technologies), and the extent of the enabling research needs that are yet to be addressed, also influenced the length of the respective discipline sections. Thus areas of research where a larger proportion of the decadal survey recommendations have been addressed may require less discussion than areas where less progress has been made.

3.1 PLANT AND MICROBIOLOGY

The 2011 decadal survey called out three high-priority areas in Plant and Microbial Science (P). As identified within the decadal survey the specific priority items are as follows:

• P1—Establish a microbial observatory program on the International Space Station (ISS) to conduct long-term, multigenerational studies of microbial population dynamics.

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¹ National Research Council (NRC), 2011, Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era, The National Academies Press, Washington, D.C.

• P2—Establish a robust spaceflight program of research analyzing plant and microbial growth and physiological responses to the multiple stimuli encountered in spaceflight environments.
• P3—Develop a research program aimed at demonstrating the roles of microbial-plant systems in long-term life support systems.

There has been strong response by NASA to these priorities. In response to these recommendations, NASA has been the sponsoring space agency, starting in 2012, for 34 grants in plant science and 26 in microbiology, as categorized in the NASA Task Book.² Progress has been good also in terms of publications (although these, as expected, lag the proposals funded by several years), with about a quarter of the articles on flight experiments, half on ground studies, and a quarter being review articles.

Novel discoveries both “enabling“ and “enabled by” have been made in all three areas. An example related to P1 is the discovery of changes in virulence and growth of potentially pathogenic bacteria in the ISS environment,³ including activation of regulatory genes not seen in ground-based controls. Examples for P2 include recognition that stress responses and cell wall biosynthetic responses dominate gene expression changes in plants in the space environment as compared to ground-based controls,⁴ and that plant genotype, even one-gene differences, can have a strong differential effect on plant gene expression in space. For long-term life support related to P3, the “Veggie” Veg-01 experiment successfully showed the growth of edible plants on the ISS in a specifically designed set of plant growth modules and that food processing was developed and the attendant regulatory hurdles were cleared in order to allow those plants to be eaten by the crew on orbit. In particular, the life sciences programs related to P1, P2, and P3 have been responsive to changing technologies for gene and gene expression omics data, following the rapid development of these new approaches and methods in the broader science community.

The new U.S. ISS National Laboratory, managed by CASIS, has contributed directly to the plant science area, such as funding of the NanoRacks-Algal Growth and Remediation project, meant to overcome barriers to use of algae for remediation of carbon dioxide to oxygen, and the Characterizing Root Attractions in Arabidopsis projects, to study how growing roots sense and respond to gravity.

NASA has implemented its plans for GeneLab and a focus on missions using omics technologies, with plant and microbial biology contributing significantly to GeneLab. As noted in Chapter 2, the GeneLab database⁵ is an integrated repository and bioinformatics system for omics data from space-based research and its ground-based controls as well as and space-relevant experiments. These implementations derive strongly from the 2011 decadal survey plant and microbial recommendations and extend to other discipline areas. Progress to date includes public website access to the repository with searchable and downloadable tables of results from many space missions and sets for ground controls, including some legacy data, and progress toward setting standards for data and metadata. The GeneLab data, Release 1.0.18 deployed on June 30, 2017, presents a total of 133 distinct data sets/studies and more than 6.5 Tb of compressed primary data, together with the associated metadata. Flight experiments have been performed to specifically add data to the GeneLab database, and several principal investigator (PI) experiments have been augmented to provide supplemental data to GeneLab. A new set of grants were conceived and awarded in 2017 to more deeply explore GeneLab data, thus making exceptional use of the omics approaches called out in the decadal survey.

In addition to the research funded directly and fully by NASA, plant and microbial investigations related to P1, P2, and P3 have been supported by CASIS. In areas of biotechnology with respect to plants and microbes, CASIS

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² National Aeronautics and Space Administration (NASA), 2015, The Space Life and Physical Sciences Research and Applications Division Task Book 7.0, NASA Research and Education Support Service, https://taskbook.nasaprs.com/publication/welcome.cfm.

³ The grant is to Cheryl Nickerson, “Titled RNA Deep Sequencing and Metabolomic Profiling of Microgravity-Induced Regulation of the Host-Pathogen Interaction: An Integrated Systems Approach,” NNX13AM01G, in NASA, 2015, The Space Life and Physical Sciences Research and Applications Division Task Book 7.0.

⁴ These grants are to Anna-Lisa Paul, NNX09AL96G, “The Biological Impact of Spaceflight and Extraterrestrial Environments on Molecular Signaling and Gene Expression in Plants,” and to Robert Ferl NNX15AB12G, “Early Stage Plant Adaptation to Spaceflight: Molecular Responses of Arabidopsis to the Transition from Terrestrial Environment to Space,” in in NASA, 2015, The Space Life and Physical Sciences Research and Applications Division Task Book 7.0.

⁵ See the NASA GeneLab website at https://genelab.nasa.gov, accessed October 5, 2017.

has supported significant studies—more than a dozen mission experiments that relate to the recommendations of the 2011 decadal survey. Through its Good Health initiative, CASIS has partnered with NASA on the major goals of establishing a Microbial Observatory within the ISS, helping to fully address recommendation P1. By exploiting existing discovery research relevant to the National Institutes of Health (NIH) Human Microbiome Project, CASIS is working to expand the breadth and depth of microbiome research in space, in part for the benefit of Earth but also in support of tying space research to the National Microbiome Initiative.⁶

3.2 BEHAVIOR AND MENTAL HEALTH

The 2011 decadal survey identified four priority areas in Behavior and Mental Health (B) research. The priorities targeted (1) mission relevant performance, (2) integrated translational research on individual and group functioning conducted through simulations of long-duration missions, (3) individual differences in resilience to stressors to inform an individualized medicine approach, and (4) enhancement of team performance, including effectiveness of multinational crews. The specific priority areas are as follows:

• B1—Develop sensitive, meaningful, and valid measures of mission-relevant performance for both astronauts and mission control personnel.
• B2—Conduct integrated translational research in which long-duration missions are simulated specifically for the purpose of studying the interrelationships among individual functioning, cognitive performance, sleep, and group dynamics.
• B3—Determine the genetic, physiological, and psychological underpinnings of individual differences in resilience to stressors during extended space missions, with development of an individualized medicine approach to sustaining astronauts during such missions.
• B4—Conduct research to enhance cohesiveness, team performance, and effectiveness of multinational crews, especially under conditions of extreme isolation and autonomy.

The Human Research Program’s (HRP) Behavioral Health and Performance (BHP) element has been strongly responsive to the recommendations of the 2011 decadal survey and has made considerable progress in reaching these goals. HRP made a strong research and development investment on projects within the BHP domain (i.e., the Behavioral Medicine (BMed), Team, and Sleep sections) through annual announcements, and in 2014, a second BHP-specific NASA Research Announcements (NRAs), primarily in the BMed and Team areas. Some solicitations included projects that were funded through the National Space Biomedical Research Institute (NSBRI). The specific research priorities listed on these NRAs focused on the recommendations of the 2011 decadal survey. The 2016 Task Book⁷ lists a total of 76 BHP/Human Factors Behavioral Performance (HFBP) funded projects; 49 of these projects address 2011 decadal survey priorities: B1, 16 projects; B2, 14 projects; B3, 6 projects; B4, 13 projects. Findings have been published in scientific journals, technical reports, and conference proceedings.

A major advance in reaching the goals of the decadal survey is the BHP priority to develop or make use of isolated, confined, and extreme environments, or enclosed simulation facilities, as analogs for different aspects of a Mars mission (B2). The Hawai‘i Space Exploration Analog and Simulation (HI-SEAS) habitat located on a Mars-like surface on the Mauna Loa volcano on the Big Island of Hawaii is an example. HI-SEAS includes the experience of both living in confinement and performing in an isolated and potentially dangerous environment by doing simulated space walks outside of the habitat. Beginning with an initial 2013 HI-SEAS 4-month mission, subsequent missions (currently Mission V) have ranged up to 1 year of confinement. Each mission has consisted of a diverse gender, ethnic, and cultural team; several groups of investigators studied each team over the course of their confinement, following the research protocol of their own NASA funded analog project. The combination of results from different groups of investigators, each pursuing their own projects in this setting, has enabled the

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⁶ Executive Office of the President, 2016, “FACT SHEET: Announcing the National Microbiome Initiative,” May 13, https://obamawhitehouse.archives.gov/the-press-office/2016/05/12/fact-sheet-announcing-national-microbiome-initiative.

⁷ NASA, 2015, The Space Life and Physical Sciences Research and Applications Division Task Book 7.0.

overall assessment of numerous individual and group variables. Further, use of the Human Exploration Research Analog (HERA) facility at NASA Johnson Space Center (JSC) and access to National Science Foundation (NSF) Antarctic stations also have provided settings for multiresearch team investigations simulating aspects of a long duration mission. The various simulation studies in isolated environments (e.g., Hi-SEAS, or HERA) address both B2 and B4 priorities. Also, there are both laboratory-based and analog setting (HERA, Antarctica) projects being conducted to identify various cardiovascular, blood-based, and saliva-based biomarkers of stress and resilience. Projects in Antarctica also are focusing on brain changes in structure and function in isolation (B3).

The Cognition test developed by Basner⁸ and colleagues was completed and is being evaluated in flight as well as analog studies as a measure of cognitive performance (B1). HRP support for team projects assessing the functioning of multiteam systems is a significant advance; ongoing projects are being carried out in both laboratory and field settings (B4). Other ongoing projects in the team area are developing computer models (composition algorithms) to predict different factors of team performance and inputting data collected on current and past studies. In addition, an important team development is the inclusion of mission controllers in a number of projects.

While not specifically addressing a decadal survey priority, other funded projects focus on specific risk factors designated in the 2006 report A Risk Reduction Strategy for Human Exploration of Space: A Review of NASA’s Bioastronautics Roadmap.⁹ Significant progress has been made, primarily by projects funded through the NSBRI, to develop countermeasures to prevent or mitigate emotional distress. Computer-interactive intervention programs for dealing with depression, anxiety, and conflict resolution are in their final stages of refinement. The development of virtual reality technologies to simulate Earth experiences and avatars to increase motivation to exercise are additional examples of innovative countermeasures that are being developed and empirically tested to deal with the stresses of a Mars mission.

Progress in the sleep area is reflected in the installation of an extensively researched lighting system on the ISS to help entrain circadian rhythms. Another sleep area project is investigating the predictive validity of a set of relevant, valid, and reliable biomarkers for distinguishing those who are more resilient versus those who are more susceptible to the adverse neurobehavioral effects of the combination of high-performance demands and total sleep deprivation stressors—two conditions commonly experienced in spaceflight.

3.3 ANIMAL AND HUMAN BIOLOGY

The 2011 decadal survey identified many high-priority areas of research for Animal and Human Biology (AH). That list (below) represents an ambitious set of priorities under conditions of limited resources and opportunities on orbit.

• AH1—The efficacy of bisphosphonates should be tested in an adequate population of astronauts on the ISS during a 6-month mission.
• AH2—The preservation/reversibility of bone structure/strength should be evaluated when assessing countermeasures.
• AH3—Bone loss studies of genetically altered mice exposed to weightlessness are strongly recommended.
• AH4—New osteoporosis drugs under clinical development should be tested in animal models of weightlessness.
• AH5—Conduct studies to identify underlying mechanisms regulating net skeletal muscle protein balance and protein turnover during states of unloading and recovery.
• AH6—Conduct studies to develop and test new prototype exercise devices and to optimize physical activity paradigms/prescriptions targeting multisystem countermeasures.
• AH7—Determine the daily levels and pattern of recruitment of flexor and extensor muscles of the neck, trunk, arms, and legs at 1 g and after being in a novel gravitational environment for up to 6 months.

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⁸ M. Basner, A. Savitt, T.M. Moore, A.M. Port, S. McGuire, A.J. Ecker, J. Nasrini, et al., 2015, Development and validation of the Cognition test battery for spaceflight, Aerospace Medicine and Human Performance 86:942-52.

⁹ NRC, 2006, A Risk Reduction Strategy for Human Space Exploration of Space: A Review of NASA’s Bioastronautics Roadmap, The National Academies Press, Washington, D.C.

• AH8—Determine the basic mechanisms, adaptations, and clinical significance of changes in regional vascular/interstitial pressures (Starling forces) during long-duration space missions.
• AH9—Investigate the effects of prolonged periods of microgravity and partial gravity (3/8 or 1/6 g) on the determinants of task-specific, enabling levels of work capacity.
• AH10—Determine the integrative mechanisms of orthostatic intolerance after restoration of gravitational gradients (both 1 g and 3/8 g).
• AH11—Collaborative studies among flight medicine and cardiovascular epidemiologists are recommended to determine the best screening strategies to avoid flying astronauts with subclinical coronary heart disease that could become manifest during a long-duration exploration-class mission (3 years).
• AH12—Determine the amount and site of the deposition of aerosols of different sizes in the lungs of humans and animals in microgravity.
• AH13—Multiple parameters of T cell activation in cells should be obtained from astronauts before and after re-entry to establish which parameters are altered during flight.
• AH14—Both to address the mechanism(s) of the changes in the immune system and to develop measures to limit the changes, data from multiple organ/system-based studies need to be integrated.
• AH15—Perform mouse studies of immunization and challenge on the ISS using immune samples acquired both prior to and immediately upon re-entry to establish the biological relevance of the changes observed in the immune system. Parameters examined need to be aligned with those in humans influenced by flight.
• AH16—Studies should be conducted on transmission across generations of structural and functional changes induced by exposure to space during development. Ground-based studies should be conducted to develop specialized habitats to support reproducing and developing rodents in space.

In response to these recommendations, NASA has funded, starting in 2012, 36 grants in Animal Biology (Vertebrate and Invertebrate) as listed in the NASA Task Book. These new proposals have been funded after severe cut backs in the budget for NASA’s Fundamental Biology Program from 2004 to 2010. However, 25 new tasks are listed for basic research in Animal and Human Biology as compared to 123 for applied research in the HRP. In terms of publications, progress has improved over papers published from research grants during 2004 to 2010, although papers from new grants typically lag the grant start-up date by 1 to 4 years.

Since the decadal survey, there have been more opportunities and funding for fundamental Animal and Human Biology research. The number of investigators for fundamental Animal and Human Biology has increased since 2004, but still is much smaller than investigators for HRP where there are annual calls for more applied, risk-based human research on the ISS (Figure 2.4). Support from the HRP for rodent research has been available for high-priority research related to vision impairment and other high-risk areas related to prolonged spaceflight. International collaborations on free flyers such as the Russian Bion mission have provided spaceflight opportunities for the space rodent community (10 NASA-funded tasks). However, rodent research in space has been confined to mice to allow higher sample sizes for the limited number of rodent habitats on orbit. Rodent research on orbit is resource- and crew-time intensive, which significantly limits opportunities on the ISS. Certain opportunities to develop and support a new generation of young researchers are available such as NSBRI’s 32 postdoctoral fellowships, but this support is mainly for more applied research related to the HRP. Only one postdoctoral task was listed for new investigators in fundamental Animal and Human Biology, and none were listed for graduate students.

The HRP Human Health and Countermeasures (HHC) element has been responsive to the recommendations of the 2011 decadal survey and has made progress in reaching these goals. It should be noted, however, that high-priority areas identified in the decadal survey are not identical to the highest risk factors identified by the HRP for exploration of deep space.

HRP made a strong research and development investment on projects within HHC. Some solicitations included projects that were funded through the NSBRI. The specific research priorities listed on these NRAs focused on the recommendations of the 2011 decadal survey. The 2016 Task Book¹⁰ lists a total of 22 HHC- and NSBRI-funded

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¹⁰ NASA, 2016, The Space Life and Physical Sciences Research and Applications Division Task Book 7.0.

projects; 9 of these projects address 2011 decadal survey priorities (AH1, 1; AH2, 1; AH4, 1; AH6, 1; AH9, 2; AH11, 1; AH13, 1; and AH14, 1).

Data are available to document the efficacy of bisphosphonates combined with exercise on the Advanced Resistive Exercise Device (ARED) to maintain bone density as compared to previously available exercise hardware. This progress was funded by the HRP at NASA JSC.¹¹ Some data on bone reversibility are available from Sibonga¹² and co-workers and Shirazi-Fard¹³ and associates. In simulated microgravity, bone density, bone architecture, and muscle mass correlate with mechanical loads.¹⁴ Also during simulated microgravity, sclerostin antibody treatment increases bone mass by increasing bone formation in both normally loaded and unloaded environments.¹⁵ New osteoporosis drugs under clinical development are being tested in animal models on the ISS by CASIS.

Other than documenting some benefits of ARED over interim Resistive Exercise Device (iRED) for the musculoskeletal system, the large individual variability in skeletal muscle changes with long-duration stays on the ISS is again an example of the challenges with muscle health with spaceflight.

Some limited progress is available concerning the effects of prolonged periods of microgravity on the determinants of task-specific, enabling levels of work capacity, but no data concern the effects of partial gravity.

3.4 CROSS-CUTTING ISSUES FOR HUMANS IN THE SPACE ENVIRONMENT

Translating knowledge from basic laboratory discoveries to human spaceflight is a challenging, two-fold task: Horizontal integration requires multidisciplinary and transdisciplinary approaches to complex problems; vertical translation requires meaningful interactions among basic, preclinical, and clinical scientists to translate fundamental discoveries into improvements in the health and well-being of crew members in space and in re-adaptation to gravity. There are significant scientific gaps in many horizontal or cross-cutting areas that span multiple physiological systems that can affect human mental health, safety, and performance. Many of these interactions also involve interactions with behavioral factors, such as effects on cognitive function. Cross-cutting, thematic areas require the collaboration of teams of experts representing different areas of physiological, behavioral, nutritional and engineering expertise. The goal of these approaches is to mobilize fundamental and applied scientific knowledge and resources in a way that optimizes their utility for human spaceflight crews.

3.4.1 Cross-Cutting Issues Unrelated to Radiation Biology

The 2011 decadal survey listed eight high priorities in the cross-cutting (CC) area unrelated to radiation biology, primarily involving human research. (Radiation is discussed in the following section.) These decadal survey cross-cutting priorities are as follows:

• CC1—To ensure the safety of future commercial orbital and exploration crews, quantify postlanding vertigo and orthostatic intolerance in a sufficiently large sample of returning ISS crews, as part of the immediate post-flight medical exam.
• CC2—Determine whether artificial gravity (AG) is needed as a multisystem countermeasure and whether continuous large-radius AG is needed or intermittent exercise within lower-body negative pressure or

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¹¹ A. LeBlanc T. Matsumoto, J. Jones, J. Shapiro, T. Lang, L. Shackelford, S.M. Smith, et al., 2013, Bisphosphonates as a supplement to exercise to protect bone during long-duration spaceflight, Osteoporos Int. 24(7):2105-2114.

¹² J.D. Sibonga, H.J. Evans, H.G. Sung, E.R. Spector, T.F. Lang, V.S. Oganov, A.V. Bakulin, L.C. Shackelford, and A.D. LeBlanc, 2007, Recovery of spaceflight-induced bone loss: bone mineral density after long-duration missions as fitted with an exponential function, Bone 41(6):973-978.

¹³ Y. Shirazi-Fard, C.E. Metzger, A.T. Kwaczala, S. Judex, S.A. Bloomfield, and H.A. Hogan, 2014, Moderate intensity resistive exercise improves metaphyseal cancellous bone recovery following an initial disuse period, but does not mitigate decrements during a subsequent disuse period in adult rats, Bone 66:296-305. doi:10.1016/j.bone.2014.06.005; erratum in 2014 Bone 71:265.

¹⁴ R. Ellman, J. Spatz, A. Cloutier, R. Palme, B.A. Christiansen, and M.L. Bouxsein, 2013, Partial reductions in mechanical loading yield proportional changes in bone density, bone architecture, and muscle mass, J. Bone Miner. Res. 28(4):875-885.

¹⁵ J.M. Spatz, R. Ellman, A.M. Cloutier, L. Louis, M. van Vliet, L.J. Suva, D. Dwyer, M. Stolina, H.Z. Ke, and M.L. Bouxsein, 2013, Sclerostin antibody inhibits skeletal deterioration due to reduced mechanical loading, J. Bone Miner. Res. 28(4):865-874.

• short-radius AG is sufficient. Human studies in ground laboratories are essential to establish dose-response relationships, and what gravity level, gradient, rotations per minute, duration, and frequency are adequate.
• CC3—Conduct studies on humans to determine whether there is an effect of gravity on micronucleation and/or intrapulmonary shunting or whether the unexpectedly low prevalence of decompression sickness on the space shuttle/ISS is due to underreporting. Conduct studies to determine operationally acceptable low suit pressure and hypobaric hypoxia limits.
• CC4—Determine optimal dietary strategies for crews and food preservation strategies that will maintain bioavailability for 12 or more months.
• CC5—Initiate a robust food science program focused on preserving nutrient stability for 3 or more years.
• CC6—Include food and energy intake as an outcome variable in dietary intervention trials in humans.
• CC10—Expand understanding of gender differences in adaptation to the spaceflight environment through flight- and ground-based research, particularly potential differences in bone, muscle, and cardiovascular function and long-term radiation risks.
• CC11—Investigate the biophysical principles of thermal balance to determine whether microgravity reduces the threshold for thermal intolerance.

There has been a strong response by NASA to some of these priorities, although it should be noted that essentially there has been no effort to date to pursue the recommendation to assess artificial gravity as a multisystem countermeasure (CC2).

Progress appears to have been made in quantifying orthostatic intolerance, and research continues to examine postlanding vertigo and its effects on performance. According to the Task Book, the 10 projects funded in this general area have focused on recovery in a broader sense: injury risk, vestibular function, sensorimotor adaptation and performance, and recovery of performance (CC1). There are no studies listed dealing with artificial gravity (CC2). Two funded projects were in the general area of assessing the effects of gravity on micronucleation and/or intrapulmonary shunting, one of which studied musculoskeletal-induced nucleation during decompression stress (CC3). One dietary strategy and food science study researched the extended preservation of pharmaceutical agents (CC4). Six projects focused on the food science program in which individual projects studied the role of vitamins, predictive models related to vitamin degradation, nutrient content, food acceptability, food storage, food stability, shelf life, and mass reduction (CC5).

3.4.2 Cross-Cutting Issues Related to Radiation Biology

NASA has funded 61 research proposals that are focused on radiation issues listed as being priorities from the 2011 decadal survey. Of these research grants, 7 have been NSCORs (NASA Specialized Center of Research)—large multi-institutional program projects that have permitted a team of investigators with different expertise to focus on questions of radiation significance from several different perspectives. The NSCORs have been extremely important because of the value in a team approach in understanding the complexities of radiation physics, biology, and chemistry in space and also because some new investigators have been brought into the field of space radiation studies through this mechanism. In addition, while these applications have focused almost exclusively on radiation, there are several others that include radiation combined with other mixed stresses such as microgravity, lack of physical activity, and others. The decadal survey had noted the need to study several stressors at one time to achieve a better understanding of the space radiation environment.

The 2011 decadal survey listed three main priorities related to radiation biology. These involved studies at all levels from cellular in vitro work to animal experiments to human studies. The following is a summary of those goals:

• CC7—Conduct longitudinal studies of astronauts for cataract incidence, quality, and pathology related to radiation exposures to understand both cataract risk and radiation-induced late tissue toxicities in humans.
• CC8—Expand the use of animal studies to assess space radiation risks to humans from cancer, cataracts, cardiovascular disease, neurologic dysfunction, degenerative diseases, and acute toxicities such as fever, nausea, bone marrow suppression, and others.

• CC9—Continue ground-based cellular studies to develop endpoints and markers for acute and late radiation toxicities, using radiation facilities that are able to mimic space radiation exposures.

The decadal survey lists radiation as a key factor potentially limiting space travel. The quality of radiation exposures in space is predominantly galactic cosmic rays (GCR) composed of protons (89 percent), helium (approximately 9 percent), and highly charged ions called HZE (high Z (atomic number) and energy) particles. These HZE particles have an atomic mass greater than helium and a high kinetic energy and, consequently, have great penetration and damaging power. While they are not as abundant as other particles found in space, they are much more damaging and of greatest concern for the long-term safety of the crew.

The decadal survey placed a focus on studies of GCR because although Earth-based X-rays and gamma-rays have been well studied since their discovery in 1895, GCR exposures have only been found important during the space travel era and therefore the consequences of exposure are not as well understood. Nevertheless, the decadal study noted that comparisons of GCR with Earth-type exposures could be valuable in understanding GCR effects. NASA has developed a Space Radiation Laboratory at Brookhaven National Laboratory to mimic the space exposure conditions; this is accomplished primarily because current in-flight exposures on the ISS and other spacecraft are shielded at least in part from GCR exposure by Earth’s Van Allen belts and also because doses on the ISS are much lower than those encountered during a Mars-type mission. The facility has the capability of doing rodent and cell exposures. The goals of the NASA program are to understand and where possible mitigate the risk of space radiation exposure.

Most estimates of doses during flight to and from Mars are in the range from 0.6 to 2 Sv. Cancer is considered a stochastic effect of radiation and therefore can occur at any dose with an increase in incidence with increasing dose. Based on this concept, any exposure to radiation can be associated with some risk of developing cancer. Most radiation-induced leukemias occur within 2 to 20 years following exposure, while solid cancers take somewhat longer to develop with a latent period of 15 years or more (except thyroid cancers from radioactive iodine incorporation which may occur as early as 8 years after exposure). This means that the cancer risk to astronauts would begin sometime after their return to Earth and is not likely to be an in-mission risk. NASA has considered this risk to be important, and the decadal survey recommended that risks associated with cancer development continue to be studied. In addition, the risk is significantly different for males and females in space, with females being more susceptible, predominantly because lung cancer risk is higher in females than males for the ages considered to be flight eligible. As a consequence, NASA has invested funding in understanding sex-based differences in cancer induction. Studies on cancer-related exposures have received less funding in the past several years and have been de-emphasized in light of possible degenerative risks that are even more poorly understood; nevertheless, the risk of cancer has not really been decreased by different approaches.

3.4.2.1 Cataracts and Deterministic Studies in Humans (CC7)

Deterministic effects of radiation exposure have a dose threshold and the incidence of effects is usually expressed as a threshold-sigmoid curve. For high-dose effects such as acute radiation syndromes (ARS), the thresholds for induction are usually considered to be higher than those that would be encountered in a Mars mission. While NSBRI conducted some studies on ARS in animal models during the early part of the decadal survey, these were phased out recently because the doses needed to induce ARS are lower than would be encountered in a worst-case scenario in a Mars-type mission.

In addition, human studies relevant to cataracts (CC7) have been given a lower priority in the past 2 to 3 years. While cataract development appears to be a deterministic effect of radiation with a dose threshold, cataracts are easily treated and are not likely to threaten a mission. Long-term follow-up of the astronauts would continue to be important, but the priority placed on it would be reduced.

3.4.2.2 Animal Models of Human Disease (CC8)

In the decadal survey, deterministic effects were focused on identified endpoints that are more poorly understood and possibly mission-threatening, such as disturbances in cognition or cognitive function due to radiation

effects on the central nervous system (CNS). Studies have been done in NASA-funded programs using normal mice and mice that are models for cognitive disorders (such as mice that are knocked-out for the ApoE gene) and have demonstrated that even low doses of HZE radiation are associated with disruption of neurons, inflammation in the CNS, and stress responses in precursors of neural cells. Functional disorders in mice that are related to neurocognitive endpoints in humans have also been identified by many groups, but their studies with radiation effects are being exploited by NASA-funded investigators.

The relevance to spaceflight is unknown, and it is not clear that endpoints in mice necessarily relate well to functional endpoints in humans; nevertheless, the possible consequences could be mission-threatening and therefore require additional study. Recent NASA work has placed a priority on CNS effects of HZE exposure, examining both single-ion and mixed-field exposures. The radiation research programs of NASA have focused on some degenerative endpoints, but stronger emphasis needs to be placed on these degenerative risks of radiation exposure that could be mission threatening, such as CNS effects. This work cannot be done in humans, and therefore, an emphasis on mechanisms is needed so that extrapolation from animal models to humans is feasible.

3.4.2.3 In Vitro Studies to Mimic Space Radiation Effects (CC9)

Many deterministic effects have not been identified, but a priority was placed on examining endpoints relevant to low-dose HZE exposures, alone or in combination with space radiation conditions (mixed field, with microgravity, etc.), including inflammation, reactive oxygen species generation, and DNA damage, all of which may play a role.

3.4.3 Other Potential Risks

It should be noted that a few studies recommended by the decadal survey are focused on cardiovascular effects. While it is known that high-dose exposures can increase the risk of heart attack and stroke, some evidence from Japanese atomic bomb survivors (which would be predominantly low- linear energy transfer [LET] radiation) has suggested that this may be possible even for low-dose exposures. Nevertheless, this risk would probably be deterministic in mechanism and thus would not be considered a mission-threatening exposure as the CNS effects could possibly be.

Recent work on topics highlighted by the decadal survey has transitioned from mechanisms-oriented work to work that is focused on mitigation. This is in contrast to past approaches for radiation programs that focused on mechanisms first and various countermeasures as a result of mechanisms-based work. This work on countermeasures is somewhat uneven because there are few countermeasures developed to be effective following radiation exposure, and those selected for study appear to be questionable in their relevance to spaceflight. The National Institute of Allergy and Infectious Diseases (NIAID) and the National Cancer Institute (NCI) in NIH have strong radiation mitigator and countermeasures programs oriented toward identifying new agents that can be used both to prevent and to decrease radiation effects for acute toxicities as well as for carcinogenesis (particularly in NCI programs). While the focus is on low-LET Earth-bound types of exposures, NASA should be able to dove-tail with those studies to include some high-LET testing of significant compounds. The countermeasures component of the radiation program currently under way was not defined in the original decadal survey and seems to be disconnected from other mitigation work on-going in the United States.

3.5 FUNDAMENTAL PHYSICAL SCIENCES IN SPACE

The 2011 decadal study provided the following four broad recommendations that should characterize NASA’s low-gravity fundamental physics (FP) research activities:

• FP1—Research on complex fluids and soft matter. Microgravity provides a unique opportunity to study structures and forces important to the properties of these materials without the interference caused by Earth-strength gravity.

• FP2—Understanding of the fundamental forces and symmetries of nature. High-precision measurements in space can test relativistic gravity, fundamental high-energy physics, and related symmetries in ways that are not practical on Earth. Novel effects predicted by new theoretical approaches provide distinct signatures for precision experimental searches that are often best carried out in space.
• FP3—Research related to the physics and applications of quantum gases. The space environment enables many investigations, not feasible on Earth, of the remarkably unusual properties of quantum gases and degenerate Fermi gases.
• FP4—Investigations of matter near a critical phase transition. Experiments that have already been designed and brought to a level of flight readiness can elucidate how materials behave in the vicinity of thermodynamically determined critical points. These experiments, which require a microgravity environment, will provide insights into new effects observable when such systems are driven away from equilibrium conditions.

Specifically, the decadal study states that “a successful exploration program in physical science necessitates first of all a ground-based fundamental sciences program.”¹⁶ Other recommendations emphasized the importance of international collaborations and partnering with other agencies. These recommendations were followed by four prioritized programmatic areas for NASA research: Soft Condensed Matter Physics and Complex Fluids, Precision Measurements of Fundamental Forces, and Symmetries, Quantum Gases, and Critical Phenomena. The decadal survey report further concluded that in order to maintain a robust program in the fundamental physical sciences a “critical mass of at least 100-150 funded investigators” is necessary to provide coverage of the areas of physical science of importance to NASA.¹⁷

Development and progress in the fundamental physical sciences in space since 2011 has been quite substantial. The design, construction, and evaluation phases of the Cold Atom Laboratory (CAL) facility have been completed and CAL is expected to be transported to the ISS in late 2017 where it will become operational immediately. Achieving microgravity Bose-Einstein condensate (BEC) will be a high-priority project while other cold atom studies should soon make contributions to quantum information and computing. The ground-based research supporting ACES (Atomic Clock Ensemble in Space) is proceeding well. Colloids are now offering new metamaterials opening the way of controlling light propagation in completely new ways. The understanding of the glass transition is progressing through the many studies of the jamming transition in granular materials, foams, and colloids.

The following comments concern projects listed in the NASA Task Book as current fundamental physics research projects. In the decadal survey report, the projects belonging to FP1, FP2, and FP3 are all rated as being of high relevance in terms of overall importance, but are rated as being of low to moderate importance to enabling exploration. The projects in FP4 concerning critical fluids received a lower overall rating.

3.5.1 Soft Condensed Matter Physics and Complex Fluids (FP1)

The primary focus for this area of microgravity research concerns the behavior of colloids and proteins near phase transitions while in a microgravity environment. An important rationale for these studies arises from observations that in a normal gravitational environment, even very small colloidal particles may aggregate during the crystallization/gelation process. This aggregation of crystals or gels is affected by gravity in subtle ways, producing deleterious inhomogeneities in the process. The suppression of gravitationally induced inhomogeneities was found to facilitate the formation of ordered phases, an important property that is desired for photonic devices used in optical communication systems.

The projects looking at protein crystallization in microgravity are generally in their early stages. Their objective is to investigate the possible role of protein aggregates in the crystallization process. There are also a number of active projects on protein crystallization managed by CASIS that are aiming to improve drug purification, delivery, or storage, or provide a better understanding of protein structures with a role in disease.

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¹⁶ NRC, 2011, Recapturing a Future for Space Exploration, p. 262.

¹⁷ NRC, 2011, Recapturing a Future for Space Exploration. p. 262.

A new liquid crystal project will address two-dimensional hydrodynamics, including thermocapillarity in the absence of convection. A foam project is proceeding in collaboration with a group of European researchers. This project concerns the hydrodynamics of “wet” foams, which are impossible to stabilize on Earth because of gravity drainage, and the investigation of the jamming transition of bubbles. Viewed collectively, a robust research program has been established—one that will obtain important properties of soft condensed matter in a microgravity environment.

3.5.2 Precision Measurements of Fundamental Forces and Symmetries (FP2)

The choice of a boundary between FP2 and FP3 is ambiguous at best. The vast majority of the ISS-based activities in these two areas will utilize the unique capabilities of CAL, which is expected to be completed, tested, and placed on ISS during the latter part of 2017. This research, especially the pico-Kelvin BEC experiments, will complement and dramatically extend Earth-based BEC experiments—very much in consonance with the decadal survey priority of establishing robust ground- and space-based fundamental physical science programs. The CAL is the very major component of fundamental physics located on the ISS, and its complexity essentially requires either ground-based or autonomous operation.

Overall, the 2016 NASA Task Book indicates 15 research projects that fall under one of two program recommendations related to precision measurements of fundamental forces and symmetries. Of these, 8 are fully carried out on the ISS, 3 are fully ground based, and 4 have both flight and ground components.

A number of the research programs involve ISS-based and ground-based clocks and precision measurements and comparisons. This work has the potential to provide improved sensitivity tests of weak equivalence and sensitive tests of symmetry breaking. The dramatic improvement in ground-based clock accuracy that has occurred over the past decade will likely not be implemented on the ISS, but even so, there is good reason to pursue observation of possible symmetry breaking.

The idea of pursuing entangled networks of clocks that include space-based clocks (with European Space Agency participation) has the potential of producing significantly improved tests of the possible time variation of fundamental constants.

3.5.3 Quantum Gases (FP3)

The CAL provides unique opportunities to investigate BEC in microgravity. It is especially responsive to the decadal survey’s emphasis on robust ground- and space-based experiments that are mutually supportive and enable unique new science. Specifically, only in a microgravity environment will it be possible to produce condensates at temperatures in the pico-Kelvin range. Achieving such an unprecedented low temperature is a unique opportunity, available only as a consequence of a microgravity environment; the microgravity environment ensures that future revolutionary BEC advances that take place on the ground can be further enhanced when carried out on the ISS. Future experiments involving condensates on the ISS can attain even lower temperatures than the enabling ground-based research. Similar benefits will likely also accrue to planned atom interferometry studies.

3.5.4 Critical Phenomena (FP4)

Critical fluids are interesting fluids with properties that change substantially when close to a critical point. The changes in these fluid properties can be observed most effectively by monitoring them as a function of temperature in the vicinity of a critical point. For example, microgravity experiments using such fluids have allowed for a better understanding of the wetting of the walls of containers, an important issue for fluids in space. At present, NASA has one active project in this area, carried out in collaboration with CNES (Centre National d’Études Spatiales). However, as noted in the introduction, the decadal survey evaluated this area as one with a lower overall relevance compared to FP1 to FP3.

3.6 APPLIED PHYSICS

The decadal survey called out three high-priority areas in Applied Physical Sciences (AP): fluid physics, combustion, and materials research. Research in these areas is deemed central to many new exploration technologies, enabling new exploration capabilities and yielding new insights into a broad range of physical phenomena in space and on Earth. It is envisioned that research focused on applied physical sciences will result in fundamental and practical improvements for propulsion, power generation, life support, fire safety, and advanced materials extraction, synthesis, and processing. The following key areas were identified in the decadal survey as having the highest priority in the applied physical sciences:

• AP1—Reduced-gravity multiphase flows, cryogenics and heat transfer database and modeling, including phase separation and distribution (i.e., flow regimes), phase-change heat transfer, pressure drop, and multiphase system stability.
• AP2—Interfacial flows and phenomena (including induced and spontaneous multiphase flows with or without phase change) relevant to storage and handling systems for cryogens and other liquids, life support systems, power generation, thermal control systems, and other important multiphase systems.
• AP3—Dynamic granular material behavior and subsurface geotechnics to improve predictions and site-specific models of lunar and Martian soil behavior.
• AP4—Development of fundamentals-based strategies and methods for dust mitigation during advanced human and robotic exploration of planetary bodies.
• AP5—Experiments on the ISS to understand complex fluid physics in microgravity, including fluid behavior of granular materials, colloids and foams, biofluids, non-Newtonian and critical point fluids, etc.
• AP6—Fire safety research to improve methods for screening materials for flammability and fire suppression in space environments.
• AP7—Combustion processes research, including reduced-gravity experiments with longer durations, larger scales, new fuels, and practical aerospace materials relevant to future missions.
• AP8—Research on numerical simulation of combustion to develop and validate detailed single phase and multiphase combustion models for interpreting and facilitating combustion experiments and tests.
• AP9—Reduced-gravity research on materials synthesis and processing and control of microstructure and properties, to improve the properties of existing and new materials on the ground.
• AP10—Development of new and advanced materials that enable operations in harsh space environments and reduce the cost of human space exploration.
• AP11—Fundamental and applied research to develop technologies that facilitate extraction, synthesis, and processing of minerals, metals, and other materials available on extraterrestrial surfaces.

3.6.1 Physical Science Informatics (Open-Access Database)

Subsequent to the publication of the decadal survey, NASA initiated a new mandatory public archive requirement for physical science investigator teams who must now upload relevant research products and data to NASA’s Physical Science Informatics (PSI) public data archive (http://psi.nasa.gov). This mechanism offers significant opportunities to expand impacts of the microgravity research on science and technology development on Earth. Moreover, the addition of ground-based theoretical and experimental studies funded through the PSI program provided extended benchmark data for model development. NRAs for fluids, complex fluids, combustion, and material science have been released with 16 investigations funded to mine the PSI database expanding and extending impacts of the space experiments.

3.6.2 Fluid Physics

The research aims, themes, and priorities within the Fluid Physics discipline of NASA’s Physical Sciences Research Program have remained largely unchanged from the time of the 2011 decadal survey, which draws from

earlier, nearly identical, reviews done by the National Research Council (now the National Academies of Science, Engineering, and Medicine) dating back to the early 2000s.^18,19 In fact, most fluids research themes (>90 percent) presently under pursuit by NASA targeting research needs for exploration have been clearly identified for many decades. Current NASA leadership has internalized the fluids research needs and priorities and has directed the currently limited resources of fluid physics funding, launch opportunities, flight platforms, and ground-based facilities to address the general exploration-critical topics of multiphase transport phenomena in variable acceleration fields—especially the nearly weightless environment common aboard spacecraft. As examples, the design challenges are manifold for managing the water cycle for life support, plant and animal habitats, and systems involving liquids fuels, propellants, and coolants, requiring a concerted effort to establish a practical theoretical foundation with which to design the next generation of highly reliable fluids systems for bolder yet safer and more affordable space exploration.

Making good use of limited resources, the current fluids program is on track for completing, preparing, and initiating new low-gravity (low-g) multiphase fluids research investigations targeting mission-enabling forced and unforced capillary flows (i.e., CCF,²⁰ CFE^21,22), flows in packed beds (i.e., BPRE²³), cryogenic fluids management (i.e., ZBOT 1, 2, and 3²⁴), forced flow with boiling and condensation (i.e., FBCE²⁵), forced flow phase separations (i.e., TPSE²⁶), enhancements (STP-H5 EHD²⁷), pool boiling heat transfer (MABE²⁸ and BXF²⁹), and others. At least 6 flight investigations are currently funded contributing to about 25 fluid physics journal publications per year. In addition to adding to the fundamental understanding of low-g fluid phenomena (i.e., CVB³⁰), such investigations have the potential to inspire practical advanced systems design. For example, NASA-supported capillary flow research performed on the ISS (i.e., CCF and CFE) and in terrestrial facilities has matured to the point of direct application to next generation spacecraft fluid systems design. This work is now being applied to omics in space using the three-dimensional (3D) printer on the ISS,³¹ semi-passive CO₂ removal,³² condensing

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¹⁸ NRC, 2000, Microgravity Research in Support of Technologies for the Human Exploration and Development of Space and Planetary Bodies, The National Academies Press, Washington, D.C.

¹⁹ NRC, 2003, Assessment and Directions in Microgravity and Physical Sciences Research at NASA, The National Academies Press, Washington D.C.

²⁰ M. Dreyer, Principal Investigator, 2017, “Capillary Channel Flow (CCF),” December 6, https://www.nasa.gov/mission_pages/station/research/experiments/303.html.

²¹ M. Weislogel, Principal Investigator, 2017, “Capillary Flow Experiment (CFE),” December 6, https://www.nasa.gov/mission_pages/station/research/experiments/978.html.

²² M. Weislogel, Principal Investigator, 2017, “Capillary Flow Experiment (CFE-2),” December 6, https://www.nasa.gov/mission_pages/station/research/experiments/459.html.

²³ B. Motil, Principal Investigator, 2017, “Packed Bed Reactor Experiment (PBRE),” July 19, https://www.nasa.gov/mission_pages/station/research/experiments/1111.html.

²⁴ M. Kessemi, Principal Investigator, 2014, “Zero Boil-Off Tank experiment (ZBOT),” last updated September 18, https://spaceflightsystems.grc.nasa.gov/sopo/ihho/psrp/msg/zbot.

²⁵ I. Mudawar, Principal Investigator, 2017, “Forced Flow Boiling Experiment (FBCE),” last updated May 12, 2017, https://spaceflightsystems.grc.nasa.gov/sopo/ihho/psrp/fcf/fcf-investigations/fbce.

²⁶ N. Hoyt, M.F. Kang, A. Kharraz, J. Kadambi, and Y. Kamotani, Cyclonic two-phase flow separator experimentation and simulation for use in a microgravity environment, Journal of Physics: Conference Series 327(1), http://iopscience.iop.org/article/10.1088/1742-6596/327/1/012056/meta.

²⁷ J. Didion, Principal Investigator, 2017, “Electro-Hydro Dynamics,” December 13, https://www.nasa.gov/mission_pages/station/research/experiments/1993.html.

²⁸ J. Kim, Principal Investigator, 2017, “Microheater Array Boiling Experiment (MABE),” December 20, https://www.nasa.gov/mission_pages/station/research/experiments/16.html.

²⁹ V. Dhir, Principal Investigator, 2012, “Boiling eXperiment Facility (BXF),” December 5, https://www.nasa.gov/mission_pages/station/research/experiments/BXF.html.

³⁰ P. Wayner, Principal Investigator, 2017, “Confined Vapor Bubble Experiment,” December 20, https://www.nasa.gov/mission_pages/station/research/experiments/465.html.

³¹ S. Wong, AI Biosciences, Principal Investigator, 2017, “A 3D Printer Enabled, High Performing, Microgravity Compatible, and Versatile Sample Preparation Platform,” NASA PH I SBIR, https://sbir.nasa.gov/firm/node/59039.

³² J. Graf, CapiSorb, Principal Investigator, 2018, “Capillary Structures for Exploration Life Support,” March 14, https://www.nasa.gov/mission_pages/station/research/experiments/2364.html.

heat exchangers, contingency urine collection,³³ brine drying,³⁴ plant/water delivery systems,³⁵ and many others. Similar application impacts are anticipated for planned research relating to packed bed reactors, phase change heat transfer systems, propellant thermostatics and dynamics, phase separations, and new exploration-enabling space fluid physics investigations. More investigations along these lines are anticipated, and improved analytical and numerical tools for advanced system design are becoming available for broader development and application.

To maximize research output, NASA is increasingly evaluating and prioritizing its fluid physics research projects, based on multiuser potential, the potential for subsequent follow-on research of greater breadth and/or depth, the value and applicability of the open-archive data to the community, and the value of further experiments with modified hardware to other communities (i.e., fluid physics experiments re-tooled and re-purposed to address further applications in life support, such as NASA Glenn Research Center’s Packed-Bed Reactor Experiment, which is under consideration for new investigations along different lines by NASA Johnson Space Center). These efforts are intended to achieve the greatest science return and engineering impact for each dollar spent. Such efforts are in motion for fluid physics, with specific demonstrations of success within the decadal survey review timeframe, with hopes of increasing technology readiness level for low-g system design.

3.6.3 Combustion Research

There are two thrusts in combustion research in the decadal survey: research that enables human space exploration and research that is enabled by the unique microgravity environment (decadal survey priorities AP6 to AP8).

Spacecraft safety measures include fire prevention, detection, and suppression. The emphasis of fire prevention is on material (mostly solids) flammability and selection. The Burning and Suppression of Solids (BASS) experiment used an existing flow tunnel in the microgravity glovebox aboard the ISS. The tests were carried out from 2010 to 2014. Although the testing conditions were limited by an oxygen range equal or less than 21 percent at 1 atmospheric pressure, and by small samples, this series was successful in investigating the effect of low-speed forced flow on flame spread, burning, and extinction for burning solids. The test database is already available in the NASA PSI archive.

The Spacecraft Fire Safety Demonstration (Saffire) is a large-scale microgravity fire experimental series. The first series of tests was conducted in the unmanned Cygnus supply vehicle before it entered the atmosphere and was destroyed. Large-scale fire tests are a high-priority objective in the decadal survey. NASA accelerated the schedule anticipated by the decadal survey for such a large-scale test and also formed a team of U.S. and international investigators to plan and conduct the work.³⁶ The funding for Saffire is provided by NASA’s Advanced Exploration Systems (AES) Division rather than the Division of Space Life and Physical Sciences Research and Applications (SLPSRA). Both BASS and Saffire projects provide valuable data for model calibration and validation.

The Solid Fuel Ignition and Extinction Experiment (Sofie) consists of five individual projects to study solid flammability under a variety of pressure and oxygen atmospheres to be carried out inside the ISS Combustion Integrated Rig (CIR). Sofie will extend the test condition to an enriched oxygen and different pressure environment, with improved velocity control and better diagnostics. Sofie is currently in a queue waiting for CIR to become available. Due to crew availability and other factors, the flight experiment may not be started until 2020.

The Flame Extinguishment Experiments (FLEX) were conducted to assess the effects of gravity on fuel burning rates, soot formation, and flame extinction using liquid droplets and to gain basic understanding of combustion science to enable energy efficient space exploration. The experiments can provide insights on fire suppression for next-generation crew exploration vehicles. The FLEX-2 experiments conducted droplet burning of pure fuels, fuel mixtures, droplet arrays, and convective droplet burning. The FLEX-2 investigation unexpectedly discovered

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³³ R. Jenson, IRPI, LLC, Principal Investigator, 2015, “Passive, Collapsible Contingency Urinal for Human Space Flight,” NASA Ph I SBIR, August 1, https://ntrs.nasa.gov/search.jsp?R=20160005400.

³⁴ M. Sargusingh, CapiBRIC, Prinicipal Investigator, 2018, “Capillary Structures for Exploration Life Support,” March 14, https://www.nasa.gov/mission_pages/station/research/experiments/2364.html.

³⁵ R. Adamson, 2017, “NASA Partners With Techshot, Tupperware to Update ISS Plant Production System,” Industry News, July 26, http://blog.executivebiz.com/2017/07/nasa-partners-with-techshot-tupperware-to-update-iss-plant-production-system.

³⁶ A European cargo ship was initially planned as the experiment platform.

“cool flames” of droplet burning after radiation extinction of the hot flame. These cool flame experiments provided excellent microgravity data for the study of low-temperature chemistry of liquid fuels, which plays a critical role in advanced internal combustion engines. These results drew significant attention in the combustion research community and have sparked renewed research interest in cool flames. FLEX-ICE-GA (FLEX-Italian Combustion Experiment for Green Air) also tested surrogate fuel mixtures as defined by the Italian Space Agency (ASI) by using the FLEX-2 experimental configuration. FLEX-2J experiment is a joint effort between NASA, the Japanese Aerospace Exploration Agency, and universities to study fuel droplet motions during flame spreading along a one-dimensional droplet array. The international collaboration provides a greater platform and extends the science impact on a broader community for microgravity combustion research.

ACME (Advanced Combustion via Microgravity Experiments) focuses on combustion science and technology using the CIR hardware in the ISS. The primary goal is to improve efficiency and reduce pollutant emission in terrestrial combustion. The secondary goal is fire prevention. ACME has five independent experiments to investigate the burning rates and soot formation in laminar, gaseous, and non-premixed flames, with and without an electric field. The ground-based research has led to a large number of publications. On-orbit testing is planned to begin in 2017. PSI-funded ground experiments and modeling have provided a generic flame regime diagram for both cool flames and hot flames in premixed and diffusive combustion systems.

3.6.4 Materials Research

The NASA Task Book indicates that a limited number of PIs (around 27 PIs for the year 2017) are currently supported for ground-based, flight experiment, and/or simulation investigations in materials sciences. These investigations build upon and complement the wealth of data and observations of more than 70 materials sciences researchers who were supported by NASA in 2004. Indeed, as stated in the 2011 decadal study, “Collectively, through the shuttle era, research in the physical sciences generated an impressive number of peer-reviewed publications, landmark measurements, and discoveries, all of which could only be achieved through access to space.” ³⁷

The decadal survey has further emphasized that materials science and engineering are central to NASA’s exploration mission, both crewed and uncrewed. The decadal survey further recommends emphasis on materials synthesis and processing and the control of microstructure and properties, as well as emphasis on advanced materials to enable the NASA mission.³⁸

The research aims of the current investigations primarily focus on the crucial understanding of the influence of processing in reduced gravity on the structure and properties of materials. However, because of the sparsity of research being funded in the materials science area, it is difficult to identify or describe specific research themes or directions for the research activities being funded. Notwithstanding, the research themes of the current investigations can be roughly categorized as follows:

• Modeling and simulation of crystal growth, dendritic microstructures, and liquid phase sintering;
• Effects of convection on microstructural transition, mushy zones and macrosegregation,
• Coarsening of solid-liquid mixtures and dendrites;
• Electromagnetic or electrostatic levitation of liquids;
• Directional solidification;
• Crystal growth of II-VI compound semiconductors; and
• Eutectics.

Continuation of the above-mentioned research activities is crucial for future space exploration and is highly recommended. At the same time, additional investments need to be made in mission-critical materials science and engineering arena. As clearly recognized in the decadal study, studies in “lightweight materials, self-healing materials, and other new materials tailored to NASA’s demanding missions, are central to the success of future

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³⁷ NRC, 2011, Recapturing a Future for Space Exploration, p. 20.

³⁸ Ibid., Table 9.1.

human and robotic exploration.”³⁹ As predicted in that report, research in reduced gravity has certainly led to new insights about how various processing methods are affected, as is the internal structure and, ultimately, the properties of such materials.

In summary, given the limited opportunities for conducting significant materials research aboard the ISS over the past 8 years, progress and technological competence in this critical area will remain sluggish and uncertain.

3.7 TRANSLATION TO SPACE EXPLORATION SYSTEMS

The 2011 decadal survey called out 16 high-priority areas in Translation to Space Exploration Systems (TSES). As identified in the decadal survey, the specific high-priority items are the following:

• TSES1—Conduct research to address issues for active two-phase flow relevant to thermal management.
• TSES2—To support zero-boiloff propellant storage and cryogenic fluid management technologies, conduct research on advanced insulation materials, active cooling, multiphase flows, and capillary effectiveness, as well as active and passive storage, fluid transfer, gauging, pressurization, pressure control, leak detection, and mixing destratification.
• TSES3—NASA should enhance surface mobility; relevant research includes suited astronaut computational modeling, biomechanics analysis for partial gravity, robot-human testing of advanced spacesuit joints and full body suits, and musculoskeletal modeling and suited range-of-motion studies, plus studies of human-robot interaction (including teleoperations) for the construction and operation of planetary surface habitats.
• TSES4—NASA should develop and demonstrate technologies to mitigate the effects of dust on extravehicular activity (EVA) systems and suits, life support systems, and surface construction systems. Supporting research includes impact mechanics of particulates, design of outer-layer dust garments, advanced material and design concepts for micrometeoroid mitigation, magnetic repulsive technologies, and the quantification of plasma electrodynamic interactions with EVA systems; dynamics of electrostatic field coupling with dust; and regolith mechanics and gravity-dependent soil models.
• TSES5—NASA should define requirements for thermal control, micrometeoroid and orbital debris impact and protection, and radiation protection for EVA systems, rovers, and habitats and develop a plan for radiation shelters.
• TSES6—NASA should conduct research for the development and demonstration of closed-loop life support systems and supporting technologies. Fundamental research includes heat and mass transfer in porous media under partial gravity and microgravity conditions and understanding the effect of variable gravity on multiphase flow systems.
• TSES7—NASA should develop and demonstrate technologies to support thermoregulation of habitats, rovers, and spacesuits on the lunar surface.
• TSES8—NASA should perform critical fire safety research to develop new standards to qualify materials for flight and to improve fire and particle detectors. Supporting research is necessary in materials qualification for ignition, flame spread, and generation of toxic and/or corrosive gases and in characterizing particle sizes from smoldering and flaming fires under reduced gravity.
• TSES9—NASA should develop a standard methodology for qualifying fire suppression systems in relevant atmospheres and gravity levels and would benefit from strategies for safe post-fire recovery. Specific research is needed to characterize the effectiveness of fire suppression agents and systems under reduced gravity and to assess the toxicity of various fire products.
• TSES10—Research should be conducted to allow regenerative fuel cell technologies to be demonstrated in reduced-gravity environments.
• TSES11—To support the development of new energy conversion technologies, research should be done on high-temperature energy conversion cycles, device coupling to essential working fluids, heat rejection systems, materials, etc. Research is also required on more efficient surface-base primary power and on

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³⁹ Ibid., p. 265.

• the technologies to enable solar electric propulsion as an option to transfer large masses of propellant and cargo to distant locations.
• TSES12—To make fission surface power systems a viable option, research is needed on high-temperature, low-weight materials for power conversion and radiators and on other supporting technologies.
• TSES13—Development and demonstration of ascent and descent system technologies are needed, including ascent/descent propulsion technologies, inflatable aerodynamic decelerators, and supersonic retro propulsion systems. The required research includes propellant ignition, flame stability, and active thermal control; lightweight flexible materials; and rocket plume aerothermodynamics and vehicle dynamics and control.
• TSES14—Research is required to support the development and demonstration of space nuclear propulsion systems, including liquid-metal cooling under reduced gravity, thawing under reduced gravity, and system dynamics.
• TSES15—Research is needed to identify and adapt excavation, extraction, preparation, handling, and processing techniques for a lunar water/oxygen extraction system.
• TSES16—NASA should establish plans for surface operations, particularly In Situ Resource Utilization (ISRU) capability development and surface habitats. Research is needed to characterize resources available at lunar and martian surface destinations and to define surface habitability systems design requirements.

As identified in the original decadal survey, these recommendations were meant to “identify technologies needed to enable exploration missions to the Moon, Mars, and elsewhere as well as the foundational research in life and physical sciences.”⁴⁰ In the decadal survey, science and technology development areas were recommended to support near-term objectives and operational systems (i.e., prior to 2020) and objectives and operational systems for the decade beyond 2020. While technologies and operational systems may be near term (prior to 2020) or longer term (2020 and beyond), supporting research is necessary for both near term and longer term during the timeframe of this decadal survey. The decadal survey not only defined research priorities in science, but also included discussions about establishing the technological knowledge required to ensure the orderly transition of new technology into operational space exploration systems.

Starting in parallel and since the publication of the decadal survey, NASA and the National Academies have expended significant effort on the NASA technology portfolio. The NASA Authorization Act of 2010 directed NASA to create a program to maintain its research and development base in space technology. In response, NASA created a set of 14 draft space technology roadmaps to guide the development of space technologies. These roadmaps were the subject of a comprehensive external review by the National Academies, which in 2012 issued the National Research Council report NASA Space Technology Roadmaps and Priorities: Restoring NASA’s Technological Edge and Paving the Way for a New Era in Space.⁴¹

NASA then began a reexamination and updating of its 2010 draft technology roadmaps,⁴² resulting in a new set of roadmaps in 2015.⁴³ A significant aspect of the updating was the effort to assess the relevance of the technologies by showing their linkage to a set of mission classes and design reference missions (DRMs) from the Human Exploration and Operations Mission Directorate and the Science Mission Directorate. The new set of roadmaps also included a roadmap that addresses aeronautical technologies.

In the spring of 2015, the updated roadmaps were released to the public for review and comment. Also in 2015, the National Academies were asked to assemble a committee to evaluate the new technologies in the updated set of 14 space technology roadmaps; this resulted in the 2016 report NASA Space Technology Roadmaps and Priorities Revisited.⁴⁴ Per that study’s statement of task, the aeronautics roadmap was not included in the most recent

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⁴⁰ Ibid., p. 299.

⁴¹ NRC, 2012, NASA Space Technology Roadmaps and Priorities: Restoring NASA’s Technological Edge and Paving the Way for a New Era in Space, The National Academies Press, Washington, D.C.

⁴² NASA, “NASA 2015 Technology Roadmaps,” https://www.nasa.gov/offices/oct/home/roadmaps/index.html.

⁴³ Ibid.

⁴⁴ National Academies of Sciences, Engineering, and Medicine, 2016, NASA Space Technology Roadmaps and Priorities Revisited, The National Academies Press, Washington, D.C., doi: 10.17226/23582.

National Academies study because the 2010 space technologies roadmaps had no such aeronautics roadmap. Other key tasks of this most recent National Academies review were:

• Identifying technologies in NASA’s 2015 roadmaps that were not evaluated by the 2012 NRC report,
• Prioritizing those technologies using the same process documented in the 2012 NRC report, and
• Recommending a methodology for future independent reviews of NASA’s technology roadmaps.

That technology committee did not asses the progress made by NASA since the originally published 2012 report. Thus, in reviewing the progress made on the 16 TSES priority items identified in the decadal survey, this committee did not have a broad and prior National Academies review to depend on, but only the knowledge contained within the committee.

The decadal survey focused its science and technology needs into seven topic categories: space power and thermal management; space propulsion; extra-vehicular activity (EVA); life support; fire safety; space resource extraction, processing, and utilization; and planetary surface construction. These areas represent a subset of the 15 technology roadmaps (see Figure 3.1). To understand the intersection of the decadal survey and these technology roadmaps, the 16 resulting high-priority TSES items from the decadal survey are best mapped into the most

TABLE 3.1 Mapping of Decadal Survey Translational Priorities (TSES) against Technology Priorities Identified in 2012 and 2016 Reviews of NASA’s Technology Roadmaps.

NOTES: Main TA # denotes which technology roadmap maps closest to the TSES; Other TA # denotes other technology roadmap(s) that are relevant to the TSES; 17 Highest denotes which highest-priority Level 3 technology maps to the TSES; 88 High denotes which high-priority level 2 or 3 technology maps to the TSES; None indicates that there were no highest- or high-priority technologies associated with the TSES. Several of the 17 highest technologies (denoted by X.1, X.2, etc.) are combinations of related Level 3 high-priority technologies (see Table 3.2 and the report for detailed descriptions of the X.x “technologies”).

relevant technology roadmaps by denoting what high-priority item maps onto what roadmap using the TSES (decadal survey) and TA (technology roadmap) designations. The relationship of the decadal survey priorities to the 17 highest-priority technologies and 88 high-priority technologies published in the 2016 National Academies technology roadmaps review⁴⁵ is shown in Table 3.1 (the technologies are listed in numerical order, not priority order). Table 3.2 provides the names of the Level 3 technologies listed in Table 3.1.

A majority (9 of 16) decadal survey TSES high-priority recommendations do align with the 2015 review’s 17 highest priorities. Several (7 of the 16) do not align with the 17 highest priorities because the decadal survey considered only those technologies that required supporting research in physical and biological sciences. Thus the National Academies 2012 and 2015 roadmap reviews provide a more complete picture of overall NASA technology development priorities.

As a part of supporting this committee’s assessment, NASA was asked to provide data on all of the projects in its biological and physical sciences portfolio and indicate how they mapped to the decadal survey. Only three

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⁴⁵ See Tables S.1 and 2.1 in National Academies of Sciences, Engineering, and Medicine, 2016, NASA Space Technology Roadmaps and Priorities Revisited.

TABLE 3.2 Key for Level 3 Technologies Listed in Table 3.1

projects, the Smolder Transition and Flaming (STaF) and Smolder Evaluation Test (SET), the Zero Boil-Off Tank (ZBOT) Experiment, and Direct Computational Simulations and Experiments for Internal Condensing Flows System-Instabilities/Dynamics in Microgravity and Terrestrial Environments, identified with TSES8, TSES2, and TSES11. This small number was somewhat surprising in that it might be expected that many areas that identify as enabling exploration would have linkages to these 16 TSES high-priority recommendations. However, the committee could anecdotally identify other projects that could be tied to these 16 priorities, so there is likely an issue of not formally identifying research project connections to the translational research priorities. This lack of formal traceability may hamper NASA in its effort to ensure that new knowledge of biological and physical behaviors is translated into the development of technology systems, including systems prioritized in the technology roadmaps, affected by those behaviors.

One of the challenges that the original decadal survey identified that appears to continue today is adequate two-way communication between the scientists doing the basic research and the technologists using those research results. Two-way communication between the two groups is critical in order to integrate their efforts. This communication process requires that engineers understand and apply the research results of scientists and that the scientists work within the context of specific missions. Successful transition from research results to implemented technology requires that program managers, engineering leaders, and research leaders create an environment where scientists interact with engineers on the specifics of system requirements. The 2011 decadal survey, in Chapter 12, “Linking Science to Mission Capabilities Through Multidisciplinary Translational Programs,”⁴⁶ contains an in-depth discussion of the issues associated with creating organizations that can successfully translate research into technologies and technologies into exploration systems. That chapter discusses ideas such as multidisciplinary teams of scientists and engineers working these challenges together, improved databases and data sharing, improved commercial sector interaction, as well as collaboration with other agencies and international partners across both science and engineering together to summarize a few key suggestions. This advice remains as important today as when the decadal survey was released.

3.8 SCIENCE STATUS IN LIGHT OF EXPLORATION MISSION DEVELOPMENT

As promised in the introduction to this chapter, the committee has assessed in discussions above the progress made in the respective science disciplines against the priorities identified in the 2011 decadal survey. This assessment occurred within the context of the overall advancement of space life and physical sciences and against the backdrop of advancement in related fields outside of the space sciences. The committee’s assessment of science

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⁴⁶ NRC, 2011, Recapturing a Future for Space Exploration, p. 369.

in the research community resulted in a picture of strong science advancement and achievement since the 2011 decadal survey. This assessment strongly suggests that the programmatic and budgetary commitment NASA and SLPSRA have made to address the decadal survey recommendations has produced results that translate into discoveries in support of exploration.

When considering these achievements in the context of planned deep space exploration missions, as requested in the charge to the committee and discussed in Chapter 2, the committee was struck by the fact that all concepts for deep space transit missions include prolonged periods of microgravity in a high radiation environment. No concepts for large-scale shielding or induced gravity exist in the defined mission plans. Rather than avoiding microgravity and radiation, NASA seeks to understand and mitigate the effects of those two spaceflight conditions in both the biological and physical systems involved in the extended missions in deep space.

Finding 3-1: Deep space exploration will take place for long periods of time in a microgravity and high-radiation environment; no large-scale induced gravity on the vehicle or station is foreseen with the current design reference missions, and the only shielding expected for radiation damage is that which is available on the space vehicle. Therefore, a fundamental understanding of both microgravity and radiation effects on biological and physical systems is essential for operational success and appropriate protection of astronauts.

Recommendation 3-1: As NASA continues to develop deep space mission scenarios involving long durations in microgravity, understanding the direct and interactive effects of radiation, microgravity and small habitats on human biology, and on the performance of biological and physical systems in space over long durations will need to have high priority in NASA science plans. NASA should also improve the coordination among the science research and engineering teams to better address the integrated effects in the design of the exploration elements and systems.