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11 The Role of the International Space Station UNIQUE STATUS AND CAPABILITIES Spanning a construction period of more than a decade and involving the coordinated efforts of many nations, the International Space Station (ISS) represents a stunning achievement of human engineering. After years of continual redesign, development, and assembly, the ISS is poised to begin fulfilling its intended role as a world- class scientific laboratory for studying biological and physical processes in the near absence of gravity. However, the ISS of today lacks a number of important research facilities, such as the 3-meter centrifuge, planned during earlier stages of its design. The assembly of major U.S., European, and Japanese components of the ISS will be completed in 2011—13 years after the launch of the first ISS component, the Russian Zarya module in 1998. (The Russians may launch their own pressurized laboratory to the station in the 2012-2013 time frame, but those plans are not yet finalized.) The ISS reached its full crew complement of six in May 2009 and should continue to hold that many until at least 2020, and perhaps beyond. Although limited by crew and equipment availability, significant science research was conducted during the construction phase of the ISS, with small observational experiments carried out shortly after the initial launch and more meaningful work beginning after the arrival of the Expedition 1 crew in late 2000. Flight research is generally part of a continuum of efforts that extend from laboratories and analog environ - ments 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 effort 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. Although research on the ISS is only one component of this endeavor, the capabilities provided by the ISS are vital to answering many of the most important research questions detailed in this report. The ISS provides a unique platform for research, and past studies of the National Research Council (NRC) have noted the critical importance of the ISS’s capabilities to support the goal of long-term human exploration in space.* These capabilities include the ability to perform experiments of extended duration, the ability to continually revise experiment parameters on the basis of previous results, the flexibility in experimental design provided by human operators, and the availability of sophisticated experimental facilities with significant power and data resources. The ISS is the only * See, for example, National Research Council, Review of NASA Plans for the International Space Station, The National Academies Press, Washington, D.C., 2006. 355
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356 RECAPTURING A FUTURE FOR SPACE EXPLORATION existing and available platform of its kind, and it is essential that its presence and dedication to research for the life and physical sciences be fully employed in the decade ahead. Before the 2010 budget announcement, the research plan of the National Aeronautics and Space Adminis - tration (NASA) for ISS utilization was expected to focus on objectives required for lunar and Mars missions in support of Constellation program timelines. Participation by the United States in the ISS was expected to end in 2016. There is now a de-emphasis at NASA on lunar missions and an extension of the ISS mission to 2020. The change in focus strengthens the need for a permanent research laboratory in microgravity devoted to scientific research in space focused both on fundamental questions and on questions posed in response to the envisioned needs of future space missions. AREAS OF RESEARCH ON THE INTERNATIONAL SPACE STATION Each of the panel chapters (Chapters 4 through 10) in this report describes critical research questions, most of which will need to progress through the use of more than one research platform, including ground-based laboratories and facilities such as drop towers or parabolic flights, to use of the ISS. The platforms and facilities required for each research area are discussed in the individual chapters, but it can be noted that for the majority of investigations, the ISS will provide the most advantageous research platform once the investigations transition to flight. In many cases, the ISS will be the only platform capable of meeting the requirements of investigations, and the ISS is the only platform that can provide a very long duration microgravity environment. Summarized in the following sections are examples of areas of past and future life and physical sciences research benefiting from, or requiring, the capabilities of the ISS. Life Sciences Research on the ISS Although it is impossible to list all the various biological research projects that were conducted on the ISS prior to the current era, insights from a 2008 report from NASA indicate a spectrum that, for plants, ranges from investigating the influences of gravity on the molecular changes in Arabidopsis thaliana to studying the mecha- nisms of photosynthesis, phototropism, and gravity sensing.1 Cellular biology studies included investigating gene expression changes in Streptococcus pneumonia and select microbes, exploring mechanisms of fungal pathogenesis and tumorgenesis, and observing changes in the responses of monocytes in cell culture, blood vessel develop - ment, and wound healing to the space environment. Also investigated were the chromosomal aberrations in the blood lymphocytes of astronauts and the effect of spaceflight on the reactivation of latent Epstein-Barr virus. Such analyses have revealed notable gaps in knowledge. For example, there has not been a comprehensive program dedicated to analyzing microbial populations and responses to spaceflight, yet microbes 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. The final report of the Review of U.S. Human Spaceflight Plans Committee (also known as the Augustine Commission or Augustine Committee)2 has emphasized 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 crew members with whom the astronaut will have to live and work effectively for many months while having limited contact with family and friends. All of these stressors are present in the ISS environment. Accordingly, ISS research studies could profitably determine mission-specific effects of these and other relevant stressors, alone and in combination, on the general psychological and physical well-being of astronauts and on their ability to perform mission-related tasks. Aspects pertaining to crew member interactions and the behavioral aspects of isolation and confinement have been examined on the ISS,3 but research with the full crew complement of six and prolonged mission durations is needed to address critical mission issues, such as the importance of sleep for astronaut performance and how best to maximize interpersonal behavior and maintain cognitive function so that the crew can function at its optimal level. Experiments related to human physiology on the ISS have examined the effects of spaceflight on the central nervous system and spinal excitability, skeletal muscle, bone maintenance and loss, cardiovascular control, pulmo -
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357 THE ROLE OF THE INTERNATIONAL SPACE STATION nary function, locomotor dysfunction, ground reaction forces, and nutritional status. Investigations have included the effects of radiation, the influence of light on the sleep-awake cycle, the risk of renal stones, and the advantages of select pharmaceutical drugs.4 This research has revealed important limitations on the current understanding of how humans react to the spaceflight environment and so to current approaches to maintaining astronaut health under these conditions. For example, recent findings for ISS astronauts who have been in space for 6 months or longer and who performed the recommended exercise regimens indicated that these countermeasures were unable to prevent loss of muscle mass or decrement in muscle performance. 5 It is clear that further research is essential for attaining an understanding of how and why human physiol - ogy is altered in space and for the design of effective countermeasures that will help to maintain the necessary functional homeostasis when humans are faced with altered gravitation on future missions. The ISS provides a unique opportunity to carry out both fundamental and translational research on organ and systemic function in the absence of the gravity variable necessary to meet these goals. The presence of humans in the space laboratory for up to 6 months enables the development of the much-needed databases for the various physiological systems as well as a thorough evaluation of select countermeasures such as exercise and pharmacological agents. Insights can be gleaned, for example, concerning the effect of radiation on coronary heart disease and pharmacological interventions to reduce bone resorption within a given tour. The prolonged access to space afforded by the ISS will also allow the probing of fundamental questions about animal biology not directly related to human health, such as the role of gravity in developmental biology, by examining how animals grow, develop, mature, and age. Notably absent from the 2008 report from NASA on ISS research accomplishments6 and in subsequent reports were references to animal research being conducted in ISS modules, even though the capability exists. Because of budgetary constraints and policy decisions, this essential component of microgravity research has not been implemented. Also eliminated was a provision for a small-animal centrifuge that the Russians had previously demonstrated as an effective countermeasure to the effects of microgravity in Cosmos 936.7 Thus, although there are some current facilities on the ISS to allow the inclusion of experiments on, for example, fruit flies or nematodes, the inclusion of an animal facility capable of housing rodents will be necessary. Without this capability, it will not be possible to conduct future experiments essential to advancing the basic understanding of animal physiology in space and to providing animal models for probing changes affecting the health of astronauts and for the development of suitable countermeasures. Thus, the availability of animals in the ISS National Laboratory would facilitate fundamental research on the effects of microgravity on inadequately studied systems, such as the immune, endocrine, reproductive, and nervous systems, while expanding knowledge of the mechanisms responsible for cellular and molecular changes in skeletal, muscu - lar, and connective tissue systems. With the availability of “knock out” and “disease” animal models, new insights on how microgravity affects physiological mechanisms can be secured from space experiments. In addition, there is the potential to gain new data on tissue healing (especially fractures) and on the growth and development of animals over multiple generations. One further element of research enabled by access to the ISS is its use as a test bed to facilitate studies on plant and microbial components of a bioregenerative life support system. Such research would allow exploration of the possibility of self-sufficiency for food production, water recycling, and regeneration of the craft’s atmo - sphere for extended crewed missions, obviating the need for costly resupply. 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 criti - cal elements shaping plant growth in space; each of the elements needs to be optimized in a rigorously tested technology platform designed to maximize 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 a long-term human presence in space. Developing a sustained research program combining the 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. These examples highlight the ISS as an essential and integral component of any implementation of the life sciences research outlined in this decadal survey.
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358 RECAPTURING A FUTURE FOR SPACE EXPLORATION Physical Sciences Research on the ISS The reduced-gravity platforms currently available to researchers in the physical sciences are aircraft, drop towers, sounding rockets (in Europe and Japan), the space shuttle, and the ISS. Aircraft provide partial gravity for 20 to 25 s, with a g-jitter of 10–2 g. Drop towers allow microgravity for a few seconds, and sounding rockets for a few minutes. In the space shuttle, gravity levels on the order of 10 –4 g can be sustained for long periods of time. However, the ISS is a very long duration experiment platform providing acceleration levels on the order of 10 –5 to 10–6 g under the right conditions.8 The premise of the ISS has been that it will serve as a laboratory for research and for the development and testing of technologies that facilitate space exploration. It also provides a platform for basic and applied research in biological and physical sciences aimed at enhancing a fundamental understanding of phenomena and processes with eventual space and terrestrial applications. The facilities available on the ISS for U.S. researchers in the physical sciences include the Microgravity Sci - ence Glovebox, the Combustion Integrated Rack, the Fluids Integrated Rack, the Materials Science Research Rack, the Space Dynamically Responding Ultrasound Matrix System (Space DRUMS), and several multiuser EXPRESS Racks.9 In addition, the European Space Agency has the Fluid Science Laboratory, and the Japanese Aerospace Exploration Agency has the Ryutai and Kobairo Racks for fluid physics and materials science research. Through international collaboration, all of these facilities can be used to advance research in the physical sciences. As of 2009, NASA had carried out 20 expeditions to the ISS. These expeditions have led to 52 experiments in the physical sciences, and 15 more were planned for expeditions 21 and 22. Some of the recent experiments that have been conducted in the basic fluid physics area include gelation and phase separation in colloidal suspen - sions, critical phenomena, crystallization of glasses, growth of dendritic crystals, properties of magneto-rheological fluids, properties of particle growth in liquid-metal mixtures, and stress/strain response in polymeric liquids under shearing. In the area of combustion and fire safety, investigations have included smoke and aerosol measurements and the study of soot emission from gas-jet flames. The fundamental and applied microgravity research in the physical sciences for which the ISS can serve as a laboratory is described in detail elsewhere in this report (see Chapters 8, 9, and 10). Here only a brief summary is presented. In the fundamental physics area, the topics of interest are soft matter and complex fluids (materials with multiple levels of structure), including colloids, polymer and colloidal gels, foams, emulsions, liquid crystals, dusty plasmas, and granular materials. Because of the gradients that develop in their properties under gravity, the micro - gravity environment provides ideal conditions for understanding the dynamic behavior of such materials, allowing the testing of ideas about fundamental physical processes—varying from examination of the constitutive equations that describe the strain-rate relationships for granular materials through to analysis of crystal growth—without the confounding effects of convection-based imperfections in material deposition. Precision measurements of funda - mental forces and symmetries are another area that can benefit greatly from the microgravity environment of the ISS. Some of the subtopics of interest are the study of the equivalence principle and theories behind the standard model and general relativity to ask whether different kinds of matter interact with gravity in the same way. The study of quantum gases can lead to a range of new technologies and understanding, from developing ultraprecise atomic clocks and quantum sensors to resolving the mechanism of superconductivity in high-temperature super- conductors. Major advances in the understanding of phenomena near the critical point can be achieved through well-conceived experiments conducted on the ISS. The completion of the Low Temperature Microgravity Physics Facility would significantly enhance the capability of the ISS to support experiments in fundamental physics. Applied physical sciences include fluid physics and heat transfer, combustion, and materials science. In the fluid physics area, multiphase flow phenomena and associated heat transfer have been identified as a critical area that would benefit greatly from experiments in the long-duration microgravity environment of the ISS. Experiments on pool boiling; forced-flow boiling, including phase separation and flow stability; closure relations for interfacial and wall heat, mass and momentum transfer; condensation; and capillary-driven flows would provide significant knowledge and a database with which computer models could be validated and systems could be designed. In addition, research aimed at increasing the efficiency and lifetime of power-generation and energy-storage systems would reduce costs by reducing mass and redundancy. All of these systems would benefit from research, proto - typing, and testing on the ISS. For example, key advantages of spaceborne power systems based on the Rankine
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359 THE ROLE OF THE INTERNATIONAL SPACE STATION 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. Unfortunately, little is known at present about the behavior of two-phase flows and associated heat transfer in a reduced-gravity environment. The possibility of developing a multipurpose, multiuser facility for multiphase flow research on the ISS should therefore be considered. Such a facility would also act as a catalyst for bringing together national and international researchers to address the problem in a cost-effective and comprehensive manner. Significant insights into the static and dynamic behavior of granular materials and dusts could be gained through experiments on the ISS. Such an understanding would be of value for applications on Earth and for human and robotic exploration of the Moon and Mars. (It is noteworthy that the Mars rover Spirit has been stuck in the martian soil, a granular material, since May 2009.) Advances in propulsion performance (specific impulse, efficiency, thrust to weight, propellant bulk density), reliability, thermal management, power generation and handling, propellant storage and handling, and strategies for refueling on orbit are all key drivers for dramatically reducing mass, cost, and mission risk. The ISS provides unique opportunities for advances in a number of these areas through research on processes such as cryogenic two-phase fluid management, propellant transfer, engine starts, flame stability, active thermal control of injectors and combustors, and cryogenic fluid management. In summary, the ISS platform is an essential and integral component of any implementation of the physical sciences research outlined in this decadal survey. Utilizing the ISS for Research The decadal survey committee strongly recommends that NASA intensify the utilization of the ISS as a world-class research laboratory engaged in both basic and applied research that enables space exploration and is enabled by the microgravity environment of the ISS. The goal should be to maximize the utilization of existing facilities and to engage world-class scientists and engineers to carry out research that leads to the development of space-related technologies. Ground-based experimental and theoretical work should form a significant component of the overall activity. Cross-disciplinary research should be emphasized, and a research portfolio with prioritization should be devel - oped and shared with the technical community.10 To develop a vibrant research community that is committed to space-related research, NASA should have a firm plan for sustaining the research by providing adequate resources. Aside from benefiting directly from the research, NASA would be contributing to the creation of the workforce for the future. The process, from the acceptance of a proposal to preparation of the flight experiment to conduct of experiments on the ISS, should be streamlined, with a reduction in time from start to finish. This is essential to keep graduate students and other researchers engaged in the research activity. Some of the experimental rigs that have already been flown on the ISS can serve as facilities for future research investigations in the physical sciences. NASA should reconsider the placement of a centrifuge on the ISS so that long-duration partial-gravity experiments can be conducted. NASA should also strengthen and expand its collaborations with international partners. This would allow access to the facilities of the partner countries, avoid a duplication of research, and allow U.S. researchers to accomplish much more than they could otherwise. Caveats Discussed throughout this report are various topics within each of the areas described above. The committee reiterates, however, that although the ISS is a key component of the research infrastructure to be utilized by a biological and physical sciences research program, it is only one component of a healthy program. Other platforms will play an important role and, in particular, research on the ISS will have to be supported by other platforms, including a parallel ground-based program, to be scientifically credible.
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360 RECAPTURING A FUTURE FOR SPACE EXPLORATION REFERENCES 1. Evans, C.A., Robinson, J.A., Tate-Brown, J., Thumm, T., Crespo-Richey, J., Baumann, D., and Rhatigan, J. 2009. International Space Station Science Research Accomplishments During the Assembly Years: An Analysis of Results from 2000-2008. NASA/TP-2009-23146-Revison A. NASA Johnson Space Center, Houston, Tex., p. 1. 2. Review of U.S. Human Spaceflight Plans Committee. 2009. Seeking a Human Spaceflight Program Worthy of a Great Nation. Final Report. Available at http://www.nasa.gov/pdf/396093main_HSF_Cmte_FinalReport.pdf, p. 113. 3. Evans, C.A., Robinson, J.A., Tate-Brown, J., Thumm, T., Crespo-Richey, J., Baumann, D., and Rhatigan, J. 2009. International Space Station Science Research Accomplishments During the Assembly Years: An Analysis of Results from 2000-2008. NASA/TP-2009-23146-Revison A. NASA Johnson Space Center, Houston, Tex., p. 1. 4. Evans, C.A., Robinson, J.A., Tate-Brown, J., Thumm, T., Crespo-Richey, J., Baumann, D., and Rhatigan, J. 2009. International Space Station Science Research Accomplishments During the Assembly Years: An Analysis of Results from 2000-2008. NASA/TP-2009-23146-Revison A. NASA Johnson Space Center, Houston, Tex., p. 1. 5. Trappe, S., Costill, D., Gallagher, C., Creer, A., Peters, J.R., Evans, H., Riley, D.A., and Fitts, R.H. 2009. Exercise in space: Human skeletal muscle after 6 months aboard the International Space Station. Journal of Applied Physiology 106:1159-1168. 6. Evans, C.A., Robinson, J.A., Tate-Brown, J., Thumm, T., Crespo-Richey, J., Baumann, D., and Rhatigan, J. 2009. International Space Station Science Research Accomplishments During the Assembly Years: An Analysis of Results from 2000-2008. NASA/TP-2009-23146-Revison A. NASA Johnson Space Center, Houston, Tex., p. 1. 7. Kotovskaya, A.R., Ilyin, E.A., Korolkov, V.I., and Shipov, A.A. 1980. Artificial gravity in spaceflight. Physiologist 23(Suppl. 6):S27-S29. 8. DeLombard, R., Hrovat, K., Kelly, E., and McPherson, K. 2004. Microgravity environment on the International Space Station. AIAA Paper 2004-0125. NASA/TM-2004-213039. NASA Glenn Research Center, Cleveland, Ohio. 9. Robinson, J.A., NASA. 2009. “International Space Station,” presentation to the Committee for the Decadal Survey on Biological and Physical Sciences in Space, August 19. National Research Council, Washington, D.C. 10. National Research Council. 2003. Factors Affecting the Utilization of the International Space Station for Research in the Biological and Physical Sciences. The National Academies Press, Washington, D.C.