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An Initial Review of Microgravity Research in Support of Human Exploration and Development of Space 1 Introduction NASA AND THE HUMAN EXPLORATION OF SPACE A major NASA goal continues to be the exploration of space by humans, a fact reflected by the inclusion of the Human Exploration and Development of Space (HEDS) enterprise in the current organizational structure of NASA. In 1995, NASA reorganized its programs into five strategic enterprises, each representing a core mission of the agency. The Microgravity Research Division (MRD) and Life Sciences Division, both formerly part of the Office of Space Sciences and Applications, were placed within the new HEDS enterprise. The four HEDS goals1 promulgated by NASA are to (1) increase knowledge of nature's processes by use of the space environment; (2) explore and settle the solar system; (3) achieve routine space travel; and (4) enrich life on Earth through people living and working in space. NASA proposes that these strategic goals will be accomplished through scientific research, engineering technology, and utilization of the Space Shuttle and the International Space Station (ISS). NASA's first objective under HEDS Goal 1 stipulates that the agency conduct scientific research to understand the fundamental role played by gravity and the space environment in biological, chemical, and physical systems. NASA's strategy for accomplishing that objective is to investigate, using a peer- reviewed research program, processes and phenomena normally obscured or complicated by the presence of gravity. The second objective under Goal 1 is to use HEDS research facilities innovatively to achieve breakthroughs in science and technology. NASA's microgravity program has for 20 years been addressing those fundamental scientific objectives currently subsumed within the HEDS enterprise. As the present administrator of that program, MRD has met this challenge primarily by supporting a broadly based program of peer-reviewed microgravity research covering the disciplines of fluid mechanics and transport phenomena, combustion, biotechnology, materials science and processing, and fundamental
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physics.2 (The Life Sciences Division holds a similar responsibility for research on gravitational effects on biological systems.) Currently, microgravity research is viewed as a complex of laboratory sciences conducted both on the ground and in space that generate fundamental knowledge in physics, chemistry, biotechnology, and engineering. A recent report issued by the Space Studies Board of the National Research Council3 found that "Access to prolonged periods in space as well as to other short-duration, ground-based microgravity facilities, is beginning to provide researchers with the opportunity to apply the methods of the physical and biological sciences to a new regime of low-gravity experiments" (p. 25). As of the writing of this report, a number of dedicated microgravity spaceflights have been completed by NASA, including the Spacelab missions USML-1 and -2, IML-1 and -2, and others, which have provided major new results and accelerated progress in microgravity science.4 HEDS TECHNOLOGIES As envisioned by the HEDS enterprise, the ability for humankind to expand and prosper beyond the confines of our planet depends on the continued development and integration of those advanced technologies that will provide safe, affordable access to space and the ability to carry out both human and robotic exploration of the Moon and inner planets. The pacing technologies for the currently planned human exploration and development of space must perform many terrestrially familiar technical activities, such as energy conversion, communications and control systems, construction and maintenance of habitats, fluid and thermal management, and fire safety. Included also are more specialized space-related technologies such as propulsion, life support, and the in situ extraction of materials, including water, oxygen, and propellants, from the surfaces of extraterrestrial bodies.5 The commonplace familiarity with a multitude of terrestrial technologies contrasts sharply with a much more limited experience in applying the technologies for the exploration and development of space. Conventional design criteria extrapolations and scaling principles, which are useful and validated for engineering systems operating in gravity environments approximating terrestrial levels, may not be applicable to systems required to function at near-zero acceleration or on small extraterrestrial bodies. This situation has the potential of greatly limiting the pace of development for some critical mission-related technologies needed to accomplish planned robotic and crewed missions to extraterrestrial bodies. In fact, even where straightforward extrapolations of terrestrial engineering experience exist to adapt systems to operate in space, or on the Moon and Mars, they still must be tested and proven by actual in-space demonstration. Moreover, where current terrestrial technologies remain immature, especially from the standpoint of engineering practice, the challenges to extend and verify them for spaceflight applications become much greater, perhaps even limiting the rate of progress in accomplishing HEDS goals.
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AN INITIAL APPRAISAL Numerous technological barriers must eventually be overcome to accomplish long-term exploration, development, and habitation of space by humans. Many of these technical issues can be resolved only through a deeper understanding of the behavior of fluids, materials, and biological systems in a reduced-gravity environment. This report takes a preliminary look at these technical issues. Many of the technologies that may be needed to fulfill HEDS objectives, such as improved solid-state electronic systems for high-volume data transfer and communication, are not likely to be affected by gravity levels. Others, such as fluid loops for heat transfer, energy production, and life-support systems, clearly will be. This report concentrates on potential HEDS technologies that require a better understanding of the low-gravity behavior of fluids, materials, and structures. Inasmuch as most of the specific mission-related technology needs are still being identified by NASA, the committee chose at this time to consider only broad areas of HEDS technology, with some specific technologies cited as illustrative examples. This initial report therefore begins to identify and address those areas of technology to which NASA's microgravity science program can directly contribute by strengthening the underlying basic knowledge needed to evaluate, improve, or create the specific solutions to mission-critical problems encountered by the HEDS enterprise. It is planned that, as NASA's plans for exploration mature and specific technologies are targeted, this committee will prepare a more detailed report for the second phase of this study. In Chapter 2, the current microgravity research program of MRD is briefly described and compared to HEDS Goal 1, and the challenges posed by the remaining HEDS goals are discussed. In Chapter 3, broad areas of HEDS technologies to which microgravity research could contribute are identified and described, and the fundamental research areas and questions connected to those technologies are reviewed. Chapter 4 contains a discussion of programmatic issues related to MRD support of the HEDS enterprise and specifies some recommendations in these areas. 1. National Aeronautics and Space Administration (NASA). 1996. NASA's Enterprise for the Human Exploration and Development of Space: The Strategic Plan. NASA, Washington, D.C. 2. Space Studies Board, National Research Council. 1995. Microgravity Research Opportunities for the 1990s. National Academy Press, Washington, D.C. 3. Space Studies Board, National Research Council. 1995. Microgravity Research Opportunities for the 1990s. National Academy Press, Washington, D.C.
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4. Space Studies Board, National Research Council. 1995. Microgravity Research Opportunities for the 1990s. National Academy Press, Washington, D.C.; see also National Aeronautics and Space Administration (NASA). 1996. NASA's Microgravity Science and Applications: Program Tasks and Bibliography for FY 1995. NASA-TM-4735, NASA, Washington, D.C. 5. National Aeronautics and Space Administration (NASA). 1991. Integrated Technology Plan for the Civil Space Program, 1991. NASA-TM- 107988, NTIS Order Number N92-31634, National Technical Information Service, Springfield, Va.; see also NASA. 1992. Advanced Technology for America's Future in Space: A Review of NASA's Integrated Technology Plan for the Civil Space Program. NTIS Order Number N92-33937, National Technical Information Service, Springfield, Va.