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1 Introduction and Overview Performing experiments in low Earth orbit has been the primary focus of much of the research funded by NASA's Physical Sciences Division (PSD) and its predecessors for over 30 years. That research examined phenomena in which the physical processes under investigation are significantly affected by gravity. Along with experiments destined for flight, in the past 10 years the division has made a concerted effort to develop an extensive ground-based research effort. The ground-based program includes research in which gravity plays a major role and that, in addition, (1) requires further experimentation to demonstrate conclusively both the need for a microgravity experiment and the importance of the results that could be obtained from a spaceflight experiment or (2) involves only theoretical investigations. More recently, the PSD has begun to expand beyond the traditional microgravity-related disciplines to include research in which gravity may have no role, such as biomolecular physics and chemistry and research in support of the human exploration and development of space (HEDS). The traditional program can be divided into five broad areas, all of which focus primarily on phenomena that are strongly perturbed by gravity. These areas are biotechnology, combustion, fluid physics, fundamental physics, and materials science. The biotechnology program focuses primarily on two fields protein crystal growth and the effects of gravity on cell and tissue formation. The combus- tion program encompasses efforts ranging from research in support of fire safety in space to studies of basic combustion phenomena. The research in fluids involves projects on topics as diverse as colloidal crystallization and pattern formation during convection. Fundamental physics had its genesis as a low- temperature physics program but more recently has been expanded to include topics such as laser cooling, cosmic rays, and atomic clocks. The materials science program has funded research in a wide variety of areas, from solidification and crystal growth to the thermophysical properties of liquids cooled far below their melting points. To these existing disciplines the PSD is considering adding research in biomolecular physics and chemistry and in nanotechnology, as well as research in support of HEDS. In its phase I report (NRC, 2001), the Committee on Microgravity Research proposed two criteria for adding research in these new areas: 12

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INTRODUCTION AND OVERVIEW 13 1. Directly address challenges at the interface between the physical sciences, engineering, and biology in support of NASA's mission, preferentially capitalizing on existing expertise or infrastructure in the Physical Sciences Division, and 2. Support research either not typically funded by other agencies or to be conducted in close partnership with other agencies. The phase I report also identified broad areas of promising research into which the division might expand: nanoscale materials and processes, biomolecular physics and chemistry, cellular biophysics and chemistry, and integrated systems for HEDS. Detailed descriptions of research in these areas are provided in this report. Establishing priorities between the existing microgravity programs and research in the new areas requires assessing the impact of the research and the quality of the investigators in the existing microgravity program. Clearly, it is not in the best interest of NASA or the nation to Reemphasize a vibrant, productive program simply to move into a new research area, while it is equally clear that poorly performing programs should not be continued. Accordingly, in this report the Committee on Microgravity Research assesses the research in the existing microgravity program, paying attention to the following: 1. The degree to which knowledge gained from microgravity research on a given topic has contrib- uted to the larger field of which the research is a part; 2. Progress in understanding the microgravity research questions posed on each topic; and 3. The potential for further progress in each area of microgravity research. To assess quantitatively the impact of the NASA-funded work, the committee employed a number of metrics. While any of these metrics taken alone can be misleading, a synthesis of more than one provides a reasonable measure of the success of a program. Literature citations of the research were one of the possible metrics used by the committee. A given paper cited in this report as an example of strong impact was generally selected because it either was known to have been highly cited in the literature (the number of citations needed to qualify varies with subfield) or because it had a high citation rate (in the case of a recent publication). Other metrics used by the committee to judge the importance of an investigation were the prestige of the journal in which the results were published, whether the results caused textbooks to be altered, and whether there is any documented influence on industry or NASA. At NASA's request the committee did not examine the NASA biotechnology effort as this program was recently reviewed (NRC, 2000~; however, in the interests of completeness the findings and conclu- sions of that study have been encapsulated in this report. The microgravity program has evolved considerably since its inception as the materials processing in space program of the Skylab era. With the exception of the biotechnology program, in the early 1990s a major emphasis was given to outreach to the science communities of which the microgravity disci- plines were a part. This outreach took the form of biannual conferences in each of the disciplines prior to the release of a NASA Research Announcement (NRA) and extensive canvasing of the community with notification of the opportunities to apply for support. The result was a large increase in the visibility of the combustion, fluid physics, materials, and fundamental physics programs and in the number of proposals submitted. The impact of this outreach became clear as the committee assessed the quality of the investigators and of the research in the program. That time frame also saw the establish- ment of the fluids and combustion programs in their current forms, and in the past 5 years, there has been an expansion of the fundamental physics program.

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4 ASSESSMENT OF DIRECTIONS IN MICROGRAVITY AND PHYSICAL SCIENCES RESEARCH AT NASA In addressing these issues in the traditional microgravity disciplines, it is necessary to remember that there are drawbacks to performing microgravity experiments that do not exist for ground-based experimentation. This problem is a basic dilemma that must be considered in any evaluation of the microgravity program. Aside from the obvious financial costs, which are not addressed further in this report, the difficulty of extracting large amounts of data from the microgravity environment cannot be ignored. An earthbound laboratory can in principle bring to bear a large array of diagnostic equipment and accommodate the often sizable space requirements of the experiment. Moreover, if long run times are needed to collect data, the ground-based laboratory routine can be adjusted to accommodate such a requirement. These advantages are difficult to achieve in microgravity. Thus, the limited data set acquired in microgravity will only be of value in instances where it is nearly impossible to extract the same information under normal laboratory conditions. Moreover, performing experiments in space frequently requires the development of instrumentation that is unique to a particular experiment. This can require a significant lead time. often on the order of a decade or more. which takes un a significant ~ ~7 ~ ~ 1 ~7 , r , , ~ Bare ~ ~ A, ~ ~ , ~ r~ - a, , , ,~ ~ ~ ~ portion of an ~nvesUgator s career. When combined with limited flight opportunities, these drawbacks explain the relative scarcity of flight experiments in many disciplines over the past decade. The recent financial problems of the International Space Station (ISS) have brought a major uncer- tainty to the future of the microgravity program. Many of the facilities that were destined for the ISS have been delayed, and the crew time available for science has been drastically curtailed. Although additional funding for a few of the facilities has been secured, their final status remains uncertain. The original 2002 operational date for the ISS has slipped by several years. Moreover, as the report of the International Space Station Management and Cost Evaluation Task Force noted, "The existing ISS Program Plan for executing the FY 02-06 budget is not credible" (IMCE, 2001~. An analysis of the effects of the ISS cutbacks on the science that can be performed on the ISS is given in Factors Affecting the Utilization of the International Space Station for Research by the NRC Task Group on Research on International Space Station (NRC, 2003~. The financial crisis has also affected the ground-based program. For example, a current NRA explicitly states the following: "EDjue to severe resource limitations, we do not plan to make flight definition awards in the combustion area from this NRA" (NASA, 2001~. Whether this is a temporary setback or the beginning of the end of the microgravity program remains to be seen. Given the uncertainty in the future, the committee did not consider the availability of ISS resources in formulating its findings and recommendations. REFERENCES International Space Station Management and Cost Evaluation (IMCE) Task Force. 2001. Report by the IMCE to the NASA Advisory Council. P. 7. Available online at . Accessed April 30, 2003. NASA. 2001. Research Opportunities in Physical Sciences, Physical Sciences Ground-based and Flight Research. NRA 01- OBPR-08, Appendix C, p. C-7. NASA, Washington, D.C. National Research Council (NRC), Space Studies Board. 2000. Future Biotechnology Research on the International Space Station. National Academy Press, Washington, D.C. National Research Council, Space Studies Board. 2001. The Mission of Microgravity and Physical Sciences Research at NASA. National Research Council, Washington, D.C. 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., in press.