Click for next page ( 38


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 Microgravity Research Opportunities for the 1990s PART I—OVERVIEW 2 Recommendations and Conclusions INTRODUCTION The microgravity environment presents unique opportunities to perform important experimental laboratory research in a number of fundamental and applied areas. The five scientific disciplinary areas that can benefit in varying degrees are (1) fluid mechanics and transport phenomena, (2) combustion, (3) biological sciences and biotechnology, (4) materials science, and (5) microgravity physics. There are important scientific questions in these disciplines that cannot be addressed by experiments at normal Earth gravity. This provides a major impetus for the microgravity research program. REPORT MENU NOTICE Microgravity research is also necessary for, and fundamental to, the MEMBERSHIP exploration of space. Fluid and thermal systems and materials processes that are PREFACE EXECUTIVE SUMMARY essential to mission-enabling technologies for extended space operations will PART I generally behave differently under reduced gravity conditions. Microgravity CHAPTER 1 research opportunities will frequently be driven by the technological needs of CHAPTER 2 NASA's programs. It is well understood that engineering, applied science, and PART II fundamental science are interconnected. Some of the obvious engineering issues CHAPTER 3 that should influence the microgravity research program are the ignition, CHAPTER 4 propagation, and extinction of spacecraft fires; the fluid dynamics and transport CHAPTER 5 processes associated with the handling, storage, and use in space of water, CHAPTER 6 waste, foods, fuels, air environments, and contaminants; the handling, joining, CHAPTER 7 and reshaping of materials in space; and the dynamics and chemistry of mining PART III and refining of resources in non-Earth environments. CHAPTER 8 APPENDIX A APPENDIX B The committee reaffirms the findings of the previous and first report, Toward a Microgravity Research Strategy,1 of the Committee on Microgravity Research that there is little potential for a successful program to develop manufacturing on a large scale in space for the purpose of returning high-quality, economically viable products to Earth. The cost of transporting raw materials into file:///C|/SSB_old_web/mgoppch2.htm (1 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 space and products back to Earth will generally be much too high to be economical. Limited amounts of certain products, however, might usefully be made in space for scientific study. A set of recommendations has been developed for the microgravity sciences that has several salient features. Five science areas are recommended for long-term support with a balance of support among these areas-fluid mechanics and transport phenomena, combustion, biological sciences and biotechnology, microgravity physics-and within materials science, the subarea of metals and alloys. Fields that will benefit significantly less from a microgravity environment are polymers, epitaxial layer growth on single-crystal substrates, large single inorganic crystal growth, and ceramics and glasses. It is noted that the common and major theme among the five recommended areas is that of fluid mechanics and transport phenomena. The committee's recommendations emphasize the development of research opportunities, modification of NASA policies and procedures, and interactions between NASA and the investigators that will provide an environment necessary for first-class laboratory science. The importance of a strong ground-based program is also stressed. The roles of microgravity research are discussed both for the advancement of general scientific knowledge and for the development of enabling technologies for space missions. The lists of scientific recommendations identify the obvious opportunities for immediate and significant scientific impact. A number of points were considered in arriving at the recommendations for each discipline. The importance and compelling nature of the scientific questions and the perceived impact on the field were given greatest weight and established the context for further recommendations. Scientific questions and objectives, however, were examined further in terms of their requirement for, and probable benefit from, a microgravity environment. Clearly, the priority of a given objective was reduced if alternative or superior approaches were available. The type of microgravity facility required for the investigations and the quality of the microgravity environment required were also considered. These considerations addressed experimental duration, maximum allowable acceleration level, permissible radiation levels, degree of human or robotic interaction, and complexity of diagnostics. The following questions were asked: Have the issues been explored sufficiently in conventional laboratories on Earth, have adequate theoretical and computational analyses been performed, and are models for the process available? Finally, the resource requirement and costs were considered in the broad context of the current, and anticipated, microgravity research program. In addition to scientific considerations, means are recommended to improve the scientific quality and increase the efficiency of microgravity research. As a result, suggestions are included that relate to instrument design and implementation, procedural matters, and interactions among the space agencies and the investigator communities. The research areas discussed in this report are subsets of much broader file:///C|/SSB_old_web/mgoppch2.htm (2 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 disciplines. Only a small fraction of the total activities in each occurs within the microgravity program, and no attempt has been made to evaluate fully or prioritize all of the research in a particular discipline. Only the microgravity component of each discipline is addressed in detail. Furthermore, the cost-benefit of a microgravity program has not been compared to the cost-benefit of experiments on similar subjects in the terrestrial environment. Experiments that can be performed adequately at Earth gravity are not recommended for spaceflight. Further, because of the limited results available from experiments that have been flown in space, the recommendations of this report cannot be highly detailed or exclusive. There are a number of subjects that require further exploratory investigation before detailed objectives can be defined. Some areas, however, can be identified as more promising than others. This report also does not address the NASA commercial program or international programs in microgravity research. These topics will be addressed in the future by this committee. In summary, the recommendations in this report emphasize the contribution of microgravity research to the advancement of science and technology in general and of space exploration in particular. The report also deemphasizes the concept of manufacturing products in space for their return to Earth. Adjustments in NASA's structures, policies, and procedures for conducting laboratory science in space are required by these recommendations. Finally, priorities are suggested for topics within certain microgravity science disciplines and subdisciplines. The duration of experiments, the regime of parameters available to experimenters, and the ability to demonstrate reproducibility of results in many microgravity experiments create the need for extended-duration orbiting platforms. The recommendations have value, however, whether such platforms become available or the microgravity program continues only with existing facilities. The findings and recommendations of this report are consistent with the preliminary statements of the first report of this committee, Toward a Microgravity Research Stategy. This second report is broader in scope and includes substantially greater detail in analysis and recommendations. AREAS RECOMMENDED FOR EMPHASIS IN MICROGRAVITY RESEARCH Microgravity science is highly interdisciplinary and broad. The major prospects and opportunities in each of the major disciplines are summarized in this section. Limitations of opportunities are also discussed. file:///C|/SSB_old_web/mgoppch2.htm (3 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 Fluid Mechanics and Transport Phenomena Fluid mechanics and transport phenomena are influenced significantly by gravity. As a consequence, different behaviors may be expected for many fluid configurations in a microgravity environment, both with and without heat and mass transfer. Also, the reduction of gravitational body forces leads to dominance by other forces normally obscured in terrestrial environments such as surface tension and electrical forces. Because fluid mechanics and transport processes are involved in most of the areas of microgravity research, they represent a common theme for much of the subject. Basic research is required to understand and describe the characteristics of transport phenomena under low-gravity conditions. Fluid mechanics and transport phenomena also play an essential role in many space-based technologies. Space system designers will be challenged to develop new enabling technologies and critical concepts that involve fluid mechanics and transport phenomena in low-gravity environments. Unfortunately, predictive models for the low-gravity performance and operation of those technologies are often inadequate. In fact, some researchers believe that useful predictive models do not exist. Strictly empirical approaches are not preferred for low-gravity applications because they are costly and time consuming, and can result in products or systems that are neither reliable nor efficient. Priority should be given to the study of phenomena that are unique to the low-gravity environment and to those that are critical to space mission-enabling technologies and commercial developments. Among the basic topics that may be studied uniquely in the low-gravity environment are the following: Surface tension gradient-driven flows and capillary effects. These are frequently obscured in a terrestrial environment but may become significant or dominant in reduced gravity. These topics warrant investigation because they are not well understood and because surface tension-driven flows are ubiquitous for many mission-enabling technologies. Multiphase flows. Many processes involve multiphase flows. Gravity imposes a specific orientation on multiphase fluids, structures, and organizations (e.g., gas-liquid, liquid-solid). In a reduced-gravity environment, orientation will be much less important; flows and associated transport phenomena become significantly different. Diffusive transport processes. At 1 g, multicomponent fluids experience various modes of thermosolutal convection. In addition, there are other effects due to different diffusivities for heat and mass. With reduced- buoyancy convection, the complex interactions can be separated and analyzed. Furthermore, transport effects masked at 1 g, such as Soret and Dufour phenomena, can become important. file:///C|/SSB_old_web/mgoppch2.htm (4 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 Colloidal phenomena. At 1 g, the nature of surface and short-range forces, and their consequences in colloidal systems, are often difficult to study because of the complications associated with competing gravitational effects. Microgravity provides an opportunity for study of colloidal systems in which short- range forces are dominant, and this can contribute in an important way to understanding these physicochemical interactions. The above topics are important to biotechnology, combustion, materials science, and other areas of science. The following topics deserve attention not only for their intrinsic scientific importance but also to provide a knowledge base for space technologies and applications: Convective processes at low Reynolds number. Investigation of low Reynolds number flows with density variations at reduced gravity levels will reveal the altered nature of transport phenomena in a new range of parametric conditions. Transport processes with a phase transition. The modified processes of condensation, evaporation, and boiling in a low-gravity environment with dominant interfacial forces require study. Complex materials. Porous, granular, and colloidal media, and foams are complex materials whose structures and functions can differ in microgravity. Research is necessary to understand the behavior of such materials in a low- gravity environment and may also lead to a better understanding of their behavior at 1 g. Materials processing. Buoyancy, sedimentation, and interfacial phenomena influence such processing methods as fluidized-bed hydrogenation, electrowinning, and vapor-phase pyrolysis and therefore should be investigated. Physical processes in life- and operating-support systems. Some of the effects indicated above apply to processes such as power generation and storage, water purification, oxygen production, and fuel and fluid storage and management. Numerous parameters govern the topics listed above. Judicious choice of the parameter ranges and configurations will be required to ensure that the information obtained is directly applicable to the reduced-gravity environment. Combustion file:///C|/SSB_old_web/mgoppch2.htm (5 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 Combustion involves fluid mechanics, mass and heat transport, and chemical reaction-all directly or indirectly subject to numerous gravitational effects. The number of parameters to be investigated is large. Several phenomena (e.g., smoldering and flame spread) require long-duration observations and measurements. Furthermore, reproducibility is an issue. Recommendations concerning equipment and facilities include the following: An extended orbiting platform capability will be required for many combustion experiments. Ground-based combustion experiments must be undertaken to develop miniaturized diagnostics and experimental apparatus and techniques for performing multiple repetitions of a specific experiment. Experimental space is at a premium in microgravity research, and because of the many variables in combustion and the difficulties in achieving reproducibility, assurance of data quality is needed. The following areas of emphasis are recommended in order of priority: 1. The highest-priority area, and one of intense practical interest, is that of fires in spacecraft and potential extraterrestrial bases. Microgravity and reduced- gravity research is required because of the potential for disaster posed by fires. Much is still unknown about fires in altered gravity conditions. A variable- gravity capability is required for a full understanding of gravitational effects and for implementation of fire safety measures in spacecraft. 2. In fire research, several subfields of combustion need to be investigated under microgravity conditions. Ignition, flammability limits, smoldering, flame spread, and extinguishment are all deserving of detailed study. Variables must include fuel type and phase, fuel/oxidizer ratio, ambient oxidizer concentration, forced and free convection, ignition source, and extinguishment methodology. 3. Turbulent combustion processes are highly important on Earth but cannot be probed at 1 g at the small size scales that typically occur. Reduced gravity would allow a scale-up in overall size without the introduction of major buoyancy effects, thus permitting access to the smallest scales of turbulence that are important to the problem. Here, the Reynolds number based on a forced flow velocity would remain fixed in the scaling process. 4. Research on laminar premixed and diffusion flames and spray-flow interactions should be conducted, again because of the importance of these processes on Earth. The same problem occurs here as with turbulent flames. Even though gravity is not an important parameter for many practical devices, the study of fundamental combustion processes is often impeded at 1 g because attempts at scale-up introduce unwanted buoyancy. file:///C|/SSB_old_web/mgoppch2.htm (6 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 Biological Sciences and Biotechnology The biological sciences and biotechnology are experimental disciplines that are highly dependent on empirical approaches to the solution of problems and on the continued discovery and development of useful research systems. Unlike many other branches of microgravity science, such as fluid dynamics or materials science, there may be no firm foundation of theory, only a limited accumulation of experience. Thus, a reasonably high tolerance for scientific risk (which is clearly distinct from safety risk) should be allowed in investigations in the biological sciences. The science community should be prepared, however, to support research in this area on the basis of its long-term potential and importance, especially its relevance to human spaceflight. In addition, since research on biological topics commonly requires experiments that take a long time to complete, an extended-duration orbiting capability is necessary. The following topics deserve priority in the order listed. The first two topics have some demonstrated successes and therefore the likelihood of further success. The last two topics are exploratory. 1. In studies to improve methods of crystallization of macromolecules for use in diffraction studies, additional experiments should focus on defining quantitatively those macromolecular crystal growth mechanisms affected by gravity. Direct, high-resolution observation of the crystal growth process by a variety of optical techniques and precise monitoring of ambient parameters such as temperature and pH should be included. Ideal test systems should be identified and carefully delineated. 2. Further experimentation is needed in both terrestrial and microgravity environments to develop new methods, materials, and techniques to exploit the potential of microgravity, where it exists, for improvements in biochemical separations. These separations are important both in terrestrial applications and in materials processing to support human spaceflight. 3. A dedicated effort should be made to evaluate the potential advantages of the microgravity environment for the study of cellular interactions, cell fusion, and multicellular assembly and to identify candidate cell systems that show maximum response to being cultured in such an environment. This effort should follow and build on the previous effort to identify mechanisms, processes, structure, and assemblies. Efforts should also be made to identify and characterize subcellular mechanisms that sense and mediate responses to the magnitude and direction of gravitational forces. 4. A systematic effort should be made to identify those cellular and biomolecular processes, structures, assemblies, and mechanisms that may be affected by gravity, and to design and carry out experiments to explore the effects of microgravity on appropriate systems. A comprehensive database should be file:///C|/SSB_old_web/mgoppch2.htm (7 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 compiled of cell types, organelles, and other assemblies, and their responses to microgravity environments. This systematic approach has substantial potential impact on our understanding of the underlying processes in the microgravity environment. It should therefore have an impact on the knowledge base for space exploration. Materials Science and Processing Metals and Alloys Carefully designed and scientifically well-conceived experiments on metals and alloys are needed to produce high-quality data and materials uniquely derived from microgravity research. Such experiments are not useful unless they produce results that cannot be obtained from terrestrial studies. Since many experiments in this field require long time scales for completion, the capability of an extended-duration orbiting platform is needed to obtain full benefits from microgravity research. Topics in the metals and alloys area that might benefit from focused microgravity research include the following items listed in order of general priority: 1. Nucleation kinetics and the achievement of metastable phase states, such as metallic glasses and nanostructures, are areas that could benefit from achieving deep supercooling in the microgravity environment, from the elimination of container surfaces, and from the reduction of melt flows due to buoyancy-driven convection. 2. Microgravity experiments on Ostwald ripening and phase coarsening kinetics would add quantitative, fundamental information about the key metallurgical issues of interfacial dynamics during thermal and solutal transport, and the question of microstructure evolution in general. 3. Observations of aligned microstructures processed reproducibly under quiescent microgravity conditions should help to provide well-defined thermal processing limits for polyphase directional solidification of eutectics and monotectics. These comprise wide classes of technologically important alloys and composites. 4. Studies of the formation of solidification cells and dendrites under well- defined microgravity conditions can add to our expanding knowledge of complex metallurgical pattern formation and, more generally, of the fundamental physics of nonlinear dynamics. Such studies, to be successful, require the most demanding control of temperature, thermal gradients, growth speed, alloy composition, and other such parametric variables. Microgravity conditions can be useful in these instances for the pursuit of sophisticated tests of theory and the quantification of metallurgical pattern dynamics. file:///C|/SSB_old_web/mgoppch2.htm (8 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 5. Some thermophysical properties can be measured advantageously in microgravity. Accurate data on these properties, frequently essential for the modeling of metallurgical processes and materials responses, are often not available from standard terrestrial measurements. Polymers Polymers potentially represent the broadest classes of "engineered" materials, permitting great innovation and precision in their design, including control at the molecular level. Although the viscous character of most high polymer melts greatly desensitizes their response to gravitational acceleration, initial experiments in some areas of vapor- and solution-phase processing of organic and polymer films in microgravity show improved texture and smoothness over terrestrial counterparts, suggesting that this area of research merits further study. Growth of Inorganic Single Crystals The microgravity environment will be particularly useful for the study of transport properties in liquids from which bulk crystals are grown, and priority should be given to these studies. Such studies probably require a steady, very- low-gravity environment (less than 10-6) such as that obtainable in a free-flyer and will provide useful data without requiring growth of bulk crystals. Precise transport data will be particularly useful for fluid dynamics computations, which are rapidly improving for terrestrial melt and solution growth. Any experiments on bulk crystal growth must be judged by their potential to contribute to the scientific understanding of the fundamental processes of crystal growth. The recommendations in this area of research are as follows: The design and execution of microgravity experiments that lead to a better fundamental understanding of crystal growth have proved elusive, and the committee recommends against the growth of large inorganic crystals under low gravity. The best approach to understanding the details of such growth will likely derive from fluid dynamical modeling and the modeling of processes at the fluid- solid surface, along with terrestrial studies of crystal growth. This analytical approach may provide the rationale for the growth of benchmark-quality inorganic crystals in microgravity. Assuming that some of the versatility of terrestrial experimentation can be achieved in the microgravity environment, there are opportunities for microgravity research that will have an impact on terrestrial bulk crystal growth. Priority should be given to transport studies, including studies of solute and self- diffusion, heat diffusion, and Soret diffusion. All of these are studies of the fluid from which crystals are grown and are amenable to routine study with repeatedly used apparatus. However, they may require a more stable environment than that provided by the space laboratory. Indeed, since such studies will undoubtedly be sensitive to the acceleration environment, they may also be useful for the study of this environment as a variable in the low-gravity range. file:///C|/SSB_old_web/mgoppch2.htm (9 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 Precise transport data will become particularly useful since fluid dynamical computational capabilities are improving rapidly for terrestrial melt and solution growth, as well as other industrial processes. These kinds of data will be required for such computations. Furthermore, transport measurements in industrially important fluids may be an important microgravity application outside the realm of large inorganic crystal growth. Growth of Epitaxial Layers on Single-Crystal Substrates During the terrestrial growth of epitaxial layers by vapor deposition, an effort is made to minimize the effects of flow, buoyancy, and boundary layer uniformity by rotating or spinning substrates during the growth process. In addition, attempts are under way to calculate precisely flow patterns and resulting growth rates in model systems. The calculations are complex, and it is not certain whether they will be able to predict occurrences in real systems that are useful for industrial production. Since the manufacture of heterostructures by vapor deposition methods will be accomplished terrestrially, it is not clear whether any relevant data can be obtained solely under microgravity conditions. A low priority is recommended for chemical vapor deposition studies under microgravity conditions. For molecular beam epitaxy methods, great gains in purity can be made on Earth provided sufficient attention is given to reducing contamination and increasing pumping speed. Epitaxial layers will be too costly to manufacture in space. At a reasonable cost, much improvement in the vacuum environment can be achieved terrestrially. Studies in orbiting vehicles are not in order until the limits of ground- based alternatives have clearly been reached. Ceramics and Glasses Most ceramic synthesis and processing is achieved at high temperatures either by solid-state processes exclusively or by those processes in which there are only small amounts of viscous liquid phases. Glasses are formed from high- temperature melts (the viscosity of SiO2 at 1700ºC is about 107 poise) where the suppression of convective mixing is generally undesirable because convection promotes compositional homogeneity. A second case in which liquids are important to ceramics is in the synthesis of ceramic powders or films from aqueous solutions or colloidal suspensions. Frequently, the requirement is for a high density of nuclei and consequent fine particle sizes of the precipitated powders. Thus, rapid mixing is used, and there is no reason to suppress convection. For these reasons, low-gravity studies are of limited advantage in this discipline. Nonetheless, a low-gravity environment might be of benefit to ceramics research and development in the following prioritized areas: file:///C|/SSB_old_web/mgoppch2.htm (10 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 1. There is interesting potential for containerless melting in microgravity. Processing of ceramics at high temperatures requires refractory containers that remain unreactive with the specimen. Availability of a general capability for containerless, high-temperature processing (to at least 1600ºC) would allow contamination-free synthesis of glasses and ceramics, such as those being considered for optoelectronic applications. Containerless melting also might allow study of nucleation and crystal growth without heterogeneous nucleation on a container wall. 2. A fundamental study of crystal nucleation and growth in glass melts in microgravity would be interesting. Crystallization is an important process, desirable in glass-ceramics and undesirable in optical glasses, that requires further characterization and understanding. 3. Mass transport and diffusion studies of glass and ceramic melts under microgravity conditions should generate more precise data than those available from terrestrial measurements. One area of research that might be aided by reduction of convection is obtaining accurate data on diffusion in ceramic melts. 4. The suppression of free evaporation from melt surfaces could allow synthesis at higher temperatures than can be performed on Earth. 5. The epitaxial growth of films from solution, including biomimetic synthesis (self-assembling monolayers) of ceramics, should be studied. Microgravity Physics Experiments in this area, with the exception of the general relativity test, Gravity Probe-B (GPB), all represent extensions of work that is currently conducted or can be conducted in Earth-based laboratories. Much of the scientific value of the proposed space experiments will depend on the strength of the connection to Earth-bound research. The topics of microgravity physics fall into two general categories: (1) development of new instruments (e.g., superconducting gyroscopes for the GPB experiment and the mass balance for the equivalence principle test), and (2) preparation and study of unique samples such as uniform fluids free from gravity- induced density gradients or low-density granular materials near a percolation limit. This program can include such important studies as fundamental physics measurements (e.g., verification of the equivalence principle), critical phenomena, dynamics of crystal growth, and low-density aggregate structures. The quality of the microgravity environment must be examined critically in the context of each possible experiment. Minimum acceleration is the most obvious parameter of concern for many of the contemplated experiments; file:///C|/SSB_old_web/mgoppch2.htm (11 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 however, the time span over which a high-quality, low-gravity environment can be maintained may be of equal importance. For some experiments, accidental large accelerations (perhaps resulting from sudden movements of personnel or the firing of small thrustors) might destroy the object of study, for example, a low- density granular structure. With regard to the quality of the microgravity environment available for experiment, only the center of the orbiting spacecraft is in true free-fall and then only to the extent that orbital drag effects and other external influences such as solar wind and radiation are negligible. In a gravity gradient-stabilized spacecraft, there will be a steady rotation of any experiment about the center of mass of the entire spacecraft once each orbit. For a low Earth orbit, this will result in accelerations on the 10-7-g level at a distance 1 meter from the center of mass of the entire orbiting system. On both the space shuttle and the space station, only a few experiments will be located close enough to the center of mass to ensure acceleration levels below the 10-6-g level. A number of scientifically meritorious projects, such as the equivalence principle experiment and GPB, will require spaceflight independent of any crewed space facilities. In the future, we may anticipate a continued requirement for low- temperature facilities in space, since low temperatures are important for the highest-resolution measurement techniques, particularly those based on SQUID (Superconducting Quantum Interference Device) technology. If a space station is to be a useful contributor to the area of fundamental science, access to liquid-helium facilities will be mandatory. GENERAL SCIENCE RECOMMENDATIONS FOR MICROGRAVITY RESEARCH Following are a number of general science recommendations that are important for microgravity research: The reproducibility of results is a crucial element of laboratory science, and flight investigators should be given the opportunity to address reproducibility in their research. Nonetheless, a balance should be established between the reflight opportunities necessary for reproducibility and the flight of experiments that address new scientific issues. The need for scientific judgment, trained observation, and human intervention and participation in certain laboratory microgravity experiments requires a greater use of payload specialists with expertise and laboratory skills directly related to the ongoing experiments. Some flight experiments would also file:///C|/SSB_old_web/mgoppch2.htm (12 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 benefit from the direct investigator interaction made possible by teleoperation capabilities, and NASA should support the development and deployment of such techniques in future microgravity experiments. As a rule, microgravity experiments should be designed and conducted to provide specific explanations for meaningful scientific questions. Scientific objectives should be clear and specific. In addition, NASA must continue to support ground-based experiments and the development of underlying theories. Theoretical understanding and ground-based experimental results support the need for microgravity experiments and the likelihood that experimental objectives will be met. Notwithstanding this, exploratory experiments can be valuable in advancing understanding of some complex systems (e.g., biological systems). There are scientific reasons to augment microgravity research in certain areas with a variable-gravity capability of extended duration. In some problem areas, the magnitude of the gravity vector is an important experimental variable in the microgravity to 1-g range. In a laboratory science where controlled model experimental systems are essential, the ability to vary an important parameter continuously should be developed whenever feasible. Therefore, if a space station centrifuge is to be developed, it is desirable to evaluate shared utilization for microgravity research. NASA should categorize experiments according to their minimum facility requirements to maximize scientific return and cost-effectiveness. Drop towers, aircraft on parabolic trajectories, sounding rockets, and orbiting platforms supply a range of acceleration levels, acceleration spectra, and experimental durations and provide opportunities for human interaction and demonstration of reproducibility. Some facilities are more suitable than others for precursor experiments to evaluate instruments and procedures and to demonstrate feasibility. General-purpose facilities (versus experiment-specific equipment) should not be imposed on principal investigators if it might degrade the scientific results. Costs are not necessarily lowered when equipment is designed for a wide range of experiments; moreover, the scientific benefits could be substantially reduced by the inherent compromises. For each flight experiment, the acceleration vector should be accurately measured locally, frequently (or continually), and simultaneously with other experimental measurements. Since the magnitude and direction of the net local acceleration environment can significantly affect experiments, they must be correlated with the primary experimental data. The net acceleration vector varies temporally and with position relative to the spacecraft center and can have major effects even at small magnitudes. Materials studied in microgravity experiments should be adequately characterized on Earth. For some materials, there is a lack of the thermophysical file:///C|/SSB_old_web/mgoppch2.htm (13 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 data essential for both experimental design and modeling. These data should be obtained by ground-based research where possible or from microgravity measurements if necessary. The qualitative effects of the acceleration environment on certain types of experiments should be studied. These effects are not generally understood and characterized. ADMINISTRATIVE RECOMMENDATIONS The following recommendations do not directly address scientific issues but instead summarize administrative issues that profoundly affect the quality and quantity of the science content of the microgravity program. Meaningful interaction should be maintained between the principal investigators and NASA staff during experiment development and integration, and communication among these groups must be continued following flight. It is essential to minimize the overlap of responsibilities in the NASA infrastructure to accomplish this goal. It is essential that the overlap of responsibilities among NASA centers and between centers and headquarters be substantially reduced in order to optimize the influence of the principal investigators and the likelihood of successful experiments. Measures should be taken to improve coordination and cooperation between the life sciences administration and the microgravity research administration concerning biological and biotechnological research on cellular and subcellular processes and mechanisms. The strong scientific coupling between biotechnology and other microgravity disciplines through the fluids and transport theme should be recognized in any administrative reorganization. All data, including acceleration measurements, should be made available immediately to the principal investigator. Current delays in providing data extend many months beyond the flights. NASA must coordinate the operations of various offices so that priority is given to the processing of experimental data. It is necessary to increase substantially the number of ground-based investigations to ensure the future supply of high-quality flight experiments. Consequently, the budget for ground-based research should be increased as a fraction of the entire microgravity program. To the maximum extent feasible, funding for ground-based research in the microgravity program should be protected from temporary budgetary fluctuations. file:///C|/SSB_old_web/mgoppch2.htm (14 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 In addition to its role in developing flight experiments, the ground- based program can provide important scientific and technical data for other purposes. A ground-based study can therefore be judged successful even if a flight experiment does not result. Microgravity research is much broader than the topic of materials processing in space and should be identified as microgravity research in all official documents, including the federal budget. Microgravity research better describes the activity and its actual and potential accomplishments. Materials processing in space characterizes only a fraction of the activity and promotes a misleading impression of the potential benefits and scope of the program. The microgravity sciences and applications program and the commercial development program have a large area of overlap and common interest. Coordination between these programs and an equally stringent review process for each should be fostered by NASA for their mutual benefit. NASA should establish mechanisms for continuous, unrestricted submission of research proposals in order to optimize quality and take advantage of scientific advances. Unrestricted submission of research proposals would parallel approaches of other funding agencies and would enable continual scientific advance. To manage the diverse disciplines in microgravity research, it is necessary to increase the breadth and experience of the scientific staff at NASA headquarters. A rotation of prominent scientists on leave from universities, national laboratories, and industry is one mechanism to be explored. Introduction of active scientists in the administration of the program would be highly beneficial. Prompt documentation of experimental results should be required and enforced. Reports of all experiments, including unsuccessful efforts, should be accessible to all interested parties. A concern is that some investigators might not report results because they are proprietary or inconclusive. The lack of an available report could lead to unnecessary duplication of efforts. NASA should organize and maintain an accessible archive of microgravity research results. This archive should contain a bibliography of all published scientific papers and reports on microgravity subjects and should preserve the original spaceflight data sets, such as photographs and electronically recorded data. An additional point of concern is that given the long time scale for the development through flight of a space experiment, there is a real danger that the scientific goals of the experiment might be bypassed by new developments or by major shifts in the value ascribed to the work. There is also the possibility that the principal investigator may lose contact with the field. Several of the above recommendations may be useful in this regard. Anything that NASA can do to file:///C|/SSB_old_web/mgoppch2.htm (15 of 17) [6/18/2004 11:16:00 AM]

OCR for page 37
Microgravity Research Opportunities for the 1990s: Chapter 2 shorten this time frame would be beneficial. This topic is explored in more detail in Chapter 8, which also contains some additional scientific and administrative recommendations specific to the flight program. REFERENCE 1. Space Studies Board, National Research Council. 1992. Toward a Microgravity Research Strategy. National Academy Press, Washington, D.C. Last update 4/12/00 at 3:48 pm Site managed by Anne Simmons, Space Studies Board file:///C|/SSB_old_web/mgoppch2.htm (16 of 17) [6/18/2004 11:16:00 AM]