The Human Exploration of Space (1997) / Chapter Skim
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Scientific Prerequisites for the Human Exploration of Space
Scientific Prerequisites for the Human Exploration of Space
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Scientific Prerequisites for the Human Exploration of Space
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Cover design by Penny Margolskee. Copies of this report are available from Space Studies Board National Research Council 2101 Constitution Avenue, N.W.
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LANZEROTTI, AT&T Bell Laboratories ELLIOTT C LEVINTHAL, Stanford University WILLIAM J
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MOSER, University of New Mexico NORMAN F NESS, University of Delaware MARCIA NEUGEBAUER, Jet Propulsion Laboratory MARK SETTLE, ARCO Oil Company WILLIAM A
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CARRIER, Harvard University GEORGE W CLARK, Massachusetts Institute of Technology MARYE ANNE FOX, University of Texas, Austin AVNER FRIEDMAN, University of Minnesota SUSAN L
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Many advocates of human space exploration now agree that the next steps in piloted flight after Space Station Freedom involve returning to the Moon and, eventually, voyaging to Mars. The space science community, however, is agreed that there is no a priori scientific requirement for human exploration of the Moon and Mars.
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Government Printing Office, Washington, D.C., 1990) , that science is "the fulcrum of the entire space effort." Since its establishment in 1958, the Space Studies Board (SSB; formerly the Space Science Board)
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Advice on some technological issues was provided by the Committee on Microgravity Research. Full membership lists for these Space Studies Board discipline committees appear in the appendix.
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Contents EXECUTIVE SUMMARY The Role of Science, 2 Enabling Science, 3 Critical Research Issues, 3 Optimal Performance Issues, 4 References, 4 INTRODUCTION The Human Exploration of Space, 6 Science and the Human Exploration of Space, 8 Enabling Science, 10 Space Station Freedom, 13 International Consultation and Collaboration, 13 Notes and References, 14 2 CRITICAL RESEARCH REQUIREMENTS Radiation, 17 Radiation Levels, 17 Sources of Hazardous Radiation, 18 Galactic Cosmic Radiation, 18 Solar Energetic Particles, 20 Relevant Measurements and Research, 22 Bone Degeneration and Muscle Atrophy, 24 x~ 6 15
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. all Cardiovascular and Pulmonary Function, 26 Behavior, Performance, and Human Factors, 28 Individual Factors, 28 Group Factors, 29 Environmental Factors, 29 Biological Issues, 30 Notes and References, 31 RESEARCH FOR MISSION OPTIMIZATION Sensorimotor Integration, 33 Immunology, 34 Developmental Biology, 36 Life Support Systems, 37 Micrometeoroid Flux on the Moon, 38 Surface and Subsurface Properties, 38 Potential Martian Hazards, 40 Aerobraking at Mars, 42 Microgravity Science and Technology, 43 Exobiology Issues, 43 Resource Utilization, 44 Notes and References, 45 CONCLUSIONS BIBLIOGRAPHY APPENDIX CONTENTS 33 46 48 51
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And then a journey into tomorrow a manned mission to Mars."2 The resulting long-term program to expand the human presence in the inner solar system has been called many things, including the Human Exploration Initiative, the Space Exploration Initiative (SEI) , and the Moon/Mars program.
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The U.S. scientific and engineering community is obliged to provide the best and most constructive advice to help the nation accomplish its space goals, as was stressed in a 1988 space policy report to the newly elected president by the National Academy of Sciences and the National Academy of Engineering.4 To that end the National Research Council's Space Studies Board established the Committee on Human Exploration (CHEX)
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This report also contains some preliminary discussion of technology requirements, aspects of international scientific cooperation, and the approach used to manage the scientific component of a program of human exploration. ENABLING SCIENCE In establishing the scientific prerequisites for the human exploration of space, CHEX has identified two broad categories of enabling scientific research.
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Some of these issues may become critical research issues relative to long-term human spaceflight and return to terrestrial gravity following extended flights, or when extraterrestrial habitation is considered. Research issues related to optimal mission performance include the: 1.
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9. Synthesis Group, America at the Threshold, Report of the Synthesis Group on America' s Space Exploration Initiative, U.S.
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And then a journeyinto tomorrow a manned missiontoMars."i This proposal to expand human presence in the solar system has been given a number of different names, including the Human Exploration Initiative, the Moon/Mars program, Mission from Planet Earth, and, most recently, the Space Exploration Initiative (SEI)
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7 rl~he fundamental premise of a Moon/Mars program, given the overarching goal of human presence and activity beyond Earth, is directly articulated by the first theme, an increase in knowledge of the universe. Thus "the Space Exploration Initiative is an integrated program of missions by humans and robots to explore, to understand and to gain knowledge of the universe and our place in it."3 As its name suggests, the Synthesis Group's report was the distillation of a nationwide outreach campaign to ascertain the nation's space exploration aspirations.
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If the goal of future space missions were solely to satisfy the "human imperative" to explore or to enhance national prestige or other nontechnical and nonscientific objectives, there would be a limited set of requirements. There would, for example, be relatively little need for precursor robotic missions to characterize the martian surface, because sufficient data are at hand from the Viking mission to allow selection of a safe landing site.
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This creates a need for precursor robotic missions and provides linkages between the scientific knowledge that is prerequisite for human exploration and the scientific opportunities deriving from such a program. The relative role of humans and robotic probes in space exploration has long been a contentious issue.
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Scientific advice is included in day-to-day decisions on the strategy and implementation necessary to execute the programs; and 4. All goals (e.g., scientific research, human presence, utilization of resources)
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A Mars sample return mission may be desirable to settle questions of forward contamination and back contamination. Indeed, the Space Studies Board has recommended that "the next major phase of Mars exploration for the United States involve detailed in situ investigations of the surface of Mars and the return to Earth for laboratory analysis of selected martian surface samples."8 In examining the enabling science for the human exploration of space, CHEX identified two categories of research topics, each with differing de
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This assumption is unwarranted. An assessment of current research in space biology and medicine shows that the major problems posed by prolonged exposure to microgravity remain no nearer solution in 1993 than they were in 1961, the year of the first human spaceflight.
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NASA's current plans for Space Station Freedom are the subject of much controversy because of the project's escalating cost, lengthening construction schedule, and declining capabilities. On several occasions, the Space Studies Board has expressed concern that the current, descoped design of Space Station Freedom does not meet all the basic research requirements outlined abovei3 and therefore will not fulfill its role as the first and necessary step in the human exploration of space.
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9. See, for example, Space Science Board, A Strategy for Space Biology and Medical Sciences for the 1980s and 1990s, National Academy Press, Washington, D.C., 1987.
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Space biology and medicine are in such a primitive state of development that knowledgeable researchers cannot state with any degree of assurance that human crews will be able to operate their spacecraft or function 15
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For this purpose, a long-term research program in adaptation to microgravity and reduced gravity, properly conducted in a suitably equipped space station in low Earth orbit, will be required. Such a research program may require 5 to 10 years because of the necessarily long duration of individual experimental protocols.
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NASA currently has no limits for exposure to radiation during deepspace missions conducted beyond the protective shield of the geomagnetic field because little is known about the physiological effects of the heavy ions found in cosmic rays. In terms of the traditional dose-equivalent for
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NASA's current limits correspond to a 3% excess risk of eventual death due to cancer and are about 10 times that allowed for terrestrial radiation workers and about 100 times that allowed for the general population. Sources of Hazardous Radiation As mentioned above, two types of radiation are hazardous to astronauts galactic cosmic rays and solar energetic particles.
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20 30 FIGURE 1 Estimates (solid curve) of the radiation dose equivalent received from galactic cosmic rays at a depth of 5 cm in body tissue (representative of, for example, bone marrow)
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Solar Energetic Particles The intensity, spectra, and composition of energetic particles from solar flares are much more variable than those of galactic cosmic rays. The flareproduced energetic-particle population can also be dramatically enhanced by strong shocks in the solar wind associated with coronal mass ejection.
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Tsao, "Galactic Cosmic Radiation Doses to Astronauts Outside the Magnetosphere," in Terrestrial Space Radiation and Its Biological Effects, P.D. McCormack, C.E.
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should be measured throughout the 22-year magnetic solar cycle using a new generation of instruments with large geometric factors, such as NASA's planned Advanced Composition Explorer; · Measurements of the intensities of the electron and positron components of galactic cosmic rays over most of a 22-year cycle would separate charge-sign-dependent effects from other cosmic-ray propagation effects, thereby leading to better understanding of the modulation process; · Measurement of the galactic cosmic-ray intensities beyond the boundary of the heliosphere would establish an upper limit to the radiation intensity independent of its modulation by the solar wind and magnetic field. Continued tracking of the Voyager spacecraft is clearly cost-effective in this respect; and · Theoretical studies of the solar- and plasma-physical processes that modulate the intensity of galactic cosmic rays are required to better understand and predict their variability.
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warning system because it would allow modeling and predictions of the paths taken by energetic particles as they are channeled from flare sites into interplanetary space. The coronagraph would allow coronal mass ejections (CMEs)
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and muscle atrophy that occur in a microgravity environment are severe hurdles to an extended human presence in space.~5 The primary risk is to the functioning of the musculoskeletal system upon reexposure to planetary gravity. At present, our understanding of the causes of space-induced osteopenia and muscle atrophy is inadequate to devise effective countermeasures to be taken on long-duration space missions.
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One approach to counteracting the physiological effects of microgravity is to subject organisms in space to artificial gravity. Although such an environment could correct bone degeneration, muscle atrophy, and other changes due to microgravity, it could also exacerbate other effects not now perceived to be major problems.
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Indeed, the provision of artificial gravity may well prove to be an architectural variable of more fundamental importance than the thematic differences between alternative mission emphases presented in the report of the Synthesis Group. CARDIOVASCULAR AND PULMONARY FUNCTION The redistribution of intravascular fluid toward the head is one consequence of exposure to a microgravity environment.
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Another topic needing attention is potential effects of the space environment on cardiovascular and pulmonary physiology when modified by disease processes or pharmacological agents.
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Despite awareness of the importance of these issues, systematic research into the determinants of human performance and adaptation under these conditions has received only minimal support. Only limited progress has been made since publication in 1987 of the Committee on Space Biology and Medicine research strategy, which included a chapter on human behavior.
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Training techniques developed to improve leadership, crew coordination, decision making, and conflict resolution in civil- and military-aviation settings need to be refined and validated in the space environment. ~ c7 1 Environmental Factors On long spaceflights, the crew's psychological environment is no less important than its physical environment.
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A recent study2i has concluded that the question of forward contamination by robotic missions is an issue only for those that include life-detection experiments, where the concern is contamination of the experiment. It would, however, be virtually impossible to avoid forward contamination of Mars or back contamination of Earth from human exploration.
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NOTES AND REFERENCES 1. Space Science Board, Space Science in the Twenty-First Century: Imperatives for the Decades 1995 to 2015: Overview, National Academy Press, Washington, D.C., 1988, pp.
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13. Space Science Board, A Strategy for Space Biology and Medical Sciences for the 1980s and 1990s, National Academy Press, Washington, D.C., 1987, p.
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In addition, increased knowledge of the physical aspects of the Moon and Mars is required to ensure that human explorers perform efficiently. As new information accumulates, and as implementation decisions are made, the significance of any or all of the areas where research is needed to ensure mission optimization could increase to the point that they become critical issues.
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Studies of vestibular function and its neuronal substrates in appropriate animal models are needed both on the ground and in a microgravity environment. Parallel studies of human sensorimotor performance in both environments must also be pursued.
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The effluent from these multiple sources will contain microflora, gases (e.g., oxygen, carbon dioxide, and methane) , and other chemical contaminants that must be collected and either disposed of or channeled through the life support system.
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Such constituents as G-proteins, phosphoinositides, actin, and calmodulin also occur in plant cells and may have active roles. The increasing applicability of techniques of molecular biology to problems in plant growth and development will be useful in attempts to understand the responses of plants to the space environment and in developing breeding programs designed to increase plant performance in microgravity environments.
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A major scientific goal is simply to grow plants in space for extended periods of time over several life cycles while carefully monitoring their performance. This goal is related to the more general need, outlined in the previous section, to investigate how diverse organisms undergo development in the space environment.
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SURFACE AND SUBSURFACE PROPERTIES Humans exploring the Moon and Mars will require knowledge about their proposed landing sites not only to ensure a safe touchdown and subsequent departure, but also to identify regions of potentially high scientific interest. Prime questions to be answered for candidate sites involve the mechanical properties of the landing zone and the surrounding terrain to be explored and sampled.
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The distribution of rock size can be obtained by precursor flights using remote sensing and in situ robotic exploration. Imaging with a resolution of less than 1 meter is necessary for selecting the landing sites themselves.
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Perhaps the spacecraft itself will have to be "cleaned" prior to its return to Earth. The data required to certify landing sites for safety may be highly desirable for other purposes such as planning surface construction, instrument installation, and the layout of extended surface traverses.
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Moreover, the movement of sand-sized particles near the surface may pit, scratch, and erode surfaces, and may foul joints. Continued remote sensing of the martian atmosphere will help define this hazard.
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the mass that must be delivered into Earth orbit for a Mars exploration mission. Aerocapture could be critical to the feasibility of such a mission, and a proper understanding of the atmospheric structure of Mars and its variability should be considered part of the enabling science for such a mission.
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The challenges occur predominantly in the life support areas but extend well beyond them. For example, modern electronics are becoming so compact that, in the near future, volumetric heat-generation rates are expected to rival those values for controlled nuclear fission.
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If there is a requirement to mine water at the landing site, then precursor flights should be designed to locate regions where subsurface ice may exist. Similarly, detailed knowledge of the local mineralogy should be obtained on precursor flights for in situ extraction of water from mined minerals.
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2. For an assessment of this problem in the context of Space Station Freedom, see Board on Environmental Studies and Toxicology, Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants, National Academy Press, Washington, D.C., 1992.
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This will remain the case even if a major Moon/Mars program is not initiated for 5 years or 25 years. The information that the committee deems critical is concerned largely with aspects of space biology and medicine and associated characteristics of the radiation environment.
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This pervasive requirement for scientific input mandates that the piloted spaceflight community develop a new understanding of and attention to the conduct of space science. It simultaneously requires that the scientific community interact constructively with those charged with implementation of a Moon/Mars program.
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Mars Atmosphere Knowledge Requirements Working Group, SKI Engineering Requirements on Robotic Missions, Roger D Bourke, (ed.)
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Office of Space Science and Applications, Space Biology Plant Program Plan, Life Sciences Division, NASA, Washington, D.C., 1991. Office of Space Science and Applications, Space Radiation Health Program Plan, Life Sciences Division, NASA, Washington, D.C., 1991.
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SCHILLER, Mt. Sinai Medical Center TOM SCOTT, University of North Carolina, Chapel Hill WARREN SINCLAIR, National Council on Radiation Protection and Measurements WILLIAM THOMPSON, North Carolina State University, Raleigh FRED WILT, University of California, Berkeley 51
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and Committee on Solar and Space Physics (CSSP) meet jointly as a federated committee and report directly to their parent National Research Council boards, the Board on Atmospheric Science and Climate for CSTR and the Space Studies Board for CSSP.
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STONE, Massachusetts Institute of Technology GEORGE WETHERILL, Carnegie Institution of Washington RICHARD W ZUREK, Jet Propulsion Laboratory COMMITTEE ON MICROGRAVITY RESEARCH ROBERT F
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