Click for next page ( 22


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 21
IV Space Science and the Human Exploration Initiative The NASA 90-Day Study reflects an initial attempt to identify the scientific components of the HEI. It identifies five themes around which the science elements of the initiative are developed and states that the "fundamental scientific themes . . . can be uniquely addressed by the Human Exploration Initiative." Several specific examples are presented of scientific objectives in precursor flights to the Moon and Mars. The 90-Day Study provides evidence of NASA's intention that scientific research be an integral part of the HEI. Nevertheless, it is clear that much of the research in the NASA scientific themes does not require an HEI. It is useful to divide the scientific research issues into three broad categories. First, there are scientific studies to enable the initiative- those that must be done before humans can travel to Mars, perform useful tasks, and return safely. Second are studies and experiments that can only be conducted as a result of the envisioned long-term human missions. Third are studies that may be undertaken in association with those missions, but could be carried out otherwise if necessary. Any scientific knowledge that might be obtained in association with long-term human missions should be evaluated in competition with other modes of gathering the same information (e.g., human-tended, telerobotics) and with other scientific research goals. This competitive category of scientific research should not be used as, nor considered to be, the primary justification for a national commitment to human exploration of space. 21

OCR for page 21
22 HUA~1N EXPLORATION OF SPACE SCIENTIFIC KNOWLEDGE AS A PREREQUISITE FOR HUMAN EXPLORATION The most important issues of prerequisite scientific knowledge concern those matters that are critical to human health and safety, including micro- gravity effects on physiologic functions, the effects of radiation, controlled environment life support systems, site-selection and contamination issues, and the psycho-social aspects of prolonged exposure in a confined habitat. In every pioneering effort there are risks, known and unknown, that are intrinsic to the endeavor. Those responsible must make the fullest efforts to reduce the known risks to reasonable levels and make clear the levels of risk that remain. Potential hazards must be explored and countermeasures devised to reduce risk. Research is required to explore the range of risk and to devise reasonable countermeasures. Life Sciences Microgravity Issues Data are incomplete regarding the effects of the microgravity environ- ment on human physiology (including the cardiovascular, vestibular, and immune systems); more research is also necessary on adequate counter- measures. As noted in the NRC Strategy for Space Biology and Medical Science, "If this country is committed to the future of humans in space, particularly for long periods of time, it is essential that the large number of uncertainties about the effects of microgravity on humans and other living organisms be recognized and vigorously addressed." The 90-Day Study envisions research to develop countermeasures to the effects of very low gravity and to promote the basis for designing artificial gravity environ- ments, if required. A rigorous research program would be based largely on facilities available in an Earth-orbiting station, designed to gain an under- standing of the effects of a microgravity environment on humans. As NASA indicates, the results of this research will have significant implications for mission architectures and mission time profiles. Radiation Issues Radiation from solar and galactic sources poses serious potential haz- ards to human health. Predictions of solar flares and of solar flare particles remain uncertain, but successful predictions are not prerequisites to human spaceflight, if adequate shielding is provided. Research on prediction tech- niques, one of NASAs objectives, should be vigorously pursued in parallel with human exploration programs. The intent would be to provide the

OCR for page 21
SPACE SCIENCE AND THE HUMAN EXPLORATION INITL4TTVE 23 earliest possible warnings, with minimal false alarms, of impending solar flares and flare particles. As the 90-Day Study indicates, it is important to learn more about the relative biological effects of radiation fluences, particularly high-, galactic cosmic rays and solar flare electrons and protons, and their relationship to cancer and cataract induction, for example, in order to set meaningful guidelines for radiation protection. The question of appropriate shielding in flight, at an Earth~rbiting station, and on the Moon and Mars is complex and requires further study. For example, NASA suggests that for modest thicknesses of shielding, the secondary radiation arising from the interaction of galactic cosmic radiation may be more harmful to living tissue than the primary dose. Consideration should be given to undertaking early flights during solar minimum conditions. Controlled Environment Life-Support Systems The 90-Day Study recognizes the challenge of providing a reliable, cost-efficient life-sustaining environment in locations that are devoid of food, air, water, and nutrients. NASA's vision of the HEI uses closed- loop systems where practical to reduce logistic requirements and open-loop systems where limitations in technology or operational capabilities dictate. It would be useful, but not mandatory, to have fully-closed life-support systems for brief visits to the Moon and to Mars. However, even for a brief visit, it is desirable to recycle water. For prolonged stays on the Moon and Mars, a completely closed regenerative system would be highly desirable to reduce requirements for resupply. Several terrestrial closed- loop experiments are under way and must be reviewed in the context of the HEI and refined until they are successful. The next step should be a test bed of a closed life-support system in micro~ravitv on or near an Earth-orbiting station. Contamination and Back Contamination , "7 , Evidence from the Viking missions to Mars suggests that terrestrial microorganisms have little or no probability of growth on that planet, but that does not rule out the possibility that life exists or may have existed there in the past. Although organic compounds and liquid water have not been detected on Mars, there is no basis for precluding their existence. There is, moreover, strong evidence that liquid water in large quantities existed in the Martian past. Furthermore, new discoveries about unusual biological niches on Earth, such as deep ocean thermal vents, illustrate the diversity of biological habitats. International law requires that activities in space be conducted to avoid the harmful contamination of celestial bodies as well as introduction

OCR for page 21
24 HUMAN EXPLORATION OF SPACE of changes in the Earth's environment by extraterrestrial matter. For example, a Mars robotic lander raises concerns about contamination of Mars (referred to as forward contamination), while a Mars sample return mission must deal with concerns about contamination of Earth (called back contamination). The NASA 90-Day Study envisions a series of unmanned precursor missions to Mars to determine characteristics of the planet The knowledge to be obtained is necessary for detailed mission planning, including dealing with the contamination issue. The Great Exploration concept does not include such precursor missions. The committee believes that, before humans go to Mars, there will have to be a highly capable set of precursor missions, whose precise definitions, numbers, and configurations require detailed research strategy development. Such precursor missions will allow assessment and management of some of the risks of carrying out a manned mission. The risks are not limited to concerns simply with pathogens. While the risk of Pathogens is admittedly low. the Potential cost.c are nn~.~iblv Vera high. , ~ ~ - ~ ~ r-~~~~~~~~ ~~~~ ~~~ rid ~ ~~~ Psychological Issues As noted in the 90-Day Study, psychological effects arising during long- duration sequestering of humans have been documented, for example, in nuclear submarines and research programs in Antarctica. Although these terrestrial analogs are useful, they do not adequately simulate conditions of long-duration missions to Mars. NASA appropriately envisions continuing research in the selection process for spacefarers. Issues of spacecraft habitability, training and command structure, as well as crew mix require study, including simulation. A review of research results to date indicates that more is known about avoiding undesirable crew characteristics than is known about selecting crew for desirable traits. Clearly, the psychological profiles for individuals and for crew composition should be well understood, to reduce risks on long voyages. As is the case with most risks to humans arising from long stays in the microgravity environment, technological advances in nuclear and other propulsion systems could alleviate some adverse effects by reducing mission duration. Physical Sciences Because the use of local resources is likely to be an essential feature of the mission architecture, additional scientific knowledge will be required about surface materials, features, and structures, both on the Moon and Mars. Four of the five reference approaches in the 90-Day Study incorpo- rate extraction of oxygen from lunar materials.

OCR for page 21
SPACE SCIENCE AND THE HUMAN EXPLORATION INITL4T[VE 25 Present knowledge of lunar and Martian surface features is adequate for lander modules, provided that high-resolution imagery is incorporated for terminal guidance to a landing that can be directed over a sufficiently large target radius. Additional knowledge will be required for site selection, however, if the astronauts will be expected to carry out significant research while on the surface. Uncertainties also exist concerning the bearing strength of the Martian surface in areas of possible landing sites. In the case of the Moon and a possible long-term lunar base, the flux of micrometeorites and its variability are major uncertainties that can affect the livability of a lunar station. As described in both the Sunday Study and The Great Exploration, covering the station with lunar regolith is one possible way to reduce the hazards from micrometeorites and radiation. A fuller examination of research emphases in this area is needed before precursor mission concepts are developed. RESEARCH OPPORTUNITIES TO BE DERIVED FROM PROLONGED HUMAN SPACE MISSIONS The NASA 90-Day Study describes a variety of opportunities presented by the HEI to advance scientific understanding through both the robotic and human exploration phases of the HEI. The opportunities are organized into a series of scientific themes. Several themes pose questions that challenge astronomers, and NASA notes, for example, that the Moon offers a number of advantages as a site for astronomical observatories. The committee believes the Moon could offer potentially unique re- search opportunities for a number of space science disciplines, including astronomy. However, the concept of an astronomical observatory on the Moon needs to be examined more critically than was suggested in the NASA report. Specifically, lack of seismic activity does not seem to be a major feature in determining whether the Moon should be used for inter- ferometry. Attractive features include the dark and cold sly advantages that come from being away from the Earth, and the advantages of building large structures in fractional gravity. Before establishing a lunar base to be used for scientific research, a number of significant issues need to be understood in order to ensure the long-term utility of the base for research purposes. For example, depending upon the specific research objectives, evaluations should be made of the effects on instrumentation of such features as the micrometeorite flux, the solar wind and solar flare particles, and the electric and magnetic environments on the surface at different lunar phases. In addition, attention will have to be given to the interactions between a human presence and specific scientific instrumentation (e.g., outgassing, vibration, dust, and electromagnetic interferences).

OCR for page 21
26 HUMAN EXPLORATION OF SPACE Additional research opportunities on and from both the Moon and Mars are sketched in the 90-Day Study. There will undoubtedly be op- portunities for the HEI and the space sciences to advance together. Each scientific opportunity to be derived from human space exploration should be defined and evaluated, with consideration of its relative priority in the research strategy of the appropriate discipline, and an assessment of the most effective means to achieve it.