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INTRODUCTION 1 1 Introduction OVERVIEW The life sciences have been and will continue to be an integral part of our space program. As anticipated in the legend of Icarus, flight can expose us to anoxia and extremes of temperature, and spaceflight adds microgravity and radiation. We cannot adapt to these conditions or protect ourselves from their effects without a sophisticated understanding of the underlying physiological responses. On spaceflights lasting for months, recycling wastes becomes economically attractive; on flights lasting for years, controlled ecological life support systems are imperative. Research into several fundamental problems in biologyâplant growth, biomineralization, vestibular function, and development âwill also benefit from access to microgravity laboratories. We are seeing the birth of a new science that combines the global perspective of the earth sciences with the principles of ecology. NASA has the expertise and the organization to be a major contributor to a global study of the interactions of the biota with the atmosphere, hydrosphere, and geosphere. A greater understanding of our biosphere will have a profound impact on our international relations and on our economy. Speculations on how life began have occupied some of the
INTRODUCTION 2 best minds for millennia. The task group believes this is now a soluble scientific problem. NASA can take a lead in the integration of planetary sciences, molecular biology, and prebiotic chemistry. The result will be a new understanding of our own origin and evolution, and a more reliable estimate of the possibility of life outside our solar system. The intellectual impact of exobiology and global biology will probably equal that of molecular biology. The four disciplines treated in this reportâexobiology, global biology, space biology, and space medicineâspan an extremely broad range of intellectual subject matter and technology. Their parent disciplinesâecology, molecular biology, chemistry, astronomy, and medicineâare well established. But there have been so few flight opportunities for studies in these fields, especially space biology and medicine, that they have yet to develop into mature space sciences. They are all young disciplines, still defining their basic questions and strategies. They are united by the study of life, and especially its evolution. EXOBIOLOGY Understanding the origin, early evolution, and distribution of life is the focus of a major scientific effort in NASA. The early environment of the Earth is being deciphered through the study of biological and chemical fossils in 3-to 4-billion-year-old rocks. Within our own solar system there are strong indications of organic reactions on the surfaces and in the atmospheres of several planets, on the satellite Titan, and in comets and asteroids. Organic molecules, many of which are constituents of living organisms, have been detected in meteorites as well as in interstellar space. Exciting discoveries of molecules synthesized in the laboratory under conditions presumed to exist on the primitive Earth have led to theoretical pathways concerning the origin of life on Earth. The current view, which is gradually being confirmed, is that the chemicals of life abound in the universe and that the conditions that gave rise to life on Earth may exist in other places. We do not yet know the details of this chemistry, nor do we know whether life has actually arisen elsewhere in our own solar system or beyond. We do not even know for certain whether planets exist outside of our own solar system, although there is good reason to believe they do. This is an area of research that is tractable to both laboratory
INTRODUCTION 3 experimentation and space exploration and involves a broad range of interdisciplinary collaborations. By 1995, the task group expects that our capabilities in the field of exobiology will have expanded markedly. By then we should be able to probe comets directly through chemical analysis and to identify and quantify the organic molecules in these bodies and their relationship to early planetary history. We should also be in a position to determine with some confidence the presence (or absence) of other planetary systems. We should be able to collect cosmic dust particles in space for detailed physical and chemical analysis, particularly for organic content. At the same time, we should be able to extend the search for clues to the history of life to other planets, particularly Mars, where only preliminary studies were done by Viking, and to Titan, Europa, and perhaps other satellites of other planets. Studies of these bodies should include a search for evidence of life forms that once existed, but are no longer present. By 1995, we should also have the ability to search our galaxy by means of radiotelescopes for signs of intelligent civilizations. GLOBAL BIOLOGY/BIOSPHERIC SCIENCE The ability to travel in space has revolutionized our perception of the universe and our place within it. Humans can now view their planet from afar and contemplate its entirety while at the same time applying their scientific armamentarium to an array of problems not approachable by any other means. Earth is essential to human existence; it is the only planet known to harbor life. Our understanding of the evolutionary relationships between living organisms and the planet is limited and based on local or regional data gathered over the years by ground-based observations. Spacecraft provide the means of obtaining a global perspective, that is, of looking at and measuring key phenomena globally and continuously. Fundamental to understanding the biosphere is deciphering the interrelationships between biological processes and geochemical-geophysical processes. For example, study of biogeochemical cycles through study of changes in atmospheric carbon dioxide and periodic measurements of global biomass and productivity is now both possible and timely. Monitoring biosphere-climate interactions, measuring biogenic aerosols, monitoring surface changes
INTRODUCTION 4 induced by phenomena such as deforestation, desertification, and agriculture, and measuring oceanic productivity are all activities that can be carried out from space. Interactions between the biosphere and the atmosphere can also be measured from space. These include the exchange of trace gases between the biosphere and atmosphere, the effects of biomass burning, tropospheric chemical cycling, and stratospheric contamination. Earth-orbiting spacecraft offer the exciting prospect of monitoring environmental conditions relevant to certain disease outbreaks, such as malaria. By global monitoring of important variables such as seasonal rainfall and temperature, predictions of outbreaks of mosquito populations can be made. Such studies will allow much more effective modeling of global ecology. This, in turn, will permit a recognition and understanding of threatening trends. The surface of the Earth, viewed in terms of temperature, water content, sediments, and atmospheric composition, is completely different from that predicted as intermediate between Venus and Mars. To understand our planet we must understand the cumulative impact of 4 billion years of life. CONTROLLED ECOLOGICAL LIFE SUPPORT SYSTEM (CELSS) Human exploration of our solar system will require missions of long duration. These, in turn, require not only our understanding of human tolerance and limitations, they also present extremely complex technical and theoretical problems of providing the air, water, and food for a livable environment. Eventually we will no longer be able to carry from Earth sufficient supplies to support extended space travel. The mere weight and volume of these expendables will be beyond the carrying capacity of the spacecraft. We will be forced to recycle ever more of these materials. Air must be cleaned and humidified or dehumidified, water purified and reused, and food produced, consumed, and the wastes processed and recycled. Virtually nothing can be discarded in the tightly closed systems required for explorations of several years' duration. These systems must be thoroughly evaluated inflight prior to planning long missions. As formidable as these engineering problems are, the biological problems of such a life support system may prove even more
INTRODUCTION 5 difficult, especially if the human palate and psyche demand the presence of higher plants. The effects of microgravity on plant reproduction, development, and growthâespecially when coupled with those of artificial lightingâare not understood. Success in this endeavor demands imaginative cooperation between engineers, chemists, nutritionists, and ecologists. Aside from the utility of a Controlled Ecological Life Support System (CELSS) as a life support aid, the concept of closing, at least partially, an artificial ecosystem is of interest to the science of ecology and may offer a research tool of considerable value for study of the principles by which nature's ecosystems function. SPACE BIOLOGY Throughout its evolution, life on Earth has experienced only a one-g environment. The influence of this omnipresent force is not well understood, except that there is clearly a biological response to gravity in the structure and functioning of living organisms. The plant world has evolved gravity sensors; roots grow ''down'' and shoots "up." Animals have gravity sensors in the inner ear. Many fertilized eggs and developing embryos orient their cleavage planes relative to the gravity vector. Access to a microgravity space station laboratory will facilitate research on the cellular and molecular mechanisms involved in sensing forces as low as 0.001-g and subsequently transducing this signal to a neural or hormonal signal. A major challenge to our understanding and mastery of these biological responses is to propagate selected species of higher plants and mammals through several generations at microgravity. As was amply demonstrated by Pasteur, as well as countless successors, investigations in medicine and in agriculture contribute to and benefit from basic research. Understanding the responses of humans and of plants to microgravity has enormous practical significance for manned spaceflight. The use of microgravity to eliminate microconvection in crystal growth, in electrophoresis, and in biochemical reactions should continue to be evaluated for both research and commercial application. Conversely, the urgent need to moderate the debilitating effects of bone and muscle wasting may lead to fundamentally new insights into biomineralization and controls of gene transcription and translation. Although serendipity is hardly the basis of a research strategy, we emphasize the value to science in generalâand to biology in particularâof
INTRODUCTION 6 creating a research environment in which a creative scientist can observe unanticipated phenomena. These questions then become the stuff of logical analysis and formal reports. HUMAN BIOLOGY AND SPACE MEDICINE Our space program should develop the capability for manned space missions of several years. So few data are available that any projection is tentative. The physiological effects of short-duration spaceflight will probably be tolerated or compensated for, if not well understood and solved, by the middle of the Space Station era (approximately 2005). However, the long-term effects of microgravity, or even the reduced gravity of the Moon, on bone and muscle metabolism and on cardiovascular function will probably remain poorly understood. Crew members are protected from ion radiation by the Earth's magnetic field while in the low-inclination, low-altitude orbits of the Shuttle and the Space Station. However, they would be exposed to significant heavy ion radiation during interplanetary missions or while inhabiting a lunar or martian base. This exposure could have disastrous effects on the central nervous system, because heavy ion radiation has recently been shown to inflict "single hit" damage, even death, on nondividing cells. The more general problem of the ability of human beings to thrive in a closed, stressful environment assumes novel importance and exigency with extended spaceflights. In addition to the problems of weightlessness and heavy ion radiation, the crew may have to deal with increased microbial density in the cabin air, organic and inorganic toxins (outgassing products), nutritional limitations, and the problems of health care delivery in space. These physical stresses will exacerbate the severe emotional stresses associated with working and living in confined quarters. Many of these problems have no terrestrial analog and must be understood in much greater depth before we can permit a manned mission to Mars. Some of the research in space biology and medicine is concerned with the health and welfare of the astronauts. Other components are of basic scientific interest and deal with fundamental questions concerning the role of gravity in life processes. The task group believes that these two objectives complement one another.
INTRODUCTION 7 IMPLEMENTATION The following chapters discuss the status and goals of these five areas of researchâexobiology, global biology, controlled exological life support systems, space biology, and space medicine. Chapter 8 discusses the instrumentation and technologies required to achieve these goals. The task group emphasizes that research on living organisms, including humans, imposes constraints not encountered in the other space sciences. On the other hand, many of the instruments, as well as the strategies, of the global biologists are common to the earth scientists. Similarly, the section treating exobiology contains numerous cross-references to the field of planetary exploration.