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space biology:see exobiologyexobiology
search for extraterrestrial life within the solar system and throughout the universe. Philosophical speculation that there might be other worlds similar to ours dates back to the ancient Chinese and Greeks.
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the group of mostly biological sciences that study (1) the characteristics of the vital activities of terrestrial organisms under space conditions and during flights on spacecraft (space physiology, ecophysiology, and ecobiology); (2) principles for constructing closed ecological biological life-support systems for the crew of spacecraft and space stations; and (3) extraterrestrial forms of life (exobiology).
Space biology is a synthetic science, having gathered together the advances made in various branches of biology, aviation medicine, astronomy, geophysics, radio electronics, and many other sciences and having based its own research methods on them. Space biologists carry out research on diverse species of living organisms, from viruses to mammals. More than 56 species have already served as subjects of this research in the USSR. More than 36 species have been studied in the USA.
The scientific foundation of space biology, like that of space medicine, was laid largely by L. A. Orbeli, V. V. Strel’tsov, N. M. Dobrotvorskii, A. P. Apollonov, N. M. Sisakian, A. V. Lebedinskii, V. V. Parin, V. N. Chernigovskii, and O. G. Gazenko in the USSR; H. Armstrong, R. Lovelace, H. Strug-hold, D. Flickinger, P. Campbell, and A. Graybill in the USA; R. Grandpierre in France; R. Margaria in France, Italy; and J. Aschoff and O. Hauer in the Federal Republic of Germany (FRG). In addition to the USSR and the USA, France, Italy, and the FRG are also active in space-biology research. It has been Soviet and American scientists, however, who have made the greatest contribution to the development of the field. The first biological experiments in the upper atmosphere and in space, using balloons, were performed in the 1930’s in the USSR and the USA. This period culminated in the genetic experiments carried out in 1935 on the stratosphere balloons USSR-1-bis and Explorer 2 (USA). These constituted an attempt to determine the effects of cosmic radiation on mutagenesis.
The most important task of space biology is to study the effect of the factors of space flight (acceleration, vibration, weightlessness, an altered gaseous medium, limited mobility, and complete isolation in sealed, pressurized accommodations) and space itself (vacuum, radiation, and the diminished intensity of the magnetic field). The research involves laboratory experiments that more or less reproduce the effect of these factors. However, biological experiments in flight are of the greatest importance, since these provide an opportunity to study the effect of the aggregate of unusual environmental factors on the living organism.
The conditions of respiratory gas exchange are the first to change with altitude. For example, at an altitude of 15 km and a barometric pressure of about 87 mm Hg, respiration is impossible even when pure oxygen is inhaled. The fluids in the bodies of warm-blooded animals begin to “boil” at 19.2 km, since (at 37°C) the barometric pressure becomes equivalent at that altitude to the vapor pressure of the fluids. At altitudes of 36–40 km, the atmospheric layer still above the craft is insufficient to absorb primary cosmic radiation, and the injurious biological effects not only of the radiation but also of ultraviolet rays (at wavelengths of 2,100-3,000 Å) are first felt. However, owing to the weak penetrating capacity of ultraviolet radiation, a sealed, pressurized spacecraft cabin provides adequate protection against this radiation. At altitudes of 100–120 km or more from the earth’s surface, there is a danger (although inconsiderable) of encountering meteorites. At altitudes beyond this range, sound waves cannot be propagated because of the virtual absence of atmosphere. Light scattering is lost, so that there are sharp contrasts between illuminated and shaded surfaces; depth perception is diminished. A situation of dynamic weightlessness arises on an artificial earth satellite, since the force of gravity is matched by the centrifugal force that develops in orbital flight.
Numerous rocket flights of dogs, monkeys, and other animals in the 1940’s and 1950’s to altitudes as great as 500 km under conditions approaching those of space flight constituted the first stage of the biological research conducted in the USSR and the USA. These experiments were used to study the possibility of creating the conditions essential for animals to live in pressurized cabins (or in special suits in nonpressurized cabins) and to devise methods of ensuring safety during flight, ejection, and parachuting from great heights. The experiments also yielded information on the biological effects of primary cosmic radiation. It was concluded from these studies that highly organized animals can tolerate rocket-flight accelerations and dynamic weightlessness for up to 20 minutes.
The next stage in space-biology research was marked by the long flight of the dog Laika on Sputnik 2. The third stage involved the development of orbital spacecraft capable of returning to earth. These made it possible to broaden the research program substantially by including in the “crew” a number of new biological objects of study and to examine the animals and plants for many months after the flights. Experiments were performed with dogs, rats, mice, guinea pigs, frogs, fruitflies, higher plants (Tradescantia; wheat, pea, onion, corn, and Nigella seeds); plant shoots at various stages of development; snail eggs; unicellular algae (Chlorella); human and animal tissue cultures; and bacterial cultures, viruses, bacteriophages, and certain enzymes. Normal barometric pressure (760± 10 mm Hg) and temperature (18 ±3°C) were maintained in the cabins during flight. The oxygen content varied from 20 to 24 percent; the relative humidity, from 35 to 50 percent. Tissue cultures and other biological objects were kept in incubators with automatic temperature control. The dogs were provided with a jellylike food from automatic feeders; the small laboratory animals had free access to the food and water. Some of the subjects were kept in an oxygen-enriched atmosphere in order to increase their sensitivity to irradiation. The dogs’ electrocardiogram, arterial pulse, pneumogram, phonocardiogram, electromyogram, seismocardi-ogram, body temperature, and motor activity were recorded by radiotelemetry, and their behavior was observed by television. Control animals were observed for all of the experiments under the same conditions, except weightlessness, as the animals in flight.
During positioning for orbit, all of the dogs exhibited the rapid pulse and respiration typical for acceleration; these effects gradually disappeared once the vehicle had gone into orbit. The most important immediate effects of acceleration are changes in pulmonary ventilation, a redistribution of blood in the vascular system (including the pulmonary circuit), and changes in the reflex regulation of the circulation. The pulse returns to normal much more slowly after acceleration under conditions of weightlessness than after centrifuge experiments on earth. Both the mean pulse rates and the absolute pulse rates were lower with weightlessness than with the corresponding experiments on earth. In addition, the rates fluctuated considerably. Analysis of the dogs’ motor activity revealed fairly rapid adaptation to the unusual conditions of weightlessness and restoration of the capacity for coordinated movement. The same results were obtained in experiments with monkeys. Studies on conditioned reflexes in rats and guinea pigs after their return from space flight failed to show any changes in relation to preflight data.
Biochemical analyses of the blood and urine of dogs, rats, and mice after space flight revealed certain transient changes corresponding to stress reactions. The two dogs on Sputnik 2 exhibited wavelike fluctuations in immunological reactivity, with periods of depression and activation. Similar but less pronounced fluctuations were observed in the dogs on Sputnik 4 and Sputnik 5. Cytological and histological examinations of the mice on Sputnik 2 revealed an increase in the number of chromosomal aberrations in bone-marrow cells, an appearance of immature forms, and some depression of hematopoiesis. The experiments with two dogs on the Soviet Kosmos 110 (1966) and with a monkey on the American Bios 3 (1969) were important for the continued progress of ecophysiological research. During a 22-day flight, the dogs were subjected for the first time not only to the conditions inevitably present on a space journey but also to a number of special stimuli (electric stimulation of the sinus nerve, compression of the carotid arteries) in order to determine the characteristics of the neural regulation of blood circulation under conditions of weightlessness. The animals’ blood pressure was recorded directly by means of vascular catheterization. The Kosmos 110 passed through the earth’s inner radiation belt during each orbit, and on-board dosimetric measurements were taken. Postflight studies and analysis of the data obtained showed that prolonged space flight results in cardiovascular deconditioning in the highly organized mammals and in a disturbance of water-salt metabolism (in particular, in a marked decrease in the calcium content of the bones, or decalcification).
During the flight of the Bios 3, which lasted 8.5 days, monkeys exhibited serious changes in their cycles of sleep and wakefulness: the fragmentation of states of consciousness, rapid shifts from drowsiness to alertness, marked contraction of the dream and deep phases of sleep, and irregularities in the circadian rhythms of certain physiological processes. The death of an animal soon after the premature termination of the flight was attributed by specialists to weightlessness, which resulted in a redistribution of blood, a loss of fluids, and a disturbance of potassium and sodium metabolisms.
Genetic studies carried out on orbital flights showed that being in space stimulated dry onion and Nigella seeds to more rapid germination and seedling growth. Cell division was accelerated in pea, corn, and wheat seedlings. A culture of a race of ac-tinomycetes resistant to radiation contained six times as many surviving spores and developed colonies as did the control; a radiosensitive strain produced only one-twelfth as many.
Fruitflies were compared after space flight to a control group with respect to both the frequency of lethal mutations in the X chromosome resulting in early death and the frequency of primary nondisjunction in the chromosomes. Analysis of the statistically significant increase in the frequency of recessive sex-linked lethal mutations in comparison with the total radiation dose received during the flights and with an evaluation of the results of special experiments on the ground showed that the genetic changes observed could not be ascribed solely to radiation but rather to the combined effects of all the factors of space flight (in particular, to the dynamic factors: acceleration, weightlessness, and vibration). It is possible that certain factors sensitize the organism to the concurrent action of others. For example, biological experiments performed on the American Bios 2 (1967), which had an artificial source of gamma radiation on board, showed that weightlessness increased radiosensitivity in some of the biological subjects but decreased it in others.
Experiments on lunar flights were the next stage in the research program. These experiments were designed to study, in the absence of the screening effect of the earth’s magnetic fields and atmosphere, the biological effects of the ionizing radiation of the Van Allen belts and of the considerable amounts of primary cosmic radiation and protons from solar flares. The work was done on flights of the Soviet automatic space stations of the Zond series from September 1968 through October 1970. Turtles, fruitflies, onions, plant seeds, various strains of Chlorella and E. coli, and other biological subjects were placed on board. The total irradiation dose was approximately the same on all of the flights. After returning to earth, the turtles were active, moving about and eating. Analysis of the blood indicators (white and red blood counts, hemoglobin) and electrocardiograms failed to disclose any essential differences between the animals that had been in space and the control animals.
The flight stimulated the growth and development of wheat, barley, and onion seeds and caused chromosomal aberrations. These changes were generally the same as the shifts recorded in the biological subjects studied in low-altitude orbits. A comparatively large number of chromosomal aberrations were noted in pine and barley seeds, and there was an increase in the number of mutants in Chlorella.
A set of experiments using various biological subjects (seeds, higher plants, frog eggs, microorganisms) was carried out on the Soviet Kosmos 368 (1970), the Soyuz, and the Salyut (1971; the world’s first orbital space station). In addition, West Germans conducted an experiment in 1970 with medicinal leeches on American and French high-altitude rockets, there was a combined Italo-American experiment in 1970 with frogs on the OFA satellite, and a microbiological experiment was performed in 1972 on the moon’s surface by the crew of the American spacecraft Apollo 16.
The results of the biological experiments performed on high-altitude rockets and ballistic missiles, unmanned and manned earth satellites, and other space vehicles showed that man can live and work in space for relatively long periods. Weightlessness was found to reduce tolerance for physical exertion and to make readaptation to normal gravity difficult. Another significant finding was that weightlessness is not in itself mutagenic, at least in terms of genes and chromosomes. In the planning and execution of future ecophysiological and ecobiological research in spacecraft, attention will be focused mainly on the effects of weightlessness on intracellular processes, the biological effects of highly charged heavy particles, the circadian rhythms of the physiological and biological processes, and the influence of several of the factors of space flight in combination.
The next major problem of space biology (and of space medicine) is to elaborate the biological principles of normal life support for man during long stays in space. This is the only way an efficient life-support system can be developed.
Experimental confirmation of the absence of life on the moon (based on the study of lunar soil) was the first important result in exobiology.
Studies in space biology enabled scientists to develop a number of protective measures and to prepare for the possibility of safe manned space flight. This has been accomplished first by the Soviets and then by the Americans. However, this has not exhausted the value of the science of space biology, which will be used in the future to solve a number of other problems—in particular, questions associated with the biological reconnaissance of new space routes. This research will require the development of new techniques of biotelemetry, the creation of implantable devices for short-range telemetry (from an object to an on-board transmitter), the conversion of various kinds of energy arising in organisms into the electric energy needed to power these devices, and the development of new methods of “compressing” information. Space biology will also play an extremely important role in the development of the biocomplexes (that is, closed ecological systems of autotrophic and heterotrophic organisms) that will be essential for long flights.
The first publication on the results of Soviet experiments in space biology appeared in 1956. The results of biological and medical research are published in the USSR in the transactions of the Institute of Biomedical Problems of the Ministry of Public Health of the USSR; in Kosmicheskie issledovaniia (Space Research), a journal of the Academy of Sciences of the USSR; in the multivolume publication Problemy kosmicheskoi biologii; in the journals Kosmicheskaia biologiia i meditsina and Aviatsiia i kosmonavtika; and in such foreign periodicals as Aerospace Medicine, Bioscience, Rivista di Medicina Aeronautica e Spaziale, Space Flight, and Space Life Sciences.
Space is becoming an arena for international cooperation, and this is true for space biology as well. The USSR carries out joint research with socialist countries according to the Interkosmos program. Work is under way on the joint Soviet-American Osnovy kosmicheskoi biologii i meditsiny (Principles of Space Biology and Medicine). An agreement was signed in 1972 between the governments of the USSR and the USA for cooperation in the study of space and its use for peaceful purposes; this applies, in particular, to cooperation in space biology.
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V. V. PARIN