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SUMMARY STATEMENT The investigation of animal and human responses to weight- lessness has become an important field of research in bioastro- nautics. However, experimentation is rather difficult because of the unusual conditions in which the state of reduced gravity and weightlessness can be obtained. In general, three types of en- vironmental situations have been employed; namely, the free-fall situation, the dynamic condition in aircraft and rockets, and the simulation of weightlessness by immersing a body in water. The devices employed in this research were described. With the exception of Laika, who was exposed to weightless- ness in an artificial earth satellite (Sputnik II) for seven days, ex- posure to subgravity and zero-G states was of only short or moderate duration. There is neither experimental evidence nor indication through subjective experience that subgravity and zero-G states as such have serious physiological consequences. However, devia- tion from normal behavior by individuals with a low tolerance was observed. This may be due to either faulty research design, such as changes of the acceleration pattern involved, or it may concern individuals having an extremely low or pathological motion sensi- tivity. On the other hand, relatively fast and reliable adaptation to these states was observed if normal or pre-conditioned subjects were employed, and if preventative and protective measurements were taken. While the early experiments on weightlessness only concerned the seated and safely secured test subject, later studies were done with subjects acting and floating about in the weightless state. The analysis of the experiments shows that subjects at rest can very well tolerate the weightless state, and that no deleterious Coriolis effects occurred during head and body movements. As far as per- formance was concerned, no special provision, such as wider spacing of switches and levers, or springs or other restraints to prevent the arm from over-shooting when reaching or aiming for objects, need be considered. Without exception, the subjects have been able to adjust themselves to weightlessness in a matter of seconds; then their motor performance was as accurate and rapid as during normal conditions. In fact, subjects who performed ex- periments in which the arm must be extended and then raised and 126
lowered over a considerable portion of reach reported that it was easier to work during zero-G. However, it is necessary to work at a solid position in order to maintain performance during weight- lessness. A normal seat with a tight safety belt has proven quite adequate in this respect. Tools, specially designed for work under zero-G conditions, facilitate the work. The most interesting experiment is the one in which human subjects were allowed to float without restraints of any kind. The experiments were done to study the ability of the individual to move during weightlessness; and to maintain his position orientation during the zero-G condition. With a little practice it was possible to maneuver in the weightless space as though it were filled with water. While the swimming type movements were not as effective as they are in a liquid, they were useful for accelerating the body and for changing its direction while floating through the weightless environment. A great number of subjects have gone through the floating experiments without ill effects or disorientation. How- ever, all subjects who have performed tumbling motions during the weightless period reported extreme disorientation, sometimes bordering on a severe case of vertigo, after a few revolutions. Undesired physiological effects were also observed during post- and pre-acceleration weightlessness; that is, when the state of weightlessness was preceded or followed by high accelerations. We are furthermore concerned that when the exposure becomes longer, there may develop minor physiological disturbances which, if cumulative and irritating, may cause or enhance psychological effects. Subjects immersed in water reported a rapid loss of orienta- tion when visual clues were excluded; and large changes in body position were made before they were noticed by the test subjects. However, the immersion technique provides a rather crude simu- lation of the weightless state with respect to the neurological and psychological parameters involved. Although the results obtained by immersion may not be directly applicable to the prediction of psychophysiological response during the true zero-G condition, further improvement of this technique may be valuable for the in- vestigation of the vestibular factors involved. In summary, research on subgravity and zero-G effects must be emphasized in the following areas:
a. Animal and human performance. Although no practical implications for short and moderate periods of time are anticipated, physiological and psychological deviations from the normal pattern may occur after exposure to long periods of zero-G. b. State of consciousness, well-being, and performance during rocket acceleration patterns including states of post- and pre-acceleration weightlessness. c. Clinical studies of certain critical physiological functions such as cardio- and hemodynamics, respiration, digestion, and basal metabolic rate, under conditions of changed gravitational vectors. d. Perception, orientation, and performance characteristics under abnormal gravitational conditions. This mainly concerns research on visual and vestibular functions under true or simulated weightless conditions. e. Application of drugs and other remedies for the prevention of adverse effects associated with accelerative changes and weight- lessness. f. Design and construction of protective devices adequate for work and life in the weightless environment. g. The design of new devices and the improvement of existing methods for training and conditioning of the astronauts. h. Studies on readaptation to the normal gravitational condi- tions after prolonged exposure to weightlessness. i. Research on the metabolism, growth, reproduction, and decay of organic matter, such as lower organisms, tissue cultures, cellular systems, plants, and lower animals. j. Investigation of the effects of the artificial gravity, sub- gravity, and differential gravity on the organism while resting and moving. 128
