Life Support for Manned Space Flight

Abstract

M AN'S successes in venturing into space are merely an extension of his early efforts to survive on earth. Prehistoric man fashioned clothing, learned to use fire, and devised equipment that enabled him to explore and take nourishment to regions of the earth where existence otherwise would have been impossible. Now that man has developed a sophistication of survival that permits him to live in virtually all regions of the earth, including the oceans and the atmosphere, his new challenge is to learn to occupy and make beneficial use of the far reaches of space. The first efforts of manned space flight by the USA and the USSR have demonstrated that man can survive beyond his sensible atmosphere. These early probing flights also have established that, when adequately supported, man can carry out meaningful tasks while under the stresses of space flight. Let us examine what we mean by adequate support for man in space. A space vehicle is unique, different from any vehicle previously designed, in that it must carry with it the total environment and all materials needed for man's existence and performance throughout an entire mission. In space there is nothing material, with the possible exception of energy from the sun, that may be of assistance in the support of man. Thus, the problem of developing a manned vehicle for space is one of engineering reliable life-support systems into a sealed capsule that will ensure an environment in which the occupant can maintain his technical proficiency. It is not sufficient to merely support a man in space. He must be supported in a manner that permits him to complete his mission. Until the tolerance limits of man's physical and functional effectiveness under the stresses of space travel are fully determined, scientists and technicians must devise life-support systems based on known data, providing redundancy and wide safety factors. To accomplish this we encase the man in a vehicle that protects him from the vacuum through which he travels. To save weight and ensure capsule integrity, the vehicle's atmospheric pressure is reduced from that normal on earth to approximately 5-7 lb per square inch. Because of the pressure reduction, the capsule's oxygen content must be increased to 100%; thus terrestrial partial pressures of oxygen are approximated. The oxygen must be carried aboard and metered to the astronaut in a regular and uniform concentration. To protect the astronaut against possible failure of capsule integrity, which would result in cabin pressure dropping below that required for normal pulmonary gaseous exchange, the man is encased in a close-fitting, gas-impervious, full-pressure suit which automatically provides required pressures in the event of such emergencies. There are several possible methods of supplying oxygen. One is to carry the total supply of oxygen, either in the gaseous form in high-pressure containers or in the space-saving and weight-saving liquid or cryogenic states. A second method is to derive oxygen from oxygencontaining chemicals, such as the superoxides and ozonides. Methods of utilizing these chemicals are being vigorously investigated. A third method is to produce oxygen with living organisms and plants such as algae. The use of algae in space vehicles is also being studied. A fourth and possibly the most promising method is dissociation of the carbon dioxide respired by the astronaut into useable oxygen and carbon. Ultimately an absolute, closed ecological system will be devised in which all chemical components carried from the earth will be utilized over and over again. Man uses very little of the total oxygen of a 100% oxygen environment during normal respiration. Since it would be improvident to dump the exhaled atmosphere overboard, the unused oxygen must be recirculated. To do this, the exhaled atmosphere is to be reconditioned by removing carbon dioxide, noxious gases, and water vapor. Lithium hydroxide beds are planned for this use in the early Gemini and Apollo vehicles; other methods are considered for more advanced Gemini and Apollo flights. Water vapor will be removed by condensation. Use of a superoxide as the source of oxygen will pay dividends: the chemical itself removes carbon dioxide and moisture from the respired air. In order to use the dissociation method effectively, the carbon dioxide of the respired air must be separated before processing. Removal of water vapor from the respired air by means of condensation will be a source of potable water with this system. Men who are supported in 100% oxygen have been