“Artificial Climate” in the Sealed Spacecraft
Because there is no atmosphere in outer space, an arti-ficial atmosphere and climate must be produced in a spacecraft. Most important, the oxygen concentration must remain high enough and the carbon dioxide con-centration low enough to prevent suffocation. In some earlier space missions, a capsule atmosphere contain-ing pure oxygen at about 260 mm Hg pressure was used, but in the modern space shuttle, gases about equal to those in normal air are used, with four times as much nitrogen as oxygen and a total pressure of 760 mm Hg. The presence of nitrogen in the mixture greatly diminishes the likelihood of fire and explosion. It also protects against development of local patches of lung atelectasis that often occur when breathing pure oxygen because oxygen is absorbed rapidly when small bronchi are temporarily blocked by mucous plugs.
For space travel lasting more than several months, it is impractical to carry along an adequate oxygen supply. For this reason, recycling techniques have been proposed for use of the same oxygen over and over again. Some recycling processes depend on purely physical procedures, such as electrolysis of water to release oxygen. Others depend on biological methods, such as use of algae with their large store of chloro-phyll to release oxygen from carbon dioxide by the process of photosynthesis. A completely satisfactory system for recycling has yet to be achieved.
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