⁹ Includes part of [ref.196].
In the first U.S. manned space flight program, Project Mercury, and in
the face of very severe weight limitations, a cabin atmosphere of pure
oxygen at one-third atmospheric pressure was adopted. This choice
probably represented the greatest simplification which could be achieved
readily and, at the same time, provide protection against some of the
risks of rapid decompression. Although breathing pure oxygen at higher
pressures was known to be attended by some undesirable physiological
effects, the short duration of the flights to be undertaken, and the low
pressure employed, suggested that no harmful results would result in
this case. That these expectations were generally borne out is now
history. Preparations for space flights of longer duration—many weeks or
months—present similar problems and require special attention to
phenomena which may be either undetectable or of trivial significance on
a time scale of a few days.