Physiological effects of space cabin atmospheres.

In the past, the pressure of engineering commitments involved in the development of spacecraft required that decisions on space cabin atmospheres be made early, often before the physiological tolerance to unnatural gaseous environments could be determined. Selection has been based primarily on engineering grounds, with the burden of proof on the physiologist that the proposed environments could not be tolerated. While this approach has been adequate for previous flights, it has serious drawbacks in the longer and more hazardous missions projected for the future.