Protective shielding, shielding chemicals, and careful monitoring of the doses of radiation received by each astronaut have been used to reduce radiation exposure to acceptable levels. The absence of the earthly cycle of day and night during space travel produces subtle effects, both physiological and psychological. These rhythms are related to human patterns of sleep and wakefulness, which in turn are based on the alternation of day and night. The nature of the artificial atmosphere astronauts breathe is an important biomedical consideration. Ideally, this atmosphere would be identical in composition and pressure to the earth's atmosphere.
Any alteration involves the risk of decompression sickness.
The space shuttle uses a pure oxygen atmosphere or a mixture of oxygen and nitrogen. The Columbia Encyclopedia, Sixth Edition. Click here to shop the Bartleby Bookstore .