Spacecraft are subject to temperature extremes that range from 400° F above zero to 400° below zero. Protecting astronauts from these extreme temperatures was a prime concern for NASA spacecraft designers.
One of the tragedies of the early space program was a fire that occurred in an Apollo module causing the deaths of three astronauts. On investigation of the fire, it was found that some of the materials utilized in the spacecraft, such as polyurethane foam in seats, were highly flammable.
One of the potential hazards confronted by astronauts is the shifting of bodily fluids that occur as a result of changing gravity levels. During the Apollo program, NASA's Ames Research Center began conducting research on the use of pilot `anti-G` suits for possible astronaut use.