Using rats as subjects, astronauts explored how learning occurs in space by measuring changes that take place in the central nervous system. We weren't sure it was going to work. The ability of the nervous system to adapt is impressive. Losing Sleep and Balance Payload specialist Jim A. Pawelczyk recounted his sleep experiments. The space shuttle is definitely not a good place to get a good night's sleep, he reported.
Astronauts become shift workers to handle their myriad tasks.
Crewmembers reported an average sleep of 5 to 6 hours, compared to the typical period of 7 to 8 hours on Earth. You are constantly thinking about how you can do this or that task better, and you take that along with you to bed. Sleep difficulty has produced a number of studies that have begun to shed light on sleep disorders on Earth as well as in space. After adapting to space, the astronauts had to readapt when returning to Earth. Upon reentering the atmosphere, a full-pressure suit worn with a helmet helped the astronauts withstand the pull of newly felt gravity.