Astronauts in places with microgravity, like on the ISS, are weightless; they can sleep or rest in any orientation.
However, when it’s time for them to sleep, they have to attach themselves so they don’t float around and bump into something.
Astronauts Thomas D. Jones and Mark L. Polansky during their sleep shift in the Destiny laboratory on the International Space Station in 2001. Photo courtesy of NASA
ISS astronauts usually sleep in sleeping bags located in small crew cabins. Each crew cabin is just big enough for one person. Astronauts also attach themselves to walls or the ceiling to sleep.
Many sleep worse on a space mission than on earth. It may be due to micro gravitation, but also to other factors such as noise, excitement, stress, jet lag or too cold or too warm temperatures causing discomfort. Another factor can be the fact that on the ISS, for example, the sun rises as many as 15 times a day.
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Astronauts have told they dream more, but sleep less in space – around six hours and not seven or eight as we usually do on earth. One theory suggests that it may be because an astronaut moves more easily in microgravity.
Weightlessness does affect the types of dreams, too.
During their sleep period, astronauts have reported having dreams and nightmares. Some have even reported snoring in space.
NOTE: Microgravity is the condition in which people or objects appear to be weightless.