It’s hard to get a good night’s sleep in space. An evaluation of astronauts serving on the Mir space station found that they experienced shorter sleep durations, more wakefulness, and changes in the structure of their sleep cycles while in microgravity.
Researchers at Harvard College, Harvard Medical School, and NASA Ames Research Center studied the sleep patterns of four cosmonauts and one astronaut before, during and after spaceflight to conduct missions on the space station. Preliminary results show that they slept an average of only 5.7 hours in space, compared with 6.7 hours on Earth. They also spent significantly more time awake in bed, leading to a 17.7% reduction in sleep efficiency.
In space their time in non-REM and REM sleep decreased by 14.1% and 25.8% respectively. On average it also took about 90 minutes after falling asleep for astronauts to reach their first episode of REM sleep in space, nearly 1.5 times longer than on Earth.