Below is one of two articles I wrote relating to sleeping in space.
In space there is no “up” or “down,” and due to microgravity, astronauts are weightless. Though NASA astronauts are allotted 8 hours every 24 hours for sleep, they have to overcome the unique challenges of sleep in space in order to maintain their sleep health.
Currently, astronauts on the International Space Station (ISS) are the only ones who do any space travel. The ISS has 13 rooms, 2 bathrooms, is the size of a football field, and has a mass of roughly 1 million pounds. It orbits about 200 miles above Earth and travels 17,000 miles per hour. That means every 90 minutes, the ISS does a full rotation around Earth, which means the astronauts get to see the sun rise and set every 90 minutes. Talk about potential circadian rhythm disorder!