Fluids shift toward the head, causing puffy faces and thinner legs. Bones lose density at roughly 1-2% per month without countermeasures. Muscles atrophy rapidly. Astronauts exercise two hours daily using specially designed treadmills, bikes, and resistance machines to slow these effects.

Sleep is complicated when there is no "down." Astronauts zip into sleeping bags attached to walls. Food is mostly freeze-dried or thermostabilized. Crumbs float dangerously — they can clog air vents or irritate eyes. Every drop of water is recycled, including from sweat and urine.