In space there is no up or down and there is no gravity. As a result, astronauts are weightless and can sleep in any orientation. However, they have to attach themselves to a wall, a seat or a bunk bed inside the crew cabin so they don't float around and bump into something.
Space shuttle and space station crews usually sleep in sleeping bags. On the space shuttle, astronauts can also sleep in the commander's seat, the pilot's seat or in bunk beds. There are only four bunk beds in the space shuttle. So that means on missions with five or more astronauts, the other crewmembers have to sleep in a sleeping bag attached to their seats or to a wall.
On the space station there are two small crew cabins. Each one is just big enough for one person. Inside both crew cabins is a sleeping bag and a large window to look out in space. Currently, space station crews have three astronauts living and working in space for months at a time. Where does the third astronaut sleep? If it's okay with the commander, the astronaut can sleep anywhere in the space station so long as they attach themselves to something.
Expedition Two Commander Yury Usachev and Flight Engineer James Voss slept in the crew quarters inside the Zvezda Service Module. Flight Engineer Susan Helms slept inside the Destiny Laboratory.
Astronaut Susan Helms slept in the huge Destiny Laboratory Module by herself while she was living aboard the International Space Station. This is on the opposite side of the station from the Service Module where her crewmates slept. The length of the International Space Station during that mission was 52 meters (171 feet) long.
Generally, astronauts are scheduled for eight hours of sleep at the end of each mission day. Like on Earth, though, they may wake up in the middle of their sleep period to use the toilet, or stay up late and look out the window. During their sleep period, astronauts have reported having dreams and nightmares. Some have even reported snoring in space!
The excitement of being in space and motion sickness can disrupt an astronaut's sleep pattern. Sleeping in close quarters can also be disruptive since crewmembers can easily hear each other. Sleeping in the shuttle's cockpit can also be difficult since the Sun rises every 90 minutes during a mission. The sunlight and warmth entering the cockpit window is enough to disturb a sleeper who is not wearing a sleep mask.
When it is time to wake up, the Mission Control Center in Houston, Texas, sends wake up music to the crew. Usually, Mission Control will pick a song for a different astronaut each day. Sometimes a family member will request a favorite song for their particular loved one. Depending on the astronaut, Mission Control will play all types of music such as rock and roll, country and western, classical, or Russian music. However, only a shuttle crew receives wake up music while a space station crew uses an alarm clock.