What is it like to sleep in space?

Spacecraft like the International Space Station have pressurized cabins and are filled with the same kind of air we breathe on Earth, so the atmosphere on board is made to feel as close to sea level as possible. But microgravity causes astronauts to experience the effects of weightlessness, and setting up a mattress on the floor can't be part of the plan because not only would the astronaut float away after dozing off, the mattress itself would also drift off, creating the potential for midair collisions.

Because of this effect, astronauts could, theoretically, sleep almost anywhere in a spacecraft. Astronauts sleeping during space shuttle missions normally strap themselves into seats or attach sleeping bags to the walls; they'll avoid the cockpit since light from the sun can cause the area to heat up significantly and make slumber uncomfortable. Most of the crew on the ISS choose to sleep in their own cabin or in an ISS module -- American crew members' sleeping quarters are well-ventilated (to prevent breathing in the carbon dioxide you just breathed out), soundproof private cabin-for-one setups where an astronaut can not only catch some Z's but also catch up on e-mail. The catch is that they need to tether themselves to something to avoid floating away in the air currents. Most astronauts choose to sleep as closely to how they would on Earth, in sleeping bags tethered to the floor, the walls, or the ceiling. In the microgravity environment there is no such thing as "up," which means it's just as easy to sleep vertically as you would horizontally back home. It's also important to secure your arms (and legs) to avoid them hovering as you sleep.

Adjusting to sleep in space takes a long time for astronauts. Our bodies and brains are used to certain circadian rhythms -- the 24-hour cycle of waking and sleeping -- and disturbing them can cause sleep difficulties.

How long you sleep and how well you sleep are important to your mood, how well you concentrate and how much energy you have, as well as how healthy your body is; chronic sleep deprivation can lead not only to irritability but also to attention deficit and an increased risk of cardiovascular disease, diabetes, hypertension, and obesity [source: American Academy of Sleep Medicine].

Despite pre-mission training and preparation living on board a space station can be disorienting for the body. To avoid any distracting light and heat from the sun, for example, astronauts will cover up any windows they may be near. Astronauts can also choose to wear black sleep masks, the same kind that some people wear on Earth when they want to shut out distracting light. On top of excessive light, strange noises are a big part of the ISS. Because fans, air filters and other noisy equipment provide life support to the astronauts, the ISS is often filled with constant whirring noises -- a constant hum. Astronauts sometimes sleep with earplugs to dampen the sound, but after a while many report they simply get used to it.

Combine the light and the noise with the unnatural feeling of floating, motion sickness, aches and pains, poor ventilation and temperature control, as well as a new sunrise every 90 minutes (the amount of time it takes the space station to circumnavigate the Earth) insomnia and sleep deprivation are a common and serious problem for humans in space; NASA reports that sleeping pills are the second most common drug astronauts take (painkillers are the most common). To help combat astronaut insomnia NASA also budgets at least 8 hours of sleep every day, promotes relaxation techniques, and provides sleep hygiene education but despite it all astronauts average between 30 to 60 minutes less sleep each night than they got at home on Earth [source: Worth]. NASA has also invested $11.4 million to update the fluorescent lights in the ISS's U.S. Orbital Segment with bulbs designed to exploit that our bodily clocks are wound by exposure to light [source: Worth].

And yes, in case you were wondering, it is possible to snore in space.