Wide Awake in Outer Space

Space travel can be exciting - and restless! NASA researchers are exploring ways to help astronauts enjoy a better night's sleep on the space station... and beyond.

Astronauts sleep poorly in space, and it's no wonder. Just consider: the excitement of blasting off on a powerful rocket, the strange sensations of floating in free-fall, the novelty of mornings that return every 90 minutes... Who could sleep through all that?

On some space shuttle missions up to 50% of the crew take sleeping pills, and, over all, nearly half of all medication used in orbit is intended to help astronauts sleep. Even so, space travellers average about 2 hours sleep less each night in space than they do on the ground.

That deficit adds up, says Dr. Ken Wright, Instructor in Medicine at Harvard Medical School, and Associate Neuroscientist at Brigham and Women's Hospital. "Research performed on Earth suggests that some of them, after a week or two on this restricted sleep schedule, are performing at the level of someone who's been awake for 24-plus hours.”

Fatigue, on Earth or in space, is a serious problem. It affects performance, increasing irritability, diminishing concentration, and decreasing reaction time. And it increases the risk of accidents.

On Earth, sleep can be disrupted by anything from a crying baby to tomorrow's exam. In space wakefulness can come from noise and excitement - and, possibly, the disruption of the circadian rhythms that ensure a good night's sleep.

Sleep is, in large part, managed by our body's master clock, which is located in the brain's hypothalamus. This clock regulates the body's daily production of melatonin, a sleep-promoting hormone, and cortisol, a hormone that promotes wakefulness, and is also associated with stress. The clock also manages a multitude of other physiological cycles, including body temperature, growth hormone production, heart rate, and urine production. The circadian clock generates these cycles all on its own. But there's a problem. Free-running, the master clock produces cycles that average about 24.2 hours - slightly longer than Earth's day. So the clock must be reset. It needs to be adjusted daily to ensure that the biological day and night don't get out of sync with the environment. On Earth, it's reset automatically, simply by our exposure to the high intensity light of day.