Wide Awake in Outer Space

But in space, the right cue isn't so easily provided. The space shuttle orbits Earth every 90 minutes. So, instead of receiving the Terran pattern of 12 hours of light followed by 12 hours of dark, astronauts on the shuttle's flight deck experience 45 minutes of light succeeded by 45 minutes of dark. This rapid-fire exposure might disrupt - or as sleep researchers say, "disentrain" - the astronauts' circadian cycle.

It's important that the cycle be entrained: that the astronaut's biological day matches the environmental one. "The circadian system is set so that you're best prepared to be alert and awake during the biological day, and to sleep at [biological night],” says Wright. If the body is required to perform activities at the wrong biological time, he explains, it will not function optimally.

For that reason NASA sometimes deliberately shifts the astronauts' cycles before sending them into space, making sure that their biological day coincides with the crucial period of launch, according to Dr. Bette Siegel, a scientist in the Bioastronautics division at NASA headquarters. Effecting the shift is easy: astronauts are exposed to high intensity light at key times for three to ten days before liftoff. By the time the shuttle is ready to leave Earth, the crew is bright-eyed and alert.

Once in orbit the biological clocks of astronauts might need to be adjusted further to align with another critical time - the moment of landing. It's done by requiring the crew to wake up earlier and earlier each day.

Researchers still aren't sure exactly what happens to the circadian clocks of astronauts under such circumstances. To help find out, astronauts wear a wrist device that tracks astronaut sleep patterns along with their light exposures. "We have models,” says Wright, "where we can take their sleeping history and their light exposure history and predict what's going to happen to their [internal] clock.” The device, along with sleep diaries kept by the astronauts, will help researchers figure out which factors - such as light exposure, temperature, or ambient noise in the close confines of a spacecraft - affect sleep most during spaceflight.