Apparently, getting sleep in space is no easy task.

According to a decade-long study, astronauts manage to get, on average, less than six hours of sleep per day during their missions. Most take sleeping pills to help get the even that much.

The study, published in Lancet Neurology, followed 21 astronauts working in space stations and 64 astronauts whose work was shuttle-based. They collected data from personal logs that kept track of sleep and medication usage. The astronauts were also hooked up to monitors that sensed movements in order to confirm the amount of sleep each person got.

Despite NASA’s regulations that 8.5 hours be designated for sleep, the study found that astronauts slept just shy of six hours a night. Nearly 75 percent supplemented their natural sleep with the sleep aid commonly known as Ambien.

An astronaut’s job can be very stressful and noisy, with varying temperatures and a completely foreign environment, all of which could contribute to a lack of sleep. However, the use of sleeping pills is a concerning issue, according to lead author of the study, Laura Barger.

“If an astronaut had to be awakened in the middle of the night for some emergency situation, their performance could be impaired,” she said.

Ambien works very well for getting people to sleep. It does this by inhibiting, or suppressing, activity in the brain, slowing it down so that sleep can be achieved. Maintaining sleep is not among its specialties, however, and Ambien has been known to cause people to do dangerous things while sleeping. Situations like this could be especially perilous for astronauts trying to perform their jobs with relative, or complete, isolation in space.

Other performance issues include drowsiness brought on by the drug that carries into the next day.

The study reveals a need for NASA to consider solutions to this issue as it plans future missions. Barger insists that proper solutions are especially necessary as longer missions, such as a journey to Mars, are planned.