You might think falling asleep in space would be easy -- the quiet, the darkness, all those stars to count. But new research suggests the majority of astronauts don't get enough asleep, and that what sleep they do get is chemically induced.

A newly published 10-year study -- lead by researchers from Boston and Colorado and featured in the latest edition of the journal The Lancet Neurology -- revealed that some 75 percent of astronauts use sleeping pills like zolpidem and zaleplon to get some shut eye.

Health researchers at Brigham and Women's Hospital, Harvard Medical School and the University of Colorado found that astronauts rarely get enough sleep in the days and weeks leading up to their expedition, their bedtimes pushed back by a combination of nerves and excitement.

That same nervous energy disrupts their sleep on board the space station, and though NASA allots crew members 8.5 hours of sleep each night, astronauts rarely use it all. And when they can't get to sleep at a reasonable hour, they resort to drugs.

"The concern is if there's an emergency situation and crew members have just taken hypnotics, they might not perform as well. You have to weigh the benefits of hypnotics against those risks," Dr. Laura K. Barger told the Boston Globe.

Barger is the lead author and a researcher at the Brigham's Division of Sleep and Circadian Disorders. "We need to have better countermeasures to improve sleep," Barger added.

The study was a the largest space-related sleep study ever conducted, spanning a decade and accounting for some 4,000 Earthbound nights and 4,200 nights floating through space.

NASA funded the study, but did not assist in conducting the research or analyzing the findings. The space agency issued a statement in response to the study's publication.

"Our astronauts work in harsh, complex environments where they are sometimes subjected to uncomfortable and high stress situations," NASA said. "The agency works hard to identify and implement countermeasures that can ensure astronauts are able to get the same quality and quantity of sleep in space as they do on Earth. The agency is committed to sending humans farther into space than ever before and we need to fully understand the implications of that prior to embarking on a mission to Mars."