WASHINGTON (January 7, 2012)—A new study finds that astronauts can experience a very down-to-Earth problem.

They don't get enough sleep.

The problem could be even worse on a long trip to Mars.

Over time, the lack of sleep could turn intrepid space travelers into drowsy couch potatoes.

In a novel experiment, six volunteers were confined in a cramped mock spaceship in Moscow to simulate a 17-month voyage.

The experience left most of the would-be spacemen lethargic, much like bears gearing up for hibernation.

The men went into a prolonged funk and four had considerable trouble sleeping.

The study was published online Monday in the journal Proceedings of the National Academy of Sciences.