On June 3, 2010, a crew of six male astronauts from Russia, Italy, and China waved goodbye to their families, entered the spaceship that would be their home for the next 17 months, and prepared for liftoff.

Next stop: Mars.

Penn professor David F. Dinges was in Moscow that day when the hatch of the mock spacecraft was closed tight, officially beginning a 520-day simulated trip to the red planet and back. Dinges returned to greet the elated six-man crew when the hatch finally re-opened in November 2011 and they emerged from the longest-ever simulated deep space flight.

“There was a lot of excitement and relief that everyone made it OK,” Dinges says.

He’s only half-joking. As part of an international team of scientists studying the psychological and medical effects of human long-term confinement, Dinges’s team had been monitoring the crew around the clock, looking for signs of anxiety, stress, and depression.

Using special wristwatch-like devices that continuously recorded the crew’s body movements and light exposure, scientists at Penn accumulated 4.396 million minutes worth of data. Through twice-weekly computer tests administered from afar, the Penn team also monitored the alertness and fatigue levels of the crew.

The data analysis, which took more than a year, showed fairly substantial changes in activity levels and sleep-wake cycles in most of the crew members. As the mission wore on, some of the astronauts became less active when awake, resting and sleeping more often. Such behavior could spell danger on a real mission.

“This was in part a function of the confinement, but it became clear also there were sleep problems occurring in the timing of sleep-wake cycles, circadian problems, as well as the amount of sleep one crew member was getting and the quality of sleep two crew members were getting,” says Dinges, chief of the Division of Sleep and Chronobiology in the Department of Psychiatry at the Perelman School of Medicine, and co-lead author of the new study. “The end result was only two out of the six had fairly normal, stable, well-timed, high-quality, adequate duration sleep periods and the other four had some sort of disturbance.”

Most of the problems emerged in the first 180 days of the mission and continued throughout for the crew members who experienced them. The crew did become more alert around the time of the Mars landing and toward the end of the mission. But during the long, monotonous stretches in between, those who most closely adhered to the structured activity schedule for work, eating, and sleeping fared best.

“Just being in a chamber for 17 months, you can easily begin to drift in terms of your self-discipline or what activities are fun. You might spend more time in sedentary activities. That we can’t have, because a crew has got to stay mentally and physically fit and capable of dealing with any emergency or event that might occur,” Dinges says.

Another key finding of the Penn study is that the design of the spacecraft interior could adversely affect the health of the crew. Onboard lighting should mimic light conditions on Earth to prevent mood and sleep disruptions. An astronaut who isn’t sleeping well might not want to exercise, which could lead to an increased rate of muscle loss due to the effects of micro gravity.

“What the study shows is the habitat is going to have to be more than just a nice engineering environment,” Dinges says. “Just having exercise equipment isn’t enough. It’s actually going to have to be a psychological, physiological, and behavioral home, and be like Earth in order to ensure they stay capable all the way to Mars and back.”

The findings were published online first in the Proceedings of the National Academy of Sciences. Other study authors from Penn include co-lead author Mathias Basner, Adrian Ecker, Christopher W. Jones, Eric C. Hyder, Adrian Di Antonio, and Namni Goel.

The research was supported by grants from the National Space Biomedical Research Institute through NASA cooperative agreement (NCC 9-58) and by the Institute for Experimental Psychiatry Research Foundation. The simulation was developed and operated by the Institute for Bio-Medical Problems of the Russian Academy of Sciences in Moscow.

For the time being, scientists and the public must be content with fascinating images of the Martian landscape from the NASA robot Curiosity; the United States isn’t planning an actual human mission to Mars until at least 2030.