Astronauts on a months-long mission to Mars and back will have more to contend with than boredom and a lack of gourmet cuisine: Disrupted sleep may be a serious side effect of extended space flight, potentially changing crew dynamics and affecting performance on high-pressure tasks.
In an epic feat of playacting, a crew of six men lived for 520 days inside a hermetically sealed 550-cubic-meter capsule in Moscow. As the grueling experiment wore on, the crew drifted into torpor, moving less and sleeping more. Four men experienced sleep problems, scientists report online January 7 in the Proceedings of the National Academy of Sciences.
Developed by the Russian Academy of Sciences, the “Mars 500” project was designed to test the feasibility of sending people on a journey to Mars and back. The simulation was realistic: The chamber was sealed, mission control was on standby 24 hours a day with built-in communications delays during parts of the mission, and the crew had specific jobs to do during transit and on a simulated landing on Mars.
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“If we at some point really want to go to Mars and we want to send humans, then we need to know how they will cope with this long period of confinement,” says study coauthor Mathias Basner, of the University of Pennsylvania’s Perelman School of Medicine in Philadelphia. Basner’s team was one of many that conducted studies on the six men during the long simulation.
Several months into the experiment, crew members seemed to drift into inactivity, sleeping more and moving less, Basner and his team found. Wristwatch-like gadgets that took measurements of activity once a minute revealed that the crew became more sedentary as the experiment progressed. The crew got more sleep, too: On average, crew members slept over half an hour more per day in the last quarter of the mission than in the first.
If a similar torpor strikes people on a real mission, it could have important effects, says study coauthor Jeffrey Sutton of the National Space Biomedical Research Institute in Houston and Baylor College of Medicine. Sedentary crews might need to ramp up their exercise to stay healthy in microgravity, for instance.
Although on average the crew became lethargic, the responses were by no means uniform. One crew member actually slept less as time wore on, and his performance on a vigilance test suffered, the researchers found. Such a seemingly small problem could have deadly consequences, Sutton says. “When you are doing high-risk behavior in space, a performance deficit can be life threatening.”
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Another crew member stretched from a normal 24-hour Earth day into a 25-hour pattern of sleeping and waking. (Coincidentally, this rhythm is close to that of a Martian day.) This means that for about a fifth of his time, this man was awake when others were asleep, or asleep when others were awake. “His timing was totally out of whack and that could cause a huge problem,” Basner says. That kind of mismatch could be dangerous if an emergency required all hands on deck.
The simulation results “help us understand what we need to do,” says Lauren Leveton of NASA’s Johnson Space Center in Houston. Knowing which people might struggle with sleep issues could help space agencies select the best crews and also devise ways to prevent problems from developing. For the most part, these sleep problems turned up early in the experiment, so a quick (relatively speaking) preflight simulation might flag some of these issues early.
Boosting levels of blue light during waking hours and reducing blue light when crews need to sleep is one way that might lessen sleep problems, Leveton says. In coming years, crews at the International Space Station will replace aging fluorescent bulbs with more thoughtfully designed lighting.