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The Secret Of The 25-Hour Day

Martian Sun Set by Pathfinder
Pasadena - Dec 23, 2003
Steven Squyres, the principal investigator for the science instruments aboard the Spirit and Opportunity Mars rovers, juggles his commitments to the four space missions he is actively involved in, as well as to his teaching and advising duties, with an energetic ease that makes some wonder if he has found the secret to a 25-hour day.

Well yes, actually, he has.

Not 25 hours, to be exact, but 24 hours, 39 minutes and 35 seconds, the length of one Martian day, or "sol."

Squyres is preparing to live on Mars time for the duration of the two-rover mission, expected to be at least four months. Spirit is scheduled to touch down in the red planet's Gusev Crater on Jan. 3 at 11:35 p.m. EST; its twin, Opportunity, will land at Meridiani Planum on Jan. 25 at 12:05 a.m. EST.

The Jet Propulsion Laboratory (JPL) in Pasadena, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA's Office of Space Science, Washington, D.C. Cornell University, Ithaca, N.Y., is managing the science suite of instruments carried by the two rovers.

"Our vehicles are tied to the Martian day/night cycle," says Squyres, who is professor of astronomy at Cornell. "They rely on a vision system to avoid obstacles," and being solar powered they must operate during daylight and "sleep" at night.

Because the rovers' daily communications windows also are tied to this cycle, Squyres, along with more than 200 other scientists and engineers, must lengthen his days to stay in sync.

Squyres admits that the longer days, at first, seem attractive -- "you get to sleep in

39 minutes later every day" -- but points out that there is "very little hard data on the physiological impact of extended Mars-time living."

The fundamental problem, says Squyres, is that team members must keep a longer day while exposed to outside stimuli that run on an exact 24-hour cycle.The entire rover team will work at the mission control center at JPL. They already have rented apartments in a quiet neighborhood equipped with light-tight blackout shades, and some of them will wear specially made Mars watches that record an additional 39 minutes, 35 seconds every day. But when rover team members step outside, they will be bombarded with external stimuli running on the 24-hour clock to which their bodies are accustomed.

"We decided we needed to get some serious advice in this area," says Squyres. When, jet-lagged and exhausted, he ran into Cornell sleep researcher James Maas at Pittsburgh airport in 2000, both realized that a collaboration would be a boon for data-hungry sleep researchers and for the rover team.

"While we were doing our own experiments, there was the opportunity for us to be the subject of someone else's experiment," says Squyres.

Consequently about 40 members of the rover team will be the subjects of the sleep study. Small wristwatch-like accelerometers will keep a record of the scientists' motion through the days and nights of the Mars mission. From the accelerometer readings, the sleep-research team will deduce when the scientists were awake and when they were asleep.

Workshops with sleep experts from Harvard, Brown, Stanford and the NASA Ames research center also have helped shape the Mars team's strategies.

"The key is not to overschedule people," says Squyres. Scientists will stick to a six-sol workweek, working four sols and taking a two-sol weekend.

But engineers on the team with permanent homes in Pasadena will get a longer, three-sol weekend. The engineers "have groceries to buy, lawns to mow, PTA meetings to go to," and must contend with more signals from the 24-hour world than the visiting scientists, says Squyres.

He is most worried, though, about the "wicked case of Martian jet lag" he will get when Opportunity lands Jan. 25. The rover's landing site is almost 180 degrees away from Spirit's, meaning that when Squyres leaves the Spirit team to join the Opportunity group, he will be about 12 hours off schedule. It is the Martian equivalent of a trip from New York to Australia -- without the benefit of a daylong plane ride during which to adjust.

There is one vestige of Earth time Squyres won't be able to escape, though: the press conference. So if, come January, Squyres looks a bit bleary-eyed in front of the cameras, remember that it might just be 2:30 a.m. back in Gusev Crater.

Related Links
Mars at JPL
MERs at Cornell
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