Mars rover Spirit misses communication session

Apr 01, 2010
Artist's concept of Mars Exploration Rover. Image credit: NASA/JPL-Caltech/Cornell University

(PhysOrg.com) -- NASA's Mars Exploration Rover Spirit skipped a planned communication session on March 30 and, as anticipated from recent power-supply projections, has probably entered a low-power hibernation mode.

In this mode, the rover's clock keeps running, but communications and other activities are suspended in order to put all available energy into heating and battery recharging. When the battery charge is adequate, the rover attempts to wake up and communicate on a schedule it knows.

"We may not hear from Spirit again for weeks or months, but we will be listening at every opportunity, and our expectation is that Spirit will resume communications when the batteries are sufficiently charged," said John Callas of NASA's Jet Propulsion Laboratory, Pasadena, Calif., who is project manager for Spirit and its twin rover, Opportunity.

Spirit's power supply is low because daily sunshine for dusty solar panels is declining with the approach of the winter solstice, in mid-May, in Mars' southern hemisphere. In the three previous Martian winters that Spirit has survived since landing in January 2004, the rover was tilted northward to put its solar panels at a favorable angle toward the sun. That preparation was not possible this winter because of impaired mobility. Spirit's wheels are dug into soft sand, and the rover lost the use of a second wheel four months ago. It had previously lost use of one of its six wheels four years ago.

Spirit's original mission was planned to last for three months. The rover has worked extended missions since April 2004. Opportunity is currently on a long-term trek toward a large crater named Endeavour.

Spirit had been communicating on a once-per-week schedule in recent weeks. During the designated time for the rover to communicate with NASA's Mars Odyssey orbiter passing overhead on March 30, Odyssey heard nothing from the rover.

"We are checking other less-likely possibilities for the missed communication, but this probably means that Spirit tripped a low-power fault sometime between the last downlink on March 22 and yesterday," Callas said. "The recent downlinks had indicated that the battery state of charge was decreasing, getting close to the level that would put Spirit into this hibernation."

In coming weeks, Spirit's core electronics will become colder than any temperature they have ever experienced on Mars. Thermal projections indicate the temperature probably will not drop lower than the electronics were designed and tested to tolerate, but the age of the rover adds to the uncertainty of survival.

"The temperature limit was for a new rover. We now have an older rover with thousands of thermal cycles on Mars, so the colder temperatures will be a further stress," Callas said.

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User comments : 3

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NotAsleep
not rated yet Apr 01, 2010
I hope Spirit comes back online... Virgle will need all the exploration it can get if it is to succeed:

http://www.google...dex.html
yyz
not rated yet Apr 01, 2010
If Spirit has entered hibernation mode, at least they saw it coming. According to a piece posted March 28 at Universe Today:

"No one knows precisely when the low power fault will occur and the team has been working diligently to find new ways of shaving off power usage to stave off the day when Spirit enters hibernation because no one knows if her critical components will last intact so that she will reawaken at a later date as the climate improves.

[PI Steve]Squyres commented regarding the potential trigger point for a low power fault by saying, "Our initial guess was 155 watt hours, and the latest number we've seen is 133 watt-hours (March 22). So I'm not even going to try to guess".

Mars rover driver Scott Maxwell reports via recent Twitters that, "Spirit is still alive and talking to us. Feisty girl. Brilliant uplink team found way to shave Spirit's energy needs; can get by with 120ish [watt-hours] now. Might stave off hibernation another couple weeks!"
Temple
not rated yet Apr 01, 2010
I hope that, in my lifetime, I'll be able to visit Spirit in the Smithsonian Air and Space museum. That may be a tall order, but this little rover is right up there with the Spirit of St. Lois, Freedom 7, and the space shuttle.

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