Mars Rover Spirit Skips Phone Call to Earth

The crippled Mars rover Spirit skipped a planned communications session with Earth this week and may have entered a hibernation mode designed to save power and help it survive the harsh Martian winter, NASA?s Jet Propulsion Laboratory said Wednesday.

Spirit, which is stuck in deep Martian sand, was expected to send a message to its mission control team on Tuesday by routing a signal through NASA?s Mars Odyssey spacecraft orbiting the red planet. That didn?t happen.

"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 rover mission project manager John Callas, of the Jet Propulsion Laboratory in Pasadena, Calif., in a statement.

In hibernation mode, Spirit?s onboard clocks would run but communications and other systems are shut down to divert as much power as possible to recharging the rover?s batteries and keeping itself warm. Once the batteries are charged enough, Spirit is programmed to wake up and call Earth on a preplanned schedule.

Spirit has been stuck in Mars sand since mid-2009 and the sand trap thwarted all attempts by NASA engineers to free the rover. Earlier this year, NASA called off those escape attempts and re-designated Spirit as a ?stationary mission? to study the area around it.

Since then, the Martian winter has set in and the amount of sunlight available for Spirit?s solar panels ? combined with frigid temperatures ? have forced the rover to save power when possible in an attempt to survive. Recently, it hit its coldest temperature yet: A chilly minus 41.8 degrees Fahrenheit (minus 41 degrees Celsius).

Lately, Spirit has been calling Earth about once a week until it missed its communications session on Tuesday, mission managers said.

"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."

Spirit had been doing well until the missed call to Earth, but there is still a big test ahead. The rover?s core electronic systems are about to experience the coldest temperatures ever while Spirit has been on Mars as winter on the red planet continues.

The rover was designed to handle extremely low temperatures on Mars, but that was when it was new.

Spirit and its robotic twin Opportunity have been exploring different parts of Mars since January 2004. Since then, their original 90-day mission has been extended several times over.

Both rovers have made substantial Martian discoveries related to the history of water on Mars and the planet?s ancient past. They are in their seventh year roving across the red planet.

"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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