Crippled Mars rover fails to phone home

LOS ANGELES — NASA says its aging Mars rover Spirit missed a communications session and may have gone into a power-saving hibernation to survive the Red Planet's winter.

The Jet Propulsion Laboratory in Pasadena says Spirit failed to communicate with the orbiting Mars Odyssey spacecraft on Tuesday.

The rover survived previous Martian winters by positioning itself with its solar panels tilted toward the sun but could not do so this time because it remains trapped in sand. Two of its six wheels also no longer work.

Mission managers expected that Spirit's power levels would reach the point where it would have to hibernate, and they drew up a plan to keep the rover running at a low level. In hibernation mode, the rover's clock continues to run, but communications and other activities are suspended in order to put all available energy into heating and battery recharging.

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When the battery charge is adequate, the rover should try to wake up and communicate on a pre-set schedule.

"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," John Callas, project manager for Spirit and its twin rover, Opportunity, said in a mission update issued Wednesday.

Callas said NASA is checking other possibilities for the lack of communication but considers them unlikely. Hibernation mode was probably triggered sometime after the last successful downlink on March 22, he said.

NASA's projections indicate that Spirit's core electronics will become colder than they've ever been on Mars, but will remain warmer than the lower limit that Spirit was designed to endure.

Spirit's age adds to the uncertainty over its fate. Spirit and Opportunity were designed for a three-month mission on Mars, but both rovers have lasted for more than six years. "The temperature limit was for a new rover," Callas explained. "We now have an older rover with thousands of thermal cycles on Mars, so the colder temperatures will be a further stress."

This report includes information from The Associated Press and msnbc.com.