Mars Rover Spirit Skips Phone Call to Earth

A panoramic view of the Mars Rover Spirit showing the terrain surrounding the location called “Troy”
This full-circle view from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Spirit shows the terrain surrounding the location called "Troy," where Spirit became embedded in soft soil during the spring of 2009. (Image credit: NASA/JPL-Caltech)

The crippled Mars rover Spirit skipped a plannedcommunications session with Earth this week and may have entered a hibernation modedesigned to save power and help it survive the harsh Martian winter, NASA?s JetPropulsion Laboratory said Wednesday.

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

"We may not hear from Spirit again for weeks ormonths, but we will be listening at every opportunity, and our expectation isthat Spirit will resume communications when the batteries are sufficientlycharged," said rover mission project manager John Callas, of the JetPropulsion Laboratory in Pasadena, Calif., in a statement.

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

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

Since then, the Martianwinter has set in and the amount of sunlight available for Spirit?s solarpanels ? combined with frigid temperatures ? have forced the rover to savepower when possible in an attempt to survive. Recently, it hit its coldesttemperature yet: A chilly minus 41.8 degrees Fahrenheit (minus 41 degreesCelsius).

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

"We are checking other less-likely possibilities forthe missed communication, but this probably means that Spirit tripped alow-power fault sometime between the last downlink on March 22 andyesterday," Callas said. "The recent downlinks had indicated that thebattery state of charge was decreasing, getting close to the level that wouldput Spirit into this hibernation."

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

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

Spirit and itsrobotic twin Opportunity have been exploring different parts of Mars sinceJanuary 2004. Since then, their original 90-day mission has been extendedseveral times over.

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

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

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