Wheel Trouble May Doom Stuck Rover on Mars

Aftermonths stuck fast in deep Martian sand, NASA?s embattled rover Spirit is facinga debilitating wheel problem that has slowed its escape efforts and couldparalyze the long-lived robot.

Spirit hasbeen trapped wheel-deep in sand for nearly eight months and engineers on Earthhave been spinning the Mars rover?s wheels in recent weeks to try and force itfree. But the rover?s right-rear wheel hasbeen stalling, and now may be broken for good.

?Thesewheel stalls have been such a complication, that we really haven't gottenstarted,? said rover project manager John Callas of NASA?s Jet PropulsionLaboratory in Pasadena, Calif., in a recent interview on Spirit?sescape attempts.

Recenttests ?continue to indicate a troubled wheel, which may leave the rover withonly four operable wheels,? mission managers said Thursday in a status update.

Spirit isabout the size of a golf cart and has six wheels in all. One of those wheels -the right-front wheel ? has been broken since 2006. Spirit and its robotic twinOpportunity ? which is working fine ? have been exploringMars since January 2004. Since then, they have outlived their initial 90-day mission several times over.

The newwheel trouble for Spirit began during recent escape attempts. The right-rear wheel beganstalling when commanded to spin in concert with the four other working wheelsin an attempt to back the rover out of its Martian quagmire.

NASAengineers are unsure if they can free Spirit with only four working wheels. Theteam is on the clock, too. The rover?s current position and tilt aren?tfavorable for surviving the next southern Martian winter, which starts in May2010.

Rovercontrollers have been testing a rock drill on Spirit?s robotic arm that usesthe same motor controller as the balky right-rear wheel to see if they canbetter understand the problem. The team has also not ruled out an external jamthat may be blocking the wheel?s motion, and is considering extra steeringtests as well.

"We have to get going,? Callas told SPACE.com. ?Winter is coming, andthere's now the question of Spirit being able to survivethe winter at its current location. So having a mobile rover gives us amuch better chance at surviving the winter. That clock is ticking; that's onlysix months away.?

• Video - Free Spirit: Plotting an Escape
• Mars Rover FAQ: The Martian Lives of Spirit and Opportunity
• SPACE.com Video Show - Rover Tracks on Mars

SPACE.comSenior Writer Andrea Thompson contributed to this report from New York.