Robot Spins Wheels to Save Stuck Rover on Mars

NASA?s Earthboundtest rover is doggedly spinning its wheels forward and back in the effort tofind a way to free its sister robot Spirit from a sandy quagmire on Mars.

Spirit hasbeen stuckin Martian dirt up to its hubcaps since May 6, when it became mired in adirt patch (now called "Troy") while driving backward.

Becausethey don't want to damage Spiritwhile trying out ways to get the rover out of its sand trap, mission engineersare using a replica model here on Earth.

At the endof June, the test rover was set up in a plywood rig in a dirt pit at NASA's JetPropulsion Laboratory in Pasadena, Calif. The rig is filled with a dirtconcoction mixed to mimic the properties of the sand in which Spirit is stuck.It is also tilted at a 10-degree angle - the same angle of the slope thatSpirit is stuck on.

Engineersalso placed a rock underneath the test rover's belly because imagestaken last month by the microscopic imager at the end of Spirit's roboticarm. After analyzing the image, mission managers determined that a dark blob inthe middle was a rock positioned underneath the rover.

Plottingan escape on Mars

Mission engineers finally began testing outpossible maneuvers on July 6 with the simplest maneuver on their list ofoptions: driving forward with all five operable wheels. (Spirit has only fiveworking wheels after its right front wheel went dead three years ago.)

In thefirst set of tests, the wheels turned enough to cover tens of meters, or yards,if there had been no slippage. The test rover moved slightly forward andsideways downslope.

On July 8,after refreshing the sandbox setup, engineers tried out straight-backwarddriving.

Next cametesting out a series of crablike moves, in which all four steerable wheels areturned to the same side angle, then rotated the wheels either forward orbackward.

By July 10,the team had tested crabwalk patterns driving forward in the test sandbox withthe wheels turned at 60 degrees to the right and 20 degrees to the right. Theangle of motion was upslope.

Theselatest tests completed four out of 11 maneuvers that the team has on its currenttesting list.

Next,engineers plan to test backward (downslope) crabbing with wheels turned 60degrees to the right.

Moretests ahead

So far thetests are going well, but what exactly the next steps will be it's too soon tosay, said Steve Squyres, lead scientist for the Mars Exploration Rover Project,in an e-mail.

Weeks offurther testing and analysis are expected before engineers identify the bestmoves to command Spirit to perform.

Meanwhile,on Mars, Spirit isn't just biding its time waiting to be freed. Mission scientists are taking the opportunity to have Spirit examine theenvironment surrounding it.

• SPACE.com Video Show - Rover Tracks on Mars
• Video - Spirit: The Little Rover That Could
• The Most Amazing Mars Rover Discoveries