NASA Unveils Plan to Free Stuck Mars Rover Spirit
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.
Credit: NASA/JPL-Caltech

Months of planning are finally coming to fruition: NASA engineers are ready to begin trying to maneuver the plucky rover Spirit out of its sandy trap on Mars.

Mission managers are sober about the prospects for freeing Spirit. They will send the first commands to the rover to try to move on Monday, "but this process could take quite awhile if it's possible at all," said Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters in Washington, D.C.

The new plan will command Spirit to try to backtrack and use the tracks it left before getting stuck to make the escape attempt.

Spirit has been stuck in a spot of soft, sandy dirt (called "Troy") on the Martian surface since April when it broke through what mission scientists call a "dirt crust" ? a hard top layer of dirt disguising a layer of soft, talcum powder-like material below.

"Spirit did the equivalent of falling through the ice over a frozen pond," McCuistion said.

Escape plan on Mars

The rover's engineering team has spent months devising a strategy to extricate the spacecraft, working with replicas of Spirit (and its twin spacecraft, Opportunity). That effort is complicated by the fact that Spirit has a bum right front wheel, forcing it to drive backwards.

The team has tried driving the replica rovers in a variety of ways ? forward, backward, and sideways ? in a mixture of dirt similar to that in which Spirit is stuck to see what has the best chance of getting the rover out and what might make the situation worse.

"If there is a way to get the rover out, we'll find it," said rover project manager John Callas of NASA?s Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

The plan is to begin driving the rover on Monday, trying to move forward out of Troy, following the same tracks it made to get into the predicament.

The rover drivers suspect that moving through the soft material already churned up will be easier than breaking through more of the dirt crust. Moving backwards also means the rover won't have to try to move uphill, said Ashley Stroupe a rover driver, also from JPL.

When moving the rover, the team also has to be careful not to scrap against a rock under the rover's belly. Moving forward should minimize the interaction between the rover and this rock, Stroupe said.

"This is clearly going to be a long process to either get to extrication or determine if extrication is going to work," Stroupe said.

The command to move will be sent up on Monday night and mission controllers expect to hear back from Spirit on its progress on Tuesday. The command will be for 5 meters (16 feet) of wheel spin, though mission managers don't expect the rover to actually move that far, Callas said. The team will take a day to analyze any movement Spirit makes before sending more commands, repeating this process as long as needed.

"The reality is that we're going to see very little motion each day at least initially," Callas said. "It's kind of like watching grass grow."

Callas said he has confidence in the rover team and the plan they have as being the best chance to extricate Spirit.

"We're in good shape; we're ready to roll on Monday," he said.

The ?spirit? of Spirit

Mars enthusiasts have been worried that Spirit's predicament could spell the end for the rover's mission, which so far has lasted 24 times longer than its original planned 90 days.

Also of concern are Spirit's periodic memory lapses, the most recent of which occurred on Oct. 24, preventing Spirit from saving science observations in its flash memory.

Spirit's sticky situation hasn't been all bad though. Mission scientists have used the forced downtime to conduct science observations of the site, which has turned out to be one of the most interesting that the rovers have encountered on Mars.

"Of course no place is a nice place to be embedded, but this turns out to be a geological treasure trove," said Ray Arvidson, deputy principal investigator for the rovers from Washington University in St. Louis.

While the rover has detected sulfate sands in a spot (called Cyclops_eye) where it punched through with its robotic arm, it detected a completely different material at another nearby spot (Polyphemous_eye), suggesting the rover is straddling some type of geologic boundary. The rover is also perched on the edge of a crater.

If the rover does remain stuck in Troy, it could end up doing more observations there. "There's still a lot of science to be had from the current location," Arvidson said.

Spirit and Opportunity have been roaming the Martian surface for nearly six years now, after landing on different sides of the planet in January 2004.

McCuistion asked fans of the rover to be "hopeful but realistic" about Spirit's prospects.

If Spirit can't get out, "it's likely that this lonely spot straddling the edge of this crater might be where Spirit ends its adventure on Mars," he said.