Image: Panoramic view of Troy
NASA  /  JPL-Caltech/Cornell
This full-circle view from the panoramic camera 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.
By
updated 11/16/2009 9:16:31 PM ET 2009-11-17T02:16:31

The effort to free NASA's Spirit rover, currently mired in sand on Mars, will begin in earnest overnight when engineers send the first escape commands to the stuck robot to try to move out of its trap.

Spirit has been stuck in the Martian dirt since April, when drove into a spot of soft terrain called "Troy" back in April.

Mission managers have spent the past six months devising strategies to move the rover out of the sand pit. They tested them with model rovers back on Earth that are essentially replicas of Spirit and its twin, Opportunity.

Rover drivers decided that the best strategy would be to have Spirit backtrack, moving forward to retrace the tracks that brought it into its current predicament. (The rover's broken right front wheel has meant that Spirit's primary mode of driving is backwards.)

NASA announced the strategy last week: The rover team wrote the commands for Spirit to drive out of Troy on Monday, and was to send them up to the rover around 1 a.m. PT Tuesday (4 a.m. ET).

The commands call on the rover to move forward in two steps, with each step involving about  2.5 meters (8.2 feet) of wheel motion. At the end of the commanded motion, Spirit will take pictures of rover underbelly as well as the ground surrounding its wheels.

The results of the drive are expected to come back later Tuesday, after which the team will spend at least a day analyzing them before sending up any more commands.

NASA's 10 greatest science missions The precarious nature of the embedding — Spirit's wheels are dug in to their hubs, one wheel has stopped spinning and a rock is sitting underneath the rover's belly, possibly even touching it — means that the team has to be very careful about any movements they make with the rover.

"This is by far the most complicated and complex" embedding the team has had, said John Callas, project manager for the Mars Exploration Rovers at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Callas said the team expects any motion the rover makes to be small at first and the process to take several weeks.

If Spirit has not yet been freed by the time the rovers' annual review rolls around in February, NASA officials will weigh whether to keep trying, to keep Spirit where it is and continue doing science there or to call it quits.

The team is upfront about the chances of getting Spirit out. Ray Arvidson, deputy principal investigator for the rovers (and based at Washington University in St. Louis) has told fans of Spirit to be "hopeful, but realistic."

And whether or not Spirit makes it out, NASA considers the mission an unqualified success, as both Mars rovers have lasted 24 times as long as initially planned. They're both coming close to rounding out their sixth Earth year on the Red Planet.

This report was updated by msnbc.com.

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