NASA will begin a long-shot attempt Nov. 16 to free the Mars rover Spirit from the "Martian sand trap" it has been mired in since April 23. "Researchers expect the extraction process to be long and the outcome uncertain," NASA said in a news release Nov. 12.
"This is going to be a lengthy process, and there's a high probability [that] attempts to free Spirit will not be successful," Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters, in Washington, said in a statement. "After the first few weeks of attempts, we're not likely to know whether Spirit will be able to free itself."
NASA plans to send Spirit commands to "rotate its five [out of six] working wheels forward approximately six turns. Engineers anticipate severe wheel slippage, with barely perceptible forward progress in this initial attempt."
The NASA statement continued, "Spirit will return data the next day from its first drive attempt. The results will be assessed before engineers develop and send commands for a second attempt. Using results from previous commands, engineers plan to continue escape efforts until early 2010."
"Mobility on Mars is challenging, and whatever the outcome, lessons from the work to free Spirit will enhance our knowledge about how to analyze Martian terrain and drive future Mars rovers," McCuistion said. "Spirit has provided outstanding scientific discoveries and shown us astounding vistas during its long life on Mars, which is more than 22 times longer than its designed life."
Spirit landed on Mars on Jan. 4, 2004, three weeks before its twin rover, Opportunity, plunked down on the other side of the planet. Their mission was originally scheduled to last 90 Martian days, but five years later, Spirit and Opportunity have continued to defy the odds, sending more than a quarter-million images of Mars' surface and providing details about the planet's chemistry, geology and atmosphere.
Then came April 2009, when Spirit stalled in the loose soil of a site dubbed Troy. By May 7, NASA quit trying to move Spirit and concentrated on extricating the rover. On the ground, NASA prepared a "shoebox" to replicate the conditions at Troy and wheeled a test rover into the sandbox. From Mars, Spirit sent images of its underside that revealed a possible rock underneath the rover. NASA even launched a Free Spirit Website.
"The investigations of the rover embedding and our preparations to resume driving have been extensive and thorough," said John Callas, project manager for Spirit and Opportunity at NASA's Jet Propulsion Laboratory, in Pasadena, Calif. "We've used two different test rovers here on Earth in conditions designed to simulate as best as possible Spirit's predicament. However, Earth-based tests cannot exactly replicate the conditions at Troy."
Data and images from Spirit show it is "straddling the edge of a 26-foot-wide crater that had been filled long ago with sulfate-bearing sands ... The deposits in the crater formed distinct layers with different compositions and tints, and they are capped by a crusty soil ... that Spirit's wheels broke through. The buried crater lies mainly to Spirit's left. Engineers have plotted an escape route from Troy that heads up a mild slope away from the crater," NASA said.
"We'll start by steering the wheels straight and driving, though we may have to steer the wheels to the right to counter any downhill slip to the left," said Ashley Stroupe, a JPL rover driver and Spirit extraction testing coordinator. "Straight-ahead driving is intended to get the rover's center of gravity past a rock that lies underneath Spirit. Gaining horizontal distance without losing too much vertical clearance will be a key to success. The right front wheel's inability to rotate greatly increases the challenge."