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Nine months after the Spirit rover sank into a Martian sand trap, NASA says the troubled traveler will have to remain stationary in order to survive the Red Planet's winter. Now the challenge is to improve Spirit's tilt so that it soaks up as much solar energy as it can.
Doug McCuistion, director of NASA's Mars Exploration Program, said Spirit ran up against "a golfer's worst nightmare: the sand trap that no matter how many strokes you take you can't get out of it."
The rover team has been trying to free Spirit for months, but McCuistion declared that the golf cart-sized robot's "driving days are likely over."
"Right now our plan is to worry about getting through the winter," he told journalists today during a teleconference.
After the winter, scientists plan to conduct stationary experiments to characterize the Red Planet's core - is it solid, or still somewhat molten? They'll also look into the interaction between the Martian soil and atmosphere, as well as the characteristics of the intriguing soil around the rover. Cornell astronomer Steve Squyres, the mission's principal scientific investigator, says the sulfate salts found in the soil suggest that Spirit is stuck in an area where steam vents were once active.
Tale of two rovers
Both Spirit and Opportunity, its twin on the opposite side of the planet, landed on Mars six years ago - and both were expected to last only 90 days. To date, NASA has spent more than $900 million on the rover missions, but the cost has leveled out to about $20 million a year. Squyres said the rovers have yielded roughly 500 scientific papers, abstracts and presentations to date. The highlight of the missions so far has been the on-the-ground discovery that Mars was once wet enough to support life.
Opportunity is still in good condition and making its way toward the 14-mile-wide Endeavour Crater. That rover is in better shape to last through the winter because it's much closer to the Martian equator, said John Callas, project manager for the rover missions.
Callas and other mission managers have been trying to free Spirit for months, but wheel failure turned out to be a killer. One of Spirit's six wheels has been out of commission for years, and another went out last month. Even if Spirit somehow found a way to escape the sand trap, it would be seriously hobbled due to its four-wheeled status. "It certainly couldn't really make any headway," McCuistion said.
In the past week or so, the rover team changed its strategy for moving the rover and made more headway, at least in terms of improving Spirit's northerly tilt. That raised some hope that the rover might still be capable of making an escape. In the end, however, mission managers decided that time was running out, and that they had to switch their top priority from freeing Spirit to surviving the winter.
"The seasons are determined by Mars, and not determined by the mobility of the vehicle," Callas said.
The road ahead
The current plan is to reposition Spirit in its sloping sand trap over the next couple of weeks to optimize the angle of its solar arrays for power production. Right now the arrays have an "unfavorable tilt" toward the south, but each degree of improvement will make a big difference, Callas said. By the end of February, the rover isn't expected to have enough power for wheel movement. In March, the rover would probably have to cut back on communication to conserve electricity.
"Getting through the winter will all come down to temperature and how cold the rover electronics will get," Callas explained in a NASA statement. The rover was built to survive temperatures of minus-40 degrees Fahrenheit (-40 degrees Celsius) with its electronics on, and minus-67 degrees F (-55 degrees C) with electronics powered down, Callas said. During the roughly six-month Martian winter, the lows are expected to be around minus-50 degrees F (-45 degrees C).
Spirit should be able to handle the winter temperatures by "hibernating" like a bear, Callas said. That's not a guarantee: The electronics might not be as hardy as they were when the rover landed six years ago. But if the NASA team can keep Spirit alive, the rover should be able to start its stationary science experiments in September or so.
Squyres said the decision to have Spirit stay put was "kind of poignant moment for us."
"We built these vehicles with the intention of driving around on the surface, and Spirit has done that magnificently for the better part of six years," he said. "So seeing us shift our focus to a different class of activities - you know, it's a change, and it's one we're going to have to adapt to."
'Not a day to mourn'
Rover driver Ashley Stroupe said the change still hasn't fully sunk in with the engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who steer the robots by preprogrammed remote control.
"At this point we've been really focused as a team on the day to day. I don't think we've necessarily fully changed our mind-set in our heads just yet ... to more stationary ops," Stroupe said.
But rover team members emphasized that it wasn't yet time to write Spirit's obituary.
"This is not a day to mourn Spirit," McCuistion said. "This is not a day of loss."
Assuming that Spirit survives, the study of Mars' core would be a primary scientific objective. During an interview last week, Callas told me that the rover would detect tiny gravitational shifts as Mars spins on its axis - shifts that could tell scientists about the planet's internal composition. He compared it to the trick of spinning an egg to figure out whether it was raw or hard-boiled.
"If the final scientific feather in Spirit's cap is determining whether the core of Mars is liquid or solid, that would be wonderful," Squyres said. And who knows? Still more discoveries may lie within Spirit's reach.
"The bottom line is, we're not giving up on Spirit," Squyres said.
NASA is offering a series of electronic postcards that Internet users can send to Spirit (and the team of scientists and engineers behind the rover). This item from last week provides further background about Spirit's troubles and the rover team's strategy. Fresh animated images show Spirit's view in the direction of movement and in the figurative rear view mirror. For the latest word from the "Free Spirit" movement, check in with the Twitter accounts for the Mars rovers and one of their drivers, Scott Maxwell.
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This report was last updated at 4:10 p.m. ET.