Mars Rovers To Last Longer Than Expected  

It took more than a month for NASA's Spirit Mars rover to finish the drive to its destination, a crater called "Bonneville," but mission planners are already looking toward more distant pastures, confident that their robust robot -- and its twin, Opportunity -- will last twice as long as originally expected. Spirit was scheduled to travel the last few feet to the rim of Bonneville Tuesday, then look around with its panoramic camera for anything interesting enough to nuzzle its science instruments against.

"We have arrived," said Jennifer Trosper, Spirit mission manager, of the rover's long journey during a press briefing Thursday at NASA's Jet Propulsion Laboratory (JPL). "Once we've finished with 'Bonneville,' we'll head on over to the East Hills."

JPL scientists had hoped that "Bonneville" crater, the remains of an ancient Martian impact, would give them a deeper look into the subsurface geology of Mars. An initial inspection shows the crater composed of the same regolith material Spirit found elsewhere in its Gusev crater landing site.

Though there are no signs of rocky outcrops like that studied by Opportunity, the rover is still identifying science targets. The East Hills, which lie a mile and a half (2.5 kilometers) from Spirit, may prove more interesting fare. According to JPL scientists, Spirit still has enough life to reach them despite the fact that it is about two-thirds through its planned 90-day mission lifetime. This week, Spirit also surpassed its minimum mission success driving distance of 984 feet (300 meters).

"Spirit is kind of post-retirement here and getting ready for her longest drive yet," Trosper said, adding that Opportunity has reached middle age. "Neither rover is showing their age and we believe they will both last 200 plus sols." A sol is one Martian day, which is 24 hours and 37 minutes long.

Spirit, now in Sol 67 of its Mars mission, was able to catch a clear view of its heat shield in a navigation camera mosaic taken from the rim of "Bonneville." The shield, which protected Spirit during its fiery entry through the Martian atmosphere, apparently landed near the crater's lip. The landing site of Spirit's parachute and backshell were also seen far behind the rover. Just reaching the crater vista was a task for Spirit, which encountered tougher terrain the closer it crept toward "Bonneville."

"If you tried to drive your car up this slope you'd probably get a flat tire and a busted oil pan," explained Chris Leger, the rover's driver. "So it was really a tricky drive."

Leger likened rover navigation to orienteering, and said Spirit's journey was a combination of constant image studies, blind driving, the autonomous control of the rover itself and stutter steps of just a meter or so to make sure the path was safe. But overall the experience seems enjoyable.

"I still can't believe they're paying me to do this," Leger said.

On the other side of Mars at Meridiani Planum, Opportunity is still sitting in the same crater it landed in 46 mission days ago, but only because there are still more experiments for it to perform. The rover has driven 239 feet (73 meters) around its landing site so far.

Phil Christensen, lead scientist for the rover's miniature thermal emission spectrometer (Mini-TES), said Opportunity could leave its crater in the next 10 to 12 days, at which time he's hopeful to study the hematite content of the Martian plains. Hematite is a mineral that can form in the presence of water, and its wide presence at Meridiani Planum from orbit was a main reason for choosing to land there in the first place. However, though Opportunity has found conclusive evidence that water existed at the site, primary through sulfates in the crater's outcrop, the hematite levels there are low.

"If the sulfate minerals formed in water, and the hematite formed in water, we really need to learn what changed," Christensen said. One possible solution is that the object that caused Opportunity's crater punched through a thin layer of hematite and hit a deeper basalt floor, he added.

Meanwhile, Opportunity did offer scientists a chance to collect a comprehensive temperature profile of Mars' atmosphere during an overhead flyby of the Mars Global Surveyor (MGS). By combining the data from the rover's Mini-TES as it was looking up and MGS's larger thermal emission spectrometer looking down, scientists were able to compile a ground-up view of the planet's atmosphere.

The rover had a small glitch with its rock abrasion tool (RAT), which started to stick due to colder than expected Martian temperatures. Rover engineers increased the voltage setting to compensate for the lower temperature and the RAT is once again chewing into Martian rocks.

FMI: www.nasa.gov