A week-and-a-half after falling ill to computer woes, NASA on Sunday declared its Mars Exploration Rover Spirit was healthy again.

Mark Adler, rover mission manager. Credit: NASA/Bill Ingalls

"We have confirmed that Spirit is booting up normally. Tomorrow we'll be doing some preventive maintenance," mission manager Mark Adler reported Sunday.

Controllers worked to fix the computer ailment afflicting Spirit by purging thousands of data files from its flash memory. The no-longer-needed files piled up on the rover and prevented its computer system from successfully accessing the flash memory, triggering Spirit's computer to reset itself over and over again.

The flash memory stores engineering and scientific data even when the power is turned off, similar to electronic products like digital cameras.

Many of the tossed files were left over from the spacecraft's cruise to Mars.

A scan of the flash memory was performed late last week, providing engineers important diagnostic information, Adler said.

"We are now able to tell that when we mount the flash memory, it does in fact take a lot of the system RAM in the process. In fact, more system RAM than is available. So that's helping confirm the theory we had that the reason the restarts were hanging up was because we were running out of memory when we are trying to mount the flash memory," he explained during a news conference Friday.

Contact with Spirit was lost after the trouble began on Wednesday, January 21. Wrestling to regain control of the craft, engineers developed a plan to put the rover into a "cripple" operating mode that didn't use the flash memory.

With the file deletions completed, Spirit's computer has been "stable" while working in the standard mode with access to the flash memory.

"To be safe, we want to reformat the flash and start again with a clean slate," Adler said Sunday.

Monday's reformatting will erase everything stored in the flash file system and install a clean version of the flight software.

In preparation for that reformatting, Spirit was expected on Sunday to transmit priority data remaining in the flash memory. The information included data from atmospheric observations made in mid-January when the European Space Agency's Mars Express orbiter flew overhead.

Engineers say the flash may need to be reformatted every one-to-two weeks to prevent further trouble. Similar measures are likely for sister-rover Opportunity.

In the upcoming days, Spirit will finish the study of its first rock, nicknamed Adirondack. The Rock Abrasion Tool will be used to scrub off the rock's surface to give the science instruments a window into Adirondack's interior.

This close-up look at Adirondack was captured by Spirit's microscopic imager before Spirit. This is the first-ever microscopic image of a rock on another planet. Credit: NASA/JPL/US Geological Survey

Spirit's Mossbauer Spectrometer made readings of the pyramid-shaped, football-sized rock's composition and the microscopic imager snapped extremely close-up views prior to the computer problems. That data was finally transmitted to Earth late last week.

"If you had a hammer and whacked that rock, it would ring," said Ray Arvidson, rover deputy principal investigator.

Adirondack is a hard, crystalline rock that contains olivine, pyroxene and magnetite minerals. Researchers say that composition is common in Earth's volcanic basalt rocks. It isn't the proof of past water on Mars that the rovers were sent to find.

"Adirondack seems to be a good, hard volcanic rock," Arvidson said. "That suggests to us that we may be looking at material either excavated from below by craters, or broken out lava flows or transported in. It's not the kind of smoking gun evidence that we are looking for in terms of climatic history."

Two of Spirit's potential target rocks, which are near the rock called Adirondack, are seen here. The rock on the left has been named "Cake," and the white rock on the right has been named "Blanco." Image Credit: NASA/JPL/Cornell

Next, Spirit will drive to a nearby light-colored rock for study. Future plans call for the rover to head toward a crater, nicknamed Bonneville, about 820 feet away to study rocks thrown outward by the crater-forming impact.

"I suspect what we will do is take a look at some of these so-called white rocks that might be dusted basaltic rocks. If they don't look interesting, as quickly as possible do a traverse up to Bonneville Crater," Arvidson said.

Nearing the one-month mark of its planned three-month mission on Mars, Spirit is just beginning its science work. Officials are quick to point out the rover's wheels won't fall off when the 90-day primary mission period ends, giving hope that the craft will continue to explore in an extended life.

"We have gone through a third of our warranty, I guess, on the mission. But we think we have quite a few more months to go. I expect once we get the vehicle back in operation we will make pretty rapid progress in getting through the science objectives that we have in sight," Adler told reporters.

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