Scientists declared NASA's Spirit rover completely "healed" on Friday, after the probe suffered computer problems that engineers now say they made worse during their diagnosis. Spirit marked its return to science operations by brushing off the dust from a rock nicknamed Adirondack, revealing a surprisingly dark surface underneath.
Meanwhile, half a world away, the twin Opportunity rover closed in on another geological mystery — an outcropping of Martian bedrock called "Snout." At the end of Friday's workday, the six-wheeled robot geologist was about half a yard (meter) away from its target, and roughly 23 feet (7 meters) from its landing platform.
Spirit and Opportunity are the identical halves of an $820 million mission to determine whether ancient Mars could have had liquid water for a long enough time to support the development of life. After a seven-month journey, Spirit landed Jan. 3 in the 95-mile-wide (150-kilometer-wide) Gusev Crater, and Opportunity came down three weeks later in Meridiani Planum, on the opposite side of Mars.
'Our patient is healed'
Spirit had been crippled for the past two weeks because its flash memory system — a setup similar to that used on digital cameras here on Earth — couldn't handle the size and number of files that were being stored onboard. After diagnosing the problem, engineers had to reboot the system remotely, and mission manager Jennifer Trosper said the rover now appears to be operating normally.
"I think I can say this morning with as much certainty as we can say anything here that our patient is healed — and we're very excited about that," Trosper told reporters at NASA's Jet Propulsion Laboratory in Pasadena, Calif. She also reported that Spirit communicated successfully with Europe's Mars Express orbiter, strengthening an "international, interplanetary communication network."
Reviewing Spirit's past failings, flight software architect Glenn Reeves said the memory glitch was a "very serious problem" that was worsened when "we managed to corrupt this file system." He said the memory management issue was not caught during the pre-launch testing process, but a review of the test data turned up hints that storing too many files might create a problem.
"In a sense, we're back to the beginning. ... We have a procedure in place so that we now believe we can work around this problem indefinitely," Reeves said. Additional software fixes may be put in place as the mission continues, he said.
Back to Adirondack
When Spirit suffed its glitch, it was in the midst of analyzing Adirondack, its first target rock. Scientists went ahead with the analysis on Thursday by commanding the rover to use a brush attachment on its rock abrasion tool, or RAT, to clear away any dust on the pyramid-shaped rock's surface.
Honeybee Robotics engineer Stephen Gorevan, who heads the RAT payload team, said he didn't expect the brushing to make any difference, since the rock appeared to be smooth and dust-free. But he and other team members were surprised to find that brushing the rock revealed a darker-colored surface beneath a lighter layer of "sticky" dust.Slideshow: Images from Mars
“I was asked in the scientific assessment meeting to try to capture this first-time action on Mars, the scientific opportunity created and the elation we felt," he said. "And I could only think of Muhammad Ali ... ‘'Ladies and gentlemen, I present you the greatest interplanetary brushing of all time.’”
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Scientists speculated that Martian dust may be stickier than previously thought because of electrostatic attraction — in other words, a cosmic case of static cling.
A close look at the brushed surface strengthens the view that Adirondack was formed through volcanic processes, said the U.S. Geological Survey's Ken Herkenhoff, who heads the science team for the rover's microscopic imager. That means the rock may not shed much new light on the liquid-water question. Nevertheless, the RAT will be used to grind away at Adirondack's surface, giving scientists their first-ever chance to study a rock's interior on Mars.
After that's finished, Spirit is likely to be sent toward a crater 800 feet (250 meters) away — an odyssey that could take several weeks to complete.
Opportunity, meanwhile, will conduct a similar survey of Snout and the rest of the outcropping within the 72-foot-wide (22-meter-wide) crater where it landed Jan. 24. The rover's mini-thermal emission spectrometer already has found ample evidence of hematite, an iron oxide mineral that can form either through interaction with liquid water or through volcanic activity.
Due to the distance between Mars and Earth, the rover can't be steered in real time: Instead, it gets its driving instructions during communication sessions, executes those instructions and then reports back the results. As the rover's remote-control drivers get more experience with the terrain, the rover's movements will become more precise, Wallace said.
Each of the rovers was designed for a primary mission lasting 90 days, but mission managers say the solar-powered spacecraft could keep going for a significantly longer time.
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