As a NASA rover sped toward a late-night landing on Mars, its identical twin was on the mend Saturday after abruptly malfunctioning days into its mission to search for evidence the Red Planet once could have supported life.
Engineers said they were closing in on the root of the problem that led the Spirit rover to spew gibberish and beeps instead of science and engineering data. They brought stability to the six-wheeled vehicle by disabling its flash memory, which is similar to the memory digital cameras use to store pictures, said Orlando Figueroa, director of NASA's Mars exploration program.
"We made good progress overnight," project manager Pete Theisinger said during a news conference at NASA's Jet Propulsion Laboratory. "The rover has been upgraded from critical to serious."
Spirit resumed transmitting data Friday, but only in limited batches. The malfunction, which appeared Wednesday, may prevent the rover from taking another drive on Mars for as long as three weeks, Theisinger said.
As Spirit shut down systems and "slept" 124-million miles from Earth, its twin, Opportunity, remained on track to make a bull's-eye landing at 12:05 a.m. today in Meridiani Planum, navigation team chief Louis D'Amario said.
Navigators skipped a last chance to trim Opportunity's path as it neared Mars. Early Saturday afternoon, it was just 64,000 miles from its destination and accelerating, tugged by the planet's gravity.
Opportunity, like Spirit, must execute a choreographed sequence of events to ensure its safe arrival on Mars. The only difference: Opportunity was to open its parachute 4,500 feet higher than Spirit did to compensate for the higher elevation of its landing site.
NASA said it could take as long as 22 hours to hear from Opportunity after it lands.
Spirit developed problems after working nearly flawlessly for days. Despite its woes, scientists said there is still a chance the rover can fully recover.
JPL director Charles Elachi said other NASA spacecraft, including Voyager, Magellan and Galileo, have recovered from even worse problems.
"I am completely confident, without any hesitation, that I think we will get that rover back to full operation," Elachi said.
Mission members were able to stop the rover from rebooting its computer _ which it had done about 130 times _ and place it in so-called "cripple" mode to bypass the computer chips that make up its flash memory.
They also succeeded in commanding the robot to sleep after it stayed up two nights in a row when it should have been turned off to conserve power.
The root cause of Spirit's problems remained elusive. NASA's inability to reproduce the problem in laboratory software tests suggests that something is awry with the rover's hardware, Theisinger said.
Not since the 1976 landing of the twin Viking landers has NASA had two working spacecraft on the surface of Mars. Together, the twin rovers make up an $820-million mission to determine if Mars ever was a wetter world capable of sustaining life.
In addition to its two rovers, NASA also have the Global Surveyor and Odyssey, and the European Space Agency has the Mars Express in orbit around the planet.
The region Opportunity is to explore is believed to be dramatically different from the reddish soil of Gusev Crater, with a dark gray or black ground and relatively dust-free environment. The region is believed to be rich in a mineral called gray hematite, which typically forms in marine or volcanic environments rich in water.
The Odyssey spacecraft has, from its orbital perch, detected a deposit of iron oxide the size of Oklahoma at Meridiani Planum. What particularly interests scientists is that this type of iron oxide, hematite, usually forms in the presence of water, at least on Earth. Further complicating the geologic picture, the hematite layer is on top of sedimentary deposits within an ancient, eroded crater.
_ Information from the New York Times and the Associated Press was used in this report.
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This image taken by the Global Surveyor spacecraft as it orbits Mars details the history of Spirit's descent and landing on Jan. 3. The two dots in the upper left are the spacecraft's backshell and parachute. To the far right, a dark streak is believed to be where the heat shield made impact. A trail of bounce marks made by the airbags as Spirit bounced to a stop can be seen in the center of the image. The white dot near the bottom is the lander. Beside it is a dot marked "surface feature localization," showing the location of the lander estimated by using sight lines to landmarks in the lander's panoramic images.