With its twin just hours from arriving on Mars, NASA's ailing Spirit rover twice reached out to anxious engineers yesterday and transmitted clues that might help them repair the disabled robot.
The brief transmissions, which began at 7:34 a.m., were the first meaningful communications to NASA engineers from the robot since Spirit suddenly went mum Wednesday.
While engineers said they were buoyed by the data dribbling back from the crippled craft, they cautioned that it could take days or even weeks to fix the rover, and it might never be fully functional again.
"We are still critical. We don't know what's broke," said Peter Theisinger, the mission project manager at the Jet Propulsion Laboratory in Pasadena, Calif.
Spirit is the first half of an $820 million double mission to learn whether Mars was once a wetter world capable of supporting life. The second spacecraft, Opportunity, is scheduled to touch down early tomorrow, at 12:05 a.m. EST.
After repeated attempts to contact Spirit yesterday morning, a giant NASA antenna dish near Madrid picked up a 10-minute transmission from the six-wheeled rover at 7:34 a.m. An hour later, Spirit sent back 20 minutes of data.
Engineers said much of what Spirit sent back was gibberish, but the craft also communicated more than 70 error messages. The errors are important clues that could help engineers trace the problem to its source, says JPL engineer Jaime Dyk.
NASA officials announced yesterday that they had formed a special forensic engineering team to pore over the error messages and other clues.
They have one promising lead: The rover's erratic behavior began Wednesday as it was executing an order to swivel its thermal emission spectrometer, a 5-pound instrument mounted on the rover's neck.
Spirit never completed the maneuver and soon after began transmitting either random sequences of zeroes and ones or brief chirps. That suggests the problem could be with Spirit's hardware, Theisinger said.
The loss of communication came as a shock to NASA engineers, who had seen the rover execute a flawless landing Jan. 3 and snap more than 1,600 pictures of its landing site, the Gusev Crater. It was preparing to drill into its first Martian rock to search for evidence of water when the trouble began.
It's not the first time NASA engineers have been forced to conduct long-distance surgery on one of their spacecraft.
Spirit's troubles are eerily reminiscent of communication glitches that occurred in 1997 on NASA's pint-sized Sojourner. Engineers eventually debugged the robot's software remotely and salvaged the mission.
But so far Spirit is proving to be a more challenging patient. Efforts to diagnose the robot's problems are being complicated by the craft's erratic responses to controller's commands. "The software kind of has a personality disorder," says Dyk.
Since Wednesday the robot has been operating in a protective "safe mode" and attempting to fix itself by rebooting its onboard computers, much as frustrated home computer users do.
Spirit has rebooted itself more than 60 times. So far, this hasn't solved the problem.
The dribble of data Spirit has sent back does show that its thermal and power systems remain mostly healthy, although engineers said yesterday that the robot doesn't appear to have slept since Wednesday. If the rover's insomnia continues, engineers said it might deplete the onboard batteries, forcing some systems to shut down.
While the situation is frustrating, NASA engineers working on Spirit say they are far from dejected. "Engineers are bored unless they have a problem to work," said Dyk. "And this is a very difficult problem."
As NASA engineers struggled to bring the Spirit rover out of its funk, scientists elsewhere speculated about the source of the rover's problems.
Sten F. Odenwald, an astronomer at the Goddard Space Flight Center, wondered whether Spirit might have been walloped by an X-ray flare.
Just hours before the trouble began on Mars, Odenwald says, a hefty flare erupted from the sun. Traveling at the speed of light, the X-rays from the flare would have reached Mars in about 12 minutes and could have zapped the robot's delicate circuit boards or memory chips.
As one team of JPL engineers works to solve the riddle, another is preparing for the arrival of Spirit's twin.
Opportunity is aiming for an area called Meridiani Planum, a 45-mile-long ellipse that is one of the smoothest and flattest places on the planet. The region is also rich in a mineral called gray hematite, which typically forms in the presence of water.
Opportunity team members said yesterday that they will try to duplicate Spirit's flawless landing - with one slight adjustment: They will pop the spacecraft's parachute earlier to ensure a soft descent.
Sun staff writer Frank D. Roylance contributed to this article.