A world away on Mars, rover stops making sense

NASA calls data errors `a very serious anomaly'

January 23, 2004|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

After sending back hundreds of striking photos for nearly three weeks, the Mars rover Spirit has suddenly begun transmitting gibberish, or refusing to communicate with Earth at all.

NASA engineers described the problem as "a very serious anomaly" yesterday and said they were scrambling to identify and correct it.

"It's not clear there is one cause that would explain the observables we've seen," said deputy project manager Richard Cook. "That's what's perplexing us at the moment."

One possible explanation, officials said, was a strike by cosmic radiation that affected the rover's hardware and scrambled its computer programs. Mission leaders nevertheless expressed confidence they could find the problem and correct it.

"We are going to do everything we can, knowing this is risky - this is exploration," said Charles Elachi, director of NASA's Jet Propulsion Laboratory.

Officials at JPL were encouraged by a series of beeps from the rover yesterday morning. They were sent to Earth on a specific radio channel that Spirit was instructed to use if a malfunction sent it into a "safe mode."

"That's probably the best news we have heard in the last 24 hours," Elachi said.

Controllers planned to tune to that same channel this morning to ask the rover to send back diagnostic engineering data that could reveal what went wrong.

"Then we can start taking some corrective action to bring it back up, slowly and methodically, to nominal operations," Elachi said.

The trouble with Spirit comes just days before the rover's twin, Opportunity, is scheduled to bounce down on the other side of the planet. Together, the missions represent an $820 million investment by the National Aeronautics and Space Administration.

Most space missions experience problems, and NASA engineers have overcome a long list of them.

But Mars missions have been especially unlucky. Two-thirds of all man's attempts to go there with orbiters or landers have failed, the most recent being the European lander Beagle 2, which vanished on landing Christmas Day. Spirit is only the fourth lander to survive and go to work on the surface, after twin Viking missions in 1976, and Pathfinder in 1997.

The Spirit mission had been unfolding almost flawlessly. It bounced down on Mars' rock-strewn Gusev Crater on Jan. 3.

In the days that followed, the rover rolled up its landing airbags and took its first look around at what scientists think may be an ancient martian lakebed. Hundreds of black-and-white, color, 3D and microscopic images have been transmitted to Earth across more than 100 million miles of space.

On Jan. 15, the 384-pound rover rolled off its lander onto the surface of Mars.

This week, Spirit took its first short excursion, a few yards away from its lander, and it was beginning to conduct the first geological studies of the dirt and rocks in the neighborhood. Geologists are hoping to find mineralogical evidence that water once flowed in the Gusev Crater, which would open the possibility that the planet might once have sustained life.

The first hint of trouble came Wednesday afternoon. Project manager Pete Theisinger said engineers at JPL sent a series of commands instructing the rover to extend its robot arm and begin its study of a football-sized rock dubbed "Adirondack."

Officials said Wednesday that those commands contained errors. At first, they blamed a thunderstorm and other problems at NASA's Deep Space Network radio antenna in Australia, where the signals were transmitted toward Mars. But those issues have since been discounted.

After getting its orders, Spirit replied that it had begun to carry them out. But later on Wednesday, the rover missed a series of scheduled communications sessions - directly with Earth and relayed through NASA's Mars Odyssey satellite.

It also failed to answer a series of calls from Earth, and did not initiate a preprogrammed call home.

To the controllers' relief, on Wednesday night JPL did finally receive a transmission from Spirit. It was relayed by another Mars orbiter, called Mars Global Surveyor. That meant that the rover was still generating electricity and transmitting radio signals.

But those signals were brief - just 2 1/2 minutes in a 12-minute satellite pass. And, they contained no science or engineering data from the spacecraft.

"It was only sending ... a random pattern of zeroes and ones," said deputy project manager Richard Cook. "It means the radio was on, but the computer wasn't sending information over to it. But we did at least see a signal."

Engineers received their most encouraging news from Spirit yesterday morning, confirming that it has received queries from Earth. The transmissions were no more than beeps. But they were enough to tell troubleshooters that the rover's radio, amplifiers, antennas and associated hardware are working.

"It's telling us, `Hey, I got the command, I heard you and here's confirmation,'" Cook said. "We think the hardware is working as it was intended. ... What we don't know is the state of the software."

If it's a software glitch, it might be possible for the JPL team to correct it remotely. But broken hardware might end Spirit's part of the twin Mars mission. Although Theisinger called the problem "very serious," he cautioned against undue pessimism.

Elachi said it's sometimes possible to work around a hardware failure. "We'll need to do things methodically and carefully," he said. "There is nothing rushing us."

NASA's plans call for Spirit to explore the martian surface for about 90 days, sending back detailed geological data from the Gusev Crater.

If the rover's problems are software-related, Theisinger said, "I think Spirit can go for quite a long time, and we can pick up the pieces again."

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