April 15, 2009 (Computerworld) As engineers continue to try to analyze what is going wrong with one of the Mars rovers, it's clear that working on the harsh surface of the red planet is taking its toll on some of the most successful technology that NASA has ever produced.

Late last week, NASA's Mars rover Spirit appeared to twice reboot its computer, unprompted from Earth. Then NASA engineers learned that the robotic rover had failed to even wake up to send its regularly scheduled downlink of information, according to John Callas, NASA's project manager for Spirit and its Mars rover companion, Opportunity. Then it didn't wake up for two other communication sessions.

Scientists knew they had a problem. But the engineering team is still looking for the specific problem, said Callas in an interview with Computerworld.

"If it just needs to be reset, we can do that," said Callas. "If something is permanently broken, that's a bigger issue. It's still very early in the analysis."

Both Spirit, which suffered a computer glitch back in January, and Opportunity, which has remained relatively healthy, have been working on the Martian surface for five years, far more than the three-month life span initially projected by NASA.

The two rovers are some of the best pieces of technology that the Jet Propulsion Lab has ever built, said Bruce Banerdt, project scientist for the Mars Exploration Rovers, in a previous interview.

The rovers, which are working on the equator but on different sides of the planet, have been sending and receiving information from Earth nearly every day, with a team of about two-dozen programmers and engineers uploading code to guide the rovers' movements and aim their cameras. All of that information travels about 200 million miles one way, taking anywhere from five to 21 minutes to travel from one planet to the other.

"It is amazing," Banerdt said. "Every day, I just have to tip my hat to the engineers who designed them.

But all that time on Mars could be finally taking its toll on Spirit.

While Callas said that NASA engineers are in the early stages of an investigation into what is plaguing the rover, he did say that the robotic machine could be starting to suffer from age-related issues.

"In the past, when something has broken, we've been very innovative in finding a work-around," he added. "It could be that some memory cells were corrupted and we need to refresh them. It could be a transient thing, like when your computer crashes and you don't know why. It could be that it's getting older and it's getting more temperamental. We're obviously aware of the fact that we have an old rover here," Callas said.

So why would Spirit be having problems while Opportunity has been working fine?

Callas said that also is unclear since both machines have the same electronics and flight software. However, they have been navigating different kinds of terrain, which might cause more wear and tear on one than the other.

"They both still have ambitious objectives ahead of them," said Callas. "We're going to operate them as much as possible. Our objectives are to wear them out and get as much scientific discovery as possible out of each of these rovers. At this point, no one knows how long they will last. They've exceeded expectations, and so far they've lasted a very long time."

NASA has been heavily focused on exploring Mars with two rovers, the Phoenix Mars Lander and the Mars Reconnaissance Orbiter studying the planet.