PHILADELPHIA — NASA engineers continued late Jan. 30 to troubleshoot the software problems plaguing the rover Spirit even as it resumed transmitting imagery of Gusev Crater on the other side of the planet from its twin Opportunity.
"Right now we’re working to get complete control of the vehicle, and we’re still not quite there," Jennifer Trosper, mission manager for the Mars Exploration Rover program at NASA’s Jet Propulsion Laboratory, said Jan. 28. "If we’re on the right track, we hope to be back doing some science by early next week. If we’re not on the right track, it could take longer than that."
Spirit did send a new photograph back from Mars Jan. 29. It was the robot’s first significant data transmission since its computer went haywire Jan. 21.
The image captured by the rover’s front hazard avoidance camera shows its robotic arm extended to a rock previously named Adirondack.
Spirit’s science operations halted just as it was about to begin drilling into the pointy rock. The rover’s computer rebooted itself more than 100 times over a two-day period and, at first, sent back beeps but no data. Engineers have since determined that the problem appears to involve too many files overloading the onboard computer memory.
A spectrometer, which would identify minerals in the rock, is still sitting in place on top of Adirondack, as it had been instructed prior to the computer glitch.
Spirit is in the Gusev Crater on Mars. Its twin, Opportunity, is on the other side of the planet. The combined mission cost is $820 million. Both rovers are designed to determine whether Mars was once wetter, possibly with the conditions necessary for life.
There remain nagging worries, however, that what ails Spirit cannot be fully understood. If that’s the case, engineers here at the Jet Propulsion Laboratory (JPL) are taking slow steps in certifying that Spirit’s twin won’t run into the same problems.
Engineers have found a way to halt Spirit’s computer from resetting itself by putting the spacecraft into a mode that avoids use of flash memory. Flash memory is a type common in many electronic products, such as digital cameras, for storing information even when the power is off. The Mars Exploration Rovers have random-access memory. But the robots cannot hold onto information during overnight sleep sessions.
To free up more memory space, JPL officials said they planned to erase from Spirit’s flash memory the files stored there from the spacecraft’s cruise to Mars from Earth. That process requires care to ensure the correct files are erased, Trosper said.
"If we are not able to successfully complete our surgical technique … we have larger hammers that we can use in order to solve this problem," Trosper said. "We actually think that the flash is not corrupted. We would like to keep the data that’s in the flash memory."
But if that proves unsuccessful, the next step is to actually delete the data that’s in the flash memory. This heavy hammer approach would wipe out science data collected by Spirit before it ran into trouble on the 18th day of Mars operations.
Trosper said that, in talks with science teams, almost all of the onboard science data is replaceable.
The scientific information that would be lost, however, includes a unique data-gathering session with Europe’s Mars Express satellite. Spirit’s instruments were looking up while the Mars Express science equipment peered down at Gusev Crater.
Trosper said that Spirit did relay thumbnail images from that coordinated session with Mars Express. "So most of the science that was desired to be done can be done from the thumbnail images," she said.
"Clearly they would like to get the rest of it down. But in order to get all of the data down it will take many sols [martian days]. We have to make a risk trade and time trade. The science team, I believe, would prefer to have more sols to do new things," Trosper said.
If surgical removal of files in flash memory doesn’t solve the problem, reformatting that memory is the next phase, in order to move forward and get back to the science of the mission.
"We can muck around with this thing for a while, clearly. There’s something that we don’t understand about the problem," Trosper said. However, if it does become necessary to reformat the flash memory, all evidence of what happened onboard Spirit would be destroyed, she added.
On the other hand, all that evidence might already have been destroyed after the initial reset, Trosper said. "We just need to weigh the risks against the time it would take to do some of these things and get back on track."
