Mars rovers on the march

Posted: Wednesday, February 04, 2009 7:00 PM by Alan Boyle

NASA / JPL-Caltech

Spirit surveys its tracks, with a rock stuck near its right wheel. Click on the image for a larger version.

The Spirit is moving again on the Red Planet, now that mission managers think they know what ailed the mixed-up Mars rover last month. Spirit has had to cope with more mundane snags as well, such as a rock that got in its way this week.

Meanwhile, Spirit's twin, Opportunity, is continuing its march on the other side of the planet - and both rovers are sending back 3-D snapshots.

Back on Earth, engineers are working on a next-generation rover that works more like a yo-yo. Read on for the latest rover update ...

Spirit back in business
A week ago, rover mission managers at NASA's Jet Propulsion Laboratory were scratching their heads over some puzzling problems that Spirit was having. First, there was a glitch that gave the rover a temporary case of amnesia. Then, the rover seemed to be having problems orienting itself. When it tried to get a read on the sun's position in the Martian sky, it didn't find it in the expected position.

These sorts of problems could be written off as signs of aging - which would be perfectly understandable. Spirit and Opportunity were designed with a 90-day "factory warranty" in mind, but last month they both passed the five-year mark. One of these days, Spirit is going to give up the ghost - but not this time. After its senior moments, the rover appeared to return to normal operation.

Since then, engineers have settled on the view that Spirit suffered an unfortunate cosmic-ray hit that turned off its flash memory temporarily. Spirit's team programmed the rover's computer with an optional no-flash mode - also known as "cripple mode" - to fix a memory problem that cropped up shortly after it landed on Mars. A cosmic-ray strike in just the right place (or actually, the wrong place) could have temporarily put the rover in cripple mode.

"It would require the confluence of a number of likely events, but it's still possible," John Callas, rover project manager at JPL, told me today.

Rover engineers also determined that Spirit's accelerometers - gadgets that the rover uses to measure its tilt - could be off by 3 degrees or so, which would have thrown off the sun-orientation exercise. All this is detailed in an update issued on Monday.

NASA / JPL-Caltech This stereo view is part of a panorama captured by NASA's Spirit rover on Jan. 26. Use red-blue glasses to see the 3-D effect. Click on the image for a larger version.

Because the accelerometers aren't used while Spirit travels, engineers gave the go-ahead for renewed roving on Saturday. Spirit's right front wheel has been gimpy for almost two years, but the rover still gets around by rolling backward and dragging the stuck wheel behind it. It was that very wheel that got hung up on a partially buried rock, just about a foot into Spirit's renewed trek.

Callas said the rover team's drivers, who steer the robots by remote control from millions of miles away, were able to get Spirit moving yet again. "On the most recent drive, they were able to move around it," he said.

Over the past few weeks, Spirit has been analyzing the soil around a formation known as "Home Plate," as part of a long-term effort to learn more about the area's geological history. Data from Spirit's alpha particle X-ray spectrometer recently indicated the presence of silica in a patch of soil called Stapledon.

An earlier analysis of silica-rich soil led scientists to conclude that the area once had hot springs or steam vents - and NASA said the findings from Stapledon indicate that "the environment that deposited the silica was not limited to the location found earlier."

Opportunities for Opportunity
Callas said Spirit's twin, the Opportunity rover, is continuing its trek through the sand-swept plains of Meridiani Planum, heading toward the 13.7-mile-wide (22-kilometer-wide) Endeavour Crater.

Opportunity has traveled about 1.2 miles (2 kilometers) in the past three months, Callas said, but there are still miles to go before the rover reaches its destination. "That's a couple of years away," he said.

Callas said the mission plan calls for Opportunity to stop every one or two kilometers along the way to take a close look at patches of exposed bedrock. Such observations will help scientists characterize how the geology changes across the 4-mile-plus (7-kilometer) stretch between Opportunity's old hangout, Victoria Crater, and its new digs.

NASA / JPL-Caltech This is part of the full-circle stereo view captured by NASA's Opportunity rover. Use red-blue glasses for the 3-D view, and click on the image for a larger version.

Opportunity may make other scientific stopovers. "There are some waypoints along the way - craters and other features that we will use as lighthouses or buoys, if you will, along the path," Callas said. "They may be scientifically interesting as well. ... It will be opportunistic."

Just in the past few days, JPL has posted 3-D stereo panoramas of Opportunity's vantage point as well as Spirit's surroundings, and the raw images just keep on coming. How long will the rovers keep marching? Callas has no idea. "We're going to keep working these rovers until we wear them out," he said.

The yo-yo rover
NASA is already working on the next generation of rovers: Some, like the pressurized rover that was part of last month's inaugural parade, will be suited for big jobs on the moon and Mars. Others will be built for small, tricky jobs - for example, shimmying down a steep cliff on another world.

Today, JPL touted a project known as Axel, which is being developed in cooperation with Caltech students for the shimmying sort of job. Axel is a robot that works like a yo-yo, reeling out a tether and pulling it back in as it rolls down and up steep terrain. The low-mass contraption is equipped with big wheels, a scoop and two 360-degree-tiltable cameras for observation.

Someday, such rovers could be anchored to the bigger, smarter descendants of Spirit and Opportunity, and lower themselves down to a crater floor on Mars.

JPL Robotics The Axel rover system being developed at NASA's Jet Propulsion System could be used as a "marsupial" rover. Axel would be lowered down on a tether from a larger, anchored rover to explore steep terrain, as shown in this illustration.

"Axel extends our ability to explore terrains that we haven't been able to explore in the past, such as deep craters with vertically sloped promontories," Axel principal investigator Issa A.D. Nesnas, who works in JPL's robotics and mobility section, said in today's news release. "Also, because Axel is relatively low-mass, a mission may carry a number of Axel rovers. That would give us the opportunity to be more aggressive with the terrain we would explore, while keeping the overall risk manageable."

Check out this video to see Axel in action. For more information, consult this JPL Web page as well as this one at Caltech. And to keep up with all the Mars missions - past, present and future - check in with our "Return to the Red Planet" section.

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