Will Mars rover roll again?

Posted: Wednesday, June 03, 2009 7:03 PM by Alan Boyle

NASA / JPL / USGS This image shows the underbelly of NASA's Spirit rover, as seen by the rover's microscopic imager on June 2. One wheel can be seen at left, another buried wheel is at right, and a pointed shape that may be an obstruction is at center. The picture is fuzzy because the camera was not designed to take these types of images, and it is tipped to reflect the rover's orientation relative to the local terrain.

NASA experts are taking fuzzy pictures and trying out different recipes for Red Planet dirt as they continue their weeks-long effort to get a stuck Mars rover moving again.

It's been more than three weeks since the Spirit rover became mired in loose dirt on the west side of the Martian feature known as "Home Plate." During that time, the mission team at NASA's Jet Propulsion Laboratory has fielded scores of suggestions for freeing up Spirit, rover project manager John Callas told me today.

Callas said he and his colleagues have heard from "farmers who have had tractors stuck in the mud and figured out how to get them out," as well as a 7-year-old boy named Julian who suggested having Spirit push itself out with its robotic arm.

The ideas are much appreciated, Callas said, but "we still have many arrows in our quiver before we have to consider more drastic operations."

Right now, Spirit is using its arm for subtler purposes: The microscopic imager on the end of the arm is being pointed under the rover's belly to size up the situation. "The images are out of focus, but they exhibit enough detail that we can tell quite a bit," Callas said.

The latest images suggest that Spirit might be high-centered on an obstruction - sort of like a car whose undercarriage is hung up on a rock. "We see something underneath the rover," Callas said. "It's hard to tell in the image whether the object is under the rover or in front of it, or if it's one object or two. ... It's rather pointy. It's pyramid-like."

That's the bad news. The good news is that Martian winds have swept the dust off Spirit's solar panels, easing mission planners' worries that they would soon have to hustle the rover to a sun-facing safe haven. "With this dust cleaning that we've had, that has greatly relieved the urgency to get the rover going anywhere," Callas said.

In addition to taking pictures, engineers at the Jet Propulsion Lab are working on a test bed where they can try out maneuvers to free the rover. So far, they've figured out that the soft soil where Spirit is stuck contains ferric sulfate. "There may be some sort of surface crust, and this may have been what got us into trouble," Callas said. The rover might have been like a hiker walking over hard-packed snow: If you break through the crust to the softer stuff below, pulling yourself out can be a tough job.

NASA / JPL

A worker at NASA's Jet Propulsion Laboratory digs simulated Martian soil in an effort to replicate the Spirit rover's situation on the Red Planet.

Experts have been trying to mix up simulated soil that duplicates the properties of Spirit's sand trap, but so far they haven't found the right formula. Once they find it, "we'll order up tons of this material and essentially do some landscaping, and shovel it into this test bed," Callas said.

"It's likely we'll want to just drive forward with the rover, but we want to make sure we don't make things worse," he said.

Figuring out the best course and giving it a try will almost certainly take weeks longer. When Opportunity got caught in a sand trap four years ago, the wheels had to spin for the equivalent of 200 meters (yards) before the rover popped out of the trench it had dug for itself, Callas said. The current situation is even more challenging, in part because one of Spirit's six wheels has been out of commission for years and must be dragged along wherever the rover goes.

"This is probably the most serious embedding that either rover has experienced," Callas said. "There is a very real risk of Spirit being permanently stuck. If that were the case, then we become a fixed lander. But we have a lot of options still, a lot of techniques to apply to this problem."

While the engineers work all that out, the scientists are using Spirit's instruments to make a detailed survey of its surroundings. They're analyzing the soil, creating a 360-degree panorama of the area, and seeing a side of Home Plate they've never had the chance to explore before.

"We've never taken the time to smell the roses, so to speak," Callas said.

Nothing has come easy for Spirit: Just days after the rover landed, it suffered a serious reset that took two weeks to repair. Losing the wheel was a big setback. And there was a time when it looked as if the rover would run out of power. More recently, Spirit suffered a worrying series of senior moments, but the faulty memory has apparently been fixed.

"None of that has returned," Callas said. "We still don't know the origin of it."

If Spirit manages to work its way out of its current fix, it could rank as the rover's greatest escape yet. And even if Spirit remains stuck, it will still be sending back valuable science data until it slowly fades into the Martian sunset. That's not a bad way to go ... particularly when you consider that NASA expected the rover to last just 90 days rather than the current 1,925-and-counting.

Each day makes the Mars missions more of a bargain: The price tag for the twin rovers' original primary mission was $820 million. Five years and five extensions later, the cost still hasn't come up to the $1 billion ballpark figure for a single space shuttle mission.

Update for 1:10 p.m. ET June 5: I've added the panorama showing Spirit's underbelly, which was released after this item was first published.

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