Controllers Testing Ways To Get Out

The Opportunity Rover bogged down in a 12-inch tall sand dune recently, leaving controllers with a challenge. The four corner wheels of the rover are about half buried into the dune, but the rover is otherwise in good condition.
 
"We choose to proceed cautiously, so we don't expect to begin actually driving out of the dune before next week, possibly later," said Jim Erickson, rover project manager at JPL in a statement. "Both Opportunity and Spirit have already provided many more months of scientific exploration than anyone expected. By taking good care of them, we hope to keep them exploring for more months to come. Tests so far have sustained our optimism about Opportunity's ability to drive out of this dune, but we have more testing ahead to understand how robust that capability is."

Opportunity had driven about 131 feet of a planned 295-foot drive when the wheels began slipping. The rover was driving backwards when it began to dig itself into the small dune. Eventually, the rover sensed that something was wrong and it stopped trying to move. It is on the ridge of a small ripple of soft sand. (NASA Mosaic Image below)

"We've climbed over dozens of ripples, but this one is different in that it seems to be a little taller and to have a steeper slope, about 15 degrees on part of its face," said Mark Maimone, a JPL rover mobility engineer.

Engineers are using a lab and various sandy and powdery materials to simulate the situation at NASA's Jet Propulsion Laboratory in Pasadena, California. A test in a simulated sand dune proved to be no challenge for the test rover to escape, but a finer and looser material was needed for more realistic tests.

Raiding several home supply and hardware stores, scientists managed to find enough play sand, diatomaceous earth, and mortar clay powder to make more than two tons of simulated Mars sand.

"We needed to do tests using material more like what Opportunity is in, something that has a fluffier texture and cakes onto the wheels," said JPL rover engineer Rick Welch, who is leading the tests.

"We found that when the wheels dig in, the material we're using does stick to the wheels and fills the gaps between the cleats, but it doesn't stick when you're just driving over it. That's good because it's the same as what we see in the images from Opportunity," said Dr. Robert Sullivan of Cornell, a rover science team member who has helped to match the test sand.

Initial experiments seem to show that a test rover positioned like Opportunity can drive out after spinning its wheels at first. Of course, more testing will be done before any commands are sent to the Rover.

While waiting, Opportunity has been looking around with its cameras. It has traveled more than 3.32 miles in the 15 months since landing on Mars.

FMI: http://marsrovers.jpl.nasa.gov