Volume: 03, Issue: 10 05/18/2005 
This mosaic of navigation-camera frames from Opportunity shows its position after it dug itself to wheel-hub depth in a small dune during its 446th martian day on April 25. Image courtesy NASA/JPL.
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Rover engineers in JPL's In-Situ Instrument Lab check how a test rover moves in material chosen to simulate some difficult Mars driving conditions. Image courtesy NASA/JPL.
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Here is the martian twilight sky at Gusev crater, as imaged by the panoramic camera on Spirit. Image courtesy NASA/JPL/Cornell.
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Other Articles in This Issue:
New Saturn Moon Makes Waves
Chandra Observatory Catches X-ray Super-flares
Titan Atmosphere Decoded
Explore Distance Learning Courses

Opportunity Takes Tentative Step Forward

Mars Exploration Rover Opportunity is slowly but steadily attempting to move out of the sand dune where it has been sidelined for more than three weeks. Opportunity rotated its wheels on May 14 for the first time since the rover dug itself into the dune while driving on April 26.

The rover had driven about 131 feet of a planned 295-foot drive on its 446th martian day when its wheels began slipping. The wheels kept rotating enough times to have covered the rest of the distance if they hadn't been slipping, but the rover eventually barely inched forward. After a turn at the end of the planned drive, Opportunity sensed that it had not turned properly and stopped moving.

Opportunity stopped across the ridge of an elongated dune or ripple of soft sand that is about 1 foot tall and 8 feet wide. JPL rover mobility engineer Mark Maimone said this ripple is different than others Opportunity has crossed in that it is taller and has a steeper slope.

After examining the area where Opportunity came to rest, Mars rover engineers began to determine how to move the rover. They used a testing laboratory to simulate specific Mars surface conditions where Opportunity has been stuck. The test rover had no difficulty driving away, even when sunk in belly-deep.

"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," said Jim Erickson, rover project manager at JPL.

Following the Earth-based testing, ground control commanded Opportunity to spin its wheels. The wheels made about two and a half rotations, as directed, and the results were a good match for what was expected from the tests on Earth. The rover advanced 1.1 inch forward, 0.19 inch sideways, and 0.18 inch downward.

While Opportunity has been sidelined, twin rover Spirit has been using all its research tools to examine an outcrop called "Methuselah," the first outcrop of layered rock the rover has found. Spirit has also been taking short movies of dust-carrying whirlwinds called "dust devils." On some afternoons, the rover sees several at once moving across the plain.

JPL, a division of the California Institute of Technology in Pasadena, has managed NASA's Mars Exploration Rover project since it began in 2000. Images and additional information about the rovers and their discoveries are available online:

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