In this view from behind a test rover at NASA's Jet Propulsion Laboratory, Pasadena, Calif., the rear wheels of the rover are turned toward the left, and the left-front wheel is turned toward the the right. Bruce Banerdt, project scientist for Spirit and Opportunity, measures the rover's position before the rover receives commands to drive a forward right arc.

The experiment was designed to assess whether this maneuver could pivot the rover around the immobile right-front wheel, since the right-front wheel on NASA's rover Spirit has been inoperable for more than three years.

This work on July 15, 2009, was part of a series of tests at JPL designed to determine the best way to get Spirit out of a Martian patch of soft soil called "Troy," where Spirit's wheels have dug in. The test setup, in a box that team members are calling the dustbin, simulates the situation at Troy. The box holds about 2.7 tons of a powdery mixture of diatomaceous earth and fire clay. This material has physical properties similar to the soil at Troy. The top surface is sloped at 10 degrees.

To see updates on the efforts to free the Spirit rover, visit the JPL Free Spirit website.