During the last set of drive commands uploaded to the Martian rover Spirit, engineers have encountered a problem in one of the rover's wheels, which jammed when the time came to spin. The entire drive attempt was therefore stopped by the robot's onboard computer, so as not to make its situation even worse than it was. As such, mission managers at the NASA Jet Propulsion Laboratory (JPL), which control the two components of the Martian Exploration Rovers (MER) program, decided to upload a set of diagnostic instructions on Tuesday, so as to assess the condition of the rover.

Their research found that the wheel that stalled during the Sol 2092 (Saturday, November 21) drive attempt, the right-rear one, was functioning according to specifications on November 24 (Sol 2095). The diagnostic showed that the wheel was free of obstructions, which made the engineers wonder what could have been that prevented it from moving during the full maneuvers. A number of other tests were conducted in addition to the one related to the wheel, including a rotor resistance one, an assessment of the rover's steering capabilities, and a small backward rotation of the right-rear wheel alone. A short, forward commanded motion was also uploaded.

The right-rear wheel is not the same wheel that stalled on Sol 1899 (May 6), the JPL experts say. “The rover had completed about 4 meters (13 feet) of commanded wheel spin before the stall terminated the drive. The center of the rover moved about 4 millimeters (0.2 inch) forward, 3 millimeters (0.1 inch) to the left and about 3 millimeters (0.1 inch) down. The rover suspension stayed within the tighter limits set for the drive, and there was only a fractional change in rover tilt,” a press release on JPL's website announced a couple of days ago.

“The cumulative results from Sols 2088 to 2095 (Nov. 17 to 24) are 8.1 meters (27 feet) of commanded motion, 15.7 millimeters (0.6 inch) of forward progress, 9.9 millimeters (0.4 inch) of movement to the left, and 4.8 millimeters (0.2 inch) of sink. The plan for a drive during the long holiday weekend is another two-step drive, with each step 2.5 meters (8.2 feet) of commanded wheel spin. All wheels will be straight and run at the same speed. Results of this commanded drive will be analyzed Monday, November 30,” experts at the laboratory reported yesterday.

Spirit has been stuck in a loose patch of Martian soil known as Troy since late April, and is unable to move out of it in large increments. JPL MER Project Manager John Callas said, even before any attempts of extricating the rover began, that the process would be cumbersome and long, and that there was a real chance that not even the best efforts on the part of the team would see the rover free again.