Spirit's Right-Front Wheel Moves

Two days after the last test drive of Spirit's wheels on Mars, on December 16, experts at the NASA Jet Propulsion Laboratory (JPL) announce that they can now confirm the rover's thought-defunct right-front wheel moved on its own. Originally believed to have permanently malfunctioned, it has not been in use since 2006, and the rover has been dragging it around, while driving backwards, ever since. Now, in four successive spin attempts, it functioned, save for the fourth, when it didn't spin for the scheduled time frame and stopped prematurely.

“The rover's right-rear wheel, which stalled nearly three weeks ago, remained immobile during the entire Sol 2117 (December 16) drive. The other four wheels all drove forward in this part of the continuing attempt to extricate Spirit from the sand trap where it is embedded. The sol's total commanded motion was 10 meters (33 feet) worth of wheel rotations,” JPL engineers announce in a press release. The lab manages the Mars Exploration Rovers (MER) mission for NASA's Science Mission Directorate, in Washington DC. JPL is, in turn, managed by the Pasadena-based California Institute of Technology (Caltech).

According to the group attempting to extricate the rover, the complete results of the last drive were two millimeters (0.08 inch) of advanced forward and four millimeters (0.16 inch) of downward motion. This ratio, the experts say, is well below the estimated one needed for a long-term extrication process. In other words, at the rate things are currently going, the rover will sooner get buried in sand than travel the distance it needs to, so that it can exit Troy. Spirit has been trapped in this patch of loose Martian soil, near the feature known as Home Plate, since late April 2009.

“The drive conducted on Sol 2117 had been planned for one sol earlier, but was delayed after analysis of the Sol 2113 test led to discovery of a new electrical issue on Spirit. Engineers learned that a persistent voltage now exists between the rover electric ground and the rover chassis where no voltage should exist. This condition might be related to problems with the right-rear wheel,” the team also announces. “The plan ahead is to perform another set of low-voltage tests on the three right-side wheels and then command another four-step forward drive. This drive would not use the right-front wheel in conjunction with the others, but that wheel would be driven briefly by itself after each step to gain more information about its possible usefulness,” the release concludes.