Spirit remains in excellent health and has survived more than 300 martian days on the red planet.
With the Sun still relatively low on the horizon in the early spring season on Mars, rover drivers are forced to seek driving routes that keep the rover and its solar panels tilted northward for energy reasons. That constraint, plus the rocky terrain, will challenge rover drivers in the coming weeks.
Over the last few weeks, the electrical "brakes" on Spirit's right-front and left-rear steering actuators (motors) apparently failed to disengage during drive attempts. The most likely cause of this anomaly is the buildup of insulating material on the electronic relay contacts that indicate that the brakes are disengaged. To help ensure successful future drives, engineers decided to permanently ignore the "brake-disengaged" indicator. If their theory is correct, the brake will actually be disengaged despite the "failure-to-disengage" indication. If they are wrong, a fuse in the brake circuit will safely blow when they attempt to move the steering actuators. In either case, driving operations will not be adversely affected.
A few sols ago, Spirit's engineering team discovered an electric-circuit grounding problem between the rover chassis and the power bus return. This incident occurred at the exact time the Spirit team was performing an inspection of the instrument deployment device, or robotic arm. The inspection sequence commanded one of the arm joints to a position beyond where it had previously been. That particular joint, joint number 5, is the rover arm turret, which rotates the four rover arm instruments into position. This coincidence may indicate that the joint 5 move somehow created the electrical short; it could also just be coincidence. The mechanical team has not found any reason to suspect a failure in the joint 5 cabling. To be safe, the engineering team has constrained the use of joint 5 on Spirit and Opportunity to avoid this extreme position. The constraint is not expected to significantly impact normal operations. The apparent short may also be the result of a failed measurement circuit. The short, if real, has no immediate effect on the rover, but does remove one layer of protection against effects of future shorts should they occur.
Between sols 292 and 298, Spirit completed its studies of the rock called "Uchben" and drove west about 2 meters (almost 7 feet) to a rock called "Lutefisk."
Between sols 299-303, Spirit finished its investigation of Lutefisk. Lutefisk, a rock with some interesting nodules, lies a site roughly 40 meters (131 feet) above and 2700 meters (1.67 miles) away from Spirit's landing site on the Gusev plain. Team members should know more about the chemistry of Lutefisk and its nodules when they receive results from the alpha particle X-ray spectrometer and Mossbauer spectrometer.
For coming sols, Spirit is in an exploration and discovery mode, continuing the rover's ascent towards "Machu Picchu" in the Columbia Hills. Spirit will stop at interesting rocks along the way.