Mars Exploration Rover Update - October 20, 2004

http://marsrovers.jpl.nasa.gov/mission/status.html
SPIRIT UPDATE: Spirit investigating ancient rocks - sol 272-278, October 20, 2004
Spirit had a productive week investigating the rock "Tetl." On sol 277, Spirit attempted a drive to the next rock target, "Uchben," which means "ancient" in the old Mayan language. Halfway into that drive, Spirit experienced a repeat problem in the steering motor control system that engineers first saw on sol 265. Engineers repeated diagnostic tests for the problem on sol 278. Those tests showed that the electronics relay in question is still functional, but appears to operate intermittently. Spirit is otherwise healthy and is in a safe location.
On sol 272, Spirit took images with the microscopic imager to create a mosaic of Tetl's layered rock face.
On sol 273, Spirit captured more microscopic images of Tetl's layered face, then put the alpha particle X-ray spectrometer in place for an early morning observation.
On sol 274, Spirit woke up at 4:00 a.m. to start the alpha particle X-ray spectrometer observation. The alpha particle X-ray spectrometer stayed on until the start of normal morning atmospheric science observations. Spirit also used its miniature thermal emission spectrometer to observe nearby rocks named "Zackuk" and "Palenque," which are possible future targets for in-depth observations. Later, Spirit changed tools on its robotic arm, placing the Mossbauer instrument on Tetl for an observation the next morning.
On sol 275, Spirit completed a 6-hour Mossbauer integration and performed daily atmospheric observations. This was the final sol of Spirit's weekend plan and was purposely simple to enable the sequencing team to complete a 3-day plan on Friday.
On sol 276, Spirit restarted the Mossbauer instrument at 4:00 a.m. for another 10 hours of integration time on the same spot. Spirit also took a few final microscopic images of Tetl, then stowed the robotic arm in preparation for the next sol's drive.
On sols 277 and 278, Spirit attempted a drive to Uchben, another layered rock roughly 6 meters (20 feet) northeast of Tetl. About 2.5 meters (8 feet) into the drive, the mobility software attempted to move a steering motor by first commanding open a relay (electronic switch) that releases a dynamic brake. The feedback from that command indicated that the relay was still closed, so the motor control software declared an error. Due to the error, the rover ignored that steering command and all subsequent driving commands. The root cause of the failed relay command is under investigation. A diagnostic test last run on sol 270 was repeated on sol 278, which ended on Oct. 14. That test showed that the steering motor's dynamic brake relay can still be opened and closed, but does occasionally (5 out of 10 times) indicate that it is still closed after being commanded open.
More diagnostics tests are needed before the source of the problem can be positively identified. Until then, engineers will continue to drive, but will steer the rover in a tank-like fashion, not using the steering actuator in question.
Future plans are to clear the drive error and attempt another drive to Uchben on sol 281. Engineers are also planning to run more diagnostic tests starting on sol 282.
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