SPIRIT UPDATE: Spirit Tries Out Visual Odometry - sol 175-178, July 09, 2004
On sol 175, Spirit analyzed the new targets "Breadbox" and "Sourdough" with its panoramic camera and miniature thermal emission spectrometer. Spirit then got an up-close look at Breadbox with the microscopic imager, and deployed the MÃ¶ssbauer spectrometer on Sourdough for an overnight integration. In the middle of the martian night, Spirit did a tool change to the alpha particle X-ray spectrometer and completed a five-hour integration before the sol 176 plan began.
Spirit spent sol 176 getting a battery re-charge and a front hazard avoidance camera calibration. The evening of sol 176, engineers commanded Spirit to wake up and enable the panoramic camera mast actuator heater so they could determine when the thermostat turns the heater on. The heater turned on when expected, which will allow Spirit to conduct a night-time miniature thermal emission spectrometer observation in a few sols.
On sol 177, Spirit successfully performed a series of observations on an interesting and shiny feature called "String of Pearls." The rover acquired two microscopic images of the target and an overnight integration with the MÃ¶ssbauer spectrometer and alpha particle X-ray spectrometer. As Mars' southern winter approaches, Spirit's energy resources become increasingly limited. Overnight tool changes and their associated heating take a big toll on the limited energy budget, and require some preparation and recovery to keep up Spirit's battery charge.
Spirit began sol 178 by stowing the robotic arm and then backing up 1.5 meters (about 5 feet) from "Hank's Hollow" in order to properly place the miniature thermal emission spectrometer to get a good view of "Pot of Gold" and nearby rover tracks. Engineers also took this opportunity to use visual odometry for the first time on Spirit. This is a technique in which the rover takes successive images of its surroundings during a drive and then matches features in those images on-board to compute how far and in what direction it has moved. Both the drive and the test went well, and ground verification showed that the matching worked quite nicely with the features in this terrain. Visual odometry will be important if and when Spirit starts driving on five wheels, since the actual drives can and will be rather different than what is commanded. The rover can use the visual odometry estimates while driving to compensate for the slipping and yawing that engineers expect with five-wheel driving.
OPPORTUNITY UPDATE: Opportunity Tests its Mettle on Slopes of 'Endurance Crater' - sol 154-158, July 07, 2004
Sol 154 consisted of Opportunity completing activities on the target "Kettlestone," including a long MÃ¶ssbauer integration, some microscopic images and placement of the arm for a little early morning alpha particle X-ray spectrometer integration to occur on the morning of Sol 155. The rover then went to sleep.
Sol 155 began with an early morning Mars Odyssey UHF relay of about 60 megabits of data, followed by a completion of the alpha particle X-ray spectrometer integration on Kettlestone. The rover then performed a calibration activity with the arm, consisiting of moving the arm into about 20 different poses and imaging each pose with the front hazard-avoidance cameras. From the stereo images and the reported position of the arm, the rover team will be able to update models and better target the instruments onto surface features in the future. Some miniature thermal emission spectrometer activity was conducted midday, and then the rover drove backwards about 1 meter (3.3 feet). The drive backwards served two purposes: first, it positioned the rover to image the most recent rock abrasion tool holes with the panoramic camera and miniature thermal emission spectrometer; secondly, it gave the team an opportunity to evaluate driving back up over the "curb" that was considered so difficult before traversing on sol 150. The drive back up over the curb went very well. Slip was estimated at around 11 percent, admirable for such a traverse.
On sol 156, due to an incorrect time conversion, the rover team failed to get the intended command load to the spacecraft at the right time. As a result, the spacecraft executed a backup set of minimal activities and returned about 80 megabits of data through Odyssey in the afternoon.
On sol 157 the rover acquired some images of the rock abrasion tool holes from previous sols. Then it drove down the hill to approach the next target. It drove beautifully and achieved its goal location. However, due to the large slopes (final rover tilt was 28.6 degrees), Opportunity ended the drive with the right rear wheel apparently slightly above the terrain (not touching anything). Even in this state the rover appears to be stable, but the team will likely take action on the next sol to get the suspension squared up (six wheels touching) before proceeding with preparations to grind with the rock abrasion tool again. On the night of sol 157 to 158 the rover gave up deep sleep in order to preserve an exceptional morning Odyssey pass.
The very early morning of sol 158, the rover woke up to chat with the Odyssey spacecraft and returned over 100 megabits of data! The rover then started the day's activities early with an attempt to image clouds around 8:30 in the morning. It then went back to sleep until about 10:30. After the morning uplink, it acquired some microscopic images of the new target area, then stowed its arm to allow a small mobility maneuver to get all six wheels squarely planted on the ground. This seemed to go as planned and reduced the total tilt of the vehicle to only 26.4 degrees, but did not appreciably change its position. This left the rover, as desired, in position to perform science investigations on the next targets of interest.