Over the Fourth of July weekend, Spirit completed a robotic-arm campaign which had some surprising results. It turned out that targets at "Independence Rock" seem to have less iron than expected. This result prompted the science team to take a closer look. On sol 536 (July 6), because the grinding teeth on the rock abrasion tool are worn, the rover team decided to remove some of the surface area by scuffing it with the front left wheel.
The scuff worked as follows:
- Spirit moved into position with a turn in place. 2. Rotated only the front left wheel -- reverse 1 radian. 3. Rotated only the front left wheel -- forward 2 radians. 4. Rover used onboard visual odometry. 5. Repeated steps 2 through 4, two more times. 6. Turned in place back to the starting position in order to present the "scuff" to the robotic-arm workspace.
Since the rover gets better alpha particle X-ray spectrometer and Moessbauer spectrometer spectral readings when we let them run long (more than 10 hours for the alpha particle X-ray spectrometer and more than
20 hours for the Moessbauer spectrometer). The rest of the weekend (sols 538 to 541) will be dedicated to work using the instruments on the robotic arm.Sol-by-sol summaries:
Sol 532 to 535 (July 2 to July 5, 2005): Over this period, Spirit took data with the alpha particle X-ray spectrometer and the Moessbauer spectrometer and made observations with the microscopic imager and remote-sensing instruments. The results motivated a decision to do more work with the robotic arm.
Sol 536: The scuff today worked nicely, except that it did not seem to remove a whole lot of material from the place Spirit scuffed. Overall, the rover only scuffed 9 radians on the rock surface, which is less than
1.5 wheel revolutions. Engineers received no errors during the drive, and it looked like all drive-related telemetry was within acceptable parameters.After the scuff and before Spirit moved back to its original position, the rover took a picture with the hazard avoidance camera in order to see the effect the scuff had on the wheel treads.
The rover team favored the forward wheel rotation because this creates a torque that needs to work against gravity in order to rotate the rover body.
Sol 537 (July 7, 2005): Spirit started an "Independence" 360-degree color panorama. This mosaic will be run all weekend.
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OPPORTUNITY UPDATE: Pushing Away from Purgatory - sol 510-517, July 11, 2005:
This week Opportunity finished examining "Purgatory Dune" and started driving again. The first few drives were to the north so that possible paths to the south could be imaged and evaluated. The next few steps took the rover east, then southward down a wide trough. A new set of "rules of the road" have been developed and implemented to prevent the rover from getting bogged down again.
The miniature thermal emission spectrometer has also been cleared for regular use, and has returned some useful science products during the last week.
Sol-by-sol summaries:
Sol 510 (June 30, 2005): Opportunity finished characterizing Purgatory ripple with microscopic imager pictures of soil (tracks and undisturbed), and took a first step back. The rover collected several images to document the 2.1-meter (6.9-foot) drive. Visual odometry confirmed that slip was less than 10 percent during the short traverse. After the drive, the rover took pictures of the surroundings to evaluate possible safe pathways to the south.
Sol 511: Opportunity backed up 8.5 meters (28 feet), and again imaged the terrain to the south. The drive used visual odometry and slip checks to stop the rover if it failed to make progress.
Sol 512: The long-term goal for Opportunity is to drive south and slightly east. Before continuing on this path the rover must either go east or west to sidestep Purgatory Dune. Extensive remote sensing with the panoramic camera and navigation camera was done this sol to assist in the decision.
Sol 513: With all imaging needed for driving already acquired, Opportunity spent the sol doing atmospheric observations, dust monitoring, and also imaging of the magnets with the panoramic camera.
Sol 514: The engineering and science team took an Independence Day break today, and the rover executed its planned runout science sequence, which included atmospheric observations with the panoramic camera.
Sol 515: Imaging acquired over the weekend showed that the path to the east contained very small ripples (less than 6 centimeters or 2.4 inches), and led to a wide trough to the south. This sol, rover planners sequenced a 5.5-meter (18-foot) backwards drive over old tracks, then turned in short segments (less than 20 degrees), and drove east 2.5 meters (8.2 feet) over one small ripple. Tilt limits, visual odometry failure limits, and cycle limits were employed to prevent the rover from bogging down. The drive succeeded as planned.
Sol 516: An 11-meter (36-foot) drive to the east crossed two small ripples and positioned the rover to enter the trough leading south. Limits and slip checks were used to ensure that Opportunity would not get stuck.
Sol 517 (July 8, 2005): A new safety check was added to this drive: The drive current limits were lowered from 1 ampere to 0.4 amperes. The standard safety checks were also used on this drive, designed to take Opportunity 4 meters (13 feet) east to the north end of the trough, then
11 meters (36 feet) south through the trough.Opportunity's total odometry after sol 517 is 5,406.6 meters (3.36 miles).
Looking ahead: Opportunity will continue the drive south, more slowly than before to ensure a safe path.