OPPORTUNITY UPDATE: Opportunity Studies “Bathtub Ring” In “Victoria Crater” - sol 1301-1308, Nov 01, 2007:
Opportunity is healthy, with energy levels ranging from about 450 watt-hours to 475 watt-hours (100 watt-hours is the amount of electricity needed to light a 100-watt bulb for one hour).
Recently, Opportunity was temporarily unable to send scientific data to Earth because the Odyssey orbiter experienced a computer crash and went into “safing” mode. While in safing mode, the spacecraft shuts off unnecessary power loads, orients itself for maximum sunlight to the solar arrays, switches to communication modes most likely to receive commands from Earth, and basically stops all unnecessary activity while waiting for the folks back home to fix it and put it back in service.
While in safing mode, Odyssey did not send communications from either Mars rover. Opportunity continued to collect as much science as possible while waiting for Odyssey to be fixed.
After Odyssey was back in service, Opportunity began making up for lost time. Following a series of “toe dips,” during which the rover drove a short way into “Victoria Crater” and backed out again, then drove a little farther and backed out again, Opportunity began examining the crater’s interior.
Victoria Crater is interesting because it affords a chance to study rock layers down to a depth of about 70 meters (230 feet) below the surrounding surface. The modern surface isn’t the original surface – it has been altered by an incoming meteor. When a meteor strikes, it throws up a huge amount of debris that falls back around the crater and creates an “ejecta blanket.” This blanket is thickest near the crater rim and thinnest farther away from the crater.
Below Victoria’s raised rim is a light-colored band nicknamed the “bathtub ring.” Scientists hypothesize that this band is the dividing line between the original surface and the ejecta blanket above it. Opportunity has now reached this area – but not without difficulty.
To reach the ring, Opportunity drove across a slope of about 25 degrees, nearly the maximum allowable tilt for the rover. The rover approached the ring on sol 1302 (Sept. 22, 2007) and then partially drove and partially slipped into closer position. On sol 1305 (Sept. 25, 2007), the rover unstowed the robotic arm and began studying the rocks that make up the top, or “Alpha,” layer of the ring. Below that are two more layers, known as “Beta” and “Gamma,” respectively.
Halfway through the last short drive of about 20 centimeters (8 inches), Opportunity automatically stopped when the rover violated the tilt limit. As a result, the rover drove laterally about 10 centimeters (4 inches) and then slid downslope 10 centimeters (4 inches). Subsequent analysis suggested that one of the downslope wheels rolled off a slight curb, producing a jolt that caused the rover to slip. Images showed that the rover had stopped on a hard outcrop of rock rather than sand or soil and was unlikely to slip farther.
Given the steep slope, Opportunity was extremely careful about moving the robotic arm. Before placing it on Alpha Layer, Opportunity moved the arm out, to the left, and to the right, while also checking for any vehicle motion with both the inertial measurement unit and cameras. The first rock target was dubbed “Steno.”
Opportunity continued to conduct untargeted remote sensing by, among other things, measuring Tau, or atmospheric opacity, several times each Martian day, or sol. Now that the dust storms are over, the dust is settling. How fast it settles is of both scientific and engineering interest because it affects solar energy levels. Opportunity also periodically checked deposition and movement of dust on the panoramic camera mast assembly and solar arrays. This provides data for estimating wind directions and speeds, dust particle sizes, and dust composition.
Opportunity performed two “Quick Fine Attitude” checks. These are calibration activities that compensate for drift, or changes in time, in the inertial measurement unit. The unit uses gyroscopes and accelerometers to estimate the rover’s motion, from which its position can be calculated. However, the gyroscopes show a slight change in attitude while the rover is still. (Older, mechanical gyroscopes drifted because of friction; newer, electronic gyroscopes drift for more complex reasons.)
The attitude checks compute where the sun should be based on the current time and the rover’s movement and then compares this to the actual location of the sun in images from the panoramic camera. The difference forms the basis of the attitude correction for the rover.
In addition to daily observations that included frequent measurements of atmospheric dust with the panoramic and navigation cameras, surveys of the sky and ground with the miniature thermal emission spectrometer, and checks for drift (changes with time) in the miniature thermal emission spectromeer, Opportunity completed the following activities:
Sol 1301 (Sept. 21, 2007): Opportunity acquired panoramic camera images of the foreground, checked for drift in the miniature thermal emission spectrometer, checked the operation of the spectrometer, and surveyed the rover’s external calibration target with the spectrometer. Before going into a deep sleep, the rover surveyed the horizon at low sun with the panoramic camera. The next morning, Opportunity monitored dust on the rover mast.
Sol 1302: Opportunity stowed the robotic arm, drove toward Alpha Layer, acquired images with the hazard avoidance cameras just prior to and after completing the drive, and completed a “quick fine attitude” update to confirm the rover’s exact location. The rover unstowed the robotic arm, acquired post-drive images with the navigation camera, and acquired panoramic camera images of the work volume (the area reachable by instruments on the robotic arm). After that, Opportunity went into a deep sleep.
Sol 1303: Opportunity assessed the external calibration target with the miniature thermal emission spectrometer, recalibrated the panoramic camera, and spent six hours measuring atmospheric argon with the alpha-particle X-ray spectrometer. The rover went into a mini-deep sleep.
Sol 1304: Opportunity surveyed the external calibration target with the miniature thermal emission spectrometer, recalibrated the panoramic camera, and went into a deep sleep. The next morning, the rover took spot images of the sky with the panoramic camera.
Sol 1305: Opportunity stowed the robotic arm, bumped (drove a short distance) to Alpha Layer, and acquired penultimate and ultimate images with the hazard avoidance cameras. The rover completed a “quick fine attitude” check, acquired panoramic camera images of the work volume, unstowed the robotic arm, and acquired post-drive navigation camera images. Opportunity recalibrated the panoramic camera and went into a deep sleep.
Sol 1306: Opportunity acquired data from the external calibration target with the miniature thermal emission spectrometer and recalibrated the panoramic camera.
Sol 1307: Opportunity completed a “quick fine attitude” check, conducted a safety test with the robotic arm, acquired left-eye images of the alpha-particle X-ray spectrometer with the panoramic camera, and acquired stereo images of Steno with the microscopic imager. The rover placed the alpha-particle X-ray spectrometer on Steno and, after relaying data to Odyssey and recalibrating the panoramic camera, collected data from Steno with the spectrometer for 12 1/2 hours.
Sol 1308 (Sept. 28, 2007): After the usual dust monitoring and imaging activities as well as data relays to Odyssey, Opportunity went into a deep sleep.
As of sol 1308 (Sept. 28, 2007), Opportunity’s total odometry was 11,572.94 meters (7.19 miles).