Last week, the rover mission had to share its Odyssey memory allocation with a project named the Mars Bi-Static UHF Radar Experiment, which had the effect of reducing the buffer space available to the rovers.

This caused a backlog of data onboard Opportunity. This week the team started to offload some of that data by taking advantage of overnight Odyssey passes. The rover buffer space is back to normal.

The planning team is also making sure that experiments do not create too much new data this week.

The planning team wants to ensure that Opportunity has enough flash memory for next week's operations since the plan calls for a continuation of the drive toward "Erebus."

The general consensus is that the rover will take the easterly route to the Erebus highway. This route is longer by about 100 meters (328 feet), but should result in much more access to outcrop during the drive. The outcrop is attractive both for rover footing and for science targeting.

During the first weekend in August, there was a sequencing error that failed to run the alpha particle X-ray spectrometer. The team had added a miniature thermal emission spectrometer observation before starting the alpha particle X-ray spectrometer, and the added sequence ran long.

The alpha particle X-ray spectrometer start sequence did not complete and the instrument did not collect any data. After discovering what happened on Monday, the team reacquired the observation on sol 548 (Aug. 9, 2005).

On sol 549 (Aug. 10, 2005), there was a mobility fault. Under the "rules of the road," the team is required to stop the vehicle if any of the driving actuators draws more than 0.4 amperes of current for more than half a second. This protects the rover from digging into a "Purgatory Dune" situation.

On sol 549, while the rover was turning into a position more favorable for communication, the front right driving actuator went above 0.4 amperes for more than half a second and stopped the drive. This is expected behavior.

The turn for better communication was an optional move done at the very end of the drive.

The front right drive actuator will sometimes (especially when performing a turn-in-place) pull more current than the other drive actuators. This is because the front right steering actuator is not working, and its drive motor is not turning in the same direction as the other five motors.

On sols 550 and 551 (Aug. 10 and Aug. 11, 2005), Opportunity moved about 2 meters (nearly 7 feet) forward into a cobble field. The team has wanted to use Opportunity's alpha particle X-ray spectrometer and Moessbauer spectrometer on some cobbles, and there has never been a better chance than this location.

Rover drivers were able to approach the targets in one sol and get multiple cobbles into the robotic arm's work volume. On sol 551, the rover planners successfully planted the Moessbauer on a cobble that is roughly 2.5 centimeters to 3 centimeters (1 inch to 1.2 inches) in size.

This precision pointing was intended to allow the spectrometer to integrate for most of the weekend and tell the science team something new about cobbles.

Sol-by-sol summaries

Sols 545 to 547 (Aug. 6 to Aug. 8, 2005): Sol 545 was used to grind a rock-abrasion-tool hole. On sol 546, Opportunity took a post-grind microscopic imager mosaic and planted the Moessbauer spectrometer in the expected rock-abrasion-tool hole.

Sol 548: The rover retracted the Moessbauer spectrometer from the target called "OneScoop," and then performed a sequence of observations of the rock abrasion tool's grinding bit. Opportunity then placed the alpha particle X-ray spectrometer back down on the rock abrasion tool hole at OneScoop to re-acquire that spectral observation.

Sol 549: The rover retracted the alpha particle X-ray spectrometer and then retook the microscopic image of the rock-abrasion-tool hole. On the previous attempt, Opportunity had not made contact with the surface of the rock, so this sol it was commanded to overdrive 2 centimeters (0.8 inches) in order to ensure contact with the bottom of the 6-millimeter hole.

After acquiring the microscopic image, the rover stowed its arm and bumped back 0.85 meters (2.8 feet) to image the rock-abrasion-tool hole.

Opportunity then proceeded about 26 meters (85 feet) south towards a group of cobbles, taking a 360-degree panoramic image with the navigation camera at the halfway point. The team commanded the rover to turn to 215 degrees azimuth for communication at the end of the drive.

Sol 550: Opportunity bumped about 1.8 meters (6 feet) over to the cobble field. The team planned to get two of the cobbles in the robotic arm work volume.

Sol 551 (Aug. 11, 2005): On this sol, Opportunity un-stowed its arm and then took a microscopic imager mosaic of cobble target "Arkansas." The rover then used its microscopic imager to inspect a soil target, followed by a placement of the Moessbauer spectrometer on cobble target "Arkansas."

As of the end of its 551st sol on Mars, Opportunity has driven 5,725 meters (3.56 miles).

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