Mars Exploration Rover Update - August 18, 2005

http://marsrovers.jpl.nasa.gov/mission/status.html

OPPORTUNITY UPDATE: Opportunity Entering Cobble Field - sol 544-551,
August 18, 2005:

Opportunity had a busy week! The rover has been using the rock abrasion
tool and all of its spectrometers and imaging instruments. It has been
healthy but slightly constrained in the flash memory. 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).