[meteorite-list] Mars Exploration Rover Update - May 8-15, 200

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 20 May 2008 17:26:43 -0700 (PDT)
Message-ID: <200805210026.RAA20654_at_zagami.jpl.nasa.gov>

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

OPPORTUNITY UPDATE: Injured Shoulder Joint Back in the Game -
sol 1525-1532, May 08-15, 2008:

Like an athlete with a shoulder injury whose arm is folded in a sling,
NASA's Mars rover Opportunity has been unable to move its robotic
shoulder joint for weeks. Early Wednesday (May 14, 2008), after a
regimen of electrical stimulation and heat, the rover finally moved its
shoulder joint and swung its robotic arm back to the front. Opportunity
accomplished this after surviving four Earth years, two Martian winters,
a major dust storm, and more than 1,500 day-to-night temperature cycles
on the red planet.

The story of Opportunity's shoulder begins way back on Sol 2 (Jan. 25,
2004), the rover's second day on Mars. That's when engineers discovered
that the heater on the shoulder azimuth joint, which controls
side-to-side motion of the robotic arm, was stuck in the "on" position.
Closer investigation revealed that the on-off switch had probably failed
during assembly, test, and launch operations on Earth. Fortunately for
Opportunity, the rover was equipped with a built-in safety mechanism
called a "T-stat box" (thermostatic switch) that provided protection
against overheating. When the shoulder azimuth joint, also known as
Joint 1, got too hot, the T-stat switch automatically opened and
temporarily disabled the heater. When the joint got cold again, the
T-stat closed. As a result, the heater stayed on all night but not all day.

The safety mechanism worked until Opportunity approached the first
winter on Mars. As the Sun began to retreat lower in the sky and solar
power levels dropped, it became clear that Opportunity would not be able
to keep the batteries charged with a heater draining power all night
long. On Sol 122 (May 28, 2004), rover operators began using a procedure
known as "deep sleep," during which Opportunity disconnected the
batteries at night. Deep sleep prevented the stuck heater (and
everything else on the rover except the clock and the battery heaters)
from drawing power. When the Sun came up the next morning and sunlight
began hitting the solar arrays, the batteries automatically reconnected,
the robotic arm became operational, the shoulder joint warmed up, and
the thermostatic switch opened, disabling the heater. As a result, the
shoulder joint was extremely hot during the day and extremely cold at
night. Such huge temperature swings, which tend to make electric motors
wear out faster, were taking place every sol.

This strategy worked for Opportunity until Sol 654 (Nov. 25, 2005), when
the Joint-1 azimuth motor stalled because of increased electrical
resistance. Rover operators responded by delivering higher-than-normal
current to the motor. This approach also worked, though Joint 1
continued to stall periodically. Typically, the rover's handlers simply
tried again the next sol and the joint worked. They determined that the
Joint-1 motor stalls were most likely due to damage caused by the
extreme temperature cycles the joint experienced during deep sleep. As a
precaution, they started keeping the robotic arm out in front of the
rover overnight, rather than stowing it underneath the rover deck, where
it would be virtually unusable in the event of a Joint-1 motor failure.
They stowed the arm only while driving and unstowed it immediately at
the end of each drive.

This strategy worked for Opportunity until Sol 1502 (April 15, 2008),
when the motor stalled at the beginning of an unstowing operation at the
end of a drive, when the arm was still tucked underneath the rover. The
motor continued to stall on all subsequent attempts, sol after sol.
Engineers performed tests at various times of day to measure electrical
resistance. They found that the resistance was lowest (essentially
normal) when the joint was at its warmest -- in the morning, following
deep sleep, after the heater had been on for several hours, and just
before the T-stat opened. They decided to try to unstow the arm one more
time under these conditions.

At 08:30 Mars time on Sol 1531 (May 14, 2008), they allowed Opportunity
to direct as much current as possible to the warm, joint-1 azimuth motor
in order to get the robotic arm into a usable position, in front of the
rover. It worked.

Because Opportunity will likely never again stow the robotic arm,
engineers are working on a strategy for driving the rover safely with
the arm deployed in front. In this way, Opportunity will continue to
explore Mars, having weathered yet another challenge!

Sol-by-sol summary:

In addition to receiving morning instructions directly from Earth via
the rover's high-gain antenna, relaying data back to Earth via the UHF
antenna on the Mars Odyssey orbiter, and measuring atmospheric dust with
the panoramic camera, Opportunity completed the following activities:

Sol 1525 (May 8, 2008): Opportunity used the alpha-particle X-ray
spectrometer to measure argon gas in the Martian atmosphere and used the
navigation camera to acquire time-lapse movie frames in search of clouds.

Sol 1526: Opportunity continued to study the Martian atmosphere.

Sol 1527: Opportunity made atmospheric measurements.

Sol 1528: Opportunity contined to make atmospheric measurements.

Sol 1529: Opportunity conducted tests of electrical resistance in the
robotic arm and acquired full-color images, with all 13 filters of the
panoramic camera, of soil. The rover began acquiring parts 3 and 4 of
the so-called "Garrels" panorama, a sweeping view of Cape Verde and the
slope where the rover will exit Victoria Crater.

Sol 1530: In the morning, Opportunity completed work on parts 3 and 4 of
the Garrels panorama. The rover took spot images of the sky for
calibration purposes with the panoramic camera and acquired six
time-lapse movie frames in search of overhead clouds.

Sol 1531: Opportunity moved Joint 1 to an unstowed position and acquired
part 5 of the Garrels panorama. The rover measured argon gas in the
atmosphere with the alpha-particle X-ray spectrometer and surveyed the
sky at high Sun with the panoramic camera.

Sol 1532 (May 15, 2008): Opportunity moved robotic arm joints 2 through
5 to an unstowed position and acquired part 6 of the Garrels panorama.
The rover monitored atmospheric dust with the navigation camera and
monitored dust on the rover mast. Opportunity acquired a movie in search
of clouds with the navigation camera and took spot images of the sky for
calibration purposes with the panoramic camera.

Odometry:

As of sol 1532 (May 15, 2008), Opportunity's total odometry remained at
11,689.53 meters (about 7.25 miles).
Received on Tue 20 May 2008 08:26:43 PM PDT