* Astronomy

OPPORTUNITY UPDATE: Evaluating Arm Positions - sol 675-681, Dec 22, 2005:

This week the Opportunity Instrument Arm Anomaly Team continued investigating the safety of different arm positions. The intent is to determine the safest position to leave the arm while the vehicle drives to new locations. The original position for the arm while driving was to tuck it underneath the rover, hooked on a small pin. This leaves the partially failed shoulder azimuth joint at 90 degrees to the direction of travel. If the arm stuck in this position we would be unable to use the arm.

The current plan is to investigate different versions of driving with the instrument arm's "elbow" sticking out towards the front of the vehicle, with the arm's instrument cluster above the solar panels. From that position the instrument arm could still be used without using the suspect azimuth joint. The variations include leaving the instrument cluster in mid air, or resting one or another instrument on different portions of the rover for stability.

These different positions are being evaluated on the test rover at the Jet Propulsion Laboratory in Pasadena, California. Meanwhile, on Mars, Opportunity is continuing to use the arm and its instruments to investigate rocks within its reach. The rover has also been acquiring images for a 360-degree, multi-filter panorama of "Erebus Crater."

Sol-by-sol summaries:

Sol 675 (Dec. 17, 2005): Opportunity completed a 17-hour reading with the alpha particle X-ray spectrometer and made observations with the panoramic camera.

Sol 676: The rover used the Mössbauer spectrometer for five hours and observed the atmosphere and a target called "Bellemont" with the miniature thermal emission spectrometer.

Sol 677: Opportunity completed a microscopic-imager mosaic of a target called "Williams," used the Mössbauer spectrometer for 11 hours, and observed targets with the panoramic camera.

Sol 678: The Mössbauer collected data about Williams' composition for 22 hours and the panoramic camera made observations.

Sol 679: Opportunity moved its robotic arm to a target called "Ted," which it began inspecting with the microscopic imager and the alpha proton X-ray spectrometer. The navigation camera took pictures of the rover's front deck.

Sol 680: Planned activities include using the rock abrasion tool to brush Ted for about 11 minutes, then placing the alpha particle X-ray spectrometer onto the target again for about 20 hours of data collection.

Sol 681 (Dec. 23, 2005): Plans for this and the following few sols are further inspection of Ted, plus targeted observations with the panoramic camera. Opportunity's total odometry remains at 6,502 meters.

OPPORTUNITY UPDATE: Robotic Arm Deployed - sol 668-674, Dec 16, 2005:

Opportunity successfully deployed its robotic arm on sol 671 (Dec. 13, 2005) and used it to position the microscopic imager. The cause of a shoulder-joint motor stall during an attempt to deploy the arm on sol 654 appears to be a broken wire in the motor windings. The motor can still be operated by changing one of the parameters so that more current is delivered. However, the behaviour is still being characterised, and stalls of the motor can still occur while the motor parameters are being adjusted. Analysis also continues for determining the best strategy for keeping the arm unstowed even when it is not in use, so that the arm could still position instruments on targets even if the motor with the broken wire becomes unusable.

While parked at "Erebus Crater," Opportunity has completed a campaign of atmospheric science, with sky surveys, photometry observations at several times of day, and atmospheric observations with the miniature thermal emission spectrometer. The rover also observed ground targets with the panoramic camera and the miniature thermal emission spectrometer.

Sol-by-sol summaries:

Sol 668 (Dec. 10, 2005): The team had planned some targeted remote sensing and atmospheric observations, but the plan did not get uplinked due to issues with ground servers.

Sol 669: The uplink succeeded, and Opportunity performed targeted remote sensing and atmospheric observations.

Sol 670: Early in the morning, the rover performed an atmospheric observation. Later in the day, some stares with the miniature thermal emission spectrometer were completed.

Sol 671: Results of diagnostic tests of the robotic arm were consistent with the performance of a motor with a broken wire in one of the windings. The motor can be operated in this configuration by modifying motor parameters. By making the necessary changes, the arm was successfully moved out of its stowed position. The team planned a two-image-by-two-image mosaic with the microscopic imager and a reading with the Mössbauer spectrometer. The first half of the mosaic completed as planned, but the arm sequence was halted after that due to a stall of the shoulder-joint motor.

Sol 672: Opportunity made atmospheric and photometric observations.

Sol 673: The plan was to complete the microscopic-imager mosaic that was started on sol 671 and place the Mössbauer spectrometer on a target called "Williams." However, the shoulder-joint motor stalled once again. Targeted observations with the panoramic camera were completed as planned.

Sol 674 (Dec. 16, 2005): After analysis of the sol 673 stall, the team redelivered a command sequence to close the microscopic imager's dust cover and to position the alpha particle X-ray spectrometer for an overnight integration on Williams. Opportunity's total odometry remains at 6,502 meters.

OPPORTUNITY UPDATE: Encouraging Results from Shoulder-Motor Testing - sol 661-667, Dec 09, 2005:

Opportunity is currently parked at "Erebus Crater," where it has continued remote-sensing science while the team made progress in diagnosing why a motor in the robotic arm stalled on sol 654. The motor turned successfully when supplied with more current on sol 666 (Dec. 8, 2005), an encouraging result. The arm was still in a stowed position after that testing. Further tests and analysis are planned for determining the best strategy for future use of the arm. The arm, which deploys four tools for examining rocks and soils, has already operated more than seven times as long as originally planned.

This motor at the shoulder of the arm is necessary for getting the arm out of its stowed position. Earlier tests made some alternative explanations -- such as a physical obstruction or degraded lubrication -- appear unlikely. The sol 666 test established confidence in a hypothesis that a broken wire in the winding of the motor caused the sol 654 stall. The test rotated the motor four revolutions at each of three different applied voltages. Tests to characterise the motor's behaviour will continue in the coming week.

In the target-rich environment of outcrop exposed in and near Erebus, Opportunity has acquired a colour panorama of the surroundings, a colour mosaic of itself, and high-resolution images of several outcrop targets. The miniature thermal emission spectrometer successfully collected data on some high-priority science targets during sol 664 (Dec. 6, 2005). Informal names for targets examined in this vicinity by the panoramic camera include "Drake," "Chino Valley," "Bellemont," "Camp Verde," "Young," "Cherry," and "Paulden."

Opportunity did not drive this week. The rover's odometry total as of sol 666 remained 6,502 meters.

These images were acquired by the Mars Exploration Rover Opportunity using its panoramic camera on sol 644 (Nov. 15, 2005).


Approximate true-colour composite.

The view looks towards the east, covering a large wind-blown ripple called "Scylla" other nearby ripples and patches of brighter rock strewn with dark cobbles.

Panoramic camera bands L4 (601-nanometre wavelength), L5 (535 nanometres), and L6 (482 nanometres) correspond to red, green, and blue bands in the false-colour image shown in the upper left.


Expand (1.12Mb, 1020 x 1024)

The blue-tinted colours associated with the scours and ripple crests are probably due to the presence of basaltic sands mixed with hematite-rich spherules. Colour patterns on the larger ripple flanks are caused by different amounts of reddish dust.
The larger ripple flanks have an intricate mixture of erosional scours and secondary ripples extending downward from the main ripple crests, suggesting that these ripples have most recently encountered a period of wind erosion and transport of their outer layers.