SPIRIT UPDATE: Three hundred sols and counting! - sol 292-305, November 18, 2004
Spirit remains in excellent health and has survived more than 300 martian days on the red planet.
With the Sun still relatively low on the horizon in the early spring season on Mars, rover drivers are forced to seek driving routes that keep the rover and its solar panels tilted northward for energy reasons. That constraint, plus the rocky terrain, will challenge rover drivers in the coming weeks.
Over the last few weeks, the electrical "brakes" on Spirit's right-front and left-rear steering actuators (motors) apparently failed to disengage during drive attempts. The most likely cause of this anomaly is the buildup of insulating material on the electronic relay contacts that indicate that the brakes are disengaged. To help ensure successful future drives, engineers decided to permanently ignore the "brake-disengaged" indicator. If their theory is correct, the brake will actually be disengaged despite the "failure-to-disengage" indication. If they are wrong, a fuse in the brake circuit will safely blow when they attempt to move the steering actuators. In either case, driving operations will not be adversely affected.
A few sols ago, Spirit's engineering team discovered an electric-circuit grounding problem between the rover chassis and the power bus return. This incident occurred at the exact time the Spirit team was performing an inspection of the instrument deployment device, or robotic arm. The inspection sequence commanded one of the arm joints to a position beyond where it had previously been. That particular joint, joint number 5, is the rover arm turret, which rotates the four rover arm instruments into position. This coincidence may indicate that the joint 5 move somehow created the electrical short; it could also just be coincidence. The mechanical team has not found any reason to suspect a failure in the joint 5 cabling. To be safe, the engineering team has constrained the use of joint 5 on Spirit and Opportunity to avoid this extreme position. The constraint is not expected to significantly impact normal operations. The apparent short may also be the result of a failed measurement circuit. The short, if real, has no immediate effect on the rover, but does remove one layer of protection against effects of future shorts should they occur.
Between sols 292 and 298, Spirit completed its studies of the rock called "Uchben" and drove west about 2 meters (almost 7 feet) to a rock called "Lutefisk."
Between sols 299-303, Spirit finished its investigation of Lutefisk. Lutefisk, a rock with some interesting nodules, lies a site roughly 40 meters (131 feet) above and 2700 meters (1.67 miles) away from Spirit's landing site on the Gusev plain. Team members should know more about the chemistry of Lutefisk and its nodules when they receive results from the alpha particle X-ray spectrometer and MÃ¶ssbauer spectrometer.
For coming sols, Spirit is in an exploration and discovery mode, continuing the rover's ascent towards "Machu Picchu" in the Columbia Hills. Spirit will stop at interesting rocks along the way.
OPPORTUNITY UPDATE: Finishing Up in 'Endurance' - sol 285-291, November 23, 2004
Opportunity has now reached the furthest point east in its travels inside "Endurance Crater." Rover drivers have determined that there is no safe path beyond the current position. Therefore, Opportunity is now in the midst of an intensive remote-sensing campaign, capturing a panorama of Burns Cliff plus super-resolution images and miniature thermal emission spectrometer observations of selected targets. When this campaign concludes, the rover will back away and head for a way out of Endurance Crater. Opportunity remains healthy and in an extremely advantageous solar array attitude.
The plan for 285 was to drive 1.5 meters (about 5 feet) east on firm rocky terrain ahead of the rover. The drive went as planned, covering 1.55 meters (5.1 feet). After integrating the results of this drive with an earlier study of Burns Cliff traversability, the team decided not to proceed farther. Opportunity has reached the easternmost point of its drive inside Endurance Crater. The rover is at the western edge of Burns Cliff and from this vantage point, it will perform super-high resolution imaging and other science observations.
Sol 286 was a restricted sol because the team did not know results of the sol 285 drive in time for planning sol 286. Opportunity recorded more than three hours of observations, took a nap, and then used afternoon and overnight communication sessions with Mars Odyssey. Solar exposure is excellent inside the crater, so Opportunity's power and battery state of charge continue to increase. The rover has not used deep-sleep mode in more than a week, and probably won't for the foreseeable future.
Sols 287 and 288 were planned together. Opportunity began super-high resolution imaging activities on sol 287. Starting at 11:15 local solar time, the rover performed the following activities: an hour of panoramic camera imaging, an hour of miniature thermal emissions spectrometer imaging and another hour of panoramic camera imaging. Sol 288 was almost exactly the same three-hour activity, but with the images targeted differently.
The Deep Space Network experienced a station transmitter problem on Saturday and Opportunity did not receive all of its two-sol uplink as planned. The rover received all except the last part of the sol 287 bundle, but none of the sol 288 bundle or data management bundle. Due to quick reaction by the weekend uplink team, bundles were successfully uplinked on Sunday, in time for execution of the sol 288 plan. The total effect of the missed Saturday uplink was a loss of about 30 minutes of science on the morning of sol 288.
Sols 289, 290 and 291 were very similar. Each was a continuation of the remote sensing campaign, with an additional panoramic camera observation. Sol 289 activities included observations of dunes and dust with the panoramic camera and miniature thermal emissions spectrometer. Also the panoramic camera was used for super-resolution imaging of "Whatanga," a contact boundary between two layers of rocks. For sol 290, in addition to the panoramic camera observation, Opportunity made several long-dwell observations of Burns Cliff targets with its miniature thermal emission spectrometer. Cloud observations on the morning of sol 290 produced a dramatic image. Sol 291 included a super-resolution observation of a target called "Bartlett."
The remote sensing campaign is generating a large volume of data at a time when, due to the rover's orientation, there is limited bandwidth available for downlink. As a consequence, Opportunity is operating with limited memory headroom, though still within planning guidelines. In order to improve the situation, the team took advantage of the Deep Space Network's 70-meter antenna availability and Opportunity's good energy state to plan a one-hour, direct-to-earth session in the middle of the day on sol 291. This resulted in the downlink of an extra 15 megabits of data.