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Mars Rovers Recover From Storms, Resume Travels; Orbiter Vision Clears

By | August 27, 2007

      The intrepid Mars rover vehicles, after six weeks of being immobilized by blinding dust storms that cut off their supply of electricity-generating sunlight, have rallied and now are moving about the red planet again.

      Separately, a telescopic camera orbiting Mars is rallying from recent problems.

      During the raging storms, rovers Spirit and Opportunity had to be immobilized to conserve battery power, desperately needing what little electricity was available to keep the temperature of their components from slipping too low.

      Opportunity advanced 13.38 meters (44 feet) toward the edge of Victoria Crater on Aug. 21. Mission controllers were taking advantage of gradual clearing of dust from the sky while also taking precautions against buildup of dust settling onto the rover.

      The storms appeared at a most inopportune time, just as Opportunity was about to descend a slope down to the crater floor.

      On the way down, NASA scientists hoped that Opportunity could perform some geological sleuthing, checking out a layer of bright-colored soil or rock to find, perhaps, what conditions prevailed on Mars long ago, such as whether there was water on the planet surface.

      One reason the rover team chose to drive Opportunity closer to the crater rim was to be prepared, if the pace of dust accumulation on the solar panels increases, to drive onto the inner slope of the crater. This would give the rover a sun-facing tilt to maximize daily energy supplies. The drive was also designed to check performance of the rover’s mobility system, so it included a turn in place and a short drive backwards.

      The next day, a favorable wind removed some dust from Opportunity’s solar panels, providing a boost of about 10 percent in electric output. This forestalled the need to hurry to a sun-facing slope. The team is still excited to get Opportunity inside Victoria Crater to examine science targets on the inner slope that were identified in June, shortly before dust storms curtailed rover activities. An estimate of how soon Opportunity will enter the crater will depend on assessments in coming days of how dust may be affecting the instruments and of how much energy will be available.

      “Weather and power conditions continue to improve, although very slowly for both rovers,” said John Callas of the Jet Propulsion Laboratory at Pasadena, Calif, project manager for the rovers. With the improved energy supplies, both rovers are back on schedule to communicate daily. Opportunity previously was conserving energy by going three or four days between communications.

      No new storms have been lifting dust into the air near either solar-powered rover in the past two weeks. Skies are gradually brightening above both Spirit and Opportunity. “The clearing could take months,” according to Bruce Banerdt, rover project scientist.

      “There is a lot of very fine material suspended high in the atmosphere.”

      As that material does settle out of the air, the powdery dust is accumulating on surfaces such as the rovers’ solar panels and instruments. More dust on the solar panels lessens the panels’ capacity for converting sunlight to electricity, even while more sunlight is getting through the clearer atmosphere.

      Opportunity’s daily supply of electricity from its solar panels reached nearly 300 watt-hours Aug. 23. That is more than twice as much as five weeks ago, but still less than half as much as two months ago. It is enough to run a 100-watt bulb for three hours.

      On Spirit, dust on the lens of the microscopic imager has slightly reduced image quality for that instrument, although image calibration can compensate for most of the contamination effects. The team is experimenting with ways to try dislodging the dust on the lens.

      Spirit’s solar arrays are producing about 300 watt hours per day as dust accumulation on them offsets clearing skies. Spirit drove 42 centimeters (17 inches) backwards on Aug. 23 to get in position for taking images of a rock that it had examined with its Moessbauer spectrometer. The rover team is planning additional drives for Spirit to climb onto a platform informally named Home Plate.

      Mars Orbiter Improves

      Separately, a NASA eye in the sky over Mars is gaining sharper vision.

      Diagnostic tests and months of stable, successful operation have resolved concerns raised early this year about long-term prospects for the powerful telescopic camera on the Mars Reconnaissance Orbiter.

      The High Resolution Imaging Science Experiment (HiRISE) camera on the orbiter has now taken more than 3,000 images of Mars, resolving features as small as a desk in targeted areas covering thousands of square miles of the Martian surface, according to NASA.

      Already, this is the largest Mars data set ever acquired by a single experiment. The camera is one of six instruments on the orbiter.

      During the first three months after the orbiter’s primary science phase began in November, researchers saw an increase in noise and pixel dropouts in data from seven of the camera’s 14 detectors. The effects on image quality were small in all but two detectors, but the trend raised concerns.

      Tests yielded an explanation for the earlier pattern, and the camera’s performance record shows the noise stopped getting worse after about three to four months of the science phase.

      Alfred McEwen of the University of Arizona, Tucson, principal investigator for the camera, said, “I’m happy to report that there has been no detectable degradation over the past five months.”

      A team at Ball Aerospace & Technologies Corp. [BLL], Boulder, Colo., designer and builder of the instrument, used an engineering model of the camera’s focal-plane system to duplicate the problem. This helped staffers to understand causes of the problem, and aided testing a procedure for warming the focal-plane electronics prior to each image. One cause is that an electrical interface lacked extra capability beyond minimum requirements.

      Another cause is an unexpected change in performance of another electronic component over the course of the first thousand or so large images. With pre-warming, the camera acquires good data from all detectors, though minor noise remains an issue in data from one of two channels of one detector collecting infrared imagery.

      McEwen said, “Given the stability we’ve seen and understanding the nature of the problem, we now expect HiRISE to return high-quality data for years to come.”

      The orbiter mission is managed by the NASA Jet Propulsion Laboratory at Pasadena, Calif., for the space agency Science Mission Directorate in Washington.

      Lockheed Martin Corp. [LMT] unit Space Systems in Denver, Colo., is the prime contractor and built the spacecraft.

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