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Spirit panorama
This amazing panorama of the martian surface at Columbia Hills was taken by the Spirit rover. Expert narration is provided by camera scientist Jim Bell. (2min 12sec file)
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Update on Mars rovers
Mars Exploration Rover project manager Jim Erickson and panoramic camera lead scientist Jim Bell offer comments on the status of the Spirit and Opportunity missions (1min 33sec file)
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Delta rocket assembly
The first stage of Boeing's Delta 2 rocket that will launch NASA's Swift gamma-ray burst detection observatory in November is erected on pad 17A at Cape Canaveral, Florida. (4min 52sec file)
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Solid boosters arrive
The three solid-fueled rocket boosters for the Boeing Delta 2 vehicle that will launch the Swift satellite are hoisted into the pad 17A mobile service tower. (4min 55sec file)
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SRBs go for attachment
The mobile service tower carries the solid boosters into position for attachment to the Delta 2 rocket's first stage. (3min 08sec file)
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Swift nose cone
The two halves of the 10-foot diameter rocket nose cone that will enclose NASA's Swift satellite during launch aboard a Boeing Delta 2 vehicle are lifted into the pad 17A tower. (4min 26sec file)
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ISS talk with students
The International Space Station crew holds an educational event to answers questions live with students at the Maryland Science Center. (24min 01sec file)
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Genesis to Houston
The solar wind samples retrieved by NASA's Genesis spacecraft finally arrive at Johnson Space Center facilities from the Utah landing site. (2min 51sec file)
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Problem with Spirit rover's steering reappears
Posted: October 21, 2004

A problem that affects the steering on NASA's Mars Exploration Rover Spirit has recurred after disappearing for nearly two weeks.

Engineers at NASA's Jet Propulsion Laboratory, Pasadena, Calif., are working to fully understand the intermittent problem and then implement operational work-arounds. Meanwhile, Spirit successfully steered and drove 3.67 meters (12 feet) on Oct. 17.

Rover engineers are also analyzing a positive development on Spirit's twin, Opportunity: a sustained boost in power generation by Opportunity's solar panels.

Both rovers have successfully completed their three-month primary missions and their first mission extensions. They began second extensions of their missions on Oct. 1.

Rover engineers refrained from driving Spirit for five days after an Oct. 1 malfunction of a system that prevents wheels from being jostled in unwanted directions while driving. Each of the front and rear wheels of the rover has a motor called a steering actuator. It sets the direction in which the wheel is headed. The steering actuators are different from the motors that make the wheels roll, and hold the wheel in a specific direction while driving. A relay used in turning these steering actuators on and off is the likely cause of the intermittent nature of the anomaly.

The relay operates Spirit's right-front and left-rear wheels concurrently, and did not operate as commanded on Oct. 1. Subsequent testing showed no trace of the problem, and on Oct. 7, the rover steered successfully and drove about 2 meters (7 feet), putting it in position to examine a layered rock called "Tetl" for several days. However, the anomaly occurred again on Oct. 13, and the problem appeared intermittently in tests later last week.

"We are continuing tests on Spirit and in our testbed here at JPL," said Jim Erickson, Mars Exploration Rover project manager at JPL. One possible work-around would be to deliberately blow a fuse controlling the relay, disabling the brake action of the steering actuators. The rovers could be operated without that feature. "The only change might be driving in shorter steps when the rover is in rugged terrain," Erickson said.

Spirit has driven a total of 3,647 meters (2.27 miles) since landing, more than six times the distance set as a goal for the mission. Its current target is a layered rock called "Uchben" in the "Columbia Hills." Opportunity has driven 1,619 meters (just over a mile). Its latest stop is a lumpy boulder dubbed "Wopmay" inside "Endurance Crater."

The daily power supply for each rover comes from 1.3 square meters (14 square feet) of solar panels converting sunlight into electricity. Just after the landings in January, the output was about 900 watt-hours per day for each rover -- enough to run a 100-watt bulb for nine hours. As anticipated, output gradually declined due to dust buildup and the martian seasonal change with fewer hours of sunlight and a lower angle of the Sun in the sky. By July, Spirit's daily output had declined to about 400 watt-hours per day. It has been between 400 and 500 watt-hours per day for most of the past two months.

Opportunity, closer to Mars' equator and with the advantage of a sunward-facing tilt as it explored inside the southern half of a crater, maintained an output level between 500 and 600 watt-hours per day in June, July and August. Since early September, the amount of electricity from Opportunity's solar panels has increased markedly and unexpectedly, to more than 700 watt-hours per day, a level not seen since the first 10 weeks of the mission.

"We've been surprised but pleased to see this increase," said Erickson, "The team is evaluating ways to determine which of a few different theories is the best explanation."

Possible explanations under consideration include the action of wind removing some dust from the solar panels or the action of frost causing dust to clump. "We seem to have had several substantial cleanings of the solar panels," Erickson said.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA's Science Mission Directorate, Washington.