WASHINGTON, Aug. 24 (Xinhua) -- After six weeks of hunkering down during raging dust storms that limited solar power, both of NASA's Mars exploration rovers, Spirit and Opportunity, have resumed driving, NASA reported Friday.

Opportunity advanced 13.38 meters toward the edge of Victoria Crater on Aug. 21. Spirit drove 42 centimeters backwards on Aug. 23 to get in position for taking images of a rock that it had examined with its spectrometer. The rover team is planning additional drives for Spirit to climb onto a platform informally named "Home Plate."

No new storms have been lifting dust into the air near either solar-powered rover in the past two weeks and skies are gradually brightening above both vehicles. With the improved energy supplies, both rovers are back on schedule to communicate daily.

"Weather and power conditions continue to improve, although very slowly for both rovers," said John Callas, NASA's project manager for the rovers.

Mission controllers were taking advantage of the gradual clearing of dust from the sky while also taking precautions against a buildup of dust settling onto the rovers.

"The clearing could take months," said Rover Project Scientist Bruce Banerdt. "There is a lot of very fine material suspended high in the atmosphere."

As that material does settle the powdery dust is accumulating on surfaces such as the rovers' solar panels and instruments. Moredust 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 on Aug. 23. That is more than twice as much as five weeks ago, but still less than half as much as two months ago.

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.

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.