Mars Rovers Resume Driving

http://www.jpl.nasa.gov/news/news.cfm?release  07-093b

Mars Exploration Rover Status Report: Rovers Resume Driving
Jet Propulsion Laboratory
August 24, 2007

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.

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.

"Weather and power conditions continue to improve, although very
slowly
for both rovers," said John Callas of NASA's Jet Propulsion
Laboratory,
Pasadena, Calif, project manager for the rovers. With the improved
energy supplies, both rovers are back on schedule to communicate
daily.
Opportunity had previously been 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," said rover Project Scientist Bruce Banerdt. "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 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. It
is enough to run a 100-watt bulb for three hours.

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.

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."

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Media contact: Guy Webster/JPL
818-354-6278