NASA to Begin Attempts to Free Sand-Trapped Mars Rover

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PASADENA, Calif. -- NASA will begin transmitting commands to its Mars
exploration rover Spirit on Monday as part of an escape plan to free
the venerable robot from its Martian sand trap.

Spirit has been lodged at a site scientists call "Troy" since April
23. Researchers expect the extraction process to be long and the
outcome uncertain based on tests here on Earth this spring that
simulated conditions at the Martian site.

"This is going to be a lengthy process, and there's a high probability
attempts to free Spirit will not be successful," said Doug
McCuistion, director of the Mars Exploration Program at NASA
Headquarters in Washington. "After the first few weeks of attempts,
we're not likely to know whether Spirit will be able to free itself."

Spirit has six wheels for roving the Red Planet. The first commands
will tell the rover to rotate its five working wheels forward
approximately six turns. Engineers anticipate severe wheel slippage,
with barely perceptible forward progress in this initial attempt.
Since 2006, Spirit's right-front wheel has been inoperable, possibly
because of wear and tear on a motor as a result of the rover's
longevity.

Spirit will return data the next day from its first drive attempt. The
results will be assessed before engineers develop and send commands
for a second attempt. Using results from previous commands, engineers
plan to continue escape efforts until early 2010.

"Mobility on Mars is challenging, and whatever the outcome, lessons
from the work to free Spirit will enhance our knowledge about how to
analyze Martian terrain and drive future Mars rovers," McCuisition
said. "Spirit has provided outstanding scientific discoveries and
shown us astounding vistas during its long life on Mars, which is
more than 22 times longer than its designed life."

In the spring, Spirit was driving backward and dragging the inoperable
right front wheel. While driving in April, the rover's other wheels
broke through a crust on the surface that was covering a
bright-toned, slippery sand underneath. After a few drive attempts to
get Spirit out in the subsequent days, it began sinking deeper in the
sand trap. Driving was suspended to allow time for tests and reviews
of possible escape strategies.

"The investigations of the rover embedding and our preparations to
resume driving have been extensive and thorough," said John Callas,
project manager for Spirit and Opportunity at NASA's Jet Propulsion
Laboratory in Pasadena, Calif. "We've used two different test rovers
here on Earth in conditions designed to simulate as best as possible
Spirit's predicament. However, Earth-based tests cannot exactly
replicate the conditions at Troy."

Data show Spirit is straddling the edge of a 26-foot-wide crater that
had been filled long ago with sulfate-bearing sands produced in a hot
water or steam environment. The deposits in the crater formed
distinct layers with different compositions and tints, and they are
capped by a crusty soil. It is that soil that Spirit's wheels broke
through. The buried crater lies mainly to Spirit's left. Engineers
have plotted an escape route from Troy that heads up a mild slope
away from the crater.

"We'll start by steering the wheels straight and driving, though we
may have to steer the wheels to the right to counter any downhill
slip to the left," said Ashley Stroupe, a JPL rover driver and Spirit
extraction testing coordinator. "Straight-ahead driving is intended
to get the rover's center of gravity past a rock that lies underneath
Spirit. Gaining horizontal distance without losing too much vertical
clearance will be a key to success. The right front wheel's inability
to rotate greatly increases the challenge."

Spirit has been examining its Martian surroundings with tools on its
robotic arm and its camera mast. The rover's work at Troy has
augmented earlier discoveries it made indicating ancient Mars had hot
springs or steam vents, possible habitats for life. If escape
attempts fail, the rover's stationary location may result in new
science findings.

"The soft materials churned up by Spirit's wheels have the highest
sulfur content measured on Mars," said Ray Arvidson a scientist at
Washington University in St. Louis and deputy principal investigator
for the science payloads on Spirit and Opportunity. "We're taking
advantage of its fixed location to conduct detailed measurements of
these interesting materials."

Spirit and its twin rover landed on Mars in January 2004. They have
explored Mars for five years, far surpassing their original 90-day
mission. Opportunity currently is driving toward a large crater
called Endeavor.

NASA's JPL manages the rovers for NASA's Science Mission Directorate
in Washington.

For updates about Spirit's progress, visit:

http://www.nasa.gov/rovers

Source: NASA