Tests on Earth simulating Spirit's predicament on Mars have reinforced
understanding that getting Spirit to rove again will be very difficult.

To supplement the tests at NASA's Jet Propulsion Laboratory in Pasadena,
Calif., the rover team is refining a detailed computer model of rover
mobility, calibrated with results from testing and measurements from Mars.

"The computer modeling will allow us to connect the results from tests
performed in Earth gravity with what to expect from the rover in Mars
gravity," said JPL's John Callas, project manager for Spirit and its
twin, Opportunity.

Spirit became embedded in soft soil at a site called "Troy" in early
May, more than five years into a mission on Mars that was originally
scheduled to last for three months. The rover team suspended further
driving attempts with Spirit while evaluating possibilities from tests
performed at JPL simulating the Troy situation.

An additional round of testing was added to the September schedule to
gain more detailed assessment of how to move Spirit while avoiding
putting the rover's center of gravity directly over a rock that is
touching or nearly touching the rover's underbelly. Other added tests
are using a lighter-weight test rover than the one used for most of the
testing this summer. A complete "dress rehearsal" test of the
extrication strategy judged to hold the best chance of success is
planned in the test setup at JPL before the team commands Spirit to
begin driving. That test and subsequent review of its results are
expected to take several weeks. Moves by Spirit will not begin before
October, according to current plans.

"We are proceeding very cautiously and exploring all reasonable
options," Callas said. "There is a very real possibility that Spirit may
not be able to get out, and we want to give Spirit the very best chance."

A dust storm that had reduced the electrical output from Spirit's solar
panels by nearly half during late August still has some lingering
effects on the skies above Spirit.

For more updates, please visit the Free Spirit site: http://www.jpl.nasa.gov/freespirit/