NASA’s Opportunity rover has untucked its front wheels and latched its
suspension system in place, key steps in preparing to drive off its
lander and onto martian soil.

Overnight tonight, mission controllers at NASA’s Jet Propulsion
Laboratory, Pasadena, Calif., plan to try tilting the lander platform
down in the front by pressing the rear petal downward to raise the

“What we want to do is lower the front edge by about 5 degrees,” said
JPL’s Dr. Rick Welch, activity lead for preparing the rover for
roll-off. Plans call for driving off straight ahead, possibly as
early as overnight Sunday-Monday, if all goes well.

Meanwhile, halfway around Mars, Opportunity’s twin, Spirit, continues
on the mend from a computer memory problem that struck it a week ago.
“Right now we’re working to get complete control of the vehicle, and
we’re still not quite there,” said JPL’s Jennifer Trosper, mission
manager. “If we’re on the right track, we hope to be back doing some
science by early next week. If we’re not on the right track, it could
take longer than that.”

Opportunity’s infrared sensing instrument, the miniature thermal
emission spectrometer, passed a health check last night. Scientists
plan to begin using it tonight. The instrument detects the composition
of rocks and soils from a distance. That information will help
scientists decide what targets to approach after Opportunity drives
off the lander.

Scientists and rover engineers are already discussing which specific
rocks within an outcropping near the lander will make the best
targets, said Dr. Jim Bell of Cornell University, Ithaca, N.Y., lead
scientist for the panoramic cameras on Opportunity and Spirit. Details
of the outcrop can be seen in a new a color-picture mosaic Bell
presented, the first portion of a full-circle panorama that has been
taken and partially transmitted.

Other new images show how Opportunity’s airbags left detailed
impressions in the fine-textured soil as the spacecraft was rolling to
a stop in the small crater where it now sits. “These marks are
telling us about the physical properties of the material,” Bell said.

Some scientists believe that dark colored granules covering most of
the crater’s surface were pressed down into an underlying layer of
powdery, lighter red material when the airbags hit. Others hold to a
theory that the dark granules are agglomerations that crumble into the
finer, lighter material when disturbed. After roll-off, soil near the
lander will be the rover’s first target for close-up examination with
a microscope and two tools for detecting the composition of the
target. The soil at Opportunity’s landing site appears to have
different properties than the soil at Spirit’s landing site, Bell

Opportunity has already validated predictions about the landing site
made on the basis of images and measurements taken by spacecraft
orbiting Mars, said JPL’s Dr. Matt Golombek, a member of the rover
science team and co-chair of a steering committee that evaluated
potential landing sites for the rovers. The predictions included that
the region of Meridiani Planum where Opportunity landed would be safe
for landing, would be safe for rover driving, would have very few
rocks and would look unlike any place previously seen on Mars.

“This bodes well for our ability to use remote sensing data in the
future for picking landing sites,” Golombek said.

Engineers have been able to confirm a diagnosis that an unplanned
drawdown of battery power each night on Opportunity is due to a heater
on the rover’s robotic arm. A switch designed to overrule the
heater’s thermostatic control has not been working. “In the near
term, it’s not providing any operational constraints,” Welch said.

JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Exploration Rover project for NASA’s Office of Space
Science, Washington, D.C.