The Spirit rover's roll-off from its landing platform will be delayed one or two days, until Thursday or Friday, because engineers were not able to retract a partially collapsed air bag from its preferred pathway.
The craft will pivot 120 degrees to the right aboard the lander before rolling off an alternative ramp, said Matt Wallace, a mission manager at Jet Propulsion Laboratory. That maneuver will probably consume an extra day.
Spirit could probably safely roll over the air bag, which sticks up a few inches, but the project team prefers not to take any chances with the craft. "I've heard it called a $400 million rover," said project manager Peter Theisinger, "but it is not. It is a priceless asset. ... We're going to be bold but not stupid."
Wallace speculated that the section of the air bag - which cushioned Spirit's evening landing Jan. 3 in Gusev Crater - that was blocking the exit ramp did not have a "tendon" attached to it for retraction or, alternatively, that the tendon had snapped during maneuvering.
Spirit began preparations for the roll-off late Thursday by completing a "stand-up" maneuver in which it reared up on its four hind wheels so the two front wheels could be extended into their normal position.
The craft flew to Mars with the wheels tucked underneath to make the rover compact enough to fit inside the lander.
Late last night - daytime on Mars - the craft's rear wheels were to be deployed in a less dramatic maneuver. Engineers will then spend some time checking the craft's systems before attempting the roll-off.
The rover spent much of its last day imaging part of the landing site with its thermal emission spectrometer, a device the engineers call Mini-TES. It studies materials in the infrared, measuring their temperature and composition.
Phil Christensen of Arizona State University, the lead scientist for Mini-TES, said yesterday that the large rocks to the south of Spirit are about 20 degrees Fahrenheit cooler than the average temperature of the soil, while the material in a depression is 10 to 20 degrees warmer.
He noted that the large rocks are cooler because heat seeps into the interior, leaving the surface relatively chilly in comparison. The hotter materials, in contrast, are very small particles, perhaps even fluffy, in which heat stays on the surface.
"We'll want to avoid regions that are warmer," he said, so the rover does not get stuck in them.
The infrared spectra also showed the presence of carbonates in the soil, Christensen noted. Carbonates are a family of minerals that are most commonly formed in water, although they can be produced by other processes as well. "We came looking for carbonates," he said, because researchers believe that Gusev Crater was once a lake.
But the team will not be able to determine if the carbonates originated in a lake until the rover leaves the lander and begins digging in the soil.
The Los Angeles Times is a Tribune Publishing newspaper.