With its six wheels stuck in powdery sand and two
wheels no longer working at all, the resilient little explorer will
become a fixed, immobile scientific observatory — if it can survive the
harsh temperatures of the upcoming winter.
“Its driving days are likely over,”
director of NASA’s Mars Exploration Program, said in a telephone news
conference Tuesday. “Its contributions will continue” if it can be
re-awakened after what could be a six-month hibernation during the
Martian winter.
If Spirit can be resuscitated, researchers will use
it to attempt to answer one of their most pressing questions: whether
the planet has a solid iron core or a liquid one. If the vehicle can’t
be revived, it will still have far surpassed scientists’ original
expectations and its design life of three months, traveling nearly 12
miles across the barren surface of Mars and finding strong evidence
that water once altered the planet’s terrain.
Spirit’s twin, Opportunity, is still moving across
the Martian surface farther north nearer the equator and on the other
side of the planet, and continues to send back valuable data. Its
efficiency has been degraded by a buildup of dust on its solar panels,
but engineers are hoping for gusts of wind that will clear the dust.
Opportunity has successfully weathered every Martian
winter so far because “it is in a different thermal environment,”
McCuistion said, and the JPL team that controls it doesn’t expect any
troubles for it this winter. “Its environment is way more benign,” he
said.
Spirit’s problems began 10 months ago as it was driving toward a pair of volcanic features named
thin Martian crust in the area — described as much like the crust on a
creme brulee dessert — and sank into a powdery sand unlike any the two
rovers had encountered before. Breaking free proved difficult because
one of the rover’s six wheels had broken down three years earlier and
had to be dragged along the ground.
A second wheel became immobilized during the
extrication attempts, leaving the vehicle with three good wheels on its
left side and only one on its right. So far, the efforts to free it
have resulted only in digging the wheels in deeper.
About a week and a half ago, with winter
approaching, the team shifted its emphasis from extrication of the
rover to positioning it so that its solar panels will receive more
sunlight, rover driver
Currently, the rover is sitting roughly flat on its
long axis and has rolled about 5 to 6 degrees to its left side. The
team would like to get it at least level and, ideally, tilted slightly
forward and to the right so that more of the solar panels will be
exposed to the Martian sunlight, which will be coming from the north.
The team has been able to move the robot a couple of
inches each time it has tried, but those attempts can come only every
few days because the batteries must be allowed to recharge. Within a
few more weeks, even that amount of maneuvering will no longer be
possible.
The most likely scenario is that Spirit’s power
supply will get lower and lower and eventually it will shut down and go
into a hibernation mode until spring brings more sunshine. The question
is whether engineers will be able to revive it to use that sunshine.
NASA engineers expect temperatures around Spirit to
fall into the minus 40s this winter. The craft was designed to operate
in temperatures as low as -40 degrees F. and to survive temperatures as
low as -67 degrees. “But that is with a brand-new rover fresh out of
the box,” said
Spirit has been on the surface for six years and has
gone through thousands of temperature cycles that include variations of
as much as 150 degrees between day and night.
“There is no guarantee that it will be able to
survive these colder temperatures, colder than it has ever seen
before,” Callas said.
If it does survive, researchers hope to get many more scientific results from it, said
the project’s principal investigator. By tracking Spirit’s radio signal
precisely over a long period of time — perhaps six months or more — the
team will be able to monitor Mars’ “wobble” in its orbit. That will
allow scientists to determine whether the planet has a solid or liquid
core.
“This is totally new science, really fundamental stuff” that can be achieved only with a stationary platform, he said.
By looking around the craft for a long period of
time, he added, the team will also be able to monitor how the planet’s
atmosphere interacts with its surface.
And finally, by continuing to dig at the current
site, the team will be able to characterize the soil much more
thoroughly than has been achieved anywhere else on Mars. “The bottom
line is, we are not giving up on Spirit,” Squyres said.
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