Months of
planning are finally coming to fruition: NASA engineers are ready to begin
trying to maneuver the plucky rover Spirit out of its sandy trap on Mars.
Mission managers are sober about the
prospects for
freeing Spirit. They will send the first commands to the rover to try to
move on Monday, "but this process could take quite awhile if it's possible
at all," said Doug McCuistion, director of the Mars Exploration Program at
NASA Headquarters in Washington, D.C.
The new
plan will command Spirit to try to backtrack and use the tracks it left before
getting stuck to make the escape attempt.
Spirit has
been stuck in a spot of soft, sandy dirt (called "Troy") on the
Martian surface since April when it broke through what mission scientists call
a "dirt crust" — a hard top layer of dirt disguising a layer of soft,
talcum powder-like material below.
"Spirit
did the equivalent of falling through the ice over a frozen pond," McCuistion
said.
Escape
plan on Mars
The rover's
engineering team has spent months devising a strategy to extricate the
spacecraft, working with replicas of Spirit (and its twin
spacecraft, Opportunity). That effort is complicated by the fact that
Spirit has a bum right front wheel, forcing it to drive backwards.
The team
has tried driving the replica rovers in a variety of ways — forward, backward,
and sideways — in a mixture of dirt similar to that in which Spirit is stuck to
see what has the best chance of getting the rover out and what might make the
situation worse.
"If
there is a way to get the rover out, we'll find it," said rover project
manager John Callas of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
The plan is
to begin driving the rover on Monday, trying to move forward out of Troy, following the same tracks it made to get into the predicament.
The rover
drivers suspect that moving through the soft material already churned up will
be easier than breaking through more of the dirt crust. Moving backwards also
means the rover won't have to try to move uphill, said Ashley Stroupe a rover
driver, also from JPL.
When moving
the rover, the team also has to be careful not to scrap against a rock under
the rover's belly. Moving forward should minimize the interaction between the
rover and this rock, Stroupe said.
"This
is clearly going to be a long process to either get to extrication or determine
if extrication is going to work," Stroupe said.
The command
to move will be sent up on Monday night and mission controllers expect to hear
back from Spirit on its progress on Tuesday. The command will be for 5 meters
(16 feet) of wheel spin, though mission managers don't expect the rover to
actually move that far, Callas said. The team will take a day to analyze any
movement Spirit makes before sending more commands, repeating this process as
long as needed.
"The
reality is that we're going to see very little motion each day at least
initially," Callas said. "It's kind of like watching grass grow."
Callas said
he has confidence in the rover team and the plan they have as being the best
chance to extricate Spirit.
"We're
in good shape; we're ready to roll on Monday," he said.
The
'spirit' of Spirit
Mars
enthusiasts have been worried that Spirit's predicament could spell the end for
the rover's mission, which so far has lasted 24 times longer than its original
planned 90 days.
Also of
concern are Spirit's periodic memory
lapses, the most recent of which occurred on Oct. 24, preventing Spirit
from saving science observations in its flash memory.
Spirit's
sticky situation hasn't been all bad though. Mission scientists have used the forced
downtime to conduct science observations of the site, which has turned out to
be one of the most interesting that the rovers have encountered on Mars.
"Of
course no place is a nice place to be embedded, but this turns out to be a
geological treasure trove," said Ray Arvidson, deputy principal
investigator for the rovers from Washington University in St. Louis.
While the
rover has detected sulfate sands in a spot (called Cyclops_eye) where it
punched through with its robotic arm, it detected a completely different
material at another nearby spot (Polyphemous_eye), suggesting the rover is
straddling some type of geologic boundary. The rover is also perched on the
edge of a crater.
If the
rover does remain stuck in Troy, it could end up doing more observations there.
"There's still a lot of science to be had from the current location,"
Arvidson said.
Spirit and Opportunity have been roaming
the Martian surface for nearly six years now, after landing on different
sides of the planet in January 2004.
McCuistion
asked fans of the rover to be "hopeful but realistic" about Spirit's
prospects.
If Spirit
can't get out, "it's likely that this lonely spot straddling the edge of
this crater might be where Spirit ends its adventure on Mars," he said.
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