NASA's Mars Rover Has Uncertain Future as Sixth Anniversary Nears

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PASADENA, Calif. -- NASA's Mars rover Spirit will mark six years of
unprecedented science exploration and inspiration for the American
public on Sunday. However, the upcoming Martian winter could end the
roving career of the beloved, scrappy robot.

Spirit successfully landed on the Red Planet at 8:35 p.m. PST on Jan.
3, 2004, and its twin Opportunity arrived at 9:05 p.m. Jan. 24, 2004.
The rovers began missions intended to last for three months but which
have lasted six Earth years, or 3.2 Mars years. During this time,
Spirit has found evidence of a steamy and violent environment on
ancient Mars that was quite different from the wet and acidic past
documented by Opportunity, which has been operating successfully as
it explores halfway around the planet.

A sand trap and balky wheels are challenges to Spirit's mobility that
could prevent NASA's rover team from using a key survival strategy
for the rover. The team may not be able to position the robot's solar
panels to tilt toward the sun to collect power for heat to survive
the severe Martian winter.

Nine months ago, Spirit's wheels broke through a crusty surface layer
into loose sand hidden underneath. Efforts to escape this sand trap
barely have budged the rover. The rover's inability to use all six
wheels for driving has worsened the predicament. Spirit's right-front
wheel quit working in 2006, and its right-rear wheel stalled a month
ago. Surprisingly, the right-front wheel resumed working, though
intermittently. Drives with four or five operating wheels have
produced little progress toward escaping the sand trap. The latest
attempts resulted in the rover sinking deeper in the soil.

"The highest priority for this mission right now is to stay mobile, if
that's possible," said Steve Squyres of Cornell University in Ithaca,
N.Y. He is principal investigator for the rovers.

If mobility is not possible, the next priority is to improve the
rover's tilt, while Spirit is able to generate enough electricity to
turn its wheels. Spirit is in the southern hemisphere of Mars, where
it is autumn, and the amount of daily sunshine available for the
solar-powered rover is declining. This could result in ceasing
extraction activities as early as January, depending on the amount of
remaining power. Spirit's tilt, nearly five degrees toward the south,
is unfavorable because the winter sun crosses low in the northern
sky.

Unless the tilt can be improved or luck with winds affects the gradual
buildup of dust on the solar panels, the amount of sunshine available
will continue to decline until May 2010. During May, or perhaps
earlier, Spirit may not have enough power to remain in operation.

"At the current rate of dust accumulation, solar arrays at zero tilt
would provide barely enough energy to run the survival heaters
through the Mars winter solstice," said Jennifer Herman, a rover
power engineer at NASA's Jet Propulsion Laboratory in Pasadena,
Calif.

The team is evaluating strategies for improving the tilt even if
Spirit cannot escape the sand trap, such as trying to dig in deeper
with the wheels on the north side. In February, NASA will assess Mars
missions, including Spirit, for their potential science versus costs
to determine how to distribute limited resources. Meanwhile, the team
is planning additional research about what a stationary Spirit could
accomplish as power wanes.

"Spirit could continue significant research right where it is," said
Ray Arvidson of Washington University in St. Louis, deputy principal
investigator for the rovers. "We can study the interior of Mars,
monitor the weather and continue examining the interesting deposits
uncovered by Spirit's wheels."

A study of the planet's interior would use radio transmissions to
measure wobble of the planet's axis of rotation, which is not
feasible with a mobile rover. That experiment and others might
provide more and different findings from a mission that has already
far exceeded expectations.

"Long-term change in the spin direction could tell us about the
diameter and density of the planet's core," said William Folkner of
JPL. He has been developing plans for conducting this experiment with
a future, stationary Mars lander. "Short-period changes could tell us
whether the core is liquid or solid," he said.

In 2004, Opportunity discovered the first mineralogical evidence that
Mars had liquid water. The rover recently finished a two-year
investigation of a half-mile wide crater called Victoria and now is
headed toward Endeavor crater, which is approximately seven miles
from Victoria and nearly 14 miles across. Since landing, Opportunity
has driven more than 11 miles and returned more than 132,000 images.

For more information about the rovers, visit:

http://www.nasa.gov/rovers

Source: NASA