Jan. 26, 2010: After six years of unprecedented exploration of the Red
Planet, NASA's Mars Exploration Rover Spirit no longer will be a
fully mobile robot. NASA has designated the once-roving scientific
explorer a stationary science platform after efforts during the past
several months to free it from a sand trap have been unsuccessful.
The venerable robot's primary task in the next few weeks will be to
position itself to combat the severe Martian winter. If Spirit
survives, it will continue conducting significant new science from
its final location. The rover's mission could continue for several
months to years.
"Spirit is not dead; it has just entered another phase of its long
life, " said Doug McCuistion, director of the Mars Exploration Program
at NASA Headquarters in Washington. "We told the world last year that
attempts to set the beloved robot free may not be successful. It
looks like Spirit's current location on Mars will be its final
resting place."
Ten months ago, as Spirit was driving south beside the western edge of
a low plateau called Home Plate, its wheels broke through a crusty
surface and churned into soft sand hidden underneath.
After Spirit became embedded, the rover team crafted plans for trying
to get the six-wheeled vehicle free using its five functioning wheels
-the sixth wheel quit working in 2006, limiting Spirit's mobility.
The planning included experiments with a test rover in a sandbox at
NASA's Jet Propulsion Laboratory in Pasadena, Calif., plus analysis,
modeling and reviews. In November, another wheel quit working, making
a difficult situation even worse.
Recent drives have yielded the best results since Spirit became
embedded. However, the coming winter mandates a change in strategy.
It is mid-autumn at the solar-powered robot's home on Mars. Winter
will begin in May. Solar energy is declining and expected to become
insufficient to power further driving by mid-February. The rover team
plans to use those remaining potential drives for improving the
rover's tilt. Spirit currently tilts slightly toward the south. The
winter sun stays in the northern sky, so decreasing the southward
tilt would boost the amount of sunshine on the rover's solar panels.
"We need to lift the rear of the rover, or the left side of the rover,
or both, " said Ashley Stroupe, a rover driver at JPL. "Lifting the
rear wheels out of their ruts by driving backward and slightly uphill
will help. If necessary, we can try to lower the front right of the
rover by attempting to drop the right-front wheel into a rut or dig
it into a hole."
At its current angle, Spirit probably would not have enough power to
keep communicating with Earth through the Martian winter. Even a few
degrees of improvement in tilt might make enough difference to enable
communication every few days.
"Getting through the winter will all come down to temperature and how
cold the rover electronics will get, " said John Callas, project
manager at JPL for Spirit and its twin rover, Opportunity. "Every bit
of energy produced by Spirit's solar arrays will go into keeping the
rover's critical electronics warm, either by having the electronics
on or by turning on essential heaters."
Even in a stationary state, Spirit continues scientific research.
"There's a class of science we can do only with a stationary vehicle
that we had put off during the years of driving, " said Steve Squyres,
a researcher at Cornell University and principal investigator for
Spirit and Opportunity. "Degraded mobility does not mean the mission
ends abruptly. Instead, it lets us transition to stationary science."
One stationary experiment Spirit has begun studies tiny wobbles in the
rotation of Mars to gain insight about the planet's core. This
requires months of radio-tracking the motion of a point on the
surface of Mars to calculate long-term motion with an accuracy of a
few inches.
"If the final scientific feather in Spirit's cap is determining
whether the core of Mars is liquid or solid, that would be wonderful
-- it's so different from the other knowledge we've gained from
Spirit, " said Squyres.
Tools on Spirit's robotic arm can study variations in the composition
of nearby soil, which has been affected by water. Stationary science
also includes watching how wind moves soil particles and monitoring
the Martian atmosphere.
Spirit and Opportunity landed on Mars in January 2004. They have been
exploring for six years, far surpassing their original 90-day
mission. Opportunity currently is driving toward a large crater
called Endeavor and continues to make scientific discoveries. It has
driven approximately 12 miles and returned more than 133, 000 images.
JPL manages the rovers for NASA's Science Mission Directorate in
Washington. For more information about Spirit and Opportunity, visit:
http://www.nasa.gov/rovers
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