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.
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.
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.
Even in a stationary state, Spirit continues scientific research.
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.
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.
SOURCE: http://www.nasa.gov/mission_pages/mer/news/mer20100126.html
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