Spirit lives on Mars
DOI: 10.1063/PT.5.024036
Physics Today : After six years of successfully exploring Mars, NASA has given up trying to drive the Spirit Mars rover out from where it got stuck several months ago. Spirit‘s twin rover Opportunity still remains free and is currently heading towards a large crater called Endeavor .
In the next few weeks, Spirit will be to optimized to survive the severe Martian winter so that it can operate as a stationary science platform for years to come. The two rovers were originally designed to last just 90 days, and have driven more than 12 miles across the surface.” 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 [Spirit] free may not be successful.”
Stuck in sand
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. In November, another wheel quit working, making a difficult situation even worse. Although some of the more recent efforts to unstick the rover looked promising, the coming winter mandates a change in strategy.
At Spirit‘s current location it is mid-autumn. 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.”
A stationary state
Even in a stationary state, Spirit can continue doing 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 the two Martian rovers.
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,” 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.
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More about the authors
Paul Guinnessy, pguinnes@aip.org
