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Despite the ongoing efforts of NASA engineers to free the stuck Mars Exploration Rover Spirit mired in a Martian sand trap, the space agency admitted Jan. 26 Spirit will no longer be a fully mobile robot. The space agency declared Spirit is now officially a stationary science platform with the initial assignment of surviving the Martian winter.
NASA hopes to slightly reposition Spirit in its new permanent home in the loose soil of a site dubbed Troy. 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.
It is mid-autumn on Mars and winter begins 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.”
“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.”
NASA said that 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.”
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 plus analysis, modeling and reviews. In November, another wheel quit working, making a difficult situation even worse.
“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.”