As NASA celebrates its Mars rover Spirit’s sixth anniversary exploring the red planet it is hunting for a way to keep the machine, which is mired in a sand trap, alive to see a seventh year. On its Web site, the space agency this week noted there may indeed be such an option.
That option would be spinning the wheels on the north side of Spirit, letting it dig in deeper in the Martian sand but at the same time improving the tilt of the rover’s solar panels toward the Sun.
According to NASA: “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, NASA stated.
"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., on NASA’s Web site.
NASA said it was determining the type of research a stationary Spirit could do in the future. For example, it could study the interior of Mars, monitor the weather and continue looking at the deposits uncovered by its wheels, a task it has already been performing.
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, NASA said.
Getting the rover moving is still the first priority, NASA stated. In the past couple weeks, Spirit's right-front wheel, which had stopped operating in March 2006, showed signs of life this week by spinning slightly during one of the attempts to move the rover. The wheel however stopped later in another test and has not worked since.
Still, NASA scientists said movement of the right-front wheel for about 3.5 minutes was a surprise. It is not clear whether the wheel will work again, since it stopped during the final drive segment and it’s not clear whether extrication from the sand trap would be possible even with an operable right-front wheel, NASA said.
NASA said Spirit’s other four wheels all drove forward in the most recent attempt to extricate Spirit from the sand trap but that positive note was tempered by the fact that while Sprit moved forward, it also dug in a little further. According to NASA, the rover moved 2 millimeters (0.08 inch) forward and 4 millimeters (0.16 inch) downward. That ratio of forward to downward movement is well below what would be necessary over longer distance for extrication, NASA noted.
Spirit has been stuck in a place NASA calls "Troy" since April 23 when the rover's wheels broke through a crust on the surface that was covering brightly-toned, slippery sand underneath. After a few drive attempts to get Spirit out in the subsequent days, it began sinking deeper in the sand trap.
Even in the best of conditions, moving the stuck rover could take weeks.
Still there is little doubt the highly successful rover might be on its last legs regardless of the approaching winter. NASA said in February, it will assess Mars missions, including Spirit, for their potential science versus costs to determine how to distribute limited resources.
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