The global dust storm that has enveloped Mars since last May is beginning to die down and the question is, what's happened to the Opportunity rover? The solar-powered robotic explorer has been silent since June 10 when dust made the air made so opaque that it blotted out the Sun. Now that energy-giving light is beginning to return, NASA is looking at whether the rover will be able to wake up again or if this is the final chapter in its 15-year career.
The problem with a mission like Opportunity is that almost all our information about its status comes from the rover itself. It's only through its radio telemetry signals that mission control can determine if the rover is still operational and its current condition. Since radio contact was lost in June, mission control in Pasadena, California has been carrying on a watching brief using the Deep Space Network, sending out a daily wake up signal, then waiting for a reply that has yet to come.
So far, NASA has run several studies as to what the condition of Opportunity might be and has concluded that, since the batteries were in relatively good condition for their age before the dust storm, they should be able to carry a charge once the solar panels come back online. In addition, Opportunity was lucky that the storm brewed up during summer in the Martian northern hemisphere and that the dust has insulating properties, so the chances are good that the onboard electronics haven't fatally frozen.
Currently, mission control is looking at a number of factors to determine if Opportunity will be able to send out a signal. The most important is the opacity or tau factor of the atmosphere. The last measurement sent back by Opportunity was that the location was tau 10.8 or as black as a cloudy, moonless night on Earth, as opposed to the average Martian opacity of tau 0.5, which allows for noon brightness equivalent to a terrestrial twilight.
NASA says that the tau factor must come down to at least 2 before the batteries on Opportunity can charge, so the agency's Mars Reconnaissance Orbiter is keeping a watch on local conditions from space.
But the real quandary is what is going on with Opportunity itself. The engineers believe that after the solar panels shut down the rover suffered a low-power fault, where it went into hibernation. This has gone on for so long that they think that it then went into clock fault, which means that the onboard clock has shut down and the rover is relying on the return of the Sun to reactivate instead of a pre-programmed schedule. However, there's also the possibility that it's been without power for so long that it's in uploss fault. That is, the communications system has shut down completely and must await the return of power before it can run a systems check and try to reestablish contact.
According to NASA, it could take weeks to contact Opportunity – assuming that it has survived. If it has, mission control will have to carry out extensive tests, ask the rover for data downloads, reset the clock, and request images to determine how much dust has piled on the rover. Even then, there will be some cautious testing of the wheels and robotic arm to make sure no dust has found its way into the joints.
Though NASA shows confidence that Oppornity will reawaken, it cautions that the rover may have suffered from its ordeal. The batteries might have been drained so much that they won't hold a new charge as well as before. Worse, routine duties like running the heaters might cause them to brown out. As to dust, the Martian variety sent up by the storm is so fine that it's unlikely to affect the solar panels too much and will blow off, though it could coat the camera lenses, reducing image quality.
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