Richard A Lovett
A giant dust storm has turned day to night over much of Mars, threatening the Opportunity rover and forcing it to shut down indefinitely.
Calculations indicate that the rover has a good chance of surviving the shutdown, says John Callas, Opportunity project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, US – but that doesn’t mean the rover team isn’t worried.
Callas compares it to having a loved one in a coma, with doctors assuring you that everything will be fine and she’ll wake up. {%recommended 7325%}
“But if it’s your 97-year-old grandmother, you’re going to be very concerned,” he says. “This team has a very strong bond with the rover.”
And he adds, “We don’t know how long this storm will last and what the environment will look like [when it’s over]. So everyone is very concerned.”
When the storm was first observed, on 30 May, the rover was operating normally, with some dust in the atmosphere but little enough that its solar panels were generating about 645 watt-hours of power per day – about normal for this time of year, Callas says.
But by 4 June, the power had dipped to 345 watt-hours, and by 5 June it had reduced to 133 — an enormous drop in a single day. By 10 June, it had slid even further, to just 22.
“That was the last communication,” notes Callas.
What’s happened, he says, is that the rover is probably experiencing a low-power fault: “That’s when it senses it doesn’t have enough power to maintain activities and essentially turns everything off except the master clock.”
The primary concern in such a shutdown, he adds, is that the spacecraft will get so cold it won’t ever be able to wake back up again. But, fortunately, the same dust that blocks daytime heat also keeps nighttime temperatures from dropping super-low. It’s also approaching the summer warm season on Opportunity’s part of Mars, and the rover has eight one-watt radioisotope heat generators (RHGs), which also provide enough to keep its critical components warm.
Putting it all together, Callas says, NASA expects the rover’s essential bits won’t drop to temperatures below about minus-36 degrees Celsius. It was designed to tolerate minus-55 degrees, he says, “so we think we can ride this out”.
Another concern is that the power might dip so low that the rover can’t even keep its clock operating. If that happens, he says the machine will have a mission clock fault, “which will be a more complicated recovery.”
Normally, Opportunity uses the clock to time its communications back to Earth, doing them during the middle of the day. If the clock fails, the rover will lose track of time and not know when to communicate. Instead, it is programmed to start making the attempt every 4 hours until if finally succeeds, going back to sleep between attempts. “It means we have to be vigilant,” Callas says.
Meanwhile, there’s a lot to be learned from the storm, says Rich Zurek, Mars Program Office chief scientist at JPL.
Mars is well known for dust storms, but big ones aren’t all that common; the last were in 2001 and 2007.
This one is interesting, says Zurek, because it started as a local storm that “kind of parked over the Opportunity site.” It then rapidly intensified and spread to the point where it now appears to be within two to three of days of girdling the entire planet.
Understanding how such storms form, spread, and eventually dissipate is important not just scientifically but for future Mars projects, including astronaut visits, says Jim Watzin, director of the Mars Exploration Program at NASA Headquarters in Washington DC.
“We need to understand these storms to the degree that we have some level of forecasting capability,” he says. “We would not want a crew operating remotely from their base to be caught off guard by a storm like this and have difficulties getting home.”
Meanwhile, atmospheric researchers not only have the data taken by Opportunity before it was forced to shut down, but also some from orbiting satellites capable of monitoring the Martian atmosphere. Even the Curiosity Rover can get into the act, studying the storm’s impact at its site, nearly halfway around the planet from Opportunity.
Curiosity itself is in no danger of losing power from the storm because its power source is nuclear. The main concern is that dust might interfere with its optics, says Dave Lavery, program executive at NASA Headquarters for the Opportunity and Curiosity rovers. But Lavery doubts this will be a problem. “Curiosity should be fine,” he says.
Meanwhile, Zurek says, the dust storm should begin to dissipate as it spreads and the winds die down: “[But] exactly when that’s going to happen — whether it’s next week or two weeks from now – we don’t know.”
Regardless of what happens, NASA officials note, Opportunity has already been a wildly successful mission.
“Keep in mind we’re talking about a rover that’s been working at Mars, hanging in there for 15 years, when it was designed for 90 days,” says Watzin. “It just doesn’t get better than that.”
