WASHINGTON — Despite conditions that have deprived the Opportunity Mars rover of solar power, NASA officials said June 13 that they expected the long-lived spacecraft to survive an intense ongoing dust storm.
In a briefing with reporters, John Callas, project manager for Opportunity at the Jet Propulsion Laboratory, said that the rover was in a power-conserving sleep mode that he believed the rover could ultimately survive.
“Our expectation at this point is that the rover has gone to sleep. It’s in this low-power mode,” he said, noting that they did not hear from the rover during a June 12 communications pass. “At this point, we’re in a waiting mode.”
What triggered that low-power mode is a powerful dust storm that has developed in the last two weeks. First detected May 30, the dust storm started to affect operations of the solar-powered rover last week.
One measure of the intensity of the dust storm is the optical depth of the atmopshere, with higher numbers representing more dust in the atmosphere. Callas said that, on June 2, Opportunity measured an optical depth of 0.6, which is normal for this time of year, and the rover was generating 645 watt-hours.
By June 10, the optical depth had grown to 10.8, a record high, and the rover’s output had dropped to 22 watt-hours. “It’s completely dark on Mars,” he said.
Despite the lack of sunlight to generate power, Callas said he was optimistic that the rover, which has been operating for more than 14 years on the surface, would survive the storm. The main concern, he said, was that the rover would get too cold. However, the dust should warm the atmosphere and keep the rover above its minimum operating temperature.
“In a couple of days we should hit that steady-state point and we should be able to sit there for an extended period of time,” Callas said. “We think we can ride this out for a while.”
One complication, he said, is if the rover’s power drops low enough that it cannot operate an onboard clock. That would require a “more complicated recovery,” he said, but one that could still be carried out. “We’re concerned, but we’re hopeful that the storm will clear and the rover will begin to communicate with us.”
That assessment is far more optimistic than what another NASA official said earlier in the day. “Opportunity is stuck in the middle of the worst dust storm we’ve ever seen on Mars,” said Jonathan Rall on NASA Headquarters during a presentation at a meeting of the Small Bodies Assessment Group June 13 in College Park, Maryland. “So there’s a very good chance it will not survive the dust storm.”
NASA described the dust storm enveloping Opportunity and now extending across much of Mars as “unprecedented,” although it is not yet a globe-spanning storm like some in the past. One difference is that the storm intensified quickly: Callas said a 2007 storm took several weeks to reach an optical depth of 5.5, while this storm reached a higher optical depth in only a week.
The storm’s effects can be seen across the planet at Gale Crater, where the Curiosity rover is operating. The dust has caused a decrease in visibility, said Rich Zurek, chief scientist in the Mars Program Office at JPL, but has not otherwise affected rover operations as Curiosity is powered by a radioisotope thermoelectric generator (RTG) rather than solar panels.
NASA sees this as an opportunity to study how global dust storms develop, and what causes them to die out, using Curiosity as well as several orbiters. “The current dust storm is providing us with an unprecedented opportunity to learn more about Mars and the many challenges it presents for exploration,” said Jim Watzin, director of the Mars Exploration Program at NASA Headquarters.
“Having this dust storm occur under the visibility of the whole fleet of orbiters that we have, and eventually Curiosity participating in the research as well, is going to teach us a whole lot about how these storms behave,” he added later in the briefing.
Watzin and Zurek also said they didn’t expect the storm to affect NASA’s InSight Mars lander, launched May 5 and scheduled to land on November 26. This storm, Zurek said, should die out before that landing, although there is a chance a second storm could later form.
Watzin said that the main instruments used to guide InSight for a landing, an inertial measurement unit and radar, wouldn’t be adversely affected by dust if a storm is taking place. “If we were to happen to end up in a situation where there was a dust storm at the time of landing, we could fly right through it,” he said.