NASA managers hopeful Opportunity will survive its trial by dust

The opacity of the Martian atmosphere is illustrated in these simulated images, starting with a brilliant sun in an essentially clear sky at far left to a dark sky in which the sun is virtually blocked out at the far right. Image: NASA

NASA’s Opportunity Mars rover, now 14 years past its original 90-day warranty, is no longer communicating with Earth thanks to a huge, fast-growing dust storm that has turned day into night at Endeavour Crater, preventing the solar-powered robot from recharging its batteries.

Project manager John Callas said the rover checked in 6 June, reporting energy levels of just 22 watt hours compared to 645 watt hours when the dust storm was first detected 30 May. An attempt to contact the spacecraft Tuesday was not successful.

He said engineers are optimistic Opportunity will survive the record storm and eventually phone home, but no one is resting easy given the rover’s age and the team’s emotional attachment to the long-lived robot.

“This team has a very strong bond with the rover, a very tight emotional connection with it,” Callas told reporters. “And we’re concerned about it, obviously. It’s like you have a loved one in a coma in the hospital, the doctors are telling you you’ve just got to give it time and she’ll wake up.

“But if it’s your 97-year old grandmother, you’re going to be very concerned. And so we are.”

Callas said the storm had essentially shrouded Opportunity in darkness as the opacity of the atmosphere, a measure of how effectively the dust is blocking out sunlight, climbed to record levels. A major 2007 dust storm had an opacity level, or tau, above 5.5 while the current storm had an estimated tau of nearly 11 as of June 6.

Steadily dropping power levels forced mission managers to halt Opportunity’s science operations on June 8. Two days later, the rover’s final transmission reported just 22 watt hours of available energy, which is believed to have triggered a protective low-power fault mode that shut down everything but the rover’s master clock

The master clock is programmed to wake up the flight computer periodically to check the battery charge and, if sufficient, to attempt contact with Earth. If the available power is too low, the computer will put itself back to sleep and the clock will set another alarm to wake it back up later for another check.

NASA’s solar-powered Opportunity Mars rover, seen here in an artist’s concept, has powered down and suspended science operations because of a widespread dust storm that has sharply reduced the energy reaching its solar cells. Image: NASA

“Our expectation at this point is that the rover has gone to sleep, it’s in this low-power mode and it will remain in that low power mode until there’s sufficient energy to charge the batteries back above a certain threshold,” Callas said.

“At that point, the rover will autonomously try to wake up and communicate with us. So at this point, we’re in a waiting mode, we’re listening every day for possible signals from the rover.”

If power levels drop far enough, however, even the clock will stop. In that case, the rover will simply remain asleep until power levels increase enough to trigge the flight computer.

But without the clock, Opportunity would not know what time it is. In that case, the computer is programmed to periodically check to see if the sun is up and if so, to phone home. Flight controllers have no way of predicting when such a signal might come in, but they plan to listen around the clock.

In any case, Callas said the rover should be able to withstand the lowest expected temperatures without major damage.

“We’ve done an estimate that shows the rover should stay above its minimum allowable operating temperatures for the long term, so we should be able to ride out the storm,” he said. “When the skies clear and the rover begins to power up, it should begin to communicate with us.”