The dust storm on Mars is over, but Opportunity has yet to wake back up. Earlier this summer, the rover was forced into hibernation mode by an extreme Martian dust storm that darkened the skies of the Red Planet to a level we’ve literally never seen before. Most of the time, Mars has a tau — a scientific term that refers to the opacity of the Martian atmosphere — of 1-2. During the largest major dust storm we’ve previously seen, the tau was roughly 6. This time, the tau from the massive storm hit 10.8 — and Opportunity is solar powered.
NASA has now announced that the window of Opportunity is remarkably short. In 45 days, if NASA hasn’t heard from the rover or been able to contact it, it’ll pull the plug on the mission. And that time frame has many engineers and scientists upset, given the mechanics of how dust and dust storms practically work on Mars.
During the 14 years its been on Mars, Opportunity’s power levels have fluctuated enormously for two primary reasons. First, the rover’s reliance on solar power means that the amount of energy it receives is dependent on Mars’ position from the Sun. Mars distance from the Sun varies from 1.38 AU to 1.67 AU, and the long Martian winters provide significantly less power overall. Second, the same wind that occasionally covers the rover in dust has also been known to clean and polish the solar panels, in some cases bringing them up to nearly full power once again. The graph below shows how Opportunity’s power levels have fluctuated over 2017 – 2018.
On June 3, Opportunity produced 468 Whr of energy. By June 6, this had fallen to 133 Whr as the dust storm approached. On June 10, just 22 Whr of energy were available. Whether the rover can wake up at all will depend in part on how clear the solar panels are. And team members who work on Opportunity are pointing out that NASA’s 45-day limit appears to have come from nowhere. When Spirit went quiet in 2010, NASA spent 10 months on actively attempting to communicate with the rover and five months passively listening for its communication. The 45-day clock won’t start until the tau above the rover is confirmed to be at or below 1.5, but as The Atlantic details, many on the NASA Opportunity team are unhappy at the idea of pulling the plug on the project without turning over every rock and making every effort to get the rover up and running.
You have to be kidding me. 45 days after a Tau of 1.5. This can't be based on any real analysis of the situation.
— Mike Seibert (@mikeseibert) August 30, 2018
There are two ways to look at this issue. On the one hand, sustaining an active mission around Opportunity costs money and NASA doesn’t exactly have a ton of it sitting around. You could make the argument that after 14 years, there are simply different places to allocate those dollars. The other argument, however, is that it’s incredibly expensive to put a new rover on Mars. It makes the most sense to extract every last scientific observation from an available instrument because new instruments are an incredibly rare event. There’s also no guarantee that any attempt to put a new rover on Mars won’t blow up on the launch pad or fail en route. Which of these arguments is right will depend on where you feel NASA should be prioritizing its spending, but the cost of trying to wake Opportunity up is a fraction of the cost of replacing the rover. You can make a cogent argument for a more aggressive contact attempt on those grounds alone.
One reason why engineers are calling for a longer active listening session is that the rover’s onboard clock may have failed and it may no longer know when to phone home for instructions. When NASA is actively listening, that means it sends a periodic communication pulse to order the rover to call home, if it happens to be alive and its radio is functional. Passive monitoring just means you listen on the frequencies you think the router may use (apparently these can drift) and hope it tries to contact you.
Hopefully, Opportunity will wake up on her own, obviating the argument. For now, NASA’s plan to pull the plug in 45 days isn’t winning the organization any fans.