An illustration of Opportunity, one of the twin Mars Exploration Rovers, which has been out of contact with the Earth since a dust storm nearly three months ago. (credit: NASA/JPL-Caltech)
by Jeff Foust
For nearly three months, the rover Opportunity has sat on the surface of Mars, silenced by one of the most powerful dust storms in decades. That storm effectively turned day into night, depriving the rover of the sunlight it needs to generate electrical power.
That dust storm is finally abating. The optical depth, a measure of the haziness of the atmosphere, has been dropping from a peak of 10.8 measured just before the storm cut off communications in early July. (A normal value for optical depth, or tau, is around 0.5.) The last values JPL provided for tau was in mid-August, when it was between 2.1 and 2.5, but has said in subsequent updates is continuing to drop.
The project soon expects tau to fall below 1.5, which will trigger a new phase in the effort to restore contact with the rover. While NASA has been listening for any signals from the rover, once the skies clear to that level—enough for the rover to start generating power again—NASA will start transmitting commands to the rover.
“Assuming that we hear back from Opportunity, we will begin the process of discerning its status and bringing it back online,” said John Callas, Opportunity project manager, in an August 30 statement about the recovery efforts.
That would seem like good news, but the plans in the statement generated some criticism because that period of active communications efforts will last only 45 days. “If we do not hear back after 45 days, the team will be forced to conclude that the Sun-blocking dust and the Martian cold have conspired to cause some type of fault from which the rover will more than likely not recover,” Callas said in the statement.
Some former project engineers reacted strongly to that news. “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,” tweeted Mike Seibert, a former Opportunity flight director and rover driver, who said efforts restore contact with Opportunity’s twin, Sprit, extended for nearly a year in 2010 and 2011. “Someone in the [Mars Exploration Rovers] Project, Mars Program or elsewhere has to be trying to kill the mission for non-technical reasons.”
“I’ll be blunt: 45 days is absurdly short, and certainly arbitrary,” Scott Maxwell, another former Opportunity rover driver, tweeted. He added that the project should wait until tau drops to a “more reasonable” level of 0.7 versus the 1.5 currently planned.
JPL officials defended the timing, and timescale, for the recovery efforts. After the active listening campaign ends, NASA still plans to continue passive efforts, listening for any signals that the rover might produce should it wake itself, through January 2019. That would be about eight months after the rover last communicated with Earth.
“The most likely recovery is for Opportunity to autonomously wake up and talk to us,” said JPL spokesperson DC Agle. “That’s why we are listening all that time.”
Reviving the Mars exploration program
As the debate about the future of Opportunity continues, there’s a bigger one about NASA’s Mars exploration programs in general. Opportunity and Spirit—collectively known as the Mars Exploration Rovers—are part of a broader exploration program of orbiters, landers, and rovers that has been operating continuously at Mars for more than two decades.
The future of that program, though, is in question. At Mars today are three orbiters—Mars Odyssey, Mars Reconnaissance Orbiter, and MAVEN—and the Curiosity and Opportunity rovers. They will be joined in November by the InSight lander (technically part of NASA’s Discovery program of low-cost planetary science missions) and, in early 2021, the 2020 Mars rover, a near-clone of Curiosity intended to cache samples for later return to Earth.
And after Mars 2020 is… nothing, at the moment. NASA has yet to formally identify any missions to go to Mars after 2020, other than studying so-called “lean” architectures for Mars sample return. That’s likely to involve two more spacecraft: one to land, collect the samples, and launch them into Martian orbit, and the other an orbiter to grab that sample canister and return it to Earth. Neither mission has been formally announced yet, although NASA and the European Space Agency announced plans this spring to study cooperation that could involve NASA leading development of the lander and ESA the orbiter.
No other missions outside of those potential sample return missions are under active consideration at NASA, despite worries by scientists about the age of existing spacecraft there. Even in the most optimistic scenarios, scientists and engineers expect many of the existing missions to fail by the mid-2020s. And it’s unlikely any new missions could be launched before the 2024 window at this point.
That got the attention of a National Academies committee that performed a midterm review of the latest planetary science decadal survey, which sets priorities for NASA’s planetary science program. One area of concern mentioned in the report is the uncertain future of the Mars exploration program.
“There is a risk that ongoing and soon-to-be landed assets on Mars will be left without telecommunications support because of the aging orbiters. The system is fragile and aging,” the committee stated, referencing the use of orbiters as communications relays in addition to their science work. “There is currently no vision for a program beyond sample return, either for scientific investigation or to prepare for future human exploration.”
The committee recommended that NASA establish—or, perhaps, reestablish—a formal Mars exploration program, or MEP, that would include an “architecture, strategic plan, management structure, partnerships (including commercial partnerships), and budget that address the science goals for Mars exploration,” according to the report. “This approach of managing the MEP as a program, rather than just as a series of missions, enables science optimization at the architectural level.”
NASA hasn’t formally responded to that recommendation in the report. Speaking August 23 at the Mars Society’s annual conference in Pasadena, California, just down the freeway from JPL, Michael Meyer, director of the current NASA Mars exploration program, focused on the program’s strengths rather than its uncertain future. “The Mars program is doing really well,” he said, so much so that a challenge was dealing with all the demands on NASA’s Deep Space Network in 2021, when NASA’s Mars 2020 rover arrives along with Europe’s ExoMars lander and China’s first Mars mission.
“We have a healthy program,” he said. “Our missions have been very successful.” However, even if Opportunity is revived in the coming weeks, the long-term health of the Mars exploration program will continue to be as hazy as the Martian skies were this summer.