Opportunity hunkers down as dust storm descends over the intrepid little rover

by Chris Gebhardt

For the second time in its career, NASA’s Mars Exploration Rover Opportunity is hunkering down on the Red Planet and foregoing scientific operations as a dust storm whirls around the intrepid little rover.  Opportunity weathered – with some difficulty – a massive, global dust storm in 2007, remarkably surviving despite extremely low power levels generated by its solar panels during the event. NASA announced last night that the current dust storm is now worse – in terms of total sunlight blocked – than the 2007 storm.

The Situation:

Dust storms were always a potential hazard for Opportunity due to the fact that it gathers and generates its power via sunlight reaching its critical solar panels that cover the majority of the “top” of the rover.

As has been seen throughout Opportunity’s lifetime, dust routinely collects on the surface of its solar panels and is, somewhat surprisingly, routinely cleaned by Mars’ wind and dust devil events, thus allowing greater power generation on the rover than would otherwise be possible if total accumulation built up over time without these cleaning events.

A major cleaning event for Opportunity’s solar panels occurred in early 2007 and greatly aided the rover in what became its worst – at the time – chances of survival when a massive, global dust storm enveloped Mars and dropped sunlight levels reaching the rover’s solar panels to critical levels.

Now, in a late-evening/night update yesterday at 16:30 PDT (2330 UTC) 10 June 2018, NASA announced that the current dust storm surrounding Opportunity at Perseverance Valley near the Endeavour Crater has grown to be worse than the 2007 dust storm, blocking even more sunlight than the global event did 11 years ago.

On Friday (8 June), Opportunity’s operators suspended all scientific observations for the rover in a power conservation effort to allow Opportunity to use what power was available to it to maintain heater operation for its critical systems – maintaining temperatures for Opportunity’s systems to combat the low temperatures on Mars.

Interestingly enough, as nature often does, the current dust storm does have one positive effect for Opportunity: it lessens the degree to which Mars’ temperatures plummet in the overnight hours as the dust absorbs heat and raises the ambient temperature surrounding Opportunity.

According to NASA, the agency’s Mars Reconnaissance Orbiter first detected the dust storm on Friday, 1 June, and NASA immediately notified Opportunity’s teams to begin preparing contingency plans in case the dust storm necessitated a change to the rover’s nominal operations.

In a matter of days, the dust storm had grown rapidly to span more than 7 million square miles (18 million square kilometers) – an area greater than North America.  Critically, the dust raised the atmospheric opacity in Perseverance Valley, and Opportunity’s power levels dropped significantly by Wednesday, 6 June, requiring the rover to shift to minimal operations.

Images from Opportunity showing progression of 2007 dust storm. The greatest tau – opacity level – seen here is 4.7. The current storm has a tau of 10.8. (Credit: NASA/JPL)

Back in 2007, at the height of that dust storm, Opportunity sustained two weeks of minimal operations and even ceased contact with Earth for several days in various attempts to conserve all the power possible aboard the rover.

During that event 11 years ago, the project’s management prepared for the possibility that Opportunity would not be able to balance low levels of power with its energy-intensive survival heaters, which protect its batteries from Mars’ extreme cold.  

Major dust storms like the current one are not surprising, but they are infrequent and can crop up suddenly and last weeks, even months.  During southern hemisphere (where Opportunity is) summer, sunlight warms dust particles, lifting them higher into the atmosphere and creating more wind.  That wind kicks up yet more dust, creating a feedback loop that NASA scientists still seek to understand.

By Sunday night (10 June), the situation had worsened, with NASA noting that the dust storm had intensified in the past several days and that a dark, perpetual night has now settled over Opportunity’s location.  

Moreso, the storm’s atmospheric opacity – the veil of dust which blots out sunlight – is now much worse than the 2007 storm that Opportunity weathered.  The previous storm had an opacity level just above 5.5. This new storm had an estimated opacity of 10.8 as of Sunday morning. The higher that number climbs, the worse the situation becomes for Opportunity.

Despite this, Opportunity did call home yesterday through a communications relay with the Mars Reconnaissance Orbiter – a positive sign despite the worsening dust storm.  The Mars Reconnaissance Orbiter, Mars Odyssey and MAVEN orbiters all routinely support Opportunity’s operations on the ground and communication back to Earth via the Deep Space Network.

Data from the Sunday morning transmission showed that Opportunity still had enough battery charge to communicate with ground controllers at NASA’s Jet Propulsion Laboratory, and Opportunity’s team requested additional communications coverage from NASA’s Deep Space Network, a global system of antennas that talks to all the agency’s deep space probes.  

The latest data transmission from Opportunity on Sunday morning showed the rover’s temperature to be about -20°F (-29°C).  If the situation continues to worsen, the next step would be to suspend Opportunity’s communications with Earth to save additional power.  

If that is not enough, and power levels drop to a specific, low level, Opportunity would trip what is known as a low-power fault program, disabling the rover’s batteries and putting Opportunity into sleep mode until sufficient available energy returns to wake it up.

As with the 2007 dust storm event, there is a very real possibility that should a low-power fault program trip and Opportunity goes to sleep that the rover will not wake up again.

Presently, engineers will monitor Opportunity’s power levels closely in the week to come.  The rover needs to balance low levels of charge in its battery with sub-freezing temperatures.  Its heaters are vitally important to keeping it alive, but also draw more power from the battery.  Likewise, performing certain actions draws on battery power, but can actually expel energy and raise the rover’s temperature.

Regardless of the outcome, it is extremely important to remember that Opportunity is currently in its 14th Earth year of operation of what was supposed to be a 90-day mission when the rover landed on the Meridiani Planum on 25 January 2004.

Opportunity has routinely beaten the odds during its tenure on Mars, has driven farther than any other vehicle on a world other than Earth, and is the longest surviving spacecraft to ever operate on the Martian surface.

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