Articulable/tilt-able solar panels planned for, or already tried on Mars or the Moon to get rid of deadly dust accumulation on solar panels?

Question

From Forbes.com's Mars Opportunity And Spirit Rovers Could Have Lived Practically Forever With One Tiny Change:

One option would be to install some mechanism such as wiper blades to remove any Martian dust that accumulates. Here on Earth, windshield wipers are so commonplace that it seems like the obvious solution to such a problem. But Mars is very different from Earth in two important ways when it comes to dust accumulating on a surface like a solar panel.

• Martian dust is extremely small and fine-grained. Atmospheric dust on Mars is approximately three microns in diameter, and adheres via electrostatic forces. You can't just "brush it off" like you would on Earth; much dust would remain.
• There is no fluid to help on Mars. Water won't remain liquid on Mars, and you can only bring a limited amount of any fluid with you. Dry wiping motions would harm the panel surfaces, making them an inferior solution.

There are better options, though. Wiper blades are heavy, complex, subject to damage at the temperature extremes that Mars experiences, and are easily broken. A second solution would be to have articulated (tilt-able) panels, where you could simply orient them vertically. Since Mars normally has low-level winds that blow continuously, any dust accumulation could be blown off by the natural environment of Mars. In fact, there are "natural" cleaning events that occur on Mars, which we didn't know about when we designed these rovers; the winds occasionally, overnight, will blow large amounts of dust off of the rovers, upping their power output. It was only when Spirit didn't get one for an entire Martian year that it wound up dying.

The panels could have been outfitted with a mechanism to electrostatically repel the dust. By charging the panels themselves, some charge would migrate onto the dust grains, causing mutual repulsion (since like charges repel). Then, any low wind would blow the levitated dust away, greatly improving the rover's performance. The drawback is that sometimes dust particles become electrically charged, and you don't get to choose the sign of the charge, particularly if they're good insulators.

Reminds me of Has a spacecraft ever actually sprayed a chemical (or anything) on to another spacecraft intentionally for any reason at all?

Question: Have articulable/tilt-able solar panels planned for, or already tried on Mars or the Moon to get rid of deadly dust accumulation on solar panels?

Answer 1

In short, for past missions NASA has said no, it was not a priority consideration.

In the future, this may change and it is being considered.

In EXPLORING MARS WITH SOLAR-POWERED ROVERS

.. there has been some interest in developing means to mitigate the effect of dust on the solar arrays for long-duration operation on Mars.. however, the engineering decision was that it would be more cost effective to oversize the arrays to account for the predicted degradation than it would be to fly a system to remove dust from the panels.

Since the operating temperature varies significantly during the day, and the spectrum of the incident sunlight varies both with time of day and with the amount of dust in the atmosphere, the performance of the solar arrays on Mars is complicated.

https://ntrs.nasa.gov/api/citations/20060013412/downloads/20060013412.pdf

With the latest Mars-bound rover (explored more below) in its current configuration, they calculated that it would be acceptable to have more than 30% loss in power output by the time the rover reached its end of life due to dust coverage, rather than try and design some kind of dust removal mechanism.

In 2017, NASA did include this provision with the request for concepts in the period 2018-2020:

Mars Surface Solar Array Structures

NASA Space Tech “seedling” study to develop a Mars power architecture with deployable solar arrays

Note requirement number 14: Ability to tilt arrays for dust removal and to feather in high winds.

Unfortunately, no concepts were delivered that satisfied this requirement.

https://ntrs.nasa.gov/api/citations/20170004910/downloads/20170004910.pdf

In 2019, dust removal of some kind was still listed as something that needs to be looked at:

Although Compact Telescoping Surface Array for Mars Solar Power was considered as most promising for future Mars solar array technology, dust removal of some kind was ... the subject of on-going studies...

Technology Gaps and Additional Trade Studies

Dust abatement/removal technology.

• Demonstrate high effectiveness (>90% dust clearing) on flexible blanket solar arrays

https://ntrs.nasa.gov/api/citations/20190000437/downloads/20190000437.pdf

With regards to ExoMars, a rover bound for Mars (or Moon, as suggested in light of the withdrawal of Russian involvement recently): It was looked at originally, and then in its current configuration they decided that no - it was too risky, and too costly.

With the rebirth of the ExoMars mission (not launching before 2028) - they are looking at it again, so this changes to a maybe.

(Note: aka Rosalind Franklin Rover, so @uhoh's question is also here Will the Rosalind Franklin (ExoMars) rover solar panels be able to clear themselves of dust by tilting?)

https://www.space.com/saving-mars-robots-from-death-by-dust

Tilting solar panels

Mike Williams, Chief Engineer at Airbus Defence and Space, agrees that NASA's approach of outsized solar panels is the best, safest and cheapest when it comes to dust-proofing Mars-exploring spacecraft. However, Airbus is currently looking at the possibility of adding a dedicated dust defense capability, and they have plenty of time to do that. The mission, built in cooperation with Russia, was suspended in the wake of Russia's invasion of Ukraine. The planned September launch was canceled, and Airbus is now storing the ExoMars rover in a clean room as some critical components, originally built by Russia, have to be replaced.

"Sizing the arrays to be able to manage the lower amount of sunlight that reaches them because of the dust is the best and simplest solution," Williams told Space.com. "It's the lowest level of complexity. It requires the least number of subsystems and functions and so it has the lowest risk. From the perspective of designing a mission, that's definitely the most preferable way of going about it."

Williams said that when the ExoMars mission was first conceived, engineers considered a plethora of dust cleaning technologies, including brushes, wipers, gas blowers and electrostatic wipers to get rid of the dust. At that time, they decided the rover, whose nominal mission in Oxia Planum was designed to last only 180 Martian days, or sols, did not need to self-clean. With the new launch date now expected no earlier than 2028, they are rethinking their approach again.

"With ExoMars now being reborn, we are looking at possibly reinstating some of that capability," Williams said. "We could use something like solar panel tilting to possibly dislodge some of that dust. It would also help point the panels more efficiently at the sun, which may also have some benefits."

Williams added that Airbus engineers, just like NASA's, have to reconcile with the fact that ExoMars, just like other spacecraft on Mars, may eventually succumb to dust, and won't be disappointed if the rover outlasts its designed mission lifetime only marginally. Although they hope to get some help from Martian weather just like Spirit and Opportunity.

"It's just, it's just the way it goes with space missions, unfortunately," Williams said.

Circa 2009, ExoMars did originally have tilting ability built into the solar array:

Although originally meant for Dawn/Dusk solar optimization, this could be revisited for dust alleviation.

https://www.lpi.usra.edu/mepag/meetings/archive/meeting/2009-07/04-Mepag_Coradini.pdf

Looking at other NASA docs, dust was a concern, but other items were higher on the list of concerns:

(The arrays in this concept lock after fold out, no tilting considered)

https://pdfs.semanticscholar.org/772a/2f6e1b9b50e64295895eb88e7c715012855d.pdf

https://www.researchgate.net/publication/24286713_Solar_radiation_on_Mars_Tracking_photovoltaic_array

InSight's self-cleaning attempt

Even though InSight wasn't built to wipe dust off of itself, NASA made some last resort attempts to help the lander remove some of the dust in the final months of its life as the amount of electricity generated by its panels dwindled.

In May (2021), ground controllers commanded InSight's robotic arm to sprinkle a bit of sand across one of the lander's dust-covered panels. As wind blew the sand grains across the panel, they actually picked up some of the dust along the way, reducing the thickness of the sun-obstructing dust blanket.

The operation enabled the lander to gain about 30 watt-hours of energy per sol at that time.

https://mars.nasa.gov/resources/25952/insights-robotic-arm-helps-remove-solar-panel-dust-trickles-sand-in-the-wind/?site=insight

InSight's Robotic Arm Helps Remove Solar Panel Dust Trickles Sand in the Wind

https://ntrs.nasa.gov/api/citations/20205004953/downloads/IAPG%20RECWG%20NASA%20July%202020.pdf