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Sabrewolf t1_iu3508t wrote

Reply to comment by djdsf in NASA spacecraft records epic ‘marsquakes’ as it prepares to die by marketrent

I work internally with some of the Mars teams at JPL, and these are the best explanations I have:

  1. Budget budget budget, many of these missions have a cost cap which can't be surpassed. Every additional thing adds system complexity, and ultimate ends up costing money to design/build/test. Even if there's an amazing idea floating around, if it's not in the project budget it's a no go. This includes solar panel dust removal, weighed against the expected science return and lifespan of the mission.
  2. Martian dust is electrostatically charged, so it "sticks" to the panels rather than sits on them. This complicates removal.
  3. Brushes are abrasive, and so is sand and dust. On top of the weight and mechanical complexity, point #2 means that you'd have to basically scrape dust *into* the super delicate solar panel to remove a marginal amount of debris. All said and done, wipers/brushes are not effective for this reason.
  4. Blowers and fans, see point #2, especially relative to the amount of force such a device could apply as compared to a wind clearing event like atmospheric wind. Additionally, Martian dust is so fine that attempting to blow it away with fans/blowers sort of causes a floating cloud that gets sucked back into the fans, essentially turning it into a sand blaster.
  5. There are methods of generating a burst of electric charge to displace the dust, but these are very expensive, very complex, and have not be fully investigated yet.
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cjgranfl t1_iu5jg2t wrote

Great info; interesting. Thanks for sharing.

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WimpyRanger t1_iu3xqde wrote

  1. There’s absolutely no way that generating a charge to displace the dust would be very complex, or very expensive relatively speaking.
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minepose98 t1_iu49j7d wrote

I wonder who is more knowledgeable about this, someone who works with this stuff, or a random redditor? Who looks at a post from someone who knows more about the subject than you explaining the difficulties of something and says "bet it can't be that hard"?

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WimpyRanger t1_iu7fl3b wrote

Well, I did go to school for electrical engineering, and a number of my friends work in space systems at Ratheon.

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PayZestyclose9088 t1_iu54b2r wrote

Omg youre so smart. You should apply to help make the rovers. I bet you will be making the next best thing

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Sabrewolf t1_iu81nw5 wrote

So the most promising technology NASA has funded for electrostatic displacement of dust in a way amenable to a space environment is called EDS, or an Electrodynamic Screen.

This is essentially a layer that fits over the solar panel with some electrodes embedded in it, patterned in a way that allows us to "walk" dust off the panel using a specific sequence of charge bursts. At first glance this seems like a silver bullet, however this technology has yet to leave the prototyping lab and make it onto a Mars mission for several reasons:

  1. Efficiency. The presence of these electrode layers has been found to cut the power output of the panels by 15-25%. This is a no-go, until further developed.
  2. Cost. Since this is very new, no industry has developed to marginalize the cost of making these. Since they are essentially still lab prototypes they are still very expensive to make, which makes allotting funding for them kind of tricky. Class B missions (like InSight) have less $$$ available, and Class A flagship missions (like the rovers) are important enough to have an RTG provide power. So at present, this technology is sort of stuck in the middle between function and price; at a certain point you have to ask, if the mission is so important that it *needs* to work long-term, why not just use an RTG? Especially when almost every previous solar panel based mission lasted decades without such a technology.
  3. Safety/Reliability. A key point of an EDS is that it produces charge using voltages in the kV level. This runs the risk of arcing/damage at a certain point (Paschen's breakdown for the engineers). The breakdown voltage at which an arc forms depends a lot on the atmosphere, and we simply need further research into the composition of Mars dust in order to safely design an EDS that guarantees minimal risk of arcing.

TL;DR - It'll get there, it's not there yet.

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WimpyRanger t1_iu87x57 wrote

What is the top layer on the rover panels? If the dust clings, the layer must hold a static charge. Given that the panels can rotate to shed the dust, and if they could also be charged to repel the dust, that seems like a clear win. If such a coating is not efficient enough, could you not use a grid type pattern? The EMF would still apply all over to some degree without absorbing much.

(Thank you for the reply)

Also, why couldn’t the panels be held near vertical to avoid the issue altogether?

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Sabrewolf t1_iu8932v wrote

You are greatly overestimating the amount of mechanical force an EM field can apply to electrostatically charged martian dust. Even at the kV level, an EDS panel cannot "pop" dust off. Nor does charging the panel allow dust to become mobile enough to passively slide off without further EM interaction, even if the panel were angled.

The way an EDS works is by shifting the dust by alternatingly charging the patterned electrodes in the screen. Because EM field intensity falls off with the square of distance, this pattern is required to keep the dust close to the charged electrodes.

And all this still ignores the issue of Paschens breakdown.

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