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Posted by: hendric May 22 2008, 05:55 PM

Just had an idea for a solar panel cleaner. Place a small, black tank on top of the deck. At the bottom of the tank is a one-way valve pointing into the tank. At the side of the tank is a pressure-relief valve tied to the dust removal tubes.

1. Starting at daybreak, the tank starts filled with cold, dense atmo.
2. As the tank warms, the pressure builds within the tank.
3. Once the pressure reaches the cut-off of the pressure relief valve, the valve triggers and opens full-bore until the pressure difference reaches zero, and it then closes.
4. Pressurized air comes out of the tank and blows off dust from dust-sensitive devices, camera, solar panels, view ports, etc.
5. At night fall, the tank cools, lowering the pressure within the tank until it is below the outside pressure.
6. The one way valve opens, refilling the tank with colder, denser air.

Because the tank isn't required to hold high pressures, it can be very light. There is about 100 degree C difference between day/night, meaning during the day the tank should reach about 50% higher pressure than night time. The pressure difference can be increased by adding a heating element.

This removes the need for storing a gas for the cleaning, as well as any need for a pump.

Ready...Set...Rip 'er apart!

Posted by: ElkGroveDan May 22 2008, 06:01 PM

Creative and simple. However, my gut feeling is that the pressure differentials would not be significant so the velocity of the venting gas will be low and the duration brief. That "air" is not very dense and it requires a whole lot of energy under those circumstances to get the dust particle to move and to break whatever electrostatic bonds might be holding the dust particles in place.

Posted by: tasp May 22 2008, 06:22 PM

Martian air is very dusty and will be passing through valve in both directions. I suspect dust will ruin the valve or it's sealing ability very quickly.

As for lack of 'pop' with the system, use a micro air pump cogged to the anemometer to pump air into the tank all day when ever wind blows. Dust problem will remain with the valving and now it is more complicated and heavier, but it will clean the panels.





Suddenly I understand mission creep.

Posted by: jasedm May 23 2008, 09:54 AM

I understand that the dust buid-up on the arrays has been gradual, with 'cleaning events' every so often improving the situation for a time. How about a plastic 'sticker' over the panels similar to the protective plastic you get over the screen of a new mobile or camera? This could be left in place until the mission is 'power-critical' and then peeled back from the arrays (taking the dust with it) by a mechanism similar to that which opens the arrays initially.
I imagine the plastic cover would be quite inexpensive, the peeling mechanism less so.

Posted by: MahFL May 23 2008, 12:56 PM

Everything that flies in space is very expensive ! All the design, testing etc makes it so.

Posted by: centsworth_II May 23 2008, 03:40 PM

That would have to be some REALLY HIGH TECH plastic to withstand years of temperature swings and solar radiation.
And remain non-brittle and clear!

Posted by: MahFL May 23 2008, 05:04 PM

And bloody expensive !

Posted by: Alex Chapman May 23 2008, 07:51 PM

The real answer is just to make the solar panels large enough so that they produce enough power throughout the mission even with dust accumulation. For long duration missions go nuke and have it powered by an RTG, they really are the way to go.

Those are the engineering choices Nasa have made and personally I think they are the best.

Next to having an astronaut with a soft bristle brush brush that is.

Posted by: Tom Tamlyn May 24 2008, 01:03 AM

I think "Roving Mars" mentions a similar plastic wrap roller idea. I think that JPL's eventual thinking was along the lines of Alex Chapman's comment; just making the solar panels bigger gives the biggest glow for the buck.

TTT

Posted by: simonbp May 27 2008, 02:54 AM

The real problem with Mars (and Moon) dust is that it is so very electrically charged. If you walked over to one of the rovers, and tried to brush the dust off, it would probably stick to your spacesuit glove. For example, look how dirty the Apollo astronauts got (e.g. Cernan below); all that dust was electrostatic cling. So, a simple solution would be to run a ground strip from the structure of the panels to the ground (which they may already do, I don't know). A more proactive solution would be to put a negative charge on the panels (or on a transparent, conductive coating on top). This, though, would probably strain both the power and fiscal budgets...

Simon

Posted by: SpaceListener May 27 2008, 03:15 AM

The Earth polar zone is very windy. I don't know if it applies the same to Mars' polar? Any way, Phoenix is programmed to have a short live and will be closed by the end of spring which is the session of low Tau factor (Atmosphere not so dusty as the ones in the summer times).

Any techniques to keep the solar panels clean s only worth when it will be living all round year as does the MER-x robots.

Hence its design is according to the Phoenix mission objectives of 3 months (by the end of August). Well, let us see if anything goes so well and its mission might be extended.

Posted by: nprev May 27 2008, 03:27 AM

Gotta agree completely, here, Phoenix's solar arrays are sufficient for its mission, which has an environmentally constrained duration. Solar panels require maintenance in Martian conditions that's probably beyond the scope of automation for very long-term missions; might be also true for lunar conditions, but of course there's no wind transport of dust there so the effect should be smaller.

Posted by: Reed May 29 2008, 03:42 AM

RTGs are unfortunately expensive, and fuel is getting scarce. The US has stopped production of Pu-238, and AFAIK the Russians are shutting theirs down as well. From what I understand, we have enough available for the currently planned missions but little beyond that.

Thinking about panel cleaning, it seems to me you don't need to run it very frequently. From the MER experience, averaging once every 3 months would probably be plenty. If you only need a few tens of cycles total, simple filters may be sufficient to make Hendrics suggestion workable from a dust POV. You'd need to be able to isolate it (lock the valves closed and cover the filters), but that should fairly straightforward. OTOH, at that level of use an expendable source might be competitive. If you use something that is liquid or solid at modest pressures, you can get a large volume without wasting too much mass on pressure vessels. CO2 seems like the obvious choice, although you may have to expend some effort keeping it in the desired state.

Larger panels are clearly the simpler (= lower technical risk) way, but being able to clean off after a major dust storm has a certain attraction.

Posted by: Steve G May 29 2008, 03:57 AM

The simplist and most weight efficient would be to have "windshield wipers". You may want to have them charged to repell dust magnetically (or attract them and then switch polarity to dump them over the side) They could be rotated after the swipe with a brush to give them a nice polish after.

Posted by: djellison May 29 2008, 07:16 AM

Wipers to cover all of the arrays on a vehicle would be complex, large and heavy. You want a non-moving, low mass, low volume solution. I reported on one in development at the IAC in '06 - something along these lines..
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/9582/30300/01391965.pdf?arnumber=1391965
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/7320/19792/00916141.pdf?temp=x
http://www.patentstorm.us/patents/6911593/description.html
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/8468/26685/01190698.pdf


Doug

Posted by: helvick May 29 2008, 07:42 AM

The simplest solution is to increase solar panel area. The long term experience with Opportunity and Spirit has shown that over a 2 year mission power from a solar panel can be expected to remain above 20% of ideal mission start capability if carefully managed. In addition worst case power performance occurs during dust storms when Tau is high so adding solar panels to non horizontal or even fully inverted surfaces is useful in terms of providing additional power under worst case conditions. Even cells located on the underside of solar panel wings would generate useful power when Tau is above 1/2. Developing lighter solar cells would be a more useful investment in my opinion.

Posted by: stevesliva Sep 13 2010, 06:06 PM

(Bump of an old but relevant thread)

News of work along the same lines:
http://www.technologyreview.com/energy/26116/page1/