Here is a question that has been bothering me since I first read about the Mars rovers. First, the preamble. Brilliantly designed, they have exceeded their mission life by a factor of more than ten. Brilliant to get them to Mars. Brilliant to land them safely. Brilliant to maneuver them so successfully. Brilliant … well, you all get it. No sarcasm intended!

With all this brilliance, why did no one think to attach a rotating brush on a telescopic arm to sweep off the solar panels???

They did think to do it. They decided not to.

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Here's my quick search...since I figured it's been here before.
Discussion: Rovers are Getting a Little Dusty

Question about Mars Rover solar panels

Quick summary of my interpretation.
- Lifespan was thought to be shorter than the expected buildup.
- vibrations from roving were thought to keep it clean.
- weight penalties.
...and more, but I'm going of a quick review.

Edit: BTW... brushes tend to scratch when dirty.

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Passport to Knowledge: Building the Mars Exploration Rovers

Cornell University: Athena Mission to Mars: FAQ

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I did that once.

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Thank you to all responders. I should not be too lazy to Google these questions myself

Still, it seems somewhat glib for JPL to say “We did not know the nature of the dust” or “Removing it could scratch the solar cells”. “The solar arrays are too large“ ???
So is the distance from the Earth to Mars. Sheesh

If the solar panels on the (very expensive, very valuable) rovers become so coated with dust they no longer function, cleaning them seems like a risk worth taking.

This would be an “as needed” rather than a routine procedure.

Kudos to the engineers and craftsmen who built these machines which have so exceeded their operational expectations. No criticism there.

So, again, I pose the original question.

I think the point of "too large" is that the cleaning apparatus would need to be large, and the added mass penalty would mean giving up science instruments. Since the original mission plan didn't expect the rovers to last long enough for the dust to be an issue anyway, why would you incur the mass penalty?

I think some of the links provided address this issue, no?

CJSF

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Two years ago moved from my town
I was looking up past the city lights
But the city lights got in my way

See the constellation ride across the sky
No cigar, no lady on his arm
Just a guy made of dots and lines

-from "See The Constellation"
by They Might Be Giants

That's exactly my memory of it. The cost of a cleaning system would have been that some instrument could not be included. And weight/size of components were critical, not only for the launch, but for the landing on Mars. And again, given the expected 3 month operating time, it was figured they would be dead before they needed a cleaning.

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At night the stars put on a show for free (Carole King)

And then, as it turned out, the dust devils did partial cleanings several times.

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What items are you prepared to take off the rover to make space (volume, mass, power, development time, money ) for a cleaning mechanism?? One of the comms systems? A couple of instruments? The rovers arm? You would need something larger than the whole of the rovers current arm to reach all the arrays so to accomodate it would involve removing something equiv. to 80% of the science payload.

They designed the arrays to be big enough to do 90 days. They've done that. 13 times over.

Doug

Don't forget the reporter who doesn't understand what they are saying, or doesn't have the space to say it who eliminates some of the reasons, or descriptions of what are being said. I don't know either the context of the quote in the article, or even your context in quoting the article since you didn't provide it.
Here's the context that I read into these statements...
True; they knew there was dust, but the nature of not knowing densities, how it collects, static cling, or other important details of the dust are and still are being studied. For an effective cleaning system, these details are important. By assuming a particular property, you run the risk of designing a system that is totally usesless because that property was not studied.
What's glib about that? They figured the risk of scratch damage is higher than the risk of buildup.
Too large for designing in a compact cleaning system. Not to large for the rover.
Because, the cleaning system may need human reaction.
If they lasted the expected mission duration, then they met the design restriction and risk. This is only one of many trade-offs that created the duration expectation.
The mission WAS a success. Everything after that IS bonus.
At least you appreciate the accomplishment.
Do you have a better design? If you do, I'm sure it would be a consideration.
But; I'm sure you haven't spent countless hours and fortunes to consider all of the variables that need to be considered.

I'm not trying to berate you, only pointing out that the issues and factors involved may be way past what you think they may be.

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Sorry to be annoying. That was not my intent. The point I was trying to make was, the 90 day life of the project was based (I think) on the assumption that dust would accumulate on the solar panels. If they could be cleaned, that period could be extended. Several posters answered that issue well (weight trade offs). Thank goodness for “dust devils”.

NEOWatcher, I stand in awe of the accomplishments of JPL/NASA and all the personnel involved. Hope I did not give any other impression.

Guess I should shut up and go back to lurking.

If that were true, I never heard it. It may have been a factor, but, I've heard may other things as risks. And it was the accumulated risk that shortened the expectation rather than any design or components that were expected to fail.
Yes; I kind of read that in between the lines of your post.
No dents here...

Why? Did you offend someone?

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Numbers are not case sensitive. (me)

Unparalleled success. Both of the Mars rovers survived the landing and unfolded and worked perfectly for a period of time that has surprised all. Yes a little good fortune has played a part in keeping those solar panels clean enough to power the rovers. Its all been fantastic. The data stream from those two rovers is ongoing. Its all a bonus. Bravo to the build team. Bravo to the operators. Just plain old 'Bravo!'

I hadn't believed that the dust accumulation was the expected limitation (I thought it was mechanical systems), but I might be wrong. This website from aerospaceweb.org states:
But they do say ONE of the reasons. It also says
I also found this from 1997
So, I'm guessing that the engineers figured something else would go wrong before the dust became the biggest problem.

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At night the stars put on a show for free (Carole King)

Correct. Dust accumulation was 'one of the reasons'. I still think it was the primary one, however.

http://aerospaceweb.org/question/spa...t/q0298b.shtml

"Spirit and Opportunity were built by the Jet Propulsion Laboratory and designed to last at least 90 days on the Martian surface. The rovers have proven quite robust and are still operating today, over 1,000 Martian days after landing. One of the reasons designers did not believe the rovers could last much beyond three months was the assumption that Martian dust would build up on each rover's solar panels that convert light from the Sun into electrical power. As dust collects on the panels, they become less efficient and produce less and less power to keep the rovers functional. NASA engineers believed this accumulation of dust would limit the rovers to no more than a few months of operation."

Ok, let's say that this was the plan, that the 90 day life-span was based on the dust on the solar panels. Looking at the long quote in my previous post, it sounds like the plan was to get all the scientific work done in a couple of weeks. So assume that you had a design for a dust removal device, but you had to give up one of the science instruments to make room. Do you trade the added value of the results from that instrument for some added life expectancy that didn't really think they needed? The design team obviously decided on more data for a shorter period of time. They lucked out on an even longer life expectancy, and came up with plans to make use of that time.

The OP:
I suspect they thought of it and made a conscious decision to go another way.

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