Probably because a dust wiper suitable for long term use without fail would actually cost 9 million dollars per.

Dr. Becky Smethurst had a good explanation, it's basically weight cost and complexity issues, but the sparknotes version was:

Can't have air compression cause of weight, can't have wipers due to the coarse nature of Mars dust would damage the panels.

yeah that makes sense. We're used to "earth dust" which is mostly organic particles. Lunar dust (and I'm guessing Mars dust as well) was super abrasive so "dusting" would really scratch your solar panels.

Another seemingly simple but really complicated space issue!

NASA might actually buy it for 9M if it extends the rover's lifespan....

If you’re talking about curiosity, that’s doubtful. It’s mission was supposed to last about two earth year ms and it’s been 11 years

https://mars.nasa.gov/msl/spacecraft/rover/summary/

So it’s doubtful they would have done anything to extend the mission when it’s already gone beyond expectations be a decade

The latest rovers don't even use solar panels so it really isn't an issue.

The design requirements for the rovers (spirit and opportunity) only calls for them to work for months. These rovers weren’t designed to work indefinitely and so they weren’t build as such because if the weight and powerbudget went to a wiper then it is taken away from the science payload; doing science is why they are there in the first place. If the mission is only suppose to last for months, why spend the weight and power on something that only helps with the longevity of the vehicle when it’s operated on the scale of years. Operations with spirit and opportunity for years also shows that you didn’t need wipers for the dust since the Martian winds periodically blew them off anyways.

Edit: curiosity uses RTG for power so it doesn’t have solar panels.

Curiosity rover was powered by RTG so it doesn’t have solar panels.

OK, here we go.

First off, this is a solved problem if you spend the money. None of the currently active Mars rovers (Curiosity and Perseverance) have this problem, because they are powered by RTGs. If you want to solve the problem more affordably, then it's still a bit of an issue.

Let's start from square one. Imagine you are adding something to a Mars rover that literally does nothing, what does that look like? Well, that doesn't come for free, you still have to do testing, modeling, integration of the component into the design planning, and so on. At the complexity of a Mars rover that could very easily cost millions. Now imagine you have something that takes up power, has mechanisms of operation, and has some purpose related to power generation. Now the testing requirement goes through the roof. At the absolute minimum that component needs to not cause a problem. It can't vibrate loose during launch or landing, it can't get in the way of anything else, it can't cause a problem with the power system, it can't short out, etc, etc, etc. Additionally, it can't make the power production worse. Imagine a windshield wiper type design which scratches the surface of the solar panels and permanently reduces the power output the first time it's used. Or something that craps out and ends up partially blocking the solar panel or making dust buildup worse.

And that's before you even get to the question of how you make something that will actually work. Sure you can theorize that a simple brush or a high powered fan or a jet of compressed air will do the trick. How do you know for sure? Do you have a room off of your garage that you can step into that has a replica Martian atmosphere, replica Martian surface conditions, and replica Martian dust? Mars isn't identical to Earth, the dust there is slightly different, it has a different consistency and it is generally more "sticky" and staticky because of how dry Mars is. These properties are why Martian dust is such a problem and why testing a solution is not that easy.

This means that realistically the R&D program to develop a solution that has a high probability of working would clock in at tens of millions of dollars, maybe more.

Meanwhile, you're trying to add all of this mass and suck up all of this budget to increase the longevity of the rover, but this comes at a cost, you have to displace something else on the rover. You're going to have to lose some other functional equipment to make room, and that's going to come at a distinct blow to the science return on the rover within the nominal mission, with the hypothetical advantage of increasing the extended mission duration. Currently nobody has thought that's a good idea so far.

On top of that, if you design a solar powered rover with absolutely no dust mitigation systems whatsoever then there's still a reasonable chance that with some luck you can have a rover that naturally lasts for 15 years on Mars.

Given these tradeoffs and uncertainties it hasn't seemed worth it for anyone (either the US, China, or Europe) to design a solar powered rover or lander that attempts to make use of a dedicated dust removal system. Eventually that technology is likely to be developed, but so far the cost vs. benefit equation hasn't hit a point where it makes sense to make that investment.

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