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Science fiction often depicts humans visiting alien planets which have unbreathable atmospheres. No problem; they are shown wearing atmosphere suits including a helmet with a transparent visor/faceplate or a transparent globe over the entire head. My question is, what happens when it rains? Most of the designs of helmet shown on SF cover art would mean that all the wearer would be able to see in heavy rain is a curtain of water streaming down the surface of the clear polycarbonate plastic or whatever the visor is made of. Our intrepid explorer would then have no option than to stay where he or she was until the weather cleared.

Two strategies immediately occurred to me. One is to have little windscreen wipers. The other is to carry an umbrella. Would these strategies work? Less drastically uncool would be to have a little brim to your helmet, possibly retractable, but with that you are still going to have difficulties if you need to look up.

I also ask this question on behalf of any aliens currently visiting my corner of Earth, where the weather is particularly dismal today.

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They would use a superhydrophobic coating.

The problem with regular glass or plastic is that it gets wet. This means the liquid falling on it sticks, changes the index of refraction in that spot, and reduces visibility via distortion.

A surface with a superhydrophobic coating doesn't get wet. Fluids don't stick to it. It's often observed with the lotus effect.

enter image description here

This is commonly known as "beading". If the water doesn't stick then it simply falls off and doesn't reduce visibility any more than the rain falling in front of an umbrella would.

The additional benefit is the glass stays very clean. Alien super-pollen is not something you want to track back into the ship.

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  • $\begingroup$ what are some methods of applying a hydrophobic or anti-dust coatings? $\endgroup$ – Jim2B Oct 21 '15 at 18:54
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    $\begingroup$ @Jim2B As a spray or a paint are existing methods. I imagine in the future more robust superhydrophobic surfaces could be fabricated as a property of the material. $\endgroup$ – Samuel Oct 21 '15 at 19:11
  • $\begingroup$ @Jim2B I'm pretty sure that is what Rain-x does... $\endgroup$ – bowlturner Oct 22 '15 at 13:48
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Do motorcycle helmets have windscreen wipers?

Not usually, and yet they work in all weather conditions.

I'm not a motorcyclist myself but I'd expect this to be due in large part to the materials used, the wind over the glass, and the fact that you can use your hands to wipe the surface when needed.

You can expect space explorers to have very good materials technology, good enough that their face plates would repel water and dust to a large degree. They can then be cleaned easily enough just by wiping them with a suitable cloth.

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    $\begingroup$ Rain is annoying on a motorcycle helmet visor. And while there is no wiper on the helmet, my heavier motorcycle gloves have wiper on the left index finger. I can only recommend that, it works like a charm. Especially in foggy conditions which create much smaller drops (that are much harder to shake off) than rain. $\endgroup$ – Burki Oct 21 '15 at 15:08
  • $\begingroup$ When you're riding, the wind generally pushes the water droplets away and makes it much less annoying, but as you say, when stopped, your gloves work well to keep the visibility manageable. $\endgroup$ – Johnny Oct 22 '15 at 0:24
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Can you still see out a window when it's raining? Granted the visibility is much worse, but you aren't blind. Really heavy rains will affect visibility even with some kind of umbrella. Speaking as someone who's worn glasses in all weather for almost 30 years, rain on the lenses does make it more difficult to see, vs. using an umbrella but all it really does is push back the clear area 18".

I think the best option would be to use rain-x to help the 'glass' shed water better. Of course there might be plenty of other chemicals that you need to watch out for that just water if you are on a planet that you can't breath the atmosphere. Many of those chemicals when you add some water make them more corrosive. So I think finding shelter would probably be more important than worrying about visibility.

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  • $\begingroup$ I was just about to post an answer about Rain-x :D $\endgroup$ – DaaaahWhoosh Oct 21 '15 at 13:41
  • $\begingroup$ @DaaaahWhoosh it works well! ;) $\endgroup$ – bowlturner Oct 21 '15 at 13:47
  • $\begingroup$ Yeah, I remember the first time I drove with it, my dad had just put it on my car without telling me. I was so confused when it started raining. $\endgroup$ – DaaaahWhoosh Oct 21 '15 at 13:48
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    $\begingroup$ You would be surprised how dirty your glasses can get before it becomes hard to see. Or rather how good your brain is at looking between the distortions/correcting them. $\endgroup$ – ratchet freak Oct 21 '15 at 14:41
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    $\begingroup$ @ratchetfreak actually I wouldn't be surprised! I'm a woodworker! :) $\endgroup$ – bowlturner Oct 21 '15 at 14:48

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