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When I drive in cold/wet weather the state of the roads is cause for concern. But more worrying is the risk of the wind-screen fogging over when least it should.

Space/Earth orbit is a different kettle of fish; an astronaut doesn't run the risk of rear-ending, or tail-gating. An astronaut doesn't drive a car either; not in space anyway - not yet. The astronaut has a space-suit, and a helmet. The risk of fogging probably does not exist - given that the suit is either in the sun ( > 100 C ), or in shade ( < -100C ).

But what about when we get to a celestial body with even a modicum of an atmosphere - E.g. Venus, Mars, Titan just to name a few.

  • Could an astronaut (nominally, celestonaut) suffer helmet fogging during the course of exploration activities?
  • How would helmet-fogging in a potentially hostile environment be avoided?
  • As an aside, were any incidents of space-suit helmet fogging recorded in the annals of human spaceflight?
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Yes, of course the fogging could occur, if not mitigated. You'd be exhaling and sweating pretty much same contents of water vapor wherever you are, and in a completely closed system like a helmet used in non-breathable atmospheres like on the surface of Mars would be, in the vacuum of space, or hazardous environments (hazmat helmets, full face gas masks, e.t.c.), exhaled water vapor could condense on inner side of your visor.

The front of the visor, the outer side that is exposed to the environment, could also condense vapor, gather electrostatically charged dust, or even ice particles obscuring your vision, but that should be easy enough to wipe off on properly treated front glass / plastic element (faceplate), usually involving some antistatic coating on top of filter coating to protect from harmful rays (gold filters are often used).

Wiping off the inside of the visor isn't as easy though, so to combat this a good in-helmet ventilation will have to be provided, like it is in all current helmets used in spaceflight, or I would hope any properly designed fully closed helmets. Quoting NASA's page on spacesuits and spacewalks:

Besides covering a spacewalker's head, the helmet has a Vent Pad. This pad directs oxygen from the Primary Life Support Subsystem and Hard Upper Torso to the front of the helmet. The helmet keeps the oxygen at the right pressure around the head. The main part of the helmet is the clear plastic bubble.

The inner visor glass / plastic element could also be treated with anti-fogging chemicals, and its sides designed to allow for sufficient air circulation. If more than a single glass / plastic elements are used, the space between them could be filled with a low thermal conductivity gas, to prevent heat exchange directly on the visor itself.

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