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Why did the A7L and A7LB moonsuits have two visors? The astronaut initially had both visors down on his helmet and later during the lunar EVA put the outermost visor up (a yellowish one) and could probably see better now with only the transparent glass visor.

Why was the lunar suit built like that? Was it just for more security (lunar dust or meteoroid impacts e.g.)?

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  • $\begingroup$ 1.) Only the original poster automatically gets notifications on comments; unless you @-tag somebody, you're talking to yourself. 2.) As for the spelling... "visor" has been the more common spelling for about 200 years. $\endgroup$ – T.J.L. Jul 8 '20 at 13:58
  • $\begingroup$ @T.J.L. I know, but I guess the question is visited by many. $\endgroup$ – LoveForChrist Jul 8 '20 at 14:00
  • $\begingroup$ @T.J.L. Thank you for lifting the veil. $\endgroup$ – LoveForChrist Jul 8 '20 at 14:00
  • $\begingroup$ Veils are totally different from visors. :) $\endgroup$ – T.J.L. Jul 8 '20 at 14:32
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For the earlier (Apollo 11-12, 13 in training) suits there were four visors:

  • an inner protective visor which is 'an ultraviolet-stabilized polycarbonate shield which affords impact, micrometeoroid, and ultraviolet ray protection' (text from ALSJ, reference below);
  • a gold-coloured sun visor which I think is to deal with visible light and IR – 'the inner surface of the polysulfone sun visor has a gold coating which provides protection against light and reduces heat gain within the helmet' (source ALSJ again);
  • two side visors which are, I think, to stop sunlight from the side illuminating the astronaut's face and the inside of the helmet (they're basically what a photographer would call a lens hood or a lens shade).

The later helmets were more complex and had, I think things a bit like peaked caps to provide further shade.

In summary the helmets had multiple mechanisms for protecting the astronauts and the pressure-tight part of the suits both from physical damage and from the UV, visible and IR components of sunlight. These mechanisms changed somewhat over the programme.

This is well described in the Apollo Lunar Surface Journal (ALSJ above), which is an invaluable resource.

As a note, it's important to remember that the Sun is quite nasty above the atmosphere: the atmosphere absorbs about 77% of solar UV, and about 25% of all solar radiation. So if you are working on the Moon (or generally above the atmosphere) you really want protection from the Sun: even though the Moon has a fairly low albedo as a whole this is not something you want to rely on, and things like spacesuits and spacecraft are fairly reflective and often in your line of sight. You also need to worry about sunburn on your face as well as your eyes. Finally the Sun will dump quite a lot of heat (IR) into the suit unless you keep it out, which will certainly cause stress to the cooling system and also probably just be uncomfortably hot: think of how hot the Sun is on your skin on a completely cloudless day somewhere close to the equator: the flux hitting your face on the Moon is about 25% over that.

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    $\begingroup$ @LoveForChrist on the moon there is no atmosphere absorbing light so general illumination level is higher than anything found on earth, and sunglasses on earth are helpful enough a lot of people wear them even when not looking at the sun. Notably all the photos of lunar surface operations appear to be with them down, and most but not all ISS space walk photos are also visor down - so it looks like generally earth adapted eyes work better with some tinting between them and space sunlight. $\endgroup$ – GremlinWranger Jul 5 '20 at 12:27
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    $\begingroup$ The gold visor should not only protect the eyes of the astronaut, the skin of his face needed protection against sunburns too. $\endgroup$ – Uwe Jul 5 '20 at 14:11
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    $\begingroup$ Small point of correction: the moon has a very low albedo: approximately 0.12 to 0.14, which is about what you get from a decently aged asphalt road $\endgroup$ – Tristan Jul 6 '20 at 14:39
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    $\begingroup$ @Tristan: thank you, I did not know that! I will correct my answer. $\endgroup$ – user21103 Jul 6 '20 at 17:44
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    $\begingroup$ can we double check this: "a gold sun visor, which is to protect the astronaut's eyes from the Sun, and his face from sunburn" To my understanding the gold attenuates visible and especially thermal infrared light to keep it from being too bright, and from letting too much heat inside the suit putting demands on the suits cooling. Many types of tempered glass and plastics will already absorb ultraviolet, is it certain that UV even gets through the fixed window of the suit even without a visor? $\endgroup$ – uhoh Jul 7 '20 at 5:57

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