3

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.)?

T.J.L.
  • 284
  • 2
  • 16
LoveForChrist
  • 2,233
  • 9
  • 24

1 Answers1

8

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.

  • 2
    @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. – GremlinWranger Jul 05 '20 at 12:27
  • @GremlinWranger Thank you. But the comparison to sunglasses is not good, sunglasses aren't necessary ever. I think we can compare the visor more to solar eclipse glasses. – LoveForChrist Jul 05 '20 at 12:31
  • 1
    @LoveForChrist: I've added a note to the answer: the Sun is bright and has a lot of UV above the atmosphere. –  Jul 05 '20 at 12:32
  • @tfb Thank you. – LoveForChrist Jul 05 '20 at 12:33
  • @LoveForChrist: Sunglasses are necessary on Earth. If you work in bright sunlight in an environment with high albedo, such as snow, your eyes will hurt and eventually you will go blind. –  Jul 05 '20 at 12:34
  • @tfb Uh, and how do Eskimos solve that? – LoveForChrist Jul 05 '20 at 12:36
  • Also, do all or many spacecraft have shaded glass then? – LoveForChrist Jul 05 '20 at 12:43
  • @LoveForChrist all the many windows in the shuttle filtered out UV except for the side hatch window, which had a removable filter and a big warning sign. https://space.stackexchange.com/a/31025/6944 The sign mentioned sunglasses. BTW Inuit used snow goggles. – Organic Marble Jul 05 '20 at 13:10
  • @OrganicMarble Thank you. Of course present-day Inuit can use goggles but how did they get along in the Middle Ages is the question here. – LoveForChrist Jul 05 '20 at 13:12
  • @LoveForChrist they were carved out of bone or wood with slits in them. https://www.canadashistory.ca/explore/first-nations,-inuit-metis/inuit-snow-goggles – Organic Marble Jul 05 '20 at 13:12
  • 1
    @OrganicMarble Very interesting. – LoveForChrist Jul 05 '20 at 13:14
  • 2
    The gold visor should not only protect the eyes of the astronaut, the skin of his face needed protection against sunburns too. – Uwe Jul 05 '20 at 14:11
  • 1
    @Uwe: very good point, I have added that. –  Jul 05 '20 at 16:14
  • 3
    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 – Tristan Jul 06 '20 at 14:39
  • 2
    @Tristan: thank you, I did not know that! I will correct my answer. –  Jul 06 '20 at 17:44
  • 2
    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? – uhoh Jul 07 '20 at 05:57
  • 1
    How does the thin gold film in the glass of spacesuit helmets block thermal IR but transmit visible? What's the property? – uhoh Jul 07 '20 at 05:58
  • 1
    @uhoh: yes, you're right, I have the things swapped. I'll repair the answer. –  Jul 07 '20 at 11:22