Visors up during EVA

[agentsmith]

Hi, there are several pictures showing the astronauts in the sunlight with their gold visors up and it is also mentioned in the Lunar logs.
Can anyone explain this? Someone's brought it up on the forum I come from and I really don't know, any ideas?

[Count Zero]

What's to explain? The visor cuts down glare, but more importantly, it protects the astronauts against ultraviolet. Without UV protection, the astronauts would get a pretty good sunburn in 20 minutes or less.
On the other hand, the astronauts often can see better without the visor.

Whenever the ground catches the astronauts out in direct sunlight with their visor up, they bust them for it and tell them to put it back down.

(Notice that I'm using the present tense. The issue is alive and well to this day. The sunlight is just as bright in Earth orbit as it is on the Moon.)

[agentsmith]

How come the UV doesn't cause damage to their faces and eyes instantly? I was under the impression that it was pretty quick - or is it another example of information being taken out of proportion like the other types of Radiation.

Sorry, but I'll get asked all these questions!

[agentsmith]

Ah found the answer - it's in the visor material!

[Count Zero]

It depends on how much the glass helmet cuts down the UV. I consider "a few minutes" to be pretty quick.

I used the "20 minutes or less" figure as a ballpark guess. When I lived in the tropics, at midday the skin would start to redden after ~15-20 minutes. When the ozone hole moved over southern Chile a couple of years ago, they gave about the same figure to warn the populace (mind you, the Sun was be shining through almost twice as much air there as in the tropics). Without any air, the sunlight is ~20% stronger.

The only case of sunburn in space that I've heard of was one of the Gemini astronauts (I think it was Cernan, on Gemini 9) who tore a seam on the outer layer of his suit. The UV penetrated the pressure layer and gave him a bad burn on his back in 30-40 minutes.

I think a safe figure to use is 5-15 minutes to start reddening, which is reason for concern when you catch someone cheating on a 6-hour EVA.

[PhantomWolf]

The gold part of the visor is like a pair of sunglasses. They could get away with it for a while, but unlike a lot of claims, it was never going to be instant blindness. If the sun had been that intence the visor would have been immovable.

[JMV]

LEVA had two visors. The clear inner visor was called protective visor and the outer gold colored outer visor was called sun visor.
And here's a video clip showing these two visors:
spaceflight.nasa.gov/gallery/video/apollo/apollo11/mpg/apollo11_dlclip12.mpg

From Apollo Operations Handboook EMU:
"The protective visor is an ultraviolet-stabilized polycarbonate shield which affords impact, micrometeoroid, and ultraviolet ray protection. It can be positioned anywhere between the full-UP and full DOWN positions and requires a force of 2 to h pounds for movement. A coating is added to the inner surface of this assembly. The elastomer seal on the upper surface of the stiffener prevents light passage between the two visors. The protective visor can be lowered independently of the sun visor, but cannot be raised independently with the sun visor in the DOWN position.

The inner surface of the polysulfone sun visor has a gold coating which provides protection against light and reduces heat gain within the helmet. The visor can be positioned anywhere between the full-UP and full-DOWNpositions by exerting a force of 2 to h pounds on the pull tabs. The sun visor cannot be independently lowered unless the protective visor is in the DOWN position, but it can be raised or lowered independently when the center eyeshade is in the full UP position and the protective visor is in the DOWN position."

So even though we see Apollo astronauts with the sun visor raised, they still had the clear protective visor down to provide protection against ultraviolet rays.

[Count Zero]

Way cool! Thanks, JMV, and welcome to the board. Was that Buzz doing the demonstration?.

[Data Cable]

Aha! You can clearly see 2 artificial light sources in the visor reflection! It's a hoax! (sorry, somebody hadda say it )

[JMV]

countzero said:

Way cool! Thanks, JMV, and welcome to the board. Was that Buzz doing the demonstration?.

Thanks for the welcomes and yep, it's Buzz.

[JayUtah]

Lexan, the material used to make the visors, is naturally fairly opaque to ultraviolet. It is used today commercially to make "UV protective" eyeglasses. Even the "transparent" visors (the fishbowl helmet and the inner LEVA visor) offer protection.