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Post by ka9q on Nov 22, 2010 3:25:18 GMT -4
Thin coatings of actual gold are sometimes used in spacecraft, particularly to stop infrared. The Apollo EVA visor is probably the best known example.
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Post by Apollo Gnomon on Nov 22, 2010 18:09:04 GMT -4
The visor was also coated with gold to give a color-neutral light reduction. Aluminum, also a good IF reflector, gives a bluish (if I remember - I looked it up a while ago) cast to the light that comes through.
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Post by ka9q on Nov 23, 2010 3:17:10 GMT -4
Gold is color neutral?
I know, it's yellow by reflected light, and transmitted light might be a different story.
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Post by tedward on Nov 23, 2010 8:28:28 GMT -4
I keep forgetting there more to light than the bits we see.
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Post by Apollo Gnomon on Nov 23, 2010 14:55:42 GMT -4
The gold visors came up at one point because someone (don't remember) was arguing about the color of the moon. This was in the "aussie genius" thread at Delusional Idiots. www.utilisegold.com/assets/file/utilisegold/pdf/Langley_4_4.pdfThis report states that some of the "gold" film was actually gold, not aluminum viewed through the amber kapton as described recently by JayUtah - specifically on the rover camera, batteries and some of the ALSEP stuff. The yellow color of the electroplated gold film is reflective, not transmissive. The electroplated gold layer is just a thin smear of metal particles, each opaque. I'll try to hunt down some of the information. It's interesting if like that kind of thing.
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Post by ka9q on Nov 25, 2010 5:40:18 GMT -4
Yes, it is interesting. Thanks. The paper you cited says that the main reason for using gold as a visible/near IR reflector instead of aluminum (which is a better reflector) was the greater maturity of the processes for depositing gold. That has probably changed in the past few decades. Note also the quoted price for gold - only $1/gram!
The other property of gold that they cited was its low emissivity in the far IR, used as part of a mixture specifically to absorb solar heat and get as hot as possible. This is not the property you want in a thermal covering designed to keep something cool!
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Post by gonetoplaid on Nov 27, 2010 8:52:52 GMT -4
The visor was also coated with gold to give a color-neutral light reduction. Aluminum, also a good IF reflector, gives a bluish (if I remember - I looked it up a while ago) cast to the light that comes through. Very true -- at least with older coating technologies. For example, older aluminized Mylar solar filters for amateur telescopes yield a very bluish cast when viewing the Sun through them.
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