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Old 05-05-2006, 09:49 AM
Phlosphr Phlosphr is offline
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Why the Gold Foil on space objects like Satellites and then like?

I am watching the Science channel and they are showing the voyager and galelio space crafts and their passes by the moons of Saturn and Jupiter, I noticed they have copious amounts of gold foil... then I got to thinking NASA likes to use the gold foil for a lot of their space crafts if not all of them...

My question if why the gold foil and not some other color, like silver foil or some other such color distinction? Is there a special purpose for that color?
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  #2  
Old 05-05-2006, 10:02 AM
Squink Squink is offline
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Wag:

Gold is a better reflector than silver or aluminum at infrared wavelengths.
Gold coatings are more durable than silver coatings.
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Old 05-05-2006, 10:40 AM
RickJay RickJay is offline
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Quote:
Originally Posted by Phlosphr
I am watching the Science channel and they are showing the voyager and galelio space crafts and their passes by the moons of Saturn and Jupiter, I noticed they have copious amounts of gold foil... then I got to thinking NASA likes to use the gold foil for a lot of their space crafts if not all of them...

My question if why the gold foil and not some other color, like silver foil or some other such color distinction? Is there a special purpose for that color?
It's not the color, it's the material.

Spacecraft have a heat buildup problem; the electronic systems and such they contain generate heat, which is its own engineering challege to get that heat dumped out into space. So they can't take on too much heat from solar radiation or they'll just fry up. Thus, they must be made to reflect that radiation.

Gold is exceptionally good at reflecting solar radiation, much better than any other substance. Lots of materials wil lreflect visible light, but as Squink points out gold's especially effective at reflecting infrared. Gold is also more or less inert, very dense, and will last forever.
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Old 05-05-2006, 10:43 AM
mks57 mks57 is offline
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It's metallized Kapton® polyimide film, not gold foil.
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Old 05-05-2006, 11:11 AM
Triskadecamus Triskadecamus is offline
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When asked by the House appropriations committee why NASA wanted to plate a rather lengthy list of parts with gold, the scientist being interviewed replied, "Because solid gold would be too heavy, and too expensive."

Tris
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"If God had intended for man to go to Mars, He would have given us more money." ~ an unnamed NASA official ~
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Old 05-05-2006, 11:28 AM
scr4 scr4 is online now
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mks57 is correct. MLI (multi-layer insulation, aka thermal blanket) is made up of many layers of aluminized polyimide. Polyimide is a type of plastic, and yellow in color. It's coated with aluminum on the inside surface so it looks gold.

Bare aluminum reflects radiation very well, which means it absorbs heat very slowly. But it also radiates heat VERY slowly. An aluminum foil sitting in vacuum in direct sunlight will heat up to a pretty high temperature. Plastic film with aluminum backing absorbs heat a little faster, but it also radiates heat a lot faster, so it works better as the outer-most layer of the MLI.

Quote:
Originally Posted by Triskadecamus
When asked by the House appropriations committee why NASA wanted to plate a rather lengthy list of parts with gold...
They may have been talking about electrical contacts, or optical elements. Gold has a good reflectivity in the infrared, and gold coating is often used on infrared mirrors. And I believe the visor on the Apollo spacesuits were coated with gold for the same reason (reflecting/rejecting infrared).
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Old 05-05-2006, 11:39 AM
scr4 scr4 is online now
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p.s.

They don't have to use something yellow. Polyimide just happens to be an excellent material for this application. It has excellent heat resistance, strength and durability. And more importantly, it has excellent outgassing properties - that is, it doesn't emit a lot of gasses that can contaminate delicate instruments on the spacecraft. Other plastics emit a lot of nasty hydrocarbons, especially when new. (That's what "new car smell" is - outgassing from all the new plastic parts.)
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Old 05-05-2006, 11:40 AM
Cerowyn Cerowyn is offline
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Quote:
Originally Posted by scr4
And I believe the visor on the Apollo spacesuits were coated with gold for the same reason (reflecting/rejecting infrared).
The Royal Bank Plaza in Toronto has gold leaf covered windows for their insulating properties.
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Old 05-05-2006, 12:24 PM
Beware of Doug Beware of Doug is offline
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I always figured it was to help justify the budget overruns.
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Old 05-05-2006, 12:29 PM
Bryan Ekers Bryan Ekers is offline
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You want maybe the ETs think we're a bunch of cheapskates?
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Old 05-05-2006, 06:59 PM
Snooooopy Snooooopy is offline
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Unbeknownst to most of the children who watched Saturday morning cartoons in the 1980s, Gargamel had a contract with NASA to deliver gold for satellite parts. THAT'S why he wanted to capture the Smurfs, who selfishly would not do their part in the exploration of space.
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  #12  
Old 05-05-2006, 09:41 PM
Staggerlee Staggerlee is offline
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Quote:
Originally Posted by scr4
p.s.

They don't have to use something yellow. Polyimide just happens to be an excellent material for this application. It has excellent heat resistance, strength and durability. And more importantly, it has excellent outgassing properties - that is, it doesn't emit a lot of gasses that can contaminate delicate instruments on the spacecraft. Other plastics emit a lot of nasty hydrocarbons, especially when new. (That's what "new car smell" is - outgassing from all the new plastic parts.)
That is great. This reminded me; can you just have a material which simulates gold's reflective properties without the expense? Like maybe buy it off those blokes selling chrome-effect-novelty-balloons?

Ps. Or is it gold's plain density?

Pps. And if so, why not lead too?
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