
Why does NASA use gold foil on equipment and gold-coated visors? - jonbaer
http://physics.stackexchange.com/questions/74412/why-does-nasa-use-gold-foil-on-equipment-and-gold-coated-visors
======
abstractbill
The question and answer are both quite fascinating. But I think they hint at
something potentially even more interesting: To figure out that they needed to
coat visors with gold, without doing it by trial-and-error and frying a few
retinas in the process, the level of planning and attention to detail in the
early days of NASA must have been phenomenal. I'd love to know more about how
they knew they had asked all the right questions.

~~~
kens
If you can dig up a copy of the 1962 book "Space Medicine" by U. Slager, it's
really interesting. It makes you realize how many questions they needed to
answer experimentally before going into space. For example, how much
acceleration can someone withstand. How much vibration and tumbling. Minimum
and maximum survivable temperatures. How long can you be exposed to a vacuum.
This was the era of putting people on rocket sleds to see what happens (
[http://en.wikipedia.org/wiki/John_Stapp](http://en.wikipedia.org/wiki/John_Stapp)
). My favorite factoid from that book is that guppies can tolerate 10000G for
30 sec. It also describes a guy who survived 482 degrees F for 4 minutes.

~~~
Keyframe
_guy who survived 482 degrees F for 4 minutes_

Can you give some more details about this?

~~~
kens
I messed up °F/°C and it was "only" 250°F. I don't have the book "Space
Medicine" available, but I found a different reference† explaining that it was
Dr. Charles Blagden and other researchers in 1774 who went into a room heated
above 250°F and cooked steak and eggs in there, proving the importance of
perspiration in maintaining body temperature. It has to be dry heat; if there
is humidity, the tolerable temperature is much lower. The original paper ‡ is
also online; in order to read it, note that "ſ" is a "long s", not a "f".

†
[http://news.google.com/newspapers?nid=1499&dat=19560213&id=4...](http://news.google.com/newspapers?nid=1499&dat=19560213&id=4VQaAAAAIBAJ&s)

‡
[http://rstl.royalsocietypublishing.org/content/65/484.full.p...](http://rstl.royalsocietypublishing.org/content/65/484.full.pdf+html)

~~~
wazoox
For people of the world, that's about 121°C. BTW, I've been in a sauna in
Sweden where the thermometer displayed 100°C. The women sauna, according to my
mother, was only 96°C.

~~~
gnerd
Out of interest, was that the ambient temperature or was the thermometer
placed above the source of steam?

~~~
sambeau
They normally keep the thermometer on the opposite wall to the source of heat.

------
zanny
This just reminds me how horribly stifling it is to the entirety of science
that so many people love hoarding bricks of gold in underground vaults rather
than use it for productive purposes. Besides the maliability and corrosion
resistance mentioned in the article, it is also a strong conductor, and very
good at heat transfer.

It has so many practical useful purposes besides rotting in a bank vault. But
a lot of that potential is wasted on those that value it so highly for its
scarcity rather than its utility. Why can't we just hoard iron oxide?

~~~
kevin_rubyhouse
Is there not a way to synthesize gold, like how diamonds can be synthesized
(obviously a different process.) I searched around, and I guess there isn't a
good process for this, yet.

Also, how much could NASA really be spending on gold, anyway? They're already
spending billions on the rest of their space program.

~~~
Tuna-Fish
Gold, being an element, needs nuclear processes for manufacture instead of
chemical processes (like diamond). Before modern particle accelerators, this
was flatly impossible, and even today, it is very, very hard and expensive.
The cost to produce an amount of gold like this is millions of times more than
it's value.

Somewhat interestingly, gold is actually being actively destroyed in particle
accelerators, as it has several properties that makes it a desirable target.
As my professor once put it, we finally have the secrets the alchemists only
dreamed of, and we use them to _destroy_ gold.

~~~
shabble
I have a rather vague recollection that gold has been transmuted from other
elements in experimental (fission, I presume) reactors as well, although the
best reference I can find right now is [1]. Accelerators do seem to be the
modern/"practical" approach though.

Which properties in particular make it a good target?

Edit: more details from wikipedia[2] suggest starting from either mercury or
platinum, although it's all a bit fiddly and isotope-specific. That page has
some other interesting facts as well - I'd never really thought of element
synthesis as economically practical (and with capital equipment costs,
probably still isn't), but tungsten ($30/kg) -> rhenium ($6k/kg) -> osmium
($12k/kg) sounds like a nice business to be in if you can solve the practical
problems.

When the balloons all run out, we might want to start making our own helium as
well, which has the bonus of being really quite easy to do.

[1]
[http://chemistry.about.com/cs/generalchemistry/a/aa050601a.h...](http://chemistry.about.com/cs/generalchemistry/a/aa050601a.htm)

[2]
[https://en.wikipedia.org/wiki/Synthesis_of_precious_metals#G...](https://en.wikipedia.org/wiki/Synthesis_of_precious_metals#Gold_synthesis_in_a_nuclear_reactor)

~~~
bradleyjg
Gold has a large cross section, which basically means it presents a big target
(amusingly such measurents are made in units of 'barns'). It's also stable, so
you don't have to worry about natural decay events polluting your data.

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sp332
Gold would be silver-colored if it weren't for special relativity.
[http://www.fourmilab.ch/documents/golden_glow/](http://www.fourmilab.ch/documents/golden_glow/)

------
ianstallings
It's not actually gold foil, it's typically a mettalised polymer film, Kapton.
This becomes part of a multi-layer insulation material where each layer is
composed of a different material that has certain advantageous properties,
with all of the layers separated by a small shim between them to avoid thermal
conduction.

I really gotta stop playing so much Kerbal Space Program.

~~~
stevenrace
Most of the shiny 'gold' things seen in aerospace and motorsports is just
vapor deposited Kapton/polymide.

But there are applications where gold is indeed used - but it's unclear (in
the literature I've read) when/where it's appropriate to use gold. The helmet
use case I can believe. I also imagine large swathes of gold would be
problematic - structural surfaces being unnecessarily conductive or
introducing inductive noise.

~~~
jloughry
The US Navy EA-6B Prowler, an airplane that emits a LOT of radio frequency
energy, has a conductive gold layer on its canopy for Faraday cage reasons, to
protect the crew from the radar jammer.

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tobiasu
You can buy your own space age gold foil from many places as "rescue blanket".
Quite cheap, around $3 for an adult sized sheet.

I've used it to insulate south-facing windows in summer. It's phenomenally
effective.

~~~
nether
The gold color in this case comes from the compound kapton, versus the
elemental gold deposited on space helmet visors.

[https://en.wikipedia.org/wiki/Space_blanket#Manufacturing](https://en.wikipedia.org/wiki/Space_blanket#Manufacturing)

[http://spinoff.nasa.gov/spinoff1997/hm2.html](http://spinoff.nasa.gov/spinoff1997/hm2.html)

------
speeder
I dunno how it is in the US, but here in Brazil, firemen also use gold-plated
helmets.

I once in a first aid training asked one fireman that was present to borrow me
his helmet, because I was doubting you could see through it (I was 12).

The nice man put the helmet correctly on my head, and to my surprise, I really
could see! Everything was blue, but I could see everything, it was really
cool.

This article explained to me WHY I could see... I was still puzzled (I thought
gold reflected 100% of visible light)

~~~
ars
> I thought gold reflected 100% of visible light

It depends on how thin it is. There is no 100%, the thinner the more is
transmitted (weighted by the curve shown in the linked article). A solid block
of steel would be transparent if you illuminated it with enough light.

------
sehugg
Note that in the 1960s gold was valued at a fraction of the cost of launching
its weight into orbit.

~~~
mh-
so you're saying we should go on an orbital prospecting trip.

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mistercow
I have known for a while (since I read Quicksilver) that gold becomes visibly
transparent if you hammer it thin enough, and transmits greenish light, but I
have never been able to find a picture of this or a video of someone
demonstrating it. How is this possible?

~~~
mercuryrising
You've seen it before... Stained glass. Stained glass was one of the first use
of nanoparticles and plasmonics to become commonplace. The wide range of
colors that you can get in stained glass is due to the nano properties of the
materials you add to the glass. The effect is due to surface plasmons -
electric field waves that travel on the surface of conductors. Much like ocean
waves, plasmons are created from light's electric field. They bounce back and
forth, and since they are only permitted on the surface of a material, there
are limits on what waves can exist. This is what gives them the weird
properties - the size and shape determine the optical properties.

On another tangent (this one's pretty cool) - since you can tune the
properties of these nanoparticles, you can make them respond in a specific
way. Let's say we have a cancer cell that we want to kill, and only that
cancer cell should die. We can create nanoparticles that bond with that cancer
cell, and only that cancer cell. But how do we kill it? We can tune the
absorption spectrum of the nanoparticle to absorb infrared light - light that
is transparent to the human body. We create a small heater that absorbs tons
of the input energy, while keeping the rest of the area cool. Localized
heating destroys the nearby cancer cell.

Plasmonics are really cool -
[http://en.wikipedia.org/wiki/Plasmon](http://en.wikipedia.org/wiki/Plasmon)

[http://en.wikipedia.org/wiki/Plasmonic_Nanoparticles](http://en.wikipedia.org/wiki/Plasmonic_Nanoparticles)

------
twoodfin
I am surprised that I can't find evidence of consumer gold foil sunglasses.
Are the optical properties really terrible for day-to-day use? I'd think
they'd be pretty sharp looking, and the cost of the gold shouldn't be
prohibitive.

~~~
speeder
As I noted elsewhere, gold visor make you really see everything blue. I think
few people would tolerate it.

~~~
Myrth
Would feel like playing BF3 all the time

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Datsundere
This reminds me of uchuu kyodai or the space brothers anime where hibito wraps
his comadre's body with a gold like foil to keep his body warm but also to
reflect sunlight when it gets too hot. This anime is pretty realistic and I
recommend you watch it if you'd like to know what it takes to be an astronaut.

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mmahemoff
Reminds me of the movie Sunshine, with their striking gold space suits. I
thought it was just for theatrical effect until I read it was actually based
on this theory.

 _The gold-leaf shielding in Sunshine was influenced by NASA satellite designs
for deflecting heat and other forms of radiant energy. Boyle designed the
gold-coloured space suits along these lines despite persistent encouragement
to model them after the NASA template._

[http://en.wikipedia.org/wiki/Sunshine_(2007_film)](http://en.wikipedia.org/wiki/Sunshine_\(2007_film\))

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sgt101
I am not qualified to understand the chemistry, but I got the idea from
somewhere that the ionization of the atmosphere filled near earth space a
highly corrosive environment because a large number of liberated hydrogen
atoms were present. Gold is inert and therefore not subject to the corrosion
that would otherwise take place, and also would not catalyse other material.

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kaiserama
Maclaren also lined the engine bay of the 90's F1 road going car with gold.
Additionally many of my friends who highly modify their turbo charged cars
line the interiors with gold foil (although I can't help but think this is
mostly for aesthetics :).

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6cxs2hd6
I misread this headline as "NSA".

Time to take a break from HN, I guess.

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coldtea
Because NASA is all about the bling.

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mercuryrising
Doesn't it look cooler if we use gold? Short of practical purposes, if you
have something that you need to convince a politician to support, wouldn't
gold be better than silver for no reason other than it looks good?

~~~
wmf
I suspect painting it red white and blue would have been even better for
political support.

~~~
mpyne
The Admiral in charge of the group that designs nuclear submarine propulsion
plants had a famous quote about switching the naming of American submarines
away from fish to things like U.S. cities, states, etc. as being because "fish
don't vote on our budget".

~~~
cynwoody
Religious objections were raised when they got around to naming a nuclear fast
attack submarine after Corpus Christi. That's why SSN-705 was christened† the
_City of Corpus Christi,_ rather than just the _Corpus Christi._

†[http://en.wikipedia.org/wiki/USS_City_of_Corpus_Christi_(SSN...](http://en.wikipedia.org/wiki/USS_City_of_Corpus_Christi_\(SSN-705\))

