When you look at NASA's James Webb Space Telescope you can't help but
see the huge gold mirrors.
But that gold is really only on the surface the rest of the mirrors
mirrors are made out of a metal called beryllium.
Why does Webb have beryllium Mirrors. Elements of Webb
Let's head to the shop that worked on these mirrors to get a better idea about why
why this metal is so remarkable.
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I’ll just follow the noises.
Engineers chose beryllium for 3 major reasons.
It is super lightweight.
It is the second lightest of all the metals and only two thirds the weight
aluminum. It's super strong.
Beryllium is 6 times stiffer than steel.
Each of these cantilevered weights are the same
except for the type of metal. They are the same length, the same weight
and size. Look at what happens when they are lifted
and released at the same time. The beryllium wiggles with less intensity
and stops moving first. That is because it is far
stiffer than the other two. So it can also hold its shape
over really broad range of temperatures, and that's especially important in the colds ones.
I measured these identical aluminum and beryllium mirrors,
and left them in some dry ice for a while. Science.
I admit, that my measuring technique could used some work
But the aluminum shrunk more than the beryllium.
Materials tend to change in shape, volume, and density
in response to temperature. When something is heated up,
the molecules begin to vibrate more and separate, a little. The amount the material
changes is predictable and is based on its
coefficient of thermal expansion. So beryllium it stops shrinking and changing
its size when it cools below 100 Kelvin.
So the mirrors we see are a little too large on Earth
and will be the exact size they need to be once they are out in space.
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Beryllium is obviously an incredible material.
But everything does have its nuances.
So, why isn’t beryllium used more often?
Machining beryllium requires extreme care. If you think about it,
beryllium is actually a powder
that is pressed together and requires
very very light cuts. Any small mistake it would crack,
and there would probably be a piece that would fall off.
And you've lost a part that can be worth anywhere between
between $1,800.00 to $2,000.00 a pound.
Under the wrong circumstances, beryllium may be fragile, and it's fairly expensive.
But it holds its shape well, is very stiff and most
most importantly it's light weight. Rockets need a lot of fuel
for each pound of payload, so any weight saving measures
are really really worth it.
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