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One of the reasons that James Webb Space Telescope will
usher in a new era of astronomy is its unique set of mirrors.
To perform at their very best, these mirrors
need to be shaped with exact precision.
To find out just how that gets done,
we're here at L3-IOS-Tinsley in Richmond, California.
So, Ed, what's going on here?
Well, we're shaping the mirror using
several different processes to take it
down to about 20 nanometers of surface area,
which is about one fifth the diameter of a human hair.
What else are you trying to get rid of?
We have to remove fine scratches down
to about eight thousandths of an inch.
Anything wider than that and it starts
to reflect light and diffuse it, so you don't get a good image
off the telescope.
So we're removing the grinding compound.
Actually, it's a rough polish compound and beryllium
that's actually on the surface of the mirror.
And we have to clean it before we go on to the next process.
He's removing it off of the part using a solvent.
The solvent he's using, is it just Windex or much more--
No, we can't use Windex.
It has chemicals in it that will actually
attack the surface of the beryllium
and cause it to corrode.
So we have to use a isopropyl alcohol in order
to clean the part and acetone.
Robert, Ed showed us the cleaning of the mirrors.
So what's going on here.
After rough polishing, we have to get rid
of the texture that's left on the surface.
The smoothing process will plane over that texture
and give us a true mirror surface.
Could you do this by hand?
People used to do this by hand, but you could not
make these mirrors.
It'd be very difficult to not have residual texture
in these mirrors.
It looks like water.
Is it water?
No, it's not water.
It has a fine, abrasive particle in it
and some other chemistries that we
know work well with beryllium.
Beryllium is a very difficult metal to polish.
So, Robert, it kind of reminds me
of what women tried to do-- exfoliate their skin,
trying to get rid of that top layer of skin cells
to show a brighter layer underneath.
Well, the mirror surface, when it comes to this process,
has a texturing on it.
And so this process will take the little peaks,
saw it off, saw it off until, finally, you
have this perfect plane.
And these are not flat mirrors, but you want that surface
to be just very continuous.
If it has roughness in it, it won't perform well.
Because each little lump and bump on the surface
then reflects light in a different direction.
And so it doesn't come back to the detectors.
So this process helps it to be extremely uniform
so you have the maximum amount of surface area returning
the light for you.
Well, thanks a lot for showing us this.
Thank you.
So these processes the mirrors go through,
like the rough polishing and the smoothing,
are done over and over again to make
sure the mirrors on the James Webb Space Telescope
have a smooth surface and the correct shape.
Thanks for joining us for another edition
of Behind the Web.
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