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Mary Estacion/Reporter: One of the reasons the 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, CA.
So Ed, what's going on here? Ed Boese/JWST Manufacturing Supervisor: Well,
we're shaping the mirror using several different processes to take it down to about 20 nanometers
of surface error, which is about 1/5 the diameter of a human hair.
Mary: What else are you trying to get rid of?
Ed: We have to remove fine stratches down to about 8/1000ths 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. Ed: 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 pro- cess.
He's removing it off the part using a solvent.
Mary: The solvent he's using... is it just Windex
or is it much more particular than that? Ed: No, 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 and acetone it.
Mary: Ed showed us the cleaning of the mirrors, so what's going on here?
Robert: 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. Mary: Could you do this by hand?
Robert: People used to do this by hand, but you could not make these mirrors by hand.
It would be very difficult not to have residual texture in these mirrors.
Mary: It looks like water, is it water? Robert: 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 Mary: So Robert, it kind of reminds of what
women try to do, exfoliate their skin, trying to get rid of that top layer of skin cells,
to show a brighter layer underneath? Robert: Well, the mirror surface, when it
comes to this process has a texturing on it, 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.
Robert: If it has roughness in it, it won't perform well, because each little lump and
bump on the surface 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.
Mary: Well, thanks a lot for showing us this. Robert: Thank you.
Mary: So, these processes the mirrors go through, like the rough polishing 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 on another edition of Behind the Webb.