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[MUSIC PLAYING]

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The James Webb
Space Telescope is

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what's known as a
reflector telescope,

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two mirrors-- one primary
and one secondary-- used

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to collect and focus light
coming from faraway objects

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they're looking at.

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The primary mirror
on James Webb is

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so huge it needs to be assembled
from 18 separate mirrors.

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To find out more
about these mirrors

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and how NASA's making sure they
work as well in space as they

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do on the ground, we've come
to the Marshall Space Flight

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Center in Huntsville, Alabama.

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We're here with Jeff Kegley.

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And he's the director of the
X-ray and Cryogenic Facility

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here at Marshall
Space Flight Center.

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So, Jeff, tell us a little
bit about where we are

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and what are you about to see?

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Mary, we are in the entry
area for our large clean room.

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These James Webb Space
Telescope mirrors

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have to stay in a very
clean environment.

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And we have that type
of environment here.

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So we're going to see
if we can get a better

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look at those mirrors.

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And to do that, we're
going to have to get

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dressed up a little bit so
that only our eyes are showing.

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We're just about to pull
the entire test and assembly

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into the vacuum chamber with
the three James Webb mirrors

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aboard.

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I notice there's
just three mirrors.

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Why is that?

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I think James Webb
has 18, right?

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Right, the James Webb Telescope
is made up of 18 mirrors.

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We're going to have each
one of those mirrors come

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through here twice.

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The first time
through, we actually

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measure the deformation as
a function of temperature

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as we transition down to
minus 400 degrees Fahrenheit.

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The second time
through, we verify

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that the mirrors actually
perform correctly

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at that temperature.

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And you said it's about
to go into the chamber.

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Can we go inside the chamber
just to see what it's like

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and maybe tell us a little
bit about the chamber?

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Yeah, we'll try to run in
there and see if we can

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beat this transition inside.

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The mirrors behind
us will be pulled in

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and will actually reside
just up in front of us

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here, inside the
chamber where they can

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be cooled to minus 400 degrees.

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Why a vacuum chamber?

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Well, we have to simulate not
only the thermal environment

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but also the vacuum
environment of space.

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You pull these in and
what kind of things

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are you looking
for in the mirror?

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Well, the Ball Aerospace
team is actually

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responsible for the testing.

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And they will
actually be looking

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at these mirrors
as they transition

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to a cryogenic temperature
through a window

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up in the front of
our vacuum chamber.

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And they'll be looking
at these mirrors

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with an instrument
called an interferometer.

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And that's going to give
them a very detailed surface

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map of what that
mirror looks like

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and how it deforms as a
function of temperature.

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And my last question
is, why is it

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so important to be so
precise with these mirrors?

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Well, the primary
mirror for a telescope

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is the part of the telescope
that really matters.

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It's gathering all the
light that ultimately

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gets focused on the instrument.

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And the larger and the
better the mirrors are,

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the better the telescope is.

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These mirrors will be
in the vacuum chamber

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for about 15 weeks, going
through seven cycles

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of temperature changes
from room temperature

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to the cold extreme of space,
414 degrees below zero.

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Thanks again for joining
us Behind the Webb.

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[MUSIC PLAYING]

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