[MUSIC PLAYING]
The James Webb Space Telescope is
what's known as a reflector telescope,
two mirrors-- one primary and one secondary-- used
to collect and focus light coming from faraway objects
they're looking at.
The primary mirror on James Webb is
so huge it needs to be assembled from 18 separate mirrors.
To find out more about these mirrors
and how NASA's making sure they work as well in space as they
do on the ground, we've come to the Marshall Space Flight
Center in Huntsville, Alabama.
We're here with Jeff Kegley.
And he's the director of the X-ray and Cryogenic Facility
here at Marshall Space Flight Center.
So, Jeff, tell us a little bit about where we are
and what are you about to see?
Mary, we are in the entry area for our large clean room.
These James Webb Space Telescope mirrors
have to stay in a very clean environment.
And we have that type of environment here.
So we're going to see if we can get a better
look at those mirrors.
And to do that, we're going to have to get
dressed up a little bit so that only our eyes are showing.
We're just about to pull the entire test and assembly
into the vacuum chamber with the three James Webb mirrors
aboard.
I notice there's just three mirrors.
Why is that?
I think James Webb has 18, right?
Right, the James Webb Telescope is made up of 18 mirrors.
We're going to have each one of those mirrors come
through here twice.
The first time through, we actually
measure the deformation as a function of temperature
as we transition down to minus 400 degrees Fahrenheit.
The second time through, we verify
that the mirrors actually perform correctly
at that temperature.
And you said it's about to go into the chamber.
Can we go inside the chamber just to see what it's like
and maybe tell us a little bit about the chamber?
Yeah, we'll try to run in there and see if we can
beat this transition inside.
The mirrors behind us will be pulled in
and will actually reside just up in front of us
here, inside the chamber where they can
be cooled to minus 400 degrees.
Why a vacuum chamber?
Well, we have to simulate not only the thermal environment
but also the vacuum environment of space.
You pull these in and what kind of things
are you looking for in the mirror?
Well, the Ball Aerospace team is actually
responsible for the testing.
And they will actually be looking
at these mirrors as they transition
to a cryogenic temperature through a window
up in the front of our vacuum chamber.
And they'll be looking at these mirrors
with an instrument called an interferometer.
And that's going to give them a very detailed surface
map of what that mirror looks like
and how it deforms as a function of temperature.
And my last question is, why is it
so important to be so precise with these mirrors?
Well, the primary mirror for a telescope
is the part of the telescope that really matters.
It's gathering all the light that ultimately
gets focused on the instrument.
And the larger and the better the mirrors are,
the better the telescope is.
These mirrors will be in the vacuum chamber
for about 15 weeks, going through seven cycles
of temperature changes from room temperature
to the cold extreme of space, 414 degrees below zero.
Thanks again for joining us Behind the Webb.
[MUSIC PLAYING]