[MUSIC PLAYING]
We're at the High Bay at Northrop Grumman,
where we are about to get a bird's eye view of the sun
shield.
To tell us more about the sun shield, which is actually
made up of five layers of a material called Kapton,
we have Andy Tau.
He's the chief engineer for the sun shield.
Andy, tell us, first of all, what is the sun shield for?
Well, the sun shield's main purpose
is to keep the energy from the sun
from getting to the telescope.
JWST looks for very faint, basically thermal objects
out in space.
It's important to keep things really cold.
So if we were to allow the telescope to heat up,
the warmth of the telescope itself
would just swamp out the sensors.
And it wouldn't be able to see anything except its own heat.
The second thing is just to keep out the visible light also.
The visible light can get inside the optical train
and cause all kinds of interference.
So we want to keep that out too.
Now, Andy, I mentioned before it has five layers
of a material called Kapton.
Before I ask you why five, what's Kapton?
Kapton is essentially a space-age plastic film
material.
It's something that's been developed
for a number of years.
And we actually use it in our thermal insulation material.
OK.
And five layers, why is that?
Five layers, well, six would be too many.
And four would be too few.
You've got this down.
Yeah.
Well, it actually has to do with the amount of energy
that we need to reject from the sun.
The sun is putting in a certain amount of energy.
And we need to reject that and make sure it
doesn't get to the telescope.
The sun shield is built so that there's
an angle between each one of the layers.
So heat that comes off of the layer one gets
bounced out and actually gets rejected out the sides.
So if the spacecraft was down here,
we actually have a couple of holes in the sun shield
that allow heat to come up from the spacecraft
and get pumped out through the sides.
So the sun shield is sort of like a giant heat
pump, passive heat pump.
This is the-- not the flight hardware, right?
This is actually just a test article.
That's right.
This is one of our series of development articles
and a very important one.
It's full size.
And it's pretty close to flight.
But there's some important differences.
All right, ready to come down?
Coming down.
Oh, boy.
These layers that you see right now
actually will be coated with a vapor-deposited aluminum.
OK.
And that aluminum, which you see here
on the underside of the thermal covers, is 99.99% reflective.
So that helps a lot when we're trying
to bounce all that thermal energy out of the sun shield.
OK.
Now, the kind of pinkish-purplish part
is actually a silicon layer.
And that's the one that's exposed to the sun?
That's right.
But we use the aluminum, the super highly reflective
aluminum everywhere else that we can to reject the heat.
All right.
Thanks a lot.
The silicon layer actually protects the sun shield
during launch.
And when the James Webb Space Telescope observatory
reaches its destination one million miles from Earth,
this silicone cover gets deployed.
Thanks for joining us for another edition
of Behind the Webb.