[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.