WEBVTT FILE

1
00:00:00.000 --> 00:00:04.000
We all know that black things get hot. Just look at these

2
00:00:04.000 --> 00:00:08.000
two identical cars. They’re made out of the same materials

3
00:00:08.000 --> 00:00:12.000
and yet the black one is going to be a lot hotter than the white one.

4
00:00:12.000 --> 00:00:16.000
And that is because it is absorbing a lot of those beautiful sun rays.

5
00:00:16.000 --> 00:00:20.000
Why is Webb’s Radiator Super Black?

6
00:00:20.000 --> 00:00:24.000
Now the James Webb Space

7
00:00:24.000 --> 00:00:28.000
Telescope has two important sides. A hot side and a cool side.

8
00:00:28.000 --> 00:00:32.000
The sunshield blocks the heat on the one side and the mirror observes

9
00:00:32.000 --> 00:00:36.000
on the cool side. It even has a radiator to keep it extra cool.

10
00:00:36.000 --> 00:00:40.000
But everything except the mirrors are black on the side

11
00:00:40.000 --> 00:00:44.000
that needs to be cool? So I was questioning why

12
00:00:44.000 --> 00:00:48.000
are Webb’s radiators coated in this super dark paint?

13
00:00:48.000 --> 00:00:52.000
This paint is made by Ball Aerospace and it’s called Ball Infrared

14
00:00:52.000 --> 00:00:56.000
Black or BIRB. And it’s somehow vital to regulating

15
00:00:56.000 --> 00:01:00.000
Webb’s temperature. So the reason temperature control is

16
00:01:00.000 --> 00:01:04.000
on this telescope is that the telescope observes in the infrared

17
00:01:04.000 --> 00:01:08.000
spectrum of light. Now we may not

18
00:01:08.000 --> 00:01:12.000
but we do perceive it as heat.

19
00:01:12.000 --> 00:01:16.000
And so to get data without any interference from Webb’s instruments

20
00:01:16.000 --> 00:01:20.000
they have to be cooled. I am so ready for this!

21
00:01:20.000 --> 00:01:24.000
To well below -400 degrees Fahrenheit.

22
00:01:24.000 --> 00:01:28.000
Webb’s instruments naturally

23
00:01:28.000 --> 00:01:32.000
create heat as they work, so the radiator

24
00:01:32.000 --> 00:01:36.000
radiates that heat out of it. I’m going to look

25
00:01:36.000 --> 00:01:40.000
and show you here. I’ve got a flashlight we use for inspections.

26
00:01:40.000 --> 00:01:44.000
If you look at it that shiny thing

27
00:01:44.000 --> 00:01:48.000
over here and then look how black that is.

28
00:01:48.000 --> 00:01:52.000
music

29
00:01:52.000 --> 00:01:56.000
So why are these radiators black?

30
00:01:56.000 --> 00:02:00.000
Well, as it turns out, things that absorb heat

31
00:02:00.000 --> 00:02:04.000
also emit heat well.

32
00:02:04.000 --> 00:02:08.000
Now the reason black objects absorb and emit heat well involves a lot of math

33
00:02:08.000 --> 00:02:12.000
and a thing called the Stephan-Boltzmann Law. But what it comes down to is that they are

34
00:02:12.000 --> 00:02:16.000
highly emissive. Emissivity is a measure of how

35
00:02:16.000 --> 00:02:20.000
well something radiates heat. And according to physics,

36
00:02:20.000 --> 00:02:24.000
and ideal radiator is an ideal absorber.

37
00:02:24.000 --> 00:02:28.000
I left this board outside for an hour and the side with the black paint

38
00:02:28.000 --> 00:02:32.000
absorbed a lot more solar radiation. And then I went back

39
00:02:32.000 --> 00:02:36.000
at night with the FLIR camera. The black side of the wood

40
00:02:36.000 --> 00:02:40.000
is cooler than the white paint. It is acting like a small radiator.

41
00:02:40.000 --> 00:02:44.000
So it released its energy from earlier in the day much more

42
00:02:44.000 --> 00:02:48.000
efficiently than side with the white paint.

43
00:02:48.000 --> 00:02:52.000
The more emissive a material, the more it can transfer heat.

44
00:02:52.000 --> 00:02:56.000
The Ball Infrared Black paint on Webb’s radiators

45
00:02:56.000 --> 00:03:00.000
happens to be one of the most emissive substances ever

46
00:03:00.000 --> 00:03:05.640
sent to space!

47
00:03:05.640 --> 00:03:05.643
music