WEBVTT FILE

1
00:00:00.000 --> 00:00:04.000
I am off to go find the coldest thing that I can get my hands on.

2
00:00:04.000 --> 00:00:08.000
And I cannot think of a more fitting

3
00:00:08.000 --> 00:00:12.000
place than this.

4
00:00:12.000 --> 00:00:16.000
Speaking of cold things, we all know that canned air

5
00:00:16.000 --> 00:00:20.000
can get things cold. But why? This can has

6
00:00:20.000 --> 00:00:24.000
pressurized liquid difluoroethane.

7
00:00:24.000 --> 00:00:28.000
Now difluoroethane has a really low boiling point. That means, when I

8
00:00:28.000 --> 00:00:32.000
push the nozzle, it escapes really quickly because it is boiling away.

9
00:00:32.000 --> 00:00:36.000
Now we use something else with a really low boiling point. In fact, it is

10
00:00:36.000 --> 00:00:40.000
the lowest of all the boiling points, to cool things

11
00:00:40.000 --> 00:00:44.000
on the James Webb Space Telescope. And that element is helium.

12
00:00:44.000 --> 00:00:48.000
How does helium make stuff cold?

13
00:00:48.000 --> 00:00:52.000
Helium's low boiling point has come

14
00:00:52.000 --> 00:00:56.000
in handy in a number of ways on this mission. The Webb Telescope traveled

15
00:00:56.000 --> 00:01:00.000
from Goddard Space Flight Center to John Space Center to be tested

16
00:01:00.000 --> 00:01:04.000
in Chamber A. now this is the only thermal vacuum chamber

17
00:01:04.000 --> 00:01:08.000
chamber large enough to fit Webb. Chamber A even got an upgrade

18
00:01:08.000 --> 00:01:12.000
so it can use helium to get even colder.

19
00:01:12.000 --> 00:01:16.000
We also use helium in a special refrigerator called a cryocooler on the telescope itself.

20
00:01:16.000 --> 00:01:20.000
Now one of the reasons that Webb has a cryocooler

21
00:01:20.000 --> 00:01:24.000
is because it has to operate at very cold temperatures. This is because it detects

22
00:01:24.000 --> 00:01:28.000
in the infrared spectrum of light. Infrared is something we experience

23
00:01:28.000 --> 00:01:32.000
as heat. And so the telescope needs to be as cold to avoid any sources of heat

24
00:01:32.000 --> 00:01:36.000
that do not come from the cosmos.

25
00:01:36.000 --> 00:01:40.000
Webb in fact is so sensitive to any infrared light, that the science instruments

26
00:01:40.000 --> 00:01:44.000
need to be cooled to avoid detecting heat it creates by just operating!

27
00:01:44.000 --> 00:01:48.000
Three of the instruments are cooled passively by sitting

28
00:01:48.000 --> 00:01:52.000
on the cool side of the sunshield. The last instrument, MIRI

29
00:01:52.000 --> 00:01:56.000
needs to be cooled more than the other instruments

30
00:01:56.000 --> 00:02:00.000
to 7 degrees Kelvin using the cryocooler.

31
00:02:00.000 --> 00:02:04.000
Now 7 degrees is unimaginably cold.

32
00:02:04.000 --> 00:02:08.000
I have here the coldest thing that I could get my hands on

33
00:02:08.000 --> 00:02:12.000
music

34
00:02:12.000 --> 00:02:16.000
music

35
00:02:16.000 --> 00:02:20.000
It is dry ice.

36
00:02:20.000 --> 00:02:24.000
And this is still 194

37
00:02:24.000 --> 00:02:28.000
degrees Kelvin. Much warmer than Webb will be at its

38
00:02:28.000 --> 00:02:32.000
coldest point. Alright, we know that Webb has to

39
00:02:32.000 --> 00:02:36.000
get cool using the cryocooler, but how does helium make it cool?

40
00:02:36.000 --> 00:02:40.000
It's because the atoms are really small and can move really fast

41
00:02:40.000 --> 00:02:44.000
Helium only has 2 protons and 2 electrons.

42
00:02:44.000 --> 00:02:48.000
That means it is super light and it means the gasses move really quickly.

43
00:02:48.000 --> 00:02:52.000
That’s why it tends to float away. And because

44
00:02:52.000 --> 00:02:56.000
the gases expand so quickly, it also means that it cools

45
00:02:56.000 --> 00:03:00.000
things really quickly. So when things go from a pressurized liquid

46
00:03:00.000 --> 00:03:04.000
liquid to a gas they tend to cool. You see that same effect if you use a

47
00:03:04.000 --> 00:03:08.000
pressurized pot. When its liquid and boiling it is very

48
00:03:08.000 --> 00:03:12.000
very hot. The steam escaping it actually cools really rapidly.

49
00:03:12.000 --> 00:03:16.000
If you were to put your hand above, right above where that steam is coming out

50
00:03:16.000 --> 00:03:20.000
its gonna be hot. But even just one foot

51
00:03:20.000 --> 00:03:24.000
above that, and that air is touchable.

52
00:03:24.000 --> 00:03:28.000
This is called the Joule-Thompson effect. If you blow on your hand

53
00:03:28.000 --> 00:03:32.000
with an open mouth, the air is going to be hot, but if you purse your lips,

54
00:03:32.000 --> 00:03:36.000
the air has to expand more rapidly and it has a cooling effect.

55
00:03:36.000 --> 00:03:40.000
The cryocooler’s liquid helium expands

56
00:03:40.000 --> 00:03:44.000
and contracts and expands again in a chamber similar to this

57
00:03:44.000 --> 00:03:48.000
And because it needs to get even colder, it has

58
00:03:48.000 --> 00:03:52.000
has two chambers. And this is going to allow us to see

59
00:03:52.000 --> 00:03:55.563
the developing Universe!