WEBVTT

1
00:00:00.330 --> 00:00:05.790
How is it possible for
astronauts to do spacewalks?

2
00:00:07.710 --> 00:00:11.730
Working outside a station
or vehicle in space is both

3
00:00:11.750 --> 00:00:13.570
difficult and dangerous.

4
00:00:13.580 --> 00:00:18.500
It is extremely cold where the
ISS orbits, and there is no air.

5
00:00:18.630 --> 00:00:22.380
Human beings would perish
after just thirty seconds out there.

6
00:00:22.380 --> 00:00:26.306
Astronauts can only survive in space
wearing special suits which are

7
00:00:26.320 --> 00:00:28.960
effectively like small spaceships.

8
00:00:28.970 --> 00:00:31.760
A rucksack supplies them 
with air to breathe –

9
00:00:31.760 --> 00:00:35.300
and also removes
exhaled carbon dioxide.

10
00:00:35.310 --> 00:00:38.780
The suits have several
layers, they need to be gas-tight

11
00:00:38.790 --> 00:00:40.950
 and withstand excess pressure.

12
00:00:40.960 --> 00:00:43.979
The outer layer is made
of fire-retardant Kevlar

13
00:00:43.990 --> 00:00:45.900
coated with aluminum.

14
00:00:45.909 --> 00:00:49.140
The suits protect against 
the vacuum and the cold –

15
00:00:49.140 --> 00:00:52.650
as well as micrometeorites 
and solar radiation.

16
00:00:53.010 --> 00:00:57.170
Special underwear with tubes through
which cool water flows prevents

17
00:00:57.180 --> 00:01:00.460
the astronauts from overheating
during their strenuous work.

18
00:01:02.140 --> 00:01:05.870
Astronauts train for space
missions in special swimming pools.

19
00:01:05.940 --> 00:01:10.107
Like divers, their more than 100
kilo-heavy suits are fitted with

20
00:01:10.107 --> 00:01:16.420
weights which allow them to float, 
corresponding to the conditions in space.

21
00:01:18.560 --> 00:01:22.270
The International Space
Station is a weightless environment.

22
00:01:22.380 --> 00:01:26.810
This is because it orbits the earth
so fast that centrifugal force and

23
00:01:26.819 --> 00:01:29.390
gravity balance each other out.

24
00:01:29.400 --> 00:01:32.640
It travels seven
kilometers per second!

25
00:01:36.090 --> 00:01:38.970
The astronauts are
moving at the same speed.

26
00:01:38.990 --> 00:01:40.830
But they don't notice it.

27
00:01:40.850 --> 00:01:45.069
Physically speaking, outside the 
station they are in their own orbit.

28
00:01:45.069 --> 00:01:50.460
Even a tiny push or movement can
alter this orbit – and cause them to

29
00:01:50.470 --> 00:01:54.863
drift away, like the objects
that astronauts have already lost.

30
00:02:01.020 --> 00:02:03.850
They wouldn't be able
to return on their own.

31
00:02:03.860 --> 00:02:07.590
That's why all astronauts
are tethered to their spacecraft

32
00:02:07.660 --> 00:02:09.540
at all times.

33
00:02:11.790 --> 00:02:15.760
In 1984, NASA tested
special jet backpacks.

34
00:02:15.810 --> 00:02:18.887
These were developed for missions
where astronauts had to move far away

35
00:02:18.940 --> 00:02:22.270
from their spaceship, for
example to capture satellites.

36
00:02:26.190 --> 00:02:30.870
In an emergency, astronauts can
ignite the thrusters to stabilize

37
00:02:30.870 --> 00:02:34.160
their position and
then return to the ship.

38
00:02:39.460 --> 00:02:42.996
During extra-vehicular 
activities on the ISS,

39
00:02:43.000 --> 00:02:46.000
astronauts are secured
with two tethers.

40
00:02:46.000 --> 00:02:48.776
These lines are attached 
to poles and handles,

41
00:02:48.776 --> 00:02:51.950
which the astronauts 
use to move around.

42
00:02:51.960 --> 00:02:56.290
When they change position, at least
one tether must always be attached.

43
00:02:58.430 --> 00:03:02.160
For long distances, the astronauts
also hover on the robotic arm

44
00:03:02.160 --> 00:03:04.060
to the deployment site.

45
00:03:04.070 --> 00:03:07.883
Special platforms for their
feet hold them securely in place.