1
00:00:15,632 --> 00:00:15,782
Oh.

2
00:00:15,782 --> 00:00:17,183
Hi there.

3
00:00:27,560 --> 00:00:28,945
Hi.

4
00:00:28,945 --> 00:00:29,813
I'm NASA astronaut

5
00:00:29,813 --> 00:00:30,563
Nick Hague,

6
00:00:30,563 --> 00:00:31,548
living and working

7
00:00:31,548 --> 00:00:33,750
aboard the International Space Station.

8
00:00:33,750 --> 00:00:36,202
Stability in spacecraft is important.

9
00:00:36,202 --> 00:00:37,587
It's what keeps satellites

10
00:00:37,587 --> 00:00:38,371
and space

11
00:00:38,371 --> 00:00:40,673
telescopes oriented

12
00:00:40,673 --> 00:00:42,142
in the right direction

13
00:00:42,142 --> 00:00:43,376
to make observations

14
00:00:43,376 --> 00:00:45,979
and send data back down to the ground.

15
00:00:45,979 --> 00:00:47,547
Here on the International Space Station,

16
00:00:47,547 --> 00:00:49,466
stability keeps the bottom of the station

17
00:00:49,466 --> 00:00:50,700
pointed toward the Earth.

18
00:00:50,700 --> 00:00:51,951
And our solar panels

19
00:00:51,951 --> 00:00:52,969
pointed toward the sun

20
00:00:52,969 --> 00:00:55,672
so we can charge up. and we have power.

21
00:00:55,672 --> 00:00:56,873
Let's face it.

22
00:00:56,873 --> 00:00:57,707
None of us

23
00:00:57,707 --> 00:01:00,110
want to spend our entire time on orbit

24
00:01:00,110 --> 00:01:01,561
feeling like we're on a gigantic

25
00:01:01,561 --> 00:01:04,547
carnival ride constantly tumbling around.

26
00:01:04,547 --> 00:01:05,899
Though, I got to say,

27
00:01:05,899 --> 00:01:06,750
you know, it's fun

28
00:01:06,750 --> 00:01:09,319
to do every now and then.

29
00:01:09,319 --> 00:01:12,322
Never gets old.

30
00:01:13,373 --> 00:01:15,959
But we have to stay stable somehow.

31
00:01:16,910 --> 00:01:18,144
Although the space station

32
00:01:18,144 --> 00:01:19,979
is equipped with thrusters

33
00:01:19,979 --> 00:01:22,198
to give us little nudges here and there,

34
00:01:22,198 --> 00:01:23,700
they require fuel.

35
00:01:23,700 --> 00:01:25,585
And that's not very efficient.

36
00:01:25,585 --> 00:01:26,719
A more efficient way

37
00:01:26,719 --> 00:01:27,837
to keep us pointed in the right

38
00:01:27,837 --> 00:01:29,005
direction is through

39
00:01:29,005 --> 00:01:31,491
using rotational stability

40
00:01:31,491 --> 00:01:33,626
from gyroscopes.

41
00:01:33,626 --> 00:01:34,410
Today

42
00:01:34,410 --> 00:01:35,211
we're going to explore

43
00:01:35,211 --> 00:01:36,262
rotational stability

44
00:01:36,262 --> 00:01:37,831
and how gyroscopes

45
00:01:37,831 --> 00:01:40,817
can be used to keep objects pointed

46
00:01:41,484 --> 00:01:44,337
where we want them.

47
00:01:44,337 --> 00:01:45,688
Every object

48
00:01:45,688 --> 00:01:47,207
has its mass distributed

49
00:01:47,207 --> 00:01:48,408
in different ways.

50
00:01:48,408 --> 00:01:49,742
How the mass of an object

51
00:01:49,742 --> 00:01:50,927
is spread out affects

52
00:01:50,927 --> 00:01:52,312
how it rotates around

53
00:01:52,312 --> 00:01:54,681
each of its three principal axes.

54
00:01:54,681 --> 00:01:55,732
For example,

55
00:01:55,732 --> 00:01:58,401
spinning an object around its minor axis

56
00:01:58,401 --> 00:02:00,120
where its mass is closest

57
00:02:00,120 --> 00:02:03,123
to its axis of rotation is stable.

58
00:02:03,356 --> 00:02:04,757
This is what keeps a spiraling

59
00:02:04,757 --> 00:02:07,577
football stable as it flies.

60
00:02:07,577 --> 00:02:08,845
Rotating an object

61
00:02:08,845 --> 00:02:10,847
around its major axis,

62
00:02:10,847 --> 00:02:12,949
where its mass is concentrated around

63
00:02:12,949 --> 00:02:15,802
the perimeter, is also stable.

64
00:02:15,802 --> 00:02:18,171
This is what keeps a spinning top upright

65
00:02:18,171 --> 00:02:20,039
and a Frisbee stable in flight.

66
00:02:21,241 --> 00:02:22,342
Finally, if

67
00:02:22,342 --> 00:02:25,411
you spin an object around the third axis,

68
00:02:25,411 --> 00:02:27,897
called its intermediate axis,

69
00:02:27,897 --> 00:02:29,182
it will be unstable.

70
00:02:29,182 --> 00:02:31,217
Even the slightest amount of imbalance

71
00:02:31,217 --> 00:02:33,303
will cause it to flip or tumble.

72
00:02:33,303 --> 00:02:34,137
This is called

73
00:02:34,137 --> 00:02:36,956
the intermediate axis theorem.

74
00:02:36,956 --> 00:02:38,958
When an object like a t handle

75
00:02:38,958 --> 00:02:40,410
or a wingnut is spun

76
00:02:40,410 --> 00:02:41,878
on its intermediate axis

77
00:02:41,878 --> 00:02:43,463
and then allowed to move freely

78
00:02:43,463 --> 00:02:46,015
in the microgravity environment of space,

79
00:02:46,015 --> 00:02:48,017
at first it appears stable.

80
00:02:48,017 --> 00:02:49,819
But as the instability

81
00:02:49,819 --> 00:02:51,437
in its axis of rotation

82
00:02:51,437 --> 00:02:52,589
increases, there's

83
00:02:52,589 --> 00:02:54,440
a sudden shift in its inertia,

84
00:02:54,440 --> 00:02:57,143
snapping it around 180 degrees

85
00:02:57,143 --> 00:03:00,063
where the process begins all over again.

86
00:03:00,063 --> 00:03:01,564
While this might look cool,

87
00:03:01,564 --> 00:03:02,932
it is not something

88
00:03:02,932 --> 00:03:04,551
we would want to have happen

89
00:03:04,551 --> 00:03:06,603
on a spacecraft

90
00:03:06,603 --> 00:03:08,721
To keep spacecraft stable,

91
00:03:08,721 --> 00:03:10,974
we use gyroscopes.

92
00:03:10,974 --> 00:03:12,809
A gyroscope is a spinning

93
00:03:12,809 --> 00:03:14,060
wheel with its mass

94
00:03:14,060 --> 00:03:15,378
concentrated far

95
00:03:15,378 --> 00:03:16,863
from its axis of rotation.

96
00:03:17,814 --> 00:03:18,831
As they spin,

97
00:03:18,831 --> 00:03:21,618
they resist rotation along any axis

98
00:03:21,618 --> 00:03:24,621
other than their spin axis.

99
00:03:26,723 --> 00:03:28,341
The International Space Station

100
00:03:28,341 --> 00:03:29,876
has four different Control

101
00:03:29,876 --> 00:03:32,879
Moment Gyroscopes, or CMGs.

102
00:03:32,879 --> 00:03:34,981
They consist of steel wheels

103
00:03:34,981 --> 00:03:36,950
at different orientations

104
00:03:36,950 --> 00:03:38,635
that spin at a constant

105
00:03:38,635 --> 00:03:41,838
speed of 6600 revolutions per minute.

106
00:03:42,922 --> 00:03:44,490
Not only do the CMGs

107
00:03:44,490 --> 00:03:46,376
keep the station stable,

108
00:03:46,376 --> 00:03:48,177
but we can also reposition them

109
00:03:48,177 --> 00:03:50,847
to induce a gyroscopic force

110
00:03:50,847 --> 00:03:53,850
to change the orientation of the station.

111
00:03:54,751 --> 00:03:56,636
Here I have a simple model

112
00:03:56,636 --> 00:03:58,888
of the gyrostat

113
00:03:58,888 --> 00:03:59,906
or device

114
00:03:59,906 --> 00:04:02,909
used to test gyroscopic control.

115
00:04:03,726 --> 00:04:04,460
It's very easy

116
00:04:04,460 --> 00:04:07,463
to make and consists of a gyroscope

117
00:04:07,880 --> 00:04:09,632
placed in the middle of sheets

118
00:04:09,632 --> 00:04:10,617
of cardboard.

119
00:04:10,617 --> 00:04:12,185
As you can see,

120
00:04:12,185 --> 00:04:15,171
we've colored one half of each side,

121
00:04:15,571 --> 00:04:16,556
so it helps us keep

122
00:04:16,556 --> 00:04:18,124
track of the orientation

123
00:04:19,175 --> 00:04:22,161
of the gyroscope.

124
00:04:22,912 --> 00:04:23,997
So there it's spinning around

125
00:04:23,997 --> 00:04:26,182
its minor axis

126
00:04:26,182 --> 00:04:29,185
and it's stable.

127
00:04:32,322 --> 00:04:34,324
Nice and stable

128
00:04:34,324 --> 00:04:37,327
on this major axis.

129
00:04:38,661 --> 00:04:39,479
I'm going to set it up

130
00:04:39,479 --> 00:04:40,296
so that I spin it

131
00:04:40,296 --> 00:04:42,665
around its intermediate axis.

132
00:04:42,665 --> 00:04:45,652
This is the one that goes through here.

133
00:04:49,022 --> 00:04:50,940
And there you can see it

134
00:04:50,940 --> 00:04:51,908
tumbles around

135
00:04:51,908 --> 00:04:54,911
another axis as it rotates.

136
00:04:55,828 --> 00:04:57,397
No matter how hard I try

137
00:04:57,397 --> 00:05:00,383
to get it to only spin around one axis.

138
00:05:01,401 --> 00:05:03,119
Now let's see if we can make the gyros

139
00:05:03,119 --> 00:05:06,773
that spin with stability by spinning up

140
00:05:06,773 --> 00:05:09,776
the gyroscope.

141
00:05:20,219 --> 00:05:22,672
With the axis of the spinning gyroscope

142
00:05:22,672 --> 00:05:23,823
in the same direction

143
00:05:23,823 --> 00:05:26,426
as the rotation of the intermediate axis,

144
00:05:26,426 --> 00:05:27,510
the gyro step.

145
00:05:27,510 --> 00:05:30,263
It's now stable,

146
00:05:30,263 --> 00:05:33,266
even is irregular as a camera.

147
00:05:33,633 --> 00:05:36,235
You can try to find where its axis,

148
00:05:38,121 --> 00:05:40,623
major, minor, and intermediate axis are.

149
00:05:40,623 --> 00:05:41,691
This looks pretty stable.

150
00:05:41,691 --> 00:05:42,542
No, no twist.

151
00:05:42,542 --> 00:05:45,545
There.

152
00:05:45,962 --> 00:05:46,763
And if I'm right,

153
00:05:46,763 --> 00:05:47,663
it's going to turn around

154
00:05:47,663 --> 00:05:48,598
and the camera's going to point

155
00:05:48,598 --> 00:05:51,601
towards you here shortly.

156
00:05:56,339 --> 00:05:57,357
And it's going to turn around

157
00:05:57,357 --> 00:05:58,641
and point toward me.

158
00:05:58,641 --> 00:06:00,209
And it just keeps repeating.

159
00:06:00,209 --> 00:06:02,245
So every object's got it.

160
00:06:02,245 --> 00:06:02,945
Well,

161
00:06:02,945 --> 00:06:04,764
I hope you enjoyed this demonstration

162
00:06:04,764 --> 00:06:06,182
and learned a little something new

163
00:06:06,182 --> 00:06:07,734
about rotational dynamics

164
00:06:07,734 --> 00:06:10,053
and gyroscopic stability.

165
00:06:10,053 --> 00:06:11,704
Now you go give it a try.

166
00:06:11,704 --> 00:06:14,607
Make your own gyrostat just like mine.

167
00:06:14,607 --> 00:06:15,808
Thanks for joining me here

168
00:06:15,808 --> 00:06:17,210
on the International Space Station.