1
00:00:04,771 --> 00:00:07,206
DAISY: The international space
station...

2
00:00:07,275 --> 00:00:10,710
It’s the satellite of science,
paving the way for

3
00:00:10,711 --> 00:00:15,115
future exploration, and
habitation on worlds beyond our
own...

4
00:00:15,950 --> 00:00:18,485
But all that doesn’t come
without challenges...

5
00:00:18,553 --> 00:00:22,421
NASA has to work hard to keep
ISS in orbit.

6
00:00:22,423 --> 00:00:26,458
Thanks to math, the space
agency can provide a boost to
keep it going...

7
00:00:26,460 --> 00:00:29,790
We’ll show you how they do
it... next on real world...

8
00:00:29,791 --> 00:00:32,248
? [music] ?

9
00:00:40,558 --> 00:00:43,476
Construction of the
International Space Station

10
00:00:43,478 --> 00:00:47,846
got underway in 1998, thanks to
NASA and space agencies

11
00:00:47,848 --> 00:00:50,316
from several other nations of
the world.

12
00:00:50,318 --> 00:00:53,420
Since then they have been
working to complete the
project...

13
00:00:53,421 --> 00:00:57,123
Lot’s of work is going on right
now to enable ISS to

14
00:00:57,125 --> 00:01:00,160
double its crew size from 3 to
6.

15
00:01:01,395 --> 00:01:04,096
And the work that’s done on the
station is helping

16
00:01:04,165 --> 00:01:06,800
scientists understand how space
conditions effect

17
00:01:06,801 --> 00:01:10,903
people, plants, microorganisms,
just about all of life.

18
00:01:10,905 --> 00:01:14,873
This work will help pave the
way as we move beyond ISS,

19
00:01:14,875 --> 00:01:19,311
to lunar habitation, and human
exploration of Mars and beyond.

20
00:01:19,313 --> 00:01:22,381
But life in space doesn’t isn’t
always easy...

21
00:01:23,016 --> 00:01:25,918
Recently, astronauts in the
space station had to hunker

22
00:01:25,986 --> 00:01:29,255
down in the Soyez escape
module, waiting to see if a

23
00:01:29,256 --> 00:01:32,125
chunk of space debris, would
hit the station.

24
00:01:32,126 --> 00:01:35,361
The debris is a chunk of an
upper stage rocket, used to

25
00:01:35,363 --> 00:01:39,631
launch a GPS satellite, more
than 15 years ago.

26
00:01:40,401 --> 00:01:43,536
Fortunately, the debris passed
harmlessly.

27
00:01:43,605 --> 00:01:47,473
That was a pretty extreme
situation. Usually the

28
00:01:47,475 --> 00:01:50,376
station has enough advanced
warning to fire its engines

29
00:01:50,378 --> 00:01:54,213
and adjust its orbit, thus
avoiding any space debris.

30
00:01:54,766 --> 00:01:59,151
The Station also needs to
adjust its orbit to compensate
for gravity.

31
00:01:59,221 --> 00:02:03,958
Gravity is the force of
attraction between all masses
in the universe.

32
00:02:04,658 --> 00:02:08,126
RICHARD BYLES: Gravity is what
holds us on earth.

33
00:02:09,063 --> 00:02:11,998
DAISY: Richard Byles is the
director of education at the

34
00:02:12,000 --> 00:02:14,766
Virginia Air and Space Center.

35
00:02:14,768 --> 00:02:19,938
RICHARD: Everything that has
mass, has gravity.

36
00:02:19,940 --> 00:02:23,410
DAISY: The weight of an object
equals mass times gravity.

37
00:02:23,411 --> 00:02:27,046
The mass of an object doesn’t
change, but weight does,

38
00:02:27,048 --> 00:02:30,150
depending on the force of
gravity on that object.

39
00:02:30,151 --> 00:02:34,020
Weight is directly proportional
to the force of gravity on an
object.

40
00:02:34,021 --> 00:02:37,290
That’s why things weigh more on
earth, than on the moon.

41
00:02:37,291 --> 00:02:41,660
The earth has more mass, thus a
stronger gravitational pull.

42
00:02:42,363 --> 00:02:45,165
RICHARD: More mass equals more
gravity.

43
00:02:45,233 --> 00:02:48,668
That’s why all the planets,
even the ones demoted to

44
00:02:48,670 --> 00:02:52,405
dwarf planets like Pluto, way,
way, way, way, way out

45
00:02:52,406 --> 00:02:56,743
there, are held in the
gravitational field of our sun.

46
00:02:56,745 --> 00:03:00,346
DAISY: Each day, the station is
pulled a little closer to
earth,

47
00:03:00,348 --> 00:03:03,616
losing about 90 meters of
altitude. That’s about the

48
00:03:03,618 --> 00:03:07,453
distance from goal line to goal
line on a football field.

49
00:03:07,455 --> 00:03:12,258
This is due to drag, as the
space station collides with air
molecules.

50
00:03:12,260 --> 00:03:15,961
Drag slows the space station
down, making it more

51
00:03:15,963 --> 00:03:18,431
susceptible to the force of
gravity.

52
00:03:18,433 --> 00:03:22,368
This orbital decay is
counteracted in several ways.

53
00:03:22,370 --> 00:03:25,671
The stations main rockets can
provide a small bump.

54
00:03:25,673 --> 00:03:29,741
Resupply vessels that visit the
ISS can push it up more.

55
00:03:29,743 --> 00:03:34,346
And the space shuttle has the
power to provide big boosts.

56
00:03:34,781 --> 00:03:39,451
The orbital decay of the
international space station can
be charted on a graph...

57
00:03:39,520 --> 00:03:42,855
But the rate of decay is not
constant. The rate is

58
00:03:42,856 --> 00:03:45,291
affected by several variables.

59
00:03:45,293 --> 00:03:48,026
By plotting points showing the
station’s altitude over

60
00:03:48,028 --> 00:03:51,163
its lifetime, engineers can see
trends and develop

61
00:03:51,165 --> 00:03:54,133
strategies for keeping the
station in orbit.

62
00:03:54,135 --> 00:03:58,405
NASA needs to keep it above
this point, 200 kilometers.

63
00:03:58,406 --> 00:04:01,606
Below that, Earth’s atmosphere
is too thick and

64
00:04:01,608 --> 00:04:04,710
will cause too much drag on the
ISS.

65
00:04:04,711 --> 00:04:08,815
There is a pretty significant
dip between 2000 and 2001.

66
00:04:08,816 --> 00:04:12,251
This is because of a period of
intense sunspots,

67
00:04:12,253 --> 00:04:15,355
which warmed the Earth’s
atmosphere causing it to

68
00:04:15,356 --> 00:04:18,758
expand out to a higher altitude
creating more drag

69
00:04:18,760 --> 00:04:22,328
on the station, making it drop
even faster.

70
00:04:23,665 --> 00:04:27,400
Fortunately, the space shuttle
was able to provide a big
boost,

71
00:04:27,468 --> 00:04:32,038
sending it back into a higher
orbit... and you can see that
on the graph.

72
00:04:32,040 --> 00:04:35,408
Sunspot activity also follows
patterns.

73
00:04:35,410 --> 00:04:38,243
So the trends can be predicted.

74
00:04:38,245 --> 00:04:42,481
Similar sunspot activity is
predicted beginning in 2012,

75
00:04:42,483 --> 00:04:47,286
by which time the space shuttle
program is expected to be
retired.

76
00:04:48,135 --> 00:04:51,056
Adjustments will come from the
thrust of the stations

77
00:04:51,125 --> 00:04:56,195
two main engines and from
resupply vessels that visit
ISS.

78
00:04:58,265 --> 00:05:02,268
NASA scientists and engineers
are looking into new ways to

79
00:05:02,270 --> 00:05:05,171
provide extra boosts that will
keep the station in

80
00:05:05,173 --> 00:05:08,140
orbit through the end of its
mission.

81
00:05:09,543 --> 00:05:15,915
Keep track of this and all
of NASA’s missions at
www.NASA.gov.

82
00:05:15,916 --> 00:05:20,776
? [music] ?