1
00:00:00,000 --> 00:00:05,160
In the past, entering into orbit around a planet or moon required precise navigation

2
00:00:05,160 --> 00:00:08,280
and the ability to slow a spacecraft with thrusters.

3
00:00:08,280 --> 00:00:12,320
Of course, thrusters require large amounts of fuel to slow the craft down to orbital

4
00:00:12,320 --> 00:00:13,320
speeds.

5
00:00:13,320 --> 00:00:18,160
The fuel carried on these missions takes up valuable space, which can be used to store

6
00:00:18,160 --> 00:00:19,360
science instruments.

7
00:00:19,360 --> 00:00:25,360
To help reduce costs and create more room, NASA researchers have developed an alternative

8
00:00:25,360 --> 00:00:29,760
to using fuel to slow the craft, called aerobraking.

9
00:00:29,760 --> 00:00:34,040
Aerobraking uses the atmosphere of the target planet as both a brake and a steering wheel

10
00:00:34,040 --> 00:00:35,720
to slow the craft.

11
00:00:35,720 --> 00:00:40,400
Jennifer Pulley spoke with Dr. Mary Kay Lockwood to find out more about aerobraking and how

12
00:00:40,400 --> 00:00:44,000
NASA is using this technique in space travel.

13
00:00:44,000 --> 00:00:52,200
The sight of spacecraft flying out of the atmosphere on the way to a distant destination

14
00:00:52,200 --> 00:00:55,320
is a familiar one to most of us.

15
00:00:55,320 --> 00:01:00,920
In order to break free of the Earth's gravitational field, a typical spacecraft needs to be traveling

16
00:01:00,920 --> 00:01:05,000
at speeds close to 25,000 miles per hour.

17
00:01:05,000 --> 00:01:09,680
Once the spacecraft does break free, it is able to continue traveling to its destination

18
00:01:09,680 --> 00:01:15,440
at high speeds because there is very little friction to slow it down.

19
00:01:15,440 --> 00:01:20,800
Once the craft reaches its destination, the craft must decelerate from very high speeds

20
00:01:20,800 --> 00:01:26,080
to much lower speeds in a relatively short period of time.

21
00:01:26,080 --> 00:01:30,920
In the past, additional thrusters would be fired to help the craft decelerate as it approached

22
00:01:30,920 --> 00:01:31,920
its target.

23
00:01:31,920 --> 00:01:36,640
But a major problem with this method is that the fuel needed for these thrusters takes

24
00:01:36,640 --> 00:01:42,200
up valuable space and weight, which could be used to house additional science instruments.

25
00:01:42,200 --> 00:01:47,760
More recently, NASA has been using an aero-assist technique called aerobraking, which adds the

26
00:01:47,760 --> 00:01:52,880
use of atmospheric drag to slow the craft rather than using thrusters alone.

27
00:01:52,880 --> 00:01:57,080
This technique allows additional science instruments to be delivered to a distant target while

28
00:01:57,080 --> 00:01:59,120
also reducing costs.

29
00:01:59,120 --> 00:02:03,720
I spoke to Dr. Mary Kay Lockwood at NASA Langley Research Center to find out more.

30
00:02:03,720 --> 00:02:10,480
Well, when we first approach a planet on a trajectory from Earth, we do a small firing

31
00:02:10,480 --> 00:02:16,000
of the thrusters and capture into a very large elliptical orbit about that planet.

32
00:02:16,000 --> 00:02:22,080
We then do several passes through the upper atmosphere of that destination to slow the

33
00:02:22,080 --> 00:02:25,400
spacecraft down into the final science orbit.

34
00:02:25,400 --> 00:02:30,560
Aerobraking is accomplished when a vehicle makes multiple passes around a planet or moon

35
00:02:30,560 --> 00:02:33,940
and uses the atmosphere to slow down the vehicle.

36
00:02:33,940 --> 00:02:39,360
This process is very slow, sometimes taking several months, because the vehicle is only

37
00:02:39,360 --> 00:02:42,840
exposed to the upper layers of the atmosphere.

38
00:02:42,840 --> 00:02:47,640
This procedure is very similar to how a rock reacts when it is skimmed across the top of

39
00:02:47,640 --> 00:02:48,800
water.

40
00:02:48,800 --> 00:02:53,360
With each skip, the rock slows down until it finally stops.

41
00:02:53,360 --> 00:02:58,040
The spacecraft is similar, because with each pass through the atmosphere, it slows down

42
00:02:58,040 --> 00:03:02,920
more and more until it finally reaches the appropriate orbital speed.

43
00:03:02,920 --> 00:03:05,680
Has the aerobraking technique ever been flown on a mission?

44
00:03:05,680 --> 00:03:09,800
Well, aerobraking was first demonstrated in the Magellan mission at the very end of the

45
00:03:09,800 --> 00:03:15,960
mission at Venus, and it has since flown in two successful Mars missions, both the

46
00:03:15,960 --> 00:03:19,360
Mars Global Surveyor mission and Mars Odyssey.

47
00:03:19,360 --> 00:03:23,760
It's also going to be used in the future on the Mars Reconnaissance Orbiter mission.

48
00:03:23,760 --> 00:03:27,560
Once a vehicle nears its destination, how does the atmosphere slow it down?

49
00:03:27,560 --> 00:03:32,640
Well, an atmosphere slows a vehicle down in the same way that if you were to put your

50
00:03:32,640 --> 00:03:36,800
hand out the window of a car while it's moving, you can feel the force of the air on your

51
00:03:36,800 --> 00:03:41,840
hand, and that is the same force that's slowing the spacecraft down when it passes through

52
00:03:41,840 --> 00:03:43,640
the atmosphere.

53
00:03:43,640 --> 00:03:47,680
Aerobraking is a good way to slow a vehicle down at a destination and capture into an

54
00:03:47,680 --> 00:03:51,920
orbit, but we're also looking at another approach called aerocapture.

55
00:03:51,920 --> 00:03:56,920
Aerocapture is similar to aerobraking because it uses the atmosphere to slow a vehicle down.

56
00:03:56,920 --> 00:04:02,120
But unlike aerobraking, which only skims the top layers of the atmosphere, the aerocapture

57
00:04:02,120 --> 00:04:07,000
technique allows the vehicle to go deep inside the atmosphere of the target.

58
00:04:07,000 --> 00:04:12,040
The vehicle maneuvers through the atmosphere using drag to decelerate to the desired orbital

59
00:04:12,040 --> 00:04:13,040
speed.

60
00:04:13,040 --> 00:04:18,760
After the vehicle exits the atmosphere, a very small thruster firing occurs to achieve

61
00:04:18,760 --> 00:04:23,040
the desired orbit around the target planet or moon.

62
00:04:23,040 --> 00:04:27,440
One of the major differences between aerobraking and aerocapture is that for aerocapture we

63
00:04:27,440 --> 00:04:29,280
need an aeroshell.

64
00:04:29,280 --> 00:04:35,000
And an aeroshell is very much the same as the aeroshell used on the Mars Exploration

65
00:04:35,000 --> 00:04:37,960
Rover missions you may be familiar with.

66
00:04:37,960 --> 00:04:42,520
But for aerocapture, of course, we're maneuvering through the atmosphere and then exiting the

67
00:04:42,520 --> 00:04:48,320
atmosphere and finally achieving an orbit at a destination, where with the Mars Exploration

68
00:04:48,320 --> 00:04:52,200
Rovers we were landing on the surface of that destination.

69
00:04:52,200 --> 00:04:56,400
For aerobraking you do not need an aeroshell because you're passing through the very upper

70
00:04:56,400 --> 00:04:58,200
part of the atmosphere.

71
00:04:58,200 --> 00:05:04,360
So the heating environment on the vehicle is not nearly as severe as it is with aerocapture.

72
00:05:04,360 --> 00:05:07,240
So do different planets need different shaped aeroshells?

73
00:05:07,240 --> 00:05:09,960
Or will one design work in all situations?

74
00:05:09,960 --> 00:05:16,800
The aeroshell shape for the aerocapture missions at places like the Earth or at Mars or at

75
00:05:16,800 --> 00:05:23,400
Titan can be very similar to those that are used with the Mars Exploration Rover missions.

76
00:05:23,400 --> 00:05:27,560
But if we're going to destinations such as Neptune, that would require a different vehicle

77
00:05:27,560 --> 00:05:32,240
shape, different aeroshell shape, and that would be more shaped like a bullet that flies

78
00:05:32,240 --> 00:05:33,720
at an angle.

79
00:05:33,720 --> 00:05:40,400
To achieve a successful aerocapture we have to stay within a very narrow corridor.

80
00:05:40,400 --> 00:05:43,560
If we don't stay within that corridor we would have a flyby.

81
00:05:43,560 --> 00:05:46,340
We wouldn't capture into the orbit.

82
00:05:46,340 --> 00:05:48,480
Or on the other side we would land.

83
00:05:48,600 --> 00:05:54,480
So it's very important to stay within a particular corridor through that destination.

84
00:05:54,480 --> 00:05:56,320
At Neptune the corridor is narrower.

85
00:05:56,320 --> 00:05:57,960
It's kind of like a little highway.

86
00:05:57,960 --> 00:05:59,760
It's like a little highway.

87
00:05:59,760 --> 00:06:05,720
And so at Neptune in order to make the highway bigger we need to have a different shape.

88
00:06:05,720 --> 00:06:10,480
So Dr. Lockwood, in addition to aeroshells, what are some other techniques that can be

89
00:06:10,480 --> 00:06:12,240
used to slow a vehicle down?

90
00:06:12,240 --> 00:06:16,720
We're looking at other techniques that might be second generation techniques that would

91
00:06:16,720 --> 00:06:20,000
use an inflatable aeroshell or even a balut.

92
00:06:20,000 --> 00:06:23,400
A balut basically looks like a giant donut.

93
00:06:23,400 --> 00:06:29,920
It's got tethers similar to a parachute, but it has a giant ring behind it and that allows

94
00:06:29,920 --> 00:06:35,120
a spacecraft to fly shallower in the atmosphere to still slow down.

95
00:06:35,120 --> 00:06:40,960
We are always working to achieve the science and exploration goals for NASA and being able

96
00:06:40,960 --> 00:06:46,160
to reduce the cost of these systems and being able to improve the performance of the systems

97
00:06:46,160 --> 00:06:49,160
is a very important part of achieving that goal.

98
00:06:49,160 --> 00:06:52,360
It's very exciting and challenging work.

99
00:06:52,360 --> 00:06:57,240
Coming up, we'll find out how specialized materials are saving lives, but first...

100
00:06:57,240 --> 00:07:02,920
Did you know that aerobraking was first tested on a Magellan mission to Venus in 1994?

101
00:07:02,920 --> 00:07:07,640
Although the Magellan mission used propulsion to slow the craft, aerobraking was tested

102
00:07:07,640 --> 00:07:10,600
at the end of the mission to validate the theory.

103
00:07:10,600 --> 00:07:16,040
With the success of this test, NASA researchers decided to use aerobraking as the primary

104
00:07:16,040 --> 00:07:21,120
deceleration method on one of its next missions, the Mars Global Surveyor.

105
00:07:21,120 --> 00:07:27,600
On February 4, 1999, history was made when the Mars Global Surveyor successfully obtained

106
00:07:27,600 --> 00:07:36,200
stable circular orbit of Mars using aerobraking as the primary method of deceleration.