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Destination Tomorrow - DT15 - Aerobraking

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Destination Tomorrow Segment exploring the function of aerobraking and how this helps reduce costs and create more room in aircraft.

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In the past, entering into orbit around a planet or moon required precise navigation 00:00:00
and the ability to slow a spacecraft with thrusters. 00:00:05
Of course, thrusters require large amounts of fuel to slow the craft down to orbital 00:00:08
speeds. 00:00:12
The fuel carried on these missions takes up valuable space, which can be used to store 00:00:13
science instruments. 00:00:18
To help reduce costs and create more room, NASA researchers have developed an alternative 00:00:19
to using fuel to slow the craft, called aerobraking. 00:00:25
Aerobraking uses the atmosphere of the target planet as both a brake and a steering wheel 00:00:29
to slow the craft. 00:00:34
Jennifer Pulley spoke with Dr. Mary Kay Lockwood to find out more about aerobraking and how 00:00:35
NASA is using this technique in space travel. 00:00:40
The sight of spacecraft flying out of the atmosphere on the way to a distant destination 00:00:44
is a familiar one to most of us. 00:00:52
In order to break free of the Earth's gravitational field, a typical spacecraft needs to be traveling 00:00:55
at speeds close to 25,000 miles per hour. 00:01:00
Once the spacecraft does break free, it is able to continue traveling to its destination 00:01:05
at high speeds because there is very little friction to slow it down. 00:01:09
Once the craft reaches its destination, the craft must decelerate from very high speeds 00:01:15
to much lower speeds in a relatively short period of time. 00:01:20
In the past, additional thrusters would be fired to help the craft decelerate as it approached 00:01:26
its target. 00:01:30
But a major problem with this method is that the fuel needed for these thrusters takes 00:01:31
up valuable space and weight, which could be used to house additional science instruments. 00:01:36
More recently, NASA has been using an aero-assist technique called aerobraking, which adds the 00:01:42
use of atmospheric drag to slow the craft rather than using thrusters alone. 00:01:47
This technique allows additional science instruments to be delivered to a distant target while 00:01:52
also reducing costs. 00:01:57
I spoke to Dr. Mary Kay Lockwood at NASA Langley Research Center to find out more. 00:01:59
Well, when we first approach a planet on a trajectory from Earth, we do a small firing 00:02:03
of the thrusters and capture into a very large elliptical orbit about that planet. 00:02:10
We then do several passes through the upper atmosphere of that destination to slow the 00:02:16
spacecraft down into the final science orbit. 00:02:22
Aerobraking is accomplished when a vehicle makes multiple passes around a planet or moon 00:02:25
and uses the atmosphere to slow down the vehicle. 00:02:30
This process is very slow, sometimes taking several months, because the vehicle is only 00:02:33
exposed to the upper layers of the atmosphere. 00:02:39
This procedure is very similar to how a rock reacts when it is skimmed across the top of 00:02:42
water. 00:02:47
With each skip, the rock slows down until it finally stops. 00:02:48
The spacecraft is similar, because with each pass through the atmosphere, it slows down 00:02:53
more and more until it finally reaches the appropriate orbital speed. 00:02:58
Has the aerobraking technique ever been flown on a mission? 00:03:02
Well, aerobraking was first demonstrated in the Magellan mission at the very end of the 00:03:05
mission at Venus, and it has since flown in two successful Mars missions, both the 00:03:09
Mars Global Surveyor mission and Mars Odyssey. 00:03:15
It's also going to be used in the future on the Mars Reconnaissance Orbiter mission. 00:03:19
Once a vehicle nears its destination, how does the atmosphere slow it down? 00:03:23
Well, an atmosphere slows a vehicle down in the same way that if you were to put your 00:03:27
hand out the window of a car while it's moving, you can feel the force of the air on your 00:03:32
hand, and that is the same force that's slowing the spacecraft down when it passes through 00:03:36
the atmosphere. 00:03:41
Aerobraking is a good way to slow a vehicle down at a destination and capture into an 00:03:43
orbit, but we're also looking at another approach called aerocapture. 00:03:47
Aerocapture is similar to aerobraking because it uses the atmosphere to slow a vehicle down. 00:03:51
But unlike aerobraking, which only skims the top layers of the atmosphere, the aerocapture 00:03:56
technique allows the vehicle to go deep inside the atmosphere of the target. 00:04:02
The vehicle maneuvers through the atmosphere using drag to decelerate to the desired orbital 00:04:07
speed. 00:04:12
After the vehicle exits the atmosphere, a very small thruster firing occurs to achieve 00:04:13
the desired orbit around the target planet or moon. 00:04:18
One of the major differences between aerobraking and aerocapture is that for aerocapture we 00:04:23
need an aeroshell. 00:04:27
And an aeroshell is very much the same as the aeroshell used on the Mars Exploration 00:04:29
Rover missions you may be familiar with. 00:04:35
But for aerocapture, of course, we're maneuvering through the atmosphere and then exiting the 00:04:37
atmosphere and finally achieving an orbit at a destination, where with the Mars Exploration 00:04:42
Rovers we were landing on the surface of that destination. 00:04:48
For aerobraking you do not need an aeroshell because you're passing through the very upper 00:04:52
part of the atmosphere. 00:04:56
So the heating environment on the vehicle is not nearly as severe as it is with aerocapture. 00:04:58
So do different planets need different shaped aeroshells? 00:05:04
Or will one design work in all situations? 00:05:07
The aeroshell shape for the aerocapture missions at places like the Earth or at Mars or at 00:05:09
Titan can be very similar to those that are used with the Mars Exploration Rover missions. 00:05:16
But if we're going to destinations such as Neptune, that would require a different vehicle 00:05:23
shape, different aeroshell shape, and that would be more shaped like a bullet that flies 00:05:27
at an angle. 00:05:32
To achieve a successful aerocapture we have to stay within a very narrow corridor. 00:05:33
If we don't stay within that corridor we would have a flyby. 00:05:40
We wouldn't capture into the orbit. 00:05:43
Or on the other side we would land. 00:05:46
So it's very important to stay within a particular corridor through that destination. 00:05:48
At Neptune the corridor is narrower. 00:05:54
It's kind of like a little highway. 00:05:56
It's like a little highway. 00:05:57
And so at Neptune in order to make the highway bigger we need to have a different shape. 00:05:59
So Dr. Lockwood, in addition to aeroshells, what are some other techniques that can be 00:06:05
used to slow a vehicle down? 00:06:10
We're looking at other techniques that might be second generation techniques that would 00:06:12
use an inflatable aeroshell or even a balut. 00:06:16
A balut basically looks like a giant donut. 00:06:20
It's got tethers similar to a parachute, but it has a giant ring behind it and that allows 00:06:23
a spacecraft to fly shallower in the atmosphere to still slow down. 00:06:29
We are always working to achieve the science and exploration goals for NASA and being able 00:06:35
to reduce the cost of these systems and being able to improve the performance of the systems 00:06:40
is a very important part of achieving that goal. 00:06:46
It's very exciting and challenging work. 00:06:49
Coming up, we'll find out how specialized materials are saving lives, but first... 00:06:52
Did you know that aerobraking was first tested on a Magellan mission to Venus in 1994? 00:06:57
Although the Magellan mission used propulsion to slow the craft, aerobraking was tested 00:07:02
at the end of the mission to validate the theory. 00:07:07
With the success of this test, NASA researchers decided to use aerobraking as the primary 00:07:10
deceleration method on one of its next missions, the Mars Global Surveyor. 00:07:16
On February 4, 1999, history was made when the Mars Global Surveyor successfully obtained 00:07:21
stable circular orbit of Mars using aerobraking as the primary method of deceleration. 00:07:27
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Idioma/s:
en
Niveles educativos:
▼ Mostrar / ocultar niveles
      • Nivel Intermedio
Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
605
Fecha:
28 de mayo de 2007 - 17:05
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
07′ 36″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
480x360 píxeles
Tamaño:
44.28 MBytes

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