Aerobraking
Program Information
Series: Destination TomorrowProgram: Episode 15
Segment Number: 2 (Watch entire program)
Duration: 00:07:36
Year Produced: 2004
Description:
NASA Destination Tomorrow Segment exploring the function of aerobraking and how this helps reduce costs and create more room in aircraft.
NASA's Destination Tomorrow™ is a series of 30-minute programs that focus on NASA research. Each exciting program gives the audience an inside look at NASA and demonstrates how research and technology relate to our everyday lives.
For more information visit: http://destination.larc.nasa.gov/Transcript
In the past, entering into orbit
around a planet or moon
required precise navigation
and the ability to slow
a spacecraft with thrusters.
Of course, thrusters
require large amounts of fuel
to slow the craft down
to orbital speeds.
The fuel carried
on these missions
takes up valuable space,
which can be used
to store science instruments.
To help reduce costs
and create more room,
NASA researchers have developed
an alternative
to using fuel
to slow the craft,
called aerobraking.
Aerobraking uses the atmosphere
of the target planet
as both a brake and a steering
wheel to slow the craft.
Jennifer Pulley spoke
with Dr. Mary Kae Lockwood
to find our more
about Aerobraking
and how NASA is using
this technique in space travel.
(Pulley)
The sight of spacecraft flying
out of the atmosphere
on the way
to a distant destination
is a familiar one
to most of us.
In order to break free of
the Earth's gravitational field,
a typical spacecraft
needs to be traveling
at speeds close
to 25,000 miles per hour.
Once the spacecraft
does break free,
it is able to continue traveling
to its destination
at high speeds
because there is very little
friction to slow it down.
Once the craft
reaches its destination,
the craft must decelerate
from very high speeds
to much lower speeds
in a relatively short
period of time.
In the past, additional
thrusters would be fired
to help the craft decelerate
as it approached its target.
But a major problem
with this method
is that the fuel needed
for these thrusters
takes up valuable
space and weight,
which could be used to house
additional science instruments.
More recently,
NASA has been using
an aero-assist technique
called aerobraking,
which adds the use
of atmospheric drag
to slow the craft rather
than using thrusters alone.
This technique allows
additional science instruments
to be delivered
to a distant target
while also reducing costs.
I spoke to Dr. Mary Kae Lockwood
at NASA Langley Research Center
to find out more.
Well, when we first approach
a planet
on a trajectory
from Earth,
we do a small firing
of the thrusters
and capture into a very large,
elliptical orbit
about that planet.
We then do several passes
through the upper atmosphere
of that destination
to slow the spacecraft down
into the final science orbit.
Aerobraking is accomplished when
a vehicle makes multiple passes
around a planet or moon
and uses the atmosphere
to slow down the vehicle.
This process is very slow,
sometimes taking several months,
because the vehicle
is only exposed
to the upper layers
of the atmosphere.
This procedure is very similar
to how a rock reacts
when it is skimmed
across the top of water.
With each skip, the rock slows
down until it finally stops.
The spacecraft
is similar because,
with each pass
through the atmosphere,
it slows down
more and more
until it finally reaches
the appropriate orbital speed.
Has the aerobraking technique
ever been flown on a mission?
Aerobraking was first
demonstrated
in the Magellan mission
at the very end
of the mission at Venus.
And it has since flown
in two successful Mars missions,
both the Mars Global Surveyor
mission and Mars Odyssey.
It's also
going to be used in the future
on the Mars Reconnaissance
Orbiter mission.
Once a vehicle
nears its destination,
how does the atmosphere
slow it down?
An atmosphere
slows a vehicle down
in the same way that,
if you were to put your hand
out the window of a car
while it's moving,
you can feel the force
of the air on your hand.
And that is the same force
that's slowing
the spacecraft down
when it passes
through the atmosphere.
Aerobraking is a good way
to slow a vehicle down
at a destination
and capture into an orbit.
But we're also looking
at another approach
called aerocapture.
Aerocapture is similar
to aerobraking
because it uses the atmosphere
to slow a vehicle down.
But unlike aerobraking,
which only skims the top layers
of the atmosphere,
the aerocapture technique
allows the vehicle
to go deep inside the atmosphere
of the target.
The vehicle maneuvers
through the atmosphere
using drag to decelerate
to the desired orbital speed.
After the vehicle
exits the atmosphere,
a very small thruster firing
occurs
to achieve the desired orbit
around the target planet
or moon.
One of the major differences
between aerobraking
and aerocapture is that,
for aerocapture,
we need an aeroshell.
And an aeroshell is very much
the same as the aeroshell
used on the Mars exploration
rover missions
you may be familiar with.
But for aerocapture,
of course,
we're maneuvering
through the atmosphere
and then exiting the atmosphere
and finally achieving an orbit
at a destination.
Where, with the Mars
exploration rovers,
we were landing of the surface
of that destination.
For aerobraking,
you do not need an aeroshell
because you're passing
through the very upper part
of the atmosphere.
So the heating environment
on the vehicle
is not nearly as severe as it is
with aerocapture.
So do different planets
need different-shaped
aeroshells?
Or will one design work
in all situations?
The aeroshell shape
for the aerocapture missions
at places like the Earth
or at Mars or at Titan
can be very similar
to those that are used
with the Mars exploration
rover missions.
But if we're going
to destinations such as Neptune,
that would require
a different vehicle shape,
different aeroshell shape,
and that would be more shaped
like a bullet
that flies at an angle.
To achieve
a successful aerocapture,
we have to stay
within a very narrow corridor.
If we don't stay
within that corridor,
we would have a flyby.
We wouldn't capture
into the orbit.
Or, on the other side,
we would land.
And so it's very important
to stay within
a particular corridor
through that destination.
At Neptune,
the corridor is narrower.
(Pulley)
It's kind of like
a little highway?
(Lockwood)
It's like a little highway.
And so at Neptune, in order
to make the highway bigger,
we need to have
a different shape.
So, Dr. Lockwood,
in addition to aeroshells,
what are some other techniques
that can be used
to slow a vehicle down?
We're looking
at other techniques
that might be
second generation techniques
that would use an inflatable
aeroshell or even a ballute.
A ballute, basically,
looks like a giant donut.
It's got tethers similar
to a parachute.
But it has a giant ring
behind it.
And that allows a spacecraft
to fly shallower
in the atmosphere
to still slow down.
We are always working
to achieve the science
and exploration goals for NASA.
And being able to reduce
the cost of these systems
and being able to improve
the performance of the systems
is a very important part
of achieving that goal.
And it's very exciting
and challenging work.
Coming up, we'll find out
how specialized materials
are saving lives.
But first,
did you know that aerobraking
was first tested
on the Magellan mission
to Venus in 1994?
Although the Magellan mission
used propulsion
to slow the craft,
aerobraking was tested
at the end of the mission
to validate the theory.
With the success
of this test,
NASA researchers decided
to use aerobraking
as the primary
deceleration method
on one of its next missions,
the Mars Global Surveyor.
On February 4, 1999,
history was made
when the Mars Global Surveyor
successfully obtained
stable circular orbit of Mars
using aerobraking as the primary
method of deceleration.