Goddard Glossary: Gravity Assist

Narration: Chyna Vargas

Transcript:

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Gravity assist. A gravity

assist is a planetary

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flyby technique that's

used by spacecraft to get

to where they're going.

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It's often used to speed up

the spacecraft's velocity

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and propel it outward

in the solar system, much

farther away from the Sun

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than the rocket it

launched on would have

been capable of doing

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so on its own.

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The technique has been used

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for multiple missions,

from the Voyagers to

the Parker Solar Probe.

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So how does it work?

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A gravity assist can change

the velocity of a spacecraft

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by entering the gravitational

influence of a large object,

like a planet.

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The orbit of a planet

around the Sun is used

as a source of energy.

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The spacecraft falls in

toward the planet under

the influence of gravity,

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and then it flies back away.

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A gravity assist can either

increase or decrease

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the energy of the spacecraft's orbit.

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If the spacecraft moves

around the planet

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in the same direction

as the planet's

orbit around the Sun,

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it'll gain a bit of energy,

as done with the Voyager

missions around Jupiter.

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The Lucy spacecraft will need

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two gravity assists to

get on trajectory to

the Trojan asteroids.

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The second assist will

happen in December 2024,

giving Lucy the energy

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it needs to cross to the

main asteroid belt, where

it will observe the asteroid

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Donaldjohanson, then

travel into the leading

Trojan asteroid swarm.