WEBVTT - How does gravity assist with interplanetary satellites?

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<v Speaker 1>That's m o z y dot com. Welcome to brain

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<v Speaker 1>Stuff from how stuff works dot com where smart Happens. Hi,

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<v Speaker 1>I'm Marshall Brain with today's question, how does gravity assist

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<v Speaker 1>work with interplanetary satellites? When NASA sends satellites out to

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<v Speaker 1>the outer reaches of the Solar System, it will often

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<v Speaker 1>send the satellites past the planet for a gravity assist.

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<v Speaker 1>The satellite speeds up in the process. The idea behind

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<v Speaker 1>a gravity assist is to use the planet's motion to

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<v Speaker 1>accelerate the satellite. For example, as satellite heads towards Jupiter

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<v Speaker 1>in the process, it accelerates because it's falling towards Jupiter

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<v Speaker 1>through Jupiter's gravity. Then it passes fairly close to the

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<v Speaker 1>planet and starts speeding away from it. However, at that point,

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<v Speaker 1>the satellites starts slowing down because gravity is pulling it

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<v Speaker 1>back towards the planet. From that description, it would seem

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<v Speaker 1>like the net effect of gravity assist is zero. The

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<v Speaker 1>satellite gains speed as it falls towards the planet, but

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<v Speaker 1>then it loses it as it heads away. The thing

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<v Speaker 1>that makes the assist work is the fact that the

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<v Speaker 1>planet is in motion in its orbit. Jupiter, for example,

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<v Speaker 1>is about five hundred million miles away from the Sun,

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<v Speaker 1>which means that the circumference of its orbit is about

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<v Speaker 1>three billion miles. Jupiter travels that distance in about twelve years,

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<v Speaker 1>so it's moving through space at about thirty thousand miles

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<v Speaker 1>per hour. If the satellite is moving in the same

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<v Speaker 1>direction as Jupiter in its orbit, then it can actually

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<v Speaker 1>increase its speed by thirty thousand miles per hour. That's

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<v Speaker 1>a huge speed increase, and it's completely free. The problem

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<v Speaker 1>with the assist is that you have to wait for

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<v Speaker 1>the planets to line up correctly for it to work.

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<v Speaker 1>That's why missions have to fly within certain time windows.

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<v Speaker 1>For more on this and thousands of other topics, is

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