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Speaker 1: That's m o z y dot com. Welcome to brain
Speaker 1: Stuff from how stuff works dot com where smart Happens. Hi,
Speaker 1: I'm Marshall Brain with today's question, how does gravity assist
Speaker 1: work with interplanetary satellites? When NASA sends satellites out to
Speaker 1: the outer reaches of the Solar System, it will often
Speaker 1: send the satellites past the planet for a gravity assist.
Speaker 1: The satellite speeds up in the process. The idea behind
Speaker 1: a gravity assist is to use the planet's motion to
Speaker 1: accelerate the satellite. For example, as satellite heads towards Jupiter
Speaker 1: in the process, it accelerates because it's falling towards Jupiter
Speaker 1: through Jupiter's gravity. Then it passes fairly close to the
Speaker 1: planet and starts speeding away from it. However, at that point,
Speaker 1: the satellites starts slowing down because gravity is pulling it
Speaker 1: back towards the planet. From that description, it would seem
Speaker 1: like the net effect of gravity assist is zero. The
Speaker 1: satellite gains speed as it falls towards the planet, but
Speaker 1: then it loses it as it heads away. The thing
Speaker 1: that makes the assist work is the fact that the
Speaker 1: planet is in motion in its orbit. Jupiter, for example,
Speaker 1: is about five hundred million miles away from the Sun,
Speaker 1: which means that the circumference of its orbit is about
Speaker 1: three billion miles. Jupiter travels that distance in about twelve years,
Speaker 1: so it's moving through space at about thirty thousand miles
Speaker 1: per hour. If the satellite is moving in the same
Speaker 1: direction as Jupiter in its orbit, then it can actually
Speaker 1: increase its speed by thirty thousand miles per hour. That's
Speaker 1: a huge speed increase, and it's completely free. The problem
Speaker 1: with the assist is that you have to wait for
Speaker 1: the planets to line up correctly for it to work.
Speaker 1: That's why missions have to fly within certain time windows.
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