Speaker 1: Welcome to brain Stuff from house Stuff works dot com
Speaker 1: where smart Happens. Hi Am Marshall Brain with today's question,
Speaker 1: how do satellites orbit the Earth? Satellites are to some
Speaker 1: degree mysterious objects. They travel in space, which feels like
Speaker 1: an exotic place because most of us have never been there.
Speaker 1: They're so far away we can't see them. They usually
Speaker 1: cost millions or billions of dollars, which means none of
Speaker 1: us will ever own one personally, and so on. Orbital
Speaker 1: mechanics can also be mysterious because there's no easy way
Speaker 1: for us to experience orbital mechanics personally. However, with a
Speaker 1: little imagination, you can understand the basic idea behind orbital
Speaker 1: mechanics very easily. Think about what happens when you throw
Speaker 1: a ball. Imagine that you're standing in a big field
Speaker 1: and you throw a baseball as hard as you can,
Speaker 1: like a picture. The ball might go a hundred feet
Speaker 1: and then hit the ground. You put the ball into orbit.
Speaker 1: It's just that the ball's orbit is very very short. Now,
Speaker 1: imagine that you shot a rifle straightened level instead of
Speaker 1: throwing a ball. The bullet might travel a mile before
Speaker 1: succumbing to gravity and hitting the ground. Now, imagine that
Speaker 1: you shoot a very large and powerful cannon that's able
Speaker 1: to give its shell an extremely high initial velocity. Imagine
Speaker 1: that the cannon is shot straight and level. The shell
Speaker 1: is going to go many miles far enough to actually
Speaker 1: follow the curve of the Earth for a period of
Speaker 1: time before hitting the ground. One thing that gums these
Speaker 1: examples up is air resistance. So imagine that you took
Speaker 1: this powerful cannon to the Moon and you mounted it
Speaker 1: on top of the highest mountain. The Moon has no
Speaker 1: real atmosphere and is completely surrounded by the vacuum of space.
Speaker 1: If you adjusted the speed of the shell just right
Speaker 1: and shot the cannon, the shell would follow the curve
Speaker 1: of the Moon perfectly. It would fall at exactly the
Speaker 1: same rate that the curve of the Moon falls away
Speaker 1: from it, so it would never actually hit the ground. Eventually,
Speaker 1: it would curve all the way around the Moon and
Speaker 1: ram right into the back of the cannon. On the Moon.
Speaker 1: You could actually have satellites in extremely low orbits like
Speaker 1: that just a few miles off the ground to avoid
Speaker 1: the mountains, and the satellites could conceivably be launched from
Speaker 1: powerful cannons on Earth. It's not so easy, because satellites
Speaker 1: have to get up above the atmosphere and into the
Speaker 1: vacuum of space to orbit for any length of time.
Speaker 1: Two miles up is about the minimum to avoid atmospheric interference.
Speaker 1: The Hubble Space Telescope orbits at an altitude of three
Speaker 1: hundred eighty miles or so, but the principle is exactly
Speaker 1: the same. The speed of the satellite is adjusted so
Speaker 1: that it falls to Earth at exactly the same rate
Speaker 1: that the curve of the Earth falls away from the satellite.
Speaker 1: The satellite is perpetually falling, but it never hits the ground.
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