How do satellites orbit the Earth?

In this episode of BrainStuff, Marshall explains the physics behind satellites and orbits.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from house Stuff works dot com
where smart Happens. Hi Am Marshall Brain with today's question,
how do satellites orbit the Earth? Satellites are to some
degree mysterious objects. They travel in space, which feels like

(00:24):
an exotic place because most of us have never been there.
They're so far away we can't see them. They usually
cost millions or billions of dollars, which means none of
us will ever own one personally, and so on. Orbital
mechanics can also be mysterious because there's no easy way
for us to experience orbital mechanics personally. However, with a

(00:45):
little imagination, you can understand the basic idea behind orbital
mechanics very easily. Think about what happens when you throw
a ball. Imagine that you're standing in a big field
and you throw a baseball as hard as you can,
like a picture. The ball might go a hundred feet
and then hit the ground. You put the ball into orbit.

(01:05):
It's just that the ball's orbit is very very short. Now,
imagine that you shot a rifle straightened level instead of
throwing a ball. The bullet might travel a mile before
succumbing to gravity and hitting the ground. Now, imagine that
you shoot a very large and powerful cannon that's able
to give its shell an extremely high initial velocity. Imagine

(01:27):
that the cannon is shot straight and level. The shell
is going to go many miles far enough to actually
follow the curve of the Earth for a period of
time before hitting the ground. One thing that gums these
examples up is air resistance. So imagine that you took
this powerful cannon to the Moon and you mounted it
on top of the highest mountain. The Moon has no

(01:50):
real atmosphere and is completely surrounded by the vacuum of space.
If you adjusted the speed of the shell just right
and shot the cannon, the shell would follow the curve
of the Moon perfectly. It would fall at exactly the
same rate that the curve of the Moon falls away
from it, so it would never actually hit the ground. Eventually,

(02:13):
it would curve all the way around the Moon and
ram right into the back of the cannon. On the Moon.
You could actually have satellites in extremely low orbits like
that just a few miles off the ground to avoid
the mountains, and the satellites could conceivably be launched from
powerful cannons on Earth. It's not so easy, because satellites

(02:34):
have to get up above the atmosphere and into the
vacuum of space to orbit for any length of time.
Two miles up is about the minimum to avoid atmospheric interference.
The Hubble Space Telescope orbits at an altitude of three
hundred eighty miles or so, but the principle is exactly
the same. The speed of the satellite is adjusted so

(02:56):
that it falls to Earth at exactly the same rate
that the curve of the Earth falls away from the satellite.
The satellite is perpetually falling, but it never hits the ground.
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(03:17):
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