How does a geostationary satellite remain over the same spot on Earth?
In: Planetary Science
Everything in orbit needs to go a certain speed to stay there, otherwise it will end up coming back inward towards the earth. The closer you are to the surface, the faster you need to go. The further you are, the slower you need to go.
At the very other extreme, if something isn’t moving sideways at all, it just falls straight down. That’s just… dropping.
Now, this has completely nothing to do with the rotation of the earth. Orbital speed and earth’s rotation are two completely separate things.
So in low earth orbit things need to go about mach 23 to stay there. The ISS completes an orbit in about 90 minutes, much faster than the 24 hours the earth itself takes to rotate.
But as mentioned, you need less speed the further away you are. At some point, which is about 35 thousand kilometres up, one orbit takes exactly as much time as it takes the earth itself to rotate. From earth’s surface, that satellite seems… Stationary.
Geostationary.
That of course assumes that this orbit actually rotates roughly around the same axis as the earth, and in the same direction. That doesn’t need to be true. As already said, orbits and earth’s rotation are unrelated. You can absolutely have a satellite orbiting at 90 degrees, overflying the poles. But then it obviously wouldn’t have the property of just hanging over a specific spot on the surface.
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