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cinemascifi t1_j8zk25s wrote

Reply to comment by Flamingotough in Where does space really begin? Chinese spy balloon highlights legal fuzziness of ‘near space’ by HarpuasGhost

It may seem wrong, but that's how GPS operates... via geosynchronous satellites in orbit all over the world.

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gms01 t1_j8zrqig wrote

Actually, the GPS satellites are not geosynchronous satellites, which would imply orbits at 22,236 miles above sea level for circular orbits. From Earth, only those orbits appear stationary (in equatorial orbit) or at least varying within a relatively small area (if not in equatorial orbit).

The GPS satellites are in Medium Earth Orbit (MEO), around 12,540 miles. The GPS satellites do not hover over one area. They don't have to hover. Each satellite broadcasts its own four dimensional position in spacetime (3 space coordinates and the time, kept by accurate atomic clocks). Based on the calculated time delays from at least 4 satellites, a GPS receiver can uniquely determine the it's position.

See the Wikipedia article on GPS: https://en.wikipedia.org/wiki/Global_Positioning_System

and on geosynchronous orbit:

https://en.wikipedia.org/wiki/Geosynchronous_orbit

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Bu22ard t1_j8zwngb wrote

GPS satellites are not geosynchronous

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Flamingotough t1_j94i4kv wrote

Earth's surface rotates at about 1000mph, and to maintain geosynchronous orbit an object must orbit at about 7000mph - that why I said 'orbital' flight speed as opposed to surface speed.

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cinemascifi t1_j95g4bd wrote

I didnt say anything about speed. Are you responding to the right comment? It seems like a non sequitur.

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Flamingotough t1_j98ap4d wrote

I may have just misunderstood you point?

I thought you critized my idea of taking speed into account, by saying that objects in geosynchronous orbit would be stationary as seen from the ground. I just wanted to note that although that is true enough for this argument, such an object would still travel it's orbit at a significantly different velocity compared to the spot on the ground underneath.

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