Until recently, nobody knew if the GPS system would work above the network of satellites. They actually orbit at 20,000 kilometers.
This was a very important information to know, because there are around 300 communications satellites. They are at 36,000 kilometers, which is the altitude at which a device might reach “geosynchronous orbit”. Which means, it will keep passing over the same part of the earth at all times.
Part of the history of the GPS system is the story of the AO-40 satellite. Back in September of 2001, one amateur satellite named AO-40, had successfully detected a GPS signal. This was done in cooperation with NASA of course, at an altitude of 52,000 kilometers.
The way GPS satellites work is, that they only beam their transmissions toward the earth. So the satellite AO-40 had to rely on small beams that were passing the earth and going to the other side of it, up to 70,000 kilometers away.
Usage of GPS In Military Industry
The need for GPS started with the military. It was initially a military device that would help the United States forces doing their job better.
