How do GPS Satellites work exactly, with emphasis on exactly. I know that GPS satellites use electromagnetic waves to send out a signal of their current location and time for GPS devices to pick up. Using at least 3 GPS satellites, GPS devices can pin point their location by knowing the distance they are at from each satellite. 3 spherical intersections will pin point the location of a satellite down to a single point on a 2D surface. What I want to know is how the GPS device knows how far away it is from each satellite. Do they use v=d/t to figure out the distance? That's what I initially thought, but I don't think this is correct. If all you get from a satellite is the time and location at which the signal was sent, then you should be able to compare that to the time that you received the signal. Unfortunately, this doesn't sound plausible to me as this would require almost every device to have an atomic clock that is set very accurately, or the calculations will be far off. Could anyone explain this to me? It's for a school project I'm working on. Thanks in advance!