GPS satellites are one of those things in our world that work really well, but no one knows how they work. In fact, life would be perfectly fine if we didn’t know how they work. But when we use GPS every day all day, we should know how they work. At least a little bit. Does a truck driver know everything about diesel engines? Not likely, but they probably know the basics. So here’s the basics of GPS satellites, for the construction guy.

Key components of GPS satellites are: orbit path, signal and time.

Orbit path – Satellites orbit the earth. The earth’s gravity keeps the satellites far from earth but not too far. When I say far from earth, I’m talking 20000km from the earth’s surface. The scale that the GPS satellite system works on is almost unfathomable. Anyway, the path that the satellite takes on its trip around the earth is called its ephemeris (or orbit path to keep it simple). And it is precisely measured by ground stations across the globe. This is so that at any given moment, the satellite’s position can be calculated based on its speed and what time it is. The ground stations upload the orbit path data to the satellite, so it can be sent to our rover. This is a key piece of the puzzle, because if we don’t know where the satellite is, how can it tell us where we are?

Signal – the satellite signal is basically some kind of super accurate microwave signal that sends data from the satellite to our GPS receivers, whether it’s a rover on a construction site or a smart phone telling you how to get to that new restaurant. In a very basic sense, (it’s way more complex than this) the data that the satellite signal contains is the satellites identification info, orbit data (or location data) as well as the time it was sent.

Time – time and signal work together with GPS satellites. GPS receivers measure distance based on time, the length of time it takes for the satellite signal to reach the receiver. The GPS receiver knows what time the signal was sent, because that time is included in the message sent by the GPS satellite. Then it compares the time it was sent, to the current time, and can then determine the distance from the rover to the satellite. Our GPS receiver then does this for 25+ satellites, and by comparing them all, computes a very precise location of your rover.

Keep in mind now that you’ve read this, this is me explaining a very, very complex process in terms that I hope a regular person can understand. Maybe we can get more in depth in a later post.