How does GPS work?

GPS, or Ground Positioning System, is a product of the space race and the military. It was initially designed to help the military navigate around the globe. Although it was designed in 1973, it didn’t become operational until 1995, and it has become a ubiquitous technology in GPS devices in our cars, boats and recently in our smart phones. Previous to this, one had to use a compass and a map to determine ones location, a system prone to error. An improvement to this primitive method came with computers in the form of a mapping program ( think Google Maps ), but one still had to determine ones location. The mapping program had no way to do this--until GPS became available.

The GPS system is based on using 32 satellites in orbits around the entire Earth. These satellites are in orbits at 12,600 miles high and they make two orbits around the Earth each day. The secret to how GPS works is that these satellites have atomic clocks that can measure time to an amazing precision. In order to find a specific latitude and longitude position on Earth, the satellite must know its exact position in three dimensions at all times and broadcast this information continuously. It uses a random digital code that a GPS receiver recognizes and can sync to. Although the GPS receiver is not as accurate as the GPS satellites, it’s still pretty good. That’s why the location it calculates is off slightly.

In order to calculate a position on Earth the receiver in your car or phone must simultaneously read continuous signals from four satellites. Using the speed of light, the GPS receiver computer determines the difference between its time and the time of each satellite. This time difference amounts to a distance because radio signals always travel at the speed of light so there’s a tiny delay that’s proportional to the distance from the receiver to the satellite. Using geometrical triangulation equations, the GPS receiver computer calculates its location as longitude, latitude and altitude. This is a simple explanation for a much more complicated mathematical process, but it is essentially what happens.

The GPS receiver can determine how fast its going and what direction its moving in using equations in its programming. Signals from the satellites can also be used to send traffic data and other information. What’s even more amazing is the fact that a GPS receiver can give one turn-by-turn directions to any location. Before this, one was forced to depend upon back seat drivers for this service. Just kidding!

Originally, the DOD (Department of Defense) crippled the accuracy of the GPS receivers in order to prevent enemies from using the system. However, this was removed to allow we civilians to get a more accurate location. That happened in 2000.

The GPS circuitry has been miniaturized to allow it to be used in cell phones. It truly is a marvel of modern electronics and space technology, and something we’ve grown to depend on for getting to a destination.

Thanks for reading.