GPS Basics: How the Global Positioning System works.

Here is a brief overview of how GPS works...

The Global Positioning System is the only fully operational global navigation system. Using a group of at least 24 satellites which transmit precise signals, the system enables a GPS unit to calculate its speed, location, direction, and time.

The Global Positioning System was developed by the US Department of Defense and is actually named NAVSTAR GPS. The system's satellites are managed and maintained by the US Air Force. The cost of managing the system is approximately $750,000,000 per year (yes... million) including the replacement of aging satellites, research and development, and upgrades to the system.

An average GPS unit calculates its location using the signals from four or more GPS satellites. Each GPS satellite contains an atomic clock, and continually transmits messages containing the current time and additional geographic information. The messages are sent at a known speed, so the GPS unit uses the arrival time of the message to determine the distance to each satellite. When a GPS unit is able to calculate its distance to four or more satellites, it determines the location of the unit and displays that in longitude/latitude or some other human readable format.