The Global Positioning System (or GPS) is a worldwide, space-based navigation system. It is made up of a collection of satellites owned by the U.S. Government which provide highly accurate, worldwide positioning and navigation information, 24 hours a day. This system is made up of twenty-four NAVSTAR GPS satellites, which orbit 12,000 miles above the earth, constantly transmitting the precise time and their position in space. The atomic clocks aboard each satellite keeps time by the vibration of atoms and are accurate to one second in 30 years!

Each GPS satellite transmits data that indicates its location and the current time. All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant. The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times because some satellites are farther away than others. The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver. When the receiver estimates the distance to at least four GPS satellites, it can calculate its position in three dimensions.