The basic design of the GPS unit is based partly on the similar ground-based radio navigation systems. These type systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II.

All additional inspirations came when the Soviet Union launched the first Sputnik in 1957. A team of U.S. scientists were monitoring Sputnik’s radio transmissions. It was then discovered that, because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.

The first satellite navigation system was first successfully tested in 1960 by the Navy. Using a pairing of five satellites, it provided a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology the GPS relies upon.