THE GLOBAL POSITIONING SYSTEM

Soon after the Soviets launched Sputnik in 1957, some scientists and engineers realized that radio transmissions from a satellite in a well-defined orbit could indicate the position of a receiver on the ground. The procedure uses the Doppler shift of radio signals as the satellite passes overhead. (A similar Doppler shift accounts for the sudden change in the tone of a train whistle as a locomotive speeds by.) Using this method, the U.S. Navy pioneered the "Transit" satellite positioning system during the 1960s. This article traces the development of Global Positioning System technology (GPS) as it exists today, its many uses, current new developments, and where GPS technology and policy is headed.