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Satellite navigation

The launch of Sputnik also planted the seeds for the development of modern satellite navigation. Two American physicists, William Guier and George Weiffenbach, at Johns Hopkins University's Applied Physics Laboratory (APL) decided to monitor Sputnik's radio transmissions and within hours realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit. The Director of the APL gave them access to their UNIVAC computer to do the then heavy calculations required.

Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem: pinpointing the user's location, given the satellite's. At the time, the Navy was developing the submarine-launched Polaris missile, which required them to know the submarine's location. This led them and APL to develop the TRANSIT system, a forerunner of modern Global Positioning System (GPS) satellites.