Over the past decade or so, the Global Positioning System has grown from a military navigation tool to a near ubiquitous tracking system. Biologists use it to follow migrating animals, while motorists depend on it to avoid getting lost on highways. But while the system’s wide availability has sparked an explosion in innovative applications, satellite navigation itself can be traced back to the first satellite in orbit: Sputnik.
On October 4, 1957, the Soviet Union launched its famous orbiter, beating the United States into space and shocking the world with its technological prowess. For 23 days, Sputnik circled the globe emitting a radio signal, a constant beep that could be heard by anyone tuned to its frequency.
A few days after Sputnik’s launch, physicists William Guier and George Weiffenbach at the Johns Hopkins Applied Physics Laboratory set up a receiver to listen for its signal. Because of the Doppler effect, the tone they heard varied slightly in frequency as the satellite passed overhead. The men realized they could use this shift to calculate Sputnik’s position relative to their receiver and soon were able to accurately predict Sputnik’s path.
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