When your phone picks up signals from GPS satellites, the information it’s receiving is a time-stamp marking of the exact moment each satellite sent out its signal. The ironic thing about GPS is that it is a technology designed to locate your position spatially that is enabled largely by an ultra-precise measurement of time. Impressed with the demo, the grad students’ supervisor suggested that the approach could be reversed: if you knew the exact location of at least three satellites in orbit above you, by triangulating their various signals you could theoretically determine your location on the ground-or, if you happened to be on one of the new Polaris nuclear submarines the military was building, you could use it to determine your location in the middle of the ocean. After the Soviets launched Sputnik, the first man-made satellite to orbit Earth, in October of 1957, a pair of graduate students at the Applied Physics Laboratory in Maryland devised an ingenious system for tracking Sputnik’s location by analyzing slight variations in the microwave signals the satellite was transmitting, in effect using an antenna’s known location on Earth to calculate the satellite’s unknown location in orbit. Like many of the core technologies that define the digital age, GPS was an offshoot of American Cold War competition with the Soviet Union and the threat of nuclear annihilation.
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