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Object

Global Positioning System

A globe with a grid overlay, depicting the continents of North America, South America, Europe, and Africa, set against a starry night sky.

A constellation of roughly thirty U.S. Air Force satellites orbiting at about 20,200 kilometres altitude, each broadcasting a precisely timed radio signal. A receiver triangulates its position by comparing arrival times from four or more satellites. The system became fully operational in 1995 and is the first piece of consumer infrastructure whose moment-to-moment function depends explicitly on Einstein's equations.

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