For most of human history, navigation required using the stars, landmarks, or maps. Only recently did a breakthrough in satellite navigation, knows as the Global Positioning System (GPS), render those methods obsolete. Today’s GPS is a highly precise system for measuring both position and time that began with a series experimental missions, including the first successful GPS transmission on July 19,1977.
On that day, the Navigation Technology Satellite-2 (NTS-2), recently launched from Vandenburg Air Force Base on June 23, 1977, successfully transmitted the first GPS signal from space. It was received at a building of the Rockwell-Collins company in Cedar Rapids, Iowa. The successful test proved that highly accurate positioning could be achieved by combining precisely timed signals from multiple satellites. The satellites and technology were developed by the US Department of Defense for military operations. As with many technologies developed by the DoD, it gradually made its way into civilian use to transform everyday life.
The GPS system today contains a network of around 30 satellites orbiting roughly 12,500 miles above Earth. Each satellite continuously broadcasts its exact location and the precise time the signal was sent, using extremely accurate atomic clocks. A GPS receiver listens for signals from multiple satellites, and by measuring how long each signal takes to arrive, it calculates the distance. Using a mathematical process called triangulation, the receiver can determine the latitude, longitude and even the current time. The GPS system has become one of the most useful tools, demonstrating how fundamental discoveries in physics and engineering can reshape how the world moves.
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