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GPS Is Operational
Roger Easton (1921–2014)
With the launch of the first global positioning system (GPS) in 1978, the world was on its way to eliminating disorientation. Although the original goal was to provide radio location and navigation for US military planes and ships, today’s GPS receivers are the size of a small coin and provide location information not just for government vehicles, but for civilian vehicles, pedestrians, and even inanimate objects such as buildings.
Each GPS satellite contains an atomic clock and electronics that beam the satellite’s identifier and its exact time down to the planet 20,000 kilometers below. The signals travel at the speed of light, meaning they take roughly 0.06 seconds to reach the surface. Each receiver has an almanac that allows it to calculate each satellite’s exact position based on the current time. Because the receiver also has an accurate clock, it can subtract the time that it gets from each satellite from the current time and determine the distance to each satellite. Knowing these distances, along with the satellites’ actual positions, allows the receiver to calculate its own position. Although the first test satellite was launched in 1978, it wasn’t until 1990 that sufficient production satellites were in orbit that the terrestrial GPS receivers could function reliably.
The idea of using radio waves for navigation dates back to World War II, when the Allies developed increasingly sophisticated systems to help bombers reach their targets. The satellite-based system was designed in the 1960s as a navigation and targeting system by Roger L. Easton, a scientist at the Naval Research Laboratory. It was only after the 1983 intentional downing of Korean Air Lines flight 007, which had unwittingly strayed into the Soviet Union’s airspace, that President Reagan decided to make GPS freely available to the international community. Even then, GPS satellites were designed to transmit two signals: an unencrypted, less-accurate civilian signal designed for general use, and a more accurate encrypted signal intended for the US military. The two classes of service were called selective availability. Unexpectedly, radio-navigation use soon became dominated by civilians. In May 2000, President Bill Clinton ended the general use of selective availability, clearing the way for GPS’s growing use as a consumer navigation system.
SEE ALSO First Wireless Network (1971)
Block II are the second generation of satellites that make up the Navstar Global Positioning System, known as GPS. Built by Rockwell International, they were the first fully operational GPS satellites.