Dec. 8, 1993: Location, Location, Location

1993: The U.S. secretary of defense opens the global positioning system to civilian use. It’s about to change how people see where they are. The GPS story starts with Sputnik, the first artificial satellite. The night after it was launched by the Soviet Union in 1957, researchers at MIT were able to track Sputnik’s orbit […]

__1993: __ The U.S. secretary of defense opens the global positioning system to civilian use. It's about to change how people see where they are.

The GPS story starts with Sputnik, the first artificial satellite. The night after it was launched by the Soviet Union in 1957, researchers at MIT were able to track Sputnik's orbit by its radio signal. And if you can track satellites from Earth, you can figure out how to locate objects on (or just above) Earth from the positions of satellites.

The U.S. Navy experimented with a satellite navigation system for its submarines in the mid-1960s. The Transit System used six satellites in circumpolar orbits, calculating the Doppler shift of radio signals to ascertain position.

Originally called the Navstar Global Positioning System, the outlines of the current GPS were conceived at the Pentagon in 1973. Testing began the following year, and the first operational GPS satellite was launched in 1978. It became clear in 1979 that the initially planned 18 satellites would not provide sufficient coverage, so the number was increased to 24 (including three substitutes).

The system was intended for military uses like targeting missiles, as well as peacekeeping uses like monitoring nuclear-bomb tests outlawed by the 1963 Nuclear Test Ban Treaty. But, after Korean Airlines Flight 007 wandered into Soviet territory in 1983 and was shot down with a loss of 269 lives, even the military thought there might be distinct advantages to sharing the GPS system with civilians.

Twenty years after the initial concept, Secretary of Defense Les Aspin wrote to Secretary of Transportation Federico Pena on Dec. 8, 1993, that the system had achieved "initial operational capability" as defined in the 1992 Federal Radionavigation Plan. The Defense Department thus opened the GPS Standard Positioning Service (SPS) to the Transportation Department.

After further testing for military use, the U.S. Air Force Space Command declared "full operational capability" on April 27, 1995. The civilian SPS initially provided an accuracy of 100 meters. The Precise Positioning Service (PPS) for authorized military users was accurate to within 22 meters.

President Bill Clinton issued an executive order in 1998 that resulted in the civilian service becoming as accurate as the military one, starting in May 2000. The disparity had in fact been artificially created by introducing random errors in the public signal. Those errors (called Selective Availability) can still be reintroduced in combat zones, so only friendly forces receive the highly accurate signal.

GPS augmentation and precise monitoring techniques known as carrier-phase enhancement, differential GPS and relative kinematic positioning can now provide accuracy down to 4 inches. GPS is integrated into so many devices today, it's as ubiquitous as cellphones.

We use GPS to navigate our car trips and manage fleets of taxicabs, trucks, buses and rental cars. First responders and package-delivery services rely on GPS. Airplanes fly with it. Fishing boats find their way to rich waters with it. Researchers track wildlife with it, and we even find our way down wilderness trails with it.

Henry David Thoreau would have been amazed. One way or another.

Source: Various

Artist's rendering of GPS satellite courtesy NASA.

This article first appeared on Wired.com Dec. 8, 2008.

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