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GPS Chronicle: The Early History

GPS Chronicle: The Early History
by Majeed Ahmad on 07-19-2015 at 4:00 am

There is really nothing new about GPS: the technology was reinvented from the old. After satellite communications was established, scientists and engineers started to look for different ways of utilizing this fascinating space marvel. Radio navigation systems had been developed during the World War II for aircraft operations, which subsequently evolved into Loran satellite system.

In 1958, the U.S. Navy began working on Loran satellite to develop a system “Transit” for indicating the position of a receiver on the ground. Two years later, the navy launched Transit-1B system to demonstrate the feasibility of using satellites for navigational aids. A receiver on a ship used the measured shift of satellite’s radio signal, along with known characteristics of the satellite orbits, to calculate the ship position.

GPS has been reinvented from satellite communications

A practical system was born out of the need of the U.S. troops to pinpoint their locations during the Vietnam War. However, this system had a limited accuracy and was difficult to use due to its bulky terminal size. So, in the mid-1970s, the U.S. Department of Defense began a project to upgrade the navigation devices built around this concept for classified military use. The solution they developed required two dozen satellites, atomic clocks, microwave radio transmitters and some heavy-duty number-crunching hardware.

A more portable unit could now pinpoint an object’s exact location anywhere on the globe by receiving signals from a network of satellites in an orbit and triangulate them to determine latitude and longitude. The military called it Navstar, after the satellite constellation it used, but the industry and users ignored this nomenclature, and technology became known to the world as Global Positioning System or GPS.

The operational system contained twenty-one satellites in three orbital planes, with three spare satellites. The GPS collection of twenty-four satellites orbited twelve thousand miles above the Earth. These satellites constantly transmitted their precise time and position in space. With GPS, a receiver on ground or in the air could calculate its position using time signals from the satellites.

The calculation itself was based on a kind of triangulation—a math technique used to locate an object based on its distance from three points. So signals from three satellites were necessary, although in practice a fourth satellite was used to improve the accuracy of the other three signals. The result was that a GPS receiver could produce highly accurate coordinates of latitude, longitude, and altitude.

GPS was originally developed for military use

The U.S. Air Force played a crucial role in nurturing the GPS technology by incorporating features like accurate digital maps and satellite photographs. As a result, the pilots were able to spot the key target areas and hit them effectively. Precision-guided munitions, dubbed “smart bombs,” increasingly used GPS to hone in on a fixed target such as a military installation or an airfield.

Content of this article is based on excerpts from Smartphone: Mobile Revolution at the Crossroads of Communications, Computing and Consumer Electronics.

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