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Article: GPS
- Article from:
- Encyclopedia of Espionage, Intelligence, andSecurity
CopyrightCOPYRIGHT 2004 The Gale Group Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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GPS
Global Positioning System (GPS) is a navigation system consisting of a constellation of 24 navigational satellites orbiting Earth, launched and maintained by the U.S. military. GPS satellites orbit at approximately 11,000 mi (17,700 km) above Earth, with orbit periods of approximately 10 hours. The final satellite was placed in orbit in 1993. Because each satellite houses cesium and rubidium atomic clocks that are periodically updated and synchronized with a ground station in Colorado, GPS receivers can decode signals from the satellites to calculate location and exact time.
To overcome shortcomings in earlier navigation systems, United States developed another system: Navstar ...