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Japan is developing the Quasi-Zenith system, a regional augmentation of the GPS signal, with a 2008 planned launch.
Read MoreEurope launched the first test satellite in the Galileo system in December 2005.
Read MoreThe U.S. NAVSTAR (Navigation Signal Timing and Ranging) GPS constellation consists of ## active and ## spare satellites in MEO. According to the DoD, the fundamental concept of GPS is to use simultaneous distance measurements from ## satellites to compute the position and time of any receiver. The GPS signal is available without cost to users around the world and has spawned many commercial applications.
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