The navigation, positioning, and timing system that is known today as the Global Positioning System (GPS) is a combination of several satellite navigation systems and concepts developed by or for the DOD (Department of Defense). The predecessors to GPS include the following satellite systems: (1) Transit, an operational system developed for the U.S. Navy by the Johns Hopkins Applied Physics Laboratory that is still in use today1 ; (2) Timation, an experimental program developed for the Navy by the Naval Research Laboratory that demonstrated the ability to operate atomic clocks on board orbiting satellites and was used as a system concept for GPS;2 and (3) Project 621B, an Air Force study program originated in 1964 by Aerospace Corporation and the Air Force's Space and Missile Organization.3 In addition, a DOD Four Service Executive Steering Group was established in 1968 to investigate the development of a Defense Navigation Satellite System that would satisfy all of the DOD's satellite navigation requirements.
By 1972, the best characteristics of each of these four programs had coalesced to form the general system characteristics and initial design parameters for the system now known as the NAVSTAR Global Positioning System.4 The system configuration and a request for developmental funding was submitted to the Director of Defense Research and Engineering, and the Air Force agreed to become the Executive Agent for this joint system.
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