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APPENDIX C 145 Appendix C Overview Of The Global Positioning System And Current Or Planned Augmentations ORIGINS AND DEVELOPMENT OF THE NAVSTAR GPS PROGRAM 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. 1 The Transit system was put into operation in 1964. To date, approximately 28 satellites have been launched, and although an 8-satellite constellation is still operating, the DOD plans to phase out its use by 1996. Source of Information: Personal conversation with Lee Pryor of the Applied Physics Laboratory, Johns Hopkins University, 24 January 1995. 2 Three satellites were launched during the experimental Timation program. 3 No satellites were actually launched as part of the 621B study program. 4 Although the system is still officially known as the NAVSTAR Global Positioning System (GPS), the NAVSTAR name is rarely used. For the remainder of this appendix, and throughout the rest of the report, the system is simply referred to as GPS.