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GPS- Introduction 1

Module by: Rami Alkubaty. E-mail the author

Summary: A historical introduction to GPS and then GPS 3 Segment : satellites + Control + user.

x. GPS "... GPS has been the biggest revolution in military affairs since the invention of atom- bomb" BBC- Documentary- The Satellite Story x.1 Preamble With the scientific revolution it brought with it, GPS is considered today as the only full functional satellite navigation system. GPS has revolutionized the science of positioning and Earth measurement. One part of that revolution is accuracy; another part is speed and simplicity. A third part is cost. The main goal of creating such system was primarily military. GPS is rapidly becoming an integral component of the emerging Global Information Infrastructure, with applications ranging from mapping and surveying to international air traffic management and global change research. The growing demand from military, civil, commercial, and scientific users has generated a U.S. commercial GPS equipment and service industry that leads the world. Augmentations to enhance basic GPS services could further expand these civil and commercial markets. GPS is managed by the "National Space- Based Positioning, Navigation and Timing (PNT) Executive Committee". This is a joint committee of department of defense (DoD) and department of transportation (DoT). x.2 Historical background The history of GPS began with a memorandum issued by the U.S. Deputy of Defense on 17th April 1973 designated the U.S. Air Force as the executive service to consolidate the TIMATION[1] and 621B[2] concepts into a comprehensive all-weather worldwide common grid navigation system. This system has been given the name “NAVigation Satellite Timing And Ranging”, or simply “NAVASTAR GPS”. Further, the development of NAVSTAR-GPS in the last thirty years can be summarized as follows:- Phase I- Concepts validation (1973-1979): ● Validation of the concept of TIMATION and 621B ● Two experimental Navigation Technology Satellite (NTS) were built and launched to support validation of the GPS ● The first NAVSTAR- GPS block I (research and development) satellites were launched in February 1978. Total number of satellites was eleven. Satellites were launched between 1978 and 1985. All eleven satellites of block I are no longer in service Phase II- Full scale development (1979-1985): Phase II included design, refinement, fabrication, qualification, testing and extension field testing of user segment. Phase III- Production and deployment (1986- present): The first block II satellite was launched on 14th February 1989. The combined constellation of block I and II satellites achieved worldwide 2D positioning capability in June 1991. Worldwide 3D capability was achieved in 1993.

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