GPS predecessor

　　The predecessor of the GPS system was a transit satellite positioning system developed by the US military, which was developed in 1958 and officially put into use in 64. The system operates on a satellite network consisting of 5 to 6 satellites, bypassing the Earth up to 13 times a day, and cannot provide altitude information, resulting in unsatisfactory positioning accuracy. However, the meridian system has enabled the research and development department to gain preliminary experience in satellite positioning and verified the feasibility of using satellite systems for positioning, laying the foundation for the development of GPS systems. Due to the enormous superiority of satellite positioning in navigation and the significant shortcomings of the meridian system in navigation for submarines and ships. The US military, land and air force, as well as the civilian sector, feel an urgent need for a new satellite navigation system.

　　To this end, the US Navy Research Laboratory (NRL) proposed a global positioning network plan called Tinnation, which consists of 12 to 18 satellites at an altitude of 10000 kilometers. In 67, 69, and 74, one experimental satellite was launched, and the atomic clock timing system was initially tested on these satellites, which is the foundation of precise positioning of the GPS system. The US Air Force, on the other hand, proposed a plan for 621-B to consist of 3 to 4 star clusters consisting of 4 to 5 satellites per cluster. Except for one of these satellites using a synchronous orbit, all other satellites use a tilted orbit with a period of 24 hours. This plan uses pseudorandom code (PRN) as the basis for transmitting satellite ranging signals, and its powerful function can detect signals when the signal density is less than 1% of environmental noise. The successful application of pseudo random codes is an important foundation for the success of GPS systems. The Navy's plan is mainly used to provide low dynamic 2D positioning for ships, while the Air Force's plan can provide high dynamic services, but the system is too complex. Due to the significant cost involved in developing two systems simultaneously and the fact that both programs were designed to provide global positioning, the US Department of Defense merged the two into one in 1973, led by the Joint Satellite Navigation and Positioning Program (JPO) led by the Department of Defense. The agency was also established at the Air Force Space Service in Los Angeles. The organization has a large number of members, including representatives from the US Army, Navy, Marine Corps, Department of Transportation, Defense Mapping Agency, NATO, and Australia.

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A - GPS positioning