The predecessor of the GPS system was a satellite transit system developed by the US military (Transit). It was developed in 1958 and put into use in 1964. The system works with a star network consisting of 5 to 6 satellites, bypassing the earth up to 13 times a day, and is unable to give altitude information. It is also not satisfactory in positioning accuracy. However, the Meridian system has enabled the R&D department to obtain preliminary experience on satellite positioning and verified the feasibility of positioning by satellite systems, paving the way for the development of GPS systems. Satellite positioning shows great advantages in terms of navigation and the Meridian system has huge defects in the navigation of submarines and ships. The U.S. Armed Forces and Air Force and the civilian sector both feel an urgent need for a new satellite navigation system.
To this end, the United States Naval Research Laboratory (NRL) proposed a global positioning network plan with 10,000-km altitude for 12 to 18 satellites named Tinmation, and launched a test satellite in 67, 69, and 74 years. Atomic clock timing systems were initially tested on these satellites, which is the basis for the precise positioning of GPS systems. The U.S. Air Force proposed a 621-B plan to form three to four constellations of four to five satellites per constellation. All but one of these satellites use a synchrotron orbit with a period of 24 h. The program spreads satellite ranging signals on the basis of pseudo-random numbers (PRNs). Its powerful function can detect when the signal density is less than 1% of the ambient noise. The successful use of pseudo-random code is an important basis for the success of the GPS system. The Navy's plan is mainly used to provide ships with low-dynamic 2-dimensional positioning. The Air Force's plan can provide high-dynamic services, but the system is too complicated. Since the simultaneous development of the two systems would result in huge costs and both plans were designed to provide global positioning, the US Department of Defense combined the two in 1973 and was jointly led by the Ministry of Defense. The Bureau of Planning (JPO) leaders will also set up offices in the Air Force Space Division in Los Angeles. The agency has a large number of members, including representatives of the U.S. Army, Navy, Marine Corps, Department of Transportation, National Defense Mapping Agency, NATO, and Australia.