When did satellite navigation rise?

In the 1970s, one of the most modern navigation equipment began to rise, which is the global ship positioning system based on 2/kloc-0 working satellites, 3 standby satellites and corresponding ground support equipment established in the United States. At present, there are 18 satellites in the system, which are arranged in six orbits on average, with an inclination of 55, and the operation period is 12 hours. Satellites spread spectrum and modulate transmission signals through pseudo codes. The pseudo-codes used are 0 code, 9 code and C/A code. 0-code and 9-code signals have high positioning accuracy and good safety performance. The actual positioning accuracy is 10 meter, which is specially used by the US military and special users. General users use C/A code, and the positioning accuracy is 100 meters. Global positioning system can cover the whole world in two or three dimensions 24 hours a day. The GPS satellite navigators used in China all receive C/A code signals. The final pattern of GPS design is that the constellation consists of 24 satellites, of which 2 1 is constant and 3 are standby.