What is GPS?

GPS is a global positioning system. Simply put, this is a satellite system consisting of 24 satellites covering the whole world. This system can ensure that four satellites can be observed at any point on the earth at any time, thus ensuring that satellites can collect the latitude, longitude and height of observation points, thus realizing the functions of navigation, positioning and timing. This technology can be used to guide planes, ships, vehicles and individuals to reach their destinations safely and accurately along selected routes.

Global Positioning System (GPS) is a new generation of space satellite navigation and positioning system jointly developed by the United States Army, Navy and Air Force in 1970s. Its main purpose is to provide real-time, all-weather and global navigation services for land, sea and air, and it is also used for some military purposes such as intelligence gathering, nuclear explosion monitoring and emergency communication. It is an important part of America's global dominant strategy. After more than 20 years of research and experiments, it cost 30 billion dollars. By1March 1994, 24 GPS satellite constellations with global coverage of 98% had been deployed.

The GPS global positioning system consists of three parts: the space part-GPS constellation; Ground control part-ground monitoring system; User equipment part -GPS signal receiver.

The predecessor of GPS

The predecessor of GPS system is the meridian satellite positioning system (Transit) developed by the US military, which was developed in 1958 and put into use in 64 years. The system works in a star network consisting of 5 to 6 satellites, which circles the earth 13 times a day at most, and can't give altitude information, so the positioning accuracy is not satisfactory. However, meridian system enables R&D department to gain the preliminary experience of satellite positioning, and verifies the feasibility of satellite positioning, which lays the foundation for the development of GPS system. Because satellite positioning shows great advantages in navigation, meridian system has great defects in submarine and ship navigation. The US Army, Navy, Air Force and civil departments urgently need a new satellite navigation system. Therefore, the US Naval Research Laboratory (NRL) put forward a global positioning network plan called Tinmation, which consists of 12 to 18 satellites with an altitude of 10000km. An experimental satellite was launched in 1967, 1969 and 1974 respectively, and the atomic clock timing system was preliminarily tested on these satellites, which is the basis of accurate positioning of GPS system. The US Air Force, on the other hand, proposed a scheme of 62 1-b, and each constellation consisted of 4 to 5 satellites. Except for 1, all these satellites adopt inclined orbits with a period of 24 hours. This scheme spreads satellite ranging signals based on pseudo-random code (PRN), and its powerful function can also be detected when the signal density is lower than 1% of environmental noise. The successful application of pseudo-random code is an important basis for the success of GPS system. The navy's plan is mainly used to provide low-dynamic two-dimensional positioning for ships, while the air force's plan can provide high-dynamic services, but the system is too complicated. Because the development of two systems at the same time will cause huge expenses, and both plans here are aimed at providing global positioning, in 1973, the US Department of Defense merged the two systems into one, which is under the responsibility of the Joint Planning Bureau for Satellite Navigation and Positioning (JPO) led by the Department of Defense, and its office is located in the Air Force Space Office in Los Angeles. The agency has many members, including representatives from the US Army, Navy, Marine Corps, Ministry of Communications, National Defense Cartography Bureau, NATO and Australia.