How many satellites are there in GPS?

1 satellite positioning system is a technology that uses satellites to accurately locate something. From the initial low positioning accuracy, it is difficult to provide navigation services in time, to the current high-precision GPS global positioning system, which can observe four satellites at any time and at any point on the earth at the same time, thus realizing navigation, positioning, timing and other functions.

Satellite positioning can be used to guide planes, ships, vehicles and individuals to reach their destinations safely and accurately along selected routes. Satellite positioning can also be applied to mobile phone tracking and other functions.

2 development and definition

Satellite positioning technology is a technology that uses artificial earth satellites to measure points. Early artificial earth satellites were only used as space observation targets, and this geometric observation of satellites can solve the problem of long-distance land-island joint positioning that is difficult to achieve by conventional geodesy. However, this method is time-consuming and laborious, which not only has low positioning accuracy, but also cannot measure the geocentric coordinates of this point. [2]?

The meridian satellite navigation system (NNSS) developed by the United States in the late 1950s is the predecessor of GPS. It works with a star network consisting of five to six satellites, and it orbits the earth 13 times a day at most, but it can't give altitude information and its positioning accuracy is not satisfactory. However, the meridian system enabled R&D department to gain the preliminary experience of satellite positioning, verified the feasibility of satellite positioning, laid the foundation for the development of GPS system, and opened a new era of sea and air navigation and a new chapter of satellite geodesy.

Because of the great advantages of satellite positioning in navigation, and the problems of meridian system, such as few satellites, long interval and observation time, inability to provide real-time positioning and navigation services, and low accuracy, the United States, the military, the 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, which consisted of 3-4 constellations with 4-5 satellites in each constellation. Except for 1 of these satellites, all other satellites use inclined orbits with a period of 24 hours. This scheme spreads satellite ranging signals based on pseudo-random code (PRN), and can detect environmental noise even if the signal density is lower than 1%. The successful application of pseudo-random code is an important basis for the success of GPS system. Because developing two systems at the same time will cause huge expenses, and both plans are aimed at providing global positioning, in 1973, the US Department of Defense merged the two systems into one, led by the Joint Planning Bureau of 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.

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 for intelligence gathering and nuclear explosion monitoring.

Working principle of satellite positioning

Some military applications, such as surveillance and emergency communication, are an important part of America's strategy of dominating the world. After more than 20 years of research and experiments, it cost 30 billion dollars. By1March, 1994, the layout of 24 GPS satellite constellations with 98% global coverage was completed.

Global Positioning System (GPS) 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.

3 application

Main uses of GPS: ① Land applications, mainly including vehicle navigation, emergency response, atmospheric physical observation, geophysical resource exploration, engineering survey, deformation monitoring, crustal movement monitoring, municipal planning control, etc. (2) Marine applications, including the determination of the best navigation route of ocean-going ships, real-time ship dispatching and navigation, maritime rescue, marine treasure exploration, hydrogeological investigation, offshore platform positioning, sea level fluctuation monitoring, etc. ; (3) Aerospace applications, including aircraft navigation, attitude control of aerial remote sensing, orbit determination of LEO satellites, missile guidance, aviation rescue and manned spacecraft protection detection, etc.

The specific application is as follows:

1, ocean navigation and water diversion into port

2, aircraft route guidance and approach landing

3. Automatic autonomous navigation

4. Ground vehicle tracking and urban intelligent traffic management.

5. Emergency rescue

6, personal travel and outdoor adventure

7. Personal communication terminal (integrated mobile phone, PDA, electronic map, etc.). ): Time synchronization of power, post and telecommunications, communication and other networks: accurate time input and accurate frequency input.

8. Surveying and mapping: setting out roads and various lines, underwater topographic survey, crustal deformation survey, deformation monitoring of dams and large buildings.

9.GIS application: construction machinery (tire crane, bulldozer, etc. ) control, precision agriculture.

reference data

Baidu encyclopedia:/item/%E5% 8d% ab% E6% 98% 9f% E5% AE% 9a% E4% BD% 8d/4761915? Fr = Aladdin