What is the GPS

　　The Global Positioning System is the second generation of American satellite navigation system. It is developed on the basis of meridian navigation satellite system, and it adopts the successful experience of meridian navigation satellite system. Like meridian system, GPS is composed of three parts: space part, ground monitoring part and user receiver. The space part of the system uses a constellation of 24 satellites at an altitude of about 20,200 kilometers. The 21+3 satellites are all in near-circular orbits with an orbit period of about 11 hours and 58 minutes. They are distributed on six orbital planes (four in each plane) with an orbital inclination of 55 degrees. The distribution of satellites allows more than four satellites to be observed anywhere in the globe at any time, with good positioning resolution accuracy geometry (DOP) maintained. This provides the ability to navigate the globe continuously in time.

　　GPS satellites have evolved to Block II-type positioning satellites, built by Rockwell International, which weigh about 1,900 pounds in orbit and have solar panels about 17 feet long. The 24th satellite was launched in 1994. Therefore, there are currently 24 GPS satellites in space for positioning. It takes 12 star hours to orbit the Earth, and it can orbit the Earth twice a day, which means that at any time, any place, there are at least four more satellites in our sky.

　　There are currently five satellite ground control stations in the world, located in Hawaii, Yasenshin Island, Diego Garcia, Guajalein Island, Colorado Springs, these satellite ground control stations also monitor the operation of GPS satellites and their precise position in space, The main ground control station is also responsible for transmitting the Ephemera's Constant correction of the satellite's Clock Offsets, which the satellite then feeds to the GPS receiver for positioning purposes.

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