What is GPS?

　　Solution: A: GPS is the Global Positioning System (full name: Navigation System with Timing And Ranging Global Positioning System, NAVSTAR-GPS). It is a new generation of satellite navigation and positioning system developed by the U.S. Department of Defense in the 1970s. It took 20 years, cost 20 billion dollars, and was fully completed in 1994. It has the ability to conduct all-round real-time three-dimensional navigation and positioning in the sea, land, and air.

　　According to the current plan, the space part of GPS uses 28 satellites (24 operating and 4 standby) with a height of about 20200km to form a satellite constellation. The 24 satellites are in nearly circular orbits, with an operation period of about 11 hours and 58 minutes, distributed on six orbital planes (four for each orbital plane), and the orbital inclination is 55 degrees. The distribution of satellites makes it possible to observe enough (more than four) satellites at any time anywhere in the world, and maintain the geometric figure (DOP) with good positioning accuracy. This provides continuous global navigation capability in time.

　　At present, the civil satellite signal is SPS (Standard Positioning Service), a Standard Positioning service that provides free universal services to the public. The US satellite signal is a PPS (Precise Positioning Service) accurate positioning service, which is limited to military applications.

　　FAQ: What are the satellite positioning systems in the world?

　　A: At present, in addition to the GPS satellite positioning system of the United States, there is also the GLONASS system of Russia and the GALILEO system being built by the European Union. China has built the Beidou Generation and is building the CNSS system. Japan is also building its regional satellite positioning system, commonly known as GNSS (Global Navigation Satellite System).

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