American GPS: It was designed and developed by the U.S. Department of Defense in the early 1970s and completed in 1993. In 1994, the United States announced that it would provide the world with the right to use GPS for free within 10 years, but the United States only provides low-precision satellite signals to foreign countries. It is believed that the system has a "back door" set up by the United States, in the event of a war, the United States can shut down information services to a certain area. EU "Galileo": In 1999, Europe proposed a plan to launch 30 satellites to form the "Galileo" satellite positioning system. The program was officially launched in 2009. Russian "GLONASS": Not yet deployed. Beginning in the 1970s, at least 18 satellites were required to ensure coverage across Russia; for global positioning services, 24 satellites were required. China BeiDou Navigation Satellite System (BeiDou (COMPASS) Navigation Satellite System): It is a global satellite navigation system independently developed and operated by China. The goal of system construction is to build an independent, open and compatible, technologically advanced, stable and reliable Beidou satellite navigation system covering the world, to promote the formation of the satellite navigation industry chain, to form a complete national satellite navigation application industry support, promotion and guarantee system, and to promote satellite navigation. Widely used in various industries of the national economy and society. Beidou satellite navigation system consists of three parts: space segment, ground segment and user segment. The space segment includes 5 geostationary orbit satellites and 30 non-geostationary orbit satellites, and the ground segment includes several ground stations such as the main control station, injection station and monitoring station. , the user segment includes Beidou user terminals and terminals compatible with other satellite navigation systems. In 2003, my country's Beidou No. 1 was completed and put into operation. Unlike GPS, the "Beidou" command plane and terminal can communicate in two directions. After the Sichuan earthquake on May 12 last year, the Beijing Armed Police Command Center and the Sichuan Armed Police Force used the "Beidou" to conduct hundreds of exchanges. The Beidou-2 series of satellites will enter the peak period of networking this year, and it is expected to form a global coverage system consisting of more than 30 satellites in 2015. At present, at 0:12 on January 17, Beijing time, my country successfully launched the third "Beidou" navigation satellite into the predetermined orbit with the "Long March 3C" carrier rocket at the Xichang Satellite Launch Center. At 23:53 on the evening of June 2, 2010, China successfully launched the fourth Beidou navigation satellite into the predetermined orbit of space with the "Long March 3C" carrier rocket at the Xichang Satellite Launch Center.

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