The US Global Positioning System GPS GPS was developed in the late 1960s. In 1973, the system program was officially born. In 1994, a practical satellite navigation system was built, costing more than 12 billion US dollars. The system consists of three parts: space segment, ground segment and user segment. The satellite constellation consists of 24 satellites distributed over 6 orbital planes and currently has 27 satellites in orbit. GPS is controlled by the US Department of Defense and can provide both military and civilian services. The military code positioning accuracy is 10 meters, which is only used by the US military and its allies. The positioning accuracy of the civilian code is about 20 meters, which is usually open to the whole world and can be partially closed during wartime. In the Gulf War, especially in the Kosovo War, GPS played an important role in the important battle links such as air platform navigation, weapon launching, precision guidance, and targeting. This system is currently the most successful satellite navigation system, and it is in an international monopoly position in practical application and industrialization. GPS has become an international industry. Especially since 24:00 on May 1, 2000, the United States announced that it has suspended the SA policy, prompting the GPS industry to enter a period of more rapid growth. "GPS applications are only limited by people's imagination."
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In the early 1970s, the former Soviet Ministry of Defense also proposed the concept of the Global Navigation Star System (GLONASS). System design began in 1978. In 1995, the system was successfully networked and put into operation, and the construction cost more than 4 billion US dollars. The system constellation consists of 24 satellites distributed on three orbital planes, controlled by the Russian military. GLONASS is similar to GPS in terms of system composition and positioning speed measurement principle, but it also has some differences in some specific technical systems. GLONASS can provide two kinds of navigation and positioning services for military and civilian. The civilian precision is about 50 meters, and the accuracy of military code is equivalent to GPS. The civilian market of GLONASS is far less applicable than GPS, but its military code system has been widely used in its weapons and equipment. Due to the economic downturn in Russia in recent years, the system was not replenished in time. As the life of the satellite in the constellation expired, only five satellites were in orbit in August 2002. Three of them (1 group) were launched in October 2000 and two were launched in December 2001. At present, starting from the needs of high-tech warfare, Russia has made up its mind to restore and further develop the system. On August 20, 2001, the Russian government passed the federal special plan No. 587 “Global Navigation Systemâ€, which clarified the normal work of restoring the system before 2005 and formulated a detailed plan for the development of GLONASS before 2010. The European GALILEO project, proposed in February 1992, is scheduled to be completed in 2008 with a planned investment of approximately US$2.8 billion. The system constellation consists of 30 satellites distributed in three orbital planes and is a civil commercial system involving 15 EU countries. . The GALILEO system provides three types of services, namely: free services for the market, positioning accuracy of 12-15 meters; commercial services, positioning accuracy of 5-10 meters; public service, positioning accuracy of 4-6 meters. The latter two services are controlled and fee-based services. The EU seeks to cooperate with Russia and China, hoping to share part of its funds and occupy the market with its products. The GALILEO system space segment consists of 30 (three of which are in-orbit backup) uniformly distributed in three circular orbits (MEO) satellites with a height of 23,716 km and an inclination of 56°. The satellite is equipped with navigation and search and rescue loads. . Compared with GPS and GLONASS, the ground segment increases the monitoring, enhancement and integrity monitoring of the system, making GALILEO have higher positioning accuracy, usability and better continuity than the above two systems. Therefore, GALILEO can meet the application requirements closely related to personal safety such as aviation and road traffic management.
The "Beidou No. 1" system was proposed in 1985. In January 1994, the project was approved for development. The system was commissioned on January 1, 2002. The completion of the system has filled the gap in the field of satellite navigation and positioning in China, breaking the monopoly of the United States and Russia in this field, making China the third country in the world with an autonomous satellite navigation and positioning system. The system has low investment and quick effect, and is suitable for China's national conditions, especially the system has the characteristics of monitoring, command and dispatching. After the system was in operation, it has played an important role in military exercises, launching 921 spacecraft, border investigations, and naval missions, and has been well received by the majority of officers and men. In the civilian field, Beidou No. 1 user machine has been tested in the fields of transportation, railway, forest fire prevention, etc., and has been highly valued by the relevant departments of the country, and has expressed their desire to apply. The "Beidou No.1" system is a regional satellite navigation and positioning system developed and developed by China with independent intellectual property rights and independent control. It is suitable for China's national conditions. It is characterized by integrating navigation and satellite communication into users in the service area. High-precision, fast real-time positioning and two-way message communication services are available 24 hours a day, 7 days a week. In addition to fast positioning and short message communication, it also features precision timing. At the same time, the Beidou system combines the information of China's autonomous GPS satellite navigation augmentation system, and can release GPS differential correction information and GPS constellation integrity detection information to improve GPS positioning accuracy and location information reliability. With the continuous improvement of the global positioning system, the continuous improvement of hardware and software, the application field is constantly expanding. Now it has spread to various sectors of the national economy and has begun to gradually deepen people's daily lives. Perhaps in the past, it is difficult for us to feel the importance of GPS, because the former GPS was mostly used for military purposes, mainly for land, sea and air navigation, fixed-point bombing and ship-borne missile guidance. The technology has played a huge role in the Gulf War and the recent war on terrorism. After the Gulf War, the use of GPS gradually increased, from military use to civilian use, and has been greatly developed in the automotive field. So, when we first used GPS to drive, we started to rely on it. The picture above shows how the GPS navigator works.
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