Why doesn't Beidou have satellites 15, 17, 18?

Beidou satellite navigation system is a global satellite navigation system independently developed by China. It should be said that it is a huge project that makes Chinese people very proud. According to the plan, China will build the Beidou satellite navigation system covering the whole world in 2020, which will be able to provide services for the whole world. You may already know that China's Beidou navigation system has 35 navigation satellites, but so far it has launched 4 1 satellite. Why is it still launching? By 2020, how many satellites will be launched to complete the deployment?

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China's Beidou satellite navigation system is based on a three-step plan, which is divided into Beidou-1, Beidou-2 and Beidou-3. The usual 35 satellites that complete global coverage and positioning refer to 35 navigation satellites, which are Beidou-3 navigation satellites. These 35 navigation satellites do not include Beidou-1 and Beidou-2 satellites. The usual 4 1 satellite also refers to 4 1 navigation satellite.

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It should be explained here that satellites and navigation satellites are different. Our Beidou-1 * * launched four satellites, but due to technical limitations, it is mainly to study the feasibility and verify the structure and basic functions of the satellites. The accuracy is very poor, and it does not have the ability of positioning and navigation, so it cannot be regarded as a navigation satellite. The navigation satellite was launched only after Beidou-2. Beidou-2 launched 24 navigation satellites, including 3 spare satellites.