Schematic diagram of GPS satellite navigation system

　　First of all, the GPS system is a passive system for our users, that is, the user's receiver is only responsible for receiving, decoding, and computing, and will not return data, so as long as the signal is covered, countless users can use the GPS system , which is similar to the principle of our radio station.

　　The standard configuration of GPS satellites is 24 satellites, but at present, due to the addition of overtime satellites and new satellites, the number has exceeded the configuration of 24 satellites, and their orbits have also been adjusted accordingly. The operating orbits of GPS satellites are distributed in 6 orbits, and the standard number of satellites on each orbit is 4, and the orbital time is approximately 12 hours (half a sidereal day), ensuring that in most places Can provide effective and stable navigation services.

　　The navigation satellites are equipped with L1 and L2 frequency band signals, and the Block IIF satellites began to increase the L5 frequency band signals. We will give a brief introduction to the development of the satellites.

　　The Block I satellite is the earliest satellite of the GPS system. The purpose is to verify the feasibility of the system design. Therefore, only 11 satellites were manufactured and launched between 1978 and 1985. However, because only 3.5 days of ephemeris can be stored on the satellites , so frequent contact with the ground is required to upload new data. If there is no ground management, the attitude of the satellite will change in a very short time, which will affect the actual navigation and positioning needs. The satellite is equipped with two rubidium and two cesium atomic clocks. Although the design life is about 5 years, many satellites have worked hard for more than twice the life, leaving valuable data for subsequent satellite design and failure analysis.

　　The Block II satellite is a second-generation satellite that has been improved after learning from the previous generation of satellites. A total of 9 satellites were launched in 1989. The built-in storage of the satellite was increased to 14 days of ephemeris, and autonomous momentum control was achieved. It can reduce frequent contact with ground control and carry multiple rubidium/cesium atomic clocks inside. The average design life is 6 years, but the length of time the satellites actually operate average about 12 years. This is also a satellite product in the early days of the GPS system.

　　Later, more Block IIA satellites appeared, which are very similar to the previous generation satellites, and enhanced some functions of the system, such as extending the autonomous operation time to 180 days, and the satellites can work continuously for 6 months without contacting the ground. A total of 19 were produced.

　　Block IIR satellites are produced for full compatibility and replacement of Block II and Block IIA satellites. They support the basic features required by GPS systems, C/A and P(Y) codes on the L1 frequency band and P(Y) codes on the L2 frequency band. )code. All Block IIR satellites are equipped with three rubidium atomic frequency standards (RAFS), which are simply more advanced and consistent standards. Block IIR also greatly strengthens the physical packaging in the design, thereby improving the stability and reliability of the satellite. . Later, there was an improved Block IIR-M satellite, and many hardware devices such as the L1/L2 transmitter were redesigned.

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