GPS space and ground control

　　space

　　The space part of GPS is composed of 24 working satellites, which are located 20 200 km above the earth's surface, evenly distributed on six orbital planes (four for each orbital plane), and the orbital inclination is 55 °. In addition, there are four active backup satellites in orbit. The distribution of satellites enables the observation of more than 4 satellites anywhere and at any time in the world, and maintains a geometric image with good positioning and calculation accuracy. This provides continuous global navigation capabilities over time. The GPS satellite generates two sets of codes, one of which is called the C/A code (Coarse/Acquisition Code 11023MHz); A group called Procise Code (10123MHz) is controlled by the US military due to its high frequency, low interference, and high positioning accuracy. It has a password and cannot be interpreted by ordinary people, mainly serving the US military. After deliberately reducing the accuracy of the C/A code through measures taken, it is mainly open for civilian use.

　　ground control

　　The ground control section consists of one main control station, five global monitoring stations, and three ground control stations. The monitoring stations are equipped with precision cesium clocks and receivers that can continuously measure all visible satellites. The satellite observation data obtained by the monitoring station, including ionospheric and meteorological data, will be preliminarily processed and transmitted to the main control station. The main control station collects tracking data from various monitoring stations, calculates the satellite's orbit and clock parameters, and then sends the results to three ground control stations. The ground control station injects these navigation data and main control station commands into each satellite as it reaches the sky. This injection is performed once a day on each GPS satellite and the final injection is performed before the satellite leaves the injection station's operational range. If a ground station malfunctions, the navigation information stored in the satellite can still be used for a period of time, but the navigation accuracy will gradually decrease.

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