A GPS satellite

　　The GPS satellite is developed by the Space Division of Rockfield International Corporation. It weighs 774kg and has a service life of seven years. The satellite is honeycomb structure, the main body is cylindrical, diameter is 1.5m. The satellite is equipped with two double-bladed solar directional panels (BLOCK I) on both sides, which are 5.33 meters long and can receive sunlight with an area of 7.2m2. The sun orientation system controls the rotation of the battery panels on both wings, so that the panel surface is always aligned with the sun, provides constant power for the satellite, and charges three sets of 15Ah nickel-cadmium batteries to ensure that the satellite can work normally in the shadow of the earth. A multi-beam directional antenna with 12 elements at the bottom of the star can transmit two L-band (19cm and 24cm waves) signals with an Angle of about 30 degrees. Omnidirectional telemetry remote control antennas are installed on the two sides of the star for communication with the ground monitoring network. In addition, the satellite is equipped with an attitude control system and an orbit control system in order to maintain the satellite at an appropriate altitude and Angle and accurately target the visible surface of the satellite.

　　According to the working principle of GPS system, the higher the accuracy of the satellite-borne clock, the higher the positioning accuracy. Early test satellites used quartz oscillators developed at Hopkins University with a relative frequency stability of 10? 11 / SEC. The error is 14 meters. After 1974, GPS satellites used rubidium atomic clocks with a relative frequency stability of 10? 12/ SEC, error 8m. In 1977, the cesium atomic clock developed by Mas Frequency and Time Systems was used in the BOKCK II, and the relatively stable frequency reached 10? 13/ s, the error is reduced to 2.9m. In 1981, Hughes developed a relatively stable frequency of 10? The 14/ s hydrogen clock puts the BLOCK IIR satellite off by just 1m.

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