GPS satellite on test stand.GPS Tracker

　　The GPS satellite was developed by the Space Department of Rockefeller International, with a weight of 774kg and a lifespan of 7 years. The satellite adopts a honeycomb structure, with a cylindrical main body and a diameter of 1.5m. The satellite is equipped with two dual leaf solar panels (BLOCK I) on both sides, with a total length of 5.33 meters and a sunlight receiving area of 7.2m2. The solar orientation system controls the rotation of the two wing battery panels to keep the panels aligned with the sun, continuously providing power to the satellite, and charging three sets of 15Ah cadmium nickel batteries to ensure that the satellite can operate normally in the shadow of the Earth. A multi beam directional antenna with 12 units is installed at the bottom of the star, which can transmit signals in two L-bands (19cm and 24cm waves) with an angle of approximately 30 degrees. Omnidirectional telemetry and remote control antennas are installed on both ends 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 to maintain the satellite at an appropriate altitude and angle, accurately aligning with the visible ground of the satellite.

　　According to the working principle of the GPS system, the higher the accuracy of the onboard clock, the higher its positioning accuracy. Early experimental satellites used a quartz oscillator developed by Hopkins University, with a relative frequency stability of 10? 11/second. The error is 14 meters. After 1974, GPS satellites adopted rubidium atomic clocks with a relative frequency stability of 10? 12/s, error of 8m. In 1977, the BOKCK II model adopted a cesium atomic clock developed by Mars Frequency and Time Systems, and its relatively stable frequency reached 10? 13/second, the error is reduced to 2.9m. In 1981, Hughes developed a relatively stable frequency of 10? The 14/second hydrogen atomic clock results in an error of only 1m for the BLOCK IIR satellite.

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