Secor electronic satellite tracking system = Le système secor pour la poursuite des satellites

Abstract

Secor is an electronic distance measuring system which uses the intermediary space positions of artificial satellites to determine geodetic positions on the earth's surface. Three ground stations are placed at geographical locations of known geodetic coordinates. Depending on the altitude of the satellite, the individual locations may be separated by as much as 2300 miles. A fourth ground station is placed at the spot whose coordinates are to be determined. When the satellite appears above the radio horizon of the ground stations, each station ranges sequentially to a transponder in the satellite on a time-shared basis. During a satellite pass of six minutes, the four stations measure approximately 29, 000 ranges. The coordinates of the unknown point are determined in two steps: First, the three stations at known coordinates are at the centers of three imaginary spheres of which the radii are ranges from the stations to the satellite at a given instant. The satellite must be in the surfaces of all three spheres, and is, therefore, at one of the two points of intersection of the three spheres. Secondly, three known satellite positions are the centers of three imaginary spheres of which the radii are distances from the unknown station to the satellite. The unknown station is at one of the two points of intersection of these three spheres. Solution of the simultaneous, quadratic equations of the spheres gives the coordinates of the unknown point.