AUTOMATIC ORBIT EPHEMERIS UPDATE IN A LOW-COST GROUND STATION

This paper examines a method of updating the orbit ephemeris of low Ea rth orbit satellites based on antenna tracking error data from a singl e ground station. The paper describes Satellites International's low c ost S-band ground station which utilizes a 2.4 m parabolic dish antenn a with full azimuth and elevation drive control. The antenna incorpora tes a diplexing feed, with a low noise amplifier in the receive path, linked to a receiver/demodulator which downconverts and decodes the re ceived telemetry before passing it to a telemetry depacketizer; and th ence to the spacecraft control centre. The uplink telecommand data is packetized and passed to a sub-carrier generator, before being upconve rted in an S-band sweeper/modulator, followed by a high power amplifie r linked to the antenna feed. The antenna controller drives the antenn a in a fine resolution program track mode derived from a 10-point orbi t ephemeris. Tracking error data is obtained in real-time during a pas s by scanning the antenna across-track and along-track with respect to the nominal satellite position. The error measurements are then fed a utomatically into the orbit generation software to provide an updated orbit ephemeris. The paper demonstrates that the orbit prediction accu racy obtainable using this method can achieve satisfactory mission per formance. (C) 1998 Published by Elsevier Science Ltd. All rights reser ved.