A Delayed-Repeater Satellite Communication System of Advanced Design

This paper describes a delayed-repeater satellite communications system consisting of an orbiting delayed-repeater radio-relay station which passes over terminal ground stations located within the viewing area of the satellite. Messages are exchanged between the satellite and a ground station operating in the 2-kmc band utilizing both polarization and frequency diversity techniques to provide a continuous transmission circuit regardless of the satellite attitude. Data storage in the satellite is accomplished by the use of newly-developed magnetic tape recorders. Signals in the band near 108 mc provide telemetry and command control functions. The telemetry used is a modified standard FM/FM system, while the command control circuit enables selection of satellite control functions. Power for the satellite electronics is derived from solar energy using solar cells which charge nickel-cadmium batteries. Each of the ground stations consists of radio transmitting and receiving equipment and an automatic-tracking 28-foot-diameter parabolic antenna. Each station will acquire the satellite and track it during a pass over a station. Data from the satellite are transmitted (tape loading) to the ground station upon command. Simultaneously, data for the other. two stations are transmitted to the satellite (tape unloading) from the ground station. Message sorting in the satellite is accomplished by use of the appropriate tape recorders, which in turn are activated by ground commands. In the ground stations, teletype messages on paper tape are converted to a serial pulse train at a 50-kilobit-per-second rate by a paper-tape reader and a magnetic recorder-reproducer.