INTELSAT V SPACECRAFT TELEMETRY COMMAND AND RANGING

Abstract

The INTELSAT V communications satellite was designed and assembled by the Ford Aerospace and Communications Corporation of Palo Alto, California, for the International Telecommunications Satellite Consortium (INTELSAT). The Communications Satellite Corporation (COMSAT) is the designated United States representative to INTELSAT and also performs technical service for INTELSAT in monitoring the design, fabrication, and test of communications satellites. The TT&C subsystem consists of two functionally redundant and independent command and telemetry channels, the major elements of which are shown in Figure 1. The telemetry subsystem provides two data channels for formatting and transmitting data received from sensors, transducers, and status indicators in the various subsystems of the spacecraft. In addition, the output of a command receiver can be connected to a telemetry transmitter to form a ranging transponder. The telemetry unit can provide normal or dwell PCM data in NRZ-M format modulated on a 32 KHz subcarrier. The telemetry transmitter phase modulates one of the data subcarriers or ranging tones on a 4 GHz band downlink carrier. The transmitter output is routed directly to an earth coverage conical horn for transmission at a level of approximately 0.0dbW. The transmitter output can also be routed through a zone communications channel TWTA to a telemetry omni-directional bicone antenna for extended coverage. Commands and ranging tones are received on a 6 GHz band uplink carrier through dual Omni pattern antennas. The received signal is routed through a passive filter to the two command receivers where the frequency modulated command or ranging tones are detected. The command tones are routed to the command units for processing. The command transmission is either a command message, consisting of 58 serial bit, or a command execute. The command message includes the address of the command unit which is to be used and what specific command function is to be executed. The command units provide the capability for pulse, discrete relay, and proportional relay command functions required by the various subsystems of the spacecraft.