The design of the mechanically despun antenna for the Intelsat III communications satellite

The use of a spin-stabilized communications satellite of large channel capacity requires a high-gain antenna which may be despun, mechanically or electronically, with respect to the satellite. The design of a mechanically despun antenna system for the Intelsat-III communications satellite is discussed. The communications signals utilize a high-gain directive antenna which is mechanically despun while an omnidirectional antenna is used for the telemetry information. Positional control of the directional antenna is provided by the control electronics subsystem such that the antenna is always pointed directly at the earth. Satellite-borne infrared earth sensors provide earth reference pulses to the control electronic subsystem for antenna despin stabilization and pointing. Also discussed is the bearing and lubrication system for the antenna drive assembly. In-orbit performance of the two systems launched is also given.