Unisat - UK direct TV broadcasting satellite

The current status of the Unisat program, a UK commercial venture comprising two satellites in GEO at 329 deg E and providing two TV channels and six telecommunications channels each, is reviewed. The satellites are designed to be launched either by STS or by Ariane IV, and launch is scheduled for 1986. The broadcasting payload uses 240-W TWTA output stages to provide beam-center EIRP of about 65 dBW with circular polarization in the 11.7-12.5-GHz band. The telecommunications payload consists of six nonredundant 36-MHz channels using the 14-GHz band for the uplink and the 12-GHz band for the downlinks, with two beams providing 45-dBW EIRP coverage of most of Europe and the eastern parts of North America, respectively. Each transponder is designed to handle 25-Mb/s BPSK TDMA signals (about 250 SCPC channels). The Unisat platform subsystems, including propulsion three-axis stabilization, 2.3-kW solar arrays, and thermal control, are briefly characterized.