Australia's national satellite company, AUSSAT Proprietary Ltd., in May 1982 selected Hughes Communications International, a wholly owned subsidiary of Hughes Aircraft Company, to develop the country's first satellite program. Under the contract, Hughes Space and Communications Group (SCG) has built three satellites and two telemetry, tracking, command and monitoring (TTC&M) stations. Also provided are launch and operational services and ground support.
The spin stabilized HS-376, an established communications satellite design, was chosen for Aussat. The first two Australian satellites were launched on the Shuttle in August and November 1985. The third was launched in September 1987 on the Ariane-3 rocket.
Aussat uses two telescoping cylindrical solar panels and a folding antenna for compactness during launch. After the satellite nears its orbital position, the antenna erects and the outer solar panel deploys, exposing the inner solar array. Aussat's dual polarized, three-reflector antenna system provides seven transmit beams and three receive beams. Five transmit beams are spot beams and serve the Homestead and Community Broadcasting Satellite Service (HACBSS): four contiguously placed over the western, central, northeast, and southeast regions of the Australian continent and one over Papua New Guinea. The other two are national beams, which use orthogonal polarizations to provide continental coverage for Fixed Satellite Service (FSS).
Aussat's third satellite serves the Southwest Pacific region by using separate, direct feedhorns for transmit and receive, which illuminate the region without the use of reflectors. The coverage of the transmit and receive beams is circular, with a 10-degree beamwidth centered between Vanuatu and Fiji.
The Aussat satellite carries 15 channels, each 45 MHz wide. Four use high power, 30 watt traveling wave tube amplifiers (TWTAs) to provide radio and television services to Australia's remote areas; the remaining 11 channels operate with 12 Watt TWTAs. It is possible to connect the communications channels individually to the transmit beams by ground command. This arrangement provides traffic assignment flexibility for the system. The electrical power system uses K7 high efficiency solar cells, which provide 1054 Watts at beginning of life. Two nickel-cadmium batteries provide full power when the spacecraft passes through Earth's shadow.
The satellite has a diameter of 2.2 meters. Stowed for launch, its height is 2.9 meters. In orbit, with antennas deployed and aft solar panel extended, the height increases to 6.3 meters. Its initial on-station weight is 654 kilograms for a shuttle launch, and 696 kg for the Ariane launch.
The satellites, which have a mission life of 7 years, operate at the 14/12 GHz Ku band, with an effective isotropic radiated power (EIRP) of 47 dBW for the spot beams and 36 dBW for FSS. The first and second satellites are located above the equator just north of Papua New Guinea at 160 degrees East longitude and 164 degrees East longitude, respectively. The third satellite is located at 156 degrees East longitude. The master control station for the Aussat system is in Sydney, and backup control equipment is in Perth. Monitoring equipment has been installed at earth stations in Sydney, Perth, Brisbane, and Adelaide.
When the Aussat satellites were launched using the Shuttle, they were contained in a special cradle that houses the ejection system and provides a protective sunshield. The spacecraft were spun up while in the cradle. Explosive bolt cutters fired, allowing four springs to eject the spacecraft. A McDonnell Douglas payload assist module (PAM-D) then inserted the spacecraft into an elliptical transfer orbit. The Ariane-3 rocket incorporates a third stage to propel the spacecraft into the transfer orbit. All three spacecraft are placed in near-synchronous orbit by a Thiokol Corporation Star-30BP solid propellant apogee motor. Four Hughes 5-pound thrusters, operating with monopropellant hydrazine, provide apogee motor augmentation and on-orbit stationkeeping and attitude control. The satellites drift into final orbit 36,000 km above the equator.
|Type / Application:
|USSAT Pty., Ltd. → Optus Communications Pty., Ltd.
|15 Ku-band transponders operating at 14/12 GHz
|Solar cells (body mounted and drop-skirt), batteries
|1250 kg (654 kg BOL)
|Aussat A1 → Optus A1
|with Discovery F6 (STS 51-I), Leasat 4, ASC 1
|Aussat A2 → Optus A2
|with Atlantis F2 (STS 61-B), Morelos 2, Satcom-K 2, OEX Target
|Aussat A3 → Optus A3
|with ECS 4