[geocentrism] geostats
- From: "Philip" <joyphil@xxxxxxxxxxx>
- To: <geocentrism@xxxxxxxxxxxxx>
- Date: Fri, 15 Apr 2005 15:03:41 +1000
Neville.
Ok so the solar panels are a Kw. The transmitters are not.. The figures quoted
here do not say whether it is input power or radiated power. which is a
multiple of the input as explained previously . In any case 12 wqtts provides
ample power to the dishes high gain recievers that sit on my roof. I do not
know off hand the meaning of this unit.> with an effective isotropic radiated
power (EIRP) of 47 dBW for the spot beams and 36 dBW for FSS.
As I also said previously, if the receiving dish is just a few degrees off
direction, the signal is seriouly degraded or lost. Philip.
Australia's First Satellite System
Aussat, the Australian national satellite communications system, provides a
wide range of domestic services to the entire continent, its offshore islands,
and Papua New Guinea. This includes direct television broadcast to homesteads
and remote communities, high quality television relays between major cities,
digital data transmission for both telecommunications and business use, voice
applications for urban and remote areas, centralized air traffic control
services, and maritime radio coverage. In addition, the third satellite will
provide a pilot communications service to the Southwest Pacific region, an area
that contains many islands and that currently has limited communications
services.
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.
Both Hughes units are today a part of Boeing Satellite Systems, Inc. (BSS).
The spin stabilized 376, an established communications satellite design, was
chosen for Aussat. The first two Australian satellites were launched on the
space shuttle in August and November 1985. The third was launched in September
1987 on the Ariane 3 rocket.(European)
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) then inserted the spacecraft into an
elliptical transfer orbit. The Ariane 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.
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