Optus-B [Boeing BSS]
Australia's national satellite communications company became the first customer to purchase the Hughes 601 body-stabilized satellite in July 1988, when it ordered two of the high-powered spacecraft to be delivered on orbit for its next-generation system. In January 1992 the Australian company, once known as AUSSAT Pty., Ltd., became part of Optus Communications Pty., Ltd., the country's new, privately owned telecommunications carrier. The spacecraft are called the Optus B series.
Built by Hughes Space and Communications Company in El Segundo, California, the Hughes HS-601 is considerably more powerful and versatile than previous Hughes satellites. Optus B is three times more powerful than and will last twice as long as Aussat A, Australia's first national communications satellite system, which was also built by Hughes. The Optus B satellites enhance existing satellite communications services throughout Australia, including direct television broadcast to homesteads and remote communities, voice communications to urban and rural areas, digital data transmission, high-quality television relays between major cities, and centralized air traffic control services.
In addition, Optus B1 introduced the first domestic mobile satellite communications network to Australia. The satellites are equipped with a 150 watt L-band transponder to permit mobile communications through small antennas mounted on cars, trucks, and airplanes. This mobile ability extends throughout the nation.
Optus B is a three-axis design that consists of a cube-shaped central body, 2.29 meters on a side, with a pair of three-panel solar array wings. Each wing extends 9.14 meters north and south from the body for an overall deployed length of 20.57 meters. A 30-element L-band antenna array covers the earth-facing surface of the spacecraft. One oval reflector deploys from the east side of the spacecraft body, and two smaller oval reflectors on the west side are attached to an A-frame structure similar to that of Aussat A. The three-reflector antenna system provides eight transmit and two receive beams in vertical and horizontal polarization. The satellite weight at beginning of life in orbit is 1659 kg.
The Ku-band communications payload consists of fifteen 50 watt linearized transponders, each with a bandwidth of 54 MHz. The transmit coverage includes two national beams to all of Australia and the offshore region; spot beams to the western, central, northeast, and southeast regions of the Australian continent; a national beam to New Zealand; and a high performance beam to major cities. It is possible to switch eight of the transponders on each satellite to provide domestic service to New Zealand and service between Australia and New Zealand. The effective isotropic radiated power varies from 41 to 55 dBW, depending on the beam.
In addition to the Ku- and L-band transponders, the Optus B satellites carry two experimental payloads, a Ka-band beacon and a laser retroreflector. Both experimental payloads are located beside the L-band antenna, where they have the required visibility of Australia. The Ka-band beacon transmits a 28 GHz signal on both horizontal and vertical polarizations for propagation experiments. The laser retroreflector permits locating the spacecraft precisely so that signals sent through Optus B can be used to set timing standards throughout Australia.
The electrical power subsystem uses two sun-tracking solar arrays to generate 3200 watts. The three-panel solar array wings are covered with large area K4-3/4 silicon solar cells. Each panel is 2.54 meters by 2.16 meters. A 28-cell nickel-hydrogen battery provides full power to the spacecraft during eclipse operations, when the satellite passes through Earth's shadow.
The satellite's integral propulsion system uses monomethyl hydrazine and nitrogen tetroxide bipropellant carried in four spherical titanium tanks. A single 490-newton (110-pound force) thruster is used for perigee augmentation and apogee burns, and thirteen 22-newton (5-pound force) thrusters are used for attitude control and stationkeeping maneuvers. Highly accurate antenna pointing control is provided by independent beacon tracking on each of the Ku-band reflector systems. The attitude control system uses an innovative combination of double-gimballed momentum wheels and magnetic field torquing, which minimizes the need for thruster use during normal on-station operations. The contract calls for a minimum in-orbit life of 10 years.
The first Optus B satellite was launched on a CZ-2E booster 14 August 1992, from Xichang, China. The second was destroyed during launch on a CZ-2E 21 December 1992 the payload fairing collapsed. The wreckage of Optus-B2 and the Star-63F Kick-Motor reached LEO. After seven months of investigation, both Hughes and the Chinese concluded that a cause for the explosion could not be determined. Immediately after the loss, Hughes began work on another satellite, Optus B3, which was successfully launched Aug. 28, 1994.
The CZ-2E places the satellite in a low earth orbit and imparts a slow spin for stability during orbital transfer maneuvers. The satellite's onboard Thiokol Star-63F perigee kick motor (PKM) is fired to boost the spacecraft into geosynchronous transfer orbit. After its solid fuel is depleted, the PKM is jettisoned. The liquid bipropellant apogee motor using the 490-newton thruster is fired by ground command on three separate apogees, with each firing raising the perigee of the transfer orbit until the orbit is circularized at geosynchronous altitude 36,000 km above the equator. As the satellite drifts toward its assigned orbital position, it is despun, the reflectors are deployed, and the solar panels are extended. The spacecraft is oriented, and the momentum wheel is activated. Optus B1 is positioned at 160° East longitude, and Optus B3 will be at 156° East longitude.
|Type / Application:||Communication|
|Operator:||Optus Communications Pty., Ltd.|
|Equipment:||15 Ku-band transponders, 1 L-band tranponder, Ka-band beacon, laser retroreflector|
|Power:||2 deployable solar arrays, batteries|
|Mass:||2858 kg (1659 kg BOL)|
|Optus B1 (ex Aussat B1)||1992-054A||13.08.1992||Xi LC-2||CZ-2E [Star-63F]|
|Optus B2 (ex Aussat B2)||1992-090 ?||21.12.1992||Xi LC-2||f''||CZ-2E [Star-63F]|
|Optus B3 (ex Aussat B3)||1994-055A||27.08.1994||Xi LC-2||CZ-2E [Star-63F]|