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Next-Generation Satellites for Western Union

STOWED

Diameter	7 ft 2 in (2.16 m)
Height stowed	9 ft (2.74 m)

IN ORBIT

Diameter	7 ft 2 in (2.16 m)
Height deployed	21 ft 7 in (6.58 m)
Weight	1280 lb (582 kg) beginning of life

When Western Union returned to Hughes Aircraft Company in 1980 for a second generation of Westar satellites, it selected spacecraft having twice the capacity of their predecessors.

Hughes' Space and Communications Group built three Hughes 376 model satellites, designated Westar IV, V, and VI, for Western Union Telegraph Company. These new spacecraft stand 21.6 feet tall in operation and carry 24 C-band transponders, each of which can accommodate 2400 telephone calls or one color TV channel. In October 2000, The Boeing Company acquired three units within Hughes Electronics Corporation: Hughes Space and Communications Company, Hughes Electron Dynamics, and Spectrolab, Inc., in addition to Hughes Electronics' interest in HRL, the company's primary research laboratory. The four are now part of Boeing's newest subsidiary, Satellite Development Center.

Westars IV and V were launched on McDonnell Douglas Delta boosters from Cape Canaveral, Fla., on February 25, 1982, and June 8, 1982, respectively. Each was propelled into an elliptical transfer orbit by a McDonnell Douglas payload assist module (PAM), and placed into near-synchronous orbit by a Thiokol Star 30 solid propellant apogee motor. The satellites drifted into final orbit and were placed in operational position through the use of the same onboard propulsion system that provides stationkeeping.

Westar VI was launched from the space shuttle in February 1984. Its PAM misfired, however, and the satellite was stranded in a useless low orbit. It was retrieved by shuttle astronauts in November 1984, and Hughes was contracted to refurbish it. Westar VI was eventually sold to the AsiaSat consortium and renamed AsiaSat I. The spacecraft was successfully relaunched on April 7, 1990, on board a Chinese Long March 3 rocket, and now provides telecommunications services to a number of Asian nations.

The Westar system was designed to provide continuous video, facsimile, data, and voice communications service throughout the continental United States, Alaska, Hawaii, Puerto Rico, and the Virgin Islands. In early 1989, Hughes subsidiary Hughes Communications, Inc., (HCI) purchased Westar III, IV, and V from Western Union, doubling the size of the HCI C-band satellite fleet. Telemetry, tracking, and control of these and the other HCI satellites is managed by Hughes facilities in Spring Creek, N.Y., and in Fillmore and El Segundo, Calif.

The Boeing 376 series of spacecraft uses two telescoping cylindrical solar panels and a folding antenna for compactness during launch. Once the satellite is in synchronous orbit 22,300 miles above the equator, the antenna is erected and the outer solar panel extended, more than doubling the spacecraft's height and power output.

The spacecraft are 7.2 feet wide. They are 9 feet high in the stowed position, and with the 6-foot wide antenna erect and the aft solar panel deployed, they stand 21.6 feet high. Each weighs 1280 pounds at beginning of life in orbit. Stationkeeping is provided by four thrusters using 313 pounds of hydrazine propellant. The K-7 solar cells generate 935 watts at beginning of life, and two nickel-cadmium batteries furnish full power during an eclipse.

The transmit and receive beams are created by a shared aperture grid antenna with two polarization-selective surfaces. The front surface is sensitive to horizontally polarized beams, and the rear surface is sensitive to vertically polarized beams. Separate microwave feed networks are used for the two polarizations. The satellites operate in the C-band, with receive from 5.925 GHz to 6.425 GHz and transmit from 3.7 GHz to 4.2 GHz. The effective isotropic radiated power over the 36 MHz bandwidth ranges from a minimum of 34 dBW in the contiguous United States to 27.2 dBW in Puerto Rico. Westar IV, V, and VI use 7.5-watt traveling wave tube amplifiers.

The satellites are stabilized by spinning at 50 rpm. Both the communications antenna and electronics are despun with respect to the earth and achieve a pointing accuracy of better than 0.05 degrees. In synchronous orbit, the satellite's velocity maintains it in a fixed position relative to the earth, thereby ensuring continuity of communications services.