Next-Generation Satellites for Western Union
| Diameter | 7 ft 2 in (2.16 m) |
|---|---|
| Height stowed | 9 ft (2.74 m) |
| 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.
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 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.