General Motors’s Hughes Aircraft Co has signed a definitive agreement to buy the Westar satellite system from Western Union Corp: the Westar system includes three C-Band communication satellites in orbit and a fourth on the ground scheduled to be launched in 1989, and they will be operated jointly with three Hughes-owned and operated C-band Galaxy satellites to give customers a more reliable system; the purchase will not include the Westar earth stations, and Western Union plans to sell these separately.