When two domestic communications satellites were launched into synchronous orbit in 1976, a new era in long-distance calling began for the nation's phone customers. Relaying calls back and forth across the country, the satellites, called Comstar, were used jointly by the American Telephone and Telegraph Company and GTE Satellite Corporation, a subsidiary of General Telephone and Electronics.

The spin-stabilized satellites, plus two others built by the Space and Communications Group of Hughes Aircraft Company, later Hughes Space and Communications Company, now Boeing Satellite Systems, are owned by Comsat General Corporation of Washington, D.C. Comsat General leased the entire communications capacity of the satellites to AT&T under a long-term lease. In turn, AT&T and GTE operated earth stations located at major metropolitan centers throughout the United States.

Comstar has a height of 6.34 meters and a diameter of 2.38 meters. Cylindrical solar panels, covered with nearly 17,000 solar cells, provided the satellite with primary power of 760 Watts. Liftoff weight at launch was 1516 kg. The launch vehicle for the Comstars was the Atlas-Centaur booster. The satellites were launched from the Kennedy Space Center in Florida by the National Aeronautics and Space Administration under a contract with Comsat General.