The Intelsat 4 antenna positioner

Abstract

The Intelsat 4 communications satellite has two spot beam antennas which are pointed to selected land masses by gimbaled positioners. The positioners employ drive motors with electromagnetic brakes and jackscrews that are self-caging during the launch. The positioner uses dry lubricants for ball bearings, spur gears, screw and nut, and various journal bearings. A coefficient of friction of approximately 0.05 was demonstrated in vacuum operation. Success of the positioner was demonstrated on the first Intelsat 4 placed in orbit in January 1971. The developmental problems that were encountered and their solutions are discussed.