TWO AXIS CLOSED-LOOP ANTENNA POINTING FOR A DUAL-SPIN SPACECRAFT

Abstract

This paper describes the control and sensing techniques and practical implementation used to obtain precision antanna pointing on a class of commercial communication satellites. The basic spacecraft bus is a dual-spin gyrostat with momentum of order 1500 ft-lb-sec. Spin is about a minimum axis of inertia and active damping using the despin motor and platform product of inertia is employed for nutation stabilization. Using two axis RF beacon tracking, steady state pointing accuracy exceeding 0.025° (3σ) in roll and pitch and 0.1° (3σ) in yaw is achieved. This accuracy is approached during orbit and attitude trim thrusting maneuvers as well.