Variable Parameter Nutation Damper for SAS-A

Abstract

This paper presents design objectives, functional description and in-flight performance of a variable parameter nutation damper for a dual-spin satellite. The damper consists of a torsion wire mounted pendulum which includes the capability of command changing the pendulum resonant frequency and damping constant in order to obtain optimum spin axis stabilization for both a dual-spin and single-spin spacecraft dynamical condition. State-of-theart features of this damper include: 1) taut-band suspension, for a pendulous mass, which has no mechanical friction of hysteresis, 2) magnetic circuit for changing the torque constant of the taut-band thereby changing the damper natural frequency, 3) chargeable magnet system for varying the damping coefficient, and 4) 7-bit optical readout for telemetering the damper motion. The damper weights 2.7 Ib and draws 20 mw power when functioning for dual-spin conditions. The minimum nutation damping time constant in this mode is 12 min with a predicted spin axis pointing accuracy of 1 min of arc. Stabilization to better than 2 min of arc has been achieved in orbit.