Transient-Suppressing Initialization for Low-Bandwidth Attitude Controllers

Abstract

The use of low-bandwidth attitude controllers is a standard solution for spacecraft facing tight frequency-domain requirements for attitude-stable payloads and platforms. However, such controllers have difficulty responding to transients both planned and unexpected. This paper introduces a novel method of controller re-initialization to counteract a transient in progress. This method, the eigenmode initialization, pursues time-optimal performance for a given controller and plant by attempting to suppress the slow eigenmodes of the closed-loop system; the dynamics that remain are a function of the remaining eigenmodes. The derivation of this method from first principles is presented alongside analytical solutions for the ideal response and specific examples for which postinitialization transients decay 5, 7, and 30 times faster than their uninitialized counterparts. The method is extended to account for actuator bias and bound the actual response in the presence of estimation error. Finally, the method is validated through the high-fidelity simulation of a critical mode transition within the attitude control system of a legacy Airbus satellite, demonstrating the eigenmode initialization’s simple and effective implementation despite considerable nonlinearities in the sensor and actuator models employed.