A Clear-Box Adaptive System for Flexible Spacecraft Identification and Disturbance Rejection

Abstract

This paper presents an automatic system for identification and rejection of unknown periodic dis turbances applicable to real-time control of flexible spacecraft. The system adaptively performs system iden tification, monitors and tracks disturbance frequencies if they are present, detects the emergence of new distur bance frequencies, predicts the contribution of each disturbance frequency on the system response, determines which disturbance frequencies should be targeted for cancellation and which should be ignored by taking into account actuator constraints, and synthesizes the necessary feed-forward control for selective disturbance cancellation. No direct measurement of the disturbances is required. New system identification results are extensively used to bring out detailed information about the system dynamics and the disturbance environ ment that is normally hidden or left unused in standard black-box approaches, hence the descriptive term clear-box is used. Intelligent decision-making logic can be built into this information-rich architecture so that selective cancellation of the disturbance frequencies can be achieved. This paper derives all the relevant re cursive expressions for multi-input multi-output clear-box system and disturbance identification and control signal synthesis. A detailed simulation study is used to illustrate the application of the proposed scheme on a high-fidelity 52-state flexible spacecraft model, followed by an extensive discussion on the lessons learned.