A mixed-mode attitude control system strategy for actuator failure accommodation

Abstract

This paper documents the development of a pitch bias momentum system and the optimal control or Linear Quadratic Regulator (LQR) design procedure developed for a Mixed-Mode Control Strategy to accommodate the loss of up to three reaction wheel assembly (RWA) mounted in a skewed four-for-three configuration. The paper contains three major sections:(1) description of the spacecraft linearized model developed for the three axes pitch bias momentum system, (2) optimal controller design procedure for various types of actuators (i.e., RWA, Torquer Bars, and Thrusters), and (3) closed-loop system performance subject to both normal and failure modes. Design guidelines on how to tune the Q and R weighting matrices subject to RWAs, magnetic torquer bars (MTBs), and thrusters are also summarized as design notes to assist designers in selecting the right set of [Q and R] matrices so that a robust control performance can be achieved. Linearized Pitch Bias Momentum Model