Adaptive Nonlinear Proportional-Derivative Type Fault Tolerant Control for Flexible Spacecraft Attitude Maneuvers under Bounded Disturbances

Abstract

Semiglobally input-to-state stable (ISS) control law is derived for flexible spacecraft attitude maneuvers in the presence of parameter uncertainties, external disturbances, and actuator fault. As a stepping stone, a nonlinear-proportional-plus-derivative (NPD) type controller plus a sign function is developed for the fault-free system. A sufficient condition under which this NPD type control law can render the system semiglobally input-to-state stable is provided such that closed-loop system is robust with respect to any disturbance within a quantifiable restriction on amplitude, as well as the set of initial conditions, if the control gains are designed appropriately. Based on the online estimation of eventual actuator faults, this controller is redesigned for the attitude control system with actuator failures by adding a new control term to the original to reduce the actuator fault effect on the system without the need for a fault detection and isolation mechanism. In addition to detailed derivations of the new controllers design and the associated stability and attitude convergence proofs, simulation studies have been conducted to validate the design, and the results are presented to highlight the ensuring closed-loop performance benefits when compared with the conventional control schemes.