Variable structure attitude manoeuvre control and active vibration damping of three-axis-stabilized flexible spacecraft

Abstract

This paper presents a dual-stage control system design method for the three-axis-rotational manoeuvre and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as the sensor and actuator. In this design approach, the attitude control system and vibration suppression were designed separately using a lower-order model. The design of the attitude controller was based on the variable structure control (VSC) theory, leading to a discontinuous control law. This controller accomplishes asymptotic attitude maneouvring in the closed-loop system and is insensitive to the interaction of elastic modes and uncertainty in the system. The advantage of this dual-stage approach is that once the desired orientation is attained under the VSC law, only the elastic motion is governed by the decoupled linear second-order systems describing elastic dynamics. To this end, modal velocity feedback and optimal positive position feedback control methods are presented and compared for actively damping the elastic oscillations using piezoelectric materials as an additional sensor and actuator bonded on the surface of the flexible appendages. In addition, a special configuration of actuators for three-axis attitude control is also investigated: the pitch attitude controlled by a momentum wheel and the roll/yaw control achieved by on-off thrusters, which is modulated by the pulse width-pulse frequency modulation technique to construct a proper control torque history. Numerical simulations are performed to show that the rotational manoeuvre and vibration suppression are accomplished in spite of the presence of disturbance torque and parameter uncertainty.