Multi-observer approach for tracking control of flexible spacecraft using exponential mapping of SE(3)

This paper is concerned with the problem of attitude-orbit tracking control for flexible spacecraft. A relative attitude-orbit-structure integrated dynamics model is derived for flexible spacecraft, where environmental disturbances and parameter uncertainty are considered as lumped disturbance. And the relative position and attitude of the spacecraft are described by the exponential coordinates of SE(3). Since the modal variables are not measurable, a modal observer is proposed to obtain the state estimation related to elastic vibration. Then, a composite control technique is proposed for attitude-orbit tracking of flexible spacecraft under lumped disturbance by combining a state observer of modal parameter and nonlinear disturbance observer with an asymptotic tracking control. The vibration mode information and the lumped disturbance are estimated and compensated by the modal observer and the nonlinear disturbance observer, respectively, in the feedback link. The stability of the composed control approach consisting of the asymptotic tracking control and multi-observer observer is guaranteed through Lyapunov method. The simulation results validate the composite control technique can effectively enhance disturbance attenuation ability, robust dynamics performance and the desired relative attitude tracking accuracy of a flexible spacecraft with multiple disturbances and parameter uncertainty.