Finite-time Attitude Tracking for Fully-actuated Flexible Spacecraft without Angular Velocity Measurements

In this paper, the problem of finite-time attitude control for fully-actuated flexible spacecraft subject to external disturbance and vibration of flexible appendages without angular velocity measurements is investigated. Firstly, a nonlinear finite-time angular velocity observer with dynamic parameters is proposed to estimate the unknown angular velocity. Then, an adaptive disturbance observer is designed to estimate the lumped disturbance which contains the external disturbance, vibration of flexible appendages and observation errors of the angular velocity observer in finite time. Next, utilizing the reconstructed information from the observers, a novel integral sliding mode (ISM) and a velocity-free attitude tracking controller are presented to achieve attitude tacking in finite-time without chatting problem. The main feature of the designed control algorithm is that the unknown angular velocity, external disturbance, and vibration of flexible appendages are addressed simultaneously without awareness of the boundary of the unknown lumped disturbance. Rigorous Lyapunov-based analyses show that the finite-time ultimately bounded stability of the observation errors and tracking errors can be guaranteed under the designed control law. Finally, numerical simulation results illustrate the effectiveness of the proposed observer-based attitude control scheme.