Exponential Attitude Tracking and Vibration Control for 3-D Flexible Spacecraft With Disturbances and Quantized Inputs

This study addresses the problem of attitude tracking and vibration suppression for 3D flexible spacecraft subject to external disturbances and input quantization, which are two critical factors that can significantly degrade control performance in harsh space environments with limited communication capacity. Using Hamilton’s principle, the spacecraft is modeled by coupled ordinary and partial differential equations to accurately characterize its infinite-dimensional dynamics. Nonlinear observers are constructed to exactly estimate unknown boundary disturbances. To deal with the difficulty caused by quantization, a linear time-varying model is introduced to describe hysteretic quantizers, and adaptive laws incorporating exponential functions are developed to estimate resulting unknown terms. Furthermore, a novel disturbance observer-based adaptive quantized control scheme is proposed, which guarantees the boundedness of all closed-loop signals and ensures that both attitude tracking errors and vibrations converge exponentially to zero, whereas existing methods typically achieve only convergence to small residual sets due to quantization effects or disturbances. In particular, the proposed scheme allows the quantizer parameters to be freely adjusted during operation for balancing communication burden and tracking performance. Simulation results show that, compared to traditional PD control, the proposed scheme exhibits faster convergence in attitude tracking and vibration elimination, and achieves higher control accuracy under unknown disturbances and changeable quantizer parameters.