This paper proposes an adaptive attitude stabilization approach for flexible spacecraft subject to uncertainties, external disturbances, actuator saturation and unknown dynamics. The approach is synthesized based on a modified nonsingular fast terminal sliding surface (NFFTSS) and ensures fast and finite-time convergence independently of the initial states. It employs time-varying gains into the sliding manifolds and the control scheme to yield improved convergence speed over fixed-time based approaches. The upper bounds of the uncertainties are estimated using an adaptive mechanism in which no prior knowledge of the lumped uncertainties is required. To cope with actuator limitations, a smooth non-affine function of the control input is used in order to approximate the saturation constraint. System stability was proven using the Lyapunov theory. The approach was validated using numerical simulations and comparison analysis with existing attitude approaches. The obtained results confirmed the controller’s superior performance in terms of convergence rate, high attitude pointing accuracy and stability. Additionally, the proposed approach is inherently continuous and exhibits chattering free dynamics.

中文翻译：

---

具有快速固定时间收敛的柔性航天器自适应姿态稳定

本文提出了一种适用于受不确定性、外部干扰、致动器饱和和未知动力学影响的柔性航天器的自适应姿态稳定方法。该方法是基于改进的非奇异快速终端滑动面 (NFFTSS) 合成的，并确保独立于初始状态的快速和有限时间收敛。它在滑动流形和控制方案中采用时变增益，以提高基于固定时间的方法的收敛速度。使用自适应机制估计不确定性的上限，其中不需要集总不确定性的先验知识。为了应对致动器的限制，使用控制输入的平滑非仿射函数来近似饱和约束。使用李雅普诺夫理论证明了系统稳定性。该方法通过数值模拟和与现有姿态方法的比较分析得到验证。获得的结果证实了控制器在收敛速度、高姿态指向精度和稳定性方面的优越性能。此外，所提出的方法本质上是连续的，并且表现出颤动的自由动态。