This paper is mainly dedicated to the challenging issue of fixed-time attitude control for a flexible spacecraft in the presence of actuator faults, external disturbances and coupling effect of flexible modes. The attitude controller is developed by employing a fixed-time nonsingular terminal sliding mode under which the convergence time is bounded and independent of the initial states. This robust attitude controller is able to provide superior properties such as fast fixed-time attitude manoeuvring with high pointing accuracy, singularity avoidance and chattering free. More specifically, a new reaching law is employed to provide convergence rate improvement as well as chattering alleviating simultaneously. The actuator fault problem is also considered and the attitude control is achieved even when the actuators experience severe faults. The proposed controller ensures that the closed-loop attitude system is stable in the sense of fixed-time stability concept. Furthermore, since the upper bound of external disturbances and flexible vibrations acting on the spacecraft is not available, an adaptation mechanism is presented. Numerical simulations demonstrate that the proposed controller is able to successfully accomplish attitude control with high attitude pointing accuracy and stability in spite of the actuator faults, flexible structures vibrations and external disturbances.

中文翻译：

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具有快速固定时间收敛的柔性航天器无抖动容错姿态控制

本文主要致力于解决在致动器故障、外部扰动和柔性模式耦合效应下柔性航天器固定时间姿态控制的挑战性问题。姿态控制器是通过采用固定时间非奇异终端滑动模式开发的，在该模式下，收敛时间有界且与初始状态无关。这种稳健的姿态控制器能够提供卓越的特性，例如具有高指向精度的快速固定时间姿态机动、奇异点避免和无抖动。更具体地说，采用新的到达定律来提高收敛速度并同时减轻抖动。还考虑了执行器故障问题，即使执行器出现严重故障也能实现姿态控制。所提出的控制器确保闭环姿态系统在固定时间稳定性概念的意义上是稳定的。此外，由于作用在航天器上的外部扰动和柔性振动的上限不可用，因此提出了一种适应机制。数值模拟表明，尽管执行器故障、柔性结构振动和外部干扰，所提出的控制器能够成功地完成姿态控制，具有较高的姿态指向精度和稳定性。