针对航天器高精度姿态跟踪控制问题，本文设计了一类基于周期滞后反馈理论的指定时间控制律。所设计的控制律可以使航天器的实际姿态在任意指定时间内跟踪上参考信号并且避免控制器的奇异性问题。此外，在设计的周期滞后滑模控制律的基础上，本文引入指定时间扩张状态观测器以实现对未知干扰的在线观测，并设计了一类融合两者的复合控制律。复合指定时间无奇异控制律可以有效消除滑模控制中的抖振现象。仿真结果表明，本文设计的控制器能够在指定时间内完成航天器姿态跟踪控制任务，并对外部干扰具有较强的鲁棒性。

Aiming at the problem of high-precision attitude tracking control for spacecraft, this paper designs a class of prescribed-time control laws based on periodic delayed feedback theory. The control law can drive the actual spacecraft attitude to track reference signals within any prescribed time while avoiding controller singularity issues. Furthermore, building upon the designed periodic delayed sliding mode controller, this paper introduces a preset-time extended state observer to achieve online estimation of unknown disturbances and proposes a composite control law integrating both components. This composite finite-time nonsingular control law can effectively eliminate the chattering phenomenon inherent in sliding mode control. Simulation results demonstrate that the proposed controller successfully completes the spacecraft attitude tracking control task within the prescribed time and exhibits strong robustness against external disturbances.