This paper develops a fixed-time trajectory tracking control scheme for Mars entry vehicle under uncertainty. First, a novel fixed-time nonsingular terminal sliding mode (FTNTSM) surface with bounded convergence time independent on the initial conditions is developed, which not only averts the singularity problem but also assures fast convergence. Second, based on the FTNTSM surface and adaptive technique, a continuous adaptive fixed-time nonsingular terminal sliding mode control (AFTNTSMC) method is proposed. Under the control scheme, the fixed-time convergence of tracking error is assured, and the chattering phenomenon is alleviated. Furthermore, by estimating the square of upper bound of the uncertainty, the designed AFTNTSMC method averts the use of boundary layer technique as imposed in most existing literature on adaptive fixed-time control. The effectiveness of the developed control approach is confirmed by numerical simulations.

针对不确定性，提出了火星进入车辆的定时轨迹跟踪控制方案。首先，开发了一种新颖的具有有限收敛时间且与初始条件无关的固定时间非奇异终端滑模（FTNTSM）曲面，它不仅避免了奇异性问题，而且确保了快速收敛。其次，基于FTNTSM曲面和自适应技术，提出了一种连续的自适应固定时间非奇异终端滑模控制方法。在该控制方案下，保证了跟踪误差的定时收敛，减轻了抖动现象。此外，通过估计不确定性上限的平方，设计的AFTNTSMC方法避免了使用大多数现有文献中关于自适应固定时间控制所强加的边界层技术。