考虑斜坡约束的固定时间行星软着陆制导律设计

An autonomous obstacle-avoidance fixed-time pinpoint soft landing guidance algorithm is proposed for the powered descent phase of planetary exploration by introducing the glide-slope constraint to constrain the landing trajectory and using sliding mode control theory and fixed-time control theory. Firstly, a constraint boundary function is defined according to the glide-slope constraint, and the nonlinear sliding surface is developed using this function, which not only ensures that the system states are fixed-time stable when they slide along the sliding surface but also ensures that the system state does not violate the glide-slope constraint. By introducing a smooth and continuous switching sliding surface, the singularity problem of the sliding surface is avoided. Next, the fixed-time guidance law is designed to ensure that the sliding surface state can converge to zero within a fixed time, the stability of the system is proved using the Lyapunov method, and the system states do not violate the glide-slope constraint under the action of the designed guidance law is analyzed. Finally, the effectiveness and robustness of the proposed algorithm are verified by numerical simulations.