Multi-constrained feedback guidance for mars pinpoint soft landing using time-varying sliding mode.

• The thruster performance and glide-slope constraint are considered. • A novel time-varying feedback guidance and its incremental form are proposed. • The guidance laws are near-fuel-optimal and can avoid subsurface flight. • The trajectory can be set as a straight line. • An optimal problem is constructed to satisfy the glide-slope constraint. Taking into account the thruster performance (total thrust magnitude constraint and control acceleration deviation) and glide-slope constraint, this paper presents two types of new feedback guidance strategies for Mars pinpoint soft landing, which are near-fuel-optimal and robust to disturbance. A novel and simple time-varying feedback guidance law is proposed at first. Next, this guidance law is extended to the incremental guidance to improve the robustness and ability to deal with the thruster performance and disturbance. An advantage of these two guidance schemes is that they can avoid subsurface flight owing to the monotonic convergence of position and velocity. Moreover, an exciting feature of these two guidance laws is that the trajectory of the vehicle can be set as a straight line by choosing the guidance laws parameters. Finally, an optimal problem is constructed and solved based on this feature to obtain the guidance laws parameters to satisfy the glide-slope constraint. Its robustness, fuel efficiency, and performance in dealing with acceleration deviation and thruster constraint are demonstrated for different simulation scenarios, especially in comparison with zero-effort-miss/zero-effort-velocity feedback guidance law. [ABSTRACT FROM AUTHOR]