Atmospheric entry guidance via multiple sliding surfaces control for Mars precision landing

Improving Mars landing accuracy will require the implementation of robust, closed-loop guidance schemes for the entry portion of the atmospheric flight. A novel non-linear atmospheric entry guidance law has been developed for a class of low-lift landers similar to the one expected to be flown in the upcoming Mars Science Laboratory (MSL) mission. Here we proposed a Multiple Sliding Surface Guidance (MSSG) approach for Mars entry guidance. The presented guidance scheme is based on a higher order sliding mode control theory adapted to account for (1) the specific 2-sliding mode order exhibited by the longitudinal motion of the entry vehicle guided, using bank angle variations and (2) the ability of the system to reach the sliding surface in a finite time. Contrary to more standard methods designed to track a drag-based profile as a function of the range-to-go, the proposed scheme does not require any off-line trajectory generation and therefore it is suitable for real-time implementation. The global stability nature of the MSSG law is proven by using a Lyapunov-based approach. A parametric study has been conducted to understand the behavior of such class of trajectories as a function of the guidance parameters. The MSSG algorithm targeting ability is analyzed through a set of Monte Carlo simulations where the guidance law is required to operate under off-nominal conditions. Simulation results show good performance under perturbations and parameter uncertainties.