Adaptive Near-Propellant-Optimal Powered Descent Initiation for Human Mars Landing

Future human Mars missions will typically require pinpoint landing, defined as achieving a touchdown error within 100 m. To ensure mission success, the powered descent phase should be initiated under favorable conditions. This paper proposes an adaptive powered descent initiation (PDI) strategy based on a constant-thrust-magnitude propellant-optimal guidance algorithm. The adaptive PDI strategy selects the initiation condition by maximizing the safety circle radius. Key supporting technologies include a rapid solution method for the optimal control problem, which leverages closed-form vehicle state expressions and dimensionality reduction of the underlying system of equations, as well as an efficient landing footprint prediction algorithm based on uniform angular interval directional search. Numerical simulations demonstrate that the proposed methods are computationally efficient and reliably establish favorable initiation conditions, making subsequent pinpoint landing not only feasible but also robust against trajectory dispersion.