UC San Diego

Safety, precision, and efficiency are the key ingredients for successful future human-scale entry, descent, and landing (EDL) missions to the Moon and Mars. In this work, a complete investigation into each component of an EDL mission, including an emergency scenario, revealed some of the necessary techniques that need to be implemented to effectively reach these goals. An often-ignored aspect of EDL is the requirement to have a safety protocol in place in case of an emergency. In this work, a newly developed abort guidance technique revealed that an ascent-abort into orbit can be achieved from any point during the lunar powered descent phase. The two-phase abort methodology is inspired in the optimal ascent guidance problem and can be activated autonomously to guide the vehicle towards a safe orbit with the least amount of propellant possible. Validation of two state-of-the-art algorithms for entry and optimal powered descent guid- ance in different mission scenarios and in a high-fidelity simulation environment, demonstrated that a complete non-optimized EDL trajectory can be generated quickly and reliably. With the addition of an adaptive powered descent initiation logic, based on the indirect method of optimal control, the total propellant consumption during powered descent can be greatly reduced even when the powered descent guidance is not optimal. The complexity of the end-to-end EDL problem limits the extent to which the problem can be optimized by the known optimal control techniques. Optimization using the direct method of optimal control can generate a theoretical solution, albeit in an impractical amount of time. Leveraging the robustness of a state-of-the-art entry guidance and an optimal powered descent guidance algorithm, a novel ap- proach to the optimization of the end-to-end EDL problem emerged. The problem is solved with a bi-level optimization approach in which an inner loop optimizes the propellant consumption during powered descent, and an outer loop modifies the entry trajectory to provide the best PDI condition. This innovative approach results in a fast and reliable trajectory with near-optimal propellant consumption in a matter of seconds. All the results from this investigation are tested for robustness in Monte Carlo simulations.