Six-Degree-of-Freedom Entry to Powered Descent Optimization for High-Mass Mars Landings

In this work a hybrid, multiphase six-degree-of-freedom (6-DoF) entry and powered descent trajectory optimization problem is formulated for a high-mass vehicle landing on Mars. The formulation addresses some new aspects not fully explored to date, such as connecting phases having a different number of states and controls, the dynamics expressed in different coordinate reference frames, as well as the dynamical determination of the optimal powered descent initiation, all with a full 6-DoF model in each phase. A multiphase Sequential Pseudospectral Convex Programming algorithm is developed for the transcription and solution of the corresponding Hybrid Optimal Control Problem. The development and algorithm are demonstrated by numerical results for the NASA Cobra Mid-lift-to-drag ratio Rigid Vehicle in a high-mass landing mission on the surface of Mars.