Multi-objective trajectory optimization of Mars hybrid rockets with in situ propellants

The adoption of in situ resources in the preparation of propellants will be a critical capability to improve the efficiency and scalability of human exploration and settlement initiatives beyond Earth. By taking advantage of Mars’ thin, carbon dioxide-rich atmosphere and locally available metals like magnesium, hybrid rocket vehicles can be optimized to support efficient point-to-point transportation and Earth return missions, facilitating inter-crater transport and logistic support for ongoing exploration efforts as well as future human settlements. As the technologies required for in situ propellants are advancing in their maturity, their consideration in mission planning and the subsequent vehicle design stages becomes necessary. This article investigates the design of hybrid rocket-based Mars Ascent Vehicles (MAV) and Martian hoppers utilizing in situ propellants through a Multi-Objective Trajectory Optimization (MOTO) framework, allowing an evaluation of performance across different mission profiles and payload masses. As part of the proposed multi-objective optimal control problem formulation, the study incorporates applicable dynamic and path constraints alongside relevant auxiliary atmospheric, aerodynamic and propulsive models. A nonlinear six degrees of freedom flight dynamics model is implemented, featuring a quaternion formulation for attitude dynamics. The formulated MOTO framework addresses the maximization of both downrange and payload mass adopting a weighted product scalarization approach. This formulation produces a good level of diversity in the calculated solutions on the Pareto front, fulfilling different mission requirements including sounding, suborbital hopping and orbital insertion trajectories. The proposed MOTO framework is implemented using open-source libraries and solution methods. Verification case studies demonstrate the capability and performance of the proposed approach using a hybrid rocket-based Martian vehicle prototype designed to operate with both Earth-sourced and in situ Martian propellants. Beyond the proposed MOTO framework formulation, this work contributes to research in the multidisciplinary design of MAV and ballistic hoppers and informs their prospective Guidance, Navigation and Control (GNC) systems development.