Hybrid Low-Thrust and Chemical Propulsion for Optimal Mars Landing Trajectories via the Indirect Method

The exploration of Mars represents one of the most ambitious missions for the conquest of space. It is not just a question of pushing man into territories never before physically reached, but also of deepening scientific knowledge through the search for possible forms of past microbial life and the analysis of rocks and craters, comparing them with those on Earth. Furthermore, a possible future colonisation of the red planet would open up significant economic scenarios linked to the exploitation of new resources and the development of advanced technologies. This thesis aims to study and optimise trajectory control during the landing phase on Mars. Trajectory optimisation is carried out using the indirect method. This approach transforms the problem of maximising the final mass into a Multi-Point Boundary Value Problem (MPBVP), solved through a multi-shooting iterative procedure based on Pontryagin’s Maximum Principle (PMP). In order to minimise propellant consumption and maximise payload, a hybrid propulsion configuration was adopted, consisting of an electric motor and a chemical motor: the former used in the initial phases to maximise energy efficiency, and the latter in the terminal phase to ensure a controlled and precise landing. The dynamic method adopted includes a two-body model, in which atmospheric resistance is considered as a perturbative effect. Atmospheric density data were calculated using NASA’s Mars Global Reference Atmospheric Model (Mars-GRAM) software, which allows the density value to be evaluated as altitude, latitude and longitude vary. The optimal descent trajectory is sought by imposing boundary conditions and internal conditions that allow the orbit to be gradually reduced. This optimisation is carried out considering both variable-time and fixed-time scenarios.