Very Low Earth Orbit (VLEO) has emerged as a promising domain for advancing satellite technology, offering significant advantages in earth observation and telecommunications. To sustain operations at these altitudes, Atmosphere-Breathing Electric Propulsion (ABEP) systems, which utilize air intakes to gather and compress atmospheric particles for propulsion, could be crucial. This thesis focuses on the development of a collisionless flow solver tailored for shape optimization of the intake of KREIOS’ ABEP engine. The main objective is to develop a Python-based computational tool that can model free molecular flow by simulating the trajectories of gas particles through various intake geometries. The methodology involves designing two computational approaches, with emphasis on a simpler approach to provide preliminary results. Although the integration of the solver into a comprehensive shape optimization loop and the implementation of full-scale computational efficiency improvements are beyond the current project’s scope, this work establishes a foundational tool for future development. The results demonstrate the feasibility of collisionless flow modeling for ABEP engine intake optimization and provide insights into necessary steps for further refinement and implementation.