In the New Space era, private companies are driving rapid advancements in rocket propulsion. Among them, OPUS Aerospace is developing a reusable micro launcher that requires the design of a new liquid rocket engine, Elanion, to deliver 45 kN of thrust using liquid oxygen and propane as propellants. This thesis presents the preliminary design of the Elanion engine’s thrust chamber, spanning from contour generation to the optimization of its regenerative cooling system. Two in-house tools were developed to rapidly iterate and refine the chamber geometry and cooling system design. Additionally, a study of propane’s cooling properties led to the development of two Nusselt correlations for modeling its convective heat transfer. The thrust chamber designed in this research meets all specifications, leaves margin on the budgeted pressure loss, and was successfully converted into a CAD model, laying a strong foundation for further development of the Elanion engine.