Abstract This Thesis work focuses on the optimization of engine design and trajectory for Hybrid Rocket Engines (HREs). In particular, the optimal choices of tank geometry and material are analyzed. HREs are well suited for many applications, among which small satellite launchers are here considered. In this Thesis work, each stage of a three-stage launcher is equipped with the same hybrid rocket engines, organized in different numbers: six, three, and one respectively in the first, second and third stage, in order to minimize the costs by means of a high system commonality. A simple blow-down feed system and an airborne launch are taken into account.