The present work has the purpose of presenting the results of a Computational Fluid Dynamic Analysis of a Hybrid rocket engine. This work has been conducted in parallel with Lucia Squillari, who did the Transient Thermal analysis of the half end of the motor, some data are directly taken from her thesis. The report describes the path followed during the analysis and calculations: identify the goals, find motivations and main parameters needed, computational process, analysis of the results obtained. The first chapters explain the motivations behind the concept of a new market based on small-satellites and dedicated mini-launchers. After an initial description of propulsion systems, hybrid propulsion is introduced, enumerating advantages and disadvantages compared to liquid and solid propulsion.