The central innovation of this work consists in the design, development and validation of a modular CubeSat Dynamic Simulator. The simulator modularity consists of its peculiar design, developed to cover a wide range of CubeSat configurations and mission profiles. CubeSats are currently a widely employed vehicle for low-cost and flexible space access for both academic and business use. Although small, they integrate advanced subsystems whose functioning is crucial to mission success, primarily in attitude control, power management, and communications. This thesis outlines an end-to-end simulation of a CubeSat mission on Matlab/Simulink. The simulator couples orbital propagation with attitude dynamics under external perturbations such as Earth's oblateness, atmospheric drag, solar radiation pressure, and the third body.