The ESA Space Rider System is designed to provide Europe with the first reusable and independent end-to-end orbital platform, to deliver an uncrewed orbital laboratory able to de-orbit, re-enter, land and be relaunched after limited refurbishment. In this context, AVIO is the prime contractor of the support module that must guarantee the guidance, navigation and control functions during the orbital phase of the system. High versatility and reliability are thus requested for the AVUM Orbital Module since the Space Rider mission foresees various in-orbit experiments, ranging from payload for commercial and institutional applications to In Orbit Verification/Demonstration missions, microgravity experiments, and Earth/Space observation.