Design and Validation of a Technology Demonstrator for an Autonomous Orbit Determination System for Small Satellite Constellation This thesis work is inserted within the context of a project for a deep??space autonomous navigation system proposed by Argotec, an Italian aerospace engineering company based in Turin. The mission considered is "Autonomous oRbit dEtermination System for Smallsats Constella??tion (ARES4SC)" which aims at developing a constellation of five small satellites capable of determining their precise ephemerides after being deployed around a planet. Son of Zeus and Hera, Ares is the Greek god of war and from its Roman counterpart, Mars, the ARES4SC mission took the reference planet, with the concept being however suitable for any other celestial body.