Thanks to the reduction in design iterations and production costs, the increasing availability of launch ridesharing opportunities and the use of standardized form factors, such as the CubeSat standard, research in the field of small satellites is rapidly growing. This interest is due to the ability of small spacecraft to fulfill payload needs in future space missions, such as in-orbit servicing and assembling. The present thesis focuses on the phase B2 study of a technology demonstration mission regarding a chaser CubeSat performing autonomous proximity operations with respect to a twin CubeSat operating as target. Guidance, navigation and control are safety critical functions for such missions, especially in close proximity phases.