Development of guidance and control strategies for a small satellite involved in proximity operations

Rendezvous and Docking (RVD) operations are among the most critical and challenging operations of in-orbit servicing missions. In this type of operation, safety plays a crucial role, as it is necessary to have extremely precise control over the satellite's position, velocity and attitude when the two bodies are in such close proximity, in order to avoid mission-compromising anomalies. This thesis is part of the SROC (Space Rider Observer Cube) project, promoted by ESA and carried out in collaboration with Tyvak International, Politecnico di Torino and Università di Padova. Initially, the mission architecture involved a CubeSat performing RVD with the Space Rider platform. However, following a design evolution, Space Rider has been replaced by a twin CubeSat, named SROC-B, thus requiring a complete redefinition of the guidance strategy and manoeuvres. The objective of this thesis is to design the guidance algorithm for the final approach phase of the RVD between SROC-A (the chaser) and SROC-B (the target). For this purpose, an orbital simulator that implements the Guidance, Navigation, and Control (GNC) functions was modelled in MATLAB/Simulink. Regarding the modelling of the system's dynamics, the Port-to-Port equations were implemented in addition to the Hill–Clohessy–Wiltshire equations to improve the accuracy of the final approach phase. The type of controller implemented is a Non-linear Model Predictive Controller (NMPC) capable of ensuring robustness and the satisfaction of requirements. The mission was simulated in both nominal and off-nominal conditions, evaluating the possible consequences of the latter case and implementing the necessary Collision Avoidance Maneuvers (CAM). The contribution of this thesis regards the definition and verification of the control strategy for nominal approach and the identification and validation of the main guidance and control solutions for off-nominal events. This contribution will be relevant during the re-scope of the mission planned for the first quarter of 2026.