Assessment of Nominal and Off-Nominal Trajectories for a CubeSat during the Docking Operations with a Larger Spacecraft

Rendezvous and Docking maneuvers (RVD) have always been one of the most challenging and complex operations in proximity operation and in orbit servicing missions. These maneuvers require high accuracy of the control systems, together with the knowledge of the relative state between the spacecraft and the space environment and the assessment of potential failure scenarios. This kind of missions are more difficult when CubeSat are involved due to the reduced dimensions and the lower technology readiness level compared with larger spacecraft. This thesis deals with the analysis of the trajectories and maneuvers of a 12U CubeSat in nominal and off-nominal cases. After the choices of the guidance and control strategies and the definition of the GNC architecture, analyses have been done to assess the robustness of the performance in nominal conditions, i.e. when the GNC works properly under boundary conditions. No return points, Collision Avoidance limits, time-to-docks, fuel consumption, accuracy at the mating points have been evaluated. Then, the off-nominal situations are deduced and new simulation sessions investigate the capability of the system to react against discrepancy between actual state and desired state and in case of system failures. Simulations are conducted by modelling the dynamic systems of SROC within MATLAB/Simulink® with a detailed Guidance Navigation and Control (GNC) simulator implementing Model Predictive Control (NMPC) as control laws. Collision avoidance maneuvers (CAM) are considered in open-loop and closed loop, in order to identify the most effective solutions in terms of safety. The case study is the Space Rider Observer CubeSat (SROC) mission, where a 12U CubeSat whose objective is to acquire visual information of Space Rider, its mothercraft from which it is initially released, while orbiting around it and up to the controlled soft-docking inside the cargo bay. SROC is a CubeSat developed by Politecnico di Torino, University of Padova, and Tyvak International and SROC project is funded by ESA and ASI. The thesis highlights the results of the analysis applied to this mission during the phase B2 of the project, confirming the effectiveness of the solutions in nominal conditions, and when an error occurs on the state vector and GNC equipment.