Study of the safety strategy for a mission of a CubeSat to observe a large, collaborative target spacecraft

Rendez-vous and Docking (RVD) features and technologies are fundamental for unlocking key capabilities for spacecraft tasked with in-orbit operations. However, in a process that can be described as a “planned collision” between two bodies, safety is key, above all in a space environment were failures that may lead to damage to vehicles pose the greatest risks, and maintenance is, if not impossible, a great challenge at best. The case study that this thesis will focus on will be SROC (Space Rider Observer Cube), a future CubeSat based technological demonstrator mission, which aims at performing Proximity Operations and Docking with a larger mothercraft, Space Rider (SR), ESA’s new orbital platform. SROC originates from a collaboration between the European Space Agency, Politecnico di Torino, Università di Padova and Tyvak International in designing a demonstrator for the Space Rider maiden flight. SROC aim to visually inspect the SR vehicle, then to perform docking for retrieval in SR’s cargo bay, to finally re-entry in atmosphere and land on ground. As a spacecraft, SROC falls in the category of CubeSats, Small Satellites of modular nature. CubeSats are gaining increasing interests in the eyes of governments and private investors, thanks to their low cost, adaptability and design advantages. Autonomous RVD is still a frontier technology for CubeSats, especially in terms of safety strategies for the final phases of approach and docking with a larger spacecraft. Starting from a solid literature basis, this thesis aims at exploring rendez-vous and docking procedures and conditions from an AOCS point of view. Then, direct numerical applications will be explored thanks to a robust and flexible simulation environment, implemented with MATLAB/Simulink® computation software, which reproduces a model of SROC’s complex dynamic systems. Always starting from a GNC design standpoint, nominal processes of docking will be explored with the aim of defining and testing requirements for positions, velocities and times. The thesis will then proceed in exploring off-nominal conditions in terms of failures to various parts of the SROC system, and their possible and effective consequence on the state vector and trajectory of the spacecraft. In this context, the definition of safety strategies for the type of scenarios and spacecrafts in consideration is the main innovation aspect of this thesis, as this kind of study is, at the time of the redaction of this document, unique in its genre.