Mission Analysis and Guidance Strategies for Small Satellites involved in Proximity Operations

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. Moreover, the guidance challenges are stressed by the constraints imposed by miniaturized platforms and related technologies. The main goals are to design a robust and safe trajectory for the RVD maneuver, given a set of operations to be performed, and to design an autonomous driving strategy to execute the planned maneuver. The thesis is organized into two main parts. The first part focuses on mission analysis, aiming to define nominal RVD concepts and strategies, with particular attention to relative trajectory design, maneuver planning, and operational constraints. The analysis is carried out using Matlab/Simulink scripts and toolboxes, while commercial software tools (e.g., STK, ESA Drama) are employed for numerical integration, accounting for perturbations, safety constraints, and the limited propulsion and sensing capabilities of the CubeSats involved. The second part of the study presents a Monte Carlo-based robustness analysis of the proposed strategy, considering uncertainties in thrust magnitude, thrust direction, and position accuracy. These uncertainties are critical in the context of miniaturized systems, and their consideration is essential to ensure both mission safety and successful execution. The expected outcomes of the mission analysis phase include the detailed definition of the ConOps, which outlines the timeline of mission phases, operational constraints, and safety margins for the RVD scenario. Particular focus is placed on studying the effects of the deployment phase on both satellites, their subsequent approach, and the proximity operations as formulated by the ConOps. A key objective in the design of the RVD trajectory is the minimization of DV, and consequently fuel consumption, while ensuring passive safety of the motion. The trajectory is expected to respect the target's KOZ, maintain the defined HPs, and allow for collision avoidance maneuvers if required. The analysis also aims to verify docking conditions, ensuring that the chaser approaches the target within acceptable limits of relative velocity, attitude, and positional accuracy. Furthermore, the model is expected to be realistic and to incorporate the main perturbative effects, including atmospheric drag, Earth's oblateness (J2), and solar radiation pressure. The results of this thesis demonstrate the feasibility of the proposed mission architecture within the imposed constraints. The developed tools have been validated through the use of COTS software, providing increased confidence in the simulation outcomes. The safety requirements of the approach are met, as well as the objectives defined by the ConOps. Therefore, the study can be further developed in future work by transitioning away from the COTS-based approach and adopting fully in-house developed code.