Dottorato in ENERGIA E AMBIENTE

Titolo della tesi: Guidance and control techniques for sustainable space exploration and utilization

New challenges are foreseen as more ambitious goals are being written in the agendas of all actors in the space economy. Under the increasing concern for sustainability, innovative strategies are required to face a rapidly changing framework. This research investigates three research areas where the development of autonomous guidance and control strategies is pursued: (i) On-Orbit-Servicing (OOS) and Active-Debris-Removal (ADR), (ii) exploration of the cislunar space, and (iii) planetary defense. With regard to domain (i), this study explores new approaches to the design of ADR and OOS missions. A two-layer approach is adopted, exploiting natural orbital plane precession to reduce the fuel consumption. Two different strategies are investigated: a metaheuristic approach leverages permutation encoding and simulated annealing to explore a large solution space; an A* search procedure is proposed to obtain the optimal sequence of visited satellites, within smaller sets of objects. The results show that the former algorithm can provide near-optimal solutions for a significantly large number of satellites, tough requiring several iterations to rule out local minima. Instead, the tree-search approach always yields the optimal solution, though within a smaller subset of objects. In the context of cislunar space exploration, a high-fidelity dynamical framework is developed, including gravitational perturbations, third- and fourth- body gravitational attraction, ephemeris-based models for all planetary bodies, and nonnominal flight conditions. A semi-analytical approach is proposed to enable a fast and efficient determination of optimal impulsive transfers between Gateway and lunar orbits. Furthermore, guidance and control techniques are developed and tested to support operations across several mission scenarios, including constellation deployment and maintenance, and rendezvous between Gateway and lunar orbits. Within impulsive strategies, a Lambert-based iterative guidance algorithm is developed and tested to compute all intermediate correction maneuvers. This approach is shown to outperform the optimal two-impulse solution in orbit transfer scenarios. Instead, a Lyapunov-based low-thrust nonlinear feedback control law is designed in the full nonlinear model and extended to track all orbital elements, including the true anomaly, despite orbit perturbations and control saturation. Finally, with regard to planetary defense, two nonlinear control strategies are interfaced to obtain a predictable motion around a Near-Earth-Orbit asteroid with a highly perturbed gravitational field, namely 433 Eros: a Lyapunov-based feedback control law performs orbit acquisition to drive the spacecraft in the proximity of the desired motion, while nonlinear Hybrid Predicted Control is intended to pursue the target orbit around Eros. Monte Carlo campaigns show that the strategy at hand is effective in achieving the desired motion around a highly irregular gravitational field, with modest fuel consumption. All the strategies operate without pre-computed trajectories or numerical integration, providing an efficient and lightweight approach to onboard guidance and control.