Multiple Near-Earth Asteroids rendezvous trajectories optimization using Electric Propulsion

Space missions require fuel to be expended, and every kilogram of fuel on-board is a kilogram of scientific equipment sacrificed to preserve the mission feasibility. The ability to optimize the spacecraft trajectory by minimizing fuel is key to greater scientific return. In some cases, this becomes the only way for the desired mission to succeed. This thesis investigates the problem of trajectory optimization for the case of multiple Near-Earth Asteroids (NEAs) rendezvous missions using Electric Propulsion(EP). NEAs are of fundamental interest for the understanding of our solar system as well as for planetary defence and are stepping stones for interplanetary human flight. Close-up observations of these objects will drastically increase our knowledge about the overall NEA population. Furthermore, low-thrust EP represents a viable option for these missions, offering a higher efficiency compared to chemical propulsion. To solve the optimization problem an indirect approach is adopted. This allows for an exact, even though numerical, optimization and presents a lower computational cost compared to direct methods. However, the capability of achieving an accurate result is highly dependent on the tentative solution. In this study suitable procedures to overcome convergence difficulties and to find low-cost optimized solutions are described. Examples show that by applying these procedures, the derivation of tentative solutions sufficiently close to the optimal ones is straightforward, resulting in a faster convergence to the optimum.