Analysis and optimization methodologies of spacecraft trajectories in multi-impulse and low-thrust mission scenarios

The aim of this thesis is to provide a number of tools and methodologies that allow the designer to perform fast preliminary analyses of spacecraft trajectories in the early design phases of a space mission. Both multi-impulse and continuous-thrust transfer scenarios are analyzed within an optimal framework. In particular, the first part of this Thesis investigates three mission scenarios of particular scientific interest. The first one is a classic orbit-to-orbit transfer using a maximum number of three tangential impulses. Then, two advanced mission concepts are investigated: an optimal transfer toward the apocenter of an elliptic rectilinear orbit and the maintenance of an elliptic displaced non-Keplerian orbit. Graphical tools and analytical results are provided for fast mission analyses, and, in some cases, a comparison is also made between the characteristics of multi-impulse and continuous-thrust scenarios. The second part of this thesis deals with a particular and fascinating form of low-thrust propulsion, that is, solar sailing. In particular, orbit-to-orbit heliocentric transfers are analyzed, and optimization techniques are proposed that can provide fast approximations of truly optimal solutions obtained with classical indirect approaches. Moreover, additional analyses are performed that consider the effects of uncertainties on optimal sail trajectories. In particular, the effects of additional sail attitude constraints and of solar irradiance fluctuations are thoroughly investigated