• solar wind uncertainties
• trajectory determination
• mission analysis
• propellantless propulsion system
• solar sail
• electric solar wind sail

The aim of this Thesis is to provide a systematic analysis of the preliminary mission analysis and design for a spacecraft equipped with a solar sail or an electric sail, which are described and modelled in the first Part.
The second Part deals with possible mission scenarios, focusing on two options, namely, displaced non-Keplerian orbits and plasma brake. The latter is a derivation of the electric sail basic concept that may be employed to perform a deorbiting from LEO.
In the third Part, an approximate model, based on an asymptotic series expansion and on the hypothesis of small thrust magnitude, is used to derive the propelled trajectory polar equation. Then, the problem of determining the optimal steering law is addressed. For a solar sail, an approximate analytical solution is found.
The fourth Part analyzes the impact of solar activity fluctuations. The case of an electric sail is involved, since the fluctuations of the solar wind dynamic pressure are relevant and chaotic, so that it is modelled as a random variable with a gamma distribution. Simulation results highlight that the trajectory of an electric sail-equipped spacecraft is very difficult to predict, so two possible control strategies are discussed to counteract this issue. Both control laws exploit a suitable adjustment of the electric sail grid voltage to modulate the thrust and compensate the effect of the solar wind fluctuations.