Quasi-optimal low-thrust orbit transfers using simplified steering laws

As the low-thrust manoeuvres are assuming more importance in the spacecraft propulsion, the analysis of this kind of transfer is essential for understanding and controlling it. In this sense, we want to study simplified steering laws that are easier to perform with the spacecraft and that we can control in each point of the transfer. The analysis starts with the Lagrange planetary equations applied with four steering laws and in case of periapsis or apoapsis centred burns, obtaining the rates of change of the Keplerian orbital parameters in one revolution. One of the most important application of this method concerns the Jupiter moons tour, a tour between the Galilean moons that nowadays is subject of many studies. Therefore, we analyse the transfer between two Galilean moons, using the four steering laws even with combinations of them. The benefit of using this method is given by the direct control over the algorithms generated and the geometrical understanding of the entire transfer. The last part of this thesis deals with the singularity that affects the Lagrange planetary equations, which is having the inclination equal to zero. The central point for the resolution is that the inclination is not a geometrical element that characterizes the orbit, but it depends on the reference system used. Thus, applying a rotation of the reference system we can resolve the singularity without having to rely on the equinoctial elements which use leads to several complications.