• Attitude and Orbit Control System
• Electric Propulsion
• Geostationary Orbit

The work relates to the design of an All-Electric attitude and control system (AOCS) for a Small-GEO (SGEO) class spacecraft. Such system would rely on a limited number of electric thrusters in order to perform all maneuvers required for the orbital movements of the vehicle among which are the following:
• LEO-GEO low thrust transfer using Electric Propulsion,
• North-South Station Keeping (NSSK) and East-West Station Keeping (EWSK),
• Attitude Control System (ACS),
• Intermediate repositioning (if needed),
• Transfer to graveyard orbit at the end of mission (if needed).
In particular, we have focused on the design of a propulsion system for North-South and East-West station keeping and attitude control.

The first part of the work is devoted to determining the thruster requirements and thrust strategies for the various functions of the mission. First, the problem of orbit raising with low thrust has been assessed and different strategies for reaching a geostationary orbit with Electric Propulsion have be investigated. Once the orbit configuration and parameters have been established, especially regarding the transfer phase, we determined orbit perturbation torques values in order to estimate the delta-V budgets and total impulses needed for Station-Keeping maneuvers.
Then, we developed an attitude dynamics model for the S/C and studied the vehicle’s motion around its center of mass, to evaluate how the Euler angles will vary during the mission. Different thrust strategies for attitude control have been investigated.
In the second part of the work several propulsion system layouts have been proposed and evaluated. With respect to the attitude control system, three options were explored: a solution in which the ACS is integrated with the orbit control system (the same sets of thrusters perform both function), a separated ACS and a solution implying the use of reaction wheels. Some considerations were made also about the Euler angles’ variations during the orbit transfer phase and the means to control them.
Finally, in the last chapter we proceeded to an evaluation of the possible candidate thrusters for the different tasks and to an estimation of the power levels needed. Furthermore, some considerations regarding the state-of-the-art in Electric Propulsion and possible developments were made.