• Station-Keeping
• On-off Control
• Low-Thrust
• Linearization
• High Accuracy
• GPOPS
• Geostationary-Satellite
• Trajectory Optimization Problem
• VOP Equations

This thesis analyses the problem of station-keeping (SK) maneuver planning for geostationary satellites, attempting to reach a target accuracy level of 0.001 deg by using electric thrusters.
Geostationary satellites are currently allowed to operate within an accuracy range between 0.1 to 0.05 deg, and are controlled with chemical thrusters, with a control frequency of two weeks. Therefore, the main challenges to be handled in this work are due to the extremely high objective accuracy and the substitution of chemical thrusters with electric thrusters, which provide limited and non-modulable thrust levels.
In this work, for a given value of nominal longitude, the SK maneuver planning is addressed as a constrained trajectory optimization problem and solved numerically using the GPOPS software on MATLAB. The performance index to be optimized is the fuel consumption, the constraints on the longitudinal and latitudinal position of the satellite are written as path constraints. By assuming firstly that electric thrusters are able to provide any thrust level and operate constantly, a continuous control profile is derived and is secondly turned into an on-off one, by taking into account the technological limitations of actual electric thrusters. This transformation operation is done by appropriately combining the required Delta-v budget and then effectively spreading it about the properly derived "time barycenters".
The resulting control strategy, unlike the traditional one, are characterized by frequent maneuvers, requiring the thrusters to be turned on several times a day.
Finally, to assess the validity of the proposed method and the influences of different values of nominal longitudes, the developed control algorithm will be applied to some representative values of nominal longitude.