Formation-Keeping Strategies At The Earth-Moon L4 Triangular Libration Point

This thesis examines the use of thrusters and solar sails for spacecraft formation keeping control at the Earth-Moon L4 point. Particular emphasis was placed on the study of underactuated control, in which fewer control inputs than the system's degrees of freedom are available. A linear LQR control scheme, an integral augmented sliding mode controller and a bang-bang controller were applied to the dynamic spacecraft system. The nonlinear controllers produced errors falling with tighter tolerances than the linear controllers in the perturbed environment. Performing similarly well as the underactuated thrusters system was the solar-sails-controlled spacecraft formation using a bang-bang controller. This shows that solar sails could be a viable propellantless technique for relative control. A linear control technique was able to bound errors to within a couple of hundred metres, using a hybrid propulsion system. Of the cases studied, only the fully-actuated thrusters-based system was able to explicitly track a circular trajectory, but had [Delta]V requirement of more than 100 times greater than that needed for tracking the natural, elliptical trajectory.