FORMATION CONTROL AT THE EARTH-MOON L4 LIBRATION POINT

Several researchers have studied the motion of a spacecraft in the vicinity of Earth-Moon libration points in the past. Few studies, however, involve formation flight about the Earth-Moon L4 equilibrium point; the stability of which is affected by the Sun's influence. This study examines the use of thrusters for spacecraft formation keeping control at the Earth-Moon L4 point under the perturbing effect of the Sun's gravity. 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 sliding mode controller was applied to the fully actuated system. An integral augmented sliding mode controller and a bang-bang controller were applied to the underactuated dynamic spacecraft system. It was found that relative motions can be bounded within about 1 km of the reference trajectory in the underactuated system.