ESA GNC Conference Papers Repository
Guidance and control of magnetic Space Tug
Magnetic tugging of a target satellite without thrust capacity can be interesting in various contexts, as for example End-Of-Life management, or to replace launchers upper stages. The aim is to gradually modify the orbit of the target by constantly exerting on it a magnetic force. To do so, the chaser is assumed equipped with a steerable magnetic dipole, able to create both forces and torques on the magnetic torque rods carried by the target. The chaser is also supposed to carry electric thrusters, creating a continuou force which modifies the orbit of the whole formation composed of chaser andtarget. The relative motions of both satellites are derived, in order to assess the feasibility of such a concept. Relative configuration (attitudes and position) trajectories are derived, which are compliant with the dynamics, and enablehe chaser to tug the target. Considering targets in Low Earth Orbit (LEO), the magnetic field of the Earth is taken into account, modeled by the International Geomagnetic Reference Field (IGRF). The position of the magnetic torque rod of the target may not be located at its center of mass. This lever-arm is taken into account in the dynamics. The existence of guidance trajectories was already derived and presented in  and . In , Two time-invariant LQ-based controllers are proposed, depending on the capacity of the target to control its own attitude with reaction wheels (semi-cooperative scenario). It was shown that the capability to control the attitude target using only the chaser steerable dipole (non-cooperative scenario) is weak and not efficient enough in the time-varying case. The main contribution of this paper is to consider the time-variant feature of the model linearized around the nominal trajectory tacking into account the time-varying Earth magnetic field. Then, a control methodology is proposed to design a time-variant structured controller allowing to share the target attitude control authority between the target own reaction wheel and the the chaser dipole. The proposed control is then evaluated through simulations involving the whole non-linear model. This study assesses the feasibility of the electromagnetic tugging of a semi-cooperative non-hostile target.