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Magnetic spacecraft attitude control is suitable for missions with moderate pointing and stabilization requirements. It would be especially preferable if an implemented three-axis magnetic control law guarantees global and moreover robust stabilization. Motivated by this consideration, in this work, the integral sliding mode control method is successfully applied to the purely magnetic attitude control problem for the first time in literature. The resulting magnetic integral sliding mode control system, which is designed via Lyapunov's direct method by taking the four major environmental disturbance torques and the full inertia matrix uncertainty into account, has the expected insensitivity against environmental disturbances in the plane of continuous actuation. Along the instantaneous direction of underactuation, which continuously varies in control space as the satellite moves along the orbit, there is no counteraction to perturbations. However, as seen in the results of the high-fidelity simulation, state trajectories are ultimately bounded in the vicinity of the reference state independently from the initial state thanks to the proven robustness of the global stability. Performance robustness of the obtained control system against disturbances and model uncertainty is evaluated to be superior through a couple of comparisons with existing control laws even though it is partial due to the intrinsic underactuation in the system. KEYWORDSintegral sliding mode control, magnetic spacecraft attitude control, time-varying sliding manifold INTRODUCTIONSpacecraft's angular motion around their center of mass, namely, their attitude, is actively controlled by actuator triads, which basically consist of three orthogonally placed devices that produce torque by direct or indirect means. A failure of one of the three reaction wheels or reaction thrusters, which directly exerts control torque on the spacecraft body along the body axis it is aligned with, results in underactuation in the control system. Rigid spacecraft's attitude subject to such an underactuation cannot be asymptotically stabilized at the reference by continuous time-invariant control laws. 1 On the other hand, the case is different with the usage of a magnetic torquer triad. Each of them directly produces a magnetic moment along its axis, and the interaction of the resultant magnetic moment with the local geomagnetic field results in 3446

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Effects of general relativity on the motion of a spacecraft moving on a particular trajectory around Earth is investigated numerically in the context of circular restricted three body problem. It is seen that the general relativistic effects are worth to be included in the calculations, since they are observable to the Earth based observation devices terrestrial or spaceborne after a reasonable period. Even the effects of framedragging of rotating Earth can be detected by the current devices.)