PD control of magnetically actuated satellites with uneven inertia distribution

This paper considers PD attitude control of magnetically actuated satellites where one axis of inertia is considerably lower than that of the other two. The classic ‘torque-projection’ method of implementing the control is unsuitable for this configuration as the nature of the torque projection controller places little significance on the low inertia axis. This paper proposes a modification to the PD approach by determining the dipole moments through minimisation of a performance index rather than projection onto the magnetic field orthogonal. This allows fairer consideration of the low inertia axis and leads to improved performance of the feedback control. This approach is taken further by introducing an element of feed-forward control to improve the disturbance rejection properties of the system. In a similar way the required feed-forward compensation is determined through minimisation of an appropriate performance index. Combination of the feed-forward and feedback control successfully regulates the satellite attitude when assessed using a high fidelity simulation model. Overall this paper presents a systematic approach to the design of an effective and easy to implement attitude control system for a satellite with an uneven inertia distribution.