Active control for initial attitude acquisition using magnetic torquers

This paper presents an active control design for spacecraft initial attitude acquisition (IAA) by using two magnetic torquers on the X and Y body axes. A very robust and fully autonomous design for IAA can be fulfilled by the use of a simple magnetic control law, a proportional-plus-derivative controller. A modified “B-dot law” provides the derivative control action while the cross product of spacecraft +Z body axis vector and geomagnetic field vector provides the proportional control action. Attitude motion of the spacecraft is reduced by forcing the spacecraft's +Z body axis to align with the Earth's magnetic field vector. Simulation results are provided to demonstrate the design. When the initial deviation is not large, the attitude convergence can be completed in one orbit.