Sun Vector–Based Attitude Determination of Passively Magnetically Stabilized Spacecraft

This paper examines the problem of attitude estimation for passively magnetically stabilized spacecraft using only sun-vector measurements. An analytical investigation of local observability is performed in the case where the spacecraft magnetic dipole is constant. This is relevant because for passively stabilized spacecraft using permanent magnets and magnetic hysteresis rods, the hysteresis rod dipole moments are nearly constant at steady state. It is shown that under reasonable assumptions on the Earth’s magnetic field, not only are the attitude and angular velocity locally observable, but if one component of the magnetic dipole moment is known, then the remaining two components of the magnetic dipole moment are locally observable also. Numerical examples of three attitude estimation schemes are presented, demonstrating successful state estimation of passively magnetically stabilized spacecraft.