Magnetic Attitude Determination and control of Inertial Pointing Small Momentum Bias Spacecraft

An attitude determination and control system for small momentum bias spacecraft based only on three-axis magnetometer and magnetic coils is proposed. Pointing error components are estimated using an Extended Kalman Filter, based on magnetometer data only, where the state vector comprises the angular momentum unit vector and a unit vector which represents the spacecraft motion about the angular momentum axis. This algorithm is then suitable to achieve any desired momentum direction during the mission and any spacecraft orientation about the momentum axis. It can be used for inertial stabilized spacecraft as well as for orbit normal pointing spacecraft. Moreover the same control law provides for nutation damping. The magnetometer based estimation process has shown a fast converge rate and small steady state errors even during maneuvers. The pointing accuracy obtained by this system is on the order of one degree, which is often suitable for small missions.