A magnetic attitude control system for precision pointing of the rolling GP-B spacecraft

A new algorithm for magnetic attitude control of spinning spacecraft is presented. This algorithm requires real time measurments of the local magnetic field. A Kalman filter type estimator is derived that can obtain the local field by applying dither current to the magnetic rods. This eliminates the need for magnetometers, guaranteeing colocation of sensor and actuator and removing a number of failure modes. An example controller design is presented for the Gravity Probe B spacecraft pointing control. This controller achieves better than 20 milliarcsec pointing accuracy using the magnetic control algorithm without magnetometer measurements.