Magnetic attitude control of near earth spinning satellites

Magnetic attitude control systems were employed in several satellite programs due to their salient features like simplicity in construction, absence of moving parts, less power and space requirements and less weight. A control law suitable for keeping the spin axis of the satellite perpendicular to the plane of a near circular orbit was derived, and a control scheme incorporating the control law is described. The control law was developed from fundamental gyroscopic principles. It was seen that the polarity of the dipole moment of the magnetorquer operated in a bang-bang pattern has to be changed four times in an orbit but not at the intervals of quarter orbit. The use of magnetic torquer to overcome the effect of orbital regression on spin axis attitude was also explained. The control law can be realized by using horizon sensors for attitude error measurements and magnetorquers to produce torque. Details about the control law were given. The dipole moments of torquers for control of RS type of satellites were calculated.