Magnetic attitude actuation for passive satellites

The orientation of a passive communications satellite with respect to the earth can be adjusted by using an electromagnetic actuator which is rigidly mounted on the structure of the satellite. The actuator consists of three mutually-orthogonal air-cored coils on the skin of the satellite. If any one of the coils is excited by current, the magnetic field generated by it tends to rotate the satellite until the generated field and the terrestrial magnetic field are aligned. The activation of the coils also produces various undesirable forces which must be supported by the satellite structure. If the actuator is mounted on an ultra-thin structure, such as the Echo II Satellite balloon, these forces can have damaging effects. In this paper equations are derived for the adjusting torque and for the undesirable forces. The conclusion reached is that the compressive force upon the coil loops caused by the terrestrial field poses the most serious danger to the satellite structure.