Fully magnetic attitude control for spacecraft subject to gravity gradient

This paper presents stability and control analysis of a satellite on a near polar orbit subject to the gravity torque. The satellite is actuated by a set of mutually perpendicular coils. The concept is that interaction betwee n the Earth's magnetic field and a magnetic field generated by the coils re sults in a mechanical torque used for attitude corrections. Magnetic actuat ion due to its simplicity and power efficiency is attractive on small, inex pensive satellites. This principle is however inherently nonlinear, and dif ficult to use since the control torque can only be generated perpendicular to the geomagnetic held vector. This paper shows that three-axis control ca n be achieved with magnetorquers as sole actuators in a low Earth near pola r orbit. It considers the problem from a time-varying, nonlinear system poi nt of view and suggests controllers for three-axis stabilization. A stabili ty analysis is presented, and detailed simulation results show convincing p erformance over the entire envelope of operation of the Danish Orsted satel lite. (C) 1999 Elsevier Science Ltd. All rights reserved.