Magnetic attitude control for nano-satellites

Abstract

The active magnetic attitude control technique is a recognized attitude control option for small satellites operated in Low Earth Orbit (LEO). The purpose of this thesis is to control a nano-satellite that is operated in LEO so that it always pointing toward the Earth. Two options of control algorithms have been considered for a gravity-gradient satellite. The first control is a passive type, structured for the gravity-gradient satellite (Satellite A). It relies totally on the orbited body's mass distribution and gravitational field. The second control is an active type, structured for the gravity-gradient satellite employing three magnetic torquers onboard (Satellite B). The control is accomplished using a set of magnetic torquers that can generate a mechanical torque thus producing control actions when the torquers interact with the geomagnetic field. The algorithm used in Satellite B is configured for controlling roll, pitch and yaw attitudes using a proportional-derivative (PD) controller. Both control algorithms are simulated using the MATLAB®/ SIMULINK® software. The control algorithms were tested using a simplified geomagnetic model for a reference space mission. Their attitude performances were compared and it is found that both controls fulfil the mission requirements. However, the system in satellite B gives a better attitude performance. Specifically, the roll axis oscillates between -2.4° and 3.2° while the pitch axis oscillates between -2.4° and 2.0°. Finally, the yaw axis swing is much controllable with an oscillation between -1.7° and 0.4°. This work provides us an insight when designing a real magnetic attitude control subsystem for nano-satellites.