Magnetic Attitude Control System for Low-Earth Orbit Satellites

A small spacecraft (SC) under consideration is intended forperforming a scientific mission on the low-Earth orbit for a long time(a year or more). A control system of the SC provides the constructionof regime of three-axis orientation of the SC in the orbital coordinatesystem and the stabilization of that regime, and must be autonomous,low-weight and low-cost. The magnetic control system that consists ofthe information subsystem based solely on three-axis magnetometermeasurings and the magnetic actuators satisfies in the best wayrequirements mentioned above. Such system can estimate both orbitalmotion parameters and attitude ones of the SC. But the absence of theadditional instruments and damping devices complicates the estimationsince the range of initial conditions uncertainly is wide and theproblem of estimating becomes essentially nonlinear. To get over thesedifficulties a recursive state estimation algorithm with enhancedconvergence is proposed. The magnetic control moment is synthesized bythe vector function Lyapunov method.