Desaturation Control Laws for a Small Satellite

This paper addresses the problem of the momentum dumping for the pitch momentum wheel onboard ALMASat, the microsatellite platform under development at the II Faculty of Engineering of the University of Bologna. While designing the attitude control system of a microsatellite, the pointing accuracy may not be the only goal, as additional constraints might come into play. As a matter of fact, because of the limitations in the available electrical power, the energy spent for the control input must be carefully taken into account and minimized. The ALMASat control systems includes three orthogonal magnetic coils for attitude acquisition manoeuvres and for coarse attitude pointing, a pitch momentum wheel for fine pitch attitude tracking and micropropulsion system for additional pointing capabilities, wheel’s momentum management and small orbital control. Attitude determination is performed using a commercial Three-Axis Magnetometer (TAM) and a set of four low-cost/high-accuracy Sun Sensors developed at the University of Bologna, as part of the same microsatellite activity. This paper focuses on the design of efficient momentum management manoeuvres, showing the theoretical background and simulation results of our approach to the synthesis of momentum dumping control laws, given certain constraints in the overall available power. Simulation results show how using our approach the power consumption is reduced with respect to classical momentum dumping techniques.