An attitude determination and control system of the ALSAT-1 first Algerian microsatellite

ALSAT-1 is a low-cost Algerian microsatellite build by Surrey Satellite Technology Ltd. (SSTL), it is designed to be part of a five microsatellites constellation for daily disaster monitoring. The microsatellite uses a Y momentum and Z reaction wheels, 3-axis magnetorquer rods and a single butane gas thruster for orbital maintenance. The magnetorquer rods do momentum maintenance and nutation damping f or Y/Z wheels and, libration damping and yaw phase control. The attitude sensor used, is a 3-axis fluxgate magnetometer and a sun sensor. Precise orbital knowledge will be obtained using an antenna GPS receiver supported by an on-board orbit estimator. This paper describes the various attitude control modes required to support: (1) initial attitude acquisition phase, (2) imager nadir pointing attitude controller. The specific attitude controllers and estimators used during theses modes are explained. Simulation and in-orbit commissioning results are presented to evaluate the performance and design objectives.