Attitude control of Earth-pointing spacecraft using the reaction jets and magnetic torquers

With the rapid developing of the scientific applications via satellites, the polar and nearly circular orbits are widely used by spacecraft for purpose of full coverage of the Earth. In most cases, the satellites fly in a three-axis stabilized Earth pointing mode during the nominal phase. For this kind of low Earth orbit satellites, attitude control by a cold gas propulsion system and magnetic torquers becomes a practical means. On-off control by the cold gas propulsion system can be used to control the pitch set while it can drive the controlled states in the roll/yaw set almost to zero except that the chatter occurs. Based on the state feedback control, the roll/yaw set can be controlled to reach desired values using the magnetic impacts. Linear-Quadratic-Regulator (LQR) synthesis is used to design the feedback control strategy in this paper.