Design and experiment of a LQ controller used in high-bandwidth fast-steering mirror system

Space-based laser communication (LASERCOM) requires precision tracking and pointing in the microradian range. However, the angular vibrations of a satellite platform may be of the magnitude of milliradian and the frequency of 100 Hz or higher. For rejection of the platform vibrations there are two ways: line-of-sight stabilization technology or a fine steering mirror (control system with high closed-loop bandwidth. The former is much more complex in structure and difficult in implement than the latter. So, the latter is always adopted in actual space optical communication engineering. This paper describes a linear quadratic (LQ) optimal controller based on modern control theory for FSM system. Compared with classical controller, the proposed LQ has several advantages: (1) the LQ controller widens the system's closed loop bandwidth; (2) the large improvement in the system dynamic performance; (3) the significant improvement of the system rejection capability on high frequencies disturbance. The FSM system with the LQ controller have been designed and tested. The results confirm the advantages of the LQ controller above and show that it is an efficient control approach for FSM system in LASERCOM.