On Line-of-Sight Stabilization of Fizeau Phased Array Telescope System With Delay Compensation-Based Disturbance Observer

In the satellite-borne Fizeau phased array telescope (FPAT), the imaging quality is significantly deteriorated by tip-tilt disturbances induced by carrier maneuvering. The long exposure time of the image sensor is usually required for a good signal-to-noise ratio, which brings the time delays into the control loop of the fast-steering mirror. As a result, a low control bandwidth is insufficient to compensate for FPAT disturbances. In this paper, a time delay compensation-based disturbance observer (TDC-DOB) is proposed to reject carrier disturbances. This new TDC-DOB is plugged into the original feedback control loop, so the disturbance rejection can be optimized by designing an appropriate delay compensation controller. An improved TDC-DOB controller is presented to reject the widespread carrier disturbances, and also reduce the amplifications induced by the waterbed effect. This proposed controller can achieve a satisfying disturbance rejection beyond the closed-loop bandwidth which breaks the limitation of the existing DOB method. Both simulations and extensive experiments are carried out to demonstrate that the TDC-DOB method can earn a significant improvement for the disturbance rejection in comparison with the conventional feedback controller.