Abstract: The design of an acquisition,pointing and tracking（APT） control system is a critical factor for the overall- inter-satellite laser communication performance. The probability density function of the APT system point error is first deduced, and then according to this function, the acquisition probability, tracking error and bit error probability are introduced in detail, which are affected by satellite platform vibration and antenna parameter perturbation in the process of inter-satellit laser communication. The impact on point error caused by satellite platform vibration in low frequency domain and uncertainty of plant in high frequency domain is analyzed by the stationary random signal power spectrum. Based on the power spectrum properties, H_∞ mixed sensitivity control method is applied to APT control system design to eliminate the impact of vibration and uncertainty. Simulation proved that the controller designed by the H_∞ control method resists vibration effectively, and possesses robustness when bounded uncertainty of plant emerges.

Key words: APT control system, satellite platform vibration, plant uncertainty, acquisition probability, H_∞ control