Design Of Spot Detection And Tracking System For Space Laser Communication

Space laser communication system has many advantages,such as small volume,large communication capacity,good confidentiality and strong anti-interference ability,which has become a hot research topic in recent years.The precondition of communication is to establish a fast and stable laser communication link.However,because the laser beam is very narrow,the point to point communication is difficult and the interference factors in the communication channel are affected,It makes the work of beam acquisition,alignment and tracking(Acquisition,Pointing and Tracking,APT)particularly important,The main works are as follows:Firstly,The three commonly used devices in the spot detection unit of the APT precision tracking system,the influence factors of spot location detection performance and the central positioning algorithm based on Gauss distribution are introduced.The detection error of annular spot on the four quadrant detector photosensitive surface is studied when Cassegrain telescope system is used as optical antenna.The mathematical model of the incident annular spot offset,the center coordinates of the spot,the width of the dead zone of the detector and the radius of the inner and outer circle of the annular spot are derived,and the simulation analysis is carried out.A annular spot error compensation algorithm is proposed to overcome the position detection error caused by the occlusion of the spot center.Secondly,An experimental system of annular spot detection based on four quadrant detector is designed,which validates the annular spot shading ratio problem and the correctness of the annular spot error compensation algorithm under the shading of the Cassegrain optical antenna sub mirror.The system experiment platform is built,including the hardware structure platform and the software environment platform.Finally,The PI control algorithm used in the fine tracking experiment system is designed.However,due to the low tracking precision of the system under the PI control algorithm,the robust sliding mode variable structure controller is designed for the APT precision tracking system with the PZT vibrating mirror as the actuator.The simulation analysis is carried out with Matlab\Simulink,and the control effect of the PI controller and sliding mode variable structure controller to the tracking system is compared.The results show that the appropriate Cassegrain optical antenna with the ratio of the primary and secondary mirrors is selected or the appropriate spot radius is selected when the ratio of the inner and outer radius of the annular spot is 30%.and the error compensation algorithm can be compensated for the detection error.After the design of the precision tracking control system,the numerical simulation shows that the sliding mode variable structure controller is superior to the PI controller in the performance of fast and anti-interference ability.