Research On Fine Tracking Technology For Deep Space Laser Communication

Compared with microwave communication,laser communication has shown great advantages in the communication speed,communication distance,system size,weight,and power consumption.Owing to the relative motion between two communication terminals,the pointing,acquisition and tracking(PAT)system is required to establish and maintain the stability of the communication channel for the free-space laser communication.Compared with the laser communication in the earth orbit,the communication distance is extremely far and the space noise is strong for the deep space laser communication.Thus,the performance requirements of PAT system are more stringent.It is necessary to conduct more research on deep space laser communication tracking technology.This paper will focus on the fine tracking technology of deep space laser communication.Firstly,the power budget analysis for laser communication in deep space environment is carried out.The influence of PAT system's pointing error on communication performance is discussed.And the requirements of fine tracking subsystem under deep space conditions are proposed.When the laser's wavelength is 1550 nm,the antenna diameter is 40 cm,we can deduce that the tracking accuracy of the fine tracking subsystem is required to be less than 1.64?rad.Secondly,accurate satellite attitude information is the premise of beam tracking.In order to obtain the micro-radial beam tracking accuracy,it is necessary to accurately measure the deflection angle of the beam at least in the micro-radius level.In this paper,a compact double-grating configuration is proposed.The double grating is properly configured to allow the incident beam to be diffracted multiple times between the two gratings.And multi-stage amplification is achieved to multiply the incident beam deflection.And it is verified by simulation and experiment.When the beam's incident angle is between-22.93 mrad and 3.85 mrad,the incident light will diffract 4 times between the two gratings and the deflection angle is amplified by more than 10 times.By measuring the amplified beam deflection,the resolution of the angle measurement can be increased by at least 10 times.Finally we applied the principle of least mean square(LMS)algorithm to the fine tracking subsystem for higher tracking accuracy.And the adaptive tracking algorithm was verified in the fine tracking simulation system built in the laboratory.Through the simulation and experiment of the adaptive tracking algorithm,the feasibility of applying adaptive filtering in the fine tracking subsystem is verified,and the pointing accuracy of the micro-arc metric can be achieved.