Characteristic Of Temperature Change In 45-Degree Reflectors And Its Impact On The Periscopic Satellite Laser Communication Terminals

More and more attentions globally are paid to satellite laser communication, a new communication technique which has many advantages including higher data rate, low probability of intercept, less volume, less mass and so on. Among others, America, Europe and Japan have come to the engineering reality of satellite laser communications, succeeding in the satellite-to-earth and intersatellite laser communication experiments, and investing more in this grow up field.Because of far communication distance and ultra-small divergence of laser beam, the pointing, acquisition and tracking (PAT) become the key technologies in founding and keeping the satellite laser communication links. Generally, a satellite laser communication system mainly includes transmitter-receiver, pointing-tracking, and communication subsystems. The pointing-tracking subsystem consists of coarse pointer and fine pointer mechanisms. A coarse pointer is usually of a periscope structure or a theodolite structure. For the periscope structure, two 45-degree placed reflectors should be set on the coarse pointer. The coarse pointer and 45-degree reflectors must be fixed outside the satellite to transmit-receive and point-track optical signal. Therefore, this makes the 45-degree reflectors on coarse pointing structure exposed to the space thermal environment. Apparently, the temperature field with temperature gradient will be formed on the reflectors and this in turn results in the deformation of the reflectors. Consequently, performance of the pointing, tracking and communication subsystems of satellite laser communication system will be affected. Therefore, it is of significance to study the temperature field distribution on 45-degree reflectors in periscopic satellite laser terminals in space and the induced influence to laser communications'performance.This dissertation is organized as follows, first, a brief review of the development status of satellite laser communications globally is given in this dissertation. We give the introduction of the research on the effect on the performance of laser communication terminals due to thermal environment in space. For periscopic satellite laser communication terminals, in-depth and systematic research is made on temperature field distribution on 45-degree reflectors in space, and its influence on pointing-tracking performance and communication performance in laser communication systems. The specific works are list as following.In this dissertation, we established the theoretical model of the effects on pointing and tracking performance due to temperature distribution on 45-degree reflectors in periscopic satellite optical terminals. Effects on pointing performance at emitter and tracking performance at receiver are analyzed respectively due to temperature distribution on reflectors. We got the variation of pointing error, tracking error and intensity distribution on receiving plane with the temperature gradient and uniform temperature difference on 45-degree reflectors.Effects on communication performance due to temperature distribution on 45-degree reflectors are studied when vibration of satellite platform exists. The theoretical model of effects on BER due to temperature distribution on reflectors is established in this dissertation with and without noise. The variation of BER with temperature gradient and uniform temperature difference on reflectors is given. Through the analysis of effects on BER because of different wavelength, vibration angle deviation and beam truncation, we got the relationship between BER and these parameters.When there is temperature gradient and uniform temperature difference on 45-degree reflectors, the effects on pointing-tracking and communication performance are compared to the back-fixing using blank and traditional around-fixing using press-board. It is found that the back-fixing method using blank is more suitable to be used to fix 45-degree reflectors comparing to around-fixing method using press-board.The theoretical model of temperature field distribution on 45-degree reflectors in periscopic satellite optical terminals on orbit is established in this dissertation. The variation regularity of temperature field on 45-degree reflectors is given most typical low earth orbit and high earth orbit. The temperature distribution on reflectors of the four different materials is given on orbit. It is found that the reflector with SiC material has the minimum temperature changing range and the minimum temperature difference on orbit. And SiC material is more suitable to be used to make 45-degree reflectors in periscopic satellite optical terminals. The experiment of temperature field distribution on orbit of SiC material reflectors under back-fixing method is given. Through the comparation of the experiment and simulation results, the simulation method computing 45-degree reflectors'temperature field on orbit is validated to be right.Finally, the influence of temperature field on 45-degree reflectors on orbit on pointing, tracking and communication performance in periscopic satellite optical terminals is studied at the end of this dissertation. The variation regularity of pointing error, tracking error, intensity distribution on receiving plane and communication BER performance with time on orbit is given.In summary, the study of this dissertation provides theoretical support guidance in the aim design of thermal control of 45-degree reflectors in periscopic satellite optical terminals, and also in choosing materials and fixing methods for 45-degree reflectors. This can serve as good reference in optimizing design of performance parameter of terminals on orbit in space, as well as theoretical support and reference in testing and evaluating of performance test of periscopic satellite optical terminals on orbit in practical application. Therefore, these research and works are of great significance.