| Traditional satellite microwave communication is facing severe capacity bottleneck.Compared with microwave communication,laser communication not only has the advantage of high transmission rate,but also has the advantages of strong confidentiality,strong anti-interference ability,high measurement accuracy,long acting distance,small volume and weight of terminal equipment and low power consumption,etc.It is an excellent alternative to satellite microwave communication.Many countries have already launched fierce competition in the field of space optical communication.In order to ensure the fast and smooth establishment of the laser communication link and the stability of the high communication transmission rate,the laser communication terminal on satellite needs to have high pointing accuracy.Considering that the laser communication system on satellite needs to have sufficient control bandwidth and undergo complex and strong vibration environment when it is launched,the laser communication terminal on satellite should have good vibration characteristics.In this paper,based on the summary of the commonly used structural forms of laser communication terminals on satellite,a relatively novel terminal structure design scheme is proposed,and the research is focused on pointing errors and vibration characteristics.On the basis of a comprehensive and detailed introduction of the research status of the laser communication terminal on satellite at home and abroad,the terminal structure is divided into three categories: two-dimensional deflection mirror type,periscope mirror type and theodolite type,and the advantages and disadvantages of each type are analyzed in detail.According to the practical requirements of the terminal,the terminal structure form of theodolite type is selected as the development route of the final laser communication terminal on satellite.After calculation,it is found that the bending deformation of the altitude axis of a T-shaped altitude-azimuth mount will cause large and complex pointing errors of line of sight,which will cause some difficulties in the ground installation,adjustment and testing,while the U-shaped altitude-azimuth mount does not have this problem.Taking into account the advantages of using coude optical path,a design scheme of laser communication terminal on satellite in the form of U-shaped altitude-azimuth mount based on coude optical path is proposed,which makes the terminal have the advantages of both theodolite type terminal and periscope mirror type terminal,including large caliber,large rotation range,small moment of inertia,light weight,small size,low power consumption,and so on.The error description theory of multi-body system is used to study the beacon light pointing error of the laser communication terminal on satellite.According to this theory,the topological structure of the terminal is extracted after analyzing the factors affecting the error of the terminal,and the coordinate systems between adjacent bodies are established.Then,the establishment of the ideal static characteristic matrix,the static error characteristic matrix,the ideal motion characteristic matrix and the motion error characteristic matrix between each pair of adjacent bodies is described in detail,and the mathematical model of the beacon light pointing error is established by using beacon light axis pointing vector.By means of numerical simulation,the influence of error sources on the beacon light pointing error is studied,and the maximum value of beacon light pointing error under constraint conditions is obtained,which is 17.5?.For the study of signal light pointing error,including the study of pointing error between signal light and beacon light and the study of pointing error between signal light and ideal direction,firstly,the calculation formula of light reflection is derived by using the vector representation of laser beam and mirror normal direction.Secondly,the coordinate systems of coude mirrors are established,and the normal vector of each coude mirror in the inertial reference coordinate system is obtained by using the error description theory of multi-body system.Then the forward directions of signal light in the coude optical path are calculated by using the calculation formula of light reflection according to the coude mirror normal vector.Then the change of propagation direction of signal light after passing through the off-axis lens is analyzed,and the mathematical model of the signal light pointing error is established.Finally,the influence of error sources on the signal light pointing error is studied by means of numerical simulation.The maximum values of the pointing errors between signal light and beacon light and between signal light and ideal direction under constraint conditions are obtained,which are 0.33? and 17.5? respectively.Using MSC / Patran finite element analysis software,the vibration analysis of the laser communication terminal on satellite is carried out,including modal analysis,sinusoidal vibration analysis and random vibration analysis.The advantages and disadvantages of explosion bolt and memory metal separation nut as locking device are introduced in detail.Finally,the memory metal separation nut with adjustable locking force,which can be reused,is selected as the locking device of the terminal in order to realize the locking function and improve the fundamental frequency of the terminal.Based on the simplification of the model,the finite element model of the whole terminal is established and the vibration analysis is performed.The modal analysis results show that the fundamental frequency of the whole terminal is 93.3 Hz,which meets the technical requirements of the fundamental frequency greater than 80 Hz.The sinusoidal vibration analysis results and the random vibration analysis results also meet the use requirements,indicating that the laser communication terminal on satellite has good vibration characteristics.The vibration test platform is built,and the terminal vibration tests are carried out based on the results of vibration analysis.The results of sweep frequency test show that the fundamental frequency of the laser communication terminal on satellite is 94.37 Hz.The results of sinusoidal vibration and random vibration tests show that the terminal can withstand the complex vibration environment during the launch.The results of vibration tests verify the correctness of the vibration analysis,and prove that the vibration characteristics of the terminal meet the design and use requirements.The effect of the locking force of memory metal separation nut on the fundamental frequency of the terminal is studied through the sweep frequency tests.The test results show that as the locking force increases from 170 kgf to 250 kgf,the frequency of the peak response of x-direction sweep frequency test increases by about 5 Hz.The accuracy of the terminal shaft systems has some changes after the vibration tests,and it meets the structural design requirements after retesting.According to the correlation tests and analysis of pointing errors,the maximum values of the pointing errors under constraint conditions after vibration tests are obtained: the maximum beacon light pointing error is 19.5?,the maximum pointing error between signal light and beacon light is 0.67?,and the maximum pointing error between signal light and ideal direction is 20.1?. |
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