Analysis Methodology Of Thermal Deformation Effects For Reflective Receiving Antennas In Intersatellite Lasercom Systems

Intersatellite laser communication,as an important means to achieve high-speed and secure transmission of information between satellites,will play an irreplaceable role in construction of the space-based information networks.Under the combined effect of space thermal environment,satellite payload’s thermal radiation,and satellite thermal control measures,a terminal’s reflective receiving antenna will thermally deform to distort the received light wavefront of the terminal,leading to changes in the light intensity level and light intensity distribution of the received light spot on the image plane,ultimately affect the terminal’s pointing,acquisuition and tracking performance and communication performance.Studying the effects of optical antenna thermal deformation on system performance can predict the sensitivity of system performance to changes of thermal environment parameters,and provide references for optical design,optomechanical structure design,device selection requirements,etc.during the system design stage.It also provides references for the design of suppression or compensation schemes for thermal deformation effects.For the intersatellite lasercom terminal using a reflective receiving antenna,this dissertation establishes a model analyzing the effect of antenna thermal deformations on system performance,studies on analysis methods for thermal deformation effect with different preconditions.The Mersenne telescope type reflective receiving antenna,which is significant promising but with poor thermal stability,is taken as an example to build the specific analysis model and conduct case study for mehod analysis.Main contents and results of this research are as follows:The model analyzing thermal deformation effects of reflective receiving antennas for intersatellite lasercom terminals is established.Based on the link-level performance analysis requirements,the characteristic parameters of the receiving antenna’s thermal deformation effect are determined.Processes for analyzing the influence of the antenna thermal deformations with different preconditions are given.And for two of the analysis processes,the Mersenne telescope is taken as an example of the reflective receiving antenna to build the thermal deformation model.Thermal deformations of the antenna’s mirror surfaces’ are characterized by mixed deformations.The subsequent focusing optical system of the receiving antenna is equivalent to an ideal thin lens,which makes the research focus on the antenna’s mirrors which are most likely to be thermally deformed.In the integrated thermal /structural /optical analysis process for analyzing the antenna’s thermal deformation influence,to solve the problem that the traditional preprocessing method for mirror deformation data works poor for the antenna with mixed deformations,the dual-step preprocessing method for mirror deformation data is proposed.This method adds an extra finte element analysis with higher mirrors’ rigidity to increase the estimation precision of the rigid boy motion parameters,further improve the preprocessing results.To solve the shortcomings that traditional evaluation methods for preprocessing are not intuitive enough,the estimation error of the deviation of acquisition pointing angle which can indicate the impact of system performance to evaluate the preprocessing results is proposed to evaluate the preprocessing effects.Case analysis shows that the new preprocessing method is significantly better than the traditional preprocessing method.In the case analysis,an empirical formula for the estimation error of the deviation of acquisition pointing angle caused by the preprocessing method for mirror’s deformation data is given,which can be used to rapidly evaluate the preprocessing results.For analyzing the effects of thermally-induced wavefront distortion,the existing researches neglected acquisition and tracking compensation effects,inadequately considered influences of photodetectors’ limited receiving radius and diffraction effects on the image plane when calculating the received optical power.In this dissertation,a deformation impact analysis model is established,taking the received optical power as the characteristic parameter.It considers all above factors,being closer to practical engineering application.By introducing characteristic parameters,the results of case analysis can be used for other different antennas.The influence rules of different wavefront distortion aberrations on the received optical power are given: when relative receiving radius is large enough,among the primary aberrations,the attenuation caused by the primary spherical aberration is the most serious;for the same type aberrations,the attenuation caused by the high-order aberrations is more serious.Suggestions for the optical system design are proposed: when compensating the primary aberration,it is prior to compensate the primary spherical aberration;choosing a photodetector with a larger receiving radius,a focusing system with a shorter focal length,and a receiving antenna with a larger exit pupil would help to reduce the influence of the wavefront distortion caused by the receiving antenna.For analyzing the effects of thermal deformation of an antenna’s mirror surface,the wavefront substitution method and the combination method of ray tracing and diffraction theory(CMRD)has shortcomings when calculating the intensity distribution of the spot in the image plane.In this dissertation,a new method called SCMRD(Simplified CMRD)is proposed based on CMRD.The new method is exempt from fitting wavefront and suitable for general apertures.It has higher computational efficiency than traditional CMRD.To be specific,for the same target accuracy,SCMRD requires less total number of sub-regions,less total number of light samples,less total computer processing time.Based on SCMRD,the influence analysis model of the thermal-induced non-confocal Mersenne telescope type receiving antenna is established.When analyzing the effect of thermal deformation on the PAT performance,the light intensity level of beacon light which is often ignored,is considered.Results of the normalized intensity distributions verse the axial non-confocal distance and results of the cases study provide references for setting the permissible maximum value of the axial non-confocal distance and selecting photoelectric detectors.The research work of this dissertation provides theoretical basis and method support for the analysis of thermal deformation effects of the reflective receiving antenna on the intersatellite lasercom terminal,lays the foundation for the establishment of the corresponding thermal/structural/optical integrated analysis simulation platform,and provides references for optical design,optomechanical design,device selection and design of thermal control scheme,etc.in the system design stage.For intersatellite lasercom terminals,the new calculation method for non-ideal light intensity distribution on the image plane,SCMRD,is expected to be further developed to be suitable for different antennas with various deformations and to be used for developing the active compensation technique for antennas’ thermal deformations.