Research On Angle Measurement Accuracy Of High Precision Star Tracker Based On Interferometry

Star tracker is a kind of high precision attitude sensitive measuring instrument,which plays an important role in the attitude control system of spacecraft,and has been widely used in missile guidance system,laser pointing sensor system and deep space laser communication system.The centroid accuracy of traditional star trackers is generally 1/10 to 1/50 pixel.To improve this accuracy,a smaller field of view is usually employed.However,a smaller field of view reduces the number of reliable star sources for tracking and reduces the required measurement rate.A smaller field of view also reduces the dynamic performance of the star tracker.The high resolution focal plane array(FPA)can improve the centroid accuracy of traditional star trackers.However,as the resolution of the FPA increases,so does the weight,size,and energy loss of the star tracker.In addition,higher resolution FPA is more susceptible to radiation.Therefore,the attitude measurement accuracy of the traditional star tracker is mutually restricted with the field of view,mass,volume and other factors,and the centroid positioning accuracy has a theoretical upper limit.In order to improve the attitude measurement accuracy of the traditional star tracker,the interference angle measurement technology can be combined with the traditional star tracker.Based on the centroid positioning technology of the traditional star tracker,the light intensity information of the star image point can be further subdivided.Therefore,the precision limitation of centroid positioning can be broken through,and the interference star tracker with high precision can be formed.In this paper,the factors restricting the angle measurement accuracy of interferometer tracker are studied deeply,especially the unreasonable segmentation of interference fringe,the uneven distribution of transverse light intensity and the influence mechanism of wide-band light incidence on the angle measurement accuracy.The specific research work of this paper is as follows:Firstly,the development history and current situation of traditional star tracker are summarized,the working principle and main technical parameters of traditional star tracker are introduced,and the research and development of star centroid positioning technology are introduced.This paper points out the limitation of traditional star tracker and introduces the research and development of interferometric star tracker which can avoid the defect of traditional star tracker.Then,the basic principle,structure and selection standard of interferometric star sensor are analyzed.Using the angular spectrum theory of Fourier optics,the transmission process of the plane wave incident by star points in the interferometer sensor is modeled.Finally,the corresponding expression between the incident Angle of the target light and the phase of the fringe is obtained after simplified derivation.This paper introduces the concrete method of accurate Angle measurement by interference Angle measurement technology and gives the related calculation expression.In order to solve the problem that the actual single star Angle measurement error of interferometric sensor is large,the restriction factors of Angle measurement accuracy are analyzed,and the influence mechanism of the shape of interference fringe on the Angle measurement accuracy and the influence mechanism of unreasonable division of interference fringe on the Angle measurement accuracy are further analyzed.Two key scientific problems restricting the accuracy of single-star Angle measurement of interferometric sensor are put forward:(1)The influence mechanism of interference fringe shape deviation from sine and cosine curve(from the non-uniform distribution of transverse light intensity and spectral distribution of target light)on the accuracy of Angle measurement;(2)The influence mechanism of unreasonable segmentation of interference fringes(including non-uniform segmentation of Moire fringes,non-complete periodic segmentation and relative tilt of Moire fringes)on the accuracy of angular measurement.Then,the influence of unreasonable segmentation of interference fringes on the accuracy of angle measurement is analyzed theoretically.The unreasonable segmentation of interference fringes is divided into three cases: unequal division of optical wedge array,mismatch between moire fringe period and optical wedge array,and non-orthogonal orientation of moire fringe and optical wedge array arrangement.The three cases are simulated and analyzed to get the degree of their influence on the measuring accuracy of the interferometer tracker.Secondly,the influence of the uneven distribution of transverse light intensity on the accuracy of angle measurement is analyzed theoretically,and the relevant mathematical model and the relevant expression of fundamental mode Gaussian beam are given.The intensity distribution of different fluctuations corresponding to different Gaussian beam parameters is studied to estimate the influence of beam non-uniformity on the accuracy of angle measurement.Finally,the influence of wideband light incidence on the accuracy of angle measurement is analyzed theoretically,and the mathematical models of Gaussian linear light source,Lorentz linear light source and rectangular spectral density light source are given.The mathematical models of three typical light sources are studied and simulated respectively,and the influence degree of wide-band light incidence on the accuracy of angle measurement is obtained.