The Research Of Star Tracker Optical System Design And Measurement

The third generation star tracker has been developed. It is the highest precisioncomponent for the attitude determination of the satellites. Ultra-high accurate star tracker isone crucial technology in the field of high-resolution remote sensing satellite andastrometry. So the precision of centroiding must be improved to develop it. Ultra-highaccuracy star tracker has the characteristics of sub-arc second accuracy, high dynamic range,and small field. There are still gaps between domestic products and the foreign similar ones,which has the defects in the performance of centroiding accuracy. The centroiding accuracyof foreign similar products can be reached0.02pixel. Obviously, it is a vital task to improvethe centroiding performance.Firstly, we analyze two kinds of centroiding algorithms in order to conclude theirdisadvantages which are the prerequisite that the PSF is treated as Gaussian function. Infact, the PSF is skew Gaussian function. After exploring the papers and technical schemesin the field widely, we find that the precise star PSF plays a key role in improving theprecision of centroiding. So we analyze the mechanism of all kinds of errors, and we clarifythem into random error and bias error. Different ultra-high accurate PSF modelingtechniques are discussed to conclude their advantage and disadvantage.Secondly, for the special requirements of the all-time star tracker, a detailed analysis ofthe various requirements about all-time and technical solutions is proposed. The threecoaxial mirrors design is employed to complete task.Thirdly, detailed analysis of the aberration correction method of ultra-high accuracystar tracker optical system is proposed, taking advantage of the expanded ZEMAXprogramming optimization technology. According to the image quality evaluation, theoptical system works steadily with high quality in the required anti-defocus performance.Fourthly, in order to obtain an accurate centroiding algorithm, it is inappropriate todirectly regard star image energy distribution as the Gaussian distribution because of theupgrading demand of ultra-high precision star tracker. It is urgent to study the actual starimage energy distribution. This paper studies the theory of mathematical statistics aboutdiscrete data model deviating from the normal distribution. The skew Gaussian distributionis proposed to describe star image energy distribution of high precision star tracker. Bothsimulation and measuring experiments prove that the actual distribution of the star image get closer to the skew Gaussian distribution. The results of this paper can be used to guidethe research of the precise correction algorithm of the star tracker which can correct thecoordinates of the centroid.Finally, we reconstruct the star PSF to note its change in space domain because ofimperfect imaging and external factors. A method for PSF modeling is proposed. First, thedistribution of star image must be got. Then reconstruct the star PSF with the extendedNijboer-Zernike theory. The experiment testifies that it is a precise way to get the PSF ofhigh SNR with the measuring equipment of repeated pointing accuracy1″. The proposedalgorithm and equipment fulfill the requirement of ultra-high accurate star trackermeasuring.