Research On Star Sensor Error Modeling And Decoupled Calibration Method

As a high-precision attitude measurement equipment,accurate calibration of internal parameters for a star sensor is a prerequisite for high-precision attitude measurement.With the increasing requirement for the star sensor and the expansion of application fields,the complexity of star sensor calibration and its influence on the accuracy are increasing.Considering the instability of star sensor calibration,the calibration models,the calibration error sources,and its propagation characteristics are researched.The characteristics of the effect of each error source on the star sensor accuracy are contrasted.The improved cosine two-step method,the partition calibration,star maps and star pairs selection policy are proposed.The proposed method is simulated and verified by experiments.The proposed method has certain reference value for high-precision calibration of star sensor.The main contents are as follows:1.Constructing a star sensor calibration simulation platform.Compared with the existing calibration methods,the limitations of the calibration method based on the principle of angular distance of star pairs invariance are analyzed.According to simulations,the coupling between the distortion error and the focal error is more serious.Especially in the case of large distortion,the result of principal point calibration is more unstable.Therefore,the improved cosine two-step calibration scheme is proposed and the calibration steps are optimized.The focal length and the principal point are optimized and calibrated together to avoid repeated iteration of the calibration error,which results in poor accuracy of the calibration result.2.In-depth study of the star sensor error sources and propagation characteristics.We analyzed the various error sources in star sensor calibration process,including the main point,focal length,distortion,tilt angle and defocus high error.The causes of different error sources and the influence on attitude accuracy and star pitch error are analyzed.We mainly focus on the analysis of the different types of distortions on the star position changes and explore the effect of high defocus error on the calibration.3.Establishing two different tilt error calibration models.Through simulation,the calibration model tilt error of rotating shaft is finally determined.By comparing the effects of tilt errors and other error sources on the star positions,the propagation characteristics of tilt errors are obtained.According to simulation,there exists a coupling among tilt error,distortion and focal error.4.The influence of image noise and tilt error on the star sensor calibration is discussed.By comparing various methods,we found that the calibration result of the star sensor increases as the image noise increases,but does not change the curve pattern.The tilt error mainly results in the fixed bias of the principal point.With the tilt error increasing,the fixed bias also increases.It can be determined that the principal point calibration results of large fluctuations and the image noise have a certain relationship.5.Study of the decoupling of different error sources.The method of partition calibration,formula correction,star map and star pairs selection are used to eliminate the coupling effect of internal parameter errors.The effectiveness of the above scheme is proved by simulations and experiments.