Research On Optical System Of Star Sensor With Large Field Of View Based On Concentric Lens

The star sensor is a high-precision attitude measuring instrument.It obtains the three-axis attitude of the aircraft by taking pictures of stars,star point extraction,centroid positioning,star pattern recognition,and attitude calculation.It is widely used in aviation,aerospace,navigation and other guidance fields.With the continuous improvement of science and technology,the demand for precise attitude control is increasing,and the star sensor is developing in the direction of high precision,large field of view,all-day time and long life,and the optical system is an important component of its measurement accuracy.In this paper,the following researches are carried out on the concentric lens optical system with large field of view and small distortion:Firstly,the status quo of relay image transmission schemes for star sensors and concentric optical cameras at home and abroad is investigated.Based on the design of large field of view,the detector is selected,and the detection ability of star sensor is analyzed from the aspects of star energy calculation,signal-to-noise ratio calculation and star detection probability calculation.The requirements of star sensor for point diagram,energy concentration,rate chromatic aberration and distortion are analyzed.Secondly,by analyzing the advantages and disadvantages of the refractive,reflective and catadioptric structures,and considering the demand of large field of view for future high-precision applications,the refractive concentric lens structure is selected,and the focal length formula,aspheric and achromatic conditions of the double concentric structure are theoretically analyzed.Based on the characteristics of the concentric lens structure,a 3×3 field of view splicing scheme is proposed.The parameters of the optical system are calculated,the field of view is 75°,the diameter of the entrance pupil is 30mm,the focal length is 50mm,and the wavelength range is460-850nm.The design and optimization of the sub-optical system are completed,the attenuation effect of the pupil projection in the full-field optical system is analyzed,and the tolerance analysis is completed.Thirdly,the sources of stray light,bidirectional scattering distribution function（BSDF）and stray light suppression level evaluation function are introduced,and the ghost image analysis of the optical system is completed.A stray light suppression method based on fiber optic plate is proposed.The transmission principle of optical fiber with vertical end face and inclined end face is analyzed theoretically.The main performance and parameters of fiber optic plate are introduced.Theoretical analysis of light transmission by single straight fiber optic plate,multiple straight fiber optic plate and curved fiber bundle is carried out.For the fiber optic plates in multiple straight fiber optic plates,different core-clad refractive indices are set in different fields of view,and models are established to complete the stray light suppression analysis.The results show that for different stray light suppression angles,point source transmittance is reduced to 10^-2after adding the fiber optic plate,and the core-clad refractive index of the split field of view is better than the maximum core-clad refractive index difference of the full field of view.The influence of optical fiber panel transmittance and pupil projection attenuation of concentric lens on signal-to-noise ratio is analyzed,and the results show that the signal-to-noise ratio still meets the requirements of star sensor in the 75°field of view.