Design Of Reflective Multi-Star Simulator Optical System Based On Free-Form Surface

The calibration accuracy of star sensor determines the accuracy of deep space exploration and interstellar navigation.Currently,the existing reflecting star simulator has a small field of view and low accuracy.This paper studies and designs a large field of view long focal distance axis three-reflection optical system for multi-star simulation,and proposes the scheme of using free-form surface reflection structure as the optical system of multi-star simulator to realize the high-precision simulation of multi-star in a large field of view.Specific research contents include:(1)The vector aberration theory and third-order aberration characteristics of the off-axis reflective optical system are studied.Combined with the surface characteristics of the free-form surface,the system is optimized and the feasibility of applying the free-form surface to the optical system design of the reflective star simulator is demonstrated.(2)Through the study of vector aberration theory,the aberration distribution of off-axis reflection optical system and the influence of component eccentricity and tilt on the asymmetric aberration of the system are clarified.On this basis,the optical structure of COOK-TMA type is selected.The determinants of the position of the aberration nodes are analyzed,and the astigmatism of the initial structure of the off-axis reflection is effectively controlled by limiting the off-axis amount of the field of view,and the expression of the aberration of the on-axis and off-axis vectors is derived.(3)The basic parameters of the coaxial initial structure are solved by using Gaussian formula and third-order aberration expression,and then the off-axis design of the coaxial initial structure is carried out to obtain the off-axis initial structure that effectively controls astigmatism.In order to further balance the image quality of each field of view,Zernike polynomial free surface and XY polynomial free surface were applied to the secondary mirror and the third mirror respectively.By analyzing the influence of polynomial coefficient on the image quality,the optimization scheme was determined and the optical system meeting the image quality requirements was designed.The image quality of the design results was evaluated by combining the aberration theory.(4)Practical analysis of optical system.The difficulty of machining the designed free-form surface is analyzed from two aspects of aspheric surface degree and slope of surface form.The feasibility of using CGH detection method to ensure the detection accuracy of free-form surface is demonstrated.In order to ensure the feasibility of installation,the sensitivity matrix method is used to analyze the influence of element misalignment on image quality,and a reasonable installation scheme is proposed.(5)Design results and conclusions.The actual design index of the optical system is F/#=10,the focal length is 1000 mm,the field Angle is 5.9°,the operating range is480nm～900nm,the distortion is less than 0.0077%,the parallelism is better than 2",and the MTF is close to the diffraction limit.The designed optical system has the advantages of large field of view and low distortion,and the parameters of spot roundness and system relative illuminance are good,which guarantees the accuracy requirements of star point simulation,and can be used for high-precision calibration of star sensor.