折反射式大入瞳星敏感器光学系统设计

Optical System Design of Large Entrance Pupil Catadioptric Star Sensor

为了提高可探测极限星等能力,观测到更多较暗较远恒星作为深空探测飞船导航定姿的参考星,设计了采用改进的卡塞格林结构与三片球面补偿镜组相结合的折反式星敏感器光学系统。其中,改进的卡塞格林结构有利于轴外消球差及彗差,同时生成系统焦距及大尺寸入瞳;靠近像面的补偿镜组校正反射结构的残余像差,同时补偿镜组像方远心的设计保证了系统全视场照度的均匀性,也降低了系统离焦对像面安装的敏感性。本系统焦距180mm,像方F数2,全视场2ω为3°×3°,有效入瞳面积5106mm2,在450-800nm的宽光谱范围内质心偏差优于2.5μm、垂轴色差小于3.5μm,80%弥散斑能量集中在3×3pixel内,传递函数接近衍射极限。采用主次反射镜遮光罩及两级外镜筒遮光设计,并在Lighttools软件中对光机系统杂散光模拟分析,设计结果表明在2°-40°杂光源成像视场范围内,点源透过率在10^-6-10^-4量级,该系统设计方案及结果可为用于深空任务的星敏感器系统的参考依据。

To develop the detection ability of ultimate stars,and use more dark stars as referenced stars of deep space aircraft navigation,a catadioptric star sensor with a proved Cassegrain configuration with three pieces of emending lens optical system is designed.In this system,the proved Cassegrain configuration is used to reduce the spherical aberration and coma out of optical axis and bring the focus and large size of entrance pupil at the same time;emending lens close to the image plane is mainly eliminating the remaining aberrations of catoptric configuration,the telecentric image plane design among the emending configuration is also benefit to the irradiance unification in full of field and decrease the sensitivity of image sensor setting.This system has a 180 mm focal length and F-number is 2,view of field is 3°×3°,the effective pupil area is 5106 mm2,energy centroid aberration is smaller than 2.5μm,lateral color is better than 3.5μm among 450-800 nm spectrum,over 80%energy of spot in less than 3×3 pixel,and modulation transfer function（MTF）is approaching to diffraction limit.The inner baffles of reflected lens and outer two-group baffles are introduced,through modeling and analyzing the stray light of system in the Lighttools,the designed result shows that in the range of 2° to 40° incident angle of stray light,the point resource transmittance is between 10^-6 to 10^-4.These results can provide a good reference for further star sensors with deep space catadioptric configuration star sensor.