摘要
以杂散光在探测器像面平均照度低至6等星为例,首先从理论及工程应用角度对星敏感器遮光罩进行论证、设计、仿真、测试,并提出在遮光罩设计阶段应该充分结合光学镜头、星点提取算法、技术要求特点,确定遮光罩有效通光口径、视场、外形包络尺寸、消光性能;其次,利用几何作图的方法确定遮光罩挡光环位置、刃口倒角角度、刃口倒角朝向,并建立起散射关键面;然后,根据仿真过程中一次散射与多次散射对像面照度的影响确定刃口厚度;最后,通过仿真和实验室测试方式证明所设计的遮光罩结构合理,可满足太阳光抑制低至6等星,星敏感器受杂散光影响测量精度偏差在2″以内。
Taking fixed stars as reference frame,the star sensor calculates attitude algorithm of fixed stars on different positions of the celestial sphere,through which accurate spacial orientation and datum to spacecraft could be accomplished.The on-orbit star sensor is usually interfered by stray light,primarily by sunlight.The illumination of sunlight in low earth orbit is approximately 1350W/m2,while the illumination of a sixth-magnitude star is approximately1.26×10−10 W/m2 in the same condition.The ratio of the above mentioned illuminations is approximately1013.Thus it can be seen that the star sensor is extremely demanding for the technology of stray light suppression.Interfered by stray light,the pixel under calculation receives starlight and stray light simultaneously.The energy of stray light affects the gray-scale value of pixel,which downgrade the accuracy of the star sensor,or severely cause failure of stellar target acquisition.Therefore,the function of stray light suppression on star sensor is necessary.Methods In the process of star sensor stray light suppression,the baffle is applied to effectively eliminate the stray light pollution in the working field of view.Taking suppression of stray light down to sixth-magnitude stars’level as an example,the paper explains the specification demonstration,scheme design,simulation of light beam tracing and stray light test of the star sensor baffle in perspective of both theory and engineering application.As a start,based on the design parameters of optical lens,the paper fully demonstrates the specification of extinction ratio,and further obtains the technical requirement applicable to the extinction ratio of the optical system,as equation 1 shown.Moreover,based on such information as the effective entrance pupil aperture of the first layer lens(Fig.1),the exit pupil aperture of baffle(Fig.2),the field of view of baffle,and the angel of stray light suppression,the paper demonstrates the initial design of baffle.Finally,the paper explains the detailed design of the position of light blocking rings(Fig.6),the structure of baffle(Fig.7),the critical scattering surface,the thickness of edge,as well as the chamfer angle and direction of edge(Fig.8).In the meantime,the design of using baffle is suggested for detecting highly sensitive stars,in order to avoid impact of stray light from single scattering.Results and Discussions Firstly,the simulation in the paper shows the influence of thickness of edge on stray light suppression(Fig.11). This conclusion is only applicable to the baffle mentionedin this paper. For other baffles, the value of thickness of edge should be analyzed according to thesimulation method in this paper. That is to discuss under situations: (1)when the thickness of edgeis zero, single scattering doesn’t occur, and the double scattering is the main source of stray light;(2)when the thickness of edge is 10μm, the energy of single scattering is less than that of the doublescattering, thus the double scattering is still the main source of stray light (3)when the thickness ofedge is 30μm, the energy of single scattering is stronger than that of the double scattering, and thesingle scattering is the main source of stray light.Secondly, the performance of stray light suppression of the star sensor is verified throughexperimental testing(Fig.12). When the suppression angle of sunlight is 30° and with one solarconstant, such necessary conditions of gray-scale to distinguish a sixth-magnitude star could befulfilled, as the mean value of 61, the maximum value of 130, and the standard deviation of 21.When the sixth-magnitude star is in the field interfered by stray light enormously, the maximumgray-scale of star point is 72. When the threshold value of offset is 20, the centroid of star pointcould be detected according to equation 2.Finally, the performance of stray light suppression of the baffle is verified through outfieldstargazing. Accuracy of star sensor without stray light is 2.13″and 2.34″;Accuracy of star sensorinterfered by stray light using regular baffle is 8.07″and 7.66″;Accuracy of star sensor interferedby stray light using the baffle mentioned in this paper is 3.89″and 4.01″. It is thus clear that theperformance of stray light suppression is better using the baffle mentioned in this paper, controllingthe deviation of accuracy within 2″.Conclusions Based on the research of mechanism, simulation analysis and experimental testing, theabove mentioned design method of star sensor stray light suppression is verified to be rationale andfeasible. On the basis of this method, the suppression function of baffle improves further, withinlimited overall dimensions. This approach enables the design of baffles applicable to different starsensors and extreme magnitudes. This design could be commonly used to obtain baffles withcorresponding extinction ratios, in order to be applied to different needs of stray light suppression.Meanwhile, various matching of adaptabilities in optical machine links are sufficiently considered.As a result, the phenomena of vignetting and stray light in field of view do not occur. The designmethod in this paper regarding to stray light suppression could be a reference to other designs of photoelectric sensitive detectors.
作者
杜伟峰
王燕清
郑循江
高文杰
谢廷安
Du Weifeng;Wang Yanqing;Zheng Xunjiang;Gao Wenjie;Xie Tinga'ann(Shanghai Institute of Spaceflight Control Technology,Shanghai,201109)
出处
《光学学报》
EI
CAS
CSCD
北大核心
2023年第6期299-308,共10页
Acta Optica Sinica
基金
国家自然科学基金(62005158)。
