Research On Optical Design And Stray Light Suppression Of All-day Star Tracker

The star tracker realizes the navigation and positioning function by observing stars as its observation target.It is widely used in space-based platforms such as satellites,spacecrafts and rockets due to its advantages.For example,the observation target of star tracker is objective existence,and it has great anti-jamming capability during work process.Besides,its precision of navigation is high.However,the celestial navigation system working on space-based and ground-based platforms is affected by atmospheric disturbances,cloudy and rainy weather and other factors.So the working time and working environment range of the celestial navigation system are limited.Compared with the celestial navigation system working in space,the one working in the atmosphere is not so well-found.At present,the celestial navigation system working in the atmosphere during all-day time has attracted extensive attention and research by researchers.In this paper,researches on the difficulties of stray light suppression in airborne all-day star tracker are conducted.The main work of the dissertation is as follows:Firstly,investigation of the domestic and international technical development of the all-day star tracker was finished.Meanwhile,the working characteristics of the airborne all-day star tracker were summarized.Besides,analyzed the advantages and existing problems which the optical system of the all-day star tracker had.Secondly,the radiation environment of the airborne all-day star tracker working platform was studied.The spectral irradiance of the 6.5 Mv K2,M2,M8 stars and the sun spectrum in the 0.3 ?m 1.7 ?m was calculated.For the 15 km aircraft platform,the influence of the observation spectrum,the observation height,the observation zenith angle,the observation azimuth and the solar zenith angle on the sky background radiant energy were analyzed respectively.The analysis results were summarized as follows:(a)In the visible to near-infrared spectrum,the sky background radiation is weakened and exponentially decreases in the near-infrared spectrum;(b)As the observation height increases,the sky background radiation has obvious attenuation;(c)The sky background radiation generally shows a downward trend with the azimuth angle changes from 0° to 180°;(d)The observed zenith angle is positively correlated with the sky background radiance;(e)The relationship between the solar zenith angle and the sky background radiation is affected by the observation zenith angle,and the effect of the observation zenith angle on sky background radiation is greater than the solar zenith angle.Thirdly,according to the characteristics that the radiant energy of the sky background is greatly weakened in the near-infrared spectrum and the energy of the target star reaches the peak value,the detection spectrum of the optical system was determined as the near-infrared spectrum.What's more,on the basis of the definition of the SNR of the detector,the optical parameters of the system required to observe the 6.5Mv K2 stars are calculated under the condition of the observation height,solar zenith angle,observation zenith angle,and observation azimuth angle.Fourthly,structural selection of the optical system was accomplished.Furthermore,optimization design and image quality evaluation were also finished.Besides,an eccentric structure was introduced to eliminate system obstruction and improve energy utilization.The suitability of the optical system was analyzed for the-40°C~+65 ° C ambient temperature range of working platform.Meanwhile,tolerance analysis was performed to determine the feasibility of the system.Finally,a follow-up stray light suppression structure was designed to adapt to the stray light suppression of different corners of the scan mirror.The design results show that the system can effectively suppress strong sky background radiation during the day.