Design Of Cryogenic Multi-band Optical System For Hypersonic Aircraft Detection

Hypersonic aircrafts have the advantages of high speed,high maneuverability,and long flight distance.They can be used in global precision strike weapon systems,as well as in detection and reconnaissance equipment.With the rapid development of hypersonic aircrafts,countries around the world are under the surveillance and threat of military powers,and existing reconnaissance satellites have limited ability to detect and supervise hypersonic aircrafts.In addition,the thermal radiation of the optical system itself has a great influence on the detection performance of the system.Reducing the temperature of the optical system can effectively reduce the thermal radiation of the optical system itself and improve the detection performance of the system.In this paper,the low-temperature optical system is applied to the detection of hypersonic aircrafts,which effectively reduces the background radiation of the optical system,improves the signal-to-noise ratio of the optical system,and improves the detection ability.First,the operating temperature of the system is determined according to the design specifications of the optical system.The design process of the optical system is determined by analyzing the impact of the low-temperature environment on the optical system.The advantages and disadvantages of various configurations of the optical system are analyzed,and the configuration of the optical system is determined in combination with the design indexes of the optical system.At the same time,the issues needing attention in the selection of materials for low-temperature optical systems were discussed.In the transmission system,the calculation and selection of the refractive index of the material are crucial.By comparing various refractive index calculation methods and applicable scope,the calculation method of low temperature refractive index parameters is finally determined.Secondly,the initial structure of the coaxial tri-reflective optical system is calculated and solved according to the aberration theory.Through the off-axis processing and optimization of the coaxial tri-reflective optical system,the off-axis tri-reflective optical system without center blocking is finally obtained.The off-axis triple-reflection optical system adopts the imaging mode of split field of view and filter to realize multi-band imaging,and the related image quality evaluation of the system is carried out.In the design of the coaxial folding system,a combination of analytical method and scaling method is adopted to realize the design of multi-band optical system.By comparing the advantages and disadvantages of the off-axis three-reflector and coaxial reflex optical systems,the coaxial reflex optical system was finally selected asthe final design result.Tolerance analysis of the coaxial foldback optical system gives the tolerance range within the acceptable range of the system.Finally,by comparing and analyzing the effects of refractive index changes and surface shape changes on the system,it is concluded that the refractive index changes have a greater impact on the optical system.The imaging quality of the system at room temperature is analyzed to provide a basis for the system's room temperature adjustment.According to the radiation law,the background radiation size of the optical system under low temperature and normal temperature environment is calculated.Taking 300 K black body radiation as the target radiation and 253 K black body radiation as the earth background radiation,SCR,SNR and contrast of the system at different temperatures are calculated and compared.