Research On Stray Radiation Analysis And Suppression Of Spaceborne Optical System

Space-based space target detection completely gets rid of the interference of the atmosphere on signals,and has many advantages such as flexibility,wide observation range,long operation time,short data update,and high observation accuracy.As an important payload form of space exploration,spaceborne optical systems have good development and application prospects in miniaturization,high accuracy,and high efficiency.Spaceborne optical systems are often used for detecting dim targets in space,and stray light will reduce the signal-to-noise ratio of the system,seriously affecting the imaging quality and target resolution ability of spaceborne optical systems.Stray radiation analysis and suppression research are important means to ensure the normal operation of spaceborne optical systems.With the diverse development of spaceborne optical systems,it can not only detect dim targets,but also have functions such as signal transmission,reception,and transmission,such as spaceborne optical communication systems,spaceborne Li DAR systems,spaceborne laser energy transmission systems,and spaceborne gravitational wave telescopes.At present,the stray light analysis technology for Tx/Rx common aperture spaceborne optical systems is not in-depth enough,especially for Galileo ultra-long afocal optical systems.In addition,due to the difficulty in constructing stray light testing equipment,the stray light analysis of most domestic spaceborne optical systems still stops at the simulation analysis stage.The Tx/Rx common aperture spaceborne optical systems can be divided into large aperture systems based on platform pointing and agile systems based on pointing mirrors.The difficulties in suppressing stray light mainly include the following three aspects:the difficulty in reducing geometrical configuration factor（GCF）due to the ultra-long afocal optical path;There are many afocal optical components and severe optical surface scattering;The irregularity of the clear aperture of the Tx/Rx common aperture spaceborne optical system with pointing mirrors.In order to solve the above problems,on the one hand,this study improves the accuracy of the stray light analysis model by studying surface scattering properties and selecting appropriate optical components;On the other hand,detailed baffles design,stray light analysis and testing have been carried out for large-aperture Tx/Rx common aperture spaceborne optical systems and space-agile Tx/Rx common aperture spaceborne optical systems with a pointing mirror.In order to improve the accuracy of the stray light analysis model,the study investigates the measurement and numerical simulation of surface scattering characteristics,and applied to the simulation and analysis model of Tx/Rx common aperture spaceborne optical systems.The bidirectional reflection distribution function（BRDF）of photomechanical structural surfaces,rough optical surfaces,ultra-smooth optical surfaces,particulate-contaminated surfaces,and thermal-controlled multilayer black polyimide films were measured.Based on the ABg model,Harvey-Shack model,dual ABg model,and polynomial scattering model,different roughness（sub-nanometer to micrometer）and material surface BRDF fitting methods were proposed.And the measured BRDF was applieds to the simulation model in this dissertation,improving the accuracy of the simulation analysis model.In addition,this study focuses on the Mie theory prediction method for the scattering characteristics of particulate-contaminated optical surfaces with known surface cleanliness levels,and compares the surface scattering data of clean ultra-smooth optical samples and particulate-contaminated optical samples.Research has found that the measured data is in good agreement with theoretical predictions.In response to the difficulty in reducing the GCF of the Galileo type Tx/Rx common aperture spaceborne optical systems,this dissertation proposes a comprehensive solution of optical design and baffles design.In the stage of optical design,this study establishes a mathematical model for the lateral displacement/rear intercept of the primary mirror,derives the structural parameters of the Galileo Tx/Rx common aperture main optical system,and designs a Gregorian detector.A mathematical model for stray light suppression requirements outside the field of view was established based on the system signal-to-noise ratio,and a large-aperture Galileo Tx/Rx common aperture system shading structure was designed.In addition,the focus is on introducing the design method of the two-stage fore baffle,establishing a mathematical model for the design of the inner baffle array for a compact multi-aperture off-axis Tx/Rx common aperture system,and proposing a design method based on the inclined mirror frame of the afocal plane mirror.A comparative analysis was conducted between the initial model and the measured surface BRDF model,and the PST at the 48°off-axis angle corresponding to different azimuth angles met the requirement of less than 10^-7.This study investigates the effects of stray radiation inside and outside the system for a compact space-agile Tx/Rx common aperture system.Based on this system,this study derives the numerical relationship between the surface profile requirements of afocal optical components and the beam quality factor,and evaluates the backscattering of optical components in the afocal optical path.Using the measured surface scattering data,the T/R isolation of the Tx/Rx common aperture system corresponding to clean optical surfaces and particulate-contaminated optical surfaces was analyzed.Analysis found that the scattering caused by particle contamination deposited on the optical components reduces the isolation of the system by 3.74 d B.Given the irregularity of the clear aperture of the coarse and fine composite detection system,this study adopts reverse ray tracing technology to establish a design method for a special-shaped mask diaphragm.Based on the two-stage fore baffle design theory,a design method for the special-shaped entrance baffle is proposed.After modeling and analysis,the efficiency of the special-shaped entrance baffle was verified,reducing the dependence on platform attitude adjustment of the space-agile system.Finally,the simulation analysis results were validated by building a system point source transmittance（PST）testing platform.