Research Of The Key Technologies On Active-thermal Optics For The Space Camera Based On Structural-thermal-optical Integration

With the continuous improvement of the imaging resolution required by space remote sensing observation for the optical system,large aperture and long focal length have become the main trends in the development of space cameras in recent years.Generally,high-resolution space cameras are required to reach or approach the diffraction limit and are very sensitive to temperature changes.Changes in the optical parameters such as the radius of curvature of the surface of the optical element,the surface shape,the relative position between the optical elements,and the refractive index of the material due to temperature changes will directly lead to a decrease in the imaging quality of the optical system.Therefore,how to ensure the imaging quality of the camera under the condition of space vacuum thermal environment is the key.At present,the main solution is to consider the influence of space environment on imaging while designing optical system,and to carry out structural-thermal-optical performance(STOP)analysis.The second is to adopt active optics to adjust the system wavefront errors caused by gravity and temperature deformation in real-time on-orbit.The traditional active optics belongs to the closed-loop wavefront control technology,which requires real-time wavefront detection.Therefore,it has high requirements for wavefront sensor,resulting in complex system and heavy weight.This paper proposes a temperature-based active optics technology for space cameras,which is called activethermal optics.It can cancel the wavefront sensor and reduce the complexity of the system.This paper focuses on high-precision temperature measurement,STOP analysis and optimization,and surface shape representation based on temperature information.The key technologies such as high-precision NTC thermistor mK-level calibration,optomechanical structure integration optimization,STOP sensitivity analysis,and surface shape active adjustment based on temperature information are studied.The calibration method of high-precision NTC thermistor temperature sensor was studied.For the MF501 NTC thermistor,the fitting agreement of different calibration equations on the temperature-resistance characteristic curve was investigated,and the Hoge-2 equation was determined as the best calibration equation.The theoretical models of two kinds of uncertainty propagation based on Lagrangian interpolation and least squares method were established,respectively.The characteristics of propagated uncertainty were analyzed and summarized.The mK-level high-precision calibration was realized in the calibration range of 5~55 °C,and the requirements of space camera high-precision temperature measurement was satisfied.The topology optimization method and parametric optimization technology commonly used in the optimization design for space camera optomechanical structures were summarized.For the lightweight design of large aperture space mirror with ribbed structure,an integrated optimization design method based on topology optimization and parametric optimization was proposed.The lightweight design of primary mirror and tertiary mirror structure of space camera was completed by using this method and parametric optimization method,which laid a theoretical foundation for the STOP analysis of the space camera.On the basis of fully studying the simulation interface technology of thermal,structural and optical disciplines,a new STOP sensitivity analysis method was proposed.And the simulation model for the STOP sensitivity analysis for the space camera was established.The sensitivity of each design parameter to the optical performance of the system was studied by using the response surface method(RSM).The characteristics and ways of the influence for the key parameters on the imaging quality of the system were emphatically analyzed.The rationalized modification of structural/thermal design was put forward and the rationality was analyzed and demonstrated.The active-thermal optics technology of space camera based on STOP analysis method was studied.For the large-diameter primary mirror supported by three points,the characteristics of mirror surface shape error under gravity field and different temperature fields were studied.The theoretical correction model for the primary mirror and secondary mirror was studied respectively.The corresponding primary mirror response matrix and secondary mirror sensitivity matrix were obtained.On the basis of completing the active adjustment simulation of the primary and secondary mirrors,the active correction ability of the space camera for gravity release and thermal deformation during the orbit operation was analyzed.Finally,the ground experimental test system was built.The STOP analysis verification experiment and active optics verification experiment were carried out to verify the technical principles in this paper respectively.