Research On Ultra-Light SiC Mirrors And Support Techniques

With the development of space remote sensing technology,higher requirements were put forward for space optical systems.Space mirrors with virtues of wide field of view,large aperture,high resolution and lightweight are being urgently demanded.Large aperture mirrors are more susceptible to gravity when the number of support points is limited.In order to keep good imaging capability of the optical system,large aperture mirrors tend to sacrifice the weight index to ensure surface accuracy.It is possible now to manufacture ultra-lightweight mirrors with the development of silicon carbide manufacturing technology.The development of ultra-lightweight mirrors not only can increase the lightweight ratio of mirrors significantly,but also to improve the level of lightweight and agile of space cameras.The primary mirror of the space camera is machined and assembled on ground.But it is operated in a microgravity environment.The mirror is subject to complex load conditions from manufacturing to operation in space.Aiming at the requirements of specific stiffness,surface error and thermal stability of the mirror,a SiC mirror with ?624mm aperture was designed in this thesis.The mirror has an open-back structure and triangular stiffener mesh,and it is supported on three points.The optimizing process of "trial-evaluation-correction" of the mirror is integrated into Isight software platform.And the automatic optimizing iteration is realized by using optical machine integration optimization method.Taking the structure size of the mirror as a variable and the surface accuracy and weight as the optimization target,global and automatic multi-objective optimization is carried out.A support structure based on multi-axis flexible hinge is proposed in this thesis aiming at the flexible support of the space mirror.The fillet radius and the position of the rotation center of the flexure hinge are set as variables.And the influence of the two variables on the surface error and the first-order natural frequency of the mirror is analyzed.The result of the analysis shows that the rotation center of the flexure hinge and the center of gravity of the mirror must be on the same plane.The results are fitted into the response surface,and the support structure is optimized.After confirming the support structure parameters,the whole mirror assembly is subjected to random response analysis to obtain the stress response and safety factor of the flexure hinges.The aluminum simulation prototype of the ultra-lightweight SiC mirror is designed and manufactured.And the first-order natural frequency of the prototype and the acceleration response under the input of the sinusoidal vibration and random vibration are obtained.The experimental study verifies the ability of the flexible support structure to withstand the random vibration environment and directs the correction of the finite element model.The area density of the ultra-lightweight SiC mirror is 37kg/m2.The surface error under the detection condition is less than 4nm and the dynamic mechanical performance is good.At the same time,the flexure mount is stable and reliable in vibration environment.The results of this thesis validate the excellent performance of the ultra-lightweight SiC mirror assembly.The method and results of this thesis are of great reference value for the design of space optical remote sensor.