大型空间望远镜次镜背板的优化设计

Optimal design of secondary mirror backplane for large space telescope

针对2 m量级大型离轴三反空间相机,采用并联机构作为次镜的调整机构。并且将调整机构动平台直接作为次镜支撑背板使用,增加了结构刚度,同时也使整机结构更加紧凑。因此,背板是次镜组件的核心零件。背板的材料采用具有良好尺寸稳定性、比刚度高的60 SiC/Al。由于背板承上启下的重要性,决定了背板对自身重量及刚度有很高的要求,因此采用以刚度为目标对其进行拓扑优化设计,并且以背板质量和基频作为目标对背板面板与加强筋的尺寸进行多目标尺寸优化;最终优化后的背板质量为1.42 kg,基频达到954 Hz。最后对次镜组件进行静力学分析及动力学分析,结果表明:重力与4℃温升耦合工况下重力方向位移与面形RMS值最大:最大位移为9.651μm,面形RMS值为7.535 nm;次镜组件约束状态下的一阶固有频率为115 Hz,满足大型空间望远镜在轨成像要求。

A parallel mechanism is used as the adjusting mechanism of the secondary mirror for a 2 m magnitude large off-axis three-mirror space camera. The moving platform of the adjusting mechanism is directly used as a secondary mirror support board, which increases the structural stiffness and makes the whole machine structure more compact. Therefore, the backplane is the core part of secondary mirror assembly. The backplane is made of 60SiC/Al with good dimensional stability and high specific stiffness. Due to the importance of the backplane as a top and bottom support, it has high requirements for its weight and stiffness, so the topology optimization design is carried out with the stiffness as the target, and the multi-objective size optimization of the backplane panel and a stiffener is carried out with the backplane quality and fundamental frequency as the target. The optimized backplane has a mass of 1.42 kg and a fundamental frequency of 954 Hz. Finally, statics and dynamics analysis of the secondary mirror module is carried out. The results show that the gravity direction displacement and surface RMS values are the largest under the coupling gravity and 4°C temperature rise conditions: The maximum displacement is 9.651 μm and the RMS value of the surface is 7.535 nm. The first-order natural frequency in the constrained state of the secondary mirror assembly is 115 Hz, which meets the requirements for in-orbit imaging of large space telescopes.