基于准焦面图像的空间拼接型望远镜对准及共相关键技术研究

The segmented mirror technology is an important way to build large space telescope to fulfill the needs of astronomical observation and military technology, among which the alignment and co-phasing of the sub-mirror on-orbit is one of the difficult problems that must be overcome. For now, the existing alignment and co-phasing techniques rely more on hardware-based detection techniques or sophisticated computational methods. The core issue to be addressed in this project is to design a new method based on the quasi-focal images to complete the whole process of alignment and co-phasing of the segmented sub-mirrors. First of all, based on the optical principle, the physical relationship model between focal and defocused images and the lager amplitude misalignments of the sub-mirror is established to overcome the limitations of existing complex alignment technology and hardware-based coarse co-phasing technology. Secondly, the linear relationship model of small amplitude sub-mirror misalignments and far-field images is established based on the linear phase diversity algorithm to break through the technical limitations of the complex and low efficiency fine co-phasing technology. Finally, a systematic sub-mirror misalignments detection technology only based on the captured images by the main imaging detector with low hardware costs, low computational overhead, wide detection range and high detection accuracy is realized. Alignment and co-phasing technology based on quasi-focal images is especially suitable for the on-orbit sub-mirror misalignments detection of space segmented telescope, and can provide an important theoretical support and technical support for the on-orbit aberrations correction of China’s large aperture space telescopes.

拼接镜技术是实现空间大口径望远镜的重要方法，能满足天文观测及军事科技的需要，其中子镜在轨对准及共相问题是必须攻克的重难点之一。现有的子镜对准及共相技术，多依赖基于硬件的探测手段或复杂的计算方法。本项目旨在设计一个基于准焦面图像完成拼接子镜对准及共相全过程的新方法。首先，基于光学原理，建立焦面及离焦面图像与大幅度子镜位置误差的物理关系模型，突破现有操作复杂的子镜对准技术及基于硬件设备的粗共相误差探测技术的局限；其次，基于线性相位差算法理论，建立小幅度子镜位置误差和远场图像的线性关系模型，突破精共相误差探测计算量大且效率低下的技术局限；最终实现一个系统的、仅基于主成像探测器采集图像、低硬件成本、低计算开销、宽探测范围、高检测精度的子镜位置误差检测方法。基于准焦面图像的子镜像差探测技术尤其适用于拼接型望远镜在轨检测，能为我国大口径空间望远镜在轨像差校正提供重要的理论支撑及技术支持。

拼接镜技术是实现空间大口径望远镜的重要方法，而对拼接镜所包含的子镜位置误差进行宽范围、高精度检测，实现子镜高精度共焦共相是拼接镜技术得以应用的关键前提。本项目针对子镜对准、粗共相及精共相三个环节，提出了一个系统性的、仅利用主成像探测器采集的图像信息、涵盖对准及共相检测全过程的、宽探测范围、高检测精度、快检测速度的子镜位置误差检测算法。. 通过构建焦面及离焦面互相关频谱图与对应大幅度Tip-tilt像差的数据集，基于EfficientNet-B0网络，实现了对拼接子镜大幅度Tip-tilt像差的高精度探测，其检测范围可达200微米，检测精度能达到2微米以下。该方法实现了拼接子镜的高精度对准，使子镜Tip-tilt像差进入共相检测阶段，为子镜对准技术提供了一种低硬件成本、低计算成本的、简便的对准方法。. 基于傅里叶光学原理，构建了系统光学传递函数的模值函数（MTF）与Piston像差的理论关系，提出了一种基于混合神经网络的Piston像差检测方法，实现了子镜粗共相误差的高精度、宽范围检测，其探测范围可达到输入宽光谱光源的整个相干长度，检测精度可到达10纳米以内，为拼接子镜粗共相提供了一种低硬件成本、低计算开销的探测方法。. 基于相位差异原理，建立了焦面及离焦面图像与小幅度共相误差的线性解析关系模型，实现了子镜精共相误差的高精度检测，其检测范围可以达到2个波长以上，检测精度能达到0.01个波长以下，得到了一种低计算成本的、高精度的、快速子镜精共相误差探测方法。. 此工作为我国未来大口径及极大口径空间望远镜在轨像差校正提供了一种新的、低硬件成本、低计算开销、操作方便、自动化程度高的子镜位置误差检测理论与法。