Fabrication of a Corner Cube Mirror for Lunar Laser-Ranging

To improve the accuracy of lunar laser-ranging (LLR), we are currently investigating a new LLR system. The new LLR system requires a corner cube mirror (CCM) with a large aperture. Owing to the size of its aperture, the CCM is difficult to produce by previous fabrication techniques. Therefore, for the production of CCM, we have proposed a process chain of shaping of its optical surface, in which polishing and ion beams figuring (IBF) are used for key fabrication techniques. In this paper, we introduce the present status of the development of polishing and IBF techniques for the process of the CCM. For the polishing step, we proposed a new method using a plate spring and developed a polishing machine to polish optical corners, which has a potential for polishing the CCM with high accuracy. IBF allows the machining of surfaces with high atomic-level accuracy because the removal progresses on the basis of the sputtering of atoms. However, to our knowledge, IBF has not yet been used for the machining of three intersecting surfaces, such as the optical surfaces of the new CCM. Thus, the application of IBF to the fabrication process of the CCM was examined by investigating the irradiation of ion beams to two intersecting plates.