A stitching method to test the segments of a large primary

摘要

The European Extremely Large Telescope will be a large optical/infrared telescope with a segmented primary mirror of 42-m diameter, and 84-m radius of curvature. Each segment, about 1.2-meters across, implies great manufacturing and measuring challenges. To determine the most adequate metrology technique for testing these segments, we report a brief comparative analysis of the four most important testing techniques used for large surfaces. The study shows that the stitching method is the most appropriate technique. We implement a proof of concept to demonstrate the viability of this technique for studying surfaces with a small curvature and estimate the challenges to overcome. The analysis confirms that the success of the stitching technique, in curved elements, ensues because the roughness does not contribute significantly to the surface tendency. Therefore, we propose the use of tendency information to solve Procrustes' problem and to improve the resultant shape of the unified map for surfaces with small curvature, as in the case of the segments of a large primary mirror.