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The traditional approach for creating very large X-ray mirror modules (with diameters exceeding 1 meter) involves dividing the optics into azimuthal and radial modules, similar to the Silicon Pore Optics used in Athena. While this method addresses the initial challenges of procuring and handling very large substrates, it introduces complexities in the later stages, particularly when thousands of segments must be assembled without compromising their optical performance. In contrast, a simpler design for large mirror modules could involve fewer than a few hundred thin monolithic shells (2-4 mm for mirror shells ranging from 0.4 to 3 meters in diameter). This configuration offers the dual benefits of design simplicity and high-resolution capability, achieved through direct polishing. Additionally, it significantly reduces the polishing time. In Italy, a technology development roadmap for this approach is being funded by ASI and led by INAF-OABrera. In this paper, we present the advancements made in the various phases of this process and in the procurement of new substrates.
Civitani et al. (Wed,) studied this question.