Important stages in the production of X-ray telescope mirrors are the selection of the mirror material and the blank manufacturing method, the machining of the blank to form, the overcoating of some metal substrates with more polishable materials such as electroless nickel and the lapping and polishing. Measurements of surface figure and quality are necessary at the various fabrication stages to ensure that the mirror will be made to the specified tolerances. Production costs rise sharply the higher the specification so that the X-ray optical design theory Must be sufficiently well developed to enable manufacturing tolerances to be calculated to ensure both that the specified tolerances can be met and that they are not more stringent than necessary.
A. Franks, A. Franks,
"X-Ray Telescope Mirrors-Materials, Manufacture, Tolerances And Metrology", Proc. SPIE 0184, Space Optics Imaging X-Ray Optics Workshop, (9 August 1979); doi: 10.1117/12.957440; https://doi.org/10.1117/12.957440