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The two Extremely Large Telescopes under discussion, the Thirty Meter Telescope and the European Extremely Large Telescope, will use a multitude of hexagonal shaped mirror segments to achieve the large aperture of 30 m and 39 m, respectively. The proper functionality of both telescopes will strongly depend upon the variation of material properties between individual segments.
SCHOTT has a well proven experience in production of mirror substrates for segmented telescopes. Today five of the world's six segmented telescopes are using ZERODUR® as mirror substrate material. Since 2003 SCHOTT delivered more than 260 mirrors of 1.5 m in diameter for industrial application not related to astronomy. In this paper the achievements during the serial production of those are presented for specified material properties and dimensional parameters. The presentation includes data on the fulfillment of the CTE specification, the achieved tolerances on surface figure and flatness and other geometrical quality parameters. The data to be presented will demonstrate the excellent reproducibility of ZERODUR®'s material properties and its manufacturing process. The production capabilities at SCHOTT for the successful delivery in time of the multitude of ZERODUR® segments are presented and discussed. They will demonstrate that ZERODUR® is well prepared for the demands of industrial scale production for the two large segmented ELT's in quality, quantity, and in the requested time period.
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