ZERODUR for the ELT: mission completed

ZERODUR® production for the Extremely Large Telescope mirror substrates concludes in 2024. The ELT M1 substrate blank contract is by far the largest serial production ever undertaken for an astronomical telescope, as well as for SCHOTT ZERODUR® manufacturing. The production results demonstrate the maturity and reproducibility of the production process in terms of material properties and dimensional processing capabilities. The installed ZERODUR® manufacturing capacities enabled a continuous ELT M1 blank production on high quality level in parallel to an extraordinary increase in ZERODUR® demand of the IC Lithography equipment industry. This paper reflects the SCHOTT contribution to the ELT. It reviews the excellent data on the coefficient of thermal expansion and the dimensional characteristics achieved for the complete set of 949 M1 segment blanks, vastly better than specified.