In the recent past, SCHOTT has demonstrated its ability to manufacture large light weighted ZERODUR® mirror blanks
for telescope projects like the GREGOR solar-telescope, for example. In 2010, SCHOTT was commissioned with a
study aimed at developing a design for the M5 mirror blank of the ESO E-ELT.
The tip and tilt M5 mirror of the European Extremely Large Telescope (E-ELT) requires a demanding approach in light
weighting. The approximately 3.1 m x 2.5 m elliptical plano mirror is specified to a weight of less than 500 kg with high
Eigenfrequencies and low deformation under different inclination angles.
The study was divided into two parts. The first part focused on coming up with an optimized light weighted design with
respect to performance and processability with finite element modeling. In the second part of the study, a concept for the
processing sequence including melting, cold-processing, acid etching and handling of the M5 blank was developed. By
producing a prototype section, SCHOTT demonstrated its ability to manufacture the demanding features, including
pockets 350 mm in depth, thin walls and sloped pocket bottoms.
This paper outlines the results of the design work, processing concept and demonstrator fabrication.