Making The Primary Mirrors For The European Large Telescope


Primary Mirrors For The European Large Telescope

The SCHOTT melting team has started casting the first mirror segments that will make up the 39-meter primary mirror (M-1) of the European Large Telescope (ELT).

To make the segments, liquid glass heated to over 1400 degrees Celsius will be poured directly into molds, and transferred into a cooling furnace and subjected to a ceramicization process lasting several weeks. The result is ZERODUR® glass-ceramic, a material with a thermal expansion of near zero that makes it especially suited to astronomy applications. The SCHOTT production facility in Mainz is expected to complete delivery of the segments by 2024.

SCHOTT, the international technology group, will produce up to 949 identical 1.52-meter hexagonal segments for the ELT. The giant mirror will be composed of a total of 798 segments, made of ZERODUR® glass-ceramic, with the balance used as replacement segments.

"Casting the mirror substrates for the M1 is a milestone in the European Southern Observatory's (ESO) project plan. The main mirror of the ELT will be humanity's largest eye on the sky, enabling us to reach unprecedented depths of space," said Marc Cayrel from ESO's ELT project team. SCHOTT has developed special casting molds for the production of the M1 segments. "The glass consumption factor will be as low as possible, so we can work very efficiently," explains Dr. Thomas Westerhoff, Director of Strategic Marketing for ZERODUR® at SCHOTT.

After ceramization, each of the round ZERODUR® blocks will be cut into five slices of approximately 60 - 70 mm in thickness. Further processing at SCHOTT will take place on state-of-the-art computer-controlled 5-axis CNC machines. SAFRAN Reosc, a company based in France, will polish the M1 segments.

ZERODUR® is a proven material that has been selected for four of the five high-precision mirror elements of the ELT. In addition to the segmented 39-meter giant mirror, these will be a convex mirror 4.2 meters in diameter (M2), the M3 concave mirror (3.8 meters in diameter) and a 2.4-meter diameter adaptive mirror (M4).

"Thanks to significant expansion of production capacity at the Mainz site, SCHOTT is very well prepared for the production of ZERODUR® glass-ceramic, both for the ELT project and for the currently very gratifying high demand from the high-tech industry," said Dr. Thomas Westerhoff, director of strategic marketing, ZERODUR® at SCHOTT Advanced Optics.

Two glass melting tanks are in parallel operation due to the high demand. Furthermore, new jobs were created for around 50 employees, and additional capacity-expanding investments are planned for the coming year.

ZERODUR® is a registered trademark of SCHOTT AG

Further information is available on our microsite and under SCHOTT Innovation.

SCHOTT is a leading international technology group in the areas of specialty glass and glass-ceramics. The company has more than 130 years of outstanding development, materials and technology expertise and offers a broad portfolio of high-quality products and intelligent solutions. SCHOTT is an innovative enabler for many industries, including the home appliance, pharma, electronics, optics, life sciences, automotive and aviation industries. SCHOTT strives to play an important part of everyone's life and is committed to innovation and sustainable success. The group maintains a global presence with production sites and sales offices in 34 countries. With its workforce of approximately 15,000 employees, sales of $2.21 billion were generated in fiscal year 2015/2016.

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