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30.05.2017, Mainz, Germany

Window to distant galaxies: SCHOTT wins major contract to produce mirror substrates for the world’s largest telescope

The gigantic 39-meter primary mirror for the Extremely Large Telescope (ELT) will soon be made up of 798 ZERODUR® glass-ceramic components. SCHOTT is set to deliver a total of 949 mirror substrates, including spares, made of ZERODUR® to the European Southern Observatory (ESO). Thanks to the headquarters’ investment of more than ten million Euros, the company is well prepared to respond to the increased demand.

Chile’s Atacama Desert is home to the ESO‘s Extremely Large Telescope – or ELT – the world’s largest telescope. By 2024, the telescope of superlatives is planned to discover unexplored galaxies as well as exoplanets and deliver unprecedented image quality of them. The gigantic primary mirror, known simply as “Mirror 1” or “M1”, has the main function of collecting light from the cosmos and transferring it further via additional mirrors onto the observatory’s scientific instruments. The international technology group SCHOTT has just been awarded the contract to provide the substrate components - 798 hexagons made of ZERODUR® glass-ceramic for the assembly of the enormous primary mirror. Thus, the reputation of ZERODUR® as the standard material in substrates has been confirmed once again with its use in the world’s largest telescope.

SCHOTT earlier provided substrates for other ELT mirrors
After the first ZERODUR® components for the segmented fourth mirror (M4) left SCHOTT’s Mainz production facility in 2016, the next order followed at the beginning of 2017 for the substrates to be used in the secondary (M2) and tertiary mirrors (M3). Thus, the first four ELT substrates will soon be equipped with ZERODUR®.

“We are very proud to play a significant role in the ELT project. We are also extremely pleased that because of our know-how, distant galaxies can finally be viewed with unprecedented sharpness,” exclaimed Dr. Frank Heinricht, chairman of the board at SCHOTT AG, adding, “The ESO order for the production of substrates for the ELT primary mirror represents the single-largest contract in terms of astronomical projects which SCHOTT has ever been awarded. At our ZERODUR® competency center in Mainz, we have invested more than ten million Euros over the last several years to secure and expand our excellent market position for the future.”

Christoph Fark, Executive Vice President of Advanced Optics at SCHOTT: “Providing more than 900 ZERODUR® panels for the hexagons with the start of series production in 2020 will place a high workload on the manufacturing facility at our Mainz headquarters. However, with the addition of a second ZERODUR® melting tank, which was recently commissioned, we are certain that we will be able to effortlessly meet the continuing high demand for the material. In addition, we have added more cutting-edge CNC machines at our facility, which contribute to fulfilling the growing customer requirements.”

Substrates made in Germany
The casting and grinding of the 949 ELT substrate elements takes place at SCHOTT headquarters in Mainz, Germany, while the polishing and coating of them is handled by the French company Safran-Reosc, which has many years of experience in working with ZERODUR®. The substrates for the primary mirror are scheduled to be gradually delivered through to March 2024.

When it comes to the production of materials for astronomical applications, SCHOTT has accumulated decades of experience. Since 1903 the company, which is part of the Carl Zeiss Foundation, has been providing substrates in various dimensions for use in both space telescopes and terrestrial ones. In 2018, ZERODUR® will celebrate the 50th anniversary of its development. The de facto standard for substrates has proven its reliability in numerous mega telescopes around the world, including the Very Large Telescope (VLT), which is positioned not far from the ELT and has a primary mirror containing four ZERODUR® segments, with an overall diameter of 8.2 meters. The VLT is also known as having the world’s largest substrate cast as single unit.

Microsite with lots of additional information about ELT
Further information focusing entirely on the fascinating astronomical project can be found at SCHOTT’s microsite, The site is home to interesting data and facts all about ELT as well as exclusive insights on the product properties and the production of ZERODUR®.


SCHOTT goes ELT – Microsite:

SCHOTT ZERODUR®: European Southern Observatory (ESO):

The European Extremely Large Telescope:

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 1.99 billion euros were generated in fiscal year 2015/2016. The parent company, SCHOTT AG, has its headquarters in Mainz (Germany) and is solely owned by the Carl Zeiss Foundation. As a foundation company, SCHOTT assumes special responsibility for its employees, society and the environment.

ELT’s optical system and how ZERODUR® contributes to it. Photo: ESO / Modifications by SCHOTT
ELT’s optical system and how ZERODUR® contributes to it. Photo: ESO / Modifications by SCHOTT
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Michael Mueller
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