Press release
June 27, 2024
The European Southern Observatory’s Extremely Large Telescope (ESO ELT), currently under construction in the Chilean Atacama Desert, is one step closer to completion. The German company SCHOTT has signed off on the last of the 949 segments ordered for the telescope’s primary mirror (M1). With a diameter of more than 39 metres, M1 will be the largest mirror ever built for a telescope.
Because it is too large to be a single piece of glass, the primary mirror, M1, will be composed of 798 hexagonal segments, each about five centimeters thick and 1.5 meters wide, which will work together to collect tens of millions of times more light than the human eye. An additional 133 segments have been manufactured to facilitate maintenance and coating of the segments once the telescope is operational. ESO has also acquired 18 spare segments, bringing the total number to 949.
The M1 blanks – pieces of material that are shaped and then polished into mirror segments – are made of ZERODUR©, a low-expansion glass-ceramic material developed by SCHOTT and optimized for the extreme temperature ranges found at the ELT site in the Chilean Atacama Desert. SCHOTT also manufactured the blanks for three other ELT mirrors (M2, M3 and M4) at its facility in Mainz, Germany.
“What ESO commissioned from SCHOTT is more than ZERODUR©”declares Marc Cayrel, Head of Optomechanics of the ELT at ESO. “In close cooperation with ESO, SCHOTT fine-tuned each production step, tailoring the product to meet and often exceed the demanding requirements of the ELT. The excellent quality of the blanks has been maintained throughout the entire mass production of the more than 230 tons of this high-performance material. ESO is therefore very grateful for the professionalism of the qualified teams at SCHOTT, our trusted partner.”.
Thomas Werner, ELT project manager at SCHOTT, says: “Our entire team is delighted to conclude what has been the largest single order for ZERODUR® in our company’s history. For this project, we successfully completed mass production of hundreds of ZERODUR® mirror substrates, when we normally have a one-piece operation. It has been an honor for all of us to play a role in shaping the future of astronomy“.
Once manufactured, all segments follow a multi-stage international journey. After a slow cooling and heat treatment sequence, the surface of each blank is shaped by ultra-precise grinding at SCHOTT. The blanks are then transported to the French company Safran Reosc, where each one is cut into a hexagon shape and polished to a precision of 10 nanometers over the entire optical surface, meaning that irregularities in the mirror surface will be less than one thousandth of the width of a human hair. Also participating in the work carried out on the M1 segment assemblies: the Dutch company VDL ETG Projects BV, which produces the segment supports; the Franco-German consortium FAMES, which has developed and is finalizing the manufacture of the 4,500 nanometer precision sensors that monitor the relative position of each segment; the German company Physik Instrumente, which designed and manufactures the 2,500 actuators capable of positioning the segment with nanometric precision; and the Danish DSV, which is responsible for transporting the segments to Chile.
Once polished and assembled, each M1 segment is shipped across the ocean to reach the ELT’s technical facilities at ESO’s Paranal Observatory in the Atacama Desert – a 10 000-kilometre journey that more than 70 M1 segments have already completed. At Paranal, just a few kilometres from the ELT’s construction site, each segment is coated with a layer of silver to make it reflective, after which it will be carefully stored until the telescope’s main structure is ready to receive it.
When it comes into operation later this decade, ESO’s ELT will be the world’s biggest eye on the sky. It will tackle the greatest astronomical challenges of our time and make discoveries yet unimaginable.
Additional Information
The European Southern Observatory (ESO) provides the world’s scientific community with the means to unlock the secrets of the Universe for the benefit of all. We design, build and operate cutting-edge ground-based observatories – used by the astronomical community to address exciting questions and spread the fascination of astronomy – and we promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom) together with the host country Chile, and with Australia as a strategic partner. ESO’s Headquarters and its planetarium and visitor centre, the ESO Supernova, are located near Munich, Germany, while the Chilean Atacama Desert – a wonderland with unique sky-observing conditions – is home to our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope together with its Very Large Telescope Interferometer (VLTI), and survey telescopes such as VISTA. Also at Paranal, ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. At Chajnantor, together with international partners, ESO operates ALMA, a facility observing the skies in the millimetre and submillimetre range. At Cerro Armazones, close to Paranal, we are building “the world’s biggest eye on the sky”: ESO’s Extremely Large Telescope (ELT). From our offices in Santiago, Chile, we support the development of our operations in the country and are committed to our Chilean partners and to Chilean society.
Translations of ESO press releases are carried out by members of the ESO Science Outreach Network (ESON), which includes science outreach experts and communicators from all ESO Member States and beyond.
The Spanish node of the ESON network is represented by J. Miguel Mas Hesse and Natalia Ruiz Zelmanovitch.
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Contacts
Barbara Ferreira
ESO Media Manager
Garching near München, Germany
Phone: +49 89 3200 6670
Mobile: +49 151 241 664 00
Email: [email protected]
Elizabeth Harvey
Marketing & Communications – SCHOTT AG
Mainz, Germany
Email: [email protected]
José Miguel Mas Hesse (Contact for media in Spain)
ESO Scientific Outreach Network and Centre for Astrobiology (CSIC-INTA)
Madrid, Spain
Telephone: +34 918131196
Email: [email protected]
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This is a translation of the ESO press release eso2410.
