Press release
June 27, 2024
The European Southern Observatory’s (ESO) Extremely Large Telescope (ELT), under construction in the Atacama Desert in Chile, is nearing completion. German company SCHOTT has successfully cast the last of 949 ordered segments for the telescope’s primary mirror (M1). With a diameter of over 39 metres, M1 will be by far the largest mirror ever made for a telescope.
Due to its size, it can M1 cannot be made from a single piece of glass. It consists of 798 hexagonal segments, each about five centimeters thick and 1.5 meters wide, which together collect ten million times more light than the human eye. An additional 133 segments were made to facilitate maintenance and coating of the segments as soon as the telescope is in operation. ESO has also purchased 18 replacement segments, bringing the total to 949.
M1 blanks, shaped parts that are then polished into mirror segments, are made of ZERODUR©one of SCOTT developed a low-expansion glass-ceramic material optimized for the extreme temperature ranges at the ELT site in the Atacama Desert. The company also manufactured the blanks for three other ELT mirrors – M2, M3 and M4 – at its plants in Mainz.
“ESO ordered more than just ZERODUR© from SCHOTT“, explains Marc Cayrel, ELT optomechanics manager at ESO.In close cooperation with ESO, SCHOTT optimized each production step and adapted the product so that it met and often exceeded the very high requirements of the ELT. The excellent quality of the blanks was maintained throughout the series production of more than 230 tons of this high-performance material. ESO is therefore very grateful for the professionalism of the competent teams at SCHOTT, our trusted partner.“
Thomas Werner, Project Manager at SCHOTT, adds: “Our entire team is delighted to have been able to finalize the largest ZERODUR® order in the history of our company. For this project, we successfully carried out the series production of hundreds of ZERODUR® mirror substrates, whereas we usually only produce individual pieces. It was an honor to help shape the future of astronomy.“
After molding browse all segments international multi-step procedure. After a slow cooling and heat treatment phase, the surface of each blank is shaped at SCHOTT using ultra-precise grinding. The blanks are then delivered to the French company Safran Reosc, where each blank is cut into a hexagonal shape and polished on an optical surface with a precision of 10 nanometers. This means that the irregularities in the mirror surface are less than one thousandth of the width of a human hair. Also involved in the work on the M1 segment assemblies are: 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 sensors with a precision of 4,500 nanometers to monitor the relative position of each segment; the German company Physics Instruments, which developed the 2,500 actuators capable of positioning the segment with nanometric precision, and the Danish company DSV, responsible for transporting the segments to Chile.
After polishing and assembly, each M1 segment across the ocean transported to the ELT technical facilities at ESO’s Paranal Observatory in the Atacama Desert – a 10,000-kilometre journey already completed by more than 70 M1 segments. At Paranal, just a few kilometres from the ELT construction site, each segment is equipped with a covered with a reflective silver layer then carefully stored until the main structure of the telescope is ready to accommodate them.
When it becomes operational later this decade, ESO’s ELT will be the biggest eye in the sky, tackling the greatest astronomical challenges of our time and making previously unimaginable discoveries.
Further information
The European Southern Observatory (ESO) enables scientists from around the world to unlock the secrets of the universe for the benefit of all. We design, build and operate world-class observatories that astronomers use to answer exciting questions and inspire fascination with astronomy, and we promote international collaboration in astronomy. Founded in 1962 as an intergovernmental organisation, ESO is led by 16 Member States (Belgium, Czech Republic, Denmark, Germany, France, Finland, Ireland, Italy, the Netherlands, Austria, Poland, Portugal, Sweden, Switzerland, Spain and the United Kingdom) and the Host Country Chile and Australia as strategic partners. ESO Headquarters and its Visitor Centre and Planetarium, ESO Supernova, are located near Munich in Germany, while the Atacama Desert in Chile, a wonderland offering unique conditions for observing the skies, is home to our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At the Paranal site, ESO operates the Very Large Telescope and its associated Very Large Telescope Interferometer as well as survey telescopes such as VUE. Also at Paranal, ESO will operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. In collaboration with international partners, ESO operates APEX and ALMA, two millimetre and submillimetre observing facilities on Chajnantor. On Cerro Armazones, near Paranal, we are building “the world’s largest eye in the sky”: ESO’s Extremely Large Telescope. From our offices in Santiago, Chile, we support our activities in the country and collaborate with Chilean partners and society.
The translations of ESO press releases into English are a service of the ESO Science Outreach Network (ESON), an international astronomy outreach network in which scientists and science communicators from all ESO Member Countries (and some other countries) are represented. It is the German node of the network. House of Astronomy in Heidelberg.
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Contact details
Barbara Ferreira
ESO Media Manager
Garching near Munich, Germany
Tel: +49 89 3200 6670
Mobile: +49 151 241 664 00
E-mail: press@eso.org
Elizabeth Harvey
Marketing and communications – SCHOTT AG
Mainz, Germany
E-mail: elisabeth.harvey@schott.com
Markus Nielbock (press contact Germany)
ESO Science Outreach Network and House of Astronomy
Heidelberg, Germany
Tel: +49 6221 528-134
E-mail: eson-germany@eso.org
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This is a translation of ESO press release eso2410.