ESO Signs Contracts for the ELT’s Gigantic Primary Mirror

Image: Artists’s Rendering of the primary mirror of the ELT

Contracts for the manufacture of the 39-metre primary mirror of ESO’s Extremely Large Telescope (ELT) were signed today at a ceremony at ESO’s Headquarters near Munich. The German company SCHOTT will produce the blanks of the mirror segments, and the French company Safran Reosc will polish, mount and test the segments. The contract to polish the mirror blanks is the second-largest contract for the ELT construction and the third-largest contract ESO has ever awarded.


Sulutpos.com, Garching bei München, Germany – The unique optical system of ESO’s Extremely Large Telescope consists of five mirrors, each of which represents its own significant engineering challenge. The 39-metre-diameter primary mirror, which will be made up of 798 individual hexagonal segments each measuring 1.4 metres across, will be by far the largest ever made for an optical telescope. Together, the segments will collect tens of millions of times as much light as the human eye [1].

Artists’s Rendering of the primary mirror of the ELT. This artist's rendering shows the huge segmented primary mirror of the ESO Extremely Large Telescope (ELT). Contracts for the manufacture of the mirror segments were signed on 30 May 2017 at a ceremony at ESO’s Headquarters near Munich. The German company SCHOTT will produce the blanks of the mirror segments, and the French company Safran Reosc will polish, mount and test the segments. The contract to polish the mirror blanks is the second-largest contract for the ELT construction and the third-largest contract ESO has ever awarded. Credit: ESO/L. Calçada
Artists’s Rendering of the primary mirror of the ELT. This artist’s rendering shows the huge segmented primary mirror of the ESO Extremely Large Telescope (ELT). Contracts for the manufacture of the mirror segments were signed on 30 May 2017 at a ceremony at ESO’s Headquarters near Munich. The German company SCHOTT will produce the blanks of the mirror segments, and the French company Safran Reosc will polish, mount and test the segments. The contract to polish the mirror blanks is the second-largest contract for the ELT construction and the third-largest contract ESO has ever awarded. Credit: ESO/L. Calçada

The contracts to manufacture and polish the ELT primary mirror segments were signed today by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members. The first contract was signed with SCHOTT by Christoph Fark, Executive Vice President Advanced Optics, and Thomas Westerhoff, Director Strategic Marketing Zerodur. The second contract was signed with Safran Reosc by Philippe Rioufreyt, Chief Executive Officer.

Tim de Zeeuw expressed his delight at the current progress with the ELT: “This has been an extraordinary two weeks! We saw the casting of the ELT’s secondary mirror and then, last Friday, we were privileged to have the President of Chile, Michelle Bachelet, attend the first stone ceremony of the ELT. And now two world-leading European companies are starting work on the telescope’s enormous main mirror, perhaps the biggest challenge of all.”

Signature ceremony with SCHOTT for ELT primary mirror segment blanks. The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members.  In this picture the first contract is being signed with SCHOTT. Tim de Zeeuw, ESO's Director General, appears in the centre, with Thomas Westerhoff, Director Strategic Marketing Zerodur for SCHOTT, to the left and Christoph Fark, Executive Vice President Advanced Optics of SCHOTT on the right. Credit: ESO/M. Zamani
Signature ceremony with SCHOTT for ELT primary mirror segment blanks. The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members. In this picture the first contract is being signed with SCHOTT. Tim de Zeeuw, ESO’s Director General, appears in the centre, with Thomas Westerhoff, Director Strategic Marketing Zerodur for SCHOTT, to the left and Christoph Fark, Executive Vice President Advanced Optics of SCHOTT on the right. Credit: ESO/M. Zamani

The 798 hexagonal segments that together comprise the ELT’s primary mirror will be produced from the low-expansion ceramic material Zerodur® [2] by SCHOTT. Previously SCHOTT was also awarded the contracts for the production of the telescope’s giant secondary and tertiary mirrors and the material is also being used for the ELT’s deformable quaternary mirror that is currently under construction.

Once the mirror blanks are ready they will be passed to Safran Reosc, to design the mounting interfaces, figure and polish the segments, integrate them into their support systems, and perform optical tests before delivery. During the polishing process, each segment will be polished until it has no surface irregularity greater than about 10 nanometres — no higher than a ladybird if each segment were as big as France!

 

Signature ceremony with Safran Reosc for production of ELT primary mirror segments. The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members.  In this picture the second contract is being signed with Safran Reosc. Tim de Zeeuw, ESO's Director General appears on the right and Philippe Rioufreyt, Chief Executive Officer, Safran Reosc on the left. Credit: ESO/M. Zamani
Signature ceremony with Safran Reosc for production of ELT primary mirror segments. The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members. In this picture the second contract is being signed with Safran Reosc. Tim de Zeeuw, ESO’s Director General appears on the right and Philippe Rioufreyt, Chief Executive Officer, Safran Reosc on the left. Credit: ESO/M. Zamani
Size comparisons between the ELT and other telescope mirrors. This infographic compares the size of the Extremely Large Telescope's (ELT) main mirror with that of other major ground-based telescopes, either in operation or planned. The ELT, with a main mirror 39 metres in diameter, will be the largest optical/near-infrared telescope in the world.  This picture was inspired by infographic made by Wikipedia Author Cmglee. Credit: ESO
Size comparisons between the ELT and other telescope mirrors. This infographic compares the size of the Extremely Large Telescope’s (ELT) main mirror with that of other major ground-based telescopes, either in operation or planned. The ELT, with a main mirror 39 metres in diameter, will be the largest optical/near-infrared telescope in the world. This picture was inspired by infographic made by Wikipedia Author Cmglee. Credit: ESO

To meet the challenge of delivering such a large number of polished segments within seven years, Safran Reosc will build up to a peak production rate of one mirror a day. It will set up a dedicated new facility at its Poitiers plant, specialising in the production of high-tech optical and optronic (electro-optical) equipment [3].

The new contract with Safran Reosc is the second-largest contract for the ELT construction and the third-largest contract ESO has ever signed [4]. Safran Reosc will also design, polish and test the ELT’s secondary mirror and tertiary mirror, and is currently manufacturing the 2-mm thick deformable shell mirrors that will comprise the ELT’s fourth mirror.

 

ELT primary mirror blank contract awarded to SCHOTT. The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members.  This picture shows key members of the contract teams, from both ESO and SCHOTT. Credit: ESO/M. Zamani
ELT primary mirror blank contract awarded to SCHOTT. The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members. This picture shows key members of the contract teams, from both ESO and SCHOTT. Credit: ESO/M. Zamani
The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members.  This picture shows key members of the contract teams, from both ESO and Safran Reosc. Credit: ESO/M. Zaman
ELT primary mirror segments contract awarded to Safran Reosc. The contracts to manufacture and polish the ELT primary mirror segments were signed on 30 May 2017 by ESO’s Director General, Tim de Zeeuw, and senior representatives of SCHOTT and Safran Reosc, a subsidiary of Safran Electronics & Defense, in the presence of key ESO staff members. This picture shows key members of the contract teams, from both ESO and Safran Reosc. Credit: ESO/M. Zaman

Both SCHOTT and Safran Reosc have long and successful involvements with ESO. Together they manufactured many optical components, including the 8.2-metre main mirrors of the four Unit Telescopes of the ESO Very Large Telescope.

The ELT is currently under construction at Cerro Armazones near ESO’s Paranal Observatory in northern Chile, and is scheduled to see first light in 2024.

Notes

[1] The ELT primary mirror segments will be installed in a common support structure and equipped with edge sensors — the most accurate ever used in a telescope — that will continuously sense the locations of the ELT primary mirror segments relative to their neighbours and allow the segments to work together to form a perfect imaging system.

[2] Zerodur® is a sophisticated material which has almost no thermal expansion even when subjected to large temperature fluctuations, is highly chemically resistant, and can be polished to a high standard of finish. The reflective layer, made of aluminum or silver, will be vapourised onto the extremely smooth surface shortly before the telescope is put into operation. Many well-known telescopes with Zerodur® mirrors have been operating reliably for decades, including ESO’s Very Large Telescope in Chile.

[3] Up to 931 segments will ultimately be produced and polished, including 133 in a maintenance set, allowing for segments to be removed, replaced and recoated on a rotating basis once the ELT is in operation.

[4] The two other contracts are those for the Dome and Main Structure of the ELT and the European ALMA Antennas.

More information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries.

ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

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