First Batch of Mirror Segments Shipped To ESO's Extremely Large Telescope

The ambitious construction of the European Southern Observatory's (ESO) Extremely Large Telescope (ELT) has achieved a significant milestone with the delivery and shipment of the first 18 segments of the telescope's main mirror (M1). 

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Zac Aubert

Zac Aubert

Published: 20th Dec 2023 00:49 GMT
Written by: Zac Aubert

The ambitious construction of the European Southern Observatory's (ESO) Extremely Large Telescope (ELT) has achieved a significant milestone with the shipment of the first 18 segments of the telescope's main mirror (M1); marking a crucial step forward in the assembly of what will be the world's largest telescope mirror.

Having departed from France last week, the 18 polished mirror segments are now en route to the ELT's construction site in the Atacama Desert, covering a journey of over 10,000 kilometers.

The M1, with a diameter exceeding 39 meters, is comprised of a total of 798 individual segments arranged in a large hexagonal pattern. An additional 133 segments have been produced to facilitate the recoating process. Unable to be physically manufactured in one piece, the mirror will play a pivotal role in advancing astronomical research.

While only 18 segments have been shipped to date, Safran Reosc is set to deliver many more to ESO. The 100th segment exited the production line on November 1, 2023, marking a noteworthy achievement in the assembly process.

The production rate has exceeded four segments per week, with an anticipated increase to five per week in the near future, showcasing the remarkable efficiency in the series production of high-accuracy optics.

The final stage in the production process involves the meticulous polishing of the M1 segments, a task undertaken by Safran Reosc at a specially refurbished facility near Poitiers, central France.

During this process, Safran Reosc developed innovative automation workflows and measurement techniques to ensure the polishing met the stringent standards required for ESO's ELT.

The mirror's surface irregularities are reduced to less than 10 nanometers, a level of precision achieved through the use of ion-beam figuring. This technique involved a beam of ions sweeping the mirror surface, removing irregularities atom by atom.

The collaborative effort to construct ESO's ELT has involved multiple companies in Europe and Chile working closely with ESO's teams, highlighting the telescope as a truly international endeavor.

The mirror segments were cast by the German company SCHOTT in Mainz, Germany, before being transported to Safran Reosc in France for polishing. Other key contributors include Dutch company VDL ETG Projects BV, responsible for producing delicate segment supports, the German-French FAMES consortium, which developed and manufactured nanometric-accuracy sensors to monitor the relative position of each segment, and German company Physik Instrumente, responsible for designing and manufacturing the actuators with nanometric precision. The complex task of transporting the segments was entrusted to Danish company DSV.

Once completed the ELT will dwarf some of the most renown Earth based telescopes, and is poised to address the most significant astronomical challenges of our time and unveil previously unimaginable discoveries when it commences operations later this decade.

Check out the size of the ELT compared to the Statue of Liberty, Roman Colosseum, and Sydeny Opera House/

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