This artist’s rendering shows a night view of the extremely large telescope in operation on Cerro Armazones in northern Chile. The telescope is shown using lasers to create artificial stars high in the atmosphere. Credit: ESO/L. Calçada
The last mirror segment of the world’s largest telescope was successfully launched
Set to finish this decade, the Extremely Large Telescope in Chile will be the largest telescope in the world, with a main mirror that stretches 39 meters and is made of 798 precision-engineered segments. It represents an important international endeavor in astronomy.
Currently under construction in the Chilean Atacama Desert, the European Southern Observatory’s Extremely Large Telescope (ESO‘s ELT) is one step closer to completion. The German company SCHOTT has successfully delivered the blank for the last of the 949 segments ordered for the telescope’s main mirror (M1). With a diameter of more than 39 meters, M1 will be by far the largest mirror ever created for a telescope.
Innovations in telescope mirror design
Too large to be made from a single piece of glass, M1 will consist of 798 hexagonal segments, each about five centimeters thick and 1.5 meters wide, working together to gather tens of millions of times more light than the human eye. An additional 133 segments were produced to facilitate maintenance and repainting of the segments once the telescope is operational. ESO has also procured 18 spare segments, bringing the total number to 949.
The main mirror of ESO’s Extremely Large Telescope (ELT), known as M1, will be the largest mirror ever built for a telescope. At more than 39 meters in diameter, M1 is too large to be made from a single piece of glass and will instead consist of 798 hexagonal segments, each about five centimeters thick and 1.5 meters wide , working together to collect tens of millions of times. as light as the human eye. An additional 133 segments were produced to facilitate maintenance and repainting of the segments once the telescope is operational. ESO has also procured 18 spare segments, bringing the total to 949. Now, the German company SCHOTT has successfully cast the blank for the last of the 949 segments, seen in this photo. M1 blanks, shaped pieces of material that are later polished to become mirror segments, are made of ZERODUR©, a low-expansion glass-ceramic material developed by SCHOTT and optimized for the extreme temperature ranges of the site of ELT in the Atacama desert. . Segment 949 is seen in this image before it is cut into its hexagonal shape and polished – steps to be carried out by French company Safran Reosc. Credit: SCHOTT
Materials and Advanced Manufacturing Techniques
The M1 blanks, shaped pieces of material that are later polished to become mirror segments, are made of ZERODUR®, a low-expansion glass-ceramic material developed by SCHOTT and optimized for the extreme temperature ranges at the site ELT in the Atacama desert. . This company has also produced the blanks of three other ELT mirrors – M2, M3 and M4 – at their facilities in Mainz, Germany.
Collaboration and Precision Engineering
“What ESO has ordered from SCHOTT is more than just ZERODUR®,” says Marc Cayrel, Head of ELT Optomechanics at ESO. “In close cooperation with ESO, SCHOTT fine-tuned every single manufacturing step, tailoring the product to meet and often exceed the very demanding requirements of the ELT. The exceptional quality of the blanks was maintained throughout the mass production of more than 230 tons of this super-performing material. Thus, ESO is very grateful for the professionalism of the skilled teams at SCHOTT, our trusted partner.”
Computer rendering showing the main mirror (M1) of the ESO Extremely Large Telescope. Credit: ESO
Thomas Werner, ELT Project Manager at SCHOTT, says: “Our entire team is excited to complete what has been the largest single ZERODUR® order in our company’s history. For this project, we successfully completed the serial production of hundreds of ZERODUR® mirror substrates, when we usually have a one-piece operation. It has been an honor for all of us to play a role in shaping the future of astronomy.”
International Logistics and Assembly
Once broadcast (see video below), all segments follow a multi-step international journey. After a slow cooling sequence and heat treatment, the surface of each blank is shaped by ultra-precision grinding at SCHOTT. The blanks are then transported to the French company Safran Reosc, where each one is cut into a hexagonal shape and polished to a precision of 10 nanometers across the optical surface – meaning the mirror surface irregularities will be less than a one thousandth the width of a human hair.
Also involved in the work done on the M1 segment assemblies are: Dutch company VDL ETG Projects BV, which manufactures the segment supports; the German-French consortium FAMES, which has developed and is finalizing production for 4500 nanometric-ACCURATELY sensors that monitor the relative position of each segment; German company Physik Instrumente, which designed and is manufacturing the 2,500 actuators capable of positioning the segment with nanometric precision; and the Danish company 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 technical facility at ESO’s Paranal Observatory in the Atacama Desert – a 10,000 kilometer journey that over 70 M1 segments have already completed. In Paranal, just a few kilometers from the ELT construction site, each segment is coated with a silver coating to make it reflective, after which it will be carefully stored until the main structure of the telescope is ready to receive them. those.
Final stages and future impact
When it becomes operational later this decade, ESO’s ELT will be the world’s largest eye on the sky. It will tackle the greatest astronomical challenges of our time and make as yet unimaginable discoveries.