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By European Southern Observatory (ESO) July 3, 2024
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. German company SCHOTT has successfully delivered the blank for the last of the 949 segments commissioned for the telescope’s primary mirror (M1). With a diameter of more than 39 meters, M1 will be by far the largest mirror ever made for a telescope.
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 across, working together to collect tens of millions of times as much light as the human eye. An additional 133 segments have been produced to facilitate the maintenance and recoating of the segments once the telescope is operational. ESO has also procured 18 spare segments, bringing the total number to 949.
The primary mirror of ESO’s Extremely Large Telescope (ELT), known as M1, will be by far the largest mirror ever made for a telescope. With a diameter of more than 39 meters, 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 across, working together to collect tens of millions of times as much light as the human eye. An additional 133 segments have been produced to facilitate the maintenance and recoating of the segments once the telescope is operational. ESO has also procured 18 spare segments, bringing the total number to 949. Now, German company SCHOTT has successfully cast the blank for the last of the 949 segments, seen in this photo. The M1 blanks, shaped pieces of material that are later polished to become the mirror segments, are made from ZERODUR©, a low-expansion glass-ceramic material developed by SCHOTT and optimized for the extreme temperature ranges at the ELT’s site in the Atacama Desert. The 949th segment is seen in this image before being cut into its hexagonal shape and polished — steps that will be performed by French company Safran Reosc. Credit: SCHOTT
The M1 blanks, shaped pieces of material that are later polished to become the mirror segments, are made from ZERODUR®, a low-expansion glass-ceramic material developed by SCHOTT and optimized for the extreme temperature ranges at the ELT’s site in the Atacama Desert. This company has also manufactured the blanks of three other ELT mirrors — M2, M3, and M4 — at their facilities in Mainz, Germany.
[...] Once cast, all segments follow a multi-step, international journey. After a slow cooling and heat treatment sequence, the surface of each blank is shaped by ultra-precision grinding at SCHOTT. The blanks are then transported to French company Safran Reosc, where each of them is cut into an hexagon shape and polished to a precision of 10 nanometers across the entire optical surface — meaning the surface irregularities of the mirror will be less than one-thousandth of 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 is producing the segment supports; the German-French FAMES consortium, which has developed and is finalising manufacturing for the 4500 nanometric-accuracy sensors monitoring the relative position of each segment; German company Physik Instrumente, which designed and is manufacturing the 2500 actuators able to position the segment to nanometric precision; and Danish company DSV, which is in charge of 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, only a few kilometers away from the construction site of the ELT, each segment is coated with a silver layer to become reflective, after which it will be carefully stored until the telescope’s main structure is ready to receive them.
When it starts operating later this decade, ESO’s ELT will be the world’s largest eye on the sky. It will tackle the biggest astronomical challenges of our time and make as-yet unimaginable discoveries.
(Score: 2) by EJ on Saturday July 06 2024, @12:03AM
That's not how telescopes work. [youtube.com]
(Score: 3, Interesting) by ChrisMaple on Saturday July 06 2024, @12:14AM (2 children)
Aluminum is more commonly used in reflector telescopes because it's tarnish resistant. Is there some particular use here that makes silver the better choice?
(Score: 5, Interesting) by StupendousMan on Saturday July 06 2024, @12:40AM (1 child)
Silver has two advantages over aluminum: it reflects slightly more light in the near-infrared, and its emissivity is slightly lower in the infrared as well. That means that a silver mirror will provide a slightly higher signal from a star, and a slightly lower noise background from thermal emission, in the near-infrared. For backyard telescopes, these small advantages do not outweigh the many practical advantages of aluminum. But for very expensive telescopes which will observe frequently in the near-infrared, the small gains are worth the expense and extra maintenance.
(Score: 0) by Anonymous Coward on Saturday July 06 2024, @01:42AM
It's been a while, but my recollection is that for any given wavelength emissivity and reflectivity always add up to exactly one. I think if they didn't then you could use that substance to violate the laws of thermodynamics.
(Score: 4, Funny) by Gaaark on Saturday July 06 2024, @02:59AM (1 child)
Geez... i need a car analogy.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. I have always been here. ---Gaaark 2.0 --
(Score: 5, Funny) by mhajicek on Saturday July 06 2024, @05:49AM
Big car too big for four wheels. Use many wheels instead.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
(Score: 3, Funny) by VanessaE on Saturday July 06 2024, @07:42AM
What, global warming isn't already bad enough, now y'all wanna bring more stars in on it? 😛
(Score: 2) by zzarko on Sunday July 07 2024, @10:12AM
... ESO’s ELT will be almost unusable due to swarms of starlink and similar satellite networks populating the sky? Or do they already have some filters to remove them from the picture?
C64 BASIC: 1 a=rnd(-52028):fori=1to8:a=rnd(1):next:fori=1to5:?chr$(rnd(1)*26+65);:next