ESO: European Extremely Large Telescope (E-ELT)

[bystander]

World’s Biggest Telescope to be Located on Armazones, Chile
ESO Organizational Release | 26 April 2010

On 26 April 2010, the ESO Council selected Cerro Armazones as the baseline site for the planned 42-metre European Extremely Large Telescope (E-ELT). Cerro Armazones is a mountain at an altitude of 3060 metres in the central part of Chile’s Atacama Desert, some 130 kilometres south of the town of Antofagasta and about 20 kilometres from Cerro Paranal, home of ESO’s Very Large Telescope.
...
Various factors needed to be considered in the site selection process. Obviously the “astronomical quality” of the atmosphere, for instance, the number of clear nights, the amount of water vapour, and the “stability” of the atmosphere (also known as seeing) played a crucial role. But other parameters had to be taken into account as well, such as the costs of construction and operations, and the operational and scientific synergy with other major facilities (VLT/VLTI, VISTA, VST, ALMA and SKA etc). ...

[neufer]

http://www.eso.org/public/teles-instr/vlt/

<<This panorama was taken by an astronaut looking southeast across the South American continent when the International Space Station (ISS) was almost directly over the Atacama Desert near Chile’s Pacific coast. The high plains (3000–5000 meters, or 13,000–19,000 feet) of the Andes Mountains, also known as the Puna, appear in the foreground, with a line of young volcanoes (dashed line) facing the much lower Atacama Desert (1000–2000 m elevation). Several salt-crusted dry lakes (known as salars in Spanish) occupy the basins between major thrust faults in the Puna. Salar de Arizaro (foreground) is the largest of the dry lakes in this view. The Atlantic Ocean coastline, where Argentina’s capital city of Buenos Aires sits along the Río de la Plata, is dimly visible at image top left.

Near image center, the transition (solid line) between two distinct geological zones, the Puna and the Sierras Pampeanas, creates a striking landscape contrast. Compared to the Puna, the Sierras Pampeanas mountains are lower in elevation and have fewer young volcanoes. Sharp-crested ridges are separated by wide, low valleys in this region. The Salinas Grandes—ephemeral shallow salt lakes—occupies one of these valleys. The general color change from reds and browns in the foreground to blues and greens in the upper part of the image reflects the major climatic regions: the deserts of the Atacama and Puna versus the grassy plains of central Argentina, where rainfall is sufficient to promote lush prairie grass, known locally as the pampas. The Salinas Grandes mark an intermediate, semiarid region.

What accounts for the changes in topography between the Puna and the Sierras Pameanas? The geology of this part of the Andes is a result of the eastward subduction of the Nazca tectonic plate underneath South America. Seismic data suggest that beneath the Puna, the Nazca Plate is dipping down steeply. Beneath the Sierras Pampeanas zone, however, the underlying Nazca plate is almost horizontal. The levelness may be due to the subduction of a submarine mountain range known as the Juan Fernández Ridge. In the simplest terms, ridges are topographic highs that are difficult to stuff down into the subduction zone, and that has profound effects on the volcanism and structures of the overlying South America plate.>>

[bystander]

ESO To Build World’s Biggest Eye On The Sky
European Southern Observatory | 2012 June 11

[i]Artist’s impression of the E-ELT (Credit: ESO/L. Calçada)[/i]

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ESO is to build the largest optical/infrared telescope in the world. At its meeting in Garching today, the ESO Council approved the European Extremely Large Telescope (E-ELT) Programme, pending confirmation of four so-called ad referendum votes. The E-ELT will start operations early in the next decade.

ESO’s governing body, the Council, met today, at the ESO Headquarters in Garching, Germany. The main topic on the agenda was the start of the European Extremely Large Telescope (E-ELT) Programme — the world’s biggest eye on the sky. The E-ELT will be a 39.3-metre segmented-mirror telescope sited on Cerro Armazones in northern Chile, close to ESO’s Paranal Observatory.

All of ESO’s Member States have already expressed very strong support for the E-ELT project (see eso1150). The Council has today voted in favour of a resolution for the approval of the E-ELT and its first suite of powerful instruments, pending confirmation of the so-called ad referendum votes.

To approve the start of the programme, two-thirds of the Member States (at least ten) had to vote in favour. At the Council meeting Austria, the Czech Republic, Germany, the Netherlands, Sweden and Switzerland voted in favour of the start of the E-ELT programme. Four further countries voted in favour ad referendum: Belgium, Finland, Italy, and the United Kingdom. The remaining four Member States are actively working towards joining the programme in the near future.

Following the resolution, spending on elements of the project other than the initial civil works will not commence until the contributions pledged by the Member States, as agreed in the funding principles approved by Council in late 2011, exceed 90% of the 1083 million euro cost-to-completion (at 2012 prices).

On the current schedule the first large E-ELT industrial contracts would have to be approved and major funding committed within the next year. This is expected to provide sufficient time for the conditions to be satisfied: the confirmations of the votes from Belgium, Finland, Italy, and the United Kingdom; other Member States to join the project; and for Brazil to complete its ratification procedure.

“This is an excellent outcome and a great day for ESO. We can now move forward on schedule with this giant project,” said the ESO Director General, Tim de Zeeuw.

Early contracts for the project have already been placed. Shortly before the Council meeting, a contract was signed to begin a detailed design study for the very challenging M4 adaptive mirror of the telescope. This is one of the longest lead-time items in the whole E-ELT programme, and an early start was essential. Further details are given in ann12032.

Detailed design work for the route of the road to the summit of Cerro Armazones, where the E-ELT will be sited, is also in progress and some of the civil works are expected to begin this year. These include preparation of the access road to the summit of Cerro Armazones as well as the levelling of the summit itself.

“The E-ELT will keep ESO in a leading position for decades to come and lead to an extraordinary harvest of exciting science,” concluded Council President Xavier Barcons.

World's largest ground-based telescope is given 'go ahead'
Science & Technology Facilities Council | 2012 June 11

Monster Telescope Takes Another Step Forward
Science Insider | Govert Schilling | 2012 June 11

Coming Soon: World’s Largest Optical Telescope
Universe Today | Nancy Atkinson | 2012 June 11

[bystander]

ESO Signs Contract for E-ELT Dome and Telescope
European Southern Observatory | E-ELT | 2016 May 25

This artist’s rendering of the E-ELT is based on the detailed construction design for the telescope. (Credit: ESO/L. Calçada/ACe Consortium)

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At a ceremony in Garching bei München, Germany on 25 May 2016, ESO signed the contract with the ACe Consortium, consisting of Astaldi, Cimolai and the nominated sub-contractor EIE Group, for the construction of the dome and telescope structure of the European Extremely Large Telescope (E-ELT). This is the largest contract ever awarded by ESO and also the largest contract ever in ground-based astronomy. This occasion saw the unveiling of the construction design of the E-ELT. Construction of the dome and telescope structure will now commence.

The European Extremely Large Telescope (E-ELT), with a main mirror 39 metres in diameter, will be the largest optical/near-infrared telescope in the world: truly the world’s biggest eye on the sky. It will be constructed in northern Chile, on a site that has already been prepared. ...

The contract covers the design, manufacture, transport, construction, on-site assembly and verification of the dome and telescope structure. With an approximate value of 400 million euros, it is the largest contract ever awarded by ESO and the largest contract ever in ground-based astronomy.

The E-ELT dome and telescope structure will take telescope engineering into new territory. The contract includes not only the enormous 85-metre-diameter rotating dome, with a total mass of around 5000 tonnes, but also the telescope mounting and tube structure, with a total moving mass of more than 3000 tonnes. Both of these structures are by far the largest ever built for an optical/infrared telescope and dwarf all existing ones. The dome is almost 80 metres high and its footprint is comparable in area to a football pitch. ...

[bystander]

First ELT Main Mirror Segments Successfully Cast
ESO Organizational Release | 2018 Jan 09

Credit: SCHOTT/ESO

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The first six hexagonal segments for the main mirror of ESO’s Extremely Large Telescope (ELT) have been successfully cast by the German company SCHOTT at their facility in Mainz. These segments will form parts of the ELT’s 39-metre main mirror, which will have 798 segments in total when completed. The ELT will be the largest optical telescope in the world when it sees first light in 2024.

The 39-metre-diameter primary mirror of ESO’s Extremely Large Telescope (ELT) will be by far the largest ever made for an optical-infrared telescope. Such a giant is much too large to be made from a single piece of glass, so it will consist of 798 individual hexagonal segments, each measuring 1.4 metres across and about 5 centimetres thick. The segments will work together as a single huge mirror to collect tens of millions of times as much light as the human eye. ...

As with the telescope’s secondary mirror blank, the ELT main mirror segments are made from the low-expansion ceramic material Zerodur© [1] from SCHOTT. ESO has awarded this German company with contracts to manufacture the blanks of the first four ELT mirrors (known as M1 to M4, with M1 being the primary mirror) (eso1704).

[neufer]

First ELT Main Mirror Segments Successfully Cast
ESO Organizational Release | 2018 Jan 09

The first 6 hexagonal segments for the main mirror of ESO’s Extremely Large Telescope (ELT) have been successfully cast by the German company SCHOTT at their facility in Mainz. These segments will form parts of the ELT’s 39-metre main mirror, which will have 798 segments in total when completed. The ELT will be the largest optical telescope in the world when it sees first light in 2024.

Denominators of Bernoulli numbers B_2n: 1, 6, 30, 42, 30, 66, 2730, 6, 510, 798, 330, 138, 2730, 6, 870, 14322, 510, 6, 1919190, 6, 13530, 1806, 690, 282, 46410, 66, 1590, 798, 870, 354, 56786730, 6, 510, 64722, 30, 4686, 140100870, 6,...

From the Von Staudt-Clausen theorem,

• the denominator of B_2n = product of primes p such that (p-1)|2n.
  
  • B₁₈ = 43867/798
  
  The denominator of B₁₈ = 798 = 2 x 3 x 7 x 19
  • (2-1)|18
    (3-1)|18
    (7-1)|18
    (19-1)|18

[b][color=#0000FF]Swiss mathematician Jacob Bernoulli[/color][/b]

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<<In mathematics, the Bernoulli numbers B_n are a sequence of rational numbers which occur frequently in number theory. For even n other than 0, B_n is negative if n is divisible by 4 and positive otherwise. For all odd n other than 1, B_n = 0.

The Bernoulli numbers appear in the Taylor series expansions of the tangent and hyperbolic tangent functions, in formulas for the sum of powers of the first positive integers, and in expressions for certain values of the Riemann zeta function.

The Bernoulli numbers were discovered around the same time by the Swiss mathematician Jacob Bernoulli, after whom they are named, and independently by Japanese mathematician Seki Kōwa. Seki's discovery was posthumously published in 1712 in his work Katsuyo Sampo; Bernoulli's, also posthumously, in his Ars Conjectandi of 1713. Ada Lovelace's note G on the Analytical Engine from 1842 describes an algorithm for generating Bernoulli numbers with Babbage's machine. As a result, the Bernoulli numbers have the distinction of being the subject of the first published complex computer algorithm.>>

[BDanielMayfield]

First ELT Main Mirror Segments Successfully Cast
ESO Organizational Release | 2018 Jan 09

Credit: SCHOTT/ESO

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The first six hexagonal segments for the main mirror of ESO’s Extremely Large Telescope (ELT) have been successfully cast by the German company SCHOTT at their facility in Mainz. These segments will form parts of the ELT’s 39-metre main mirror, which will have 798 segments in total when completed. The ELT will be the largest optical telescope in the world when it sees first light in 2024.

The 39-metre-diameter primary mirror of ESO’s Extremely Large Telescope (ELT) will be by far the largest ever made for an optical-infrared telescope. Such a giant is much too large to be made from a single piece of glass, so it will consist of 798 individual hexagonal segments, each measuring 1.4 metres across and about 5 centimetres thick. The segments will work together as a single huge mirror to collect tens of millions of times as much light as the human eye. ...

As with the telescope’s secondary mirror blank, the ELT main mirror segments are made from the low-expansion ceramic material Zerodur© [1] from SCHOTT. ESO has awarded this German company with contracts to manufacture the blanks of the first four ELT mirrors (known as M1 to M4, with M1 being the primary mirror) (eso1704).

Why cast a round blank when 798 hexagonal segments are needed? Seems like building a hexagonal mold would have simplified construction.

Bruce

P.S. Therefore, I rather doubt that the photo matches the story.

[rstevenson]

Why cast a round blank when 798 hexagonal segments are needed? Seems like building a hexagonal mold would have simplified construction.

I wonder if the corners of a hex casting would cool just a bit quicker than the rest of it, causing distortion. Maybe it's just easier to get the quality of blank they require by casting it round and machining it hexagonal. Maybe round is traditional and they didn't think outside the cylinder.

Rob

[Chris Peterson]

Why cast a round blank when 798 hexagonal segments are needed? Seems like building a hexagonal mold would have simplified construction.

I think it makes the entire process simpler. Keep in mind that we're not seeing a single mirror segment in the image. Each casting consists of a cylindrical block that (after ceramicization and cooling) gets sliced into five separate mirror segments, which are then shaped using CNC machines. Only then are they precision ground and polished.

[neufer]

Why cast a round blank when 798 hexagonal segments are needed? Seems like building a hexagonal mold would have simplified construction.

The actual blank is thin and unobservable (deep inside of a protective cylindrical casing).

[Chris Peterson]

Why cast a round blank when 798 hexagonal segments are needed? Seems like building a hexagonal mold would have simplified construction.

The actual blank is thin and unobservable (deep inside of a protective cylindrical casing).

The actual casting is thick (400 mm) and unobservable inside the mold. What's inside will be cut into five blanks 60-70 mm thick.

[BDanielMayfield]

Why cast a round blank when 798 hexagonal segments are needed? Seems like building a hexagonal mold would have simplified construction.

The actual blank is thin and unobservable (deep inside of a protective cylindrical casing).

The actual casting is thick (400 mm) and unobservable inside the mold. What's inside will be cut into five blanks 60-70 mm thick.

Ok. Very likely then the hexagonal shape is concealed inside the mold. I was just thinking that making 6 x 798 precision side cuts would be costly.

[neufer]

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Ok. Very likely then the hexagonal shape is concealed inside the mold.
I was just thinking that making 6 x 798 precision side cuts would be costly.

Three SCHOTT glasses of varying shape and size.

[Chris Peterson]

The actual blank is thin and unobservable (deep inside of a protective cylindrical casing).

The actual casting is thick (400 mm) and unobservable inside the mold. What's inside will be cut into five blanks 60-70 mm thick.

Ok. Very likely then the hexagonal shape is concealed inside the mold. I was just thinking that making 6 x 798 precision side cuts would be costly.

No. The casting is a cylinder. The hexagonal shape, as well as the rough surface cut, are made with CNC machines after the cylinder is sliced.

[geckzilla]

Here's an article that shows a better angle of the molten material.
http://www.eso.org/public/news/eso1715/

[neufer]

Here's an article that shows a better angle of the molten material.
http://www.eso.org/public/news/eso1715/

But this is:

The casting of the secondary mirror blank for ESO’s Extremely Large Telescope (ELT) has been completed by SCHOTT at Mainz, Germany. The completed mirror will be 4.2 metres in diameter and weigh 3.5 tonnes. It will be the largest secondary mirror ever employed on an optical telescope and also the largest convex mirror ever produced.

[geckzilla]

Oops.

[bystander]

ELT Tertiary Mirror Takes Shape
ESO Announcement | Extremely Large Telescope | 2020 Mar 05

Engineers inspect the blank for ELT's tertiary mirror. Credit: ESO/M. Cayrel

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ESO’s Extremely Large Telescope (ELT), the world’s biggest eye on the sky, will have a pioneering five-mirror optical system that will allow it to unveil the Universe in unprecedented detail. The tertiary mirror in this system, M3, has completed a key production stage and has now been delivered to French company Safran Reosc for final polishing.

Each of the mirrors on the ELT presents a significant technological challenge, with extreme precision required at each production stage to ensure flawless optical quality. The German company SCHOTT produced the mirror blank for M3 — a cast block of a glass-ceramic material known as Zerodur^Ⓡ measuring more than four metres from edge to edge and weighing in at over three tonnes. After casting and machining the M3 blank to its approximate shape, SCHOTT delivered the mirror to Safran Reosc, who will now grind and polish it to a precision of 15 nanometres across the entire optical surface.

M3 is a notable feature of the ELT. Most large telescopes, including ESO’s Very Large Telescope (VLT) and the NASA/ESA Hubble Space Telescope, use just two curved mirrors to form an image, with a small, flat, tertiary mirror sometimes introduced to divert the light to a convenient focus. However, in the ELT the tertiary mirror also has a curved surface, as the use of three curved mirrors delivers a better image quality over a larger field of view than would be possible with a two-mirror design. This design will allow the ELT to image the night sky with unprecedented quality.

The five mirrors on the ELT all have different shapes, sizes and roles. The primary, M1, is the most spectacular, a giant 39-metre concave mirror made up of 798 hexagonal segments, which will collect light from the night sky and reflect it to the secondary mirror, M2. Measuring 4.2 metres across and hanging above M1, M2 will be the largest secondary mirror ever employed on a telescope, as well as the largest convex mirror ever produced. It will reflect light back down to M3, which in turn will relay it to an adaptive flat mirror (M4) above it. This fourth mirror, which will be the largest adaptive mirror ever made, will adjust its shape a thousand times a second to correct for distortions caused by atmospheric turbulence. M5, a flat tiltable mirror, will then stabilise the image and send it to the instruments.