ESO: First ELT Main Mirror Segments Successfully Cast

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ESO: First ELT Main Mirror Segments Successfully Cast

Post by bystander » Tue Jan 09, 2018 9:14 pm

First ELT Main Mirror Segments Successfully Cast
ESO Organizational Release | 2018 Jan 09
[img3="Credit: SCHOTT/ESO"]https://cdn.eso.org/images/screen/eso1801a.jpg[/img3][hr][/hr]
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).
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by neufer » Tue Jan 09, 2018 10:19 pm

bystander wrote: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.
https://oeis.org/A002445 wrote:
Denominators of Bernoulli numbers B2n: 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 B2n = 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
https://en.wikipedia.org/wiki/Bernoulli_number wrote: <<In mathematics, the Bernoulli numbers Bn are a sequence of rational numbers which occur frequently in number theory. For even n other than 0, Bn is negative if n is divisible by 4 and positive otherwise. For all odd n other than 1, Bn = 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.>>
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by BDanielMayfield » Wed Jan 10, 2018 1:27 pm

bystander wrote:First ELT Main Mirror Segments Successfully Cast
ESO Organizational Release | 2018 Jan 09
[img3="Credit: SCHOTT/ESO"]https://cdn.eso.org/images/screen/eso1801a.jpg[/img3][hr][/hr]
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.

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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by rstevenson » Wed Jan 10, 2018 2:56 pm

BDanielMayfield wrote: 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.

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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by Chris Peterson » Wed Jan 10, 2018 3:18 pm

BDanielMayfield wrote: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.
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by neufer » Wed Jan 10, 2018 3:33 pm

BDanielMayfield wrote:
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).
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by Chris Peterson » Wed Jan 10, 2018 3:40 pm

neufer wrote:
BDanielMayfield wrote:
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.
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by BDanielMayfield » Thu Jan 11, 2018 3:00 pm

Chris Peterson wrote:
neufer wrote:
BDanielMayfield wrote:
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.
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by neufer » Thu Jan 11, 2018 3:11 pm


BDanielMayfield wrote:
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.
:arrow: Three SCHOTT glasses of varying shape and size.
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by Chris Peterson » Fri Jan 12, 2018 5:27 am

BDanielMayfield wrote:
Chris Peterson wrote:
neufer wrote: 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.
Last edited by Chris Peterson on Fri Jan 12, 2018 3:00 pm, edited 1 time in total.
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by geckzilla » Fri Jan 12, 2018 6:22 am

Here's an article that shows a better angle of the molten material.
http://www.eso.org/public/news/eso1715/
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by neufer » Fri Jan 12, 2018 3:15 pm

geckzilla wrote:
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.
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Re: ESO: First ELT Main Mirror Segments Successfully Cast

Post by geckzilla » Fri Jan 12, 2018 6:05 pm

Oops. :(
Just call me "geck" because "zilla" is like a last name.