How to make from glass dissolved the primary mirror with a diameter of 8.4 meters to be used in the "Giant Magellan Telescope," the world's largest

Production is proceeding with the aim of starting test observation in 2021Huge Magellan Telescope(Giant Mageran Telescope:GMT), By combining seven huge circular mirrors with a diameter of 8.4 meters, it is supposed to realize a huge mirror with a pseudo diameter of 24.5 meters. A process requiring high precision for astronomical observations and producing a huge single mirror that is unparalleled in its own way is extremely labor-intensive and time consuming.

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https://motherboard.vice.com/en_us/article/bj7d3z/mirror-giant-magellan-telescope-extremely-large

The huge Magellan telescope is a very large ground telescope decided to be built at the Las Campanas Observatory in the Republic of Chile and will be the successor to the Hubble Space TelescopeJames Webb Space TelescopeIt is a telescope which becomes the essential part of a system that enables super high precision astronomical observation in cooperation with the telescope.

Construction of the next generation space observation facility "Huge Magellan telescope" started, its image movies and images are on display - GIGAZINE


In the interior of the telescope, a huge main mirror with a composite effective aperture of 24.5 meters, which is a combination of seven mirrors, is set up to collect light arriving from space and observe. If this mirror has distortion, accurate observation can not be performed, so various correction mechanisms are incorporated, but it is no doubt that it is an absolute requirement to "create a mirror that can be accurately reflected" than anything else. For that reason, seven mirrors are made over a long period of several years per piece.


A circular mirror with a diameter of 8.4 meters is made with a huge furnace installed at Richard F. Caris Mill Lab of the University of Arizona. There is an inner frame in the iron frame that is likely to be 10 meters in diameter, spreading a ceramic hexagonal tube in it, placing a hexagonal flat lid, melting the glass and solidifying it as it is It is made.


A state that hexagonal ceramic tiles are spread. A melting mirror is made by dissolving and solidifying the glass on this. It is used for making flat glass sheets in glass factories etc.Float glass manufactureNot interesting to be made on solid tiles, not.


The staff who spreads the lump of glass as the raw material on the tile by hand. The total amount of glass used is as much as 20 tons.


I do not know if it is called "cullet" like a glass factory, but I will arrange glass of fist size.


It can be seen in the following movie. You can see how the glass is spread over the furnace while rotating it, and then packing it further with reversing.

Glass loading for GMT mirror 5 - YouTube


After spreading the glass, close the furnace lid ... ...


Blow fire inside, heat up to 1165 degrees Celsius and gradually melt the glass.


When the glass is melted, how it turns the whole furnace. By rotating at a speed of 5 revolutions per minute, moderate centrifugal force is generated, the peripheral edge of the glass is made thicker, and the central portion is made thinner, so that the surface curvature required for the finished state is created And that.


Once the molding of the glass is completed, the cooling speed will be entered by slightly slowing down the furnace rotation speed. The time it takes to completely cool the glass is three months. It seems that it is aiming at producing glass without distortion by applying enough time.

Incidentally, comparing the size of the main mirror used for reflecting telescopes around the world, like this, the huge Magellan telescope is the world's largest telescope in the size of a single mirror. A telescope of a size larger than the huge Magellan telescope such as "European Extremely Large Telescope" larger than the gigantic Magellan telescope was also planned, but because of the budget problem and the like, the huge Magellan telescope was the world largest It is said that it can be called a reflection telescope.


After cooling is completed, we start polishing the surface. I use a computer-controlled polishing machine to finish the surface very smoothly, but the time I can spend here is a year and a half. We will eliminate the irregularities of the surface with tolerance of several microns which is 1/1000 of the thickness of the hair. For example, the magnitude of unevenness allowed when the diameter of a mirror is enlarged to the same size as the continental continues to be only 1 cm.


Mirrors made in this way are contained in huge shipping containers and transported from Arizona State to Sea via sea transportation in a strict regime.

GMT's First Giant Mirror Segment Starts Journey South - YouTube


On November 3, 2017, the fifth of the seven mirrors of the huge Magellan telescope started manufacturing. Using a mirror made over a very long time, the gigantic Magellan telescope is scheduled to begin testing for production in 2021.