“We then enclose the mold and put it in the electric furnace, which is in pieces enabling the team to assemble it around the mold. Martin tells IndustryWeek, his team starts by piling the chunks of Ohara glass on top of the mold, weighing each block first to ensure the right volume of glass. “What you're trying to overcome in a telescope is the bending of the mirror that would occur due to gravity, its own weight causing it to sag as the telescope points in different directions and bending due to wind as the mirror is exposed to the outside air and the wind,” says Martin. In fact, the final mirror only has 20% of the mass of a solid mirror with the same exterior dimensions. The honeycomb design is crucial in making a lightweight mirror. Martin’s team uses a mold that is the negative of the honeycomb – essentially a big tub filled with roughly 1700 hexagonal boxes to form the honeycomb. The GMT uses lightweight honeycomb mirrors, which gives them the best mechanical and thermal properties to work in a telescope, while keeping their shape to an accuracy of a few millionths of an inch, forming the best possible images nature allows. “When we then later melt these blocks together in our big mold, they fuse together without any trace of individual blocks – a difficult accomplishment in itself,” says Buddy Martin, project scientist for the mirror polishing at University of Arizona's Mirror Lab. Once the E6 glass has passed all of the quality control and inspection criteria, it is ready for packaging and shipment to the mirror lab. We take E6 samples from each lot and measure the Coefficient of Thermal Expansion (CTE). Areas of the glass found to contain high stress are scribed and removed. The chunks are also inspected for stress birefringence using a cross polarization method. The E6 chunks are visually inspected for bubbles, inclusions, and striae. The E6 chunks are now a manageable size and are sent to inspection. The large glass block is then downsized using a scribing and high intensity flame cutting technique. Afterward, the pot is broken to reveal the finished E6 glass. Once annealing is complete, the clay pot is removed from the oven and the chain is unwound. A separate annealing operation is performed to reduce the stress birefringence within the glass. The melting process takes about 53 hours to complete.Īfter melting, the clay pot is removed from the furnace and a chain is wound around the pot to prevent breakage. To reduce striae and bubbles, the melted glass is periodically stirred. Once properly mixed, the initial batch is ready for the melting process.ĭuring the melting process, the temperature reaches as high as 1500 degrees C and the powders are transformed within the clay pot from a solid to a liquid state. The materials are weighed and evenly mixed using a V-shaped blender. This clay pot melting method is similar to those used in the earliest days of optical glass production.Įach lot of Ohara E6 glass requires 1.5 tons of various raw materials in powder form. It takes about 4 months to complete the entire process. Once shaped, the clay pot must be air dried and then baked. This process is performed almost entirely by hand.

Ohara uses a production process that begins with the forming of an 800 liter clay pot. Pure glass foundationĬreating the GMT mirrors starts with borosilicate glass from Ohara.

Such viewing power is ten times greater than the famed Hubble Space Telescope. Why is this such a meaningful moment? Once the GMT becomes fully operational, its seven mirror-array will be able to see the torch engraved on a dime from nearly 100 miles away. In a marvel of modern engineering that takes four years of effort, the 8.4-meter (28 feet) mirror manufacturing is well underway. Caris Mirror Lab where six of the world’s largest mirrors are under construction using the world’s purest glass, within a giant spinning oven. The process is happening far beneath the University of Arizona football field at the Richard F. While some complex production processes can take days or weeks, creating something as monumental as the Giant Magellan Telescope (GMT) is in its own realm with individual steps measured in months and years.Ĭonsider the production of the massive yet highly accurate mirrors needed for the one of a kind telescope.

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