Casting of the sixth of the seven largest monolithic mirrors in the world has been completed for the Giant Magellanic Telescope. These mirrors will allow astronomers to look into the universe in greater detail than any other optical telescope has photographed before.
The sixth 8.4-meter mirror is about two stories high and was made in the Richard F. Caris Mirror Laboratory at the University of Arizona, and took almost four years to make. Mirror casting is considered a marvel of modern engineering. Due to the coronavirus pandemic, work on the sixth mirror was carried out behind closed laboratory doors to protect the health of a team of 10.
“The most important part of a telescope is the light-collecting mirror. The larger the mirror, the deeper we can look into the Universe and the more details we can observe. The unique design of the main mirror consists of seven of the largest mirrors in the world. The casting of the sixth mirror is an important step towards the completion of the telescope. Once launched, the Giant Magellanic Telescope will provide images ten times sharper than the Hubble Space Telescope. The discoveries that these mirrors will make will change our understanding of the Universe. “James Fanson, Giant Magellan Telescope Project Manager
The giant mirror casting process at Richard F. Karis’s laboratory in Arizona involved melting nearly 20 tons of high-purity low expansion borosilicate glass (called E6 glass) in the world’s only spinning furnace designed to cast giant telescope mirrors. At the peak of the melting process, the furnace rotates at five revolutions per minute, heating the glass to 1165 ° C for about five hours, until the liquid takes the desired shape.
The peak temperature event is called a “strong fire” and occurred on March 6, 2021. The mirror then goes into a firing process for a month, during which the glass is cooled and the kiln rotates at a slower speed to relieve internal stress and harden the glass. The mirror will cool down to room temperature for another 1.5 months. This “centrifugal casting” process gives the mirror surface a special parabolic shape after cooling.