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In 1966, Hans Elsässer, the founding director of the Max Planck Institute for Astronomy (MPIA), asked the company if it could produce large castings of almost 4 meters using low-expansion glass-ceramic for telescope mirror substrates. In 1969, the MPIA ordered a 3.6 m (12 ft) mirror blank, along with ten smaller mirror substrates.
Today, glass-ceramic products such as transparent mirror blanks and stove tops, and cookware are manufactured and in daily use. These products include trade names of Zerodor, Hercuvit, and Pyroceram, most of which have low or zero thermal expansion, which allows them to be exposed to rapid temperature changes or localized heating or cooling.
The mirror had a physical diameter of 104 cm and was made from Cer-Vit low-expansion glass. [7] In the 21st century, the 41 inch was placed on the robotic Skynet telescope network, along with a 24-inch telescope at Yerkes.
Ultra low expansion glass has an coefficient of thermal expansion of about 10 −8 /K at 5–35 °C. [2] It has a thermal conductivity of 1.31 W/(m·°C), thermal diffusion of 0.0079 cm 2 /s, a mean specific heat of 767 J/(kg·°C), a strain point of 890 °C [1634 °F], and an estimated softening point of 1490 °C [2714 °F], an annealing point ...
Construction of the Perkin-Elmer mirror began in 1979, starting with a blank manufactured by Corning from their ultra-low expansion glass. To keep the mirror's weight to a minimum it consisted of top and bottom plates, each 25 mm (0.98 in) thick, sandwiching a honeycomb lattice.
A special 240 in (6.1 m) 25,000 lb (11 t) mirror cell jig was constructed which could employ five different motions when the mirror was ground and polished. [20] Over 13 years almost 10,000 lb (4.5 t) of glass was ground and polished away, reducing the weight of the mirror to 14.5 short tons (13.2 t).