An exciting moment: The cover of the casting mold is lifted. The viscous glass inside still has a temperature of 1,000 degrees Celsius.
Through the Fire to Reach
for the Stars
Precision mirrors for telescopes owe their optical qualities to ZERODUR®, a special glass ceramic that retains its unique characteristics, despite variations in temperature.
On June 2, 2006, at SCHOTT in Mainz, the elements were cast that will help us to see the world beyond. A glass mass that glows white was on its way to becoming a four-meter mirror substrate for use in a telescope.
“The melted mass that flows into the casting mold has a temperature of over 1,500 degrees Celsius,” explains Peter Hartmann, head of the company’s astrospace department. The men who continually check the fill level of the mold all wear shiny silver heat protection suits. However, experience in handling this proven material has been gathered over the last 30 years. In twelve to fifteen months, this molten mass will have turned into the glass ceramic ZERODUR®, which is an ideal material for many different applications, because its dimensions hardly change at all with changes in temperature.
Dr. Helmut Olyschläger, Head of the Optical Materials Business Segment, explains, “The steel rails of ten kilometers of train tracks increase in length by two meters when the temperature rises by 20 degrees Celsius. A piece of ZERODUR® with the same length would expand by only one centimeter.” For this reason, a ZERODUR® telescope mirror retains the same imaging characteristics, regardless of the temperature.
Heat wave of over 1,000 degrees Celsius
Customized: Not only manufacturing, but also transporting the four-meter telescope substrate that had just been poured requires the highest precision.
The journey progresses
at a snail’s pace
on a main road that
The valuable component will most likely be sent to the National Optical Astronomy Observatory in Tucson, Arizona. If all goes as planned, five projects involving a total of eight four-meter mirrors will be realized over the next few years. As soon as the telescope mirrors begin to deliver extremely sharp images of the night sky, no one will even remember how much heat was involved in producing them.
100 Years of Astronomical Mirrors from SCHOTT
ZERODUR® glass ceramic: extremely temperature resistant
More about SCHOTT ZERODUR®
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