eso8808-en-gb — Organisation Release
ESO Places Contract for World's Largest Mirror Blanks
12 September 1988
After a period of intense negotiation, the European Southern Observatory and Schott Glaswerke, Mainz (F.R.Germany) reached agreement about the delivery of four giant mirror blanks for the ESO Very Large Telescope (VLT) (ESO8716). The blanks will be made of Zerodur, a glass ceramic material. Each will have a diameter of 8.2 metres, an area of more than 50 square metres and a thickness of only 17.5 centimetres.
These optical mirrors are far larger than any others ever made for any purpose, requiring radically new, technological procedures.
In 1984, Schott performed the preliminary design study for these blanks. Since then, while the VLT design progressed at ESO, Schott undertook a technical development programme which culminated in the successful manufacture of spin-cast Zerodur blanks with diameters up to 4 metres.
The same technique will be used for the VLT blanks; it consists of pouring the molten material into a rotating, concave form. Due to the centrifugal force, the surface of the spinning blank takes on the desired concave shape, thereby minimizing the amount of material to be removed during the subsequent grinding phase. The use of the heat-insensitive Zerodur material will also allow fast testing during polishing.
The contract was signed this morning at the ESO Headquarters in Garching bei München, by Professor Harry van der Laan, Director General of ESO, and Mr. Erich Schuster, Member of the Board of Directors of Schott Glaswerke.
The decision to grant this important contract to Schott represents a crucial milestone in the VLT project and a major step forward in European optical technology.
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