eso9711 — Organisation Release
The Giant Coating Plant for the ESO VLT
16 May 1997
In August 1995, the European Southern Observatory signed a contract with Linde A.G. (Germany), for the supply of the coating unit for the giant mirrors of the ESO Very Large Telescope (VLT). Together with the main subcontractors, BOC coating technology (UK) , and Deggendorfer Werft (Germany), Linde has meanwhile completed the development, construction and pre-commissioning of the coating unit in Deggendorf, a town located at the Danube River, some 150 km northeast of Munich.
On May 14, 1997, the preliminary acceptance review meeting took place and it was concluded that the coating unit is fully capable of producing aluminum coating on the VLT mirrors with the specified quality.
The coating unit is a large vacuum chamber with a diameter of 9.4 meters and a volume of about 122,000 liters. The required ultra-high vacuum is generated by 8 cryo-pumps which are located on top of the vacuum chamber.
The chamber is divided into two halves by a horizontal flange sealed by two large O-rings. The mirror is loaded into the lower half of the chamber onto a whiffle-tree support system with 27 axial pads and laterally secured inside the central hole by 6 pads.
This support system is fixed on a central shaft which is driven by a high precision motor gear system arranged below the vacuum chamber. The 80 nanometer (80 millionth of a millimeter) thin aluminum coating is produced by utilizing the sputtering technology. During the coating process the mirror is rotated with a speed of 5 revolutions per hour under the sputter source, which is fixed inside the upper half of the vacuum chamber
The lower half of the vacuum chamber is mounted onto an air-cushion vehicle via 4 large spindles for closing and opening of the vacuum chamber. For loading and unloading of the mirrors the lower half of the chamber is moved on 8 air-cushions from the coating unit location to the mirror handling tool and vice versa.
Within the next weeks the coating unit will be dismantled at Deggendorfer Werft, packed and loaded onto a river barge. The vacuum chamber with its 9.4 meter diameter and 60 tons overall weight will be one of the largest pieces shipped for the VLT project.
The special transport will move from Deggendorf on the Danube, Main and Rhine rivers to Antwerp in Belgium. There the coating unit will be loaded onto an ocean-going ship leaving in the beginning of June for the Chilean port in Antofagasta, some 130 km north of the Paranal Observatory, the site of the VLT.
It is expected that the coating unit will arrive at Paranal by the end of July 1997. There it will be installed inside the new mirror maintenance building.
The completion of the erection and provisional acceptance of the coating unit is planned for the end of October 1997.