Sir William Herschel Telescope Enclosure

Overview

The Sir William Herschel Telescope Enclosure, designed and built for the Science and Engineering Research Council of the U.K. , offered many logistical challenges as it was built on a remote site on the Island of La Palma . The 4.2-meter telescope was the last telescope built using conventional primary mirror technology. Large mirrors require large telescope structures to move them, and these big structures have large thermal time constants, so the enclosure that surrounds them have to be designed to protect the telescope thermally.

For more information on WILLIAM HERSCHEL see http://www.ing.iac.es/PR/wht_info/

Challenge

The 600-ton enclosure structure continually tracks in azimuth as the telescope moves across the night sky so high manufacturing precision is necessary to ensure the enclosure runs smoothly, as do the shutter doors when they open and close to protect the telescope against wind. Our challenges were to design a large, movable structure that could be constructed on this remote site, and to design insulation and venting systems that could be manipulated with a changing environment.

Solution

Special self-steering bogies, with the ability to re-adjust their tracking as they moved off theoretical position, were designed to support the 600-ton structure. This feature allowed the enclosure structure to move thermally without imposing large radial loads into the lower supporting structure.

A continuous insulation skin placed on the inside of the dome reduced the solar radiation that entered the enclosure, and large purging fans removed warm air from the space between the outer shell and the read of the insulation skin. By carefully managing the thermal control system it was possible to hold the internal temperature to within +/- 1 degree F of the anticipated nighttime temperature.

A special crane was designed to handle both the enclosure and telescope components. It was shipped to the site in containers and manually erected on-site using hand winches.

Outcome

The Sir William Herschel Telescope continues to provide valuable support to the astronomical community. Many of the design features developed for both the telescope and enclosure are still being used in today's state-of-the art instruments.

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