Design And Performance Of Large Telescopes Operated In Open Air

Abstract

Innovative designs of enclosures are being studied for the generation of large telescopes which are presently being developed, essentially in order to keep costs from increasing unacceptably with the size of the telescopes. These studies and the generally positive experience with MMT-type buildings, largely open to the wind during observation times, are confirming the trend toward a radical change of phylosophy in the concept for telescope enclosures, which recognises that in many cases the open air environment is more favourable to optimum telescope operation than the nominally stable and controlled environment inside a classical dome. This approach has been fully taken in the preliminary design of the ESO Very Large Telescope array which sees the telescopes operated essentially in theAfree atmosphere, being only protected against strong winds by a semi-permeable wind screen'. The aim of the preliminary studies was to achieve a comprehensive view of the different aspects of the open air environment and their influence on the design of the telescope and its performance. The paper describes some of these studies where we have tried, sometimes at the price of simplifying approximations that sacrifize quantitative accuracy, to identify the real phenomena and the parameters that most influence them, evidencing the orders of magnitude of the physical quantities involved.