The requirements of telescope enclosures

Telescope enclosures are a very particular type of buildings. They must fulfill an unusual set of requirements, which may be briefly outlined as follows:

1. In the closed position, the enclosure shall provide weather protection and a controlled environment (in particular with respect to thermal conditioning and cleanliness) for the telescope and its instrumentation.
2. In the configuration for observation, the enclosure shall allow a free field of view to the telescope. The enclosure should also provide the best atmospheric environment for the telescope observations. This has multifold aspects from the protection of the telescope from wind loads that may affect its guiding accuracy to the prevention or minimization of local seeing effects. These objectives represent the greatest challenge to the designer.
3. The enclosure shall provide access to the telescope for normal and extraordinary maintenance and include handling facilities for installing and removing large pieces of equipment like the primary mirror and the instruments that have to be removed and replaced regularly.

In Appendix one finds a brief description of the enclosure designed by the author for the ESO VLT 8-m telescopes, which illustrates in particular all the practical aspects related with servicing and maintainance that must be taken into account in the design of these buildings.

With all its multifold requirements the design process of a telescope enclosure is a complex matter which should require a rigorous concurrent engineering approach. A main task within this process is constituted by the system analysis of the interaction of the enclosure characteristics with the optical performance of the telescope. Very schematically, the design process may be illustrated by the figure below.

  
Figure: Schematic of the concurrent engineering process required for the design of telescope enclosures

The next section outlines the evolution of engineering and design concepts for telescope enclosures during the past 20 years. Some case histories will illustrate the main problems associated with the design of these special buildings.