Why not exposed extreme large telescopes?

Abstract

In designing and building extreme large optical telescopes of sizes above 10m main aperture diameter, the effort for protecting the telescope against environmental influences gets remarkable large in engineering efforts as well as in costs. Large radio telescopes of similar size are built in "exposed" design, which means, that the protections for the sensitive components are integrated into the telescope itself. Long ranging experience even for sub-millimeter wavelength radio telescopes is available. Why not thinking the unthinkable and design exposed extreme large optical telescopes? The paper describes methods to protect the optics, to protect the structures and mechanics, and to overcome the wind and temperature induced disturbances during operations. It shows also means to integrate large and comfortable rooms for the science instruments with free access during operations into the protected area of the telescope.