Towers for Antarctic Telescopes

Abstract

To take advantage of the exceptional seeing above the boundary layeron Antarctic sites, a high-resolution telescope must be mounted on asupport tower. An open transparent tower of framework minimizes theupward temperature-disturbed airflow. A typical minimum height is30 m. The tower platform has to be extremely stable againstwind-induced rotational motions, which have to be less thanfractions of an arc second, unusually small from a mechanicalengineering viewpoint. In a traditional structure, structuraldeflections result in angular deflections of the telescope platform,which introduce tip and tilt motions in the telescope. However, astructure that is designed to deflect with parallel motion relativeto the horizontal plane will undergo solely translation deflectionsin the telescope platform and thus will not degrade the image. Theuse of a parallel motion structure has been effectively demonstratedin the design of the 15-m tower for the Dutch Open Telescope (DOT)on La Palma. Special framework geometries are developed, which makeit possible to construct high towers in stories having platformswith extreme stability against wind-induced tilt. These geometricsolutions lead to constructions, being no more massive than a normalsteel framework carrying the same load. Consequently, theselightweight towers are well suited to difficult sites as onAntarctica. A geometry with 4 stories has been worked out.