To take advantage of the exceptional seeing above the boundary layer
on Antarctic sites, a high-resolution telescope must be mounted on a
support tower. An open transparent tower of framework minimizes the
upward temperature-disturbed airflow. A typical minimum height is
30 m. The tower platform has to be extremely stable against
wind-induced rotational motions, which have to be less than
fractions of an arc second, unusually small from a mechanical
engineering viewpoint. In a traditional structure, structural
deflections result in angular deflections of the telescope platform,
which introduce tip and tilt motions in the telescope. However, a
structure that is designed to deflect with parallel motion relative
to the horizontal plane will undergo solely translation deflections
in the telescope platform and thus will not degrade the image. The
use of a parallel motion structure has been effectively demonstrated
in the design of the 15-m tower for the Dutch Open Telescope (DOT)
on La Palma. Special framework geometries are developed, which make
it possible to construct high towers in stories having platforms
with extreme stability against wind-induced tilt. These geometric
solutions lead to constructions, being no more massive than a normal
steel framework carrying the same load. Consequently, these
lightweight towers are well suited to difficult sites as on
Antarctica. A geometry with 4 stories has been worked out.