This paper work reports the results of the Preliminary Design Phase of the Floating Sphere Telescope that has been presented during the AOMATT in
Xi'an, China, November 2005. The FST represents a new design for the realization of an ELT with a 40-metre primary mirror. The innovative concept
of the structure and the sub-systems that constitute it as well as the use of new materials and technologies allow to obtain an instrument able to comply
with very extreme specifications for structure such as ELTs. The structure allows to improve the stiffness to weight ratio of the structure, to introduce
higher damping while maintaining under control the construction and maintenance costs.
In comparison with the previous study, the following steps have been implemented:
• Refining and optimizing the structural design and the FEA model, in particular we have included a realistic model of the constraint provided
by the fluid used for flotation by characterization of its viscous and elastic properties in order to estimate the additional modal damping
introduced by the flotation as function of fluid properties and geometry.
• Designed (and introduced in the FEA model) various types of drives such as friction drives, tensioned ropes in "hexapod" configuration,
"gravity" drives (moving ballast) and combinations of them to evaluate potential tracking performances
• Designed the necessary connections for various types of utilities (power, data, cooling)
• Included in the structural design a more elaborate optical design to satisfy specific science requirements (e.g. multiconjugate AO)