Mr. Gianmarco Franceschini Profile

Gianmarco Franceschini

at Cimolai SpA

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Proceedings Article | 13 December 2020 Poster + Presentation + Paper

ELT design progress: The main structure

Leo Colussi, Marco Colussi, Gianmarco Franceschini, Pascal Martinez, Maximilian Kraus

Proceedings Volume 11445, 114455G (2020) https://doi.org/10.1117/12.2562429

KEYWORDS: Structural design, Telescopes, Optical instrument design, Large telescopes, Mid-IR, Mirrors, Buildings

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The Main Structure (MS) of the Extremely Large Telescope (ELT) is a 40 m class optical, near and mid-infrared telescope, under construction at Cerro Armazones, in the Chilean Andes. The MS is characterized by an Alt-Azimuth mounting weighting about 3700 t. It is divided in three major sub-systems: the Azimuth tracks, fixed to a concrete pier, which sustain the whole telescope weight; the Azimuth Structure, which allows the rotation around the vertical axis and sustain the Altitude Structure; the Altitude Structure, which allows the rotation around the horizontal axis. The MS consists in a steel space-frame structure, highly optimized to guarantee dynamical requirements and system level performances in general, not least pointing stability and tracking capabilities, reducing the rotating mass as much as possible. A fundamental design constraint has been the need for minimizing repeatable and non-repeatable deflections, particularly for the Altitude Structure, that hosts the segmented M1 mirror unit and all the main optics. Care has also been taken to guarantee survival conditions, particularly in the design of an effective seismic isolation system, capable to adequately limit Hosted Units (HU) accelerations and deformations. Finally, the major design challenge, in general, has been the need to design the system, having its overall dimensions and masses characteristics of large civil structures, like modern steel buildings and sports arenas, in order to be compatible with the strict requirements typical of extremely high precision machines and telescopes.

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