Ultra weighted support panels for main mirrors in the Extremely Large Telescopes

摘要

In the ELTs the weight of the mirror-systems is very important. In fact, the dimensioning both of the support structure and the auxiliary components, such as bearings and drives, depend on it. The mirrors require very stiff structures able to react quickly to dynamic and static stresses. Lightness and stiffness are therefore decisive elements to have a constant and excellent control of the mirror itself. An ultra-light and ultra-stiff panel, directly coupled to the mirror through actuators, allows to reduce to the minimum the quantity of material for the mirror and thus reducing also the weight, always guaranteeing the stiffness requirements. Therefore, this panel becomes an element constituting the mirror itself and it is also charged with the task of connection with the main structure of the cell. A chance for guaranteeing this weight-stiffness ratio is given by the use of the carbon fibre. Particularly, the use of high modulus fibre (pitch fibre) allows to obtain ultra-light mirror support structures with a 60% saving of weight compared to an equivalent steel structure. The in-depth study of the materials used (resin system, Carbon fibre type, adhesives, inserts) and the construction process, the number and the repeatability of the pieces, the experience acquired during the design and construction phases of the ALMA Prototype (Atacama Large Millimeter Array) allow to guarantee a proper control of the quality of the product with accessible and convenient costs considering also that the use of these materials allows to have lighter structures with lower operational costs and the maintenance of the materials in the years requires a lower use of resources.