ELT design status: the biggest dome in astronomy

The ELT Dome has been conceived for protecting the 39m ELT telescope, with its 86m base diameter and its almost 80m height. The rotating Dome is spherical to enhance the aerodynamic behavior; it weights about 6000 tons and it is provided with a 42m wide slit, to allow the telescope observation. The bearing structure of the Dome is a truss structure made of steel, having a base ring and a series of arch girders as its main elements. The Dome Rotation is performed by 36 trolleys, which are fixed to the top of the reinforced concrete Dome Base. Safety against seismic events is guaranteed by a dedicated Isolation and Damping System at the Dome Pier. The Dome is covered by a custom Cladding System, that has been tailored in order to provide the required thermal insulation and withstand the harsh Environmental Conditions of the ELT Site. With the aim of controlling the airflow around the Telescope, the ELT Dome is provided with a series of 89 Louvers, which are distributed among the rotating and the fixed structures. Besides, a Windscreen made of four permeable aluminum panels protects the Telescope; each panel spans over the 42m slit and is 10m high. The Windscreen is able to track with the Telescope on a 20 to 70deg range of the altitude angle. The Auxiliary Building is a ring surrounding the Dome Pier and houses the Dome Technical Rooms, thus guaranteeing a radial distribution of all the Services. Among the Dome Supplies, a custom HVAC System is able to control the Telescope Chamber temperature with a ±2°C precision. The ELT Dome is provided with specific Plants so to supply Power to all the relevant loads and to the Electrical Equipment, as well as with a custom Global Control System and a series of Safety Systems.