The European Southern Observatory (ESO) is at present constructing the Extremely Large Telescope (ELT), a 40-m class astronomical telescope on top of the 3046 m high mountain Cerro Armazones in the central part of Chile’s Atacama Desert. In combination with its powerful facility instruments, it will be the largest optical/near-infrared telescope in the world, also known as the biggest eye on the sky. The instrument roadmap lists up to eight scientific instruments, whereof the first light instruments were already completing their final design phase. Nowadays massive instruments, each weighing about 20 to 40 tons, are requiring powerful cryogenic systems for cooling the cold mass of several tons of each individual instrument.
The paper outlines the cryogenic requirements defined by the ELT instrument suite and describes concept and design of the cryogenic infrastructure. A centralized and fully automated system combining open loop Liquid Nitrogen cooling in combination with low-vibration mechanical cryo-coolers is the baseline for providing the required cooling capacity and temperature levels as low as 4 Kelvin. Project status and timeline are presented.
For the ELT, a total of 931 M1 Segment Assemblies will be manufactured. These will be of 133 different types, 7 copies each, with different optical and mechanical properties. The manufacturing of the segment support, the glass blank and the polishing will be done by industrial partners. ESO will be responsible for the shipment of the Segment Assemblies to Chile, for the integration of the edge sensors and their electronics, and for the cleaning and coating. After performing several health- and quality-checks, the Segment Assemblies will be temporarily stored in the warehouse, before being installed at the telescope and eventually recoated around every 2 years. The telescopes and instruments for optical astronomy are usually prototypes, while a new approach is required to manage such a series production of crucial components, which differ in small but significant aspects. In this paper, we will present the processes we have developed to manage the series production of M1 Segment Assemblies for the ELT, starting from the reception of the Segment Assemblies in Chile, inspection, installation of sub-components, health-checks, storage, and installation at the telescope.
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