ESO’s ELT halfway through construction (Invited Paper)

The construction of the ESO’s Extremely Large Telescope (ELT) passed it 50% completion milestone in 2023. There has been good progress on all fronts over the past two years. The construction site at Armazones (Chile) went from a flat landscape dominated by rocks and lean concrete to a mountain top housing finished structural concrete foundations and an 80m-high dome steel structure. In Europe, the manufacturing of the telescope structure is half complete; tens of M1 segments have been polished to excellent optical quality; the M2 mirror is quickly approaching its final figuring accuracy; the M4 adaptive mirror has received all its six Zerodur® thin shells and is progressing to full laboratory integration; the M5 has reached a critical step with the brazing of the six CVD-coated SiC petals; the two large Pre-focal Stations are close to start their final testing; the four instruments are all in final design phase with some having started procurement and more. This paper summarizes the current status of the ESO’s ELT Construction.