ESO's Extremely Large Telescope Reaches 50% Complete Milestone

The European Southern Observatory's (ESO) Extremely Large Telescope (ELT) is making remarkable progress in its construction, having just surpassed the 50% completion milestone.

The ELT is set to become the largest telescope in the world for visible and infrared light, boasting a revolutionary 39-meter main mirror and earning its reputation as the "world's biggest eye on the sky." Located atop Cerro Armazones in Chile's Atacama Desert, the ELT's dome structure is rapidly taking shape, with engineers and construction workers assembling it at an impressive pace.

The ELT's main mirror and various other components are being manufactured by European companies, where work is also progressing smoothly.

Notably, the ELT will feature a groundbreaking five-mirror optical design, incorporating a massive main mirror (M1) composed of 798 hexagonal segments.

The manufacturing process for over 70% of the blanks and supports for these segments has been completed, while the casting and polishing of M2 and M3 are currently underway. Particularly impressive progress has been made on M4, an adaptive mirror that will continuously adjust its shape a thousand times per second to correct for atmospheric turbulence. All six of M4's thin petals have been finalized and are being integrated into their structural unit.

Additionally, all six laser sources, vital components of the ELT's adaptive optics system, have been produced and delivered to ESO for testing.

The development and production of all other systems required to complete the ELT, including the control system and the necessary equipment for assembly and commissioning, are also advancing well. Furthermore, the four scientific instruments that will equip the ELT are in the final design phase, with some already entering the manufacturing stage.

Extensive progress has also been made on the support infrastructure for the ELT, with most of it now in place at or near Cerro Armazones. For instance, the technical building, which will be used for storage and coating of various ELT mirrors, has been fully erected and fitted out. Additionally, a photovoltaic plant that supplies renewable energy to the ELT site has been operational since last year.

The construction of the ELT commenced nine years ago with a groundbreaking ceremony, and in 2014, the top of Cerro Armazones was flattened to make way for the colossal telescope.

While the initial phase of the project involved the meticulous design finalization of the majority of components and prototyping, along with testing of mirror segments and supporting elements, the completion of the remaining 50% is expected to progress much more swiftly.

The construction process faced challenges due to the COVID-19 pandemic, resulting in temporary site closures and delays in the production of telescope components. However, with production processes now fully resumed and optimized, the finalization of the ELT is projected to take only five more years. Nevertheless, building such a vast and intricate telescope carries inherent risks until it is fully operational.

“The ELT is the largest of the next generation of ground-based optical and near-infrared telescopes and the one that is most advanced in its construction. Reaching 50% completion is no small feat, given the challenges inherent to large, complex projects, and it was only possible thanks to the commitment of everyone at ESO, the continued support of the ESO Member States and the engagement of our partners in industry and instrument consortia. I am extremely proud that the ELT has reached this milestone.” - Xavier Barcons, ESO Director General

Planned to commence scientific observations in 2028, ESO's ELT is poised to address fundamental astronomical questions, including the existence of extraterrestrial life, the universality of the laws of physics, and the origins of the first stars and galaxies. Its revolutionary capabilities will transform our understanding of the Universe and prompt a reevaluation of our place within it.