Announcement

Contract Awarded for Coating Plant for ELT Primary Mirror Segments

18 June 2018

The contract for the design, manufacture and installation of the coating plant for the primary mirror segments of ESO’s Extremely Large Telescope has been awarded to Belgium-based AGC Glass Europe. The company will be responsible for the construction of the facilities at ESO’s Paranal Observatory in northern Chile which will be used to coat the telescope’s individual primary mirror segments with a protected layer of highly reflective silver.

The contract was signed by Patrick Van Bortel, Vice-President of Industrial Glass and New Businesses, AGC Glass Europe, and Xavier Barcons, Director General of ESO, at a ceremony held at ESO Headquarters in Garching, Germany on 18 June 2018. A third signatory, Philippe Bastien, Regional President Building and Industrial Glass, AGC Glass Europe, was unable to attend the signature event and signed the contract beforehand.

Christian Klima, the Honorary Consul of the Kingdom of Belgium in Bavaria and Quentin Derzelle, the Trade and Commercial Attaché to the Honorary Consulate of the Kingdom of Belgium in Bavaria were also in attendance, as was the Belgian Delegate to the ESO Finance Committee, Alain Heynen from Belspo.

ESO’s Extremely Large Telescope — currently under construction on Cerro Armazones, high in the Atacama Desert — will have a 39-metre primary mirror consisting of 798 individual mirror segments.

The planned coating plant will use a process known as magnetron sputtering to coat each individual mirror with a thin layer of silver and a protective coating. A similar process is currently used to coat the 8.2-metre mirrors of the Very Large Telescope with aluminium. However, by using a more reflective silver coating the ELT will be able to gather more light — allowing ESO astronomers to observe the night sky in astonishing detail.

The contracts for the casting and polishing of the mirror segments have already been signed. The 798 hexagonal segments will be produced from the low-expansion ceramic material Zerodur® by SCHOTT, before being passed to Safran Reosc, who will design the mounting interfaces, polish the segments, integrate them into their support systems, and then perform optical tests before delivery [1].

The new contract secures the facility needed to coat the mirror segments, both before and during ELT operation. As the giant mirror will be open to the night sky each night, the mirror segments will accumulate dust and become less reflective over time, and will have to be regularly recoated — at a rate of several mirror segments per day.

AGC Glass Europe has a long history of innovation in glass technology, and will use its experience to meet the challenge of keeping the ELT mirror at peak optical performance — allowing ESO to tackle some of the biggest scientific challenges of our time.

Notes

[1] Each mirror segment will have surface irregularities no larger than 10 nanometres. This is extraordinarily precise — roughly 10 000 times smaller than the width of a human hair. If the mirrors were scaled up to the size of France, the largest irregularities would be the size of a ladybird!