An artist’s rendering of the planned internals of the European Extremely Large Telescope (ELT), including its vast, segmented primary mirror, M1. Two European firms, the German company Schott and the French company Safran Reosc, have been awarded contracts to create the mirror segments for M1—which, when assembled, will be the largest mirror ever made for an optical telescope. [Image: ESO/L. Calçada/M. Kornmesser]
Five months ago, the European Southern Observatory (ESO) announced a round of contracts to make the technically challenging secondary and tertiary mirrors and associated controls for its behemoth European Extremely Large Telescope (ELT). Now, ESO has announced final agreements with the firms that will build the scope’s big enchilada—the 39-m primary mirror, which, when completed, will be the largest ever made for an optical telescope.
One of the big winners, as in previous rounds, is the German firm Schott AG, which will make the mirror blanks for the each of the 798 1.4-m-diameter hexagonal segments of the ELT’s primary (M1) mirror. Schott will fashion the blanks out of its proprietary low-expansion-coefficient ceramic Zerodur. Previously, Schott had won contracts to use the same material to create the substrates for the scope’s substantial secondary (M2) and tertiary (M3) mirrors, as well as the deformable quaternary (M4) mirror; the new contract confirms that the facility will be an all-Zerodur show.
The French company Safran Reosc, meanwhile, obtained the contract to create the mounting structures for the M1 segments, and to figure, polish, mount and test the systems before delivery. The polishing, to a maximum surface irregularity of 10 nm, will represent a formidable technical challenge. Over the course of seven years, according to ESO, Safran will gradually scale up until it is producing the finished mirror segments at a rate of one a day. The work will take place at the company’s high-tech facility in Poitiers, France. Safran had already, in previous bid rounds in 2015 and 2016, received contracts to handle work on the ELT’s M2, M3 and M4 mirrors.
Both Schott and Safran have a previous track record with ESO, having worked on the organization’s Very Large Telescope (VLT). ESO says that the new M1 contract with Safran in particular will be the second-largest contract for ELT construction, and the third-largest contract that ESO has ever let.
Indeed, the ELT seems to be a project that invites superlatives. ESO points out that, once the primary mirror is built, it will be “by far the largest ever made for an optical telescope,” and that its 798 segments will together “collect tens of millions of times as much light as the human eye.”