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Safran Reosc produces key optics for Europe’s future ELT


In May 2017, the European Southern Observatory (ESO) awarded Safran Reosc the contract to polish, mount and test all segments in the M1 primary mirror for Europe’s Extremely Large Telescope (ELT). Including this contract, Safran Reosc is now responsible for polishing and integrating four of the five mirrors on what will be the world’s largest telescope.

Safran Reosc to polish four mirrors on world’s largest telescope

The ELT will be able to gather 16 times more photons than today’s best telescopes, which means it can detect stars with 1/16 of the brightness, while also providing four times better resolution. Being built in Chile on the Cerro Armazones mountain (3,046-meter altitude), it will allow astronomers to make significant progress on stellar archeology, the discovery and characterization of exoplanets, etc. In particular, it will be the first earthbound telescope capable of detecting water on small exoplanets in orbit around stars similar to our Sun. “First light” (start of operation) is expected in 2024.

A technological tour de force by the world leader in advanced optics for astronomy

A telescope’s precision depends on how well the mirror is polished – a crucial and highly demanding step.

The M1 primary mirror is 39 meters in diameter, and is designed to collect light and transmit it successively to the M2, M3 and M4 mirrors.

Safran Reosc will polish all 931 optical segments over the course of this contract, lasting seven years. Each segment is an aspherical, hexagonal glass-ceramic mirror, measuring 1.5 meters from point to point. All segments will be polished until their surface irregularities are so small that they would be no higher than a ladybug if each segment were as big as France! During the production phase, lasting three years, the segments will be delivered at a rate of one per day.

The M2 secondary mirror is also a technology challenge: it will be the largest single-piece convex mirror ever made. To measure its optical quality, Safran Reosc will design and build a large, very-high-precision interferometry test bench.

The M4 mirror represents another daunting technology challenge. Comprising six petals of a glass-ceramic material, it will be polished by Safran Reosc until it is barely two millimeters thick, varying no more than a few microns. These parts, the only ones of their kind in the world, will take months of work. The M4 mirror is based on the adaptive optics principle, in which the surface is deformed automatically to compensate for atmospheric disturbances. It will give scientists images with resolution equivalent to a telescope in space, making it a highly critical part.


The company expands to meet the ELT challenge

Safran Reosc will create 90 new jobs to meet the demanding specifications for the ELT contract. Forty of these positions will be at its main facility in Saint-Pierre-du-Perray, near Paris, where the company is reconfiguring its installations and developing the powerful robots and test equipment needed for such a large-scale project. Fifty more jobs will be created at Safran’s Poitiers plant, specialized in optics and optronic (electro-optical) equipment. For this contract, the Poitiers plant will open a new production center dedicated to segments for the M1 mirror.