What will be the largest telescope in the world is already under construction. Its lens takes up so much space (39 meters in diameter) that, to give us an idea, it is almost as big as an arena. And its construction is so complex that it is made in several parts.
To keep the name from getting too complicated, its creators called the telescope the Extremely Large Telescope (ELT), and it is powered by the European Southern Observatory (ESO).
At the moment the first 18 segments of the telescope’s main mirror (M1) are already on their way to Chile, where construction is underway. Once arrived, the segments will be transported to the ELT’s technical facility at ESO’s Paranal Observatory in the Atacama Desert, where they will be coated in preparation for future installation on the telescope’s main structure.
Because it cannot physically be manufactured in one piece, M1 will be composed of 798 individual segments arranged in a large hexagonal pattern, with 133 additional mirrors intended to facilitate cladding of the segments, according to the Observatory.
The last stage of the production process of the M1 segments (polishing), was carried out by the world leader in the production of optical systems, Safran Reosc, located near Poitiers (in central France), in a completely renovated building to work on this delicate task .
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As part of the process, Safran Reosc developed new automation workflows and measurement techniques to ensure that polishing meets the high standards required for ESO’s ELT.
The irregularities of the mirror surface are less than 10 nanometers (less than one thousandth the width of a human hair). To achieve this level of performance, Safran Reosc used a technique called ion beam calculation, in which a beam of ions passes through the mirror surface and removes irregularities atom by atom. While only 18 segments have been delivered so far, Safran Reosc will soon deliver many more to ESO.
The construction of ESO’s ELT required the close involvement of numerous companies from Europe and Chile with ESO teams, highlighting that the telescope is a truly international endeavor, according to its creators.
The mirror segments were cast by the German company SCHOTT at its factory in Mainz, Germany, before being delivered to Safran Reosc (France) for polishing. Other companies involved in the work on the segment assemblies were the Dutch company VDL ETG Projects BV, which produced the delicate segment supports; the Franco-German consortium FAMES, which has developed and produced precision 4,500 nanometer sensors that monitor the relative position of each segment; and the German company Physik Instrumente, which designed and produced the 2,500 actuators capable of positioning each segment with nanometer precision.
After leaving France a few days ago, the 18 mirror-polished segments will travel more than 10,000 kilometers to the ELT construction site in Chile’s Atacama Desert. From there, ESO’s ELT will tackle the greatest astronomical challenges of our time and make yet unimaginable discoveries once it comes into operation at the end of this decade.
2024-01-01 14:13:00
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