Mirror mirror on the wall... err, sorry: on ESO's Extremely Large Telescope! The first segments of the primary mirror of the ELT now have a shiny layer of protected silver.
Once fully assembled, the primary mirror will be 39 m wide. It will consist of 798 of these hexagonal segments, working together as a single mirror thanks to a complex system of sensors and positioning actuators with nanometric accuracy.
@Lafiel The segments will be recoated every couple of years. Since there are 798 segments, every day we'll have to remove 2 of them for recoating, and replace them with spares.
Each segment can be pushed above the neighbouring ones. Then a special crane will grab it from dedicated gripping points – those trumpet-shaped tubes you see under the segments.
@Lafiel To clarify: polishing and coating are two different things. The polishing is done in Europe and the coating at Paranal in Chile. During normal use all that happens is that the coating slowly loses reflectivity, hence the need for recoating.
@astro_jcm - I saw some work on this telescope being done in the observatory in Edinburgh, Scotland. Do you happen to know what work they are doing there? Not the mirror, I think.
@Lafiel The spares will be used all the time. Every day we'll have to remove 2 segments for recoating, replacing them with spares. Another 2 segments the next day, etc, every single day, so that each segment has a fresh coating every ~2 years or so.
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