VLT´s UT2 coating

The VLT's Unit Telescope 2 (Kueyen) primary mirror (M1) on its way to being recoated. A special truck carries the whole M1 cell, which weighs 45 tonnes, from the VLT platform down to the Main Maintenance Building (MMB). The truck moves at no more than 5 km/h, allowing engineers to follow it by walking fast. The driver has to be extremely careful and must never touch the brake! The cleaning of the VLT´s primary mirrors is a very delicate operation which takes place every 18 months and consists in removing the reflective aluminum layer by chemical washing and then recoating the mirror.