Episode 120 // Chile Chill 10 - "VLT Main Mirror Recoating," Music: breitbandkater - Traumtierchen
Far away in Chile’s Atacama Desert, ESO’s Very Large Telescope (VLT) sits 2635 metres above sea level.
These four huge telescopes contain some of the biggest mirrors in the world, capturing billion-year-old light.
To catch as much faint light from the cosmos as possible, these mirrors have to be extremely reflective.
A layer of aluminium, just 80 nanometres thick, coats the mirror surface
— more than 50 square metres of ZerodurⓇ glass ceramic.
Over time the mirrors are exposed to dust and other pollutants.
To maintain high-quality astronomical images,
the mirrors must be cleaned and the aluminium coating regularly replaced.
Recoating is an intense and laborious procedure.
It is vital that the mirror is not scratched or damaged in any way.
There is no replacement mirror if this goes wrong!
The eight-day operation begins by carefully driving the 23-tonne mirror to the recoating plant.
First, the underside is cleaned by hand to remove all oils, particles and other contaminants
The mirror is then taken to the clean room for another round of cleaning,
to ensure that no large pollutants or dust remain on the mirror’s surface.
Acid then removes the aluminium film, revealing the true amber colour of the material underneath.
After final rinsing and drying, the mirror is moved to the vacuum chamber.
After the air is sucked out,
electrically-stimulated plasma completes the last cleaning and drying of the optical surface.
Finally, aluminium particles are vapourised onto the mirror to create a thin, new, perfectly-reflecting coating.
A total of only 12 grams!
One final check is made to measure the reflectivity.
The mirror is then returned home to the VLT
to continue producing some of the most remarkable observations ever made.
Transcribed by ESO; Translated by --.