The first mirrors intended for Extremely Large Telescope (ELT) of the European Southern Observatory (ESO) They have arrived punctually at their future location in Chile, coinciding with the Christmas celebration. However, the unpacking process will take a little longer, especially considering that everything related to the ELT must be done carefully.
These 18 mirrors, which completed their journey around the world in late December, constitute just a fraction of the 798 hexagonal pieces that will eventually be assembled to create a mirror of colossal dimensions, spanning 128 feet. This mirror, the largest in the world in the category of optical and infrared telescopes, has the mission to begin capturing light from alien worlds, ancient galaxies and supermassive black holes in the year 2028if everything goes according to plan.
Manufacturing a telescope mirror approximately 8 meters wide remains an almost impractical process, even with the most advanced modern facilities for working with glass. Most of the world’s large telescopes have main mirrors that are arrays made up of multiple smaller mirrors, perfectly aligned and mounted in a structure. Each of the segments that make up the ELT mirror has dimensions of around 1.4 meters wide and a thickness of less than 0.7 cm. The surface of the glass must be absolutely smooth, and the margin of error is extraordinarily small, less than one thousandth of the width of a human hair.
Marc Cayrel, optomechanics project manager for the ELT, notes (via Inverse): “To achieve the necessary optical performance, the segments must have a precision in their shapes that is within fractions of the wavelength of light. The average surface quality required for the segments is 15 nanometers, while the width of a full human hair is about 70,000 nanometers.”
The long journey of the telescope segments
The mirror segments made a long journey from a manufacturing facility in Germany, where the glass was melted, to another facility in France, where they were polished using a microscopic ion beam. This process, known as ion beam imaginghas been used in the manufacture of numerous telescope mirrors, including those at the Keck Observatory in Hawaii and the Gran Telescopio Canarias on the island of La Palma.
The main challenge has been adapting existing techniques and processes to allow for mass production of the segments, at a rate of approximately one per day after the initial adaptation period, Cayrel says.
Each batch of segments, starting with the first 18, undertakes a long sea voyage from France to Chilefollowed by a shorter drive through the Atacama Desert to your final destination at the summit of Cerro Armazones.
The protection of these segments goes beyond the usual use of bubble wrap. Mirrors must be transported in temperature-controlled containers, equipped with special air cushions. Each segment is stored in a special bag filled with dry nitrogen to prevent deformation of the thin sheets. glass due to humidity or condensation, and motion dampers are installed inside the container to protect them from vibrations, shocks and other possible impacts.
According to Cayrel, “although segment protection is maximized, sea containers use common trade routes and the risk of damage is typically very low.”
Mission: capture deep space
Once in Chile, the mirror segments must still receive an extremely thin coating of silver, just 150 nanometers thick. The process of applying silver to meticulously polished glass is carried out using a technique called magnetron sputtering, which involves applying a super-thin, super-smooth layer of silver onto the mirror surface in a vacuum environment.
Once all the segments are covered, the first 18 of them must wait patiently until their 780 companions join them. When finally assembled, the 798 glass and silver hexagons will be meticulously aligned to form the ELT’s primary mirror. This mirror will capture light from distant objects and redirect it toward a secondary mirror, which in turn will direct it toward the instruments. intended to help astronomers interpret all those images.