ELT (Extremely Large Telescope) M2 M3 Cells

The project consists of the design, construction, validation and delivery of the cells of the secondary Mirror (M2) and the Tertiary Mirror (M3) of the ELT (Extremely Large Telescope), whose client is the European Southern Observatory (ESO), next to be installed on Cerro Armazones (northern Chile).

The ELT is the largest optical/infrared ground telescope ever built on the ground (39m diameter of the primary Mirror). Within its functionalities, the telescope will provide ESO with extremely sharp images, will have unmatched pickup power and an ability to compensate for the adverse effect of atmospheric turbulence. All this will allow detailed studies on planets and stars, the first objects in the Universe , supermassive black holes and the nature and distribution of dark matter and energy that dominate the Universe.

The particular design of the ELT allows the telescope to be characterized as a three-mirror anastigmat, which allows it to minimize the main optical aberrations (spherical, coma and astigmatism), used to allow fields of vision with greater amplitude: a 39 m segmented primary mirror (M1), a 4 m convex secondary mirror (M2) and a 4 m concave tertiary mirror (M3). Additionally, there are two flat mirrors that provide the folding of the three mirrors mentioned above, which send the beams to any of the Nasmyth bulbs along the telescope's elevation axis.

With respect to cells M2 and M3, their mechanisms guarantee the alignment of the telescope during observation and correct the deformations of the optics. They provide positioning adjustment at 5 degrees of freedom to align the mirror within the telescope and mirror shape adjustment, compensating for shape and fixed errors due to gravitational effects. They compensate for tens of nanometer errors on the mirror surface, using deformable structures and lateral supports, and provide the ability to align and track with absolute precision of tens of microns. The complete cells will exceed 6.5 meters and their weight will approach 12 tons. In the case of the mirrors, both mirrors have a measurement of 4 meters and their approximate weight is 3.2 tons.