The ELT M2 and M3 cells: key design aspects

Abstract

The European Extremely Large Telescope (ELT) is a 39-m Class telescope with active and adaptive capability included into the telescope being developed by the European Southern Observatory (ESO). The Telescope Secondary (M2) and Tertiary (M3) Mirrors are 4-metre class Zerodur mirrors close to 3.2 Tons that are passively supported by Cells with an 18 points axial whiffletree and a warping harness system that allows to correct low order deformations of the Mirrors. Laterally the Mirrors are supported on 12+2 points by Lateral Supports. In addition, the Cells have alignment capabilities by means of a high precision hexapod. SENER has been contracted by ESO for the design, construction, validation and delivery of the ELT Secondary Mirror (M2) and Tertiary Mirror (M3) Cells. The Cells’ mechanisms guarantee the alignment of the Telescope during observation while correcting optics deformations. In this process, a high precision hexapod will be responsible for aligning and tracking the mirrors and an active structure will be used to compensate errors in the mirrors’ surface. These are large-size critical elements of the Telescope that require extremely high precision levels to give the Telescope optimal image quality. This manuscript describes the preliminary design and key aspects of the ELT M2 and M3 Mirrors Cells mechanisms, in particular the Mirror Suppor.