The PLATO TOU optical design: description, properties, and nominal performances

The ESA M size mission PLATO (PLAnetary Transits and Oscillation of stars) is planned to be launched in the 2026, with the aim of discover exoplanets that will be characterized with unprecedented precision. The optical elements of PLATO are 26 small telescopes, the TOUs (Telescope Optical Units), that using partially overlapping Fields of View will permit instantaneous sky coverage larger than 2100 square degrees. Each TOU has an aperture of 120 mm diameter assured by an internal stop, and it is composed by 6 lenses, the frontal one having an aspherical surface and the last acting as field flattener. The mechanical structure is realized mainly in AlBeMet. We here describe the optical design, summarizing several optical properties (materials, coatings, etc.), and report on nominal performances of the TOU system.