PLATO: detailed design of the telescope optical units

The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the three medium class (M class) missions selected in 2010 for definition study in the framework of the ESA Cosmic Vision 2015-2025 program. The main scientific goals of PLATO are the i) discovery and study of extra-solar planetary systems, (including those hosting Earthlike planets in their habitable zone) by means of planetary transits detection from space and radial velocity follow-up from ground, and ii) the characterization of the hosting stars through seismic analysis, in order to determine with high accuracy planetary masses and ages. According to the study made by the PLATO Payload Consortium (PPLC) during the PLATO assessment phase, the scientific payload consists of 34 all refractive telescopes having small aperture (120 mm) and wide field of view (greater than 1000 degree2) observing over 0.5-1 micron wavelength band. The telescopes are mounted on a common optical bench and are divided in four families with an overlapping line-of-sight in order to maximize the science return. In this paper, we will describe the detailed design of the Telescope Optical Units (TOUs) focusing on the selected optical configuration and the expected performances.