Initial estimation of the effects of coating dishomogeneities, surface roughness and contamination on the mirrors of Ariel mission telescope

Ariel is ESA M4 mission to survey exoplanet atmospheres through transit spectroscopy in the 0.5-7.8 μm waveband. Launch is scheduled for 2029. Ariel payload consists of a 1-m class, all-aluminum telescope operating below 50 K. Telescope mirrors will employ a protected silver coating to improve reflectivity and to prevent degradation. An initial estimation of the overall throughput achievable by the telescope for the entire scientific duration of the mission is presented here. The starting point is the reflectivity of the coated mirrors as measured on samples, and throughput losses caused by surface roughness, particulate and molecular contamination, and cosmetic defects.