The Actual Optical Design and Preliminary Optomechanical Tolerances of the High Resolution Imaging Channel for the BepiColombo mission to Mercury

This paper deals with the optical design and preliminary optomechanical tolerances of HRIC, the High Resolution Imaging Channel of the SIMBIO-SYS instrument, selected as part of the scientific payload for the ESA cornerstone BepiColombo mission to Mercury. Under the lead of Italy (Principal Investigator: E. Flamini), the project is based on an international co-operation with Institutes from France and Switzerland. Starting from the stringent scientific requirement of 5m ground pixel scale @ 400 km from the planet surface, a robust optical design based on a catadioptric Ritchey- Chretien configuration modified with a dedicated corrector camera has been achieved. The optimized configuration is convenient in terms of image quality, number of optical elements, and total length. The channel guarantees a corrected FoV of about 1.5° and allows the achievement of the required resolution with a detector of 2k × 2k pixels. The telescope is diffraction limited, thanks to its focal ratio (F/8), and shows an optimised radiometric flux within the operative spectral range (400 - 900 nm). The channel is equipped with one panchromatic and 3 selective filters. The operation plan foresees the coverage of at least 20% of the whole Hermean surface with the HRIC. The preliminary optomechanical tolerances and the corresponding image quality have been analyzed. Further thermo-mechanical analysis is in progress, which is beeing analyzed by means of ray-tracing tools for image quality evaluation.