Validation of the thermal model of BepiColombo’s SIMBIO-SYS HRIC and its application to MPO’s orbits at Mercury.

This thesis work investigates the fidelity of a simplified thermal model of the High spatial Resolution Imaging Channel (HRIC) instrument, a component of SIMBIO-SYS (Spectrometer and Imagers for MPO BepiColombo-Integrated Observatory SYStem). It presents simulations results performed on the thermal model using the foreseen orbits of the Mercury Planetary Orbiter (MPO). SIMBIO-SYS comprises an integrated suite of imaging instruments onboard BepiColombo, including a stereo imaging system (STC), a high-resolution imager (HRIC), and a visible–near-infrared imaging spectrometer (VIHI). BepiColombo is a collaborative mission between the European Space Agency (ESA) and the Japanese Space Agency (JAXA), and it aims to explore Mercury's surface composition, morphology, geology, and magnetosphere. Launched in 2018, it consists of two orbiters: the ESA Mercury Planetary Orbiter (MPO), equipped with remote sensing and radio-science instrumentation, and the JAXA Mercury Magnetospheric Orbiter (MMO). MPO is scheduled to enter its orbit around Mercury by the end of 2025. Due to Mercury proximity to the Sun, its orbital resonance, inclination, and geological characteristics, MPO will encounter an extremely harsh thermal environment. Therefore, the orbiter, and in particular the instruments exposed to thermal fluxes, are equipped with sophisticated thermal control devices. Temperature detection systems onboard BepiColombo detected temperature increases in 2023, exceeding predictions made before launch. Additionally, the planned orbits of MPO were adjusted to accommodate constraints imposed by BELA (BepiColombo Laser Altimeter). These temperature increases must be carefully monitored to ensure optimal performance of sensitive instrument such as HRIC. Thus, new studies on the HRIC thermal model were necessary, and its reliability was assessed through validation procedures using the ESATAN-TMS software. Leveraging deep knowledge of the thermal environment in which HRIC will operate and analysing data obtained from the mission so far, comparisons were made between predicted thermal behaviour based on the model and actual thermal performance in space. Incident heat fluxes were calculated under direct Sun illumination and in orbits around Mercury. This analysis facilitated the identification of the most critical thermal scenarios. The methodology employed involved meticulous examination of temperature variations recorded by HRIC in different environmental conditions and orbital configurations. Insights gained contribute to the refinement and optimization of the HRIC thermal model, enhancing its accuracy and reliability for the future of the BepiColombo mission.