Consolidated Thermo-Mechanical Modelling of the ESA THESEUS Mission Infrared Telescope

The InfraRed Telescope (IRT) is a cornerstone instrument of the Transient High-Energy Sources and Early Universe Surveyor (THESEUS) mission, candidate for the M7 Cosmic Vision call and designed to detect transient cosmic events through near-infrared photometry and spectroscopy. Operating in Low Earth Orbit (LEO), the IRT faces severe thermo-mechanical environment that directly threatens its submicron optomechanical stability. To address this primary engineering challenge, this paper presents the application of an advanced, dual-track finite-element modelling pipeline tailored on the instrument's telescope Structural, Thermal, and Optical Performance (STOP) requirements. The first track employs a high-fidelity thermoelastic design model: by mapping discrete temperature fields from mission-level solvers onto the structural mesh, it isolates local reflecting surface deformations from rigid global misalignments. The second track establishes a masstuned, neutral model optimized for industry-standard solvers, ensuring seamless structural integration at the spacecraft bus level. Validated through an extensive and detailed numerical campaign, this systematic approach provides a deterministically controlled baseline, proving robust versus orbital perturbations and paving the way for the upcoming experimental correlations.