Multispectral thermal imager STOP analysis for the Harmony mission

Harmony is an ESA Earth Explorer mission slated for launch in 2029. Harmony is dedicated primarily to the observation of small-scale motion and deformation fields of the ocean surface, glaciers and ice sheets, and solid Earth. It will operate two satellites in formation with Copernicus Sentinel-1D. Each Harmony satellite will carry a passive radar receiver and a multispectral thermal imager. Each imager has five cameras pointed at different view angles. Their data will be used to reconstruct 3D cloud fields and to obtain sea surface temperature. Given the stringent optical performance requirements, it is critical to assess the structural and thermal contributions to the performance of the thermal infrared imager. A comprehensive opto-mechanical STOP (Structural-Thermal-Optical Performance) analysis is performed using the telescope’s finite element model, accounting for thermoelastic deformations and thermal gradients induced from the orbital environment. The initial workflow employed Sigfit software to post-process Ansys Mechanical structural analysis displacements results and export the corresponding optical surface deformations and rigid body motions into Ansys Zemax OpticStudio for optical performance evaluation. The same analysis was then repeated using the Ansys integrated approach, which combines Mechanical software with a STOP Add-on to generate files compatible with the STAR module in Zemax OpticStudio. This paper presents the impact of thermal effects on the Harmony telescope’s optical performance and compares both workflows.