Dimensional stability testing in thermal vacuum of the CHEOPS optical telescope assembly

摘要

The CHEOPS mission (CHaracterising ExOPlanet Satellite) is dedicated to searching for exoplanetary transits by performing ultra-high precision photometry on bright stars already known to host planets. A 32cm diameter on-axis Ritchey-Chretien telescope is used for imaging onto a single cooled detector. With integration times up to 48 hours the thermal stability of the telescope and its structure are key to the performance. Using a multi-lateration interferometer setup TNO has successfully demonstrated the μm-level stability of the Structural Thermal Model (STM2) of the Optical Telescope Assembly (OTA) in thermal vacuum. This OTA was later upgraded to become the Flight Model. Experiments comprise thermal vacuum cycling, thermal vacuum stability testing where axial and lateral deformations are measured to the nm-level sensitivity.