Euclid: Ice Contamination Testing

Abstract

Euclid is a medium-size ESA mission which will map the geometry of the Universe for a better understanding of dark matter and dark energy. Due to the mission profile and stringent performance requirements, the in-orbit contamination environment is a key aspect to control. Cryogenic operational temperatures root a particular concern over water/ice contamination on optical elements, since increased light scattering could potentially cause a significant impact on the performance of the payload. This challenging work under representative conditions closes the link between performance and ice contamination on specular surfaces (e.g. Mirror M1). The publication covers in detail the design and execution of the test campaign performed in ESA’s TEC-QEE Yuta vacuum facility, resulting in a data-set of spectral information at cryogenic temperatures. The optimised translation/rotation mechanisms incorporating fiber optics allowed scanning in different angular configurations: both the specular reflection as well as scattered light at different levels of surface contamination. The test results show that the effects of ice contamination are most noticeable in specular configuration. A summary is also given about ice-kinetics measured on the black paint used on the external baffle. The work supports Euclid’s calibration team in predicting expected performance and tuning the frequency and duration of in-flight decontamination processes.