Effect of space environment on NV14 ceramic white coating of high gain antenna of BepiColombo spacecraft: long duration test

Wide temperature range, high UV/VUV intensities, and long duration of the BepiColombo mission impose stringent requirements on the materials of the spacecraft. One of the challenges is to keep critical parts of the spacecraft within acceptable temperature limits in the harsh conditions close to the Sun and Mercury. To this purpose, the High Gain Antenna (HGA) reflector and edges of the solar arrays are coated with the low solar absorptance, high emissivity NV14 white ceramic coating. However, UV/VUV radiation induces deposition of contaminants on the coating, potentially leading to significant increases of the solar absorptance values. Therefore, a prediction of the contamination effects on the solar absorptance of the coating during the entire mission is one of the crucial tasks. Several short environmental tests were initially performed aiming to investigate the contamination deposition on NV14 coating under UV/VUV radiation. However, the complexity of contamination deposition processes and the unknown influence of the large acceleration factors applied in these tests did not allow the development of a reliable model to predict the evolution of the solar absorptance during the mission lifetime. Therefore, it was decided to perform a long duration test (LDT), with a close to 1:10 test to mission duration ratio. Dedicated in-situ measurements techniques were developed to reduce actual test duration and avoid sample exposure to air.