  Protection of silver mirror stacks from environmental degradation before
launching is crucial for space applications. Hereby, we report a comparative
study of the advanced protection of silver mirror stacks for space telescopes
provided by SiO2 and Al2O3 coatings in conditions of accelerated aging by
sulfidation. The model silver stack samples were deposited by cathodic
magnetron sputtering on a reference silica substrate for optical applications
and a surface-pretreated SiC substrate. Accelerated aging was performed in dry
and more severe wet conditions. Optical micrographic observations, surface and
interface analysis by Time-of Flight Secondary Ion Mass Spectrometry (ToF-SIMS)
and reflectivity measurements were combined to comparatively study the effects
of degradation. The results show a lower kinetics of degradation by accelerated
aging of the stacks protected by the alumina coating in comparable test
conditions.
