Mirrors are a central element of space instrumentation. In front of the lenses, they have the advantage that they can be made much lighter. In addition, they can work in a very wide spectral range, and in some spectral ranges, such as extreme ultraviolet and soft X-rays, they are the only option. Space instruments, particularly mirrors, are exposed to an aggressive environment, which can range from exposure to highly reactive atomic oxygen in low earth orbits to bombardment with high-energy electrons and protons in higher orbits, among other aggressive species. In addition to the deterioration produced by these environments, it is very difficult, usually impossible, to repair these mirrors once they have deteriorated. Therefore, when designing optical systems that will operate in space, it is necessary to know their resistance to the specific environment to which they will be exposed. This allows us to estimate the efficiency for the instrument during its entire life span.
Since the beginning of the space age, a large amount of information has been accumulated in the literature on the behavior of mirrors, that is, substrates and coatings, in various space environments, both real and simulated. This article makes an effort to collect and organize that information in a way that the authors have not found to exist before. The article places special emphasis on the spectral range of the far ultraviolet, because of its interest to the fields of astrophysics, solar physics and atmospheric physics, and because in this range the absorption of materials, such as pollutants, produces more pernicious effects than, for example, in the visible.
The article has gathered information on deterioration caused by the following agents or processes:
- Atomic oxygen
- Thermal processes
- Ultraviolet radiation
- Degassing and contamination
- Charged particles
- Dust and space garbage

Link to the paper

This work is a collaboration between the Institute of Optics, Faculty of Science and Technology of the Free University of Bozen in Italy, NASA Goddard Space Flight Center (CRESST II) of Michigan Ave, CNR-IFN of Padova, Italy, the Istituto Italiano di Tecnologia de Genova, Italy and the Cixi Institute of Biomedical Engineering - Ningbo Institute of Materials Technology and Engineering of the Chinese Academy of Sciences in Zhongguan, China