The Hazard of UV-Induced Oxidation to Solar-Viewing Spacecraft Optics

The two most prevalent outgassing contaminants on spacecraft are organic molecules and water vapor. Adsorbed organic molecules can degrade a solar-viewing instrument when they are cracked by ultraviolet radiation (UV) and become a light-absorbing layer of carbon. In earlier work, we examined the transmission loss of the extreme-ultraviolet (EUV) aluminum filters used onboard the Solar Dynamics Observatory , and we showed that the degradation was not caused by carbonization. Here, by comparing the losses of the spacecraft filters with the losses induced on similar filters by synchrotron radiation, we demonstrate that the degradation was likely due to oxidation caused by the ultraviolet activation of adsorbed water vapor.