Thin-film aluminum filters degrade in space with significant reduction of their Extreme Ultraviolet (EUV) transmission, ~66% loss in three years. This degradation was observed on the EUV Spectrophotometer (ESP), onboard the Solar Dynamics Observatory’s EUV Variability Experiment and the Solar EUV Monitor (SEM), onboard the Solar and Heliospheric Observatory. One of the possible causes for deterioration of such filters over time is contamination of their surfaces from plumes coming from periodic firing of their satellite’s Monomethylhydrazine (MMH) – Nitrogen Tetroxide (NTO) thrusters. When adsorbed by the filters, the contaminant molecules are exposed to solar irradiance and could lead to two possible compositions. First, they could get polymerized leading to a permanent hydrocarbon layer buildup on the filter’s surface. Second, they could accelerate and increase the depth of oxidation into filter’s bulk aluminum material. To study the phenomena we experimentally replicated the contamination of such filters in a simulated environment by MMH-NTO plumes. We apply, techniques like Scanning Electron Microscopy (SEM) and X-Ray photo-electron spectroscopy (XPS) to characterize the physical and the chemical changes on these contaminated sample filter surfaces.

Based on our improved understanding, a carbon based mono-layer protective coating was developed (and tested) that significantly reduces aluminum filters susceptibility to degradation by a satellite's attitude thruster plumes (MMH-NTO) and solar radiation (UV and below) in outer space.

My dissertation can be found in the attachments in Bio/CV section.

CONTAMINATION SYNTHESIS

This experiment was designed to synthesize molecular-radiation induced contamination of aluminum filters (as witnessed on SDO/EVE/ESP and SOHO/CELIAS/SEM) in laboratory environment. This test also help verify the effectiveness of our protective mono-layer coatings viz a viz original aluminum filter.

A long cylindrical three mouth reaction quartz chamber was designed for a controlled fuel (MMH) and oxidizer (NTO) combustion. An 8 inch long Teflon cylindrical shell (1 mm thick) structure lines the inside wall of this chamber and acts as a mounting assembly for the filter samples. At its very top, four slots are cut that hold one sample each. Helium, as a carrier gas is used to extract plumes away from the reactor towards a liquid Nitrogen based cold trap. A Hanovia high pressure mercury lamp was used as UV radiation source. The condensed plumes were then chemically characterized and analysed using FTIR.