Enhanced Optical Coated Witness Plates for the in Situ Monitoring of Spacecraft Health

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In the field of aerospace, contamination control is an engineering field that develops a strategy to mitigate molecular and particulate contamination effects on spacecraft performance. Molecular contamination is known as the hidden risk that interferes with the performance of optical, thermal, electronic, and mechanical systems. Traditional methods for monitoring spacecraft health involves the use of rinsate from a witness surface to collect molecular films known as non-volatile residues (NVR). In order to identify a chemical fingerprint of potential harmful contaminants, Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography-Mass Spectrometry (GC-MS) are tools for characterizing the NVR. Unfortunately, these passive characterization tools limit the ability to find problematic NVR during the early phases of the assembly of space flight hardware. A common method is the optical witness plate program that uses FTIR to monitor the collection of NVR within a 28 day period. The witness plate program has a limit of detection within several microns of NVR. Often nanometer thick molecular films can interfere with sensitive surfaces. In this work, we evaluate the use of enhanced optical coatings deposited onto witness surfaces as a practical sensing application to monitor the health of spacecraft. This method has the potential to enable in situ monitoring of spacecraft by utilizing the enhanced optical coated surfaces coupled with a portable Raman Spectrometer during the assembly, integration, and test phases to qualitatively identify egregious contaminants that may adversely impact spacecraft system cost and schedule.