Throughout the assembly, integration, and test process, molecular contamination levels of space mission hardware are monitored to meet system performance requirements. Qualitatively, reflective surfaces and witness mirrors are continuously inspected for the visible presence of molecular contaminant films. Quantitatively, periodic reflectance measurements of witness mirrors indicate changes of mirror reflectivity over time due to the accumulation of molecular contaminant films. However, both methods only consider the presence of a contaminant film and not the molecular composition. Additionally, there is a risk that hardware may appear to be “visibly clean” even with a molecular contaminant film present on critical surfaces. To address these issues, experiments were performed to quantify the maximum molecular contaminant film that could be missed in visual inspections on witness mirrors with five different contaminants present. The corresponding changes in mirror reflectivity were modeled using the program STACK to determine the impact to space mission hardware performance. The results of this study not only show the criticality in considering the chemical make-up of molecular contaminant films on system performance, but also the need to recognize and understand the limitations of traditional visual inspection techniques on detecting molecular contaminant films.

Mitigating molecular contamination during the assembly, integration, and testing of space systems requires quantitative and qualitative methods to detect the presence of molecular films on sensitive surfaces. Atomic layer deposition (ALD) is a self-limiting deposit of a variety of films layer by layer in the vapor phase on multiple types of substrates. The controlled layer-by-layer deposition enables the user to change orientation, morphology, and grain size in films, which directly impacts optical and electronic responses. In this study, the authors demonstrate the ability to use ALD-grown metal oxide thin films coupled with a Raman spectrometer to provide early detection of molecular films on witness surfaces during the assembly, integration, and testing of space flight hardware.