Molecular contamination and space radiation are known to degrade spacecraft performance, but the synergistic effects of the two are less understood. Optical systems are particularly vulnerable to degradation from exposure to contamination and/or space radiation. While traditional contamination assessments throughout the industry generally neglect radiation effects, our study demonstrate the importance of accounting for the space radiation environment when implementing contamination control. In this study, we investigate the impact of these complex degradation mechanisms on optical coatings. Our methodology consists of exposing optical coating coupons to flight-representative contamination and simulated space radiation environments, and we quantify the level of degradation by measuring the transmittance loss after each exposure. Our results show that the cumulative effects of molecular contamination and space radiation degrades optical performance more than either effect alone. In this report, we also discuss the effects of substrate and radiation exposure on the vacuum stability and morphology of the contaminant films.
The tape lift method using 3M 480 tape per ASTM E1216 is commonly used to determine surface cleanliness in the aerospace industry. However, the ease and accuracy of this methodology can be limited due to challenges with the tape adhesive, and sample processing is often manually intensive and subject to human error. As a result, alternative methods such as Gel-Pak® are evaluated against the current 3M 480 tape standard in terms of sampling efficiency, ease of image processing and analysis, and potential for adhesive cross-contamination. We show that alternative surface sampling methodologies can improve efficiency and accuracy of sampling efforts.
Molecular contamination of optical surfaces, thermal control components, or other spacecraft components can lead to end-of-life performance degradation. In particular, exposure to vacuum ultraviolet (VUV) radiation is known to enhance contaminant deposition rates. Known mechanisms for photodeposition and photopolymerization of contaminants are here reviewed to provide insight into the underlying chemistry and reaction mechanisms. Previous works have shown that many variables influence the rate of contaminant uptake, including temperature, VUV energy, and material properties of both the contaminant molecules and the substrate. Additionally, the photochemistries of three common spacecraft outgassing contaminants (DOP, BPA, and DC 704) are discussed to provide insight into future modeling efforts.
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