Blind to Chemistry: Molecular Contaminant Films We Could Be Missing During Visual Inspections and the Potential Impact to System Performance
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.Abstract
Contributor Notes
ABOUT THE AUTHOR
Dr. Elaine Seasly is the Deputy Planetary Protection Officer for NASA. She began her career in contamination control of missile defense programs at Raytheon Missile Systems and later transitioned to NASA to lead the contamination control and planetary protection efforts at NASA Langley Research Center. Currently at NASA Headquarters, she brings the systems engineering perspective to the planetary protection discipline. Her focus is to ensure spacecraft are biologically clean enough to visit other worlds when searching for life or signs of past life, and any material samples brought back from visits to other worlds do not pose a risk to life on Earth. She holds a Bachelor’s in Chemical Engineering from the University of Arizona, Master’s in Patent Law from the University of Notre Dame, and a Doctor of Engineering from George Washington University.