1. Introduction “The threat that orbital debris poses to international space activities is presently not large, but it may be on the verge of becoming significant. If and when it does, the consequences could be very costly - and extremely difficult to reverse. By contrast, the cost of reducing the growth of the hazard can be relatively low . ... The committee believes that spacefaring nations should take judicious, timely steps now to understand the risk and agree on ways to reduce it.” - The National Research Council’s (NRC’s) Committee on Space Debris, 1995. [1] 1 1.1 Is the ISS Safe from MMODs? One of the greatest threats facing the International Space Station (ISS) and other space-based systems are micro-meteor & orbital debris (MMOD) impacts. This is evident by the continuous barrage of damage the ISS has sustained throughout its operation (Figure 1-2). Though critical systems have not yet been affected, active monitoring, damage assessment, repair and recovery options are high priority items in ISS operations. ISS solar arrays are especially vulnerable to impacts due to their large deployed area and minimal cover glass protection (Figure 1), which necessitates routine monitoring of array health. 66 th International Astronautical Congress, Jerusalem, Israel. Copyright ©2015 by Mr. Joshua Fogel. Published by the IAF, with permission and released to the IAF to publish in all forms. IAC-15-B3-5.5 Page of 11 joshuafo@usc.edu 2 University of Southern California, Los Angeles, CA, USA. 3 Millennium Space Systems Inc., El Segundo, CA, USA. IAC-15-B3.5.5 A PROPOSED PHOTOELASTICITY-BASED ENHANCED VISUAL INSPECTION TOOL FOR ASTRONAUT EVA Joshua A. Fogel 1 University of Southern California, Los Angeles, CA, USA Millennium Space Systems Inc., El Segundo, CA, USA Prof. Madhu Thangavelu 2 and Nathan Turner 3 Space debris & micrometeor impacts pose a significant threat to the ISS, as evident by the continuous barrage of damage sustained throughout its operation. Though critical systems have not yet been affected, active monitoring, damage assessment, repair and recovery options are high priority items in ISS operations. Solar arrays are especially vulnerable to impacts due to their large deployed area and minimal cover glass protection, which necessitates routine monitoring of array health. Only direct visual inspection can confirm the full extent and location of possible cracks, torsions and penetrations. The concept architecture for an Enhanced Visual- Inspection System (EVIS) for use by astronauts during EVA and IVA is proposed that promises to expand astronauts’ visual senses. Current MMOD protection and inspection methods employed by astronauts, as well as a notable inspection and repair EVA, are summarized. The proposed EVIS system is a direct line-of-sight visual tool that uses simple optical elements to locate abnormal stress and thermal patterns in certain exposed, semi- transparent materials in real-time. The EVIS concept is comprised of a passive polariscope inspector, with an active forward looking infrared (FLIR) system for thermal imaging as a future addition. The polariscope inspector is a simple, low mass device that visualizes induced stress geometry of certain observed components using birefringence properties of the material via the photo-elastic effect. The process renders a colorful isochromatic contour map depicting lines of constant shear stress. Trained astronauts may use these stress signatures to identify distressed components, and characterize anomalous stress gradients indicative of possible damage. This allows the structural integrity of critical components (such as solar cells, truss structures, panels and windows) to be verified in-situ. Certain distressed components may be identified prior to failure so that appropriate action may be taken by the crew. The thermal infrared inspector is a streamlined, low-power device based on existing FLIR systems that enables quick assessment of the thermal conditions of exposed radiators and components. Both inspectors are hand-held, and may be attached to the EMU spacesuit through appropriate hooks and scars. Other potential future enhancements such as robotic inspection platforms and helmet visor integration are also explored. The EVIS concept promises astronauts advanced situational awareness that enhances the quality, quantity, and rate of acquisition of visual inspection data during both routine and emergency operations, with the potential to significantly reduce the duration of inspection EVAs. 1 11