NASA/TM—2009–000000 Mitigation of EMU Glove Cut Hazard by MMOD Impact Craters on Exposed ISS Handrails Shannon Ryan Lunar and Planetary Institute Johnson Space Center, Houston, Texas Eric L. Christiansen Johnson Space Center, Houston, Texas Click here: Press F1 key (Windows) or Help key (Mac) for help April 2009 This page is required and contains approved text that cannot be changed. NASA STI Program ... in Profile Since its founding, NASA has been dedicated • CONFERENCE PUBLICATION. Collected to the advancement of aeronautics and space papers from scientific and technical science. The NASA scientific and technical conferences, symposia, seminars, or other information (STI) program plays a key part in meetings sponsored or co-sponsored helping NASA maintain this important role. by NASA. The NASA STI program operates under the • SPECIAL PUBLICATION. 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Christiansen Johnson Space Center, Houston, Texas Insert conference information, if applicable; otherwise delete Click here: Press F1 key (Windows) or Help key (Mac) for help National Aeronautics and Space Administration Johnson Space Center Houston, TX 77058 April 2009 Acknowledgments All testing was performed at NASA JSC White Sands Test Facility in Las Cruces New Mexico. Click here: Press F1 key (Windows) or Help key (Mac) for help Available from: NASA Center for Aer oSpace Information 7115 Stand ard Drive Hanover, MD 21076-1320 443-757 -5802 Click here: Press F1 key (Windows) or Help key (Mac) for help This report is also available in electronic form at http:// Summary Recent cut damages to crewmember extravehicular mobility unit (EMU) gloves during extravehicular activity (EVA) onboard the International Space Station (ISS) has been found to result from contact with sharp edges or pinch points rather than general wear or abrasion. One possible source of cut-hazards are protruding sharp edged crater lips from impact of micrometeoroid and orbital debris (MMOD) particles on external metallic handrails along EVA translation paths. During impact of MMOD particles at hypervelocity an evacuation flow develops behind the shock wave, resulting in the formation of crater lips that can protrude above the target surface. In this study, two methods were evaluated to limit EMU glove cut-hazards due to MMOD impact craters. In the first phase, four flexible overwrap configurations are evaluated: a felt-reusable surface insulation (FRSI), polyurethane polyether foam with beta-cloth cover, double- layer polyurethane polyether foam with beta-cloth cover, and multi-layer beta-cloth with intermediate Dacron netting spacers. These overwraps are suitable for retrofitting ground equipment that has yet to be flown, and are not intended to protect the handrail from impact of MMOD particles, rather to act as a spacer between hazardous impact profiles and crewmember gloves. At the impact conditions considered, all four overwrap configurations evaluated were effective in limiting contact between EMU gloves and impact crater profiles. The multi-layer beta-cloth configuration was the most effective in reducing the height of potentially hazardous profiles in handrail-representative targets. In the second phase of the study, four material alternatives to current aluminum and stainless steel alloys were evaluated: a metal matrix composite, carbon fiber reinforced plastic (CFRP), fiberglass, and a fiber metal laminate. Alternative material handrails are intended to prevent the formation of hazardous damage profiles during MMOD impact and are suitable for flight hardware yet to be constructed. Of the four materials evaluated, only the fiberglass formed a less hazardous damage profile than the baseline metallic target. Although the CFRP laminate did not form any noticeable crater lip, brittle protruding fibers are considered a puncture risk. In parallel with EMU glove redesign efforts, modifications to metallic ISS handrails such as those evaluated in this study provide the means to significantly reduce cut-hazards from MMOD impact craters. Table of Contents List of Figures .......................................................................................................................... 2 List of Tables ............................................................................................................................ 3 Glossary of Terms and Abbreviations .................................................................................... 4 Notation .................................................................................................................................... 5 Introduction .............................................................................................................................. 6 Background .............................................................................................................................. 8 Test Articles and Target Setup .............................................................................................. 11 Handrail Overwraps .............................................................................................................. 11 FRSI Overwrap ................................................................................................................. 11 Open-cell polyurethane foam overwrap with beta-cloth cover (OCF+BC) ......................... 13 Double-layer open-cell polyurethane foam overwrap with beta-cloth cover (DROCF+BC) ................................................................................................................... 14 Beta-cloth overwrap (Beta-cloth) ...................................................................................... 15 Alternate Handrail Materials ................................................................................................. 16 Metal Matrix Composite (MMC) ............................................................................................ 17 Carbon Fiber Reinforced Plastic (CFRP) .......................................................................... 18 Fiberglass ......................................................................................................................... 19 Fiber Metal Laminate (FML) .............................................................................................. 19 Test Results ............................................................................................................................ 21 Conclusions............................................................................................................................ 26 References .............................................................................................................................. 28 Appendix A: Test Protocols .................................................................................................. 29 1 List of Figures Figure 1: Damge to crewmember Curbeam’s Phase VI glove following EVA 3 of STS-116. ...................... 6 Figure 2: Damage to returned handrail surfaces by possible MMOD impacts. Left: ISS Airlock handrail (~1.8 mm outer diameter crater); Right: SASA handrail (~0.5 mm diameter crater). ..................... 7 Figure 3: MMOD impacts on the returned NTA handrail. Top: Location of impacts; Below: Close- up of impact craters (from left-to-right: impacts 3, 4, 5, 15, 16). .................................................................. 7 Figure 4: Vectran TurtleSkin reinforcement patches added to index finger and thumb of the Phase VI EMU glove for STS-124. .......................................................................................................................... 8 Figure 5: Crater formation in a 0.48 cm thick Al6061-T6 plate impacted at normal incidence (0°) by a 0.15 cm diameter Al2017-T4 sphere at 6.86 km/s. Left: front view; Right: side view of entry (upper) and exit (lower) crater lips. ............................................................................................................... 9 Figure 6: ISS tube handrail (P/N SDD33107728-073) subject to HVI testing in [5]. .................................... 9 Figure 7: Crater formation on an ISS handrail resulting from oblique (45°) impact of a 1.0 mm diameter Al2017-T4 sphere at 6.94 km/s. Maximum crater lip height measured as 1.7 mm on side of handrail. .................................................................................................................................................. 10 Figure 8: Thermal Protection System (TPS) constituent materials (Space Shuttle Columbia). ................. 12 Figure 9: Felt-Reusable Surface Insulation (FRSI). Left: front view; Right: rear view. ............................... 12 Figure 10: Photograph and schematic of the FRSI overwrap target configuration. ................................... 13 Figure 11: Open-cell non-reticulated polyurethane foam. Left: microstructure; Right: front view. ............. 13 Figure 12: Photograph and schematic of the non-reticulated polyurethane open-cell foam/beta- cloth (OCF+BC) overwrap target configuration. ......................................................................................... 14 Figure 13: Open cell reticulated polyether polyurethane foam. Left: foam microstructure; Right: front view. ................................................................................................................................................... 15 Figure 14: Photograph and schematic of the double layer reticulated polyurethane open-cell foam/beta-cloth (DROCF+BC) overwrap target configuration. ................................................................... 15 Figure 15: Photograph and schematic of the beta-cloth overwrap target configuration............................. 16 Figure 16: Nextel/Al metal metrix composite. Left: test sample; Right: magnified view showing individual layer orientations within the composite laminate. ....................................................................... 17 Figure 17: Photograph and schematic of the Nextel/Al MMC target configuration. ................................... 18 Figure 18: Visual inspection of the CFRP target material. Left: outer fabric layer plain weave (x200 magnification); Right: varying orientation of the u.d. layers (x30 magnification). ............................. 18 Figure 19: Photograph and schematic of the IM7/954-2A CFRP target configuration. .............................. 19 Figure 20: Photograph and schematic of the NP500CR fiberglass target configuration. ........................... 19 Figure 21: Glare fiber metal laminate. Left: top view; Right: magnified view showing individual aluminum and glass composite layers........................................................................................................ 20 Figure 22: Photograph and schematic of the Glare fiber metal laminate target configuration. .................. 20 Figure 23: Definition of handrail overwrap damage measurements........................................................... 21 Figure 24: Definition of handrail damage measurements. Top: cratered handrail. Bottom: perforated handrail. .................................................................................................................................... 21 Figure 25: Comparison of impact crater profile in an unshielded Al 6061-T6 plate (representative of an ISS handrail) and overwrap shielded plates impacted by a 1.0 mm diameter Al 2017-T4 sphere at 6.77 ± 0.22 km/s with normal incidence (0°). ............................................................................. 24 Figure 26: Comparison of impact crater profile in an unshielded Al 6061-T6 plate (representative of an ISS handrail) and overwrap shielded plates impacted by a 1.5 mm diameter Al 2017-T4 sphere at 6.94 ± 0.09 km/s with oblique incidence (45°). ........................................................................... 25 Figure 27: Comparison of impact crater profile in a simulated ISS aluminum handrail and alternate handrail materials (from left to right: Al 6061-T6, MMC, CFRP, fiberglass, FML) impacted by a 1.0 mm diameter Al 2017-T4 sphere at 6.91 ± 0.08 km/s with normal incidence (0°). ............................................................................................................................................................. 26 2 List of Tables Table 1: Handrail overwrap configuration details. ...................................................................................... 11 Table 2: Alternate handrail materials subject to testing. ............................................................................ 16 Table 3: Mechanical properties of common ISS handrail materials and alternative candidates. ............... 17 Table 4: Handrail overwrap test results and damage measurements. ....................................................... 22 Table 5: Alternate handrail material test results and damage measurements. .......................................... 22 3 Glossary of Terms and Abbreviations Al Aluminum BC Beta-cloth CFRP Carbon Fiber Reinforced Plastic CRV Crew Return Vehicle DROCF Double layer Reticulated Open Cell Foam EMU Extravehicular Mobility Unit EVA Extravehicular Activity FML Fiber Metal Laminate FRSI Felt Reusable Surface Insulation HITF Hypervelocity Impact Technology Facility HVI Hypervelocity Impact ISS International Space Station JSC Johnson Space Center MLI Multi Layer Insulation MMC Metal Matrix Composite MMOD Micrometeoroid and Orbital Debris n.a. not applicable NASA National Aeronautics and Space Administration NIST National Institute of Standards and Technology NTA Nitrogen Tank Assembly OCF Open Cell Foam OMS Orbiter Maneuvering System PPI Pores Per Inch (linear) RTV Room Temperature Vulcanizing SASA S-band Antenna Structural Assembly STS Space Transportation System TPS Thermal Protection System 4