A frayed wire was found inside the extravehicular mobility unit (EMU) spacesuit, which led to concerns that it may be possible to ignite materials in the EMU by electrical arcing. As a result, the NASA Johnson Space Center (JSC) White Sands Test Facility was requested by JSC to conduct arc-ignition tests on multiple EMU materials placed in varying oxygen concentrations. Because understanding the ignitability of materials requires simulating the worst-case scenario, three test methods were developed to understand what conditions were the most severe. The most severe method was then used to characterize the materials presently used in the EMU by determining the minimum levels of current necessary to initiate combustion at a given voltage. These arc-ignition tests were performed in 100 % oxygen at 23.5 psia and in 50 % oxygen at 50 psia. The following materials were tested: cotton fabric; polyester fabric; polyurethane cable jacket; Gore-Tex® woven polytetrafluoroethylene (PTFE) fabric; nylon/Lycra® knit fabric; moleskin; nylon/spandex knit fabric; nylon tricot fabric; cotton-flocked Rucothane;® urethane-coated nylon; Kerlix® cotton dressing, Estane® polyurethane; and Capilene® hollow fiber polyester fabric.
Revelations of excessive property variation in polychlorotrifluoroethylene (PCTFE) semifinished and finished parts led to concerns that leaks or part failure could occur in service, possibly leading to catastrophic component or system failure by flow friction and/or kindling chain mechanisms. Such concerns led to the issuances of an internal Kennedy Space Center (KSC) Problem Advisory and a Government-Industry Data Exchange Program Materials Advisory on PCTFE. The advisories led to an engineering analysis review of PCTFE-containing ground support equipment used in “at-risk” high-pressure oxygen and air systems at KSC Representative PCTFE replacement parts used in “at-risk” systems were removed from inventory and tested. Tests included determination of (1) dimensional stability by thermomechanical analysis and metrology, (2) percent crystallinity by specific gravity, and (3) the effect of annealing on engineering tolerances. While dimensional instability was determined not to be a major issue in existing inventories, establishing traceability back to the semifinished article (starting rod or sheet stock) was often not possible. Percent crystallinity varied widely depending on part origin and thickness. Annealing was found to lead occasionally to out-of-tolerance parts. The pneumatic impact ignition threshold of PCTFE in enriched air was also determined at pressures up to 41.4 MPa. Results show that ignition does not occur at ambient oxygen concentrations. Last, hazard analyses were performed on “at-risk” systems. Two problematic designs were discovered, but based on operational histories, a recommendation was made to redesign or repair and replace on a noninterference basis.
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