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National Aeronautics and Space Administration

EVA23Water Intrusion

so doing, help provide a finer-grained observation of operation during the failed condition. With the improved data in hand, a repeat of the screening test after removal and replacement of the Item 134 check valve and filter could provide a better means of determining the status of the EMU. Previous testing had been performed using a sample rate of one reading every two minutes, while the high-rate data provided a sample rate of 10 Hertz (Hz) which is stored on an onboard laptop to be downloaded at a later time. There was a concern about imposing yet another “wetting” of the fan motor bearings, which have been known to suffer long-term degradation by exposure to water, but the value of obtaining better data was deemed more important than the potential for damaging the bearings, since they had been wetted several times already and the fan motor appeared to keep functioning normally. Accordingly, on 8-27-13, a screening testing similar to that carried out on EMU’s 3005 and 3010 was performed. A chart of results is presented as Figure 3-23.

FAN SPEED

Figure 3-23. EMU 3011 Screening Test Data The plot of particular interest is the one for fan speed. Just after 13:39, the Item 125 was manually actuated, and almost immediately the fan speed went into a steep decline, indicating that the fan was experiencing severe loading, presumably from a quantity of liquid water. At approximately 13:42, water was noticed in the helmet. At about 13:51, the Display and Control Module (DCM) purge valve (Item 314 in Figure 3-3) was opened, effectively reducing the ventilation circuit pressure. As can be seen from the data curves, fan speed immediately increased as pressure was lowered. At around 13:58, the oxygen supply was shut off, which resulted in venting of the pressurizing oxygen in the water system to ambient. As can be seen from the plot of fan speed, the fan was rapidly cleared of water, which allowed the fan speed to increase back to normal. The reason for this effect occurring before the time that the water tank

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ISS EVA Suit Water Intrusion Mishap Investigation Report  

Report of the NASA Mishap Investigation Board examining the high visibility close call event of July 16, 2013 when ESA astronaut Luca Parmit...