Page 85

National Aeronautics and Space Administration

EVA23Water Intrusion

3.6 Root Cause Analysis This investigation followed two distinct paths: 1) what caused the failure in the hardware and 2), how the operations community dealt with the failure during the EVA. First, the hardware failure has been traced to inorganic materials blocking the EMU water separator drum holes. This failure had not been experienced during EVA before and is still undergoing a concurrent investigation. The results of this investigation will ultimately lead to resolution of this issue, however, since the concurrent investigation into the source of the debris is expected to continue for many months, the MIB does not yet have the required data to determine the root causes of the contamination source. The root causes of this issue must ultimately be determined to prevent future mishaps. The focus on the hardware failure investigation centers on understanding of the hardware involved, work that has been completed to date, preliminary results, and future work needed to determine root causes. Discussion of the hardware investigation can be found in ECFT-2 of our Event and Causal Factor Tree. The latest version of the Engineering Fault Tree which details the possible causes of this EMU failure is included as Appendix G. Second, the report then focuses on the real-time operations activities that can be improved to help the ground control teams more quickly recognize and react as quickly as possible to emergencies of this type. Discussions of the operations investigation can be found in ECFT-1, ECFT-3 and ECFT-4 of our Event and Causal Factor Tree. To determine causes and contributing factors of the event, the MIB applied the NASA Root Cause Analysis (RCA) method. The Undesired Outcome (UO) was identified as EVA crew member (EV2) exposed to potential loss of life during EVA 23 to reflect the severity of the HVCC related to not just water in the helmet but also the response to that event. Next, the MIB established a Timeline of events and conditions that were relevant to this investigation, capturing significant historical events related to the suit development, management decisions, and analyses up to and immediately following the mishap. The Timeline of Events is shown in Table 3-1. Concurrent with Timeline development, the MIB identified key events directly before the UO and brainstormed possible causes. Proximate Causes, the events or conditions that occurred immediately before or existed at the time of the UO, were established and the NASA Root Cause Analysis Tool (RCAT) Fault Tree model was used to identify and capture possible causes. The MIB employed two aids to ensure a broad scope was covered in our brainstorming. SHELL-D, which stands for Software, Hardware, Environment, Liveware (Team), Liveware (Individual), and Documents from the NASA RCA training and PPPEE, or Paper, People, Part, Equipment, and Environment, from our consultant’s Failure Recovery Planning training. As data was gathered, elements on the Fault Tree (FT) were ruled out with disputing data or ruled in where there was sufficient data to support causal logic. All of the substantiated causal events, conditions, and contributing factors that were ruled in were reflected on an Event Causal Factor Tree (ECFT) (Appendix I). The ECFT tree was expanded (discussed in the following sections) by continually asking “why” for the elements above until a logical endpoint emerged. The RCA Tool produced an .rca file for the mishap. The .rca file for this mishap RCA will be maintained in IRIS along with this report. Items that were identified as Significant but not causal were captured and are discussed throughout Section 3.6.2 as Contributing Factors, and in Section 3.7 Observations.


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...