NASA team close in on root cause of Luca's leaking EMU
NASA’s Anomaly Resolution Team (ART) are continuing to investigate the cause of the water leak that terminated EVA-23 last week. Evaluations on Luca Parmitano suit have ruled out numerous root causes, with the remaining credible failure sources all in the PLSS (Portable Life Support Unit), with a sublimator, the gas trap, an I-134 filter clog and check valve failure or a water separator failure in focus.
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Parmitano was conducting his second spacewalk alongside NASA’s Chris Cassidy, with the Italian focusing on routing an Ethernet cable between the US segment of the station and the future Russian Multipurpose Laboratory Module (MLM).
Around one hour into the EVA, Parmitano noted he felt water was starting to collect inside his helmet, specifically in his Comm Cap.
Such an observation has been made before, resulting in communication issues during STS-130′s EVA-1 and EVA-2. However, post EVA observations failed to note any significant water in the hardware.
Parmitano continued to work through his EVA tasks, before being joined by Cassidy, who also noticed water collecting in Luca’s helmet.
While it was initially thought Luca’s drinking bag may have been leaking, which by this time had been sucked empty, more water started to collect around the spacewalker’s face. At this point, Parmitano decided to try and remove some of the liquid by sucking water away from his visor – as seen in photography gained by L2.
Parmitano noted the liquid tasted strange, which is consistent with the water coming into contact with the anti-fogging chemicals on his visor plate.
With the situation worsening – as water started to get into Luca’s ears, eyes nose and mouth – mission controllers inside Johnson Space Center’s ISS Flight Control Room (FCR) opted to terminate the EVA.
“At about 39 minutes into the EVA, the carbon dioxide (CO2) sensor in the EMU reported a bad indication. At about 45 minutes into the EVA, EV2 (Luca) first reported feeling water at back of helmet. At that time EV2 was asked if more water was pooling near his head and the answer was no,” according to notes on L2.
“At about 55 minutes into the EVA, EV1 (Chris) reached EV2 and confirmed a large amount of water inside the suit, which soaked his communication cap and covered EV2′s ears and eyes. EV2 reported a hard time seeing shortly after this point and then communication was lost with EV2.”
With professionalism and purpose – both on the ISS and on the ground – Luca was helped back inside the Quest Airlock by Cassidy, as they then expedited the process to get the spacewalking duo back inside the safety of the ISS.
With the priority task of ensuring Parmitano’s safety successfully executed, the ISS crew then conducted their initial observations of what was proven to be a large amount of water in Luca’s helmet. Photos – via L2 – show large collections of water in several areas of the hardware.
NASA’s Mission Operations Directorate (MOD) immediately began an investigation on the ground, convening an Anomaly Resolution Team (ART) to find the root cause and propose forward actions.
“An Anomaly Resolution Team (ART) was held to discuss the water leakage in Short Extravehicular Mobility Unit (SEMU) 3011 during US EVA 23,” according to the opening notes, via L2′s specific section into the leak.
“During that EVA, EV2 reported water located in his Communication Cap, helmet bubble and the vent loop.
“No data or crew report exists that pinpoints the source of the water leak nor points to the root cause of the leak.”
Post EVA, the crew removed an estimated 1 to 1.5 Liters of water from the EMU, which was pooled primarily in the helmet and in the area of the liquid transport lines near the upper back of the HUT (Hard Upper Torso), while the rest of the suit felt dry from the chest
The initial ART meeting also discussed the impact to upcoming on-orbit vehicle operations, the EMU water leakage fault tree, discuss forward troubleshooting steps, and discuss hardware readiness to support any future EVAs.
Per the opening round of investigations – that also included the post EVA crew conference – the team were told the water leaking into the suit was reportedly cold, while Luca confirmed that the drink bag water from the Disposable In-Suit Drink Bag (DIDB) was warm. Upon inspection, the crew did find traces of water in the helmet vent pad, known as the T2 port.
EVA specialists also reviewed the EMU telemetry collected during the spacewalk, which did not provide any major leads into the cause of the leak.
“The suit pressure remained nominal throughout the EVA. There was no indication of low water/water pressure indication of the suit, meaning the suit did not run out of primary water. The pressure data is inconclusive in confirming a leak. The combined water fill of both suit volumes prior to EVA 23 was in family of previous fills,” added a summary of a the large set of notes in L2.
“There was a slight amperage change on the air flow fan, but this seemed in family with other EVAs and expected changes to EMU battery temperature during an EVA. The CO2 sensor fail indication was seen in the telemetry, this could have been an indication of the water leak, but in the past similar failure have been seen due to condensation build up.
“Other data from the EMU is limited, it was confirmed that there was O2 ventilation flow, although the presence of water could not be discerned from the data.”
A second ART meeting – in collaboration with the EVA Problem Resolution Team (PRT) – worked to narrow down the root cause, following additional testing on the EMU on orbit.
“The Disposable In Suit Drink Bag (DIDB) was filled, folded and squeezed with no leaks,” continued the notes. “There were no leaks reported in the Liquid Cooling and Ventilation Garment (LCVG), Hard Upper Torso (HUT) liquid transport lines, the Water Line Vent Tube (WLVT), the Multiple Water Connector (MWC) and the T11 line.
“During early troubleshooting steps, no gross leakage from T2 port, although water drops were visible in the T2 line.
“Given the observations from troubleshooting, the EVA PRT has tentatively ruled out the DIDB, leakage of the HUT liquid transport circuit lines, leakage from the LCVG and bodily fluid as sources for the internal water leak during EVA 23.”
Per the failure modes identified to date, the team believe the most likely path of the water leak is thought to be through the T2 port, sometimes referred to as the helmet vent, with the source specifically inside the PLSS.
“For this path, the remaining credible failure sources are all in the PLSS and include a failure in the sublimator, the gas trap, an I-134 filter clog or check valve failure or a water separator failure,” the notes continued, with forward on-orbit troubleshooting required to further isolate the source of the leak and to address the remaining legs of the fault tree.
While the team work on the forward actions, the ART noted that no further EVAs using any EMU ORU should be conducted. If an emergency arose – part of the “Big 12″ ISS problems (L2) – then a risk discussion concerning the risk of using an alternate EMU other than 3011 is recommended.
Alternate EMU hardware does exist on orbit and could be re-sized to accommodate the crew if required. However, the ART could not rule that other EMUs on orbit could experience a similar failure. Further, a review of EVA procedures and safety documentation is needed in the event this water leakage occurs again.
EVA-23 was set to be the last US spacewalk until 2015. However, per contingency events, some on-orbit activities – such as the upcoming translation of the Mobile Transporter (MT) – usually require a contingency EVA on standby.
For the interim, the IMMT will hold a risk discussion meeting to potentially accept a waiver for the requirement to have EVA capability as a backup.
A third ART is scheduled for the upcoming week, which will review and revisit the remaining legs of the fault tree, discuss troubleshooting findings, discuss root cause – if the source of the leak is found by then – and discuss the technical, safety and operational review steps required to be able to go EVA utilizing the other EMU spares.
It is also possible the suspect elements of the EMU hardware could catch a ride back to Earth for further investigation, via the next SpaceX Dragon spacecraft – the only real downmass capability available to the ISS – during the CRS-3 (SpX-3) mission at the end of this year.
(Images: L2′s ISS Section and NASA – L2 Members, click this link for rolling updates into this investigation)
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