EVA-35 investigation clears suit as ISS prepares for major battery change
An investigation into the water leak in Tim Kopra’s Extravehicular Mobility Unit (EMU) – which forced the early termination of EVA-35 in January – has revealed no hardware issues with the suit. The news comes as the ISS gears up for a series of critical EVAs that will replace the batteries on the Station’s solar arrays.
International Space Station (ISS) manager Kirk Shireman was providing an overview to the NASA’s oversight body, the Aerospace Safety Advisory Panel (ASAP) – portraying an orbital outpost in good health as it continues to work in its new era of utilization, following years of assembly.
EVAs are a critical element for keeping the Station operational.
Recent EVAs also looked to the future, with the installation of a new docking port – to which Commercial Crew vehicles will dock in the near future – successfully completed this summer.
The new port – one of two International Docking Adaptors to be installed on the Station – will allow for an increase in Station utilization, via the expected increase of the ISS crew size to seven.
However, spacewalks also provide some of the greatest risks to astronauts, with the US EVA-35, conducted back in January, terminated ahead of schedule for safety reasons.
The spacewalk successfully replaced a failed electrical component, called the Sequential Shunt Unit (SSU), in order to restore the station to its full power generation capacity.
The spacewalk was the first ever to be conducted by a British astronaut, Tim Peake. However, due to water entering “EV1” Tim Kopra’s helmet – a potentially life-threatening incident – the EVA was terminated ahead of the pre-planned schedule.
Due to well-practised procedures, both spacewalkers safely made it back into the Quest Airlock around two hours earlier than scheduled – with all primary tasks complete. No emergency ingress was required.
Tim Kopra’s suit (EMU 3011) was immediately investigated via the collection of suit samples during the post-EVA procedures. The suit was then returned back to Earth onboard the CRS-8 Dragon spacecraft, in order to aid the Anomaly Resolution Team (ART) meetings that had already begun at the Johnson Space Center (JSC).
NASA had already focused on the smoking gun of “sublimator carry-over”, where excess water from the sublimator overwhelms the pick-up tubes – known as “slurper tubes” – that are supposed to return water back to the cooling loop.
However, the reason for the issue was yet to be fully understood. Issues with how the suits are stored when not in use was investigated, which could be deemed a wider issue and potentially related to the anomaly where four times as much water entered Luca Parmitano’s helmet – in what was a far more serious incident.
The EMUs are stored in the Leonardo Permanent Multipurpose Module (PMM). However, the storage of some “hygiene products” in the module was deemed as a possible source of contaminating chemicals. The impact of such chemicals on the hydrophilic coating of the suit’s inner working was already known, which is why there are strict rules on astronauts using items such as after-shave and lotions.
However, thanks to the suit being returned to Earth on the Dragon, the problem with Kopra’s suit was deemed to be more an unfortunate coincidence, as opposed to a wider issue with the EMUs on Station.
Mr. Shireman told the ASAP that the conclusion reached was that the incident was not an example of the same failure as in the previous water-in-the-helmet instance.
“In this case, the likely cause was a combination of both environmental and operational factors that blocked outlet port slurper holes. The finding was that the amount of water was considerably smaller than before, and the conclusion reached was that this was a non-hazardous occurrence, even if it occurs in the future.”
As a result, the NASA team recommended a “go” for nominal and planned EVAs. Two EVAs, with special contingency allowances, were conducted since EVA-35, both without issue.
The positive news on the EMUs is a boost ahead of a critical set of EVAs that will play into the Station’s longevity.
The EVAs will involve the first-ever changeout of the large solar array batteries. The six lithium-ion batteries will replace 12 aging nickel-hydrogen power packs.
Mr. Shireman noted that if things go well, the work might be able to be completed in two EVAs, but plans are in place for six EVAs if required. The amount of EVAs is dependant on how the Canadian robot Dextre (SPDM) performs in its assistance of the task.
A recent test – known as the “Main Bus Switching Unit (MBSU) Demonstration” – was designed to validate the robotic transfer of battery style Orbital Replacement Units (ORUs) prior to the delivery of the new ISS batteries.
The goal was to validate the plans to reduce the number of EVAs required to install the batteries to just two spacewalks.
“The existing batteries are being replaced with a newer, improved version – smaller, lighter, and more capable. The existing batteries are probably good until mid- to late-2017, although it is hard to predict lifetimes on that type of hardware,” added the ASAP minutes.
The batteries will be delivered to the Station on the delayed HTV-6 mission, now scheduled for December 9.
Such is the vital nature of the successful replacement of the batteries, the ASAP Panel queried the ISS Program about its contingency planning in the event of a launch failure with the Japanese craft.
NASA noted the Program is prepared and has other batteries available and a production line is in place.
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