There has been a lot of press (example) and commentary about the near drowning in space of Italian astronaut Luca Parmitano on July 16, 2013. We have a question Would the blast clearing technique used in snorkeling work in an EVA situation? on how to clear the problem. But for me the bigger question is, where did the water or fluid come from? You are in a space suit surrounded by vacuum, there are not a lot of options for sources. All of the articles I have read give theories on where it did not come from. Is there any hard data on what the cause of the fluid build up was?
We don't know yet exactly what caused it, but all tests so far ruled out everything else but the PLSS (Portable Life Support Unit). In fact, just today (Aug. 27, 2013) Chris Cassidy and Luca Parmitano managed to recreate the water leak that terminated EVA-23:
Flight Engineer Chris Cassidy, along with Parmitano, performed a checkout of the spacesuit that Parmitano wore during a July 16 spacewalk that was cut short when its helmet began to fill with water. After assembling and powering up the empty suit as if it were about to go out on another spacewalk, the two astronauts observed water once again leaking into the helmet. With the issue reproduced, NASA now has a baseline configuration for the crew to begin swapping out parts for additional tests to pinpoint the problem. There are also opportunities to either launch replacement parts on upcoming cargo flights or return parts to Earth for further study once more is known about the cause of the issue.
YouTube video is available of NASA's ISS update on Aug. 27, 2013 including Luca's spacesuit test
Previously, the NASA’s Anomaly Resolution Team (ART) evaluations on Luca Parmitano suit ruled out other causes and everything pointing towards the PLSS (Portable Life Support Unit). Among the remaining possible root cause are the sublimator, the gas trap, a filter clog and check valve failure, or a water separator failure.
Update: NASA made the full report on the Mishap Investigation Board investigating US EVA 23 mishap and its root causes available to the public in the International Space Station (ISS) EVA Suit Water Intrusion, IRIS Case Number S–2013–199–00005 (PDF):
In summary, the causes for this mishap evolved from (1) inorganic materials causing blockage of the drum holes in the EMU water separator resulting in water spilling into the vent loop; (2) the NASA team’s lack of knowledge regarding this particular failure mode; and (3) misdiagnosis of this suit failure when it initially occurred on EVA 22.
The source of the inorganic materials blocking the water separator drum holes had not been experienced during an 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, which must ultimately be determined to prevent future mishaps.
Related article on Space.com: Spacesuit Leak That Nearly Drowned Astronaut Could Have Been Avoided
There are several potential sources:
- Drinking Water. Some suits are configured with a tube for drinking water, using a suction demand system - when you suck on the tube, the valve opens, and water under gentle pressure is released. A stuck valve could release drinking water into the helmet.
- Thermal Control Garment leak. Most TCGs use water in tubes affixed to the garment itself. A damaged or improperly connected TCG coolant loop could release water into the suit.
- Oral Moisture. It is possible that the astronaut may have had excess moisture in his mouth which escaped. In gravity, unintentional releases are called "drool" while intentional ones are expectoration/spittle.
- Dislodged condensate. If the astronaut is faced one direction for some time, it's possible for the helmet to be cool enough to condense moisture. That moisture is most likely to bead up and remain on the surface, but a sudden movement could dislodge such moisture. Note that moisture is lost to atmosphere with every breath, and suits need to regulate humidity to prevent condensation.
- Dislodged sweat. While astronauts should be thermally regulated by the TCG such that they aren't sweating from insolation heating¹, they may still sweat from exertion or illness. As with condensate, it should just bead up on the individual, but a sharp movement might dislodge some.
- Micro-cometary penetration. A small fragment of comet might create a hole which freezes closed from vacuum thermal loss condensation, but have a chunk that melts in the helmet itself. This can be ruled out since no penetrations were found, and the astronaut would almost certainly have noticed a pressure loss and the impact.
Until the final report we really won't know.
We can, however, rule out oral moisture, dislodged sweat, and cometary penetration, since the replication has shown it occurs in an empty suit.
¹: heating from direct sunlight. See insolation at the free dictionary