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Ammonia Leak Alarm On the ISS Forces Evacuation of US Side: Crew Safe
New submitter BabelBuilder writes: An alarm signaling a possible ammonia leak aboard the ISS this morning caused the crew to evacuate the U.S. side of the station. All crew aboard the station are safe. "Flight controllers in Mission Control at NASA's Johnson Space Center in Houston saw an increase in pressure in the station's water loop for thermal control system B then later saw a cabin pressure increase that could be indicative of an ammonia leak in the worst case scenario. Acting conservatively to protect for the worst case scenario, the crew was directed to isolate themselves in the Russian segment while the teams are evaluating the situation." They don't yet know whether it was caused by a faulty sensor, a problem in the relay box, or another malfunction.
I emailed a friend who worked on Station's ECLSS back in the 90's, and this was his reply:
"Ammonia has a great specific heat (ability to carry the thermal load), plus its boiling and freezing points work really well in space applications. It's also (aside from toxicity) a very well-known, simple, cheap and fairly easy material to work with. The way the TCS loops work on ISS, the ammonia loop is external; it never mixes with the internal (water) loops. There are external heat exchangers to pass the thermal loads from inside to outside; the water loops out of the pressure vessels through the end cones to the heat exchangers and back inside. The only way for ammonia to get into the water loop (it seems to me) would be a debris strike or something like that in a heat exchanger (and they're protected by MMOD shielding, as well as being rather out of the way)."