Jul 18, 2019 | Updated: 10:03 AM EDT

ISS Alarm: Why Astronauts Had to Evacuate... Twice

Jan 14, 2015 09:46 PM EST

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International Space Station
(Photo : NASA)

Astronauts on the U.S. side of the International Space Station had quite a scare today after an apparent false alarm raised concerns about an ammonia leak on that side of the station; forcing a partial evacuation.

The alarm itself went off twice, forcing the evacuation of the six crew members from the United States side of the station to the Russian side for much of the day, while ground controllers  worked on the problem.  Eleven hours after the alarm, mask-wearing astronauts went back to the evacuated side of the station and sampled the air.

In a tweet NASA reported, "No ammonia indication." NASA space station project manager Mike Suffredini stated during a televised update that the likeliest cause of the alarm was a malfunctioning card in a signal-processing box.

"At this point, the team does not believe we leaked ammonia. ... What we are dealing with is a failure, probably of a card inside a multiplexer-demultiplexer," Suffredini says. The space station has a number of multiplexer-demultiplexer boxes that process readings from components aboard the orbital outpost, which has as much livable space as a six-bedroom house.

How did NASA fix the problem?  It seems even on the International Space Station sometimes you just have to reboot.  Simply shutting the box off and then back on cleared the worrisome readings.

The alarm was first raised at 4 a.m. ET, when Mission Control saw pressure changes that could have been caused by an internal link in the station's cooling system, which uses water on an inside loop and toxic ammonia on an outside loop.  "If this is possible, then we immediately safe the vehicle and get the crew in a safe place," Suffredini says.

"The safety of the team was preserved thanks to swift actions of the cosmonauts and astronauts themselves and the team on the ground in Moscow and Houston," said Maksim Matyushin, the chief of Russia's Mission Control.

Follow-up readings found no sign of an actual ammonia leak into the station, although fluctuations in cabin pressure continued to cause concern.  Suffredini stated those fluctuations were probably the system's "normal  reaction to the events that started to unfold."

The ISS crews have had to deal with external leaks of ammonia from the coolant system before, most recently in 2013, but they have never had to cope with an actual leak inside the cabin.

"Really, there was never any risk to the crew," Suffredini says. "It seemed like the team, as you would expect, reacted appropriately to the event."

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