False Alarm Sends USOS ISS Crewmembers to Russian Segment

What turned out to be a malfunctioning data relay caused the three International Space Station (ISS) crew members who spend most of their time in the U.S. Orbital Segment (USOS) to evacuate into the Russian segment while ground controllers determined just what was going on.  Initially it appeared there had been an ammonia leak.

ISS program manager Mike Suffredini explained at an 11:00 am EST briefing that at 4:00 am EST (3:00 am Central) systems indicated that four measurements were “off scale.”   An alarm indicated that water was building up in one of two coolant loops (Loop B)
used to transfer heat out of the interior of the space station.  The
water carries heat away, through a heat exchanger, to an ammonia loop
on the exterior of the station.  The system is designed to prevent
ammonia from getting into the interior of the facility, but there are
failure scenarios that could cause such an incursion.  One sign is that the water level rises in one of the loops.

Consequently NASA astronauts Barry “Butch” Wilmore and Terry Virts and European Space Agency (ESA) astronaut Samantha Cristoforreti were ordered to don protective masks and move into the Russian segment.  

Suffredini said that initial checks indicated there was no ammonia leak and the crew members were allowed to return to the USOS, but shortly after that an air pressure spike was detected, another “cue” there could be an ammonia leak.  The crew was sent back to the Russian segment.

Ground control teams troubleshot the issue and after several hours determined that a “transient error message” in a multiplexer-demultiplexer (MDM) computer relay system had, by chance, sent erroneous data that mimicked an ammonia leak. Ground controllers recycled the MDM and the false readings disappeared.  The crew returned to the USOS at 3:05 pm EST, still wearing protective masks, to sample the atmosphere.  No ammonia was detected.

Suffredini said that the research being conducted by the astronauts would have to be replanned because of the “impromptu” day off, but did not expect any major impacts.  

The ISS is a modular facility with part composed of modules and equipment built by Russia (the Russian Orbital Segment-ROS) and the other part by the United States, Japan, Europe and Canada (the USOS segment).  A hatch separates the two segments so in circumstances like this, one can serve as a safe haven if there is a problem in the other.  The Russian segment uses a different type of cooling system and was not affected by this problem.