On December 11, the International Space Station (ISS) experienced an ammonia coolant loop failure resulting in excessive cooling. The loop is located on the exterior of the station; it is suspected that a faulty control valve may be to blame for the issue. The coolant pump automatically shut down when it exceeded it’s temperature limits. NASA reports that the crew is in no danger.

Some non-critical systems have been powered down inside the Harmony node, the Kibo laboratory and the Columbus laboratory while the teams work to figure out what caused the valve to not function correctly and how to fix it. The crew is safe and preparing to begin a normal sleep shift while experts on the ground collect more data and consider what troubleshooting activities may be necessary.

Shutting down equipment reduces heat generation to a level that the remaining coolant loop is able to handle.

In the meantime, NASASpaceflight.com has been pulling some of the pieces together with their usual thorough analysis.

The coolant issue relates to a component known as a Flow Control Valve (FCV), which regulates the temperature of ammonia coolant in the ISS’ external cooling loops by mixing cool ammonia exiting the radiators with warm ammonia that has bypassed the radiators.

Early indications are that the FCV in the loop A coolant system is not closing properly, which is likely to be causing too much cool ammonia to enter into the cooling loop, which in turn has caused the loop A system to operate at a temperature which is much too low for normal operation.

As with earlier coolant loop issues, (albeit in different subsystems), it might be necessary to send astronauts on an unscheduled extravehicular activity (EVA) to attempt to fix the hardware. How that might play out is unclear, though, since NASA has not yet lifted restrictions on using the Extravehicular Mobility Unit spacesuit in the aftermath of a severe accident in July in which astronaut Luca Parmitano nearly drowned in his suit during an EVA.

Stay tuned for more as the situation develops.

Pictured above is a 2010 EVA in which  astronauts Douglas Wheelock and Tracy Caldwell Dyson replaced the same pump over the course of three EVAs, courtesy of NASA. 


About the author

Merryl Azriel

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Having wandered into professional writing and editing after a decade in engineering, science, and management, Merryl now enjoys reintegrating the dichotomy by bringing space technology and policy within reach of an interested public. After three years as Space Safety Magazine’s Managing Editor, Merryl semi-retired to Visiting Contributor and manager of the campaign to bring the International Space Station collaboration to the attention of the Nobel Peace Prize committee. She keeps her pencil sharp as Proposal Manager for U.S. government contractor CSRA.

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