U.S. part of space station evacuated

Jan 14, 2015 10:59 AM by News Staff

Concern about a possible ammonia coolant leak early Wednesday prompted astronauts aboard the International Space Station to evacuate the U.S. segment of the complex, joining three cosmonauts in Russian modules while flight controllers studied telemetry to figure out if alarms were triggered by an actual leak, a sensor problem or some other issue, officials said.

The alarms were triggered just after 4 a.m. EST (GMT-5) when an apparent pressure increase was detected in a water coolant loop in the forward Harmony module. Water is circulated inside the station to carry away the heat generated by the lab's electronics. The water then flows through components called heat exchangers, transferring the heat to ammonia coolant that flows through huge external radiators to keep the station within temperature limits.

The pressure spike in coolant loop B was a possible indicator of an ammonia leak, and playing it safe, flight controllers told Expedition 42 commander Barry "Butch" Wilmore, Terry Virts and European Space Agency astronaut Samantha Cristoforetti to don masks and move into the Russian segment of the space station.

Joining cosmonauts Alexander Samokutyaev, Elena Serova and Anton Shkaplerov, Wilmore, Cristoforetti and Virts closed a hatch between NASA's Unity module and the Russian Zarya module, isolating all six crew members in the Russian segment of the lab complex, which uses a different cooling system.

"Flight controllers here in Houston detected an increase in pressure in the water loop for thermal control system B, or bravo, on the station, one of two redundant cooling loops, which triggered the alarm," said NASA mission control commentator Rob Navias. "Acting in very, very conservative fashion, the crew was directed to isolate themselves in the Russian segment."

He said the crew members were "safe and in good shape," adding "we need to emphasize there is no data to suggest there was, in fact, a real ammonia leak despite a number of reports that are circulating to that effect."

Later in the morning, a NASA official said in a Twitter posting the problem may have been caused by "an errant sensor or computer relay." In any case, there was no direct evidence of an actual ammonia leak.

In an exchange with the crew, astronaut James Kelly at the Johnson Space Center in Houston told Wilmore and company to stand by pending additional analysis.

"We're still trying to figure out exactly what happened," Kelly said. "We're not entirely convinced this is an ammonia leak. ... There's a possibility of a combination of sensor problems, MDM (computer) partial failures and thermal effects all thrown together in the exact wrong way to make this thing look like it was your classic ammonia leak.

"Bottom line is we've got all the experts coming now. Everybody's poring over the data. We've got all the smart folks taking a look at it, and we're trying to figure out exactly what's going on."

He said pressure in the U.S. segment was stable and "we've got at least a full day before we hit any kind of limit right now for positive pressure relief or anything like that.

"So bottom line is we're pretty much staying in this configuration we're in right now while all the folks come in and talk about it, take a look at the data, deconstruct this thing and try to figure out exactly what happened."

"Thank you, we really appreciate that summary," Wilmore replied. "We'll just stand by ready to do anything from our end that you have for us."

Kelly told the crew to stand by for additional updates and in the meantime, "enjoy your impromptu day off."

"We'll keep you guys informed as to what's going on, and we'll also let you know as the conventional wisdom comes around on the story," Kelly said. "But like I said, the good news right now is we're not utterly convinced that we had a very bad problem that we had indications of. Clearly, we did the right thing with the indications we had, but we're still trying to figure out what the actual event is."

The International Space Station is equipped with two independent coolant loops that use water and ammonia circulating through a complex arrangement of heat exchangers, pumps, valves and radiators to get rid of the heat generated by the lab's electrical systems.

While either loop can handle the heat produced by critical life support, communications, stabilization and key computer systems, both are needed to cool those components, the station's major science experiments and other non-essential equipment.

Inside the station's pressurized modules, electrical components are mounted on "cold plates" that use water flowing through internal lines to keep equipment cool. The warmed water in the "moderate temperature loop," or MTL, is pumped to heat exchangers that transfer the thermal load to the ammonia coolant that circulates through the station's external thermal control system, or ETCS.

Powerful pumps in each coolant loop push the ammonia through an intricate system of valves and lines to large radiators mounted on the back side of the lab's main solar power truss where the heat is radiated to space. The cooled ammonia then is returned to the heat exchangers for another cooling cycle.

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