Spacewalk Delay for Ammonia Leak

By Kim Smiley

Astronauts at the International Space Station ran into problems during a planned replacement of a broken ammonia cooling pump on August 7, 2010.  In order to replace the pump, four ammonia hoses and five electrical cables needed to be disconnected to remove the broken pump.  One of the hoses could not be removed because of a jammed fitting.  When an astronaut was able to disconnect it by hitting the fitting with a hammer, it caused an ammonia leak.

Ammonia is toxic, so the leak impacted both the safety and environmental goals.  Because the broken pump kept one cooling system from working, there was a risk of having to evacuate the space station, should the other system (which was the same age) fail.  This can be considered an impact to the customer service goal.   The repair had to be delayed, which is an impact to the production/schedule goal.  The loss of a redundant system is an impact to the property/equipment goal.     The extended spacewalk is an impact to the labor/time goal.

Once we fill out the outline with the impact to the goals and information regarding the problem, we can go on to the Cause Map.   The ammonia leak was caused by an unknown leak path and the fitting being removed by a hammer.  The fitting was removed with a hammer because it was jammed and had to be disconnected in order for the broken pump to be replaced.  As we’re not aware of what caused the pump to break (this information will likely be discovered now that the pump has been removed), we leave a question mark on the map, to fill in later.

The failed cooling pump also caused the loss of one cooling system.  If the other system, which is near the end of its expected life, were to fail, this would require evacuation from the station.

To aid in our understanding of this incident, we can create a very simple process map of the pump replacement.  The red firework shows the step in the replacement that didn’t go well.  To view the outline, Cause Map and Process Map, click on “Download PDF” above.