CHAPTER 10 DAY IN THE LIFE: PREPARING FOR THE UNEXPECTED 174 A close-up of the Node 2 module (center), one of the areas where toxic ammonia can leak into the habitable volume of the International Space Station. At 2:49 a.m. Central Standard Time, a red alarm illuminated the giant front wall display in Mission Control in Houston. The alert read: TOXIC ATMOSPHERE Node 2 LTL IFHX NH3 Leak Detected. The meaning was clear. Ammonia was apparently leaking into the Interface Heat Exchanger (IFHX) of the Low Temperature cooling Loop (LTL) in the Node 2 module. “Flight, ETHOS, I expect the crew to be pressing in emergency response while I confirm,” said the flight controller from Environmental and Thermal Operating Systems (ETHOS). In other words, the crew needed to don oxygen masks to protect themselves from ammonia while ETHOS looked more closely at these data. This was not a drill. When the red alarm appeared, the flight director turned her full attention to ETHOS. The words—unwelcome at any time from ETHOS—were especially jarring at an hour when the crew and the ground were humming along on a busy day of running experiments. Of the many failures for which the flight control team prepares, especially in simulations, this failure presents one of the most life-threatening situations, and one the team never wants to encounter on the actual vehicle. On January 14, 2015, this scenario happened on the International Space Station (ISS). Data on the ETHOS console indicated toxic ammonia could be bleeding in from the external loops, through the water- based IFHX, and into the cabin (see Chapter 11). Software on the ISS immediately turned off the fans and closed the vents between all modules to prevent the spread of ammonia. At the sound of the alarm, crew members immediately began their memorized response of getting to