CHAPTER 20 DAY IN THE LIFE: WHEN MAJOR ANOMALIES OCCUR 362 issue would be a subsequent failure of the Loop B pump (or failure of its power supply), which would cause a loss of heat rejection for all/ most internal components on the USOS. This would mean all of the computers, pumps, lights, etc., would need to be turned off. There might be some available limited capability if power could be supplied via jumpers (such as extension cords) from the Russian Segment and cooling ducts could be set up to blow air from the Russian Segment to keep US components from overheating. However, the Russian Segment was not designed to support six crew members or cooling of US equipment for long periods of time. Also, we would have to rely on a Russian EVA using Orlan spacesuits to change out components on the other end of the ISS if the USOS airlock had to be powered down. The team would be extremely handicapped if the previously designed spacewalks using the EMU and Space Station Remote Manipulator System (SSRMS) could not be used for changing out a large Pump Module. Waiting to fix the current problem meant spending more time at risk that a problem could develop with the second ammonia loop, and a repair in that situation would be much more difficult. Pump Module Locations External Stowage Platform 3 ExPRESS Logistics Carrier 2 Loop A Pump Module ExPRESS Logistics Carrier 1 Final EVA Pump Module Worksites External Stowage Platform 3 Spare Pump Module Loop A Pump Module Figure 5. The degraded Loop A Pump Module was installed on the forward face of the truss on the starboard side of the ISS. The chosen spare was located on the External Stowage Platform #3, also on the starboard side of the ISS but below the failed pump (top). The going-in plan was that the two would eventually be swapped so that the degraded Pump Module would be placed on External Stowage Platform #3 (bottom). Extravehicular Activity Decisions Some important decisions would need to be made over the course of the next few days. With a lot of open questions flying around, “collapsing trade space” was needed so that the team did not spend too much time performing unnecessary work. Trade space referred to risk assessment of the pros and cons for each of the options. Narrowing the options meant less work and a faster end result. In this case, the spacewalk crew members could spend a lot of EVA time stowing the degraded Pump Module neatly in a spot on the truss, or they could throw it out into space and let it burn up on reentry through the Earth’s atmosphere. Each option trades some risk to the ISS