361 DAY IN THE LIFE: WHEN MAJOR ANOMALIES OCCUR CHAPTER 20 Expedition 38 Spacewalkers Rick Mastracchio Flight Engineer ExtraVehicular 1 Mike Hopkins Flight Engineer ExtraVehicular 2 Koichi Wakata Flight Engineer Robotics Operator Figure 4. The spacewalkers: Rick Mastracchio and Mike Hopkins. Robotic arm operator: Koichi Wakata. Prior to launch, the Flight Operations Directorate and the ISS Program had determined who would perform spacewalks during the increment, if needed. In December 2013, the full six-crew-member team on board included US astronauts Rick Mastracchio and Mike Hopkins, Japanese astronaut Koichi Wakata, and Russian cosmonauts Oleg Kotov, Sergey Ryazanskiy, and Mikhail Tyurin. Prior to the mission, it had been discussed that if an EVA was required for an unplanned repair on the US Segment, Mastracchio and Hopkins would perform the necessary spacewalks and Wakata would operate the robotic arm (Figure 4). Cygnus Considerations The Cygnus mission was scheduled to launch in a few days however, Team 4 and the ISS Program management had not yet finalized whether the mission could take place as planned or whether the ammonia loop needed to be working before Cygnus arrived. The health of the ISS would of course remain the priority, but until the decision to slip was required, the ISS Program wanted to keep their December launch options open. The ISS Program research team determined that the decision “need date” was a couple of days before launch day. The research group wanted to load the short-life science such as ants and a vaccine experiment into the Cygnus just prior to launch to ensure the science would last the entire mission. The Cygnus team had another couple of days to thoroughly consider their situation should Loop A not yet be repaired when they arrived. Among other things, the current loss of heat rejection from Node 2 meant that one of the two close-proximity communication units (see “Ship-to- Ship Communication Systems” in Chapter 13) between the ISS and the Cygnus would not be powered up. If the one unit that was powered had a problem during rendezvous, the Cygnus vehicle would abort as it approached the space station. Also, after berthing, half of the power feeds to the berthing mechanism on Node 2 and half of the power feeds to Cygnus itself would not be available, thus exposing the mission and the ISS to bigger problems if the remaining systems experienced a failure. Next Worst Failure Concerns The overall state of the ISS was concerning. The ability to perform science was severely impacted since a lot of equipment was powered off. This was especially true in the Japanese and European research modules. Some critical-but-redundant items were not operational. For example, the United States On-orbit Segment (USOS) oxygen generator was not being used therefore, the station relied on the Russian oxygen generation system for the time being. Also, any time the ISS is not in an expected configuration, a lot of little-used or not-yet-created analysis comes into play—e.g., whether cooling loops can handle more or less heat load, and how long some boxes can sit in a certain environment without overheating. To determine what level of risk the ISS Program was willing to accept and how quickly repairs needed to be performed depended on the answer to this question: “What is the worst thing that could happen right now?” These potential watch items were called the “next worst failures,” and some of them would put the ISS in a precarious position. A large team scoured the various scenarios, but the most significant