CHAPTER 17 SYSTEMS: EXTRAVEHICULAR ACTIVITIES—BUILDING A SPACE STATION 292 combination of the EMU, SAFER, tools, and himself of herself around the structure. The team on the ground has to come up with a choreography and order of events for the EVA, in advance. The flight control team creates the EVA timelines based on a high-level prioritized list of tasks determined by ISS management (e.g., move a specific antenna, install a particular avionics box). The flight controllers start with the top ISS priority task and assesses the other tasks that can fit into the EVA based on multiple factors such as how long the tasks will take based on past experiences, whether both crew members need to work together, task location on the ISS, how much equipment will fit into the airlock, the tools required, crew experience level, and the level of crew effort to complete the task. A task that might fit (but only if the team is efficient) is put on the list as a “get-ahead” task. See also Chapter 4. Real-time discussions in Mission Control of EVA time remaining, crew fatigue, and suit consumables could allow the get-ahead task to be accomplished in addition to the planned tasks. Some tasks are performed on a “clock” i.e., if power is removed from an item, it might get cold and need heater power in a matter of hours or sometimes within minutes to prevent damage. While a timeline is still in a draft version, the team conducts testing as required to prove out the operations. The team then trains the crew and refines and/or changes the timeline, sometimes up to the day of the EVA. Figure 12. Modules had to be connected, by hand, with stiff hoses for ammonia transfer as well as electrical power connections. Hand and EMU access was often tight. The crew had to carefully avoid snagging the lines with tools and tethers. The actual “flight hardware” connections were piecemeal tested to the extent possible, but the full three-dimensional (3-D) geometry with the crew in real EMUs was impossible to fully simulate on the ground. The Laboratory (top) and Node 1 (bottom) are the silver modules under all of the cabling in this photo from STS-110/ISS-8A.