CHAPTER 18 DAY IN THE LIFE: RISKY AND REWARDING SPACEWALKS—SPACE SHUTTLE MISSION STS-120/ISS-10A 306 Doug Wheelock and Scott Parazynski (in the spacesuits—left and right, respectively) are assisted in the airlock during Space Shuttle mission STS-120/ISS-10A by European Space Agency astronaut Paolo Nespoli and International Space Station Commander Peggy Whitson. The International Space Station (ISS) Program always presents new and sometimes daunting challenges. Each morning, the individuals working in Flight Operations never know whether the day might present one of the most critical problems in the history of the space station—whether the team will have to do something that has never been attempted. Scripting and training a spacewalk (i.e., extravehicular activity [EVA]) in advance is a major effort however, the real-time execution of spacewalks usually requires deviating from the original plan. Problems with the ISS systems that require an EVA fix can arise, tasks may take longer than expected, or a spacesuit issue might end an EVA early. Quick- decision moments are fairly common. Spacewalks are physically rigorous. The “human-in-the-loop”—both in space and on the ground—often necessitates flexibility. None of the space station parts were ever able to be tested preflight by a suited crew member in space-like thermal, zero-g, and vacuum conditions. When these factors come together in space, problems such as stuck bolts or problematic hinges can occur. The critical decisions made in the midst of never-before-seen technical or human problems during EVAs intensely draw upon the Foundations of Mission Control (see Introduction). Take one Space Shuttle mission to the ISS, as an example. Space Transportation System (STS)-120/ ISS-10A launched late in October 2007. Despite extensive EVA choreography preparations for the mission objectives, the planned spacewalks changed dramatically once the mission was under way. This chapter discusses the work that was done preflight and how it changed— not once, but multiple times—as the flight control team adapted to an ever- changing situation.