CHAPTER 18 DAY IN THE LIFE: RISKY AND REWARDING SPACEWALKS—SPACE SHUTTLE MISSION STS-120/ISS-10A 312 sometimes shook, as if there was increased friction somewhere on the circular travel surface or in a drive mechanism. It was speculated that this could be caused by a piece of thermal blanket that was dragging, the presence of foreign object debris (i.e., something that is not supposed to be there such as a piece of wire or washer), or something misaligned in one of two drive lock assemblies that houses the motor and lockdown mechanism. The starboard rotary joint had been on orbit a significantly less amount of time than the port side, which did not show any increased current thus, age was not causing the starboard side to degrade. The biggest concern was that friction would eventually increase to the point that either the motor couldn’t overcome the force or the motor would fail, resulting in the inability to position the solar arrays. In addition to needing good array pointing to generate enough power, the arrays needed to be pointing in “safe” directions so they could endure the shaking and jet forces from visiting vehicle dockings and undockings (see Chapter 9). In fact, to ensure the arrays would be pointed in a good direction for the docking of Discovery, the team had preemptively “parked” (i.e., stopped rotation of) the starboard SARJ before the mission with the arrays aligned in a position that would allow for the docking and also have adequate power generation for that time of year while minimizing potential wear and tear. After so much speculation about what could be causing the SARJ issue, the engineering team wanted to have the EVA crew look at it. The flight control team worked with the SARJ hardware experts on an external inspection plan (Figure 6) and the removal of at least one protective panel to get a good look at the rolling surface and gears. Space Station Program management initially requested this to be a task for a later spacewalk, but the EVA team identified a good time frame in the middle of EVA 2, requiring deferral of only one lower-priority task to a later EVA. The flight control team was already adapting to the changing needs of the flight. If MLI Cover is removed, race rings (2), trundle bearing assembly (TBA) and SARJ ring structure are visible. • Inspect all hardware for scoring, damage or foreign object debris • Inspect race rings for missing/damaged teeth Outboard Race Ring Inboard Race Ring Trundle Bearing Assy Race Ring Gear Teeth – inspect for visible damage and foreign object debris What You Will See With MLI Cover Removed P3 SARJ with All MLI Covers Removed Figure 6. Instructional information that the Mission Control team sent up to the crew members to study before they performed an EVA to inspect the S3 SARJ. This SARJ hardware would be seen under the white multilayer insulation (MLI). Photo credit NASA-JSC/John Ray, taken at the Kennedy Space Center prior to S3 launch. Flight Days 4-5 (Friday, October 26 and Saturday, October 27) EVA 1 was executed as planned. EVA crew members encountered relatively minor anomalies e.g., some bolts were sticky (i.e., difficult to remove) and some ammonia ice flakes had floated out during the initial crew disconnection of P1 from Z1. As discussed in Chapters 4 and 17, the ground team had to track that the crew spent enough time baking out (i.e., allowing the ammonia to sublimate off of the suit) and had the crew members perform a test in the airlock to verify the absence of toxic quantities on their suits, which could