321 DAY IN THE LIFE: RISKY AND REWARDING SPACEWALKS—SPACE SHUTTLE MISSION STS-120/ISS-10A CHAPTER 18 the tip of the boom (i.e., without a WIF Extender). The test was intended to prove that an astronaut could stand at the tip of a long boom on the shuttle robotic arm to repair the shuttle, since it was theorized that the boom would feel bouncy and move quite a bit as the astronaut moved his or her heavy spacesuit. In the case of STS-121, the shuttle robotic arm grasped the end of the boom. Figure 16. The team took advantage of a previously constructed tool called the hockey stick, due to its shape. It was not as large as a hockey stick, however. It measured 46 by 18 cm (18 by 7 in.). Parazynski could use it as a defensive tool if the array swayed near him, since it was made of nonconductive material. He would tether to the blue tie wrap loops (redundant in case one of them broke) and hold the stick near the end with the tethers. The shorter part of the “L” could be used to push the array away if it got too close. The hockey stick is shown floating in the laboratory during Expedition 15. The proposed configuration for the solar array repair was with a stronger robotic arm—the ISS robotic arm— grasping the middle instead of the end. Although the configuration was not tested at these specific arm angles with this arm and WIF Extender, it was hoped that Parazynski could perform his work safely despite some bounciness in the system. Team members tested the configuration using software in the Virtual Reality laboratory just to be sure. They crafted into the EVA a small test— the ground team planned to have Parazynski lean in and get a feel for the bounciness of his platform before starting the repair work. 6. The Airlock Would Be Far Away Typically, EVAs are choreographed such that an EVA crew member could get back to the airlock within 30 minutes in an emergency. If, for example, the fan/pump/water separator unit in the spacesuit (see Chapter 17) were to stop working, the EVA crew member could open a valve in the suit to help with cooling. In a worst-case scenario, the suit would have enough oxygen for 30 minutes in which the crew member would return to the airlock while the suit expended oxygen through the valve. In this case, it was initially estimated that it would take Parazynski up to an hour to get back to the airlock in an emergency. This was eventually refined down to 30 to 45 minutes by planning where he would tether himself, having a quick robotic maneuver to the truss ready to go, and making sure the on-board crew was ready for such a scenario. But, because of the critical ISS need to have this repair done, additional risk had to be accepted when sending Parazynski that far from the airlock. This risk was debated extensively in Team 4 and program meetings since standard crew safety practices would have to be waived to accomplish the task. The 30-minute emergency airlock ingress constraint was used throughout the ISS assembly and was the basis of many decisions related to operations and hardware design to avoid delaying crew members if they needed a quick translation back. Therefore, accepting this crew risk was not taken lightly. One of the factors in accepting the risk was that 30 minutes is often not an exact number when it comes to EVA. For example, in this case, there might be some extra oxygen in the main tanks, there might be less tethers than normal to disconnect to start the return, and Parazynski was highly experienced. Inherently, spaceflight requires taking risks. The final decision was that this situation was deemed worthy of the elevated risk, with the operations team making sure an emergency return was very well planned to be as efficient as possible, should a spacesuit failure occur when Parazynski was far from the airlock. 7. The Boom Sensors Might Break Using the ISS robotic arm to grab the boom instead using of the shuttle robotic arm would cause the delicate