CHAPTER 18 DAY IN THE LIFE: RISKY AND REWARDING SPACEWALKS—SPACE SHUTTLE MISSION STS-120/ISS-10A 320 Various experts on electrical shock and plasma weighed in. The EVA console brought in safety experts to brief the EVA team on the hazard and how to prevent it. They were told the path to shocking the crew could be as follows: a hot (i.e., electrically energized) part of the array comes in contact with a metal tool, the tool touches a metal part of the suit such as the hard wrist connection, the astronaut touches the same part on the inside of the suit and is sweaty, another sweaty body part touches another metal part of the suit such as the waist bearing, and that metal part touches a grounded part of the array such as a guidewire. This scenario would result in an electric current traveling through the astronaut’s body. The EVA team relayed this information to the crew, via private video conference, to make sure everyone understood the hazards. The team went about ensuring this chain of events would not be possible. Parts of the suit and the tools were taped with insulating Kapton orange tape. The tape would keep electric charge from conducting between the array and the tool. Also, the ground had the crew tape up the metal wrist area of the Extravehicular Mobility Unit where the gloves attached. The number of tools Parazynski had with him was kept to a bare minimum, which provided a better chance of preventing tools from floating into the array. One question was whether sparks could jump through space, similar to lightning, if electrical charge differences were present. Although there is very little atmosphere at the altitude of the space station, charged particles surround the Earth. Plasma Contactor Units on board the ISS are turned on for spacewalks to specifically emit electrons into space. This creates a “grounding strap” and helps avoid the buildup of a large difference in electrical potential between the ISS structure and the surrounding environment. These units would be used, but would they be enough to mitigate the risk? As it turned out, the time of year was favorable and the solar cycle was closer to a minimum level of activity, so there would not be as many charged particles at the ISS altitude to create the plasma that would allow for a significant jumping of sparks/ arcs through space. Current flows from the array cells to the edges of the arrays, and then down to the base, with more and more current built up closer to the base after gathering input from cells along the way down. With the damage more than halfway up the array, the voltage and current of the specific area was known. The team determined that a spark could not jump more than about half an inch between electrically hot spots on the array therefore, a jump between the array and Parazynski’s metal neck ring on the suit was not possible as long as he kept the array at a comfortable distance. Parazynski might expect to see some small arcs, but they wouldn’t jump across free space to him. Furthermore, the creation of molten metal would require a much greater level of energy than deemed possible, considering where Parazynski could potentially come in contact and the fact that the tools were taped up. Many sharp areas on the array could nick a glove, or many areas could be energized. Parazynski was told not to touch the array with his gloved hand. Instead, he had with him a tool that had been built inside the ISS, a few months prior, to keep a swaying array from contacting a crew member during an EVA on an earlier mission. This tool, called the hockey stick, was made of nonconductive material wrapped in Kapton tape. The hockey stick could be used as a defense to push the array away if it came near (Figure 16). Vibrations, pushing, or the act of the repair could cause the array to flap and move, like a sail in the wind. This complicated the repair because Parazynski needed to keep the array close enough to perform the repair, yet keep the array at a distance using the hockey stick—all the while trying to enact the repair and holding additional tools. 5. The Boom Might Be Too Bouncy The plan was to have the ISS robotic arm grasp the boom at its center, with Parazynski standing in a foot restraint on a Worksite Interface (WIF) Extender, which would add approximately 0.9 to 1.2 m (~3 to 4 ft) to the overall reach to the damage site. He would essentially be on the end of an approximately 27 m (90 ft) pole. Movement of his spacesuit could cause ups and downs like a fish caught at the end of a fishing pole. The team had concerns about how much Parazynski would bounce around after making small movements and his ability to avoid smashing into the array, inadvertently. Imagine trying to perform delicate surgery while bouncing on a trampoline. Not easy to accomplish! Although the Space Shuttle boom had not been intended for the purpose of getting a crew member close to a dangerous solar array, the STS-121/ ISS-ULF1.1 crew in July 2006 had performed testing while standing on a foot restraint attached directly to