CHAPTER 17 SYSTEMS: EXTRAVEHICULAR ACTIVITIES—BUILDING A SPACE STATION 294 Johnson Space Center and is where most of the EVA choreography is currently tested. However, the Weightless Environment Test System in Tsukuba, Japan, and the Neutral Buoyancy Simulator in Huntsville, Alabama, have also made major test contributions to ISS EVAs. Space Shuttle crews for ISS assembly missions were trained multiple times in the NBL on their EVA choreography using the specific tools and required tethers. ISS crews remain on station for a much longer amount of time, and they have long preflight training periods in multiple countries and can’t be expected to remember fine details for extended periods. EVA priorities often change after months of ISS operation anyway. Therefore, the ISS crews are trained on some specific EVA tasks, but their training focuses mainly on skill building (e.g., giving robotic arm operator directions, rescuing the other EVA crew member) rather than on memorizing choreography. EVA teams use a variety of other locations for testing and training. Vacuum chambers are used to verify that spacesuits do not leak in the vacuum of space. They are also used to test when reduced pressures (sometimes coupled with extreme temperatures) might affect operations, such as with the friction between moving parts, bubbling of substances, or stiffness of hoses. Moving massive objects by hand is not feasible when simply standing on the ground, so teams put high-mass objects on a system that blows air onto a polished steel floor and allows movement via principles similar to an air hockey table (Figure 15). This gives astronauts and test subjects a more- realistic feel for starting and stopping movement of heavy equipment since neutrally buoyant objects in a pool still tend to twist and float when affected by trapped air. Pads that blow air onto the polished floor, like “reverse air hockey” Figure 15. The Precision Air Bearing Facility, with a test subject inside an EMU. Air blows out of pads on which the EMU is resting, so the unit will slide based on how the person inside the EMU moves or when pushed. In this case—a test that followed the Columbia accident—the subject was pushed to slide along the floor as if flying a SAFER while using a tool to measure damage to Space Shuttle tiles. Another key training facility is the Virtual Reality laboratory, which allows the test subject to view a graphic ISS in 3-D (often while wearing a helmet with goggles). This makes it possible for the teams to envision the workspace and practice EVA-robotics choreography (Figure 16). One famous testing platform was the “Vomit Comet” aircraft that allowed for intermittent periods of weightlessness. The KC-135 aircraft (later replaced by a DC-9) was outfitted to fly a parabolic trajectory and provide approximately 20 to 25 seconds of microgravity at a time. This allowed for quick tests with flight-like materials that could not be done underwater or that needed microgravity. Often, the team proves out techniques and uses EVA tools on real flight hardware while it is still in an assembly facility on the ground. It is better for NASA to discover that something is too difficult to reach/manipulate/turn by EVA crew members, or that tools don’t fit their interface, while on the ground rather than in space. Hardware obviously cannot be ground-tested in this way after it is already on orbit, which adds to the challenge now that ISS assembly is complete.