CHAPTER 3 SYSTEMS: STRUCTURE AND MECHANISMS—THE INTERNATIONAL SPACE STATION’S SKELETON 54 Racks With a pressure shell, protective debris shielding, and windows in place, it is time to discuss a piece of the ISS modules with which crews interact on a continual basis. In the US Segment, the cylindrical modules are broken up into four quadrants. For each module, there is a floor (“deck”), ceiling (“overhead”), a left side (“port”), and a right side (“starboard”). An empty square- shaped space runs the length of the center of each module this is where the crews live and work (Figure 22). A series of racks separate the pressure shell from the crews’ living and working space. Figure 22. Cosmonaut Sergei Krikalev, flight engineer for the Expedition 1 crew, floats in the US Laboratory shortly after it was installed on STS-98/ISS-5A (2000). The four walls are actually the front faces of different racks. Note the empty central corridor. This photo was taken before the numerous science racks were launched and installed in the Laboratory. The numerous types of racks on the ISS can be broken down into four major categories. The avionics racks contain the computers, fans, power converters, air conditioners, etc. that are required to keep the vehicle functioning and the crew alive. Payload racks house the various science facilities and experiments that are conducted. Crew support racks contain items such as the galley, food refrigerators, food warmers, and the toilet. (See Figures 23 through 28.) Finally, there are stowage racks. Given that stowage space is at a premium on the ISS, the crew can find stowage spaces not only in dedicated stowage racks but also in various compartments in all the other racks. Stowage space is also found in standoff areas, endcones, hatchways, and pretty much any other nook and cranny that may not have an alternate dedicated use.