CHAPTER 15 SYSTEMS: ROBOTICS—THE CONSTRUCTION EQUIPMENT FOR THE INTERNATIONAL SPACE STATION 256 a Cargo Transportation Carrier, which contains a spare unit. Using one of its arms, the SPDM opens the container and retrieves one of the new Remote Power Control Modules. The other arm would then close the container. A similar process is repeated at the site of the failed component to swap units, and then again to return the failed unit to a storage location. PDGF Arm Arm Stowage Platform LEE Tool Holster Figure 8. This drawing of the SPDM shows the individual elements including the LEE, where it can be mounted, or a PDGF, where it can be grappled by the arm. Drawing courtesy of CSA Payload ORU Accomodation Power and Data Grapple Fixtures (four places) Mast Camera Mated Umbilical Mating Adapters MBS Common Attach System Figure 9. This picture shows the MBS right after it was delivered to the space station on STS-111/ ISS-UF-2. Note the four PDGFs, one of which has the arm attached, the Payload Orbital Replacement Unit Accommodation, the Mast Camera and the Umbilical Mating Adapters mated at a worksite. The MBS Common Attach System similar to the UCCAS is also shown. See also Chapter 3. Mobile Remote Servicer Base System and Mobile Transporter In addition to “walking” around the station, the SSRMS can also hitch a ride and be carried along the truss. The MBS is a workbench for the SSRMS and SPDM (Figures 1 and 9). It contains four separate PDGFs that can be used as base points for either system. Depending on whether the operation to be performed is port or starboard, zenith or nadir, one of the four base points will be ideal for the activity. The MBS sits atop and is permanently attached to the NASA- built Mobile Transporter. A set of “tracks” is built in along the forward face of the ISS truss structure. These tracks allow the transporter with the MBS to move up and down the truss. Often, the transporter is moved to a different worksite, as seen in Figure 10, so that the SSRMS can reach some area of the space station. For those moves, the SSRMS and/or the SPDM are first attached to the MBS (Figure 11) and the transporter relocates everything to a new worksite. However, the transporter cannot stop at just any