255 SYSTEMS: ROBOTICS—THE CONSTRUCTION EQUIPMENT FOR THE INTERNATIONAL SPACE STATION CHAPTER 15 can be repeated multiple times to move the arm around. In the vernacular, the arm is designed to “walk” much like a Slinky® toy (Poof-Slinky, Inc., Plymouth, Michigan) or an inchworm. Figure 6. (Left) Looking down the open end of the LEE, showing the snares in their open position. A ring that is holding the snares begins to rotate when the robotic arm is over a grapple pin (Figure 7), thus causing the snares to trap the rod. (Right) In this image, the inner snare mechanism has rotated, thus causing the LEE snare cables to form a web across the opening. Doors (4) Gear Teeth Figure 7. A PDGF. The grapple shaft is in the center with the white semisphere at the end. The three gold lobes align with identical indentations on the LEE to help align the arm. A black-and-white target allows the operator, using a camera at the end of the LEE, to make sure the arm is directly over the pin. Note the curvic coupling (gear teeth) and the four doors. Special Purpose Dexterous Manipulator Another robot on the ISS, the SPDM (Figures 1 and 8), arrived on STS-123/ISS-1J/A in 2008. The SPDM is comprised of several components, including a LEE, a Power Data Grapple Fixture, two robotic arms, a tool holster, and a stowage platform. The fine control of the SPDM arms facilitate the manipulation of various hardware components on the outside of the ISS, thereby allowing for a number of operations that do not require a spacewalking astronaut. For instance, the SPDM allows the replacement of failed components such as the Remote Power Control Modules (see Chapter 9). To change out failed items such as Remote Power Control Modules, the SSRMS first retrieves the SPDM from wherever it is currently stowed and maneuvers it close to