263 SYSTEMS: ROBOTICS—THE CONSTRUCTION EQUIPMENT FOR THE INTERNATIONAL SPACE STATION CHAPTER 15 meant another failure could leave the arm stuck. A module stranded on the end of the SSRMS would be an extremely critical scenario. First, critical cables that provide power to heaters that keep the equipment from freezing have to be disconnected from the shuttle payload bay and reconnected after the module is berthed. Hardware stuck on the arm could freeze in a matter of hours. Second, this configuration would not be stable enough for the space shuttle to undock because vibrations and thruster plumes from the shuttle could jolt the SSRMS during the undocking process. This could damage the arm and even cause the hardware to be inadvertently released, possibly colliding with the ISS. Figure 18. Mission Specialists Franklin Chang- Diaz (red stripes on legs) and Philippe Perrin repair the wrist roll joint on STS-111/ISS-UF-2 on June 11, 2002. (Top) Crew members set up to perform the replacement. The shuttle robotic arm (Canadarm), in the left of the image, acts as a “cherry picker” to move one of the astronauts around. An articulating portable foot restraint near the feet of the other astronaut acts as a fixed boot plate during the repair. (Middle) After installing the portable foot restraint in the shuttle robotic arm, Chang-Diaz inserts his feet in the boot plate. Astronauts inside the shuttle maneuvered him to a location where he could remove the station robotic arm’s LEE. The LEE had to be removed to get to the failed roll joint, which is the next joint in line. (Bottom) The new roll joint, installed on the station robotic arm. Note how the multilayer insulation (MLI) on the new joint is much whiter in color than the MLI on the other station arm components. Off-gassing of the MLI changes its color over time on orbit. Both crew members in this picture are maneuvering the old LEE to reinstall it. Since there was no way to replace only a motor on the arm, the entire joint containing the two drive motors would need to be replaced. Unfortunately, the spare joint motor could not be delivered and