CHAPTER 15 SYSTEMS: ROBOTICS—THE CONSTRUCTION EQUIPMENT FOR THE INTERNATIONAL SPACE STATION 262 Several days after arrival, the SSRMS removed the exposed pallet from the HTV trunk. The pallet contained a new payload for the Japanese Experiment Module exposed facility. Additionally, two completed and used-up experiments were placed on the exposed pallet, which was eventually installed back in HTV5 for disposal (Figure 17). Reversing the capture and berthing process, the crew and ground removed the HTV from the ISS on September 28. The HTV then reentered the Earth’s atmosphere and disintegrated. Figure 17. Astronaut Kjell Lindgren operates the Canadarm2 to install the exposed pallet into the HTV5 trunk area. The exposed pallet contained two experiments that had been completed and were ready for disposal. NASA video. Operational Challenges and Triumphs The SSRMS was delivered to the ISS in 2001 during the STS-100/ ISS-6A assembly mission. Its activation and commissioning did not go smoothly, however. Not long after the arm had been activated, the ISS Primary Command and Control (C&C) Multiplexer/DeMultiplexer (MDM) (see Chapter 5) failed. This by itself was not critical. Computers are known to have problems now and then, which is why there are three of these on the ISS. However, by all indications, it was not a software problem rather, the spinning hard drive had failed. The robotic systems relied heavily on the hard drive, reading critical programming files and recording key data about the system performance for flight controllers to monitor. Due to this reliance and use of the hard drive, it was first believed that the SSRMS was the cause of the failure. This concern increased when a second C&C MDM failed with a similar signature. The situation became more critical when the third computer failed (see also “When Computers Crash,” Chapter 5). As the Onboard Data Interfaces and Network (ODIN) (see Introduction) flight control team figured out how to recover the computers, the robotics flight controllers were challenged to complete the operations on ISS-6A. These operations included returning the pallet on which the arm had been delivered back to the shuttle payload bay, and putting the arm in a safe configuration for the shuttle undocking. Fortunately, the arm was already activated when the MDMs failed because, normally, it loads all of its operating software from the same hard drives that failed. However, the crew’s displays on the Portable Computer System, which is used for operating the SSRMS, also depend on the hard drive. ROBO was faced with a brand new robotic arm with no way to control it. Ground control had not yet been invented. The ground team worked rapidly to figure out how to have the crew maneuver the SSRMS to the needed position, and then have the astronauts fly the last little bit using the hand controllers, which still worked. This had to be accomplished without the displays that the crew had been trained to use, and had to be executed under the direction of ROBO using video and telemetry on the ground. In this fashion, the team “limped” through the remaining robotics operations. After the mission, the ROBO team began working out concrete plans for ground control operations. After detailed investigation by the flight control and engineering teams over several weeks, the flight control team determined that various problems during years of testing on the ground had caused the C&C MDM hard drives to literally fracture. Although this had significant implications for the space station since these computers controlled the US On-orbit Segment, it directly and severely impacted the robotic operations. The next mission, STS-STS-104/ISS-7A, was scheduled to deliver the airlock module the SSRMS was required to successfully install it, as was the case with all remaining modules. Flight controllers worked hard over the next 3 months to install spare hard drives and reload all the software from scratch, including the robotics software. No further problems occurred during the installation of the airlock on ISS-7A. New challenges soon emerged. On March 5, 2002, one of the two redundant electrical drive motors on the wrist roll joint on the “A” end (see Figure 4) failed on the SSRMS. Two systems were built into the arm so that if one failed during a critical operation, such as while installing a module, the second motor could take over and complete the job. However, to start a major operation with one system already failed