CHAPTER 7 SYSTEMS: MOTION CONTROL SYSTEM—NAVIGATOR OF THE HEAVENS 136 replaced, as well. A postmortem investigation indicated design issues within the spin bearing that caused the ball bearings to skid instead of roll, exacerbated by relatively high gimbal rate limits. The CMGs exhibited no additional signs of distress following software modifications to slow down the maximum rates of the gimbals from 3 deg/s to 0.8 deg/s. Furthermore, the two spares stored on the ISS have an improved bearing design based on lessons learned from the failures of CMG-1 and CMG-3. Figure 17. Astronaut Dave Williams works to replace a CMG during STS-118/ISS 13A.1. Conclusion Although the MCS can only fully support the ISS by combining the vastly different US Segment and Russian Segment systems, both systems complement each other well. The USOS system provides a smooth microgravity attitude control capability that minimizes the use of on-board propellant consumables, and the Russian Segment system provides the necessary thruster capabilities to handle reboosts and attitude control situations beyond the capabilities of the CMGs. As with the systems on orbit, flight controllers in both MCC-H and MCC-M work closely together to keep the complete ISS MCS in good health for the purpose of supporting a stable platform for both the crew and the research program.