Fisheye view, showing the Solid Rocket Booster (SRB) Thrust Vector Control (TVC) Service Panels. The red and green colors represent two independent, and redundant, systems inside the Aft Skirt. TVC gimbals the Solid Rocket Motor (SRM) nozzles for 80% gimbal authority during ascent. The Space Shuttle Main Engines (SSMEs) and Orbiter aerosurfaces provide the other 20%.