One last look at my hardware: the SRB Thrust Vector Control (TVC) subsystem. These six octagons are the Service Panels which provide access to the hydrazine-powered fuel systems and hydraulic systems inside the SRB Aft Skirt. The TVC subsystem gimbals the Nozzle for vector control and is critical during ascent. Therefore, there are two independent subsystems, known as Rock and Tilt, as indicated by the green and red lines. Near the bottom center of the picture (black, diamond-shaped object) is the Tilt system's Auxillary Power Unit (APU) Exhaust Duct. To the right at about the 4:30 position is the Rock system's Exhaust Duct.