Disc brakes may be actuated mechanically by cable, or hydraulically. SMA actuators are typically actuated electrically by Joule heating. Stage separation is accomplished with explosive bolts and a pneumatically actuated pusher system. All control surfaces are actuated by dual hydraulically boosted irreversible systems. They are actuated hydraulically and controlled by the boom operator using a control stick. The previously manual flaps were now electrically actuated through a panel-mounted flap switch. The ejector is a plunger on the bolt face actuated by a coil spring. The butterfly valve is actuated through hydraulic linkages. SMA actuators are typically actuated electrically, where an electric current results in Joule heating. All this is actuated automatically, and operated through the electrohydraulic actuators of the transmission's computer. The traverse of the turret was electrically actuated. Rim brakes are typically actuated by a lever mounted on the handlebar. Hydraulically actuated blowout preventers had many potential advantages. It also now had a four-speed transmission with a hydraulically actuated clutch. The vented gas drove a piston which in turn actuated the breech block.