• The actuator consists of the control surfaces and associated servomechanisms, and is used to change the missile attitude and trajectory or flight path. 

       - Most actuators for missile applications can be of the hydraulic, pneumatic, electro-mechanical or piezoelectric type, depending on the maximum hinge moment of the control surface.

• The selection and design requirements for actuators usually depend on the following: 

       - The bare airframe - space requirements
       - Flight conditions - forces and torques
       - Guidance system - bandwidth and delays
       - Noise feeding into other sub-systems - EMC

• For example, for a missile of limited flight duration, a hydraulic system has very attractive performance, weight and volume, as shown from experience with the Sparrow and Hawk missiles. 

       - However, it can suffer from problems after long storage i.e. from dirt, deterioration of seals etc.