Abstract: A directional drilling control system for a drill stem carrying a conventional drilling head includes an elongated actuator housing fixed in a borehole being drilled. The drill stem passes through the housing and is generally coaxial with it, and an actuator within the housing is selectively activated to deflect the drill stem with respect to the axis of the housing. The actuator is selectively driven to regulate the direction and amount of deflection to thereby control the direction of drilling. An electrical controller in the housing in communication with a surface controller and/or with feedback sensors in the housing controls the actuator.