A compact, axially aligned brushless servo motor actuation unit configured to manipulate a choke valve to control the pressure within a borehole during managed pressure drilling. The actuation unit including a brushless servo, a gear reduction assembly and a planetary roller actuator substantially aligned along a longitudinal axis and housed within a tubular housing, the gear reduction assembly defining a hollow core sized to enable a portion of a roller screw of the planetary roller actuator to pass therethrough for the purpose of reducing the overall length of the actuation unit along the longitudinal axis.