Abstract: A reactionless momentum compensated payload positioner adapted to be mounted on a supporting body for providing momentum compensation of an oscillatory and scanning payload and for suppressing reactions in the supporting body to the torques that occur as an aiming angle of the payload is changed. The payload positioner includes a gimbal assembly having at least two axis of rotation including an elevation axis and an azimuth axis. A pair of reactionless drive module are provided for rotating the payload about both axes. Each reactionless drive module includes a housing, a main drive shaft connected to the payload, a DC electric motor for rotating the drive shaft, and a flywheel. The main drive shaft is freely rotatably suspended within the housing by main bearings and the flywheel is freely rotatably mounted to the main drive shaft by bearings. ?In operation, the flywheel counter rotates with respect to the main drive shaft.