Abstract—A new control moment gyro (CMG) using a gimballess design is developed for attitude control of a spacecraft. Although benefits of a conventional CMG system include cleanliness, replenishability of power source, and generation of high torque to change direction of a spacecraft, it is necessary to design a complex control system to avoid impassable and escapable singular states that are caused by gimbals. The proposed CMG system using a spherical rotor does not require gimbals for three-axis attitude control. The spherical rotor, which is driven by three pairs of omni wheel attached at a shaft of a motor, consists of a spherical shell, a flywheel, a battery, and IMU to measure the angular velocity of the rotor. Singularity analysis of the proposed CMG is described, and a preliminary experiment is performed to verify the validity of the CMG.