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An attitude control system consisting of motor-driven inertial wheels in conjunction with an over-riding mass ejection system is proposed for use in space vehicles. Control by mass ejection is usedto compensate for initial distrubances during separation from the booster, and for removal of unwanted momentum stored in the wheels. The use of reaction wheels permits fine, damped attitude control. A laboratory model of a single-axis control system was constructed for experimentation and evaluation. The choice of a suitable platform configuration, selection of a prime mover for the inertial wheel, and the philosophy in the design of the electronics and pneumatics are discussed. Emphasis was placed upon minimization of weight and power consumption. System evaluation includes a discussion of efficiencies, reliability, and torque-speed-power relationships. Sources of disturbances, methods of sensing, and general equations of motion are presented in the Appendix.