A spacecraft attitude control apparatus, comprising: first and second reaction wheel assemblies comprising: first and second reaction wheels; first and second motor-generator (M/Gs) rotationally coupled to the first and second reaction wheels respectively for adding energy to or removing energy from the first and second reaction wheels; respectively; and first and second power flow controllers electrically coupled to the first and second M/Gs respectively, and, adapted to control operation of the first and second M/Gs as motor or generator; and wherein, when no torque command is being executed, said first and second reaction wheels are driven by said respective first and second motor-generators at a first predetermined speed, a power bus coupling to the first and second power flow controllers of the first and second RWAs for transferring energy between the first and second M/Gs, whereas when a torque command is received requiring that the first RWA decelerate and the second RWA accelerate, the first power flow controller configures the first M/G as a decelerating generator and the second power flow controller configures the second M/G as an accelerating motor and power flows from the decelerating first M/G to the accelerating second M/G via the power bus while an output voltage derived from the first decelerating M/G exceeds a back electromotive force (back EMF) of the second accelerating M/G. first and second reaction wheel assemblies comprising: first and second reaction wheels; first and second motor-generator (M/Gs) rotationally coupled to the first and second reaction wheels respectively for adding energy to or removing energy from the first and second reaction wheels; respectively; and first and second power flow controllers electrically coupled to the first and second M/Gs respectively, and, adapted to control operation of the first and second M/Gs as motor or generator; and wherein, when no torque command is being executed, said first and second reaction wheels are driven by said respective first and second motor-generators at a first predetermined speed, first and second reaction wheels; first and second motor-generator (M/Gs) rotationally coupled to the first and second reaction wheels respectively for adding energy to or removing energy from the first and second reaction wheels; respectively; and first and second power flow controllers electrically coupled to the first and second M/Gs respectively, and, adapted to control operation of the first and second M/Gs as motor or generator; and wherein, when no torque command is being executed, said first and second reaction wheels are driven by said respective first and second motor-generators at a first predetermined speed, a power bus coupling to the first and second power flow controllers of the first and second RWAs for transferring energy between the first and second M/Gs, whereas when a torque command is received requiring that the first RWA decelerate and the second RWA accelerate, the first power flow controller configures the first M/G as a decelerating generator and the second power flow controller configures the second M/G as an accelerating motor and power flows from the decelerating first M/G to the accelerating second M/G via the power bus while an output voltage derived from the first decelerating M/G exceeds a back electromotive force (back EMF) of the second accelerating M/G.