Flywheel simultaneous attitude control and energy storage using a VSCMG configuration

Space vehicle programs consistently endeavor to reduce satellite bus mass to increase payload capacity and/or reduce launch and fabrication costs. At the same time, performance demands on satellite systems continue to increase, creating a formidable challenge to space vehicle technology development. Flywheel-based systems providing both energy storage and attitude control functionality address both of these issues. In particular, the flywheel attitude control, energy transmission and storage (FACETS) system should combine all or part of the energy storage, attitude control, and power management and distribution (PMAD) subsystems into a single system, thus significantly decreasing bus mass. The control problem of mechanically-based simultaneous energy storage and attitude control is far from trivial, however, even in its simplest conceivable form. While decoupling the attitude control and energy storage may be a workable solution to the problem, research in related areas suggests it may not be the best approach. It has been shown that simultaneous momentum management and power tracking can be accomplished with four or more wheels in reaction wheel mode using the null subspace of the angular momentum dynamics of the wheels. In this way the energy storage or power tracking function does not induce attitude disturbance torques to the spacecraft. Furthermore, the null subspace was shown to be sufficient for tracking a variety of practical satellite power profiles. For some applications, however, reaction wheels produce insufficient control torque and control moment gyros (CMGs) are required. The paper extends the null subspace approach for simultaneous power tracking and attitude control, proven for flywheels in a reaction wheel mode, to an array of flywheels in a CMG configuration.