Momentum transfer in two-rotor gyrostats

The orientation of a spacecraft can be changed efficiently by transferring angular momentum between the platform and internal momentum wheels using internal torques. The speed of such maneuvers depends on the size of the internal torques and may be limited by the effects of excitation of any flexible elements of the spacecraft, The internal torques required to accomplish such maneuvers arise in various forms. Three types of torque are considered: constant torques for a simple momentum transfer, viscous torques attributable to bearing friction, and time-varying torques defined by a suitable control law. A previously developed graphic result for single-rotor gyrostats is extended to the multiple-rotor case and used to illustrate the different trajectories for the two-rotor gyrostat. A novel feature is the development of stationary-platform rotational maneuvers in which the platform's angular velocity is small throughout the maneuver, These maneuvers are based on a simple control law and are not restricted to small angles.