Reaction-boom attitude control systems

Abstract

Active gravity-gradient stabilization systems are shown to permit significant improvement in the stabilization and maneuvering capability of Earth-pointing satellites compared to more conventional momentum storage and mass expulsion techniques. The proposed configuration consists of the pay load body and a properly arranged array of gimballed reaction booms. The appropriate boom gimbals are torqued on the basis of pay load attitude and gimbal sensor data. Qualitatively, the system may be viewed as a hybrid that derives rapid momentum transfer and payload maneuvering capability from active torquing between the component parts of the satellite, while obtaining the necessary momentum dumping from gravity-gradient torques acting on the over-all configuration. The number, geometry, and hinging of the booms is dependent on the specific control or maneuvering requirements; therefore, three distinct system types are proposed. Procedures for selecting control laws are developed on the basis of simplified dynamic models, and the expected system performance is verified through simulation of both linearized and full nonlinear system models. The observed payload response resembles that of a fast reaction-wheel system. Low-frequency, gravity-gradient modes are effectively decoupled from payload motion and boom oscillations are satisfactorily constrained even for large-angle payload steering maneuvers.