Rapid Rotational Maneuvering of Rigid Satellites with Hybrid Actuators Configuration

A new attitude control method for agile rigid spacecrafts that is based on combining single gimbal control moment gyros together with reaction wheels is presented. The method is expected to suit remote sensing spacecrafts that are required to perform multiple rapid retargeting of their line of sight. The main advantage of single gimbal control moment gyros is rapid rotational maneuvering, but their application for high quality pointing requires a very accurate gimbal mechanism. On the other hand, the reaction wheels may be more easily applied for accurate pointing, but their torque-to-power performance is inferior for maneuvering compared to single gimbal control moment gyros. The paper shows that careful coordination between reaction wheels and single gimbal control moment gyros, together in a hybrid configuration, draws more performance from single gimbal control moment gyros in terms of agility and achieves quality pointing between maneuvers by using only reaction wheels. The high-level control is based on a braking curve that relates angular rate to any given three-dimensional altitude, which is calculated according to the satellite eigenaxis deceleration capability. The required angular rate as produced by the braking curve is converted to angular momentum and is then translated into gimbal angles. The lower level control is based on a steering law in the gimbal angles’ domain, where the gimbals are steered to track angular commands.