Single-axis pointing of a spacecraft with two skew control moment gyros

The single-axis pointing of a spacecraft using two skew single-gimbal control moment gyros (CMGs) is investigated. First, two types of restrictions are enforced on the gimbal motions of two skew CMGs, with each restriction yielding control torque along a principal axis of the spacecraft. Then, a two-step eigenax rotation strategy, executing by the two single-axis torques respectively, is designed to point a given body-fixed axis along a desired direction. All the body axes that can be pointed toward an arbitrary inertial direction by two single- axis rotations are identified. Moreover, the amplitude of each rotation is analytically derived and CMG singularities are avoided by limiting the maximum slew rate for each rotation.