Predicting and preventing reaction torque coupling in gimbal system mounts

As pointing system performances continue to increase while gimbal and vehicle weights decrease, structural considerations of the gimbal-base interface become more problematic and important. We begin by presenting the generalized structural transfer function equation in modal superposition form. We emphasize that the reaction torque of an actuator must be included in practice. From this theoretical basis, we assume stiff gimbal structures and evaluate the structural coupling due only to mount flexure. We show that in some inertially stabilized precision pointing systems the effect of the actuator reaction torques cannot be ignored. We show that structural stiffness is less important than properties of the mount symmetry. In particular, asymmetries in the system mount (the structure between the reaction torque and the base) allow dangerous coupling between gimbal axes. The observed coupling may depend on the angles of the gimbals, making experimental testing and validation more challenging.