Universal thruster selection logic for spacecraft attitude control

Abstract

A three-axis stabilized spacecraft includes a plurality of primary attitude control thrusters, the torque vectors of which lie in, or parallel to a primary plane. It also includes at least two more secondary attitude control thrusters, the torque vectors of which lie in a secondary plane which is not parallel to the primary plane. The control system produces attitude error signals, which are processed with a PID characteristic to produce impulse demand signals, all in known fashion. The impulse demand signals are transformed into an auxiliary coordinate system, in which two of the three auxiliary axes lie in the primary plane, and the third is orthogonal thereto. One of the secondary thrusters is selected, which has, along the third auxiliary axis, the largest torque magnitude and the same sign as the transformed impulse demand. The augmented impulse demand in the primary plane is determined, and the two primary thrusters are selected whose torque vectors in the primary plane bound the augmented impulse demand. The selected primary thrusters and the selected secondary thruster are fired with a pulse width which provides the desired impulse.