Nonlinear controller to reduce resonance effects during despin of a dual-spin spacecraft through precession phase lock

The capture dynamics of precision phase lock (PPL) of a dual-spin spacecraft (s/c) are described. During PPL, the motion of the rotor unbalance becomes synchronized with the inertial free precession of the s/c. If the despin motor torque is constant and small relative to the unbalance size, then PPL causes a large secular deviation of the bearing axis from its desired direction. One common despin strategy to avoid this behavior is to apply constant torque at the maximum capability of a relatively large motor. The authors develop an alternative strategy based on nonlinear closed-loop feedback control of despin motor torque. Their feedback-control strategy produces dynamic behavior which drives the s/c through the PPL resonance condition. It is demonstrated that this strategy leads to successful despin through PPL even when motor torque is relatively limited