Stability as a function of gear train stiffness for solar array alpha gimbal pointing control system on space station Freedom

The baseline design of the solar array alpha joint control system on the space station Freedom utilizes an analog angular rate feedback loop with collocated sensor and effector to phase-stabilize torsional structural resonances whose frequencies occur below the 90° lag frequency of the electronics. This approach is preferred over gain stabilization because it allows the controller to add significant damping to these phase-stabilized modes. The alpha joint controller design capitalizes on the soft gear train compliance to ensure gain stability above the 90° electronic lag frequency. The author explores the transition between phase and gain stability of the analog rate loop. He studies the gain attenuation of structural modes above the gear train resonant frequency, which makes the design approach possible. The designs and analyses described herein are preliminary