SELF-BALANCED ACTIVE MODAL DAMPING FOR FLEXIBLE SPACECRAFT 89-3536-CP USING THRUSTERS AND BANDPASS FILTERS

A self-balanced active modal damping scheme is developed forelastic modes of free space structures using thrusters, gyros, and bandpass filters - - self-balanced because it results in no net change in spacecraft's attitude. This scheme is necessarily open loop because owing to adjacent modes a bandpass filter, whether an ideal one or Minimum Rise Time optimumfilter used here, may not haveenough bandwidth to track an actively damped mode. Modeling uncertainties, nonetheless, pose no problem because the Minimum Rise Time filter can determine the modal frequency accurately, and the errors in modal coefficients and damping can be compensated for with vernier thrusters. When the filter acquires steady state, it furnishes the modal frequency, modal amplitude, and phase which are then used to determine optimum pulse width of the thrusters ; the modal coordinate is then propagated open loop, firing thrusters around peak modal rates. The scheme is illustrated on agenericspacecraft whose first symmetric transverse bending mode (0.28 Hz) and the first in-plane antisymmetric bending mode (0.97 Hz) are both actively damped to a few thousandths of their initial amplitudes.