Elastically Coupled Precision Pointing by Slew-Induced Deformation Shaping

Computed torques for pointing and tracking require compensation for slew-induced structural, forebody/aftbody, or optical train alignment deformations. Thus even if only line-of-sight variables are to be commanded yet full state feedback is needed, with consequent high bandwidth control requirements. The solution investigated here is to decouple the unwanted deformation state by feedforward of the line-of-sight slew dynamics into the deformation control forces or moments, for an apparatus consisting of a mirror mounted on an optical bench, that is itself mounted on a rotating table. Adjustable elastic interfaces are used to model slew-induced deformations as angular differences between mirror mounting, optical bench and rate table. Low bandwidth control with fewer actuators than degrees of freedom is shown to be possible, by correcting the computed torques so as to force the interstage angular differences (standing for slew-induced deformations) to evolve in a "slow" integral manifold wherein they are modeled as functions of the mirror pointing angle. Simultaneous mirror pointing and independent rate table pointing is also shown to be possible, which represents the situation of pointing an instrument elastically mounted on a maneuvering platform.