Imbalance identification and compensation for an airborne telescope

Airborne telescopes are typically supported by spherical bearings to prevent angular motions of the aircraft from affecting telescope pointing accuracy. Mass balancing of the telescope about the center of rotation is necessary to minimize the motor torque requirements. A static-balancing procedure that uses peg-mounted and moving counterweights to make the telescope center of mass coincident with the center of rotation is presented. Force-transducer measurements of the imbalance torque were used to identify the mass imbalance. A least-squares-directed search algorithm was developed to optimize placement of peg-mounted and moving counterweights for coarse and fine balancing. When implemented on a ~100 kg laboratory prototype, the procedure achieved balancing to within a mass-moment error of 0.005 kg-m in less than 5 minutes. This is more accurate and up to 50 times faster than had been accomplished using previous methods. Two key developments for the achievement of these results were (1) imbalance identification using force transducers with both high accuracy near zero and high load capabilities and (2) an optimization method to place the discrete counterweights