In response to challenges encountered in the dynamic balancing of the Windsat instrument, a novel approach to dynamic balancing of dual-spin spacecraft was developed. The Windsat instrument is a 675-lb microwave radiometer consisting of a small, 200-lb stationary module topped by a large rotating truss structure approximately nine feet in height. A 72-in.-diameter reflector atop the truss, designed to direct microwave energy into the Windsat radiometer, was a significant source of aerodynamic lift and drag during spin balance testing. The approach developed in this study allows the spacecraft integrator to balance the vehicle while spinning under its own power and about its own spin axis. This balancing system is also capable of operating in a vacuum environment, thus eliminating aerodynamic forces that result in test-induced errors. The balancing system consists of a two degree of freedom (DOF) suspension system similar to that found in conventional balancing machines. Unbalance forces and moments are reacted through two piezo-electric force transducers, the outputs of which are recorded using a vibration lab data acquisition system. To prove viability, a prototype of this system has been developed and integrated into existing Naval Research Laboratory (NRL) spacecraft vibration test facilities. Using existing instrumentation and data acquisition systems, extensive experimentation with this system prototype has demonstrated this concept to be viable, yielding results that agree closely with analytical predictions.

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