A semiactive isolator filled with liquid-crystal type electro-rheological (ER) fluid was developed to attenuate the disturbances generated by a momentum-wheel and to improve pointing performance. The principal characteristics of an ER isolator were measured in dynamic tests, and a mathematical model of the isolator was proposed. Two control laws for a semiactive approach were proposed. Numerical simulation results indicated that the proposed semiactive control system produced much better isolation performance than a passive system.

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