Summary: Both classical and state-space synthesis methods for active control of flexible space structures in the presence of persistent disturbances are presented. The methods exploit the so-called internal model principle for asymptotic disturbance rejection. A generic example of flexible space structures is used to illustrate the simplicity of the proposed design methodologies. The concept of a disturbance rejection dipole is introduced from a classical control viewpoint. It is shown that the proposed design methods will invariably make use of disturbance rejection dipoles and non-minimum-phase compensation for a class of noncolocated control problems in the presence of persistent disturbances. The need for tradeoffs between performance and parameter robustness is also discussed.