Active vibration suppression of a gossamer spacecraft

Inflated space-based devices have become popular over the past three decades due to their minimal launch-mass and launch-volume. Once inflated, these space structures are subject to vibrations induced mechanically by guidance systems and space debris as well as thermally induced vibrations from variable amounts of direct sunlight. Controlling the vibrations and shape of space-based structures is critical to ensuring their optimal performance. Inflated materials, however, pose special problems when testing and trying to control their vibrations because of their extremely lightweight, flexible, and high-damped properties. In this study, we showed that Macro-Fiber Composite (MFC) patches, which is recently developed at the NASA Langley Center and can be integrated in an unobtrusive way into the skin of the torus, could be used as sensors/actuators in order to find modal parameters. The data measured with the MFC patches has a good agreement with the measurements with an accelerometer. Further, it is obvious during the tests that the MFC excitation produced less interference with suspension modes of the free-free torus than excitations from the conventional shaker. In order to control and reduce vibrations of the torus, we used positive position feedback methods since they are fairly robust to parameter uncertainties. Both separate sensor/actuator combination and self-sensing actuators have been used for vibration control. Our experimental results clearly indicate that this control strategy and actuators can reduce vibration, and provide the potential of smart materials for use in the dynamics and control of inflated structures.