VIBRATION TESTING AND CONTROL OF AN INFLATABLE TORUS USING MULTIPLE SENSORS/ACTUATORS

Inflated space-based devices have become popular over the past three decades due to their minimal launch-mass and 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 vibration 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 highdamping properties. This paper presents the results from vibration tests performed on a scaled free-free torus using Macro Fiber Composite (MFC), which were recently developed at the NASA Langley Center. Our experimental results clearly show that additional sensors and actuators allow for global control of the inflated torus. While adding additional sensors/actuators increases the authority over the structure, when using positive position feedback control techniques, control is limited to the location of sensors/actua tors and the mode intended to be controlled. This can be attributed to the phase differences in the mode being measured incurred by the relative location of the sensors and actuators to one another. These results led to the integration of self sensing actuators, cutting the number of MFC applied to the torus in half and showing significant advantages over separate sensors and actuators. Our results clearly show the advantages of multiple sensors/actuators for use in control of inflatable structures.