Characterization of a constant force suspension mechanism

Space structures are often very flexible and cannot support their own weight when they are on Earth; therefore, they have to be supported externally during Earth-based testing. There have been many attempts to devise a system that emulates a zero gravity environment on Earth, for testing of models and prototypes of flexible space structures. Many of the techniques used to support these structures neglect the vertical dimension and restrict testing to the two dimensions of a surface in the horizontal plane. This thesis describes a suspension mechanism for ground testing that allows three-dimensional vibrational testing of large space structures and their physical models. The constant force mechanism (CFM) is a passive device that consists of a spring, cables, a cam, and a pulley. A spiral cam compensates for the change in force developed by stretching the support spring. The profile of the cam was determined from the equilibrium condition to balance the weight of the test article against the force of the support spring. Ideally the suspension mechanism should not add any inertia, damping, or residual stiffness to the tested structure. The individual-component mass, stiffness, and damping were determined experimentally, as well as theoretically where possible. A mathematical model was developed by the author to predict the response of the entire system, including the test article. The solution to the differential equation was determined numerically. The mechanism was constructed and experiments were conducted to see how the motion of the test article was affected by the suspension system and to verify the mathematical model.