Dynamics of an Elastically Deployable Solar Array: Ground Test Model Validation

Abstract

This paper presents an analytical, computational and experimental study of the deployment dynamics of an elastically deployable solar array. The thin film array is folded in multiple stages with elastic hinge and deployed depth stiffening elements and then allowed to deploy under its own elastic strain energy. A computational model of the geometrically nonlinear deployment is assembled using reduced order models of the elastic hinge elements. Restoring torque models developed for each hinge line are validated through isolated testing of each of three deployment stages. Both linear and nonlinear models of the corresponding elastic mechanisms are updated from the results of these experiments. The ground tests use a simple low-stiffness suspension system and videometry to measure the angular displacement of the deploying panel to be measured. The angular velocity and acceleration are computed from this data for use in the model updating process. The testing is performed on an early version of the array, called the engineering model (EM), and on the flight unit. For the first stage, the root hinge, the classical and computational models adequately predicted experimental results. The second stage, or z-fold deployment, experimental results indicated a stiffness that was 2.3 times smaller than the predicted stiffness for the EM. Flight unit results more closely matched predictions. For the final stage of deployment, the tri-fold, the nonlinear elastic response of the shallow shell, or tape hinges, is predicted by analytical models of their post-buckled mechanics. For this stage, the observed long range stiffness is greater than the expected results based on thin plate theory and computational simulation. Further testing of flight unit components and updating model parameters will improve the understanding of the deployment dynamics of the array.