Dynamics Analysis of Origami-Folded Deployable Space Structures with Elastic Hinges

Spacecraft design is inherently limited and dictated by available launch vehicle capabilities, motivating the development of a wide variety of deployable spacecraft structures.  These structures are developed to meet the communication, operation, and scientific objectives of the spacecraft mission, and therefore the successful deployment of the structure is required for overall mission success.  Typical analysis of deployable spacecraft structures spans questions of structural stiffness and stability, vibration modes, thermal stability, and deployment dynamics.  In this thesis, only the deployment dynamics are of interest.  Validation and verification of deployment for deployable structures is primarily achieved through rigorous testing, and this is sometimes presented in tandem with complex finite element simulation or a simplified model approximation.  The key questions of this validation typically regard what the deployment motion looks like and are answered through analysis of the deployment dynamics states.  Therefore, deployment dynamics analysis plays a key role while also providing a central challenge for deployable structures development. 
           
An emerging area in the deployable structures field is referred to as origami structures and takes primary inspiration from origami folding techniques.  These are developed to stow flat structures with large area to size ratio relative to the spacecraft bus, such as solar and phase arrays, star occulters, and reflector antennas. A central challenge for origami structures is the deployment dynamics and deployment actuation of the folded structure and spacecraft system.  A novel lightweight solution for deployment actuation is to integrate strain energy hinges that can also facilitate folding.  Deployment dynamics of such a system would typically be studied through finite element analysis (FEA).  However, for a structure with multiple high strain hinges, FEA modeling would require significant computational time and skill, as these hinges exhibit large deformations of shell structures with non-linear behavior.  This limits the ability to explore parameter design spaces and iterate towards more optimal solutions. An alternative method for studying the system dynamics that uses multi-body dynamics and a simplified hinge representation is the focus of this thesis.  In this approach, fold panels are treated as rigid bodies and the flexible joints are represented by internal forcing functions.  In this thesis, a model to represent the hinge mechanics is designed as a function of the hinge's multiple degrees of freedom, as defined by the relative position and orientation states.  This model is designed to be implemented in a multibody dynamics algorithm customized for origami-folded deployable spacecraft structures.  The methodology aims to provide an approximation that enables sufficient deployment dynamics simulation accuracy without a full FEA simulation of the system.  
           
The multibody dynamics modeling approach for this thesis implements the Articulated Body Forward Dynamics algorithm and Spatial Operator Algebra for free-flying spacecraft systems with closed-chain constraint enforcements and the applications of this approach for deployable structures is demonstrated.  Constraint stabilization is discovered to be the primary challenge for scaling this approach to systems of many folding panels.  An approach for modeling high strain tape spring hinges for simulation of free deployment dynamics is presented and applied to a high strain composite hinge sample.  This study includes both an FEA database and experimental measurements, and concludes that the high strain composite materials contain a level of variability that makes repeatability and behavior prediction challenging.  An additional study of a folding hinge with two spring steel tape springs is developed and implemented in prototype structure validation efforts. A novel folded deployable structure is designed and constructed with a segmented, multi-DOF hinge, and a rigorous suite of deployment tests are conducted using videogrammetry for deployment data measurement.  A full simulation of the prototype is constructed from the multibody dynamics model and the multi-DOF hinge model, and the predicted deployment behavior is evaluated against the testing.  Additionally, the prototype deployment is replicated using an explicit dynamic FEA analysis for a performance comparison.  The models demonstrate strong correlation for deployment time predictions across the states.