Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 171384

Active Deployment Control of Ultra-Thin Composite Space Structures 

Controllable deployment is critical in a wide range of engineered space systems such as antennas for telecommunication, solar arrays for power generation, and in-space manufacturing platforms. This capability is required for preventing incomplete expansion or operational failure of mission critical components and payload. The current state of the art for controlling the deployment of space structures is to quasi-statically guide the expansion through motorized deployers or dissipate the energy release with complex restraint mechanisms. These methods significantly contribute to the system mass, bulk, and mechanical complexity when compared to freely self-deploying composite shell structures. However, instability-driven deployment has implementation challenges due to the difficulty of balancing the stored strain energy. Excessive packaging leads to prolonged and disordered motion while inadequate packaging induces risk for partial deployment due to not generating enough extension force.  

To address this problem, a highly mass and volume efficient deployment control technique is developed with flexible piezocomposite actuators called Macro Fiber Composites (MFC). Active perturbations are applied to initiate or alter the occurrence of elastic instabilities within composite structures during their expansion. MFCs are highly compatible with the lightweight and high strain characteristics of ultra-thin composite materials in terms of having sufficient authority and frequency response. By manipulating the localized shape of bonded regions through voltage actuation, large and disordered motion that arise from shell buckling, snap-through events, and propagating folds can be suppressed. Likewise, perturbing bistable coilable structures beyond their strain energy peak can initiate a smooth unrolling transition between the stowed and deployed states through limit point behavior. The enabling mechanic is the MFC altering the cross-sectional curvature of the bonded area when it becomes directly adjacent to a highly deformed section. This induces a large shape change in the deformed section due to the tendency of the shell to maintain a consistent ploy region (i.e. transition area between the deformed and undeformed regions). The efficacy of these techniques has so far been demonstrated with a simple cantilevered composite tape spring in Abaqus FEA and experimentally validated with manufactured specimens using real-time motion capture and high-speed digital image correlation experiments.

To achieve a closed-loop deployment control scheme, optical fibers with Fiber Bragg Grating (FBG) arrays are embedded between the composite plies for in-situ distributed strain sensing. Locally inscribed FBGs within the fiber core operate by each reflecting a different wavelength when a light spectrum is transmitted down the fiber. Each reflected Bragg wavelength shifts when there is a calculable strain change. Though fiber optic sensing has been widely applied towards structural health monitoring, it is a novel sensing method for ultra-thin deployable composite shell structures. It has the potential to alter the state of the art in remote deployment monitoring because FBGs allow for thousands of distributed point strain measurements along a single optical fiber, providing ease of scalability with large structures. Its effectiveness in tracking the unfolding and uncoiling motion has so far been demonstrated with a single FBG sensor. For active deployment control, an array of localized FBG strains will be correlated against both motion capture and high-speed DIC data to create a link to the mechanical state during deployment.

Presenting Author: Andrew Lee North Carolina State University

Presenting Author Biography: Andrew Lee is an Assistant Professor of Mechanical and Aerospace Engineering at North Carolina State University. He received his B.S.E., M.S.E., and Ph.D. in Aerospace Engineering at the University of Michigan and was a postdoctoral scholar at the California Institute of Technology. His research focuses on the mechanics of lightweight space structures including problems related to packaging, deployment, stability, dynamics, and active control. Dr. Lee is the recipient of the NSF CAREER Award, AFOSR Young Investigator Program Award, ASME Haythornthwaite Young Investigator Award, AFOSR Summer Faculty Fellowship, and the Rackham Merit Fellowship.

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