R&D PULSE
A Boom that Deploys Itself
The use of 3D laser scanning can improve the designs of self-deployable tape spring booms in aerospace applications.
Written by Kayt Sukel
IT SEEMS TO HAPPEN IN EVERY MOVIE in every movie about space flight. At some point, an astronaut must, against all odds, deploy a vital payload to save the crew—and, often, the world. But then the equipment fails, requiring the astronaut to MacGyver a solution just in the nick of time.
In the real world, aerospace designers rely on metallic booms to deliver antennae, solar arrays, and solar sails. Engineers have been working tirelessly to improve these systems, said Deven Mhadgut, a graduate student in the Department of Aerospace and Ocean Engineering at Virginia Polytechnic Institute and State University (Virginia Tech).
“These large, metallic structures—which are state of the art right now—are used to deploy optical or communications payloads,” he explained. “That requires a certain level of pointing accuracy and vibration tolerance. You want them to be as stable as possible.”
But the more stable they are, the heavier they are—increasing their fuel mass. As a result, many are looking toward more flexible materials, like carbon fiber, to create self-deployable tape spring booms to deliver payloads in space. Virginia Tech has designed the Ut ProSat-1 (UPS-1), a 3U CubeSat, that can repeatedly self-deploy a parabolic tape spring boom on orbit. There’s only one problem, Mhadgut said. When engineers try to characterize boom dynamics experimentally, their models come up short.
The research team’s experimental setup for modal analysis using a laser vibrometer and an impulse hammer, plus a measurement grid (all dimensions are in millimeters, not to scale). Photo: Virginia Polytechnic Institute and State University
“Predicting how [the boom] will work during a passive deployment is challenging because of uncertainties in the mass and stiffness, as well as the complex boundary conditions, because these booms are really lightweight and flexible,” he said. “They are extremely sensitive to tiny imperfections, and we realized even a small fraction of a millimeter difference in a model can completely change the natural frequencies, the vibration parameters, and even the mode shapes of the structure.”
In fact, when Mhadgut and colleagues built a finite element analysis model based on the CAD model of a self-deployable tape spring boom, they learned it did not match experimental data of the same device. The question then became how to make a more accurate model.
“We decided to flip the process and take a civil engineering approach,” he said. “We realized if, instead of starting with the design, we could start with the reality using a high-resolution, 3D laser scanner. It allowed us to easily capture the as-built geometry and the shape of the boom down to a submillimeter accuracy.”
“Recently, there’s been advances in morphing aircraft structures like wings, changing shape to change the drag coefficient. You could even see this type of modeling being used in precision robotics for surgery or other biomedical devices.”
—Deven H. Mhadgut, a graduate student in the Department of Aerospace and Ocean Engineering at Virginia Tech
Once the research team did that, they were able to generate a new finite analysis model based on the 3D laser scanning data. And the new model, based on the high-density, high-accuracy 3D data, performed much better than other models. In fact, Mhadgut said it aligned almost perfectly with the experimental data and frequency prediction.
“The new model improved from 25 percent error down to 1 percent error,” he said. “Even trying other methods, including taking 21 different levels or measurements, I couldn’t capture the geometry as accurately as with a high-fidelity 3D scanning model.”
The new point cloud model achieved a position error of 0.1 millimeter, compared to other models with larger errors of 13 millimeters and 7 millimeters. In terms of modeling mode frequency, the point cloud model had a 1.2 percent frequency error, compared to 7.7 percent and 27 percent for other modeling methods.
A built out boom prototype. Photo: Virginia Polytechnic Institute and State University
Displacement mode shapes for the point cloud model. Photo: Virginia Polytechnic Institute and State University
Mhadgut said their research shows that integrating serial geometric data into simulations for these innovative self-deployable spring tape booms can dramatically improve predictions for performance and natural frequencies. What’s more, he added, it can not only benefit the design of booms, but other devices or engineered structures where geometry plays a critical role.
“Recently, there’s been advances in morphing aircraft structures like wings, changing shape to change the drag coefficient. You could even see this type of modeling being used in precision robotics for surgery or other biomedical devices,” he said. “These kinds of new and data-driven modeling approaches can help us better understand the system dynamics.”
Kayt Sukel is a technology writer and author in Kansas City.
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