Flight Testing High-Expansion-Ratio Deployable Structures (HERDS) for Kilometer-Scale Space Structures

This solution is a high-expansion-ratio deployable structure (HERDS) built from mechanical metamaterials. Specifically, the solution uses the novel pop-up extending truss (PET) and kresling mechanisms with the goal of producing structures with a 50-100x expansion ratio. Practical applications could include large space structures, deployable infrastructure, and medical devices.

Structures and materials with geometric hierarchy commonly exhibit enhanced strength-to-weight ratio. The HERDS project is designed to show that non-planar hierarchical compositions can dramatically improve deployable beams’ extension ratios and mechanical stiffness.

HERDS includes a pop-up extending truss (PET) that uses scissor-like structures to enable multi-axis reorientation, enhancing the bending stiffness by over 100% compared to other scissor-like variants with equal mass and linear packing. By combining PETs with Kresling origami mechanisms, HERDS is designed to support 10x higher bending, compressive, torsional, and tensile stiffness at 25x to 200x extension ratios compared to non-hierarchical structures.

Problem Statement
The goal of this solution is to provide a structure that folds small enough to fit on a rocket and then automatically expands to one kilometer long upon release into orbit — the size needed to provide artificial gravity to astronauts during long-duration spaceflight. Sustained human presence in space poses serious challenges for the human body due to the lack of gravity, including muscle atrophy, bone loss, eyesight degradation, and immunosuppression. The ability to generate artificial gravity would eliminate the root cause of many problems; however, rotating space habitats cause discomfort at rates of 3 RPM or faster. Producing artificial gravity near 1 g at rotation rates of 1-2 RPM requires a kilometer-scale structure. In addition to enabling large space structures, this technology also could be used for rapidly deployable infrastructure on Earth.

Technology Maturation
The primary objective of the flight test is to evaluate the deployment dynamics of multiple pantographic structures — specifically, the PET, translational scissor, and angulated scissor mechanisms — when actuated passively by centripetal force in microgravity. With the complexity of the designs, parts of these structures can occasionally jam and break, creating a need for highly accurate testing environments to make improvements. The team developed 1/10th-scale prototypes of these structures in the lab and then sized down to 1/1000th-scale prototypes to observe their dynamics under varying initial spin velocities during parabolic flight. The experiment aims to capture high-resolution motion data using a multi-view setup of eight GoPro cameras and four OptiTrack cameras to study deployment behavior and transient dynamics.

A key objective is to validate the physics-based simulation models by quantifying the sim-to-real gap observed during deployment in microgravity.

Summary of April 15 to May 8, 2025 Flight Test
During this flight campaign, the HERDS (Hierarchical Extension from Reorienting Deployable Systems) team, consisting of members from Carnegie Mellon University, Northeastern University, and the University of Washington, successfully tested multiple pantographic deployable structures in a microgravity environment. Using a combination of high-speed GoPro cameras and OptiTrack motion capture, we captured detailed data on the passive deployment dynamics of multiple mechanisms. The experiments demonstrated a potential opportunity to leverage passive deployment of pantographic structures from payload tumbling after rocket fairing release. The captured data is also being used to validate a full-element rigid body simulator that accounts for joint friction and clearance, enabling digital twin testing to prevent jamming or deployment failures.

This project aims to create foldable structures small enough to fit on a rocket yet capable of expanding to up to a kilometer long once released into orbit, with the goal of supporting astronauts in microgravity environments and long-term mission planners. It can serve to support large space structures for projects like future space stations as well as rapidly deployable infrastructure for Earth applications, such as cell communication towers that can stow in a backpack for easy transport to support disaster relief efforts.

This work could have short-term and long-term impact for NASA objectives. In the near term, such structures would make sustained human habitation in cislunar space, for example as part of the lunar Gateway, possible. In the medium-to-longer term, such structures would be critical to sustaining humans in deep space. Finally, large structures would also advance astronomy by supporting large-scale telescope arrays.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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