Stochastic Self-Assembly via Magnetically Programmed Materials


Steve Boxall/ZeroG

Steve Boxall/ZeroG

By Martin Nisser

The ability to deploy large space structures is key to enabling long-duration and long-distance space missions, supporting permanent habitation, large scale science experiments and solar power generation and transmission. However, launching and assembling large structures today remains a challenge; structures launched to space must be designed to fit within the confines of a rocket fairing; during transport, they must be built to withstand the rigors of launch; and once in orbit, they need assembling by a team of highly trained astronauts in some of the harshest conditions we know of. The engineering of modular structures capable of self-assembly would address many of these challenges; such structures could be partitioned across multiple launch vehicles and transported sequentially; once in orbit, self-assembly would void the danger, life-support overhead and expertise required for astronaut assembly; and once assembled, such structures could be engineered to reconfigure to acquire new configurations in order to adapt to new loads and use cases. 

This project outlines a method to discretize a desired 3D structure into cubic building blocks, and introduces a method to magnetically "program" these cubes to stochastically self-assemble from a random arrangement into a target structure without explicit control. We accomplish this by encoding re-programmable magnetic signatures onto the faces of the cubic building blocks using a custom-built magnetic plotter. Key to enabling self-assembly is the design of unique magnetic signatures that ensures that the face of every cube can only mate with particular other faces, and further, can only do so in particular configurations in translation and rotation. Importantly, the corollary of this feature is that every face remains magnetically agnostic to all cube faces to which it is not intended to bond. Given some initial perturbation, the cubes can thereby self-assemble over time via random collisions, bonding to their intended mates while colliding elastically with unintended mates. These magnetic signatures and the final 3D prototype are therefore programmable, reusable, and not power-consuming during operation. On this parabolic flight, we demonstrate the utility of this system by encoding a self-sorting behavior that can be performed within the 15 seconds of a single parabola. We magnetically program a set of 150 cubes into two compatible sets indicated by blue and yellow coatings.  Starting from a random initial distribution in each parabola, the cubes are able to stochastically self-assemble into two meaningfully distinct groups, one blue and one yellow, within seconds of a perturbation.