Deployable Unit Cells for Space Lattice Structures

Abstract

Autonomously actuated deployable structures are increasingly relevant for space applications where compactness, low mass, and autonomous assembly are critical. Additionally, lattice structures are structures assembled by repeating unit cells in a particular pattern and are also particularly interesting given their high stiffness to weight ratios and high design controllability. Existing deployable systems are often mechanically complex, require multi-part assembly, or lack reversible deployment, limiting their practicality for modular robotic construction. This thesis addresses these challenges by developing a compact, print in place deployable unit cell primary structure that can deploy with springs, lock, and unlock using a motorized actuator.

The goal of this study is to design, manufacture and characterize a deployable unit cell that achieves high packing efficiency and reversible deployment with its primary structure being printed entirely in place using fused deposition modeling (FDM) in PLA (Polylactic Acid). The system studied is a 100 x 100 x 100 mm cubic unit cell with collapsible vertical struts, each made of two arms connected by a revolute pin at mid length. A ball clip mechanism locks the struts after deployment, torsion springs mounted at the central pin provide actuation torque, and nylon strings routed through the struts enable undeployment by spooling onto an integrated motor driven spool. The cell is printed with appropriate clearances between moving parts to enable print in place manufacturing, and achieves a packing coefficient of 10\%, which means that it collapses to 10\% of its deployed volume, and occupies a deployed volume equal to that of the CubeSat standard. In its compact form, 10 cells can be stacked within the same volume.

The printed cell showed predictable mechanical behaviour under compression, with edge struts unclipping sequentially and unclipping forces ranging from ~220 N after 40 cycles to ~310 N for a pristine cell. Deployment tests demonstrated a 100\% successful deployment rate over 20 deployment cycles. Upon optimization through printing trials, a print success rate of 100\% was also achieved for the last 10 unit cells printed.

These findings confirm that a reversibly deployable, low volume, single material unit cell can be reliably manufactured using FDM. The results highlight the potential for integrating such cells into modular robotic construction for large space structures, with future work focusing on improved materials, refined locking and actuation, enhanced packing efficiency, and multi cell robotic manipulation.