Modular Isoperimetric Soft Robotic Truss for Lunar Applications

TL;DR

This work tackles the challenge of creating adaptable, safe, and stowable infrastructure for lunar missions by introducing a modular, isoperimetric inflatable truss that preserves a constant perimeter while deforming. The system combines inflated fabric tubes, two active roller units, a passive roller unit, and a novel spherical joint to connect multiple triangles at a vertex, enabling scalable configurations beyond a single octahedron, including stacked octahedra. Key contributions include a redesigned modular hardware stack with high-pressure-tube operation, a robust actuation and control framework with inverse-kinematics-based motion planning, and demonstrators showing a 12-DOF solar array and a 14-DOF locomotion gait, all with a stowed-to-deployed volume ratio of approximately 1:18.3. The approach offers lightweight, reconfigurable, and safe robotic structures for lunar operations, reducing assembly time, enabling autonomous deployment, and enhancing mission versatility in space environments.

Abstract

We introduce a large-scale robotic system designed as a lightweight, modular, and reconfigurable structure for lunar applications. The system consists of truss-like robotic triangles formed by continuous inflated fabric tubes routed through two robotic roller units and a connecting unit. A newly developed spherical joint enables up to three triangles to connect at a vertex, allowing construction of truss assemblies beyond a single octahedron. When deflated, the triangles compact to approximately the volume of the roller units, achieving a stowed-to-deployed volume ratio of 1:18.3. Upon inflation, the roller units pinch the tubes, locally reducing bending stiffness to form effective joints. Electric motors then translate the roller units along the tube, shifting the pinch point by lengthening one edge while shortening another at the same rate, thereby preserving a constant perimeter (isoperimetric). This shape-changing process requires no additional compressed air, enabling untethered operation after initial inflation. We demonstrate the system as a 12-degree-of-freedom solar array capable of tilting up to 60 degrees and sweeping 360 degrees, and as a 14-degree-of-freedom locomotion device using a step-and-slide gait. This modular, shape-adaptive system addresses key challenges for sustainable lunar operations and future space missions.

Figures (17)

• Figure 1: The isoperimetric truss robot with its main subsystems highlighted: the inflated tubes, the spherical joints, and the active and passive roller units. a) Solar array configuration. b) Locomotion configuration.
• Figure 2: Active roller unit showcasing its external components.
• Figure 3: Comparison between the active roller design in 14_usevitch_untethered (left) and this work (right). The top figures show dimensioning between roller shafts, while the bottom figures show differences between the gear train.
• Figure 4: Construction and operation of the active unit and its sub-assemblies. a) Gearbox assembly (with gearbox cover removed) and motion, illustrating how each gear is actuated to produce the linear motion of the tube. b) Architecture of the active roller unit, highlighting its various components. c) Detailed view of the roller-shaft construction.
• Figure 5: Passive roller unit showcasing the connection between the two ends of the tube along with the plugs, cross bars for fastening the tube to the passive unit, and the interface for connecting to a spherical joint.