Design and manufactring of an ultra-lightweight semi-rigid indoor airship for underground exploration

Abstract

Robotic exploration of confined or hazardous environments, such as tunnels, industrial interiors, and underground caverns, remains constrained by the endurance, safety, and disturbance limits of conventional aerial platforms. Although multirotor drones offer precise control and hovering capability, their reliance on continuous thrust severely limits flight duration and payload capacity. Lighter-Than-Air (LTA) airship platforms offer a promising alternative. By generating lift through buoyancy rather than propulsion, they enable lower energy consumption, reduced aerodynamic disturbance, and inherently safer operation. While significant progress has been made in the design of large, outdoor airships for stratospheric or tethered missions, where payload and endurance dominate design priorities, indoor LTAs operate at a drastically smaller scale (approximately one cubic meter), enabling navigation through narrow corridors and doorways. At this scale, stringent weight constraints mean that even marginal increases in structural mass reduce useful payload and endurance. The envelope, which can account for more than 30% of available lift, therefore becomes the most critical component governing overall system performance and reliability. This thesis addresses these challenges through an integrated experimental and numerical investigation of robust but ultra-light indoor airship envelopes. Mechanical characterization of candidate materials led to the development of a coated polymer envelope optimized for minimal mass, mechanical durability, and improved gas retention, suitable for use in harsh mission environments. Complementing this effort, a finite element modeling framework was established in Abaqus/Explicit to evaluate structural responses under pressurization and low-velocity impact with environmental obstacles, comparing purely inflatable envelopes with semi-rigid designs reinforced by lightweight skeletons intended to protect the flight system in cluttered environments. The findings demonstrate that semi-rigid reinforcement effectively mitigates deformation and damage during impacts, allowing the envelope to maintain structural integrity and continue operating while preserving buoyancy margins. The developed envelope achieved an excellent balance between strength and permeability and was successfully validated during an underground exploration mission, confirming performance beyond laboratory testing. The main contributions of this work include (i) a new dataset of mechanical properties for ultra-thin membranes benchmarked against conventional materials, (ii) a patented coated envelope design for indoor LTA platforms, and (iii) a reproducible impact simulation framework for semi-rigid and non-rigid LTA system configurations. Collectively, this research advances the development of next-generation indoor LTA vehicles capable of persistent, safe, and energy-efficient operation in previously inaccessible environments.

Date	9 Feb 2026
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	David St-Onge (Supervisor) & Ilyass Tabiai (Co-supervisor)