Mechanical, Thermal, and Chemical Design of The Mission ‘Illinois’ On-Orbit Fabricator of Composite Longerons

In-space Servicing, Assembly, and Manufacturing (ISAM) will unlock new space opportunities by overcoming launch vehicle frequency and volume constraints. In particular, ISAM could enable ultra large-scale space structures, such as gigawatt scale photovoltaics. Mission ’Illinois’ is an on-orbit technology demonstration experiment designed to validate the manufacturing of a carbon fiber reinforced polymer (CFRP) composite longeron directly in space. This strategy uses the high volumetric packing during launch of carbon fiber sleeves, flattened and pre-impregnated with uncured resin. These sleeves will then be formed into hollow cylindrical structural elements and cured via incremental reactive extrusion (IRE) for CFRP manufacturing. The experiment targets in-space curing of a 2.5 mm thickness, seamless composite longeron using frontal polymerization (FP), a fast, energy-efficient curing process suited for power-limited environments. The composite prepreg is incrementally cured and translated through a compact fabricator. The fabricator integrates a kinematically constrained mandrel (KCM) that allows for the axial translation of a seamless tube while constraining an inner mandrel, and an electromechanically actuated collet that applies uniform internal pressure. This article presents the integrated mechanical, thermal, and chemical design of the Mission ’Illinois’ fabricator, including subsystem architecture, material system, and operational sequencing. Thermal analysis and experimental validation are presented. Modal analysis of the integrated payload and the critical internal mechanisms confirms compliance with launch vibration requirements.