Effects of microgravity and reduced atmospheric pressure on manufacturing photopolymer specimens

In-space manufacturing especially for external satellite structures has a huge potential to increase the packaging density of a satellite in launch configuration and enables large structures for advanced mission requirements. However, the processes and materials do have to withstand the harsh environmental conditions in space. These conditions have immediate effects on the manufacturing process as well as long-term effects on the structure manufactured in orbit. The experiments presented here are based on a photopolymer extrusion process by UV-radiation curing that is intended to be used as an in-space manufacturing technology. In order to understand the influence of reduced atmospheric pressure and microgravity on the process, we demonstrated the successful extrusion and curing of rod-shaped elements during a sounding rocket flight. Simultaneously, the same experiment was performed on the ground under normal gravity and ambient pressure. By comparing both groups of specimens, it was shown that the morphological artifacts and geometric deviations are more significant for the specimens manufactured during flight. This evaluation was performed by visual inspection, by comparison of the laser-scanned specimens with a reference model and by measuring and comparing the mass, length and diameter of the specimens. On a microscopic level, conducted by computer tomography, no influence of the reduced atmospheric pressure on the extrusion of the liquid photopolymer can be recognized as this was probably not low enough at the altitude reached by the rocket. As a result of this article, measures are proposed to avoid the morphological artifacts observed during the experiments and thus achieve higher accuracy and a resilient in-space manufacturing process.