The Use of Stereolithography (SLA) Additive Manufacturing in Space-Based Instrumentation

Abstract

Stereolithography (SLA) Additive Manufacturing (AM) is a fabrication technique in which three dimensional parts are made by selectively curing layers of the part in a vat of UV photopolymer resin. Because this process is performed at near ambient temperature, unlike laser sintering or direct melting techniques, and there is minimal contact with the final part during the build such as for polymer extrusion methods, SLA manufacturing produces parts with low applied stress throughout the build. This allows highly complex geometries, tight tolerances, fine surface finish, and detailed features to be readily achieved. The process is not without drawbacks, however. The SLA process generally only produces polymer parts which are undesirable for space applications due to effects such as outgassing, charge accumulation, and creep. Additionally, the SLA resins must be formulated to cure with UV exposure which leads to compromises when compared with conventionally produced polymers. Finally, AM methods in general have less well-defined material properties, exhibit geometry dependent material properties, and are anisotropic. This work examines five commercially available materials to assess their usefulness in space-based instrumentation. The materials are chosen to span a variety of material properties including strength, temperature rating, resolution, and opacity. Utilization of these materials requires consideration of the materials' response to the harshness of the space environment, particularly with respect to vacuum and ionizing radiation which is not data readily available from the manufacturer. As such, experimental outgassing data is presented on each material with and without a vacuum prebake. The response to ionizing radiation is then considered for a high-resolution SLA material that is being used in an upcoming CubeSat mission in GTO. Samples make from this material are subjected to ionizing radiation from a Cs137 source to absorbed doses up to 10 Mrad. Tensile and flexural testing is performed on these samples and the change in mechanical properties relative to radiation does is characterized. Current applications of the material are then explored, including the silicon detector holder that will be flown on the upcoming ESRA CubeSat mission. The detector holder, made of a high-resolution SLA material, locates the detectors and provides provisions for wire routing and vacuum venting on a miniaturized scale. The use of SLA allows this part to be manufactured quickly and affordably with features that would not be possible using conventional manufacturing techniques. Lastly, ongoing work is presented including characterizing additional materials ionizing radiation response and investigating the potential to metallize SLA parts.