The engine used by the FRETS1 satellite is patent pending and has been 3D printed! The patent is pending in the US and was filed under the older first-to-invent rules. Because it is not yet an international patent, images and descriptions will be limited to those that don’t reveal enough information to reproduce the engine. Perhaps a future post will expound on how the US ITAR law prevents me from disclosing this information anyway.
Onto something more fun: 3D printing. The engine is pretty small and requires some interesting interior detail for experimentation. Things like embedded wires, high voltage guards, mounting holes, and sockets for sensors are all required. And it all has to be made from a good strong dielectric that can withstand the electric field stress required for the engine to be useful. Acrylic is my choice as it is plenty strong and still clear enough to see what is occurring within the chamber. The first plans were to laser cut pieces and use plastic cement to weld them together.
Then I found that TechShop offers 3D printing in acrylic and wax. In this process, voids are filled with wax, avoiding the use of supporting struts that would have to be cut away. Instead, the part is placed in hot oil and the wax drains away. Some of our wire slots are 0.5 mm diameter and the wax didn’t fully drain. To get the wire into these slots, we heated a test wire and worked it in until the wax melted and pulled out.
Draft 1 of the engine is show below, near a US quarter coin for size comparison. There are plenty of mounting holes, wire slots, and holes for sensors. OpenSCAD was used to create the model. I must say it was quite nice to script an engine design.