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40 Focus | Additive manufacturing coolant channels, which contain high- pressure coolant fluid that protects the walls from the high temperatures a nozzle must withstand. Nozzles are actively (or regeneratively) cooled, meaning the propellant used later in the combustion cycle is routed through the nozzle to cool the walls so that they do not overheat. To cool the nozzles regeneratively, a series of channels are fabricated within the nozzle and are then closed out, or sealed, to contain the coolant. LWDC puts a support jacket in place, eliminating several steps in the traditional manufacturing process. For such high-pressure/high-efficiency liquid rocket thrust chambers, a good surface finish is essential. There must be no critical defects and the AM material must have strength properties equivalent to its parent. This is at the limit of the current capabilities of powder-based AM machines using non-standard alloys. One practical application of AM in space systems is for the Vega small launcher being developed by the European Space Agency (ESA). It is the first project to use a new ESA centre focusing on 3D printing. The Vega engine will use 3D printing on copper-based thrust chambers to produce a one-third scale thrust chamber that can then be used for firing tests. The next step would be to scale it up to full size and start the formal qualification of the process for flight use. Printing in space The Archinaut printer is being developed to implement AM in the vacuum of space. A polymer-alloy 3D printer is at the heart of the unit, coupled with assembly robotics, feedstock and some prefabricated components. During launch, Archinaut would be packaged extremely tightly, but once in orbit it would be able to print reflectors, antennas, trusses, booms and radiators to be assembled in situ. Complete motors An interesting direction of development is combining AM materials to produce complete systems. With that in mind, researchers in Germany have used FDM techniques for the first time to build a complete electric motor from iron, copper and ceramics. The process uses metallic and ceramic pastes simultaneously, which are extruded layer by layer into a predetermined form and then sintered together to produce the motor. The motor’s coils are produced by placing particles of the desired materials – such as iron, copper or ceramics – and specially adapted bonding agents in the appropriate places as the motor is printed. To achieve the necessary degree of precision to build the coils, the researchers worked closely with a local paste supplier to get the right consistency for the AM process. This builds on a 3D-printed coil developed two years ago by the same team that is capable of withstanding temperatures of more than 300 C. The researchers’ goal in recent years has been to increase the temperature at which the motor can operate. This was made possible by replacing conventional polymer-based insulation materials with specialised ceramics that can be 3D-printed.  This research should lead to smaller, more efficient motors, as the maximum winding temperature of 220 C June/July 2018 | Unmanned Systems Technology The Archinaut 3D printer is intended to be launched into space to print larger components in situ (Courtesy of Made in Space) Researchers have used AM with ceramic pastes to build a complete motor (Courtesy of Chemnitz Technical University)