To experts from NASA recently succeeded in producing and testing a 3D printed aluminum rocket engine nozzle, which is lighter than conventional nozzles thanks to the material used and the manufacturing method. The new procedure could allow space flights to increase the amount of cargo carried. Engineers from the Marshall Center in Huntsville, Alabama followed up as part of the NASA Announcement of Collaborative program Opportunity collaboration with Elementum 3D of Erie, Colorado, to jointly create a weldable type of aluminum alloy that would be durable enough for use in rocket engines. Compared to other metals, aluminum has a lower density and thus enables the production of high-strength, yet lightweight parts. However, due to its low resistance to extreme temperatures and tendency to crack during welding, aluminum has not been used for the most part in additive manufacturing methods for rocket engine parts – until now.
Now the latest project implemented within the RAMFIRE program (Reactive Additive Manufacturing for the Fourth Industrial Revolution) is coming to the scene. This NASA-funded program aims to advance the development of lightweight 3D printed aluminum rocket engine nozzles. These nozzles are already in the design phase equipped with small internal channels that keep the nozzle cool enough so that it does not start to melt. Using traditional manufacturing methods, a nozzle can require up to a thousand individual parts to be joined together. However, the RAMFIRE nozzle is manufactured as a single piece, so it requires far fewer joints and significantly reduces production time.
Manufacturing of an integrated ducted aerospike engine demonstration nozzle by RPM Innovation in Rapid City, South Dakota. The LP-DED (laser powder directed energy deposition) method uses a laser to create a melt into which powder is blown, thereby depositing the material layer by layer. NASA engineers will use this jet as a test concept that will serve as a basis for future part designs.
Experts from NASA and Elementum 3D first developed an innovative aluminum alloy called A6061-RAM2 that seemed suitable for making the nozzle. They subsequently modified the powder used in the LP-DED (laser powder directed energy deposition) method. Another commercial partner, RPM Innovations (RPMI) of Rapid City, South Dakota, then used the newly developed material and modified powder to manufacture nozzles using the LP-DED method. “Industry partnerships with specialty manufacturing providers help expand the supplier base and make additive manufacturing available for NASA missions and the broader commercial and aerospace industries,” said Paul Gradl, Chief Scientist of the RAMFIRE Project at the Marshall Center.
NASA’s current Moon to Mars program will require the ability to send larger payloads into deeper space. An innovative alloy can play an important role in this process by enabling the production of lightweight rocket parts that will be able to withstand high structural loads. “Mass is critical for future deep space missions,” says John Vickers, chief advanced manufacturing technologist for NASA’s Space Technology Mission Directorate, adding: “Projects like this are helping additive manufacturing technologies mature while also providing advancements in the field of materials. As a result, they will help develop the new propulsion systems, space manufacturing and infrastructure necessary for NASA’s ambitious missions to the Moon, Mars and beyond.“
A vacuum-jacketed demonstration tank developed by the Marshall Center in Huntsville, Alabama, from the same 6061-RAM2 aluminum alloy used in Project RAMFIRE. The part, manufactured to store cryogenic liquids, is designed with a series of integrated cooling channels that have a wall thickness of approximately 1.5 mm.
In the course of this year, two RAMFIRE jets underwent multiple static ignitions at the Marshall Center, while not only a mixture of liquefied oxygen and hydrogen, but also liquefied oxygen and methane were tested as propellants. Thanks to pressures in the combustion chamber of over 5.5 MPa, pre-test expectations were exceeded. Both nozzles together successfully managed 22 ignitions, which lasted a total of 579 seconds, i.e. approximately 10 minutes. During the tests, it was verified that the jets can function even in the most demanding conditions of deep space. “This test series marks a significant milestone for this nozzle,” admits Paul Gradl, adding: “By subjecting the thruster to a challenging series of static fires, we demonstrated that the thruster can withstand the thermal, structural and pressure stresses expected of an engine the size of which could be used on a lunar lander.“
Experts from the Marshall Center inspect the nozzle after a series of test static fires.
In addition to the successful production and tests of the rocket engine nozzle, the RAMFIRE project managed to use the developed aluminum alloy and additive manufacturing processes to produce other advanced large-scale parts for demonstration purposes. This includes, for example, the aerospike engine nozzle with a diameter of 90 cm with complex integrated cooling channels, or a tank with a vacuum jacket for cryogenic substances. NASA and its industrial partners work to share knowledge, data and processes with commercial stakeholders and academic institutions. Various aerospace companies are working on the development of innovative LP-DED alloys and manufacturing processes. At the same time, they are looking for ways to use these attributes to produce parts for satellites, as well as other applications.