A team from the U.S. space agency NASA moved toward building a completely 3D-printed, high-performance rocket engine by manufacturing complex engine parts and test firing them together with cryogenic liquid hydrogen and oxygen to produce 20,000 pounds of thrust.

“We manufactured and then tested about 75% of the parts needed to build a 3D-printed rocket engine,” says Elizabeth Robertson, project manager for the additively manufactured demonstrator engine at NASA’s Marshall Space Flight Center in Huntsville, Ala. “By testing the turbopumps, injectors and valves together, we’ve shown that it would be possible to build a 3D-printed engine for multiple purposes such as landers, in-space propulsion or rocket engine upper stages.”

Additive manufacturing, or 3D printing, is a key technology for enhancing space vehicle designs and manufacturing and enabling more affordable exploration missions. Over the last three years, the Marshall team has worked with various vendors to make 3D-printed parts and test them. To test them together, they connected the parts so that they work the same as in an actual engine.

“In engineering lingo, this is called a breadboard engine,” says Nick Case, the testing lead for the effort. “What matters is that the parts work the same way as they do in a conventional engine and perform under the extreme temperatures and pressures found inside a rocket engine.” Case says an engine like this could produce enough power for an upper stage of a rocket or a Mars lander.

Engineers prepare a 3D-printed breadboard engine. Image credit: NASA/MSFC/Emmett Given.Engineers prepare a 3D-printed breadboard engine. Image credit: NASA/MSFC/Emmett Given.Seven tests were performed, with the longest lasting 10 seconds. During the tests, the 3D-printed demonstrator engine experienced similar environments to those inside a flight rocket engine, where fuel is burned at more 6,000 degrees Fahrenheit (3,315 degrees Celsius) to produce thrust. The turbopump delivers the fuel in the form of liquid hydrogen cooled below 400 degrees Fahrenheit (-240 degrees Celsius).

“These NASA tests drive down the costs and risks associated with using additive manufacturing, which is a relatively new process for making aerospace quality parts,” says Robertson. “Vendors who had never worked with NASA learned how to make parts robust enough for rocket engines.”

To make each part, a design was entered into a 3D printer's computer. The printer then built each part by layering metal powder and fusing it with a laser, a process known as selective laser melting. The 3D-printed turbopump, one of the engine’s more complex parts, had 45% fewer parts than similar pumps made with traditional welding-and-assembly techniques.

Complex parts like valves that normally would take more than a year to manufacture were built in a few months. This made it possible to assemble the parts on the test stand sooner than if they had been made and procured via traditional methods.

Future plans include performing engine tests with liquid oxygen and methane. These are key propellants for Martian landers, because methane and oxygen production might be possible on Mars.

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