Two years ago, NASA awarded aerospace and defense company Aerojet Rocketdyne a $1.6 billion contract to supply the agency with its RS-25 rocket engines until 2024, which will be used to power NASA’s powerful Space Launch System (SLS) heavy-lift rocket. The ultimate goal for the SLS is to bring a crew to the surface of Mars sometime in the 2030s, so the reliability of the RS-25 engine makes it a good choice. To lower the cost of the rocket’s future missions, 3D printing technology was used to modify some of the RS-25 engine components, and the first hot-fire test took place in May of 2015, as Aerojet Rocketdyne and 3D printing will continue to impact the future of space flight.
This week NASA reported that, together with Aerojet Rocketdyne at the Stennis Space Center in Mississippi, it had completed the year’s final hot-fire test for the heavy-lift RS-25 rocket engine, which now contains its largest 3D printed component – a pogo accumulator assembly roughly the size of a beach ball.
The “green run” test of the development engine 0528 (E0528) flight controller ran for 400 seconds, though it was cut short of a full duration firing by 70 seconds, according to NASA SpaceFlight, due to a facility issue, and not a problem with the engine; Stennis personnel explained that all test objectives for the engine were achieved, and initial NASA reports show that the 3D printed component performed as expected.
Eileen Drake, CEO and President of Aerojet Rocketdyne, said, “This test demonstrates the viability of using additive manufacturing to produce even the most complex components in one of the world’s most reliable rocket engines. We expect this technology to dramatically lower the cost of access to space.”
This was the eighth RS-25 test of 2017, as well as the sixth flight controller tested for NASA’s SLS vehicle, and Aerojet Rocketdyne was able to evaluate how the 3D printed pogo accumulator assembly performed during the test. The component is a complex vibration dampening device, manufactured at Aerojet Rocketdyne’s Los Angeles facility using SLM technology, that acts as a shock absorber: its job is to dampen the oscillations (vibrations) caused by the propellants as they flow between the RS-25 engine and the SLS vehicle. The part, which is critical to the safety of the engine’s flight, is made up of two separate components: a pogo-z baffle and the pogo accumulator.
By using 3D printing technology to manufacture the pogo accumulator assembly, which is connected in the oxidizer system of the engine between the low and high pressure liquid oxygen turbopumps, the number of parts needed to assemble it were reduced from 28 to just 6, as well as eliminating a bolted joint and 123 welds; in addition, the unit cost decreased by a third. The part is a little heavier than it normally would be for being 3D printed, but it was built using a metal alloy similar to a conventionally manufactured one, which gives it “slightly increased strength,” according to NASA SpaceFlight.
Aerojet Rocketdyne Additive Manufacturing Lead Jeff Haynes said, “This is one of the larger parts to be built with the AM/SLM process and we are using one of the largest machines available to achieve this part manufacturing. Previously, we did extensive machining, which included welding structures from forgings and sheet metal [The redesigned manufacturing process] reduced the fabrication cycle time by 50 percent — printing the part is just a fraction of the total fabrication cycle time.”
According to NASA, this hot-fire test was part of the SLS Program’s RS-25 affordability initiative, which is a collaborative effort between the agency and Aerojet Rocketdyne with the goal of reducing overall production costs for the engine, while maintaining its safety and reliability, by using advanced manufacturing techniques. 3D printing technology helps reduce production for many of the engine’s thousands of components and parts, as well as allowing for more design flexibility and reducing development timelines.
One of the main objectives for the hot-fire test was to, according to Benefield, demonstrate the new 3D printed part “at nominal operating conditions.” The engine was throttled at thrust levels ranging from 80% to 111% of rated power level (RPL) during the firing, which means that the production restart engines will be certified to fly at 111%.
Philip Benefield, Systems and Requirements Team Lead for the SLS Liquid Engines Office, said, “This is the first RS-25 hot-fire test with production restart hardware. All future RS-25 tests plan to incorporate production restart hardware.”
When the rocket for the SLS Exploration Mission-1 finally launches, four Aerojet RS-25 engines will be used to power it, sending up an un-crewed Orion spacecraft.
“As Aerojet Rocketdyne begins to build new RS-25 engines beyond its current inventory of 16 heritage shuttle engines, future RS-25 engines will feature dozens of additively-manufactured components. One of the primary goals of the RS-25 program is to lower the overall cost of the engine while maintaining its reliability and safety margins. Additive manufacturing is essential to achieving that goal,” said Dan Adamski, RS-25 Program Director at Aerojet Rocketdyne.
The next hot-fire test for the RS-25 engine is currently scheduled for the middle of January 2018.
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