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Aerojet Rocketdyne Completes RS-25 Certification Testing for Artemis V and Beyond

Aerojet Rocketdyne
Apr 3, 2024 | 2 MINUTE Read

After successfully completing 45 development tests and 24 certification tests at NASA’s Stennis Space Center, Aerojet Rocketdyne, an L3Harris Technologies company, and NASA have finished all the hot-fire tests required to certify new versions of the RS-25 engine for the agency’s SLS (Space Launch System) rocket. These engines will be used on Artemis missions starting with the fifth flight of SLS. 

Four Aerojet Rocketdyne RS-25 engines, generating more than 2 million pounds of combined liquid-propulsion thrust, help to power the core stage of the SLS at launch. The first four SLS missions are utilizing RS-25 engines remaining from NASA’s Space Shuttle Program that have been refurbished and outfitted with modern flight computers and avionics.

“At the end of the Space Shuttle Program, NASA had 16 engines remaining in its inventory, which is enough for four SLS flights,” said Mike Lauer, RS-25 program director at Aerojet Rocketdyne. “To power the flights that follow, our team was challenged to design and build a modernized version of the RS-25 that is more affordable without sacrificing its outstanding reliability, and, if we could increase its performance, even better.” 

The new engines will operate at 111% of rated thrust level on SLS, an increase from the shuttle program, where they ran at 104.5%, and the first four Artemis missions, which will run at 109%. 

Since the RS-25 successfully powered 135 shuttle flights, the team knew they had a solid design that was reliable enough for astronaut-carrying missions. So, they went to work identifying parts that could be redesigned, simplified, and improved. In the end, about 70% of the components on newly built RS-25s are upgraded designs that, along with the other major components, have been tested to beyond their normal operational limits. 

Did You know?

The RS-25 is so powerful that if it were generating electricity instead of propelling rockets into space, it could provide twice the power needed to move all 10 existing Nimitz-class aircraft carriers at 30 knots.

Learn More About the RS-25

Our Support of Artemis

L3Harris’ contributions to NASA’s Artemis missions include propulsion and components for the Space Launch System rocket, Orion spacecraft and Gateway lunar space station.

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Introducing redesigned components required restarting supply chains and production lines across the nation, and qualifying new processes and suppliers where necessary. The major redesigned RS-25 components include:

Pogo Accumulator

One of the first components to be upgraded was the Pogo Accumulator Assembly, which the team chose to additively manufacture, or 3D print. The “Pogo,” which is about the size of a beach ball, is a complex and critical component that dampens pressure oscillations that can cause a rocket to become unstable in flight. The team successfully reduced the number of system welds by 78% and confirmed that 3D printing was a viable path for other components. Today, more than 30 components on the new engine design leverage 3D printing.

Main Combustion Chamber

The Main Combustion Chambers (MCC) for the new production engines are assembled using a bonding technique called Hot Isostatic Pressing (HIP) that employs high pressure and heat to create bonds between engine details that can withstand extremely high-stress applications. In the case of the RS-25 MCC, where the engine’s “smoke and fire” initiates, that means withstanding combustion temperatures exceeding 6,000 degrees Fahrenheit and pressures over 3,000 psi. Additionally, HIP bonding is a more predictable process, which greatly reduces process variation. The HIP-bonded MCC is the single-largest affordability improvement incorporated into the new RS-25 engines. It cuts in half both the cost and fabrication cycle time compared to the heritage space shuttle main engines.

Engine Controller

The controller is often referred to as the “brain” of the engine because it translates the vehicle’s commands into engine action while monitoring engine health.  It makes real-time adjustments to control engine thrust and mixture ratio and monitors critical parameters, such as turbopump speed, combustion pressures, and engine vibration. The new controller has 20 times the processing capability of the shuttle-era controller, weighs 50% less, and offers increased reliability.


RS-25 Nozzle

The team upgraded the nozzle, which directs engine thrust, for better producibility. The

 nozzle is the RS-25’s most labor-intensive and difficult-to-manufacture component. It also must withstand the minus 423 degrees Fahrenheit temperatures from liquid hydrogen flowing through its tubes and hot combustion gases at roughly 6,000 degrees Fahrenheit passing just a fraction of an inch away. The team learned as it incorporated new manufacturing tools and techniques into the initial production units of the new design. For example, between the first and fourth units, the team reduced tube-stacking touch labor hours by 50%. On the fourth unit, the team beat their affordability target by 17%, and reduced scrapped tubes by 90%, compared to the previous three units.

“When we fly, we want to see the engine perform perfectly. When we test, we’re testing to the extreme limits of operation to ensure the engines can complete the mission with margin. This includes different inlet conditions, high-power, low-power, emergency shutdowns, turning off and on hydraulics, etc.,” said Lauer. “This test series also demonstrated the engine’s performance at off-nominal conditions, which is critical to the flight safety of the vehicle.”

The engines were put through their paces with 69 hot-fire tests to ensure they could meet the new performance demands of the next design block of the SLS rocket, Block 1B.

“Successfully completing this rigorous test series is a testament to the outstanding work done by the team to design, implement, and test this upgraded version of the RS-25,” added Lauer. “We accumulated about 34,000 seconds of hot fire test time between the development, retrofit, and certification tests, demonstrating these new engines are ready to safely launch astronauts to the Moon and beyond.” 


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