An integrated team representing Aerojet Rocketdyne, support contractor Syncom Space Services (S3), and NASA’s Stennis Space Center recently experienced a different kind of R&R. On Oct. 13, the team members successfully performed an uncommon remove-and-replace (R&R) procedure on an RS-25 engine’s nozzle while the engine was installed on the Fred Haise Test Stand.

In fact, the event marked the first nozzle removal and replacement performed on an installed RS-25 engine since the space shuttle main engine testing era at Stennis, the nation’s largest propulsion test site located near Bay St. Louis, Mississippi. Space shuttle testing at Stennis ran from May 19, 1975, to July 29, 2009. The last flight of the Space Shuttle Program, STS-135, occurred July 8-21, 2011.

The R&R procedure involves completely removing the nozzle – the bell-shaped component bolted to the powerhead that directs and accelerates 6,000-degree exhaust to generate powerful thrust – and reattaching another nozzle, while the turbopumps, combustion chamber, fuel ducts, and other parts remain secured in place.

The mid-October removal and replacement served as a practice run to ensure the blended team had the proper procedures and tools in place to complete the action, so the same RS-25 nozzle was removed and replaced on the test stand’s engine deck.

With the success of the rehearsal using development engine No. 0528, the same procedure now will occur at least once again in the spring of 2022 during a series of engine certification tests. Multiple RS-25 nozzle R&Rs also are slated for 2023 and 2024. The spring series will involve multiple hot fires of an RS-25 certification engine to verify the safety and reliability of new and different components, some of which have been created using 3-D printing, a cutting-edge additive manufacturing technique.

The new nozzle that needs to undergo testing will be available after the certification series begins, so the R&R procedure will allow the team to remove the conventional nozzle that will be used early in the series and install its replacement. Successful certification testing is a critical milestone to producing a new generation of RS-25 engines that will be used in later Artemis missions.

Because the RS-25 nozzle is a highly complex assembly, it normally takes several weeks to fully connect it to a test stand, and the engine is installed and removed as one complete unit. Vehicle transport of an RS-25 engine between Aerojet Rocketdyne’s on-site Engine Assembly Facility and the Fred Haise Test Stand is a meticulous process, as is lifting and lowering the engine by crane during installation and removal.

Typically, if a nozzle needs to be replaced, the engine must be removed from the test stand in order to complete the procedure. As a unique procedure, then, nozzle R&R can produce major benefits.

“The ability to remove and replace a nozzle at the test stand can provide both cost and schedule gains for the RS-25 project,” said Matthew Scardino, rocket engine test operations manager at Aerojet Rocketdyne. “As many as four to six weeks can be cut from the typical test schedule if the engine does not need to be removed from the test stand to replace the nozzle at the Engine Assembly Facility and then reinstalled at the test stand.”

Although nozzle R&Rs are a part of Stennis’ rich history of propulsion testing, the new RS-25 test project powering Artemis missions to the Moon required some modifications to the test stand infrastructure. For example, the current RS-25 project required a modification of the vertical engine installer (VEI), a hydraulic lift table, with a newly designed tabletop and platform for safety of personnel and ease of use.

The VEI slides on rails to the edge of the engine deck when an RS-25 engine is incoming or outgoing, and it then slides to and from the area beneath a new thrust frame adapter, a strong cross-shaped  metal beam structure to which the engine is bolted for testing. To fit the new adapter, the engine interface was rotated 90 degrees to accommodate the new structure.

Meanwhile, the thrust frame adapter itself is affixed to a thrust measurement system that measures upward and lateral force as the engine “gimbals,” or purposefully redirects its aim, during a hot fire test.

While the RS-25 nozzle R&R does not necessarily require a larger crew than the same procedure did for a space shuttle main engine, the team took advantage of the opportunity to train additional personnel on the operation, especially newer hires who were not involved in, or on-site during, the space shuttle main engine test era.

The uniqueness of the R&R procedure makes it a valuable learning opportunity for identifying process improvements and information gathering. As a standard practice, Aerojet Rocketdyne conducts after-action reviews to identify opportunities for improvement and capture lessons learned for corrective action prior to the next execution of the task.

“The nozzle R&R was executed flawlessly by a combined NASA/S3 and Aerojet Rocketdyne team working collaboratively together,” Scardino said. “The lessons learned and opportunities for improvement we captured will provide tremendous value to our processes. The demonstration also enabled us to increase our skill-base through the hands-on training made available through the activity.”