L3Harris testing brand new RS-25 engines for future Artemis launches

RS-25 prime contractor L3Harris continues to ramp up production of new flight engine hardware at their Los Angeles area facility and final assembly at the Stennis Space Center. NASA certified production restart of the former Space Shuttle Main Engine (SSME) in mid-2024, with the new engines slated to operate at higher performance levels in four-engine clusters in the Space Launch System (SLS) Core Stage.

While engine component production in Canoga Park increases towards a four engine per year delivery rate for NASA, the L3Harris team is also supporting upcoming Artemis flights to take astronauts back to the Moon. SSMEs that flew the final Shuttle flights 15 years ago were adapted to SLS operating requirements are ready to fly today, and the engine maker is ready to support the Artemis II launch and install the Artemis III and IV engines when SLS is ready.

Ramping RS-25 production up to support one SLS launch per year

The first four new RS-25 engines would fly on the SLS Core Stage for Artemis V. L3Harris acceptance tested the first one, serial number 20001, in late June. “It’s an acceptance test where we’re characterizing that engine’s performance,” Mike Lauer, RS-25 program director, Aerojet Rocketdyne, L3Harris, said, during a visit to L3Harris’ Canoga Park manufacturing plant.

“So, [things like] the engine thrust level, the specific impulse. We’re checking the calibration coefficients and we’re basically running all the new parts through a [hot-fire] sequence to accept it, and once that check is good, there’s nothing more that we need to do. We go through what we call our second “E & Ms,” where we check our mechanical, electrical stuff afterwards and then we basically package it up and we store it in place until it’s called down to KSC [for SLS installation].”

“We ran that whole test and it was fabulous because it’s a brand-new engine, we had all sorts of ‘brand new,’ so it was a huge deal when we ran through that full sequence and it worked great,” he added. “You’re monitoring lots of parameters and so we had a couple of after-test instrumentation glitches that we had to work out, but those are all resolved, so that engine has been removed, it’s back in the engine assembly facility, and it will be ready when called up for Artemis V.”

They have already delivered many of the components for the next two engines, 20002 and 20003, which are in final assembly at their facility on Stennis grounds, and the components for the fourth one, to complete the Artemis V set, are being prepared for shipment.

RS-25 engines 20002 (foreground) and 20003 (background) at Stennis Space Center this summer. Credit: L3Harris.

“We’ve got our second one that’s well along the way, production engine number [20002],” Lauer said. Our third engine is being ‘kitted,’ our fourth engine is getting ready to be kitted. ‘Kitted’ means you start gathering the parts up from the stock rooms [at Stennis] and you get them all ready to go out to the floor where they can start assembly.”

“You have the majority of the components necessary to really start the core of the engine, and you put these boxes of parts together that are now designated to the engine, and you move them to their special area so the technicians can start putting the puzzle together,” he added. “We’re starting all that at Stennis on those early engines.”

Beginning with Artemis V, the RS-25 engines will run at 111 percent of the original rated power level for the SSMEs back in the late 1970s. That’s compared to 109 percent for the first four SLS launches and 104.5 percent at the end of the Shuttle program. NASA contracted with then-Aerojet Rocketdyne in late 2015 to restart production of new RS-25 engines for the expendable SLS; they are now a subsidiary of L3Harris.

Although new engines retain the same form, fit, and function as before, engine components are now built using modern manufacturing methods, such as additive manufacturing. The upgraded RS-25, with its modernized manufacturing and production, completed its design certification review over a year ago in mid-2024.

“There’s a [NASA] requirements document that the engine shall meet all these requirements,” Lauer explained. “We generate reports that are called verification requirements documents. We’re basically delivering to NASA a set of paper that [covers all the] test, analysis, and inspections saying we meet all of these requirements…based on this test program and design work we’ve done and some things you can’t test perfectly so you do analysis.”

“We give that to NASA and NASA goes off and has a whole independent panel, this is at Marshall Space Flight Center, and they divvy it off to all of their experts and they page through all of that documentation. It culminates in that final review, which is where you boil it down to are there any discrepancies.”

“We came out of that review with about 40 discrepancies, which is pretty good,” he added. “As of today we’re down to the last three. You always have RIDs, review item discrepancies, out of any of those. But we [NASA and L3Harris] all agree that the engine is in great shape, we’re just shoring up paper at this time.

An RS-25 engine powerhead takes shape at the L3Harris facility in the Los Angeles area. Credit: L3Harris.

The initial goal for NASA’s Exploration programs, better known as Artemis, is to fly one mission per year, which means that four RS-25 engines need to be delivered every year. From a production standpoint, the engines are a collection of pumps, valves, manifolds, and combustion chambers, and L3Harris has already surpassed that delivery rate for some components and subassemblies.

“You saw out there [on the shop floor] ducts and main combustion chambers and aft manifolds and nozzles [and] powerheads and half-shells and so…what we’re doing at our supply base and out on the manufacturing floor is monitoring our rate for each of those parts,” Lauer said. “Realizing that every part has to be built at least a four plus per year [rate] to support a final engine assembly.”

Numerous components and subassemblies have already met or exceeded the target of four per year, such as the main combustion chamber. “It’s way faster to build [than Shuttle-era production], far less time spent, and in fact that was our first core component that started this whole thing off and that is now at a consistent, easy four per year rate,” Lauer noted.

Lauer also noted that the powerheads and nozzles are elements that are still working towards the goal. “Powerheads are slowly getting there, nozzles are still the most time-consuming thing, that and the turbopumps,” he said. “It’s a bunch of parts coming up to production speed, everything geared toward eventually Stennis has to perform, with building up an engine, sending it to the test stand, doing the post-test stuff, then the next one and the next one and the next one.”

L3Harris has dozens of subassemblies in the production flow; for example, the jacket for the 25th new nozzle was seen on the floor being set up for integrating the hatbands to it.

“There are some interim steps in our nozzle manufacturing, it’s not all done here in Los Angeles,” Lauer explained. “[Machining] that inner contour, where the tubes go on the nozzle shell, we actually do that out at Major Tool and Machine in Indianapolis.”

“You saw nozzle [6025] on the robotic welder, as soon as that’s done, we’ll put that in a big oven for heat treat, but then we’ll send it to Indianapolis and the Major Tool guys, because they have some very large machines [there]. They’ll do the final machining on that, to get that inner contour, and then they’ll ship it back.”

One of at least a dozen RS-25 engine nozzles in production in Los Angeles this summer. Credit: L3Harris.

In addition to the large nozzles, several powerheads in different phases of manufacturing and assembly were seen in different locations and workstations. The hot-gas manifold is the structural core of the engine; the main injector and the two pre-burner injectors are integrated to them, and eventually the high-pressure turbopumps are installed to help form the overall powerhead.

That final assembly work is now done at Stennis Space Center in southern Mississippi, where the single-engine Fred Haise Test Stand is used for hot-fire testing on the ground. Flight engines are typically only fired on the ground once, for acceptance, but development engines are hot-fired much more frequently. Stennis is a federal city and L3Harris has a large facility there for RS-25 final assembly, storage, and maintenance.

Lauer said that their workforce at Stennis is also ramping up to support the four engine acceptance test and delivery rate. Engine 20002 was forecast to be ready for its acceptance test in this last quarter of 2025, followed by engine 20003 next year.

“We’re talking the first quarter of next year [for final assembly], paced by our nozzle delivery, that one will be our next one and we’ll follow that out to the test stand probably in the second quarter, Lauer said, “and then [engine 20004] will be shortly behind it. We’re on track to have three done next year, [we’d have] the full set [for Artemis V], and then we’d just keep rolling in to the next units after that and then if you look in our schedules out beyond 26 and 27, you start seeing that pace of [the] Stennis side seeing engine [delivery] rates.”

“Where we trying to go is to sort of overshoot the delivery rate, so that when we’re actually out there in [2027/2028] we’re doing even more than four a year,” he added.

Supporting Artemis II, III, and IV

L3Harris is also supporting the RS-25 “adaptation engines,” which flew on Shuttle flights at the end of that era, and are flying a final time on the first four SLS launches. The first set flew on Artemis I and the remaining engines are ready to support Artemis II through IV. The engine set for Artemis II was installed in the Core Stage two years ago in September 2023, and L3Harris completed final servicing and maintenance tasks on the Artemis III and IV sets in 2023 and 2024, respectively.

Earlier this year, after the Core Stage was mated to the Artemis II Solid Rocket Boosters (SRB) on Mobile Launcher-1 in the Vehicle Assembly Building (VAB) at Kennedy Space Center (KSC), NASA decided to remove and replace the number four engine, removing RS-25 engine 2063 and installing engine 2061 from the Artemis III set. This was the first vertical RS-25 engine changeout in an SLS Core Stage.

An RS-25 nozzle is prepared for heat treatment at the L3Harris facility in the Los Angeles area. Credit: L3Harris.

“We partnered with [prime launch processing contractor Amentum] and EGS (Exploration Ground Systems) and [prime SLS Core Stage contractor] Boeing and we had a pretty good team together and we talked on a daily basis about issues and concerns,” Bill Muddle, lead RS-25 field engineer at Aerojet Rocketdyne, L3Harris, said, during the interview. “I think that was part of our success was that we all got together as a team and were able to walk through every issue or every part of the process to be able to complete this in a very short amount of time for doing it for the first time.”

Engine 2063 had a small hydraulic leak in the actuator for its main oxidizer valve, which was addressed offline to minimize disruptions to the integrated test and checkout and launch preparations schedule for the stacked Artemis II SLS.

The engine changeout was also the first flight engine use for the newly reactivated RS-25 engine service area in the VAB. The SSME shop was used throughout the 1980s and most of the 1990s by the Shuttle program for on-site service and maintenance, and to prepare engines for installation. It is now ready to support installation of the Artemis III and Artemis IV engines when those Core Stages are ready for them.

“Part of our validation of the engine servicing area, the ESA as I call it, [was that] we had to go do a first article test,” Muddle said. “We took a pathfinder engine and basically demonstrated the flow of how we’re going to go process the Artemis III engines through the ESA.”

“Once again we storyboarded it out and we worked through the process and I’m saying that it went relatively very smoothly. We had some minor little things, but we’ve already corrected those things and so when [engine] 2061 came in [for the Artemis II changeout], it was very smooth. The result was that it was good, it was really good.”

“We don’t have any problems and we’re ready to go for Artemis III,” Muddle noted. “All our GSE (ground support equipment) has been certified, it’s all been delivered, we’re just waiting on getting the engines here.”

Engine 2061 was assigned to the same position, number four, for Artemis III as engine 2063 was for Artemis II; a result of the engine swap is a rotation of engine assignments for that number four Core Stage position between Artemis II, III, and IV. Engines one and four “face” the aft booster separation motors for the SLS boosters, and they have some additional thermal protection on the exterior of the nozzles for that.

A pathfinder engine is seen the L3Harris engine service area on the floor of the Vehicle Assembly Building. Credit: L3Harris.

The engines could be reconfigured for other positions, but the plan is to rotate engine 2052, which was assigned to the number four position for Artemis IV, to Artemis III. Engine 2063 then rotates into that position for Artemis IV.

The engines assigned to Core Stage-3 for Artemis III will stay in storage at Stennis Space Center until that stage is closer to completion. Currently, the forecast is that the engines would be shipped from Stennis to Kennedy in the first quarter and NASA recently said that the final join of the stage would be in the spring of next year, 2026, so engine installation might not be until the middle of the year.

Looking at future development and testing options

Beyond acceptance testing of the flight engines for Artemis V through Artemis IX, L3Harris is continuing to look at options for developing further engine upgrades. The first full build of all new RS-25 engine components was serial number 10001, which was used to help certify the design, the upgrades, and the new manufacturing. Several set of some engine components were built, but 10001 had the first new powerhead and first new nozzle.

The company is working with the SLS program to figure out the best way to use that ground asset to continue improvements to the RS-25.

“We’re working with NASA to build up another engine that basically consists of that hardware on the certification engine that we ran,” Lauer said. “That will be our testbed for on-ramping new things or if we had to deal with a flight anomaly. It’s not on our contract yet, but we’ve been working closely [with NASA] because it makes sense for the program, the test stand, to have that testbed ready.”

“If you think about our intended [production] flow, which is about four engines per year, it’s an engine test per quarter. Those are ample gaps in the flow to bring another engine, run a test or two, and remove it, without interrupting the next one.”

(Lead image: The inside of a new RS-25 nozzle in production in Los Angeles. Credit: L3Harris.)

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