NASA has issued a lengthy explanation behind the decision to contract Aerojet Rocketdyne to restart production of the RS-25 engine, mainly centering on the claim it is less expensive – and safer – than developing a new engine. Six new RS-25s will compliment the existing stock of 16 engines, allowing the Space Launch System (SLS) to have enough engines through to her fifth flight.

RS-25 Order:

NASA selected Aerojet Rocketdyne of Sacramento, California to restart production of the RS-25 engine for the SLS via an official statement at the end of November. The deal was always in the pipeline, although the official procurement process meant the details of the deal remained embargoed.

Under the deal – worth $1.16 billion – Aerojet Rocketdyne will modernize the engine to make it more affordable for SLS – previously tagged as the switch from the reusable RS-25D used on the Space Shuttle to the expendable RS-25E. The engine will be known only as the RS-25 during its SLS career.

While the contract officially restarts the firm’s production capability – including furnishing the necessary management, labor, facilities, tools, equipment and materials required for this effort, implementing modern fabrication processes and affordability improvements, and producing hardware required for development and certification testing – it also “allows” for a “potential” future modification that would enable NASA to order six flight engines.

Per the forward plan in the contract, NASA issued a “Justification for Other Than Full and Open Competition (JOFOC)” in accordance with the Federal Acquisition Regulation (FAR).

The JOFOC notes that NASA’s Marshall Space Flight Center (MSFC) “proposes” to procure six additional RS-25 flight engines from Aerojet Rocketdyne, to support a total of five SLS missions.

The estimated value is tagged as $1.5 billion, which is the total cost of the new engines with the aforementioned restart effort.

“The proposed action follows directly in line with the strategy for cost minimization by continuing with the use of the same core-stage engine design, with minimal modifications, and with the restart of a historically proven (though currently dormant) production line,” the JOFOC document noted.

Interesting details on the mechanics and requirements of production restart are provided, details that provide a reminder of the battle near the end of the Shuttle era where the Shuttle Program argued for the protection of RS-25 production assets.

The problem’s began when NASA’s complicated and troubled transition to the since-defunct Constellation Program (CxP) saw the RS-25 initially provided with a second life role with the Ares I Upper Stage. However, the engine’s future was then placed into doubt, as Ares managers opted to move to the J-2X for the Upper Stage role.

NASA’s Transition Control Board (TCB) – a body that was tasked with redirection of agency assets to the CxP – directed the shutdown of engine production capabilities in 2007, claiming only four more engines would be required throughout the remainder of the Space Shuttle Program (SSP).

Only a year later, the situation became more convoluted, as a NASA Authorization Act in 2008 placed a temporary hold on the complete shutdown of RS-25 fabrication assets – mainly from the standpoint of spare hardware availability – but also in relation to continued evaluations into short-term and long-term Shuttle extension possibilities.

Ares died with the end of the CxP, but the RS-25s yet again fought against retirement, as lawmakers realigned NASA future vehicle aspirations – via the law of the 2010 Authorization Act – to select a vehicle that used both Shuttle and former Constellation Program hardware.

Evaluated via the RAC (Requirements Analysis Cycle) effort – tasked with finding the best baseline for the new Heavy Lift Launch Vehicle (HLV) rocket – the RS-25s were confirmed as the preferred option for all derivatives of the evolvable HLV, albeit under the weighted guidelines of utilizing hardware associated with Shuttle and CxP heritage.

A total of 15 RS-25Ds left the Kennedy Space Center (KSC) to be reunited with spare engines and parts that have since congregated at Stennis. The shipment from Florida included nine of the last SSMEs to fly with the Space Shuttle, all of which performed admirably.

A 16th engine was recently added to the stock, built out of spare parts at the Stennis Space Center where the RS-25s are being tested.

The restart of the factory floor – and the return of contractors shut down during the end of the Shuttle Program – for the RS-25 requires several steps.

“The first part is the recertification of the newly produced RS-25 for flight. This activity will involve the restart of the RS-25 production lines, both at the prime contractor and supplier facilities, and then the rigorous process of testing and demonstration necessary to show that the newly produced hardware meets the SLS Program requirements and consistent with historically-based technical expectations,” the document added.

“The second part of the overall RS-25 Production Restart effort is the production of six RS-25 flight engines.”

The restart of the production lines includes re-establishing prime contractor internal manufacturing, engineering support, and quality management processes, and includes similar activities at suppliers with re-certification of these suppliers and their processes and products as required.

“Some of this restart activity may include process redevelopment and minor redesign efforts due to obsolescence issues or to take advantage of modern manufacturing technologies in pursuit of lower productions costs, all while maintaining the form, fit, function, and performance of the historical and heritage RS-25 engine components and subsystems.”

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The work is mainly conducted at two Aerojet Rocketdyne centers. The machining, welding, assembly and test of subassemblies takes place at its Canoga Park, California Strategic Fabrication Center. Turbopump assembly takes place at the West Palm Beach, Florida facility. Testing then takes place at Stennis.

The six new engines will allow for full flight sets of engines through to the fourth flight, with a spare set ready to take over the fourth mission if required – a scenario utilized during Shuttle.

Providing there are no problems during the early lifetime of SLS, the fifth engine set will fly with the fifth mission.

“In order to meet SLS Program flight manifest requirements, production of RS-25 flight engines will be concurrent with the engine recertification effort. The number of new flight engine: to be included as part of this action is six (6).

“This amount of flight hardware is necessary to fulfill the needs of one SLS launch (four engines are used per launch) and two complete sets of engine hardware (i.e., the equivalent of two engines) necessary for risk mitigation in the form of spare hardware for both newly certified engines and residual RS-25 engines.

“This engine hardware will also serve as risk mitigation when the last four of the existing RS-25 inventory are used in support of the fourth SLS flight.”

NASA went to great lengths to note the heritage of the RS-25 hardware, noting that this proposed effort will be based on the restart of a previously existing production line for an engine system with thirty years of human spaceflight history.

“It is not a new engine development effort,” the document stressed.

The engines have proved their worth with Shuttle, with only one major malfunction during its flight history, namely STS-51F (ME-1), resulting in a safe Abort To Orbit (ATO).

The engines will remain closely matched to the Shuttle era, with wholesale changes to the engine design considered, but rejected because it was determined the cost, schedule, technical, and safety risks of that approach outweighed the potential beneﬁts.

Another alternative was to move to a different engine during SLS’ career. However, that was also rejected as an option due to the impacts it would have on the vehicle’s design – which is specific to the RS-25.

“Every liquid propellant rocket engine design has unique interfaces, interface conditions, physical features and performance characteristics. These factors drive the design of the stage main propulsion system, the sizing of the propellant tanks, the constituents, and capabilities of the ancillary systems used to support engine operation such as pneumatic and hydraulic fluid supply, communications, electrical power and thrust vector control,” the overview continued.

“They also can influence ground systems including handling and test equipment and even engine test stands. The engine performance also drives mission design at the vehicle level in terms of payload manifest, trajectory design, and abort scenario development.

“Thus, once an engine is chosen for a launch vehicle architecture and that vehicle is certified for flight, changing to another engine with substantive differences in form, fit, function, or performance would necessitate significant stage and vehicle redesign and recertification.”

Other negative factors included the fear of a gap ahead of the fifth flight, as SLS underwent a redesign to cater for a different engine, while the costs associated with a new engine that could compete with the RS-25 would be in the billions of dollars.

“A recent, parametric estimate performed by NASA suggests that just the design cost for creating and certifying an RS-25 equivalent engine would be approximately $2.23 billion, which is 40 percent greater than the total estimated cost of this procurement action to acquire six RS-25 flight-ready engines.”

The document takes several opportunities to press home the value of the RS-25’s flight history, pointing out no alternative engine in its class is as matured as the RS-25 from a technical perspective, with over one million seconds of accumulated hot-fire test time and the equivalent of over four hundred human spaceflights (three engines per Shuttle mission).

The outline emphasized that the RS-25 is the only real option for the lifetime of the SLS, even adding that remains the case even “if money was no object” – based on heritage (safety) and schedule.

The rationale in the document is aimed at providing ammunition against a potential objection being lodged against the removal of a competition from the procurement process – noting such a protest could threaten a delay in the schedule.

Ironically, the document notes the engines aren’t required until 2027, which – providing it’s not an error in the document – is a schedule delay when compared to the projected SLS manifest for the fifth mission.

“Even with Aerojet Rocketdyne’s extensive knowledge base and existing manufacturing infrastructure with regards to RS-25 engine development and production for meeting SLS requirements, the current schedule is challenging,” the document continued.

“It would be an unacceptable risk of schedule delay for the SLS Program if this challenging schedule was burdened by the addition of a competitive procurement process and if the effort was not leveraging all of the existing infrastructure knowledge and experience resulting from NASA’s previous contracts with Aerojet Rocketdyne.”

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Aerojet Rocketdyne (and its predecessor companies) has been a part of every human space flight launch from the United States, with engine production for NASA ranging back to the 1960s.

Interestingly, the document’s pages of praise for Aerojet Rocketdyne – aimed at mitigating any potential protest in the procurement path – is unlikely to be required.

It took 10 pages before the document referenced that only “a small (unnamed) company, which has not previously developed or produced rocket engines”, had applied to compete for the engine contract.

“Thus, a review by NASA of viable options from the historical perspective, from the corporate perspective, and as informed by the active market research performed via the RFI has determined that there is only one available source – Aerojet Rocketdyne – for obtaining SLS RS-25 core stage engines while optimizing safety, cost, and schedule performance.”

While the document stressed the Agency is sensitive to the need for competition, there are no other known interested sources other than the two identified (the unnamed small company and Aerojet Rocketdyne).

“Should other sources present themselves as a result of the pro-solicitation synopsis, they will be given appropriate consideration as required.

“(However,) with its unique knowledge of and experience with the RS-25 engine, its components, and its processes, Aerojet Rocketdyne is the only responsible party that can meet the SLS Program requirements for additional engines.

“For the reasons discussed above, full and open competition for the NASA requirement is not feasible at this time.”

(Images: Via NASA and L2 – including SLS renders from L2 artist Nathan Koga – The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)

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