The utilization of heritage RS-25 engines, also known as the Space Shuttle Main Engine (SSME), has enabled rapid progress in the development and certification of the NASA Space Launch System (SLS) toward operational flight status. The RS-25 brings design maturity and extensive experience gained through 135 missions, 3000+ ground tests, and over 1 million seconds total accumulated hot-fire time. In addition, there were also 16 flight engines and 2 development engines remaining from the Space Shuttle program that could be leveraged to support the first four flights. Beyond these initial SLS flights, NASA must have a renewed supply of RS-25 engines that must reflect program affordability imperatives as well as technical requirements imposed by the SLS Block-1B vehicle (i.e., 111% RPL power level, reduced service life). Recognizing the long lead times needed for the fabrication, assembly and acceptance testing of flight engines, design activities are underway to improve system affordability and eliminate obsolescence concerns. These key objectives are enabled largely by utilizing modern materials and fabrication technologies, but also by innovations in systems engineering and integration (SE&I) practices

Ballard, Richard O.

NASA Technical Reports Server

Next-Generation RS-25 Engines for the NASA Space Launch System

The utilization of heritage RS-25 engine, also known as the Space Shuttle Main Engine (SSME), has enabled rapid progress in the development and certification of the NASA Space Launch System (SLS) toward operational flight status. The RS-25 brings design maturity and extensive experience gained through 135 missions, 3000+ ground tests, and over a million seconds total accumulated hot-fire time. In addition, there were also over a dozen functional flight assets remaining from the Space Shuttle program that could be leveraged to support the first four flights. Beyond these initial SLS flights, NASA must have a renewed supply of RS-25 engines that must reflect program affordability imperatives as well as technical requirements imposed by the SLS Block-1B vehicle (i.e., 111% RPL power level, reduced service life). Recognizing the long lead times needed for the fabrication, assembly and acceptance testing of flight engines, design activities are underway at NASA and the RS-25 engine provider, Aerojet Rocketdyne, to improve system affordability and eliminate obsolescence concerns. This paper describes how the achievement of these key objectives are enabled largely by utilizing modern materials and fabrication technologies, but also by innovations in systems engineering and integration (SE&I) practices

Next-Generation RS-25 Engines for the NASA Space Launch 
System 
 
 
Richard O. Ballard 
M/S XP20 
NASA Marshall Space Flight Center 
Huntsville, AL USA 35812 
rick.ballard@nasa.gov 
 
 
Abstract 
The utilization of heritage RS-25 engine, also known as the Space Shuttle Main Engine (SSME), has 
enabled rapid progress in the development and certification of the NASA Space Launch System (SLS) 
toward operational flight status.  The RS-25 brings design maturity and extensive experience gained 
through 135 missions, 3000+ ground tests, and over a million seconds total accumulated hot-fire time.  In 
addition, there were also over a dozen functional flight assets remaining from the Space Shuttle program 
that could be leveraged to support the first four flights.  Beyond these initial SLS flights, NASA must 
have a renewed supply of RS-25 engines that must reflect program affordability imperatives as well as 
technical requirements imposed by the SLS Block-1B vehicle (i.e., 111% RPL power level, reduced 
service life).  Recognizing the long lead times needed for the fabrication, assembly and acceptance testing 
of flight engines, design activities are underway at NASA and the RS-25 engine provider, Aerojet 
Rocketdyne, to improve system affordability and eliminate obsolescence concerns.  This paper describes 
how the achievement of these key objectives are enabled largely by utilizing modern materials and 
fabrication technologies, but also by innovations in systems engineering and integration (SE&I) practices. 
https://ntrs.nasa.gov/search.jsp?R=20170008992 2019-08-29T23:19:55+00:00Z


READINESS ASSESSMENT
National Aeronautics and Space Administration
S P A C E  L A U N C H  S Y S T E M
Next-Generation RS-25 Engines for the NASA 
Space Launch System
Richard O. Ballard
SE&I Manager
SLS Liquid Engines Office
NASA Marshall Space Flight Center
www.nasa.gov/sls EUCASS’17 Briefing.1
https://ntrs.nasa.gov/search.jsp?R=20170008946 2019-08-29T23:14:15+00:00Z
Overview
Use of heritage RS-25 engines, also known as the Space 
Shuttle Main Engine (SSME), has enabled rapid progress in the 
development and certification of the NASA Space Launch 
System (SLS) toward flight status.
• 16 flight engines and 2 development engines were recovered from 
the Space Shuttle program to support the first four flights.
– The recovered flight SSMEs were adapted to replace the obsolete engine 
controller unit (ECU) with a modern system and certify the engine to the new 
SLS vehicle loads and environments.
• The adapted engines are sufficient to support the first four missions
– Beyond these initial SLS flights, NASA must have a renewed supply of 
engines that reflect program affordability imperatives as well as technical 
requirements imposed by the SLS Block-1B vehicle.
– Activities are underway to update and restart RS-25 production using modern 
materials and fabrication technologies, but also by innovations in systems 
engineering and integration (SE&I) practices.
www.nasa.gov/sls EUCASS’17 Briefing.2
RS-25 Evolution for SLS
www.nasa.gov/sls EUCASS’17 Briefing.3
The SLS Core Stage Engine (CSE):
• Aerojet-Rocketdyne (AR) RS-25
• Demonstrated high performance, high reliability 
staged-combustion cycle LOX / LH2 engine
• Flight certified in 1979, first flown in 1981
Configuration Heritage (SSME) Adaptation Restart
Thrust (kN, vacuum) 2188 (104.5% RPL) 2281 (109% RPL) 2321 (111% RPL)
Isp (secs, vacuum) 450.2 450.7 450.8
Service Life (starts/secs) 55 / 27000 6 / 2500 4 / 1700
• 405 engine missions
• >3000 ground hot-fire tests
• >1 million secs hot-fire time
SLS Vehicle Block Evolution
www.nasa.gov/sls EUCASS’17 Briefing.4
Transitioning to RS-25 Production Restart
• While the inventory of Adaptation engines would support the first 4 SLS 
missions, the long lead times for engine production emphasized the 
need for a renewed flow of RS-25 engines.
• Before committing to re-opening the RS-25 production line, it was 
recognized as vital to update the engine design baseline to reflect SLS 
programmatic imperatives and technical requirements.
– Emphasis on affordability and sustainability to support projected long-term 
mission launch rate.
• Deliver up to 4 engines per year at an affordable unit cost by compressing long-
lead times and using state-of-the-art materials and fabrication technologies.
– Evolution of the RS-25 design baseline from Adaptation to Restart required 
a thorough trade evaluation of SLS-unique technical requirements versus 
time/cost versus available enabling technologies.
– Working these trades allowed a development path to be defined with 
flexibility to respond to unforeseen risks and opportunities.
• The development path for the Restart engine also needed to be phased 
in parallel to the ongoing Adaptation activity
www.nasa.gov/sls EUCASS’17 Briefing.5
RS-25 Development Phasing
www.nasa.gov/sls EUCASS’17 Briefing.6
Setting the Stage
www.nasa.gov/sls EUCASS’17 Briefing.7
• In order to initiate the Restart development activity, an interim contractual line 
item (CLIN-5) was authorized for AR to evaluate and identify near-term 
candidates for development into the RS-25 engine design.
– Candidates were assessed against the Technology Readiness Level (TRL) involved 
in pursuing the design change.  The minimum allowable TRL was 5.
– Selection was based on budget, available time and level of technical risk
• The CLIN-5 activity 
identified a number 
of design initiatives 
that could result in 
reducing production 
costs across the 
entire RS-25 
engine.
• The goal was to 
reduce the unit cost 
of the engine by 
one third (33%).
Basic
Research
Feasibility
Research
TRL 1   Basic Principles Observed and Reported
Components and subsystems are possible with basic principles selected; electrical vs pneumatic, etc.
TRL 2   Technology Concept and/or Application Formulated 
Basic concepts for the selected component or subsystem are conceived and defined as to preliminary 
concept layout, etc.
TRL 3   Analytical and Experimental Critical Function and/or Characteristic Proof-of-Concept
Selected concept and implementation methodology are analyzed, modeled, simulated, etc. such that a 
preliminary system characterization is completed and understood.
Examples:  Subcomponent and materials testing and/or preliminary design analysis of critical design 
features to demonstrate  proof-of -concept.
TRL 4   Component and/or Breadboard Validation in  Laboratory Environment
Breadboard type hardware is designed, fabricated, and subjected to developmental testing to 
experimentally demonstrate concept validity, characterize individual component and subsystem 
operational characteristics, and provide data for product improvement.
Examples:  Component test such as subscale thrust chamber/injector or turbopump subcomponent 
testing such as bearing and seals, turbine air test rigs, thermal shock testing of turbine blades.
TRL  5  Component and/or Breadboard Demonstration in Relevant Environment
Breadboard hardware is subjected to informal environmental testing; shock, vibration, thermal, life, etc., 
such that additional proof-of-concept data is obtained as well as operational characteristics under 
expected operational conditions.
Examples:  Full scale component test such as thrust chamber/injector or turbopump performance testing 
to demonstrate component functional characteristics that can be simulated independent of total system.
TRL 6   System/Subsystem Validation Model or Prototype Demonstrated in Relevant 
Environment (Ground or Space)
Testing or integrated systems and/or individual components in a static firing test environment to finalize 
ground test exposure prior to full scale development for flight.  This could also involve testing in a system 
level simulation
facility for operation of components and systems in anticipated environments including loads.
Examples:  Full scale engine system test to demonstrate component interactions  May be workhorse (no 
flight weight)  system or prototype (flight weight) system.
TRL 7     System Prototype Demonstrated in Space Environment
TRL 8     Actual System Completed and “Flight Qualified” Through Test and Demonstration 
(Ground or Flight)
TRL 9     Actual System “Flight Proven” Through Successful Mission Operations
Technology
Development
Technology 
Demonstration
System/Systems
Development
Systems Test, Launch
and Operations
NASA Techology Readiness Levels (TRLs)
Ground
Laboratories
Space
Managing the Restart Development Path
• Once the CLIN-5 activity defined a portfolio of Restart design 
candidates, the management of the portfolio was taken over by 
the LEO Affordability/Obsolescence Review Board (AORB).
– The AORB responsible for monitoring the progress of each design activity 
to insure that the expected programmatic benefit in terms of cost 
reduction is realized.
– The development path of each design initiative is laid out with key 
decision points and potential “off-ramps” that can be triggered by the 
AORB if the affordability benefit is reduced or threatened.
• Example: Offramp to replace the fuel flowmeter
• As the design changes are completed and verified, they will be 
documented as a series of Engineering Change Proposals 
(ECPs) to modify the Adaptation design baseline.
– The ECPs will be used to establish the Restart design baseline at the 
completion of the Restart Design Certification Review (DCR).
www.nasa.gov/sls EUCASS’17 Briefing.9
Milestone Reviews
• Periodic milestone reviews are a useful tool for providing an 
independent review of development work in progress and also 
to demonstrate to other stakeholders that useful work is being 
effectively pursued and the risk portfolio is being successfully 
managed.
• Like the milestone reviews executed for the Adaptation effort 
(no PDR or CDR), the Restart activity took credit for the 
established operational record of the RS-25 and defined a set of 
milestone reviews to provide a composite assessment of work 
underway at particular points in the Restart development cycle.
– Critical Design Summary Review (CDSR)
– Certification Readiness Review (CRR)
– Design Certification Review (DCR)
– Development Checkpoints (DCPs)
www.nasa.gov/sls EUCASS’17 Briefing.10
Affordability Enablers
• Achieving the affordability goals for the Restart baseline will be 
enabled by the two key focus areas:
– Hardware definition – this includes not only exploitation of modern 
fabrication techniques such as Additive Manufacturing (AM), but easing 
design and operational sensitivities imposed by reusability / supportability 
requirements.
– Business practices - this is largely influenced on how AR operates in 
performing its business processes and depends on optimizing and 
evolving lean practices.
• Achieving the affordability goals for the Restart RS-25 cannot be 
attained exclusively by selective redesign of the engine 
hardware.
– A thorough examination of all areas and organizations involved in 
producing the engine have been made, starting with raw materials and 
vendor components arriving at the AR facility, and ending with engine 
delivery at the NASA Michoud Assembly Facility (MAF).
www.nasa.gov/sls EUCASS’17 Briefing.11
Technical Focus Areas
• Increased minimum power level requirement to eliminate the need for an engine test stand 
equipped with a diffuser for throttle testing
• Making the RS-25 expendable allowed reduced structural margins and simplified operational 
maintenance requirements/tests
• Reduced gimbal angle requirement to enable the use of flex hoses instead of flex ducts –
reduced hardware complexity reducing fabrication costs
• Selected use of Additive Manufacturing (AM) technologies, including Selective Laser Melting 
(SLM), Near-Net Shape forgings
• Leverage design and manufacturing experience and lessons-learned from recent J-2X engine 
development (e.g., replace MCC plated liner with hot isostatic pressed (HIP) manufacture; AM 
valve housings).
• Reduce sub-assembly parts and welds
• Eliminate nonconformance drivers for manufacturing rejects and assembly reworks
• Selective use of Manufacturing Technology Demonstrators (MTDs) to validate affordability 
approach
• Eliminate unnecessary instrumentation and supporting bosses, sense lines and harnesses
• Eliminate outdated inspection and maintenance operations
• Eliminate or mitigate failure modes that drive maintenance-intensive hazard controls
• Push for reductions in touch labor and fabrication cycle times
• Push for innovations in supplier selection and management
• Incorporate lean manufacturing practices to optimize scheduling and factory flows for fabrication 
machinery/tooling
www.nasa.gov/sls EUCASS’17 Briefing.12
Institutional Focus Areas
• Challenge entrenched paradigms and “sacred cows”, allow freedom to innovate and adapt
• Seek and prosecute inefficiencies
• Encourage fresh perspectives, opinions, ideas
• Establish guidance on risk tolerance (i.e., perfection is unnecessary when “good enough” is 
acceptable)
• Seek new technologies for evaluation and exploitation
• Leverage documented lessons-learned and nonconformances (e.g., Unsatisfactory Condition 
Reports (UCRs), Material Reviews (MRs)) to identify preemptive corrective actions that can be 
implemented in the design, processes, or operations
• Establish a methodical approach to affordability with quantifiable tracking, including 
development of a business case for each change that trades development cost and risk against 
run-out cost savings
• Grant credit for the long history of the RS-25 system (40+ years), AR experience, and NASA 
insight skills
It is understood that the items listed above are largely philosophical common-sense 
mantras, it is important to note that they can and should be applicable to both AR and 
NASA.
Pursuing technical perfection and affordability are not generally compatible and will 
rely on contractor and customer coordination to establish the necessary balance.
www.nasa.gov/sls EUCASS’17 Briefing.13
Challenges and Opportunities
• (Challenge) Lack of vehicle integration engagement requiring 
designing the engine to integrate into a vehicle core stage that 
does not yet exist.
– The prime contractor for the SLS core stage is not on contract to support 
vehicle integration of the Restart engine with the Block-1B vehicle.
• The difference is power levels between Adaptation and Restart (i.e., 109% RPL 
vs. 111% RPL) poses a design gap in integrated coupled loads between the 
engine and vehicle.
• (Opportunity) Immediate availability of development engines to 
provide a platform for hotfire testing.
– Rapid prototyping enabled by AM technology allows Restart design 
initiatives to be tested quickly.
www.nasa.gov/sls EUCASS’17 Briefing.14
Over the Horizon – RS-25 Block-IV
• The CLIN-5 assessment activity limited the scope of affordability 
candidates to those that could be implemented with minimal 
technology development (TRL  5).
– Selected candidates are being developed as part of the RS-25 Restart 
design activity.
• In addition, NASA and AR are working on a “Block-IV Upgrade” 
study to enable the development of a longer-term strategic plan 
to possibly pursue more aggressive affordability options for the 
RS-25 engine beyond the Restart configuration.
– The Block-IV study looks at low-TRL, higher risk, higher payoff 
candidates deferred by the Restart initiative.
www.nasa.gov/sls EUCASS’17 Briefing.15
Summary
• Evolving the RS-25 into the next generation design baseline 
will be challenging in order to accommodate the numerous 
programmatic and technical imperatives imposed by the 
SLS program.
• Work completed to date by AR and the SLS Liquid Engines 
team shows good progress and rapid response to 
overcome both anticipated and unanticipated challenges.
• The path ahead for making the RS-25 Restart Production a 
reality is focused on helping NASA open a new era of 
exploration and discovery by leveraging the best of this 
nation’s investment in space technology.
www.nasa.gov/sls EUCASS’17 Briefing.16
www.nasa.gov/sls 17


Next-Generation RS-25 Engines for the NASA Space Launch System

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server

NASA Technical Reports Server

NASA Technical Reports Server