Evaluation and Test Requirements for Liquid Rocket Engines
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Evaluation and Test Requirements for Liquid Rocket Engines

Summary

This standard (Aerospace Report No. TR-RS-2023-00026) establishes test and evaluation requirements for the development, qualification, and acceptance of liquid propellant rocket engines (LREs) and associated propulsion systems. Drawing upon historical guidelines, industry collaboration, and recent lessons learned, it defines comprehensive structural, functional, performance, and life verification standards to ensure mission success for space launch vehicles. The document details requirements covering component- and engine-level testing, margin demonstrations, additive manufacturing, damage tolerance, and reusable operations.

Title Page

AEROSPACE REPORT NO. TR-RS-2023-00026 Evaluation and Test Requirements for Liquid Rocket Engines January 15, 2023

Jeffrey Murphy1, Nacer Thomas1, Zachary Kier2, James Tuck-Lee3, and Vinay K. Goyal4 1Propulsion Department, Vehicle Performance Subdivision 2Thermostructures, Structures Department 3Structures Department, Structural Mechanics Subdivision 4Launch Systems Division, Launch and Enterprise Operations

Prepared for: United States Space Force Space Systems Command 483 N. Aviation Blvd. El Segundo, CA 90245-2808

Contract No. FA8802-19-C-0001 Authorized by: Space Systems Group Distribution Statement A: Approved for public release; distribution unlimited.

Notice and Approval

This report was submitted by The Aerospace Corporation, El Segundo, CA 90245-4691, under Contract No. FA8802-19-C-0001 with the Space Systems Command, 483 N. Aviation Blvd., El Segundo, CA 90245. It was reviewed and approved for The Aerospace Corporation by Kevin Bell, Senior Vice President. Mr. Alejandro Prieto was the project officer for the SSC/BZEE program.

This report has been reviewed by the Public Affairs Office (PAS) and is releasable to the National Technical Information Service (NTIS). At NTIS, it will be available to the general public, including foreign nationals.

This technical report has been reviewed and is approved for publication. Publication of this report does not constitute Air Force approval of the report’s findings or conclusions. It is published only for the exchange and stimulation of ideas until adopted or otherwise implemented by the government.

© The Aerospace Corporation, 2023 All trademarks, service marks, and trade names are the property of their respective owners.

Report Documentation Page (SF 298)

REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188

  1. REPORT DATE: 15-01-2023
  2. REPORT TYPE: Technical Report
  3. DATES COVERED: -
  4. TITLE AND SUBTITLE: Evaluation and Test Requirements for Liquid Rocket Engines 5a. CONTRACT NUMBER: FA8802-19-C-0001
  5. AUTHOR(S): Jeffrey J. Murphy, Nacer Thomas, Zachary Kier, James P. Tuck-Lee, Vinay K. Goyal
  6. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES): The Aerospace Corporation, Vehicle Systems Division, 2310 E. El Segundo Blvd., El Segundo, CA 90245-4691
  7. PERFORMING ORGANIZATION REPORT NUMBER: TR-RS-2023-00026
  8. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES): Space Systems Command, United States Space Force, 483 N. Aviation Blvd., El Segundo, CA 90245-2808
  9. SPONSOR/MONITOR’S ACRONYM(S): SSC
  10. DISTRIBUTION/AVAILABILITY STATEMENT: Approved for public release; distribution unlimited.
  11. ABSTRACT: Liquid propellant rocket engines enable rocket vehicle design and space launch capability. These systems are susceptible to numerous potential failure modes, which can produce catastrophic results. Furthermore, engine testing and test hardware costs have historically represented a major portion of engine development program costs. For these reasons, an engine development test and evaluation standard was developed to convey best practices and establish consistent requirements across the industry to support the successful development and qualification of liquid rocket engines. Non-binding guidelines (JANNAF-GL-2012-01-R0, Test and Evaluation Guidelines for Liquid Rocket Engines, Joint Army Navy NASA Air Force Liquid Propulsion Subcommittee Test Practices and Standards Panel, December 2012) were previously developed, and the release of TR-RS-2017-00026 (SMC-S-025) established requirements. This is an update to TR-RS-2017-00026, incorporating lessons learned from collaboration with launch vehicle and liquid rocket engine contractors subsequent to the initial release. These lessons draw upon historical guidelines and recent experience to provide best-in-class liquid rocket engine qualification practices.
  12. SUBJECT TERMS: Liquid rocket engines, design requirements, test requirements, acceptance test, system test
  13. SECURITY CLASSIFICATION: UNCLASSIFIED
  14. NUMBER OF PAGES: 92 19a. NAME OF RESPONSIBLE PERSON: Jeffrey J. Murphy (310) 336-6080

Document History

Document History:

TR-RS-2017-00026, 16 Jun 2017 (SMC-S-025, 26 Jul 2017): Original release of Evaluation and Test of Liquid Rocket Engines standard.

TOR-2021-01879, 10 May 2022: First version of proposed update to SMC-S-025, including documentation of the internal Aerospace Corp. stakeholder review of the updates that took place from 25 Aug 2021 through 15 Oct 2021. Summary of changes include § 4.1 General Test Considerations, § 4.4 Number of Total Tests, § 4.6.1 Material Selection, § 4.6.2 Loads, § 4.6.3 Factors of Safety, § 5.3 Strength Assessment, § 5.3.4 Joints and Seals, § 5.4.3 Damage Tolerance (Safe-Life) Assessment, § 5.6 Bellows, § 7.2.5 Thrust and Mixture Ratio Excursion Tests, § 7.3.5.4 Shutdown Transients, § 7.9.2 Post-Test Inspections, and Appendix B.

TOR-2022-01071, 5 Apr 2022: Update to TOR-2022-01879 based on internal review comments. Changes include § 4.3.1 Number of Verification Engine Samples, § 4.6 Material Selection, § 4.6.2 Loads, § 5.1 Structural Model, § 5.6 Bellows, § 6.12 and § 7.6.5 Electromagnetic Compatibility Tests, § 7.3.5.4 Shutdown Transients, § 7.6.1 Thermal Environment, § 7.9.4 Gas Liquefaction Control, § 7.9.5 External Icing, § 7.10.2 Mass Properties.

This document (TR-RS-2023-00026): Version of TOR-2022-01071 for release. No external review comments were received. References to TR-RS-2022-00005 were updated to TR-RS-2023-00005 to reflect actual numbering upon release of that standard.

Background

Liquid propellant rocket engines enable rocket vehicle design and space launch capability. These systems are susceptible to numerous potential failure modes, which can produce catastrophic results. Furthermore, engine testing and test hardware costs have historically represented a major portion of engine development program costs. For these reasons, an engine development test and evaluation standard was developed to convey best practices and establish consistent requirements across the industry to support the successful development and qualification of liquid rocket engines. Non-binding guidelines (JANNAF-GL-2012-01-R0, Test and Evaluation Guidelines for Liquid Rocket Engines, Joint Army Navy NASA Air Force Liquid Propulsion Subcommittee Test Practices and Standards Panel, December 2012) were previously developed, and the release of TR-RS-2017-00026 (SMC-S-025) established requirements.

This is an update to TR-RS-2017-00026, incorporating lessons learned from collaboration with launch vehicle and liquid rocket engine contractors subsequent to the initial release. These lessons draw upon historical guidelines and recent experience to provide best-in-class liquid rocket engine qualification practices. In the General Requirements section there is new information and references pertaining to additive manufacturing, and maximum expected operating pressure requirements. In the Structural Analysis section there is new information regarding factors of safety, damage tolerance, and bellows requirements. In the Engine Requirements section there is added information regarding the definition and qualification of the flight/trim box and testing requirements. Additionally, there are numerous clarifications and editorial revisions made throughout the document.

Table of Contents

  1. Scope of this Standard 1.1 Purpose 1.2 Application 1.3 Tailoring
  2. Reference Documents 2.1 Applicable Documents 2.2 Guidance Documents
  3. Acronyms and Definitions 3.1 Acronyms 3.2 Definitions
  4. General Requirements 4.1 General Test Considerations 4.2 Verification Approach 4.3 Engine Samples 4.3.1 Number of Verification Engine Samples 4.4 Number of Total Tests 4.4.1 Functional Objectives-Based Approach 4.4.2 Modeling and Simulation 4.5 Relationship to Other Standards 4.5.1 Systems Safety 4.5.2 Pressure Vessels and Pressurized Structures 4.5.3 Pressure and Pressure-Loaded Components 4.5.4 Ordnance 4.5.5 Moving Mechanical Assemblies 4.5.6 Pressurized Systems 4.6 General Structural Requirements 4.6.1 Material Selection 4.6.2 Loads 4.6.3 Factors of Safety
  5. Structural Analysis Requirements 5.1 Structural Model 5.2 Failure Modes 5.3 Strength Assessment 5.3.1 Strength and Yielding 5.3.2 Buckling 5.3.3 Inadvertent Contact 5.3.4 Joints and Seals 5.3.5 Failure Modes of Ablative Thermal Protection System (TPS) 5.4 Life Assessment 5.4.1 Fatigue 5.4.2 Creep 5.4.3 Damage Tolerance (Safe-Life) Assessment 5.5 Turbomachinery Operation 5.6 Bellows 5.7 Structural Qualification by Similarity 5.8 Structural Approach Documentation
  6. Unit Requirements 6.1 Unit Verification by LRE Test 6.2 Unit Inspection 6.3 Unit Performance Requirements 6.3.1 Ignition System 6.3.2 Turbomachinery 6.3.3 Combustion Devices and Combustion Stability 6.4 Unit Functional Characteristics 6.4.1 Cold Flow Tests 6.4.2 Transient Characterization 6.4.3 Net Positive Suction Pressure (NPSP) Margin and Cavitation 6.4.4 Pogo and Pump Compliance Characterization 6.4.5 Engine Controls 6.5 Unit Leak Test 6.6 Unit Shock Test 6.7 Unit Vibration and Acoustic Test 6.8 Unit Acceleration Test 6.9 Unit Thermal Test 6.10 Unit Climatic Test 6.11 Unit Structural Test Requirements 6.12 Unit Electromagnetic Compatibility Test 6.13 Unit Life and Wear-in Test
  7. Engine Requirements 7.1 Test Types 7.2 Performance 7.3 Functional Characteristics 7.4 Structural Tests 7.5 Pressure and Leak Testing 7.6 Environments 7.7 Life 7.8 Controls 7.9 Operations 7.10 Process Controls 7.11 Unique Requirements
  8. System Requirements 8.1 Stage and System Test 8.2 Pre-Launch Validation and Operational Tests Appendix A. Tailoring Guidance Appendix B. Operational Keep-Out Zones

1. Scope of this Standard

This Standard establishes test and evaluation requirements related to the development, qualification, and production unit acceptance of liquid propellant rocket engines and associated propulsion systems. Requirements include those associated with integrity, strength, life, interface conditions, and functional performance. Requirements should be understood and applied early in the design phase to enhance success in the development, test, and evaluation phases. Tests generally include component-level testing, engine system-level testing, and vehicle stage-level testing. Development is addressed herein largely to the extent that it increases the likelihood of successful qualification and/or provides additional necessary verification samples. Thus, development requirements outside those applicable to minimum verification requirements are treated less rigorously. Evaluation includes relevant and appropriate analyses for verification of requirements. In some cases, requirements are expressed by reference to other standards.

1.1 Purpose The requirements in this Standard should be used to define a test program, primarily for qualification and production acceptance, that will appropriately verify the design, identify latent defects, ensure adequate functional performance, and help ensure a high level of confidence in achieving successful launch missions. It is expected that the overall program will include a thorough development program and use other good engineering practices to help maximize the success of the test program.

1.2 Application This document is intended for compliance in government acquisition programs, and the requirements herein are to be flowed, as applicable, throughout the supply chain. The test requirements herein focus on design verification and the identification of latent defects to help ensure a high level of confidence in achieving successful space missions. Unless otherwise specified by the Approval Authority, the requirements herein are intended to apply to new or modified liquid rocket engine (LRE) designs, new or modified LRE unit designs, use of existing LRE designs in a new application or environment, and procurement from a new supplier or manufacturing location.

This Standard applies to LREs and associated propulsion systems for expendable and re-usable applications. Relevant LREs include those using pump-fed or pressure-fed designs, with various propellant combinations including hydrogen/oxygen, hydrocarbon/oxygen, storable, and monopropellants. This Standard addresses development, qualification, acceptance, and pre-launch testing for main propulsion systems (i.e., steady-state, non-pulsing, thrust greater than 4,500 N / 1,000 lbf) for space launch vehicles (including booster, upper stage, and in-space propulsion). This Standard focuses on testing of an LRE at the individual engine and integrated propulsion system levels but includes lower-level testing where warranted. Here, the LRE is defined to include those components from the engine inlet flanges to the thrust chamber nozzle, including all interface connections to the launch vehicle and launch facility.

This Standard is intended to be used with other mission assurance documents listed in Section 2, including TR-RS-2014-00016 (SMC-S-016) [1] and TR-RS-2023-00005 [2]. The requirements in this Standard take precedence over documents referenced in Section 2 in the event that conflicts are encountered. Within the nomenclature of TR-RS-2014-00016 [1], an LRE is categorized as a subsystem. Within the nomenclature of TR-RS-2023-00005 [2], an LRE is categorized as a pressurized system, meaning there are pressure-containing elements within the LRE. This Standard uses these documents and provides more detailed and specific requirements applicable to LREs and their integration.

All requirements in this document are numbered and indicated by the word “shall,” thereby differentiating requirements text from explanatory or guidance text. All guidance text is presented in italics.

1.3 Tailoring The requirements contained herein may be tailored based on the project-specific acquisition situation/environment, design complexity, design margins, vulnerabilities, technology state of the art, in-process controls, mission characteristics/criticality, lifecycle cost, number of vehicles involved, prior usage, and acceptable risk. All tailoring of requirements must achieve the intent of this Standard. As part of the tailoring process, sufficient rationale with supporting technical data for each tailored requirement must be documented. Tailoring rationale should include risk assessment per the process detailed in MIL-STD-882E [15]. The tailoring rationale and risk assessment shall be subject to review and acceptance by the Approval Authority. Otherwise, the requirements of this document stand as written.

Herein, requirements for engines used on vehicles transporting personnel are intended to be the same as those for engines used on vehicles transporting only hardware. Engines used on vehicles transporting personnel, however, may have additional program-specific verification and/or safety requirements to be consistent with the established program-specific risk levels for mission success and flight crew safety.

2. Reference Documents

2.1 Applicable Documents

  1. TR-RS-2014-00016: Test Requirements for Launch, Upper Stage and Space Vehicles, The Aerospace Corporation, 25 Jun 2014. (SMC-S-016, Air Force Space Command Space and Missile Systems Center Standard, 5 Sep 2014.)
  2. TR-RS-2023-00005: Space Flight Pressurized Systems, The Aerospace Corporation, 5 Jan 2023. (Expected to supersede SMC-S-005, Air Force Space Command and Missile Systems Center Standard, 28 Feb 2015.)
  3. CPIA Publication 655: M. D. Klem and R. S. Fry, Guidelines for Combustion Stability Specifications and Verification Procedures for Liquid Propellant Rocket Engines, The Johns Hopkins University Chemical Propulsion Information Analysis Center, Jan 1997.
  4. ANSI/AIAA S-080A-2018: Space Systems - Metallic Pressure Vessels, Pressurized Structures, and Pressure Components, American National Standard, 20 Mar 2018.
  5. AIAA S-110-2005: Space Systems – Structures, Structural Components, and Structural Assemblies, American Institute of Aeronautics and Astronautics, 12 Jul 2005.
  6. ANSI/AIAA S-081B-2018: Space Systems – Composite Overwrapped Pressure Vessels (COPVs), American National Standard, 20 Mar 2018.
  7. AIAA S-113A-2016: Criteria for Explosive Systems and Devices on Space and Launch Vehicles, American Institute of Aeronautics and Astronautics, 28 Nov 2016.
  8. AIAA S-114A-2020: Moving Mechanical Assemblies for Space and Launch Vehicles, American Institute of Aeronautics and Astronautics, 14 Jun 2021.
  9. TR-RS-2015-00011: Parts, Materials, and Processes Control Program for Expendable Launch Vehicles, The Aerospace Corporation, 21 May 2015. (SMC-S-011, Air Force Space Command Space and Missile Systems Center Standard, 31 Jul 2015.)
  10. TR-RS-2003-00004: Independent Structural Loads Analyses of Integrated Spacecraft / Launch Vehicle Systems, The Aerospace Corporation, 22 Aug 2003. (SMC-S-004, Air Force Space Command Space and Missile Systems Center Standard, 13 Jun 2008.)
  11. NASA-STD-5020A (W/ CHANGE 1): Requirements for Threaded Fastening Systems in Spaceflight Hardware, National Aeronautics and Space Administration, 2 Nov 2019.
  12. NASA MSFC-DWG-20M02540: Assessment of Flexible Lines for Flow Induced Vibration, Rev. E, National Aeronautics and Space Administration, 15 Jan 1992.
  13. NASA MSFC-SPEC-626: Test Control Document for Assessment of Flexible Lines for Flow Induced Vibration, NASA Marshall Space Flight Center, 11 May 1990.
  14. TR-RS-2008-00008: Electromagnetic Compatibility Requirements for Space Equipment and Systems, The Aerospace Corporation, 1 Jan 2008. (SMC-S-008, Air Force Space Command Space and Missile Systems Center Standard, 13 Jun 2008.)

2.2 Guidance Documents 15. MIL-STD-882E: System Safety, Department of Defense Standard Practice, 11 May 2012. 16. AS6500: Manufacturing Management Program, SAE International, 2014. 17. TOR-2014-02537-REV A: The Test Like You Fly Process Guide for Space, Launch, and Ground Systems, The Aerospace Corporation, 20 Sep 2016. 18. AS9103: Variation Management of Key Characteristics, SAE International, 2012. 19. JANNAF-GL-2012-01-R0: Test and Evaluation Guidelines for Liquid Rocket Engines, Joint Army Navy NASA Air Force Liquid Propulsion Subcommittee Test Practices and Standards Panel, Dec 2012. 20. AFI 91-217: Space Safety and Mishap Prevention Program, Air Force Instruction, Department of the Air Force, 17 April 2014. 21. NASA-STD-5012B: Strength and Life Assessment Requirements for Liquid-Fueled Space Propulsion System Engines, National Aeronautics and Space Administration, Jun 2016. 22. NAFEMS Guidelines: Management of Finite Element Analysis – Guidelines to Best Practice, National Agency for Finite Element Methods and Standards (NAFEMS), Glasgow, UK, 1 Feb 1995. 23. NASA SP-8007A: Buckling of Thin-Walled Circular Cylinders, National Aeronautics and Space Administration, Jan 2021. 24. M. J. Manjoine: “Damage and Failure at Elevated Temperature,” Journal of Pressure Vessel Technology, volume 105, pages 58–62, Feb 1983. 25. NASA-STD-5019A W/ CHANGE 3: Fracture Control Requirements for Spaceflight Hardware, National Aeronautics and Space Administration, 14 Aug 2020. 26. NASA-STD-5009A: Nondestructive Evaluation Requirements for Fracture-Critical Metallic Components, National Aeronautics and Space Administration, Jun 2018. 27. M. Singh, J. Vargo, D. Schiffer, and J. Dello: Safe Diagram – A Design and Reliability Tool for Turbine Blading, Dresser-Rand Company, 2002. 28. NASA SP-8123: Liquid Rocket Lines, Bellows, Flexible Hoses, and Filters, National Aeronautics and Space Administration, Apr 1977. 29. C. E. Brennen: Hydrodynamics of Pumps, Concepts ETI, Inc., pp. 67–69, 1994. 30. A. Mulder: Water Flow Characterization of the Unsteady Environment Upstream of the Space Shuttle Main Engine Low Pressure Fuel Pump with Flow Liners, JANNAF paper 2005-0356BA, NASA MSFC, 2005. 31. R. B. Randall: Vibration-based Condition Monitoring, Wiley, 2011. 32. ANSI/AIAA S-120A-2015 (2019): Mass Properties Control for Space Systems, American Institute of Aeronautics and Astronautics, 23 Nov 2015. 33. LE-S-010: Supplemental Requirements for Reusable Launch Systems, Air Force Space Command Space and Missile Systems Center, 27 Mar 2019. 34. LE-P-018: Guide for Reusable Launch Systems, Air Force Space Command Space and Missile Systems Center, 1 Apr 2019.

3. Acronyms and Definitions

3.1 Acronyms ALF: allowable load factor ATP: acceptance test procedure CDI: cumulative damage index CMP: critical manufacturing process COPV: composite overwrapped pressure vessel DDT&E: design, development, test, and evaluation DOP: detailed operating procedure ECF: environmental correction factor ELCF: external load correction factor EOM: end of mission FAF: fatigue analysis factor FID: failure identification FoS: factor of safety GG: gas generator HCF: high-cycle fatigue Isp: specific impulse KC: key characteristic KPP: key process parameters LCC: launch commit criteria LCF: low-cycle fatigue LEFM: linear elastic fracture mechanics LRE: liquid rocket engine LRU: line replaceable unit MCC: main combustion chamber MDC: maximum design condition MDCL: maximum design condition load MEOP: maximum expected operating pressure MMA: moving mechanical assembly MMPDS: Metallic Materials Properties Development and Standardization MR: mixture ratio MS: margin of safety NAFEMS: National Agency for Finite Element Methods and Standards NDI: non-destructive inspection NPSP: net positive suction pressure PB: pre-burner Pc: chamber pressure PL: power level SAFE: Singh’s advanced frequency evaluation SCC: start commit criteria SL: service life TLYF: test-like-you-fly TPA: turbopump assembly TPS: thermal protection system TVC: thrust vector control UF: uncertainty factor XLB: demonstration factor with respect to the longest burn XSL: demonstration factor with respect to the service life

3.2 Definitions A-Basis Allowable: The mechanical strength values such that 99% of the population will meet or exceed the specified values with a confidence level of 95%. Acceptance Test (or Acceptance Test Procedure, ATP): The required formal tests (or procedures) conducted to demonstrate acceptability of an item for delivery. Allowable Load Factor: Ratio of the allowable load to the Maximum Design Condition Load (MDCL); ALF × MDCL = load resulting in failure. Ambient Environment: The actual external environment surrounding an engine or subsystem. Reference ground test: 23 ± 3 °C, 101 +2/–23 kPa, 50 ± 20% RH. Analysis Validation / Verification: Validation quantifies accuracy of results against experimental data; verification determines correctness of model input data and numerical solution accuracy. B-Basis Allowable: The mechanical strength values such that 90% of the population will meet or exceed the specified values with a confidence level of 95%. Booster: The lowest stage of a multi-stage launch vehicle. Bootstrap: The portion of an LRE start transient where the engine cycle becomes self-sustaining. Buckling and Crippling: A failure mode in which an infinitesimal increase in load leads to sudden collapse or detrimental deformation. Burst Factor / Burst Pressure: Multiplying factor applied to MEOP to obtain design burst pressure; burst pressure is the minimum pressure level at which failure occurs. Damage-Tolerance Life (Safe-Life): The required period of time or number of cycles that the structure, containing the largest crack undetectable by NDI, survives without leaking or catastrophic failure. Detrimental Yielding: Deformation preventing intended function, interfering with other components, or reducing probability of mission success. Factor of Safety (FoS): Multiplying factor applied to maximum expected operating conditions for analytical assessment and/or test verification. Fatigue: Progressive, localized, and permanent structural change from fluctuating stresses/strains. Maximum Expected Operating Pressure (MEOP): Highest pressure that pressurized hardware is expected to sustain during service life. Service Life (SL): Starts at completion of fabrication through acceptance testing, storage, prelaunch, flight, recovery, and reuse.

4. General Requirements

4.1 General Test Considerations Testing should demonstrate engine operation with flight-representative hardware and under flight-representative conditions (Test-Like-You-Fly). Testing must expose the flight design to the operational flight envelope and include margin testing against ground-to-flight dispersions, manufacturing tolerances, and variations.

4.2 Verification Approach [4.2-1] An LRE test plan satisfying the requirements of this Standard shall be developed, reviewed and approved by the Approval Authority, and executed.

Table 4-1. LRE Verification Engine Samples and Margins/Demonstration Factors:

  • Fatigue and Damage Tolerance Factor: 4 XSL (Unit/Subscale)
  • Unit Single Burn Operation Demonstration Factor: 1.1 XLB
  • Minimum Verification Engine Samples: 4 engines (includes 2 qualification engines)
  • Minimum Qualification Engine Samples: 2 engines
  • Thrust/MR Margin Demonstration: 2%
  • Life Demonstration Factors: 4 engines (4 XSL on 1, and 2 XSL on 3)
  • Single Burn Endurance Demonstration Factor: 1.1 XLB
  • Nozzle Operational Demonstration Factor: 1.2 XSL on 4 samples (ablative), 1.1 XSL on 4 samples (non-ablative)

4.3.1 Number of Verification Engine Samples [4.3.1-1] Verification engines shall be unique engine samples structurally and functionally equivalent to the flight design. [4.3.1-2] Qualification engine samples shall be of the flight design, produced using flight materials, tooling, processes, and personnel competency. [4.3.1-3] The minimum number of qualification and verification engine samples shall be as specified in Table 4-1. [4.3.1-4] All engines used for verification activities shall include a common instrumentation suite. [4.3.1-5] Each engine utilized to satisfy total engine sample numbers shall successfully complete testing verifying functional requirements, propellant/interface conditions, duty cycles, and performance. [4.3.1-6] Engine activities resulting in failures/anomalies requiring design modifications shall not be counted towards Table 4-1 without Approval Authority credit.

4.4 Number of Total Tests [4.4-1] The test program shall verify each specific engine system performance requirement and functional objective in Table 4-2 on the specified number of unique engine samples.

4.5 Relationship to Other Standards [4.5.2-1] Metallic pressure vessels/structures shall comply with AIAA S-080A-2018 and AIAA S-110-2005. [4.5.2-2] COPVs shall comply with AIAA S-081B-2018. [4.5.3-1] Pressure components shall comply with AIAA S-080A-2018 with exceptions in Sections 5, 6.11, and 4.6.3. [4.5.4-1] Ordnance shall comply with AIAA S-113A-2016. [4.5.5-1] MMAs shall comply with AIAA S-114A-2020. [4.5.6-1] Pressurized systems shall comply with TR-RS-2023-00005 with exceptions noted.

4.6 General Structural Requirements [4.6.1-1 to 4.6.1-9] Material selection, temperature limits, fluid compatibility, property characterization (including additive manufacturing), A-basis/B-basis allowables, mean curves for fatigue/creep, and environmental degradation testing. [4.6.2-1 to 4.6.2-4] MEOP and MDCL definition, dynamic loads, and fatigue load spectra. [4.6.3-1 to 4.6.3-2] Design analysis and test factors of safety per Table 4-3; fitting/casting/joint factors ≥ 1.0.

Table 4-3. LRE Structure and Pressure Component Design Factors of Safety

Table 4-3 Summary of Design Factors of Safety:

  • Unpressurized Metallic Structures (Analysis Only): Yield 1.25, Proof N/A, Ultimate 2.0
  • Unpressurized Metallic Structures (Analysis and Test): Yield 1.2, Proof 1.2, Ultimate 1.4
  • Pressure Components with Safe-Life: Yield 1.2, Proof 1.2, Ultimate 1.4
  • Lines and Fittings, Dia < 1.5 in (without Safe-Life): Yield 1.5, Proof 1.5, Ultimate 4.0
  • Lines and Fittings, Dia ≥ 1.5 in (without Safe-Life): Yield 1.5, Proof 1.5, Ultimate 2.5
  • Fluid Return Sections / Hose (without Safe-Life): Yield 1.5, Proof 1.5, Ultimate 3.0
  • Other Pressure Components (without Safe-Life): Yield 1.5, Proof 1.5, Ultimate 2.5
  • Joints (welds, brazes, bonds) with Safe-Life: Yield 1.2, Proof 1.2, Ultimate 1.4
  • Composites with Safe-Life: Yield N/A, Proof 1.2, Ultimate 1.4
  • Rotary Components with Safe-Life: Yield 1.2, Proof 1.2, Ultimate 1.4
  • Joints and Seals: Yield N/A, Proof 1.1 or 1.2, Ultimate 1.2 or 1.4
  • TPS Structural Evaluation: Yield N/A, Proof 1.2, Ultimate 1.4
  • Buckling: Yield N/A, Proof N/A, Ultimate 1.4
  • Inadvertent Contact: Yield N/A, Proof N/A, Ultimate 1.4

5. Structural Analysis Requirements

5.0-1: Engine elements shall comply with the structural qualification strategies in Figure 5-1 (Option 1: No safe life, proof/structural test to ultimate; Option 2: Proof test + comprehensive post-proof NDI for 4X SL; Option 3: Pre-proof NDI + proof test for 4X SL; Option 4: Proof test logic critical flaw size 4X SL). 5.1 Structural Model: [5.1-1 to 5.1-3] Modeling criteria, element quality, mesh convergence, minimum margin dimensions, and structural dynamic models per TR-RS-2003-00004. 5.2 Failure Modes: [5.2-1] Uncertainty factor (UF) ≥ 1.0 applied for unanchored analyses of composites and complex joints. 5.3 Strength Assessment: [5.3-1 to 5.3-2] MS = ALF/(FoS x UF) - 1 > 0; multi-axial stress triaxiality factor CTF = 2^(1-TF). 5.3.1 Strength and Yielding: [5.3.1-1] Positive ultimate MS; negative local yield acceptable under specific conditions. 5.3.2 Buckling: [5.3.2-1 to 5.3.2-5] Instability margins, imperfection knockdown factors, non-linear collapse analysis. 5.3.3 Inadvertent Contact: [5.3.3-1] Clearances > 0 under nominal at 1.4 x MDCL or worst-case at MDCL. 5.3.4 Joints and Seals: [5.3.4-1 to 5.3.4-4] Separation-critical joints, NASA-STD-5020A adherence, seal deflections, and leakage criteria. 5.3.5 TPS Failure Modes: [5.3.5-1] Positive margins at 1.4 x MDCL for ablated structure. 5.4 Life Assessment: [5.4.1-1 to 5.4.1-4] Fatigue life factors (10.0 for HCF, 4.0 for LCF; FAF 1.25 rotating / 1.15 nonrotating; CDI < 1.0); [5.4.2-1 to 5.4.2-3] Creep life >= 10.0 service lives; [5.4.3-1 to 5.4.3-4] Safe-life 4x service life, NDI 90/95 POD. 5.5 Turbomachinery Operation: [5.5-1 to 5.5-2] Minimum 20% frequency separation on Campbell/SAFE diagrams. 5.6 Bellows: [5.6-1 to 5.6-4] Bellows proof/ultimate factors, fatigue/safe-life test to 4x SL, ANSI/AIAA-S-080A compliance, and FIV evaluation. 5.7 Qualification by Similarity: [5.7-1] Similarity criteria per TR-RS-2014-00016. 5.8 Structural Approach Documentation: [5.8-1 to 5.8-2] Structural Assessment Plan (SAP) and Fracture Control Plan.

6. Unit Requirements

6.1 Unit Verification by LRE Test: [6.1-1 to 6.1-2] Hot-fire testing required on engine for all units except approved exclusions; LRU characterization. 6.2 Unit Inspection: [6.2-1] Compliance with TR-RS-2014-00016 Para 4.6. 6.3 Unit Performance Requirements: [6.3-1] Compliance with TR-RS-2014-00016 Para 6.3.2; [6.3.2-1] Full-scale turbomachinery mapping test. 6.4 Unit Functional Characteristics: [6.4.1-1] Cold flow tests; [6.4.2-1] Transient characterization; [6.4.3-1 to 6.4.3-7] NPSP margin, cavitation mapping, 4x exposure duration; [6.4.5-1 to 6.4.5-3] Engine controls tests. 6.5 Unit Leak Test: [6.5-1 to 6.5-2] Leakage tests per TR-RS-2014-00016; 1.4 x MDCL catastrophic / 1.2 x MDCL non-catastrophic. 6.6-6.10 Environmental Tests: Shock [6.6-1], Vibration/Acoustic [6.7-1, 6.7-2], Acceleration [6.8-1], Thermal [6.9-1], Climatic [6.10-1] per TR-RS-2014-00016. 6.11 Unit Structural Test Requirements: [6.11-1 to 6.11-9] Ultimate strength, proof testing, boundary conditions, buckling tests, fatigue testing to 4x SL, safe-life testing. 6.12 Unit EMC Test: [6.12-1] Compliance with TR-RS-2008-00008 (SMC-S-008). 6.13 Unit Life and Wear-in Test: [6.13.1-1] Operational life testing; [6.13.2-1] Single burn duration (1.1 XLB); [6.13.3-1] Operational life starts; [6.13.4-1] Acceptance wear-in.

7. Engine Requirements

7.1 Test Types: Development, Qualification [7.1.2-1], Acceptance [7.1.3-1, 7.1.3-2]. 7.2 Performance: [7.2.1-1 to 7.2.1-7] Steady-state thrust/flow rate measurements, power levels, throttling, nozzle corrections; [7.2.2-1 to 7.2.2-4] Repeatability (3 tests on same engine, 3 unique engines, 2 acceptance tests per engine); [7.2.3-1, 7.2.3-2] Run-time trends; [7.2.4-1] Steady-state model influence coefficients; [7.2.5-1 to 7.2.5-6] Thrust/MR excursion tests and binning (5% PL, 5% MR bins, 50% time at worst-case inlet in perimeter bins, 1x bin-specific SL, 2x power level SL); [7.2.6-1, 7.2.6-2] 2% Thrust/MR margin demonstration (10% cumulative flight duration dwell); [7.2.7-1 to 7.2.7-7] Ignition system verification, spark delay, hypergolic/pyrotechnic qualification; [7.2.8-1 to 7.2.8-4] Turbomachinery qualification and instrumentation; [7.2.9-1, 7.2.9-2] Combustion devices and stability per CPIA 655; [7.2.10] Contamination and debris tolerance. 7.3 Functional Characteristics: [7.3.1-1] Cold shock; [7.3.2] Cold flow; [7.3.3-1 to 7.3.3-4] Acceptance propellant conditions; [7.3.4-1 to 7.3.4-6] Engine propellant inlet conditions, chilldown, start box, shutdown behavior; [7.3.5-1 to 7.3.5-12] Start, restart, throttle, shutdown, and on-pad abort transients; [7.3.6-1, 7.3.6-2] NPSP margin; [7.3.7-1, 7.3.7-2] Pogo and pump compliance; [7.3.8-1 to 7.3.8-6] Ancillary systems (pressurization, purge, electrical); [7.3.9-1 to 7.3.9-13] TVC, gimballing, and deployment. 7.4 Structural Tests: [7.4-1 to 7.4-3] Engine-level ultimate MDCL tests, no detrimental deformation at proof factor x MDCL. 7.5 Pressure and Leak Testing: Compliance to TR-RS-2023-00005. 7.6 Environments: [7.6.1-1, 7.6.1-2] Thermal model validation (within ±11 °C / ±20 °F); [7.6.2] Climatic; [7.6.3-1, 7.6.3-2] Vibration, shock, acoustics; [7.6.4-1] Interface loads; [7.6.5-1] EMC testing. 7.7 Life: [7.7.1-1 to 7.7.1-5] Operational lifetime (4x SL on 1, 2x SL on 3 engines); [7.7.2-1, 7.7.2-2] Burn duration endurance (1.1 XLB); [7.7.3-1 to 7.7.3-7] Nozzle endurance (1.2 XSL ablative, 1.1 XSL non-ablative); [7.7.4-1] Life starts; [7.7.5-1] ATP validation. 7.8 Controls: [7.8-1 to 7.8-4] Control system startup/throttling/shutdown, response times, fault accommodation, vehicle communication. 7.9 Operations: [7.9.1-1 to 7.9.1-6] Pre-test checkouts; [7.9.2-1 to 7.9.2-3] Post-test teardown and inspection; [7.9.3-1, 7.9.3-2] Drying and heated purges; [7.9.4-1, 7.9.4-2] Gas liquefaction control; [7.9.5-1, 7.9.5-2] External icing; [7.9.6-1] LRU demonstrations; [7.9.7-1] Reusability operations (2 sets of 2 mission sequence simulations); [7.9.8-1] Operability; [7.9.9-1] Preflight procedures. 7.10 Process Controls: [7.10.1-1 to 7.10.1-7] Manufacturing KCs, CMPs, KPPs, traceability, volumetric NDI; [7.10.2-1] Mass properties measurements. 7.11 Unique Requirements: [7.11.1-1] Mission-unique requirements; [7.11.2-1] Delta-qualification requirements.

8. System Requirements

8.1 Stage and System Test [8.1-1] Engine qualification shall include an engine-integrated stage test to verify system interactions and control during engine prestart, start, dwell, and shutdown, including demonstration of design-maximum engine-out capability for engine clusters. [8.1-2] Integrated testing or analysis for multiple engine vehicle configurations to ensure interactions are acceptable. [8.1-3] Real-time observation and post-test inspection verifying TVC, thermal shields, flexible boots, and adjacent structures remain intact through movement.

8.2 Pre-Launch Validation and Operational Tests [8.2.1-1] Compliance with TR-RS-2014-00016 Paragraphs 9.1–9.4. [8.2.2-1] Receiving inspection: external condition, desiccants/closures, FOD check upon cover removal. [8.2.3-1] Validation of purge operations (pressures, temperatures, flow rates, fluid quality). [8.2.4-1 to 8.2.4-4] Vehicle Readiness Test: functional checks via airborne flight control system, physical movement inspection, TVC clearance and interface compatibility. [8.2.5-1 to 8.2.5-6] Vehicle Tanking Test: preflight timeline demonstration, preflight sequences, thermal conditioning/chilldown verification, SCC verification, TVC demonstration before/after propellant load, post-test inspection. [8.2.6] Prelaunch Countdown: execution of launch commit criteria (LCC) and detailed operating procedures (DOP), disposition of all failure identifications (FIDs).

Appendix A. Tailoring Guidance

Provides guidance on altering the baseline verification program using Weibull statistical reliability analyses (50% confidence bounds):

  • Option A.1: More Engines Tested (6 total, 2 qual) at Lower Qualification Demonstration Factor (2x SL each, total 12x SL experience vs baseline 10x SL). Improves early life / random reliability (beta = 0.5, 1.0) but increases wear-out failure risk (beta = 3, 6).
  • Option A.2: Accepting Increased Risk (4 total engines: 1 at 4x SL, 1 at 2x SL, 2 at 1x SL; total 8x SL experience).
  • Option A.3: Pressure-Fed Engine Design (2 total engines: 1 qual at 2x SL, 1 verification at 2x SL; unit life margin 2x). Simpler design with fewer component interactions permits reduced engine sample count with test-anchored high fidelity analyses.

Appendix B. Operational Keep-Out Zones

Defines methodology for handling rotor-dynamic instabilities, combustion instabilities, or self-induced vibration via operational keep-out zones within the power level vs mixture ratio space. Details requirements to demonstrate rapid and safe throttling through restricted zones without dwelling beyond demonstrated experience.

Signatures and Distribution

Approvals:

  • Mark J. Silverman, Chief Engineer / General Manager, Office of EVP
  • Bruce H. Mau, Principal Director, Launch Systems Division, Space Systems Group
  • Kevin D. Bell, Senior VP Space Systems Group, Office of EVP
  • Jeffrey J. Murphy, Senior Engineer Specialist, Propulsion Dept

Technical Peer Reviewers:

  • David A. Reese, Director, Vehicle Performance Subdivision
  • John C. Klug, Director, Structural Mechanics Subdiv
  • Wayne M. Van Lerberghe, Principal Director, Vehicle Systems Division
  • Alvar M. Kabe, Principal Director, Vehicle Systems Division
  • Amy Weir, Senior Project Leader, Enterprise Interoperability Standards
  • Jeff B. Juranek, Senior Project Leader, Corporate Chief Engineers Office

External Distribution:

  • Alejandro Prieto, SSC SSIO/BZEE
  • Eric Mattessich, SSC SSIO/BZEE
  • Mark Honda, SSC SSIO/BZE
  • Jon D Strizzi, USSF/SSC/AATS
  • John Wong, USSF/SSC/AATS
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