SMC-S-025.pdf

SMC Standard SMC-S-025

26 July 2017

Supersedes:

New Issue

Air Force Space Command

SPACE AND MISSILE SYSTEMS CENTER

STANDARD

EVALUATION AND

TEST REQUIREMENTS

FOR

LIQUID ROCKET

ENGINES

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED

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 Philosophy

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 NPSP Margin and Cavitation

6.4.4 Pogo and Pump Compliance Characterization

6.4.5 Engine Controls

6.5 Unit Leakage Test

6.6 Unit Shock Test

6.7 Unit Vibration and Acoustic Test

6.8 Unit Acceleration Test

6.9 Unit Thermal Tests

6.10 Unit Climatic Test

6.11 Unit Structural Requirements

6.12 Unit Electromagnetic Compatibility Test

6.13 Unit Life and Wear-in Test

6.13.1 Operational Lifetime

6.13.2 Single Burn Operation Duration

6.13.3 Operational Life Starts

6.13.4 Unit Acceptance Wear-In

7. Engine Requirements

7.1 Test Types

7.1.1 Development

7.1.2 Qualification

7.1.3 Acceptance

7.2 Performance

7.2.1 Steady State Performance Characterization

7.2.2 Repeatability

7.2.3 Run-Time Trends

7.2.4 Steady State Analytical Models

7.2.5 Thrust and Mixture Ratio Excursion Tests

7.2.6 Thrust and Mixture Ratio Margin Demonstration

7.2.7 Ignition System

7.2.8 Turbomachinery

7.2.9 Combustion Devices and Stability

7.2.10 Contamination and Debris Tolerance

7.3 Functional Characteristics

7.3.1 Cold Shock Tests

7.3.2 Cold Flow Tests

7.3.3 Acceptance Propellant Conditions

7.3.4 Engine Propellant Inlet Conditions

7.3.5 Transient Characterization

7.3.6 NPSP Margin and Cavitation

7.3.7 Pogo and Pump Compliance Characterization

7.3.8 Ancillary Systems

7.3.9 Thrust Vector, Gimballing, and Deployment

7.4 Structural Tests

7.5 Pressure and Leak Testing

7.6 Environments

7.6.1 Thermal Environment

7.6.2 Climatic Tests

7.6.3 Vibration, Shock, and Acoustics

7.6.4 Vehicle Interface Loads

7.6.5 Electromagnetic Compatibility Tests

7.7 Life

7.7.1 Operational Lifetime and Durability

7.7.2 Single Burn Endurance Test

7.7.3 Nozzle Endurance

7.7.4 Life Starts

7.7.5 Acceptance Test Procedure Validation

7.8 Controls

7.9 Operations

7.9.1 Pre-Test Inspections and Checkouts

7.9.2 Post-Test Inspections

7.9.3 Drying and Heated Purges

7.9.4 Gas Liquefaction Control

7.9.5 External Icing

7.9.6 LRU Demonstrations

7.9.7 Reusability

7.9.8 Operability

7.9.9 Preflight Procedures and Flight Sequences

7.10 Process Controls

7.10.1 Manufacturing

7.10.2 Mass Properties

7.11 Unique Requirements

7.11.1 New or Mission Unique Requirements

7.11.2 Delta-Qualification Requirements

8. System Requirements

8.1 Stage and System Test

8.2 Pre-Launch Validation and Operational Tests

8.2.1 General Requirements

8.2.2 Receiving Inspection

8.2.3 Purges

8.2.4 Vehicle Readiness Test

8.2.5 Vehicle Tanking Test

8.2.6 Prelaunch Countdown

Appendix A. Tailoring Guidance A.1 More Engines Tested, But Lower Qualification Demonstration Factor A.2 Accepting Increased Risk A.3 Pressure Fed Engine Design vii

Figures

Figure 4-1. Percentage of failures encountered as a function of qualification test program completion for the F-1, J-2, and SSME programs (JANNAF-GL-2012-01-R0 [17])

Figure 5-1. Qualification strategies for engine elements, excepting qualification by analysis (no test option), and by similarity. ECF - Environmental correction factor, ELCF - External load correction factor, UF - Ultimate Factor, PF – Proof Factor

Figure 7-1. Notional diagram of power level versus mixture ratio trim box, flight box (with internal and perimeter bins), and margin box (showing margin demonstration locations)

Figure A-1. Weibull analysis of a qualification program with one engine sample taken to 4xSL, and three engines samples taken to 2xSL, with no failures

Figure A-2. Weibull analysis of a qualification program with six engine samples taken to 2xSL (no failures)

Figure A-3. Weibull analysis of a qualification program with one engine sample taken to 4xSL, one engine sample taken to 2xSL, and two engine samples taken to 1xSL (no failures)

Figure A-4. Weibull analysis of a qualification program with two engine samples taken to 2xSL (no failures)

Tables

Table 4-1. LRE Verification Engine Samples and Margins/Demonstration Factors Table 4-2. LRE Verification Engine Objectives and Minimum Unique Engines Samples

Required for Each Table 4-3. LRE Structure and Pressure Component Factors of Safety Table 7-1. Relationship between SMC-S-016 [1] Bus Subsystem Requirements and the LRE

Standard Table A-1. Example Alternate LRE Verification Engine Samples and Margins/Demonstration

Factors, Which Have Different Associated Risk Levels Than with the Standard Recommendation

1. Scope of this Standard

This Standard establishes test and evaluation requirements related to the development, qualification (or certification), and acceptance (flight production unit) of liquid propellant rocket engines and associated propulsion systems. Requirements include those associated with integrity, strength, life, interface conditions, and functional performance. These requirements should be understood and applied early in the design phase to enhance success in the development, test, and evaluation phases. Test generally includes component level testing, engine system level testing, and vehicle stage integrated propulsion system level testing. Development addressed herein is largely with respect to how 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 in general. Evaluation includes relevant and appropriate analyses for verification of requirements. In some cases, requirements are expressed by reference to other standards.

1.1 Purpose

This Standard establishes the test and evaluation requirements for liquid propellant rocket engines. These requirements shall 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 also 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 when levied by the Performance Work Statement (PWS), Statement of Work (SOW), and/or contract, and are intended 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 Procurement Authority, the requirements herein are intended to apply to new or modified liquid rocket engine (LRE) designs, new or modified LRE unit designs, use in a new application or environment, and procurement from new supplier or a new manufacturing location. This Standard applies to LREs and associated propulsion systems for expendable and re‐usable applications. It is expected that as reusable engine technologies evolve over time, adjustments to the Standard may be needed. No distinction is made between non-human-rated and human‐rated systems. Relevant LREs include those using pump‐fed or pressure‐fed designs, with various propellant combinations including hydrogen/oxygen, hydrocarbon/oxygen, storable, or mono‐propellants.

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.

The engine system as a whole is generally defined to encompass those components from the engine inlet flanges to the thrust chamber nozzle, and includes all interface connections to the launch vehicle and launch facility.

This Standard is intended to be used with other mission assurance documents, including SMC-S-016 [1] and SMC-S-005 [2]. Within the nomenclature of SMC-S-016 [1], an LRE is categorized as a subsystem.

An engine system, which may include multiple LREs, and the entire launch vehicle propulsion system are also considered subsystems within the SMC-S-016 [1] nomenclature. Within the nomenclature of SMC-S- 005 [2], an LRE is categorized as a pressurized system, meaning there are pressure-containing elements within the LRE. This Standard utilizes these documents and provides more detailed and specific requirements applicable to LREs and their integration. The terminology within this document is only intended to provide clarification of the appropriate requirements, and not to supersede the test category classifications of other mission assurance standards.

Within this Standard, all requirements are numbered and indicated by the word shall, thereby differentiating requirements text from explanatory or guidance text.

1.3 Tailoring

The requirements contained herein can be tailored with the Approval Authority concurrence based on each project-specific acquisition situation/environment, design complexity, design margins, vulnerabilities, technology state of the art, in-process controls, mission characteristics/criticality, life cycle cost, number of vehicles involved, prior usage, and acceptable risk. All tailoring of requirements must achieve the intent of the requirements in this Standard and be consistent with the Approval Authority’s risk posture. As part of the tailoring process, technical rationale with supporting data for each tailored requirement must be documented. Tailoring rationales should include risk assessment per the process detailed in MIL-STD-882 [3]. If the baseline requirements in this Standard are not tailored by the contract, the requirements of this document stand as written.

Herein, requirements for engines used on vehicles transporting personnel are generally intended to be the same as for engines used on vehicles transporting hardware only. However, engines used for flight systems transporting personnel 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

The following documents, of the issue identified, form a part of this Standard to the extent specified herein. The documents are listed in order of occurrence within this Standard. Where conflicts exist between the requirements of other documents and this Standard, the requirements of this Standard take precedence.

1. SMC-S-016 Test Requirements for Launch, Upper-Stage and Space Vehicles, Air Force Space Command Space and Missile Systems Center Standard, 5 September 2014.

2. SMC-S-005 Space Flight Pressurized Systems, Air Force Space Command Space and Missile Systems Center Standard, 28 February 2015.

3. MIL-STD-882E System Safety, Department of Defense Standard Practice, 11 May 2012.

4. CPIAC Publication 655 Klem, M. D. 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, January 1997.

5. AFI 91-217 Space Safety and Mishap Prevention Program, Air Force Instruction, Department of the Air Force, 17 April 2014.

6. AIAA S-080-1998 Space Systems - Metallic Pressure Vessels, Pressurized Structures, and Pressure Components, American National Standard, ANSI/AIAA S-080-1998, 13 September 1999.

7. AIAA S-110-2005 Space Systems – Structures, Structural Components, and Structural Assemblies, American Institute of Aeronautics and Astronautics, AIAA S-110-2005, 12 July 2005.

8. AIAA S-081A-2006 Space Systems – Composite Overwrapped Pressure Vessels (COPVs), American National Standard, ANSI/AIAA S-081A- 2006, 24 July 2006.

9. AIAA S-113-2005 Criteria for Explosive Systems and Devices on Space and Launch Vehicles, American Institute of Aeronautics and Astronautics, AIAA S-113-2005, 10 November 2005.

10. AIAA S-114-2005 Moving Mechanical Assemblies for Space and Launch Vehicles, American Institute of Aeronautics and Astronautics, AIAA S- 114-2005, 30 June 2005.

11. SMC-S-011 Parts, Materials, and Processes Control Program for Expendable Launch Vehicles, Air Force Space Command Space and Missile Systems Center Standard, 31 July 2015.

12. SMC-S-004 Independent Structural Loads Analysis, Air Force Space Command Space and Missile Systems Center Standard, 13 June 2008.

13. NASA-STD-5020 Requirements for Threaded Fastening Systems in Spaceflight Hardware, National Aeronautics and Space Administration, 12 March 2012.

14. ISO Standard 10785 Space Systems – Bellows – Design and Operation, International Organization for Standardization, First Edition 2011-10-01.

2.2 Guidance Documents

15. AS6500, Manufacturing Management Program, SAE International, 2014.

16. AS9103, Variation Management of Key Characteristics, SAE International, 2012.

17. 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.

18. NASA-STD-5012B, Strength and Life Assessment Requirements for Liquid-Fueled Space Propulsion System Engines, National Aeronautics and Space Administration, June 2016.

19. NASA SP-8007, Buckling of Thin-Walled Circular Cylinders, National Aeronautics and Space Administration, August 1968.

20. NASA-STD-5019A, Fracture Control Requirements for Spaceflight Hardware, National Aeronautics and Space Administration, January 2016.

21. NASA-STD-5009 Nondestructive Evaluation Requirements for Fracture-Critical Metallic Components, National Aeronautics and Space Administration, 2008.

22. M. Singh, J. Vargo, D. Schiffer and J. Dello, “Safe Diagram – A Design and Reliability Tool for Turbine Blading,” Dresser-Rand Company, 2002.

23. NASA SP-8123, Liquid Rocket Lines, Bellows, Flexible Hoses, and Filters, National Aeronautics and Space Administration, April 1977.

Unless otherwise indicated, copies of federal and military specifications, standards, and handbooks are available from Department of Defense Single Supply Point at http://quicksearch.dla.mil.

AIAA standards must be procured directly from the owner.

http://quicksearch.dla.mil/

3. Acronyms and Definitions

3.1 Acronyms

ALF allowable load factor

ATP acceptance test procedure

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 ft-lbf foot-pound(s) force

GG gas generator

HCF high-cycle fatigue

Isp specific impulse

KC key characteristic

KF knockdown factor kPa kilopascal(s)

KPP key process parameters

LCC launch commit criteria

LCF low-cycle fatigue

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

NDE non-destructive examination

NDI non-destructive inspection

NPSP net positive suction pressure

PB pre-burner

Pc chamber pressure

PL power level

SCC start commit criteria

SL service life

TLYF test-like-you-fly

TPA turbopump assembly

TPS thermal protection system

TVC thrust vector control

XLB demonstration factor with respect to the longest burn

XSL demonstration factor with respect to the service life

3.2 Definitions

The following definitions of significant terms are provided to ensure precision of meaning and consistency of usage. In the event of a conflict, the definitions listed here apply.

A-Basis Allowable: The mechanical strength value above which at least 99% of the population of values is expected to fall, with a confidence level of 95%.

Acceptance Test (or Acceptance Test Procedure, ATP): The required formal tests (or procedures) conducted on the flight hardware to ascertain that the materials, manufacturing processes, and workmanship meet specifications and that the hardware is acceptable for intended usage.

Allowable Load Factor: A multiplier to the Maximum Design Condition Load corresponding to failure.

Ambient Environment: The actual external environment surrounding an engine or subsystem. The environment will vary depending on whether operation is during ground test or flight test. Unless otherwise noted, the reference ambient environment for a ground test is defined as temperature of 23 ± 3°C (73 ± 5°F), atmospheric pressure of 101 +2/–23 kPa (29.9 +0.6/–6.8 in Hg), and relative humidity of 50 ± 20%. Actual ground test ambient environmental conditions should be documented, particularly when they are outside of this range.

Analysis Validation: Quantification of the accuracy of analysis results through comparison to experimentally measured data, and subsequent confirmation that the model’s accuracy is satisfactory for its intended use.

Analysis Verification: The process of determining the correctness of model input data, the numerical accuracy of the solution obtained, and the correctness of the output data for a particular simulation.

Assembly: Completed functional subsystem, system, engine, vehicle, or other hardware, which itself is assembled from smaller parts.

B-Basis Allowable: The mechanical strength value above which at least 90% of the population of values is expected to fall, with a confidence level of 95%.

Booster: The lowest stage of a multi‐stage launch vehicle that lifts the vehicle off of the launch pad and injects an upper‐stage space vehicle and satellite into a trajectory (typically sub-orbital).

Bootstrap: The portion of an LRE start transient where the engine cycle becomes self-sustaining.

Breadboard: Representative components in a laboratory or facility test environment that is representative of the functional relationship of the final system, but is not configured in the final system configuration or with all of the components.

Buckling and Crippling: The propensity of a structure to collapse under loads because of material-load or geometry-induced lateral instability.

Burst Factor: A multiplying factor applied to the maximum expected operating pressure (MEOP) to obtain the design burst pressure. Burst factor is synonymous with ultimate pressure factor. The factor is adjusted to account for differences between test and flight conditions.

Burst Pressure: The minimum pressure level at which failure of the pressurized hardware item occurs.

Burst pressure can be estimated by analysis and/or measured by test. The burst pressure is, by definition, greater than or equal to the design burst pressure.

Chamber Pressure (Pc): Force per unit area within the enclosed chamber between the injectors and throat where combustion takes place. Often referenced as injector-end Pc (static pressure at the injector face), or nozzle stagnation Pc (calculated from injector-end Pc and Rayleigh losses).

Chilldown: Process for a cryogenic engine, prior to start, that cools engine components down to the cold temperatures needed to avoid excessive propellant boiling, and facilitate proper pumping and bootstrap.

Typically most important for the turbomachinery of cryogenic LREs.

Component: A functional unit or elementary part of a system that is viewed as an entity for the purpose of analysis, manufacturing, maintenance, or recordkeeping (e.g., valve, injector, chamber, turbopump).

Critical Manufacturing Process (CMP): A process that creates or substantially affects a key or critical characteristic. (Source: AS6500, "Manufacturing Management Program," SAE International [15])

Damage-Tolerance Life (Safe-Life): The required period of time or number of cycles that the structure, containing the largest crack undetectable by the implemented NDI, is shown by analysis or testing to survive without leaking or failing catastrophically in the expected service load and environment.

Demonstrator (or Prototype) Program: Program to increase confidence in the likely success and provide risk reduction for proposed new designs, concepts, applications, or technologies prior to a full development program.

Design Burst Pressure: A pressure that the pressurized hardware must withstand without rupture in the applicable operating environment; equal to the product of the maximum expected operating pressure (MEOP) and the burst factor.

Design, Development, Test and Evaluation (DDT&E): The phase of a program during which a new design or concept is initiated, refined, and implemented up to manufacturing of qualification or flight hardware. Activities during this phase will provide confidence that the new design and concepts will accomplish mission objectives. See also development phase.

Design Service Life: See service life.

Detrimental Yielding or Deformation: The structural deformation, deflection, or displacement that prevents any portion of the structure from performing its intended function, or it interferes with the intended function of other components, or that reduces the probability of successful completion of the mission.

Development Hardware (or Development Test Article): Vehicle, subsystem, or unit hardware dedicated to provide design requirement information. Generally full scale and similar to the flight hardware. Design changes are often required during the development program as information is collected, but by the time the development program is completed, the test articles should be equivalent or nearly-equivalent to the flight hardware in all aspects of flow‐path and design. Development test articles are not intended for flight.

Development Phase: The development phase usually provides the first true demonstration of the capabilities of a proposed design. Development testing is used to identify problems early in their design evolution so that any required corrective actions can be taken prior to starting formal qualification testing.

Development Test: Tests conducted on representative articles to assess design concepts, characterize engineering parameters, gather data, and validate the design approach.

Duty cycle: See service life.

Engine: See liquid rocket engine.

Engine Cycles: A thermodynamic cycle that describes how liquid propellants are used within the engine to generate thrust. Common LREs include pressure fed, expander, gas generator (GG), and staged‐ combustion cycles.

Engine System: A term used to describe the liquid rocket engine (LRE) portion of the integrated stage, whether it is a single engine or a multi‐engine configuration.

Environmental Correction Factor: A factor applied to the structural test loads to compensate for material strength differences between test and flight conditions.

Expendable Engine: An engine that is discarded after use on a single mission.

External Load Correction Factor: A factor applied to the structural test loads to compensate for differences in test configuration (e.g., loads, boundary conditions) between test and flight conditions.

Factor of Safety (FoS): A multiplying factor applied to the maximum expected operating loads/stresses for the purposes of analytical assessment (design factor) and/or test verification (test factor) of structural design adequacy. The FoS is used to account for build-to-build hardware variability, uncertainty in internal load paths and stress/strain levels, and uncertainty in ultimate failure modes. The FoS provides separation between the statistical distributions for loads and material properties.

Failure: Rupture, collapse, excessive deformation, or any other phenomenon resulting in the inability of a structure to sustain specified loads, pressures, and environment; or the inability of a unit to otherwise function as designed.

Fatigue: The process of progressive localized permanent structural change occurring in a material subjected to conditions which produce fluctuating stresses and strains at some point or points, and which may culminate in cracks or complete fracture after a sufficient number of fluctuations.

Fatigue Analysis Factor (FAF): A factor to compensate for large changes in life that occur because of small changes in stress. It is applied to the limit stress/strain before entering the stress versus cycles to failure (S-N) design curve to determine the fatigue life.

Flight Design: Final production design intended for the “as‐flown” hardware.

Flight Operational Phase: This phase begins at launch. It includes test flights prior to the first mission and the actual mission flights themselves. Flight data generated during this phase may be used to generate performance reconstructions and detailed post‐flight data reviews, with the goal of verifying in‐flight specification performance, interface compatibility and predictions (e.g., engine and vehicle operating environments), calibration/control, and the ability to meet future mission requirements. The accumulation of flight data generally leads to refinement of flight simulations and revision of expected flight dispersions.

Functional Test: A test performed to assess the operability and/or capability of the item under test within the boundaries established by design requirements. For example, the test screens for malfunctions, failure to execute, sequence of action, interruption in continuous function, or failure in cause and response.

Functional tests are conducted in the most applicable environment.

Hazard: A real or potential condition that could lead to an unplanned event or series of events (i.e.

mishap) resulting in death, injury, occupational illness, damage to or loss of equipment or property, or damage to the environment.

Hot-Fire Test: A test of the engine propulsion systems and components that includes actual ignition and combustion of propellants within the engine, simulating flight conditions to the extent possible.

Impulse: Integral of thrust over a specified time period.

Key Characteristic (KC): The features of a material or part whose variation has a significant influence on product fit, performance, service life, or manufacturability. (Source: AS9103, "Variation Management of Key Characteristics," SAE International [16])

Key Process Parameters (KPP): Attributes of a manufacturing process that are considered most critical or essential to control for a successful outcome.

Line Replaceable Unit (LRU): A unit (e.g., igniter or closed‐loop control valve) that may be removed and replaced by a separate unit without requiring engine removal, and without need for a repeat of hot‐fire test.

Liquid Rocket Engine (LRE): Launch or space vehicle propulsion subsystem utilizing a combination of components and liquid phase chemical reactants to provide thrust. Generally includes the nozzle, thrust chamber, pumps, valves, regulators, and plumbing. An engine system may consist of one or more LREs to satisfy full stage and vehicle propulsion needs.

Loads: Any condition, such as pressure, force, moment, thermal environments, acceleration, and moisture that can produce a non-zero stress state in the structure.

Margin: Capability in excess of worst‐case operating conditions.

Margin of Safety (MS): A metric that predicts the structural integrity of an engine element based on the required factor of safety (FoS) and the predicted worst-case conditions against allowable limits.

Equivalently, MS expresses the structural capability with respect to the design safety factor.

Maximum Design Condition (MDC): The most severe environment specified for the engine and its components.

Maximum Design Condition Load (MDCL): This load condition is based on the most critical condition, considering all loads and combinations of loads and environments that the engine and its components are expected to experience, and that they must survive without failure. All phases in the life of the hardware, including fabrication, assembly, testing, transportation, ground handling, checkout, firing, launch, flight, and return, are to be considered in defining the MDC load. The MDC load may be a worst-case combination of loads that a structure may experience during its service life in the specified environments. When a statistical estimate is applicable, this load corresponds to a 99% enclosure with a 90% confidence level.

Maximum Expected Operating Pressure (MEOP): The maximum pressure which the pressurized hardware is expected to experience during its service life in association with its applicable operating environments (includes worst-case dispersions).

Maximum and Minimum Expected Temperatures: The highest and lowest temperatures that an item can experience during its service life, including all test and operational modes.

Mixture Ratio (MR): Ratio of the oxidizer mass flow rate to the fuel mass flow rate. For engine MR, this is measured at the engine inlets.

Net-Section Failure: A ductile mode of failure in which the net cross section loses its capability to sustain the mechanical load. The applied mechanical load is checked against the net-section failure load.

Non‐Destructive Inspection (NDI): Methods of inspection for integrity that do not impair serviceability, life, or performance.

Operability: the ability to support required flight rates and schedules and to meet a variety of operational characteristics while minimizing cost and risk.

Operating Envelope: Outer boundaries of conditions to which hardware may be subjected during intended operation and which encompass all possible intended variations of a set of parameters with dispersions (e.g. thrust and mixture ratio boundaries).

Operating Environment: Thermal, pressure, dynamic and/or electromagnetic conditions to which the system is exposed during its operational life.

Operational Life: The total allowed starts and run‐time including ground acceptance testing, on‐pad firings/aborts, and flight exposure.

Part: A single piece (or two or more joined pieces) that is not normally subject to disassembly without destruction or impairment of the design use. Examples are resistors, integrated circuits, relays, and roller bearings.

Physical Envelope: Dimensional boundary which encompasses the component or system.

Pogo Effect: Self‐excited, sustained vibration and deflections (typically associated with vehicle axial motion) due to interaction of structural dynamic modes and engine thrust oscillation.

Powerpack: Subsystem test article which typically includes turbomachinery and major combustion devices. It is intended to test these items in combination as risk mitigation prior to or in parallel with full-up engine testing.

Prelaunch Operational Phase: This phase begins when the flight hardware and software are received at the launch site and continues until launch. It includes all preparatory operations and checkout testing to verify flight readiness. It may also include separate flight readiness static firings and/or autonomous engine health monitoring and checkout during the engine startup and main stage operation immediately prior to lift‐off. It is intended to ensure the readiness of the hardware, software, personnel procedures, and mission interfaces to support launch and the program mission. On some occasions, the prelaunch operations may include unexpected or out‐of‐sequence inspection, testing, or modification of flight hardware to resolve identified concerns after the hardware has been delivered to the launch site.

Prelaunch Tests: Testing following system delivery to vehicle factory or launch site prior to launch. This is intended to verify system readiness for integration, system integrity, safety, and performance.

Pressure Component: a component in a pressurized system, other than a pressure vessel, pressurized structure, or special pressurized equipment, that is designed largely by the internal pressure. Examples include lines, fittings, valves, and bellows with no significant external load.

Pressure-Loaded Component/Structure: A component/structure not intended to store a fluid under pressure but experiencing a combination of internal pressure and external loading. The pressure-loaded component/structure is generally considered to be part of the engine. Examples include pump housings, main propellant lines/valves, and combustion chambers.

Pressure Vessel: A container designed primarily for the storage of pressurized fluids, and which

1. contains stored energy of 19,307 joules (14,240 ft-lbf) or greater, based on adiabatic expansion of a perfect gas; or

2. contains gas or liquid which will create a mishap (accident) if released; or

3. will experience a MEOP greater than 700 kPa (100 psi).

Pressurized System: A system that consists of pressure vessels, or pressurized structures, or both, and other pressure components such as lines, fittings, valves, and bellows that are exposed to and structurally designed largely by the acting pressure. Not included are electrical or other control devices required for system operation. A pressurized system is defined as a system on the engine that stores and/or supplies pressurized hydraulic/pneumatic/purge fluid or gas for the actuation of engine system components or other system functions. The usage is consistent with that used in SMC-S-005 [2].

Proof Factor: A multiplying factor applied to the maximum design condition load or MEOP to obtain the proof load or proof pressure for use in a proof test. The proof factor is adjusted using an environmental correction factor and external correction factor to account for differences between test and flight conditions.

Proof Load: Value established by taking the calculated maximum design condition (e.g., MEOP) and multiplying it by the proof factor.

Proof Pressure: Pressure equal to the product of the MEOP and the proof factor, where the proof factor has been adjusted for differences between test and flight conditions. Test pressure used to give evidence of satisfactory workmanship and material quality and/or establish maximum initial flaw sizes for damage-tolerance life (safe-life) demonstration. Synonymous with proof load.

Proof Test: A static load or pressure test performed as an acceptance workmanship screen to prove the structural integrity of a unit or assembly. Gives evidence of satisfactory workmanship and material quality by the absence of failure or detrimental deformation. The proof test load and/or pressure compensates for the difference between test and flight conditions, if applicable.

Propulsion System: The system producing thrust, which includes the engine system; propellant tankage and feedlines; off‐engine valve, fill, vent, purge, chilldown and drain systems; pogo suppression devices;

and propellant tank pressurization systems, as applicable. A propulsion subsystem within SMC-S-016 [1] is termed a propulsion system within this document.

Prototype: First example build of a preliminary design under consideration for production. Intended to be as representative of the definitive article as possible, but often deficient in various respects. Many times the prototype will be focused on replicating only specific parameters of key interest since its purpose is to guide future development, permit customer evaluation, and demonstrate critical new technologies.

Prototype Phase: This phase precedes development and may also be referred to as feasibility, risk reduction, or demonstration testing. Tests in this phase are intended to assist design definition by providing engineering data to confirm analyses and/or help define expected operating conditions. Often this testing includes Research & Development to explore and/or validate new technologies that might be beneficial to the engine system. Prototype hardware is typically designed to be more robust with greater margins compared to flight hardware because the design and operating conditions have higher uncertainty during this phase. The hardware may contain facility components in place of flight components, modified components from earlier engine models, or component simulators to gain the engineering information needed to complete the initial flight design. Breadboard and/or bench‐level type engines or subsystems may be used in some cases, and subscale testing is also common.

Qualification Hardware: Production articles that go through a series of qualification tests to demonstrate readiness for flight operation. Qualification hardware is to be produced from the same drawings, using the same materials, tooling, manufacturing processes, and level of personnel competency as will be used for actual flight hardware. Often the qualification engines are the first engines off of the production line.

Qualification Phase: The qualification phase includes the production and testing providing the formal verification that the final design, manufacturing processes and facilities, and acceptance program produce flight hardware/software that meet specification and performance requirements with adequate margin to accommodate variations in hardware and engine operation. It generally follows completion of the development test program. The phase includes validation of test techniques, procedures, equipment, instrumentation, and software, as well as potential rework and repeat test cycles.

Qualification Test: The required formal tests (typically to satisfy contractual requirements) intended to demonstrate that the final design, manufacturing, assembly, and acceptance testing yield hardware designs conforming to specification requirements. Qualification testing verifies compliance to engine specification requirements and vehicle interface requirements over the range of expected operating conditions, including worst‐case conditions for all intended applications. Required margin conditions (e.g., operating life margin, thrust margin) are also verified.

Quasi-Static Load: A time-varying load in which the duration, direction, and magnitude are significant, but the rate of change in direction or magnitude, and the dynamic response of the structure, are not significant.

Restart: Engine start after previous shutdown, without interruption of the environment, or modification of the hardware or setup.

Reusable Engine: An engine that is to be used for multiple space launch missions. The service life of a reusable engine includes all testing, initial use and reuses (mission operation times), refurbishment, and retesting.

Reusable Item: A unit, subsystem, or vehicle that is to be used for multiple missions. The service life of reusable hardware includes all testing, initial use and reuses (mission operation times), refurbishment, and retesting.

Reuse: Recovery and use of an engine for another space launch mission after completion of a prior space launch mission.

S-Basis Allowable: The mechanical material strength value which represents the minimum specified by the governing industry specification, or federal or military standard, or a specified contractor quality-control requirement.

Safe Life: See Damage-Tolerance Life (Safe-Life)

Safety Factor: See factor of safety.

Service Life (SL): The SL of an item starts at the completion of fabrication and continues through all acceptance testing, handling, storage, transportation, prelaunch testing, all phases of launch, orbital operations, disposal, re‐entry or recovery from orbit, refurbishment, retesting, and reuse that may be required or specified.

Service Life Factor: A multiplying factor to be applied to service life to assess design adequacy in fatigue or creep.

Similarity: The process of assessing by review of prior data, hardware configuration, and applications that the article is similar or identical in design and manufacturing process to another article that has been previously qualified to equivalent or more stringent specifications.

Specific Impulse (Isp): Engine Isp is the instantaneous total thrust divided by the instantaneous total mass flow rate of propellants through the engine inlet, at a specific altitude (e.g., sea level and/or vacuum conditions).

Steady State: Operation during which key engine performance parameters are no longer varying significantly over time or are slowly changing at a constant rate.

Storage Life: The time that a unit can be stored after acceptance tests, without replacement of parts, and subsequently operate successfully and within specification limits.

Structural Integrity: The ability of the structure to meet the structural requirements.

Subassembly: An item containing two or more parts, which is capable of disassembly or part replacement.

Test-Like-You-Fly (TLYF): The general test philosophy that all testing should be representative of flight conditions and flight operation to the maximum extent possible. Analogous to the “fly-like-you-test” philosophy.

Ultimate Load (Design): The load that the structure must withstand without rupture or collapse in the expected operating environments. Equal to the product of the maximum design condition load and the ultimate design FoS.

Ultimate Pressure Factor: See burst factor.

Ultimate Strength: Corresponds to the maximum load or stress that a structure or material can withstand without incurring rupture, collapse, or cracking.

Unit: A functional item (hardware and, if applicable, software) that is viewed as a complete and separate entity for purposes of manufacturing, maintenance, and record keeping.

Upper‐Stage Vehicle: An upper‐stage vehicle is one or more stages of a flight vehicle capable of injecting a space vehicle or vehicles into orbit from the sub orbital trajectory.

Validation: To show to be accurate and correct (as in, validate requirements or validate results).

Validation can be by inspection, demonstration, or analysis.

Verification: Confirmation that ground and flight hardware and software are in compliance with design and performance requirements (as in, verify capability). Verification can be done by inspection, test, or analysis.

Verification Engine: A unique engine sample that is of the flight design, or structurally and functionally equivalent to the flight design. It is suitable as one of the required engine test samples (including all qualification engines and appropriate development engines).

Yield Strength: The load or stress that a structure or material can withstand without incurring permanent deformation. (The 0.2-percent offset method is usually used to determine the load/stress.)

4. General Requirements

The primary objective of any test program is to maximize the probability, within programmatic constraints, that the flight design will function properly and successfully when used in actual service for the intended application. Flight risks are mitigated via prudent and effective analysis and testing. While analysis can sometimes be used in place of test, proper analytical techniques utilize test data as the basis for model correlations. The combination of analysis and test verification is used for both qualification of the LRE design as well as workmanship verification of each LRE flight unit.

4.1 General Test Philosophy

Certain key tenets of testing have served the liquid propulsion test community well as it has tried to accomplish that objective. One particular “tried and true” philosophy is the “Test-Like-You-Fly” (TLYF) approach. TLYF means that testing should demonstrate engine operation with flight-representative hardware and under flight-representative conditions, including expected worst-case conditions. The overall test program should encompass and explore as much of the operational flight envelope as possible on the flight design to accomplish the ideal objective to avoid operating any particular flight hardware configuration under any particular set of conditions for the first time in flight. Some flight environments (e.g., acceleration) cannot be replicated during ground test. Margin testing with respect to the expected flight conditions should be included to protect against known and unknown uncertainties in the flight conditions (e.g., ground-to-flight dispersions), as well as known, anticipated, and unknown hardware variations (e.g., manufacturing tolerances, non-conformances, and undetected deficiencies). If it is impractical to test or simulate a particular flight condition on the ground, then additional margin may be appropriate. Furthermore, testing should consider and account for engine hardware experience and exposure throughout all phases of the required life cycle, including manufacturing, acceptance testing, transportation, handling, storage, vehicle integration, checkout testing, launch preparations, aborts, liftoff, and flight. Exceptions to this approach should be carefully evaluated and include a risk determination. It is prudent that LREs be deliberately designed to provide margins equal to or greater than the specified margin test requirements so as to provide high probability for test success and high reliability for flight operations.

A corollary to TLYF is the “fly-as-you-test” approach. “Fly-as-you-test” means that flight operation should remain within demonstrated ground-tested and qualified regimes, and that design and process differences between qualified test hardware and flight hardware should be minimized and ideally avoided.

A successful development and qualification program will anticipate all potential flight conditions and ensure those conditions are validated by a robust test program. If an engine has multiple applications, ideally the engine should be developed and qualified to the most demanding requirements, however programmatic considerations may dictate a phased approach.

Hot-fire testing to verify that an LRE design is ready for flight typically consists of four phases of major program activity: prototype testing, development testing, qualification testing, and integrated system testing. The first three test phases typically occur at the component level as well as the engine level. The integrated system testing phase is performed at the propulsion system and/or vehicle level. After an LRE design has completed the qualification program (i.e., production phase), each individual flight engine is acceptance tested by hot-fire to verify that specific engine’s suitability for flight. Prelaunch operational testing is performed prior to engine start and liftoff to verify readiness for launch. Finally, additional testing can be performed or additional data obtained for the system during the operational phase of a test flight or actual space launch mission.

Specific requirements are placed upon qualification, production unit acceptance testing, and integrated system testing. There is an allowance, and in fact an expectation, that engines not meeting the full requirements of qualification will be used as a part of the overall design verification effort in order to increase the sample size of suitable engines. "Verification engines" include qualification engines, and may also include development engines that are structurally and functionally equivalent to the qualification and flight design. Hereafter, references to the qualification requirements are meant to include testing on formal qualification engines as well as development engines that are suitable as verification engines.

Prototype and earlier development tests are not specifically required herein, but these tests are expected and it is strongly recommended that qualification testing be preceded by a significant number of development engine samples, and associated testing, to increase the likelihood of success in the qualification phase.

4.2 Verification Approach

There are four critical aspects of an LRE test program related to verification and qualification of the design and build: (1) the total number of verification engine samples (including qualification engine samples), (2) the number and duration of tests on each verification engine, (3) the specific test and safety factors used in test and analysis margin assessments, and (4) the degree of reliance on, and maturity of, analysis. The specifics of each of these elements are discussed in the following sections. Table 4-1 lists the parameters and required conditions yielding baseline risk for a typical LRE utilizing turbomachinery.

Requirements for other LRE configurations will be noted if they are different. Tailoring of Table 4-1 must balance engine complexity with the program risk posture, to fit within cost and schedule constraints.

Further guidance on tailoring of requirements (including Table 4-1) is…