1、I A 9 The Engineering Society cor Advancing Mobility and Sea Air and SDace. AEROSPACE ARP4900 IN TERN AT NA L -m-.im-nI Submitted for recognition as an American National Standard I SuDersedinn ARD50009 LIQUID ROCKET ENGINE RELIABILITY CERTIFICATION TABLE OF CONTENTS 1 . 2 . 2.1 2.1.1 2.1.2 2.1.3 3 .
2、 3.1 3.2 3.2.1 3.2.2 3.3 3.4 4 . 4.1 4.1.1 4.1.2 4.1.3 4.2 4.2.1 4.2.2 4.2.3 4.2.4 SCOPE . 4 REFERENCES 6 Applicable Documents . U.S. Government Publications 6 6 FAR Publications . 7 Other Publications . 7 INTRODUCTION 10 The Need for a New Approach . 10 Current Certification Processes 13 Rocket Eng
3、ine Certification Process 14 Deterministic Design Methodology . 20 Introduction to the Recommended Approach . 21 Jet Engine Certification Process . 18 DESIGN CERTIFICATION METHODOLOGY 24 Introduction 24 Overview 26 General Approach 27 Benefits 30 Design for Reliability Approach . 31 Detailed Design
4、35 Design Feedback . 39 Conceptual Design . 33 Preliminary Design . 33 CAE Technical Standards Board Rules provide that This report is published by SAE to advance the state of technical and engineering sciences . The use of this report is entirely voluntary . and its applicability and suitability fo
5、r any particular use. including any patent infringement arising therefrom. is the sole responsibility of the user.“ CAE reviews each technical report at least every fwe years at which time it may be reaffirmed . revised. or cancelled . SAE invites your written comments and suggestions . Ccpyright 19
6、96 Society of Automotive Engineers . Inc . All rights reserved . Printed in U.S.A. SAE ARP*YRQ 96 RI 7943725 0542726 339 SAE ARP4900 4.3 4.3.1 4.3.2 4.3.3 4.3.4 5 . 5.1 5.2 5.3 5.3.1 5.3.2 5.3.3 5.3.4 5.3.5 5.3.6 6 . 6.1 6.2 6.3 6.4 7 . 7.1 7.1.1 7.1.2 7.1.3 7.2 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5 7.2.6 7
7、.2.7 7.2.8 7.2.9 7.3 7.3.1 7.3.2 7.3.3 TABLE OF CONTENTS (Continued) Reliability Design Tools 40 Reliability Allocation 40 Screening for Probabilistic Design Assessment . 46 Fault Tree Analysis . 42 Failure Modes and Effects Analysis (FMEA) . 42 RELIABILITY CERTIFICATION TEST PROGRAM 47 Introduction
8、 47 New Requirements . 48 Test Program . 49 Durability 52 Design Verification/Substantiation (DVS) . 53 Reliability Testing 56 Operability/Functionality . 51 Performance . 53 Margin Testing 54 AGGREGATION OF TEST RESULTS 59 Individual Component Tests 59 Procedure for Weighing Tests That Are Not Full
9、 Duration Firings 63 Integrating the Results for Multiple Components 60 Test Data Base 65 PROBABILISTIC METHODOLOGY . 66 Probabilistic Assessment of Reliability 66 Information Used in Probabilistic Design Reliability Assessment 66 Probabilistic Design Reliability Assessment Approach and Structure .
10、67 Probabilistic Life Modeling 70 Approach 70 Statistical Characterization of Life Drivers. 75 Engineering Modeling . 78 Life Driver Transformation 81 Materials Modeling . 84 Bayesian Statistical Analysis 84 Application Example . 88 Fracture Mechanics/Nondestructive Evaluation . 103 Simplified Proba
11、bilistic Life Modeling . 106 Event Consequent Modeling . 107 The Event Consequent Modeling Approach 108 Simplified Event Consequent Models 109 Failure Mode Model Types . 70 Introduction . 107 -2- SAE ARP+45I00 96 7943725 0542727 275 I SAE ARP4900 TABLE OF CONTENTS (Continued) 7.4 7.4.1 7.4.2 7.4.3 7
12、.4.4 7.4.5 7.4.6 7.4.7 7.5 7.5.1 7.5.2 7.5.3 7.5.4 Computational Methods for Probabilistic Life Modeling and Their Applicability . 115 Introduction . 115 Direct Integration . 115 Numerical Integration 116 Direct Monte Carlo Simulation . 116 Propagation of Errors 119 g-Function Methods . 120 Introduc
13、tion . 124 Interactions of Components 25 Efficient Monte Carlo Simulation 117 Mission Risk 124 System Definition as a Function of Components . 124 Computational Methods and Models . 25 b -3- SAE ARP4900 1. SCOPE: Current design and development practices leading to formal liquid rocket engine qualifi
14、cation (USAF) or certification (NASA) will not achieve the specific reliability objectives of future programs. New rocket engine programs are dictating quantified requirements for high reliability in parallel with a cost-constrained procurement environment. These specified reliability levels cannot
15、be validated with the necessary confidence in a timely or cost-effective manner by present methods. Therefore, a new improved process is needed and has been developed. This new reliability certification methodology will be discussed in detail in the five sections that comprise this document. Primary
16、 purposes of this report are to: a. Define and illustrate this process b. Point out its strengths and weaknesses c. Provide guidelines for its application on programs which have specified reliability requirements Increased emphasis on rocket engine reliability and cost has prompted the Liquid Rocket
17、 Certification Subcommittee (Society of Automotive Engineers for Reliability, Maintainability, and Supportability) to thoroughly examine current rnethodologies to qualify or certify liquid rocket engine systems. For example, new liquid rocket engine programs, such as the joint NASNAir Force effort f
18、or the National Launch System (NLS) or the Air Force XLR-132 storable propellant upper stage engine, include documented requirements for high levels of reliability. These new requirements exceed those historically demonstrated over the operational life of most current rocket propulsion systems. Cert
19、ification of reliability was not required for past liquid rocket engines developed for the Air Force or NASA. The importance of demonstrated reliability was low, relative to such requirements as performance, schedule, and cost. Engines were formally qualified or certified by test programs aimed prim
20、arily at demonstrating design maturity and operational readiness in terms of performance and durability. In general, relatively little propulsion system testing, as distinguished from engine system testing, was implemented on past flight hardware for launch vehicles. Reliability estimates prior to t
21、he first flight of a new engine historically have been based largely upon results from qualification or certification tests which formally declared the engine ready to fly. Many changes typically were made during the engine development period, until the engine was considered mature enough to qualify
22、 or certify. The process, therefore, precluded the gathering of test results applicable to reliability assessment during this development phase of a program. As a consequence, predicted reliability levels, at high confidence, prior to the first flight of a new engine have been consistently low. This
23、 was due to the small number of engines tested, especially identical units, and the limited number and type of tests performed on each engine during a typical qualification or certification test program. Reliability levels for current operational rocket engines are based upon a combination of ground
24、 test experience supplemented by the accumulation of data derived from actual flights. This process typically takes years and hundreds to perhaps thousands of tests to develop a satisfactory level of reliability and confidence for a particular engine system. I -4- SAE ARP4900 1. (Continued): The Liq
25、uid Rocket Certification Subcommittee advocates a new approach to rocket engine reliability certification as a result of reviewing current methods to qualify or certify engines. It is felt that this new approach is an improvement over current qualification/certification methods. The recommended new
26、approach, described in the following sections of this report, involves a judicious combination of analysis and test efforts that begin at an early stage of the design prior to formal certification. This methodology quantifies reliability estimates by focusing upon early identified weak links in the
27、design and system reliability drivers. The recommended approach includes development tests that assist in establishing the necessary information base for probabilistic analyses and engine system certification testing to demonstrate structural, thermal, and dynamic capabilities, as well as the more t
28、ypical performance and life requirements. The new approach begins with a traditional deterministic preliminary design of the engine. A failure modes and effects analysis and a fault tree analysis are then conducted. At this point, the improved approach departs from typical methodology by screening e
29、ngine components for criticality. A critical component has one or more critical failure modes. This screening is based upon the accumulated knowledge which impacts the design at this point. Critical components typically are complex in geometry, difficult to analyze, susceptible to catastrophic failu
30、re, and sensitive to such things as environments, loads, or material properties. Experience has shown that a majority (about 80 to 90%) of the components of a rocket engine can be classified as noncritical, and their reliability is essentially unity. Therefore, a conventional deterministic design ap
31、proach is satisfactory for these components. However, probabilistic analysis may be desirable for these noncritical components to realize other benefits such as weight savings. The remaining engine components have a higher probability of failure as well as being engine system critical and require th
32、e more intensive probabilistic analysis. A probabilistic analysis recognizes dimensional tolerances, variability in material properties, inadequacies in modeling techniques, load distributions, manufacturing variabilities, and so forth, involved in each critical failure mode. Components that utilize
33、 the more intensive probabilistic analysis techniques will yield quantified reliability estimates, while those designed deterministically are assessed only for serviceability. The process is iterative and continuous in nature, whether the component follows the deterministic or probabilistic path, an
34、d utilizes the best information available at the time of the analysis. Data deficiencies identified by the probabilistic analysis approach provide guidance for establishing a cost-effective test program during the development phase of the engine program. The final step in the recommended new approac
35、h is a formal, hot firing, test of the engine system which simulates, to the maximum extent possible, the complete propulsion system. Tests will be conducted to engine operational limits to validate structural, thermal, and dynamic margins. A careful review of earlier rocket engine certification and
36、 re-certification test programs revealed a number of weaknesses in these formal programs. For example, tests were implemented on a very limited number of like engines. Similarly, most tests were conducted at nominal engine operating conditions with little or no testing at or near anticipated flight
37、operational boundaries. Few attempts were made to demonstrate structural, dynamic, or thermal margins. Duration typically was -5- SAE ARP*i490 96 H 7943725 0542730 BbT I SAE ARP4900 .e., flight units can be utilized up to one-half the duration demonstrated by the ground test fleet leader). Problem a
38、reas identified by fleet leader data or actual flight experience may result in limiting the life of the involved items until design changes can be implemented through the process shown in Figure 2. 3.2.1.1 Component and Subsystem Testing: Following completion of the initial engine design phase, comp
39、onent and subsystem testing are conducted to verify component designs. The number of tests has been determined historically by experience factors and programmatic/requirements such as hardware and facility availability and schedule constraints. Component and subsystem testing occurs prior to engine
40、system testing. For example, all major Space Shuttle Main Engine (SSME) components were subjected to structural tests. Rotating parts were spin tested. The main combustion chamber and ducting were fatigue testing, and some components were subjected to dynamic and proof pressure tests. Of the compone
41、nts tested, about 6% failed the test criteria and were redesigned. Similarly, all SSME subsystems were subjected to limited development testing to verify operational capability. These include the igniters, preburners, main injector, turbopumps, and software subsystems. Component testing of the RL-1
42、O involved the testing of turbopumps, valves, controllers, and injectors during the first two years of development. Structural, fatigue, and proof-pressure tests were conducted. Subsystem testing of the RL-1 O was limited to operational verification and characterization of the fuel turbopumps in the
43、 early 1960s. Component testing of Titan engines included testing of the thrust chamber, gas generator, turbopumps, and start cartridges for structural and operational integrity. Dynamic and proof- pressure tests also were performed. Titan subsystem testing included testing of the gas generator/turb
44、opump combination and the thrust chamber (injector and chamber) during engine development to verify operational capability. -15- SAE ARP*47O 7h 7743725 05423YO 709 SAE ARP4900 3.2.1.2 3.2.1.3 3.2.1.4 System-Level Development Testing: Engine system level development tests demonstrate system operating
45、 capability, system tolerance to off-nominal conditions, and define engine environmental conditions. Operating parameters which are characterized include performance, controllability, repeatability, and durability. Engines are tested at off-nominal conditions within the operating envelope including
46、propellant inlet conditions, propellant mixture ratios, and vehicle-induced anomalies such as abnormal voltages. Testing verifies required engine environments, such as vibration levels, temperatures, and pressures. During system level development testing, the SSME was subjected to system level durab
47、ility, thermal, operational, and margin testing. The engine used in the majority of SSME system- level development tests was essentially the same configuration as the flight engine. Early Titan engine, system-level development tests demonstrated operating capability and margins on thrust, engine fra
48、me structural loads, turbopump speeds, mixture ratio, inlet conditions, and chamber pressure. Tests included vibration, thermal cycling, and durability. In addition, engine storage capability in a fueled, operationally ready mode was evaluated to satisfy Titan weapon system requirements. For the mos
49、t recent version of the RL-1 O Centaur engine, approximately 400 development tests were run prior to start of the qualification cycle. As with the Titan engines, RL-1 O margins were demonstrated during system-level development testing over a range of thrust, mixture ratio, and inlet conditions. Types of tests include dynamic, durability, thermal, and operational verification tests. Certification/Qualification Testing: Rocket engine systems are certified primarily by engine system level tests. Nominal performance, selected margins, and design life of rocket engines are demons
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