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Open: Systems Engineering Handbook, NASA


This handbook was written to bring the fundamental concepts and techniques of systems engineering to NASA personnel in a way that recogruzes the nature of NASA systems and the NASA environment. The authors readily acknowledge that this goal will not be easily realized. One reason is that not everyone agrees on what systems engineering is, nor on how to do it. Thcre are legitimate differences of opinion on basic definitions, content, and techniques. Systems engineering itself is a broad subject, with many different aspects. This initial handbook does not (and cannot) cover all of them. The authors fully recognize that perhaps no topic will be covered to the satisfaction of all.

The content and style of this handbook show a teaching orientation. This handbook was meant to accompany formal NASA training courses on systems engineering, not to be a stand-alone, comprehensive view of NASA systems engineering. Systems engineering, in the authors' opinions, cannot be learned simply by starting at a well-defined beginning and proceeding seamlessly from one topic to another. Rather, it is a discipline that draws from many traditional disciplines and intellectual domains. The boundaries are not always clear, and there are many interesting intellectual offshoots. Consequently, this handbook was designed to be a top-level overview of systems engineering as a discipline; brevity of exposition and the provision of pointers to other books and documents for details were considered important guidelines. The material for this handbook was drawn from many different sources, including Center systems engneering handbooks, NASA Management Instructions, Center briefings on systems engineering processes, non-NASA systems engineering textbooks and guides, and three independent systems engineering courses taught to NASA audiences. The handbook uses this material to provide only top-level information and suggestions for good systems engineering practices; it is not intended in any way to be a directive.

By design, the handbook covers some topics that are also taught in Project Management Program Control (F'MPC) courses, reflecting the unavoidable connectedness of these three domains. The material on the NASA Project Cycle is drawn from the work of the Inter-Center Systems Engineering Working Group (ICSEWG), which met periodically during 1991 to construct a strawman project cycle. Inclusion of this material does not imply that closure was reached on the project cycle; it reflects only the state of that work at the end of 1991.

This handbook consists of four core chapters:

(1) systems engineering's intellectual process,
(2) the NASA Project Cycle,
(3) management issues in systems engineering, and
(4) systems analysis and modeling issues. These core chapters are supplemented by appendices, which can be expanded to accommodate any number of templates and examples to illustrate topics in the core chapters. The handbook makes extensive use of sidebars to define, refine, illustrate, and extend concepts in the core chapters without diverting the reader from the main argument. There are no footnotes; sidebars are used instead. The structure of the handbook also allows for additional sections and chapters to be added at a later date. The authors in fact are planning an additional core chapter on the techniques used in specialty engineering disciplines.

Introduction 1
Purpose 1
Scope and Depth 1
Fundamentals of Systems Engineering .. 3
Systems. Supersystems. and Subsystems 3
Definition of Systems Engineering 4
Objective of Systems Engineering 4
Disciplines Related to Systems Engineering 6
The Doctrine of Successive Refinement 6
The Project Cycle for Major NASA Systems 13
Pre-Phase A - Advanced Studies 13
Phase A - Conceptual Design Studies 14
Phase B - Concept Definition 14
Phase C - Design and Development 18
Phase D - Fabrication, Integration, Test and Certification 18
Phase E - Pre-Operations 19
Phase F - Operations and Disposal 19
Funding: The Budget Cycle -20
The Role of Systems Engineering in the Product Development Process 20
Management Issues in Systems Engineering 27
Harmony of Goals, Work Products and Organizations . 27
Managing the Systems Engineering Process: The Systems Engineering Management Plan 28
Role of the SEMP 2 8
Contents of the SEMP .. 28
Development of the SEMP 29
Managing the Systems Engineering Process: Summary 30
The Work Breakdown Structure 30
Role of the WBS 31
Techniques for Developing the WBS 31
Common Errors in Developing a WBS 32 -
Scheduling 33
Role of Scheduling 33
Network Schedule Data and Graphical Formats 33
Establishing a Network Schedule .. 34
Reporting Techniques 35
Resource Leveling 3 5
Budgeting and Resource Planning 37
Risk Management 37
Types of Risks 39
Risk Identification and Characterization Techniques 40
Risk Analysis Techniques 41
Risk Mitigation and Tracking Techniques 42
Risk Management: Summary . 44
Baseline Management 44
Baseline Evolution 44
Configuration Management 4 5
Change Control and Version Control 4 7
Data Management and Requirements Traceability 48
Reviews, Audits and Control Gates 48
Purpose and Definitions 4 8
General Principles for Reviews 49
Specific Types of Reviews 50
Status Repolting and Assessment 55
Cost and Schedule Control Measures 56
Technical Performance Measures 57
Systems Engineering Process Metrics 60
Systems Analysis and Modeling Issues 63
The Trade Study Process . 63
Controlling the Trade Study Process 66
Using Models 67
Selecting the Selection Rule 69
Trade Study Process: Surnrnaty . 72
Cost Definition and Modeling 73
Life-Cycle Cost (LCC) and Other Cost Measures 73
Controlling Life-Cycle Costs 75
Cost Estimating 76
Effectiveness Definition and Modeling 79
Strategies for Measuring System Effectiveness 79
NASA System Effectiveness Measures 80
Availability and Logistics Supportability Modeling 8 1
Probabilistic Treatment of Cost and Effectiveness 83
Sources of Uncertainty in Models 83
Modeling Techniques for Handling Uncertainty 84
Appendix A -- Acronyms .. 87
Appendix B -- Systems Engineering Templates and Examples .. 89
Appendix B.l -- A "Tailored" Project Cycle for R&D Projects 89
Appendix B.2 - A Sample SEW Outline .. 92
Appendix B.3 - A "Tailored' WBS for an Airborne Telescope 93
Appendix B.4 - A Sample Configuration Management Plan Outline 96
Appendix B.5 - Characterization, Mission Success and SRM&QA Cost Guidelines for Class A-D Payloads 97
Appendix B.6 - An Example of a Critical Items List 98
Appendix B 7 - Techniques of Functional Analysis 99
B.7.1 Functional Flow Block Diagrams 99
B.7.2 N Diagrams 99
B.7.3 Time Line Analysis 101
Appendix B.8 - The Effect of Changes in ORU MTBF on Space Station Freedom Operations 104
Appendix C Use of the Metric System 107
C.1 NASA Policy . 107
C.2 Definitions of Units 107
(2.2.1 SI Prefixes 107
C.2.2 Base S1 Units 107
C.2.3 Supplementq SI Units 108
C.2.4 Derived SI Units with Special Names .. 108
C.2.5 Units in Use with SI 109
C.3 Conversion Factors . 110
Bibliography 113
Index 117