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					Introduction to Systems
 Engineering Practices:
   Session I - Requirements


       John Azzolini


                              SEC jda: July, 2000
Essential Systems Engineering:

For Each System:
     Requirements Analysis
     Operations Analysis
     Design Analysis
     Risk Analysis
     Verification Analysis
     Validation
                                 2
           Essential Systems Engineering:
   EIA 632, Process for the Engineering of a System: Summary
SUPPLY PROCESS REQUIREMENTS     REQUIREMENTS DEFINITION       REQUIREMENTS VALIDATION
1—Product Supply                PROCESS REQUIREMENTS          PROCESS REQUIREMENTS
ACQUISITION PROCESS             14—Acquirer Requirements      25—Statements Validation
REQUIREMENTS                    15—Other Stakeholder          26—Acquirer Requirements
2—Product Acquisition           Requirements                  Validation
3—Supplier Performance          16—System Technical           27—Other Stakeholder
PLANNING PROCESS
REQUIREMENTS
                                Requirements                  Requirements
                                SOLUTION DEFINITION PROCESS   Validation
4—Process Implementation        REQUIREMENTS
Strategy                                                      28—System Technical
                                17—Logical Solution
5—Technical Effort Definition                                 Requirements
                                Representations
6—Schedule and Organization                                   Validation
                                18—Physical Solution          29—Logical Solution
7—Technical Plans               Representations
8—Work Directives                                             Representations
                                19—Specified Requirements
ASSESSMENT PROCESS              IMPLEMENTATION PROCESS
                                                              Validation
REQUIREMENTS                    REQUIREMENTS                  SYSTEM VERIFICATION PROCESS
9—Progress Against Plans and    20—Implementation
                                                              REQUIREMENTS
Schedules                       TRANSITION TO USE PROCESS
                                                              30—Design Solution Verification
10—Progress Against             REQUIREMENTS                  31—End Product Verification
Requirements                    21—Transition to Use          32—Enabling Product Readiness
                                SYSTEMS ANALYSIS PROCESS      END PRODUCTS VALIDATION
11—Technical Reviews            REQUIREMENTS                  PROCESS REQUIREMENTS
CONTROL PROCESS
REQUIREMENTS                    22—Effectiveness Analysis     33—End Products Validation
12—Outcomes Management          23—Tradeoff Analysis
13—Information Dissemination    24—Risk Analysis

                                                                                                3
  Essential Systems Engineering:


System Requirements Analysis
    Identification of Functional and
     Performance Requirements
    Allocation to Sub-elements
    Development of Hierarchy


                                        4
  Essential Systems Engineering:


System Operations Analysis
   Launch,    Separation, and Deployment
   In-Orbit   Checkout
   Science    Observations
   Housekeeping

       Partitioning of Functions Among
   First
   Launch, Ground, and Flight Segments

                                            5
  Essential Systems Engineering:


System Design Analysis
   Conceptualize     and Synthesize Design
   Analyze   Design
   Trade   Studies




                                              6
  Essential Systems Engineering:


System Risk Analysis
   Tight   Margins
   Low    maturity
   Tight   Schedule
   Cost    Risk




                                   7
  Essential Systems Engineering:


System Verification Analysis
   Identify   Verification Methods
   Identify   Verification Levels
   Identify   Verification BTE and GSE
   Develop    Verification Procedures
           Methods, Levels, Procedures,
   Validate
   and BTE and GSE

                                          8
  Essential Systems Engineering:
System Validation
   Assumptions

   Requirements     to Objectives
   Operations     Concept to Objectives
   Designto Requirements and
   Operations Concept
   Verification   Plans to Requirements
   System   Validation Testing


                                           9
         Essential Systems Engineering:
                          NPG 7120.5A Table of Contents
Chapter 1: Overview               2.3.5 Deliver Products and Services    Assessments
1.1 Introduction                  2.3.6 Capture Process Knowledge        3.4.2 Capture Process Knowledge
1.2 Framework                     2.4 Program Evaluation                 Chapter 4. Program/Project Management
1.3 Themes                        2.4.1 Plan and Conduct Reviews and     Systems Requirements
1.4 Process Description           Assessments                            4.1 Resources Management
1.5 Document Structure            2.4.2 Capture Process and Knowledge    4.1.1 Financial Management
1.6 Program/Project Management    Chapter 3. Project Management          4.1.2 Life-Cycle Cost (LCC) Management and
Initiative (PPMI)                 Process and Functional                 Accounting
Chapter 2. Program                Requirements                           4.1.3 Information Technology Management
Management Process and            3.1 Project Formulation                4.2 Risk Management
Functional Requirements           3.1.1 Project Planning                 4.2.1 Purpose
2.1 Program Formulation           3.1.2 Systems Analysis                 4.2.2 Requirements
2.1.1 Program Planning            3.1.3 Technology Requirements          4.3 Performance Management
2.1.2 Systems Analysis            Synthesis                              4.3.1 Earned Value Management (EVM
2.1.3 Technology Requirements     3.1.4 Develop Technology and           4.3.2 Performance Assessment
Synthesis                         Commercialization Project Plans        4.3.3 Schedule Management
2.1.4 Develop Technology and      3.1.5 Operations and Business          4.3.4 Work Breakdown Structure (WBS)
Commercialization Program         Opportunities                          4.3.5 Program and Project Management Process
Plans                             3.1.6 Assess Infrastructure and Plan   Metrics
2.1.5 Operations and Business     Upgrades/Development                   4.4 Acquisition Management
Opportunities                     3.1.7 Capture Process Knowledge        4.4.1 Acquisition
2.1.6 Assess Infrastructure and   3.2 Project Approval                   4.4.2 Identifying
Plan Upgrades/Development         3.3 Project Implementation
2.1.7 Capture Process Knowledge   3.3.1 Project Control                  Requirements/Strategizing Implementation
2.2 Program Approval              3.3.2 Customer Advocacy                4.4.3 Executing Contracts and Non-procurement
2.3 Program Implementation        3.3.3 Requirements Management          Instruments
2.3.1 Program Control             3.3.4 Design, Develop, and Sustain     4.4.4 Monitoring Performance
2.3.2 Customer Advocacy           3.3.5 Deliver Products and Services    4.5 Safety and Mission Success, and
2.3.3 Requirements Management     3.3.6 Capture Process Knowledge        Environmental Management
2.3.4 Design, Develop, and        3.4 Project Evaluation                 4.5.1 Safety and Mission Success
Sustain                           3.4.1 Plan and Conduct Reviews and

                                                                                                                         10
             Essential Systems Engineering:
                    NPG 7120.5A Table of Contents (cont’d)
4.5.2 Nuclear Launch Safety            4.6.1 Purpose                          Appendix D. Responsibilities for
4.5.3 Application of Lessons Learned   4.6.2 Requirements                     Program and Project Management
4.5.4 Program/Project Emergency        4.6.3 PPMI Responsibilities            Appendix E. Key Document Contents
Planning/Response                      Appendix A. References Available Via   Appendix F. Independent Reviews List
4.5.5 Environmental Management         NODIS                                  of Figures and Tables
4.6 Program/Project Management         Appendix B. Definitions
Development                            Appendix C. Acronyms




                                                                                                                     11
Essential Systems Engineering:

          PART I:

REQUIREMENTS
  ANALYSIS

                                 12
   Essential Systems Engineering:
   Requirements Analysis



Introduction and Definitions

The Requirements Analysis Process

Summary


                                    13
     Essential Systems Engineering:
     Requirements Analysis

   An engineer doesn't know what he's doing until a
    REQUIREMENT has been agreed to
   You can't do a job without a PLAN
   A professional makes a COMMITMENT to meet
    the Requirements Analysis within his planned
    resources
   If you can't demonstrate TRACEABILITY from
    your plan to where you are, you're trying to fool
    the public

                                    A. Thomas Young     14
  Essential Systems Engineering:
  Requirements Analysis



“Research is what I'm doing when
   I don't know what I'm doing.”
      Attributed to Wernher Von Braun




                                        15
          Essential Systems Engineering:
          Requirements Analysis
     A SYSTEMATIC ENGINEERING PROCESS                       From EIA 632

Understand customer needs and establish                Requirements Definition
objectives
Develop evaluation and rating criteria                 Solution Definition

Determine functions to be accomplished (functional     Transition To Use
analysis)
Develop concept architecture (with alternatives)       Systems Analysis

Define performance requirements for each function      Requirements Validation
Synthesize and iterate the designs (trade studies)
                                                       System Verification
Evaluate the designs for acceptability (validate and
verify)                                                End Products Validation
Rate the acceptable designs and select the best
alternative
Document the selected design

                                                                                 16
                  Essential Systems Engineering:
                   Requirements Analysis
                                                                             MIL SE Handbook

Input Requirements
                                  Functional                    Acceptable      Evaluation
•Mission Objectives
•Mission Environments                               Synthesis                  and Decision
                                   Analysis                      Solution
•Mission Constraints                                                            (Trade-off)
•Measures of Effectiveness



                             OR                OR
                                                                                    Will
Technology Selection Factors                                                    Alternatives
                                                                                   Work?
•Hardware
•Software
•Reliability
•Maintainability
•Personnel/Human Factors
•Survivability
•Security
•Safety
                                                                               Description of
•Standardization                                                              System Elements
•Integrated Logistics Support
•EMC
•System Mass Properties
•Producibility
•Transportability
•Electronic Warfare
•Computer Resources
                                                                                               17
               Essential Systems Engineering:
               Requirements Analysis
                                                                                     NASA SE Handbook


 Define / Identify                                                        The following questions
Goals / Objectives                                                        should be considered:
 and Constraints                       Define          Define
                                     Plausible        Selection           • Have the goals / objectives and
                                    Alternatives        Rule
Perform Functional                                                          constraints been met?
     Analysis
                                                                          • I the tentative selection
                                                                            robust?

Define measures and               Collect data on
                                                                          • Is more analytical refinement
measurement methods for:          each alternative
                                                                            needed to distinguish among
                                    to support
• System effectiveness                                                      alternatives?
                                    evaluation
• System performance or             by selected
  technical attributes                                                    • Have the subjective aspects of
                                   measurement
• System cost                                                               the problem been addressed?
                                     methods



• Compute an estimate of system effectiveness,                         Is
                                                        Make a                       Proceed to further
  performance or technical attributes, and cost for                tentative
                                                       tentative                       resolution of
  each alternative                                                 selection
                                                       selection
• Compute or estimate uncertainty ranges.                           accept-           system design,
                                                      (decision)
• Perform sensitivity analyses                                       able?                 or to
                                                                                      implementation

      Analytical Portion of Trade Studies                                                                   18
 Essential Systems Engineering:
 Requirements Analysis
    Recognize
     Need or             Principle of Successive
    Opportunity                Refinement
                            (Boehm’s Spiral
                          Development Model)




Perform
Mission
                                              19
     Essential Systems Engineering:
     Requirements Analysis
   At each stage
       Document the results
       Identify trade studies
       Identify risks
       Identify issues
       Prioritize and work trade studies, risks, and issues
       Iterate


   At the end of each phase
       Baseline the new results
       Update existing baselines
       Put into configuration management


                                                               20
Essential Systems Engineering:
Requirements Analysis
          Requirements Analysis
          Requirements Validation

        Requirements Specifications

             Design Synthesis
             Design Validation




                                      Trades

                                      Issues
                                       Risks
           Design Specifications

           Verification Analysis
           Verification Validation

             Verification Plans


           Baseline New Results
         Update Existing Baselines
                 Configure
                                               21
  Essential Systems Engineering:
   Requirements Analysis

A SYSTEM
   The  solution to a problem in the full context of
    its environment over its useful life - B. Pittman
   The entirety needed to meet a defined set of
    requirements - Code 700 SE Implementation
    Plan

My subsystem may be your system



                                                        22
   Essential Systems Engineering:
   Requirements Analysis

DEFINITIONS
     A system is defined by a set of objectives
     System objectives are a set of goals and constraints that
      define the success of the system. These include what the
      system must accomplish, the system lifetime, the
      environment in which the system must perform, and cost,
      schedule, legal, and mandated constraints.
     A successful system is one which meets the set of objectives.
     Functional Requirements define what functions the system
      must perform to be successful
     Performance Requirements define how well the system must
      perform these functions to be successful
     Assumptions are derived objectives which are defined in
      order to proceed with the development process. Generally,
      assumptions define a subspace of the solution space.
                                                                      23
    Essential Systems Engineering:
    Requirements Analysis

   A constraint is a requirement which is imposed on the
    system.
   An Operations Concept is a set of plans and requirements
    defining the manner in which the system will be operated.
    This includes operations activities, facilities, equipment,
    commanding and data collection, and staffing. The
    operations concept evolves into operations plans and
    procedures.
   A Validation Basis is a set of functional and performance
    requirements which define the success of a system element.
    In the case of the full system, the validation basis is the set of
    objectives.
   All requirements can be type classified as functional, or
    performance, however, it is sometimes useful to think in
    terms of requirements categories

                                                                         24
  Essential Systems Engineering:
  Requirements Analysis

REQUIREMENTS CATEGORIES
     Level I Requirements are the top level requirements agreed
      to by NASA Headquarters and the developing installation to
      define mission success
     Operational Requirements define how users and operators
      interact with the system and its command and data products
     Apportioned Requirements are requirements which are
      quantitatively distributed to lower levels and for which the
      units of measure remain unchanged
     Derived Requirements are requirements defined by the
      decomposition of higher level requirements for which the
      units of measure may change

                                                                     25
Essential Systems Engineering:
Requirements Analysis

   Reflected Requirements are requirements uncovered in the
    Requirements analysis process that another subsystem or
    element must meet
   Interface Requirements are requirements which specify
    details of the command, data, electrical, thermal, and
    mechanical characteristics at the boundaries of a subsystem
    or element
   Environmental Requirements are requirements which are
    defined in order for the system to meet the test, transport,
    launch, ascent, and on-orbit environments
   Design Requirements are requirements which define the
    standards and guidelines which a particular design must
    adhere to
   Programmatic Requirements include fault tolerance, risk,
    cost, schedule and other resource constraints
                                                                   26
      Essential Systems Engineering:
      Requirements Analysis

THE REQUIREMENTS ANALYSIS PROCESS
    Requirements Analysis is a part of systems
     engineering
    Everyone has systems engineering
     responsibilities
    A system of any complexity will always
     require many iterations

                                                  27
   Essential Systems Engineering:
   Requirements Analysis




"Requirements should be based on a
 combination of need and capability."

                           Dr. Wiley J. Larson



                                             28
  Essential Systems Engineering:
  Requirements Analysis

FUNCTIONAL ANALYSIS
  Also called functional decomposition
  The process of allocating or decomposing
   functions to lower system levels
  Defines system functional architecture
  An example:
  REQUIREMENT     DESCRIPTION
  2.3.1           Point HGAS antenna at TDRS
  2.3.1.1         Compute S/C to TDRS LOS vector
  2.3.1.2         Compute required gimbal angles
  2.3.1.3         Send command to gimbals




                                                   29
  Essential Systems Engineering:
  Requirements Analysis




"When your only tool is a hammer,
 every problem looks like a nail."

                    Bruce Pittman & Others



                                             30
         Essential Systems Engineering:
          Requirements Analysis

                                                     N2 chart example
Instrument Data   Spacecraft



                                Data
                               Capture


                                          Data
                                         Archive


                                                   Operations
                                                    Console


                                                                Science
                                                                          Science Results
                                                                Console




                                                                                            31
           Essential Systems Engineering:
           Requirements Analysis

                               Data Flow Diagram Example
                               Valid Cmds   TL Cmds
Commands      Command
               Capture                                     Command Timeline
                                                              Executive
                          Cmd Status           TL Status
                                   Command
     CC TM                         Executive                    TL Cmds   Cmd Status
                                                    RT Cmds
                      CE TM


              Telemetry                        CE TM
               Output
                               CTE TM                            Other
                                                               Elements

                                 Other TM

                                                                                       32
             Essential Systems Engineering:
             Requirements Analysis
                         Control Flow Diagram Example
Interrupts
                             Interrupt Requests
              ISR




                                             Real Time Executive



               Resume                   Resume                     Resume
                              Status                  Status               Status
               Suspend                  Suspend                    Suspend


                    Task A                        Task B                       Task N




                                                                                        33
                  Essential Systems Engineering:
                   Requirements Analysis

Input Requirements
                                                                Flowchart Example
                                  Functional                       Acceptable     Evaluation
•Mission Objectives
•Mission Environments                               Synthesis                    and Decision
                                   Analysis                         Solution
•Mission Constraints                                                              (Trade-off)
•Measures of Effectiveness



                             OR                OR
                                                                                      Will
Technology Selection Factors                                                      Alternatives
                                                                                     Work?
•Hardware
•Software
•Reliability
•Maintainability
•Personnel/Human Factors
•Survivability
•Security                                                                        Description of
•Safety
•Standardization                                                                System Elements
•Integrated Logistics Support
•EMC
•System Mass Properties
•Produceability
•Transportability
•Electronic Warfare
•Computer Resources
                                                                                                 34
Essential Systems Engineering:
Requirements Analysis
      Understand User
                                                               Demonstrate and
    Requirements, Develop
                                                              Validate System to
     System Concept and
                                                             User Validation Plan
       Validation Plan


          Develop System                                   Integrate System and
     Performance Specification                                Perform System
            and System                                         Verification to
          Verification Plan                              Performance Specification


           Expand Performance                   Assemble CIs and Perform
           Specifications Into CI                  CI Verification to CI
         “Design-to” Specifications                    “Design-to”
            and Inspection Plan                       Specifications


                  Evolve “Design-to”
                                                 Inspect to
                  Specifications into
                                                 “Build-to”
               “Build-to” Documentation
                                               Documentation
                  and Inspection Plan




                              Fabricate, Assemble, and
                                 Code to “Build-to”
                                   Documentation




                                                                                     35
  Essential Systems Engineering:
  Requirements Analysis
DESIGN MARGINS
     An integral part of the requirements analysis and design
      synthesis process
     Proper margins minimize risk
     Reduce the impact of requirements changes
     Allow the balancing of allocations between subsystems and
      subsystem elements
     Margin levels (percentages) may be reduced as the design
      matures
     Robustness is the capability of a design to meet functional and
      performance requirements as the environment or design
      parameters change
     Flexibility is the ability of the design to adapt to failures, modeling
      inadequacies, changes in requirements , or operational changes
                                                                                36
  Essential Systems Engineering:
  Requirements Analysis

SOME GENERAL GUIDELINES
     Look one level up in the hierarchy to clearly understand the
      objectives, constraints, and environment of your system
     Use creative thinking processes
         First diverge then converge

         Turn off the critic as you diverge

     Work top-down - a level at a time - work for breadth rather
      than depth at each iteration
     Do not ignore standard assemblies, components,
      subsystems, etc. - Do not force fit either
     Take a step back occasionally to consider how the system
      "feels" - can you envision it meeting its objectives, or is the
      feeling discordant?


                                                                        37
     Essential Systems Engineering:
     Requirements Analysis

THE REQUIREMENTS GOSPEL ACCORDING TO
JOHN - Version 4
   A SYSTEM is defined by a set of OBJECTIVES, its environment,
    its useful life, and its constraints
   A system cannot be VALIDATED until the objectives are defined
    by a set of measurable SYSTEM (FUNCTIONAL AND
    PERFORMANCE) REQUIREMENTS
   System requirements are ALLOCATED and DECOMPOSED to
    define lower level requirements
   Confirm the TRACEABILITY of lower level requirements to
    system requirements

                                                                    38
      Essential Systems Engineering:
       Requirements Analysis

THE REQUIREMENTS GOSPEL ACCORDING TO
 JOHN - Version 4 (cont’d)
   A system is VERIFIED when it is shown to meet all
    requirements
   A system is VALIDATED when its requirements are shown to
    satisfy all objectives and its design is shown to satisfy all
    requirements
   If lower level requirements are not traceable (ORPHAN
    requirements), then the system being built is not JUSTIFIED
   If system requirements are not allocated (UNALLOCATED
    requirements), then the system being built is not VALID

                                                                    39
    Essential Systems Engineering:


      Background Charts
   RAVISH
   Example: The XTE Requirements
    Database
   Current Practice



                                     41
Essential Systems Engineering:
Requirements Analysis


        Requirements
        Analysis for
        Verification
        In a
        Structured
        Hierarchy
                                 42
  Essential Systems Engineering:
  Requirements Analysis

RAVISH: Motivation
     Design is a top-down process:
      Functional allocation flows from mission to system to
      subsystem to assembly, to component

     Verification is a bottom up process:
      Verification flows from component to assembly to subsystem
      to system

     At integration verification becomes system level

     Most work breakdown structures assign subsystem
      responsibility to a single subsystem lead (or manager)

     The result is that it is most efficient to develop a requirements
      hierarchy which reflects the WBS hierarchy

                                                                          43
  Essential Systems Engineering:
  Requirements Analysis

RAVISH: Requirements Analysis
methodology consists of:
     A strict top-down allocation of requirements

     Allocation flow is from system to subsystem, to mission
      phase, to functional category, to function, to performance
      specification

     Functional requirements are specified without performance
      numbers using a single simple sentence for each

     Performance requirements which quantify each functional
      requirement are attached to the functional requirement

     [A requirements validation walkthrough is conducted]
                                                                   44
  Essential Systems Engineering:
  Requirements Analysis

 The  verification method for each functional
  and performance requirement is specified
 [A requirements verification methods
  walkthrough is conducted]
 The verification procedure for each
  functional and performance requirement is
  specified
 [A verification specification walkthrough is
  conducted]

                                                 45
     Essential Systems Engineering:
     Requirements Analysis

THE XTE REQUIREMENTS DATA BASE
Spacecraft Requirements Organized
Hierarchically by:
    Subsystem
    Mission Operational Phase
    Functional Category
    Function
    Performance Required
                                      46
    Essential Systems Engineering:
    Requirements Analysis

THE XTE REQUIREMENTS DATA BASE
An Example:
    First Level: System: 01: XTE Spacecraft
    Second Level: Subsystem: 08: Mechanical
    Third Level: Mission Phase: 00: General
    Forth level: Functional Category: 01: Design
    Fifth Level: Function: 01: Strength
    Sixth level: Performance: 01: Limit Loads
       Safety Factor
“An ultimate factor of safety of 1.4 on limit loads
shall
be used for design requirements.”                     47
  Essential Systems Engineering:
  Requirements Analysis
RATIONALE FOR RAVISH METHODOLOGY
     By making each functional requirement separate from its
      associated performance requirements, functional validation of
      the requirements is simplified. (Associatively)

     By associating performance requirements with each functional
      requirement, the items which are needed to verify the functional
      requirement are clearly identified as a group. (Modularity)

     By grouping requirements by subsystem, each subsystem lead
      has a definitive set of system level requirements which drives
      the design. (Clarity)
         The fundamental functional and performance requirements
          for the subsystem are known
         This provides each subsystem with a validation basis



                                                                         48
Essential Systems Engineering:
Requirements Analysis

   By specifying requirements for each mission phase, design
    consideration is given to each phase equally. This avoids
    "band-aid" approaches to providing the functionality
    required. (Uniformity)

   By specifying the verification methods, procedures for each
    requirement, early identification of special verification tasks,
    equipment, and facilities is provided. (Verifiability)

   By conducting walkthroughs for requirements validation,
    verification methods, and verification procedures, the quality
    (correctness and completeness) of the process is ensured.




                                                                       49
       Essential Systems Engineering:
       Requirements Analysis
REQUIREMENTS VALIDATION WALKTHROUGH
     Identify and correct
         Unallocated system requirements

         Orphan requirements



     Validate
        From the bottom up ensure that all top level requirements
          (objectives, constraints, environment, and lifetime) are being
          met

     Establish margins

     Identify trades , risks, and issues
         Identify and prioritize trade studies

         Identify risk mitigation efforts - prototyping, special testing, etc.
                                                                                  50
  Essential Systems Engineering:
   Requirements Analysis

Current Practice
  The Operational Phase level has been eliminated.
  It proved to be cumbersome.
  For early iterations only 3 levels are often needed
  Commercial tools like DOORS and SLATE are
  increasingly being used at NASA




                                                        51
  Essential Systems Engineering:
  Requirements Analysis
SUGGESTED READING:
    Center for Systems Management, “PPMI SYSTEMS
     ENGINEERING”, Course materials
    Pittman & Associates, “DYNAMIC SYSTEM ENGINEERING”,
     Course materials
    Shisko & Chamberlain, NASA SYSTEMS ENGINEERING
     HANDBOOK, Draft, September 1992
    Wertz & Larson, SPACE MISSION ANALYSIS AND DESIGN
    Azzolini, John, Essential Systems Engineering: A Life-cycle
     Process, 5th Annual Symposium of NCOSE, 1995
    Martin, James N., Overview of the EIA 632 Standard -
     “Processes for Engineering a System”
    NPG 7120.5A <<http://nodis.hq.nasa.gov/Library/ Directives/
     NASA-IDE/Procedures/ Program_Formulation/
     N_PG_7120_5A.html>>

                                                                   52

				
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