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Principles of Systems Engineering Introduction & Overview

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1 Principles of Systems Engineering Introduction & Overview
Jim Andary NASA Goddard Space Flight Center October 22, 2009

2 Agenda Definitions of system and systems engineer
The role of a systems engineer Systems engineering vs. project management Systems engineering functions and processes Requirements Development and Management Operations Concept Decomposition Technology Planning System analysis and design System Integration Resource Management Quality Control Verification and Validation

3 Definitions What is a System?
“A System is a set of interrelated components which interact with one another in an organized fashion toward a common purpose” NASA Systems Engineering Handbook SP6105

4 Definitions (Continued)
What is Systems Engineering? “Systems Engineering is an interdisciplinary approach and means to enable the realization of successful systems.” INCOSE Handbook

5 Definitions (Continued)
Another Definition “Systems Engineering is a robust approach to the design, creation, and operations of systems.” NASA Systems Engineering Handbook SP-6105

6 Definitions (Continued)
In simple terms, the systems engineering approach consists of: Identification and quantification of system goals, Creation of alternative system design concepts, Performance of design trades, Selection and implementation of the best design, Verification that the design is properly built and integrated, and Post implementation assessment of how well the system meets (or met) the goals

7 Definitions (Continued)
“Engineering of Systems” Anyone involved in engineering a system should exercise good systems engineering practices.

8 Twelve Systems Engineering Roles
1. Requirements Owner 2. System Designer 3. System Analyst 4. Validation and Verification Engineer 5. Logistics & Operations Engineer 6. Owner of the “Glue” among subsystems 7. Customer Interface 8. Technical Manager 9. Information Manager 10. Process Engineer 11. Coordinator of the Disciplines 12. “Classified Ads” Systems Engineer To solve a complex problem, we must deal with the problem in a way that fits with how we think. Engineering at any level involves some of this type of thinking—we always break the problem up into more manageable chunks. Systems engineering typically refers to problems which are so complex that different people must work on the different pieces of the problem. Specialists handle the details and systems engineers make sure the pieces work together to form something which is more than the sum of its parts. INCOSE-- System designer decides how to break up system. Requirements owner manages requirements which define system and subsystems. System analyst confirms that the designed system will meet requirements. Val/Ver Engineer makes sure the system does meet requirements. Ops Engineer maintains system through operations and end-of-life. Glue role makes sure things don’t fall through the cracks. CI, TM, IM, PE are fairly obvious. Coordinator facilitates group actions. Last one refers to engineers involved with information technology—formerly maintainers of mainframe computer system. 1. Requirements Owner Requirements manager, allocator, and maintainer Specifications writer or owner Developer of functional architecture Developer of system and subsystem requirements from customer needs System Designer Owner of "system" product Chief engineer System architect Developer of design architecture Specialty engineer (some, such as human-computer interface designers) “Keepers of the holy vision" [Boehm 94] 3. System Analyst Performance modeler Keeper of technical budgets System modeler and simulator Risk modeler Specialty engineer (such as electromagnetic compatibility analysts) 4. Validation and Verification Engineer Test engineer Test planner Owner of the system test program System selloff engineer 5. Logistics and Operations Engineer Logistics Operations Maintenance and disposal engineer Developer of users’ manuals and operator training materials 6. Owner of the "Glue" among subsystems System integrator Owner of internal interfaces Seeker of issues that fall "in the cracks" Risk identifier “Technical conscience of the program" [Fisher 92] 7. Customer Interface Customer advocate Customer surrogate Customer contact 8. Technical Manager Planner, scheduler, and tracker of technical tasks Owner of risk management plan Product manager Product engineer 9. Information Manager Configuration management Data management Metrics 10. Process Engineer Business process reengineer Business analyst Owner of the systems engineering process 11. Coordinator of the disciplines Tiger team head Head of integrated product teams (IPTs) System issue resolver 12. “Classified Ads” Systems Engineering What ever special engineering is necessary to keep things from falling through the cracks. from Sarah A.Sheard (INCOSE proceedings of 1996)

9 Systems Engineering vs. Project Management

10 Key Systems Engineering Functions
Verification and Validation Project Objectives and Constraints Requirements Development and Management Architecture and Design Tools help engineers evaluate their systems more quickly and more efficiently, but they do not replace the “Art” and “Creativity” necessary to conceive them Verification and Validation Verification and Validation Project Objectives Met, Ready for Operations Operations Concept Systems Engineering Management Plan “The objective of systems engineering is to see to it that the system is designed, built, and operated so that it accomplishes its purpose in the most cost-effective way possible, considering performance, cost, schedule and risk.” NASA Systems Engineering Handbook SP6105

11 Systems Engineering Process “V”
Understand User Requirements, Develop System Concept and Validation Plan Demonstrate and Validate System to User Validation Plan Develop System Performance Specification and System Verification Plan Integrate System and Perform System Verification to Performance Specification Expand Performance Specifications Into CI “Design-to” Specifications and Inspection Plan Assemble CIs and Perform CI Verification to CI “Design-to” Specifications Evolve “Design-to” Specifications into “Build-to” Documentation and Inspection Plan Inspect to “Build-to” Documentation Verification Sequence Integration and Decomposition & Definition Sequence Fabricate, Assemble, and Code to “Build-to” Documentation CI = Configuration Item

12 Systems Engineering Process “V” (Continued)
Developed by Kevin Forsberg and Harold Mooz* Starts with user needs on the upper left and ends with a user-validated system on the upper right Adds concurrent risk management User involvement User approval and in-process validation Adds verification problem resolution Promotes a risk-responsive, phased system development process *Kevin Forsberg and Harold Mooz, "The Relationship of System Engineering to the Project Cycle," Proceedings of the First Annual Symposium of National Council on System Engineering (NCOSE), Chattanooga, Tennessee, Oct. 1991, pp

13 Requirements Development
Collect top-level requirements from customers and stakeholders Develop an operations concept Derive lower-level requirements to support top-level requirements and the operations concept Writing requirements without a fully understood, agreed upon and documented operations concept will result in poor and misunderstood requirements, cost overruns and schedule slips.

14 Requirements Development (Continued)
Writing Good Requirements “Functional Requirements” - What needs to be done Functional Requirements are generally not Verified because Performance Requirements specify how good the function needs to be Functional Requirements define a logical breakdown “Performance Requirements” - How well it needs to be done Performance Requirements are Verifiable Requirements Decomposition and Parent-Child Relationship Requirements flow from higher to lower levels Requirements at lower levels (“children”) must trace from a higher level requirement (“parent”) Eliminate any “orphan requirements” (requirements without parents) Add rationale or comments to the requirements to help trace “why” that requirement was created

15 Requirements Development (Continued)
Decompose the requirements in a hierarchical, parent-child relationship Requirements flow from higher to lower levels Requirements at lower levels (“children”) must trace from a higher level requirement (“parent”) Eliminate any “orphan requirements” (requirements without parents) Add rationale or comments to the requirements to help trace why that requirement was created

16 Requirements Development (Continued)
Writing the right requirements What is necessary to Achieve Full Mission Success Criteria? Levels of requirements (Level 1, Level 2, etc.) Level 1 Generally Highest Level Agreement with Ultimate Customer Lower Levels up to each Project to choose Traceability (Parent, child, orphan, widow, etc.) Priorities Organizing the requirements (templates and guidelines) Reviewing Requirements Gate keepers Formal reviews (SRR, PDR, CDR) Verification Plan must addresses how each requirement will be verified

17 Requirements Development (Continued)
Use the word “shall” when defining requirements and only for requirements: “The attitude control system shall point the instrument boresight to within 6 arc seconds of the commanded attitude.” Make it clear to the reader exactly what must be done. Requirements should be: Measurable Avoid vague statements like “shall point as accurately as possible” Verifiable If no one can demonstrate that a system does or does not meet a requirement, then there is no requirement: shall not exceed 55 kg, but we aren’t going to weigh it Document rationale! Capture the “why” while it is fresh. Enable future changes—people are afraid to change things they don’t understand.

18 Requirements Development (Continued)
What the Proposal Promised Preliminary Design Design Drawings The Customer’s Swing The customer requested a new kind of swing that allowed the customer more than one way of swinging. As Built by Manufacturing Following Inspection and Rework What the Customer Wanted Design Change Specification After Rework What Happened to The Engineering Team Communication and Understanding is Key!

19 Requirements Management
Collect top-level requirements from customers and stakeholders Develop operations concept Derive lower-level requirements to support top-level requirements and the operations concept Choose an appropriate tool to store and manage the requirements This can range from an Excel spreadsheet for simple projects to sophisticated tools such as DOORS, Team Center, CORE, etc. for more complex projects Baseline the requirements at a System Requirements Review (SRR) “Baseline” means requirements are signed off and put under configuration control Control any future changes to requirements through a configuration management process

20 Requirements Management (Continued)

21 Operations Concept An Operations Concept is a vision (in general terms) for what the system is, and a description of how the system will be used. An Operations Concept consists of a set of scenarios describing how the system will be used during all of its operational phases. The scenarios are often accompanied by illustrations of the system operations. An Operations Concept: Serves as a validation reference for the design throughout the life cycle Describes how the design can accomplish the mission described by the objectives Key to defining all the requirements Evolves into the flight operations plan later in the life cycle

22 Operations Concept (Continued)
Stakeholders participate in the development of the Operations Concept Trade studies and analyses are used to demonstrate that the operations concept will meet the mission requirements within cost and schedule constraints

23 Operations Concept (Continued)
Considerations for developing an Operations Concept for a Space Mission: Allocation of functions between ground segment and flight segment Mission operational modes and configurations Time ordered sequence of mission activities Identification of facilities, equipment and procedures needed to ensure the safe development and operation of the system Operations team size, staffing and extent of automation Ground segment functions Contingency concepts Ground test configurations necessary to accomplish verification including GSE, BTE, simulators and non-flight articles such as ETU’s Description of functions that cut across various subsystems Observation strategy Date collection, storage and downlink Ground station utilization Mission orbit maintenance and maneuvers Power and battery management

24 Operations Concept (Continued)
Military Planners Satellite Operators Control Center Request for Data Data Inter -Satellite Link Data Download Command Transmission Image Recording

25 Many types of decomposition
Requirements Decomposition Functional Decomposition Functional Architecture Physical Decomposition Physical Architecture Operational Architecture Allocates functions to physical subsystems Provides complete description of the system design Integrates the requirements decomposition with the functional and physical architectures

26 Decomposition (Continued)
System Requirement User Defined non-exhaustive inclusive based on content and allocation Effectiveness Measure Functional Requirement Performance Requirement Physical Property Requirement Interface Requirement Imposed Design Requirement Reference Requirement

27 Technology Planning Projects are sometimes initiated with known technology shortfalls Technology “Pull” Often there are areas for which new technology will result in substantial product improvement Technology “Push” Technology development can be done in parallel with the project evolution and inserted as late as the PDR Risk mitigation requires a parallel approach that is not dependent on the development of new technology The technology development activity should be managed as a critical activity

28 Technology Readiness Levels

29 Systems Analysis and Design
Modeling Models are the language of the designer. Models are representations of the system-to-be- built or as-built. Models are a vehicle for communications with various stakeholders. Models allow reasoning about characteristics of the real system. Models can be used for verification by analysis. All models must themselves be verified.

30 Systems Analysis and Design (Continued)
There are two basic approaches that are commonly used for system design and integration Structured Analysis Object-oriented Analysis and Design It can be shown that either approach can be translated into the other.

31 Structured Analysis Structured Analysis
Process Modeling, also known as Data Flow Modeling or Functional Decomposition IDEF0* SADT (Structured Analysis & Design Technique) Data Modeling IDEF1x Entity-Relationship Diagrams Behavior Modeling Rules State Transition Diagrams *The IDEF process was developed by the Air Force in the early 1970’s as part of the ICAM program (Integrated Computer Aided Modeling). IDEF originally stood for “ICAM Definition” but NIST later changed it to “Integration Definition”.

32 Structured Analysis (Continued)
IDEF0 Student Registration System

33 Structured Analysis (Continued)
“ICOM” Control Input Function Output Mechanism

34 Structured Analysis (Continued)
Behavior Modeling: State Transition Diagram Ready User ID and Password entered (User_ID, Password)/ accept Verifying start Do: display login page Do: wait for login Do: verify user [Invalid user]/Display:”Access Denied” [Valid user] Validating Options Retrieving [Option selected not allowed]/ Display error message: “Option not allowed” Request for course search Do: display user options Do: check option vs access permission Do: display course search page Do: retrieve course selections [Registration rejected] Request to register (course_nr, user_ID) Request to generate report (User type) Request to register (course_nr, user_ID) Registering Validating Report [Report not allowed]/ Display error message “Option not allowed” Do: display report page Do: validate user vs report selected See superstate diagram [No Conflicts] (course_nr) Report printed (Report type) [Report allowed] Drop request (course_nr) Updating Schedule Generating Report Do: update student schedule Updating complete/ University-updated class roster Do: send database request (report parameters) Do: format report Do: print (report)

35 Structured Analysis (Continued)

36 Object-Oriented Analysis and Design
The concept of “object” or “object class” is the result of a long history of software engineering design. From a programming viewpoint, an object is a collection of specialized data packaged with the functions (operations and methods) which are needed specifically by that specialized data. From a systems design viewpoint, an object is a system or component which maintains its own information and is able to perform some specific functions. Developed more recently for software engineering, object- oriented design is now migrating to systems engineering. Object-oriented design defines the relationships between object classes and the behavior of the classes.

37 Unified Modeling Language (UML)
UML is a language for visualizing, specifying, constructing and documenting the artifacts of software-intensive systems, as well as for business modeling and other non-software systems. UML supports the entire development lifecycle. UML is supported by many tools (e.g., IBM Rational ROSE, Visio, etc.). SysML is the extension of UML to systems engineering.

38 Domain of Interest System View Realization View System Requirement
(3) contained in Domain of Interest contained in Category (2) built from reference for C categorizes (63) (5) System View Functional Breakdown (64) (7) (6) System Breakdown has view Stakeholder Environment Element exhibits part of Physical Breakdown C (1) (65) has (62) (61) (8) (4) Interacts with Design View Realization View Stakeholder Need satisfied by System (9) (11) allocated to System Requirement C Reference Document Property represented by statement of reference for (10) derived from verifies (12) (14) (13) Physical Property Structure Verification Behavior C C allocated to budgeted to

39 Unified Modeling Language (UML)
(3) Domain of Interest Box means Class or Meta Class (top is name) or type 2nd box means attributes 3rd box means Methods or member functions Diamond means aggregation/decomposition Line means relationship (words on line describe relationship) (XX) Means look at Concept semantic dictionary Diamond with a C in the middle means a Complete decomposition Loop line with Diamond means hierarchal decomposition of items of the same type Arrow/triangle means specialization/generalization Depending on direction A number on each end of a line means multiplicity (1) C (4) (22.10) 1 1 From MDSD Workshop 5 Feb 2003

40 UML vs. SysML

41 Integrated Mission Design Center (IMDC) at Goddard Space Flight Center
“Concurrent Design” Integrated Mission Design Center (IMDC) at Goddard Space Flight Center

42 Preliminary design in one week vs. six months
“Concurrent Design” Collaborative, Rapid Design Improves Quality of Conceptual Designs Preliminary design in one week vs. six months

43 Small Explorers (SMEX) Built at GSFC
Submillimeter Astronomy Satellite (SWAS) Transition Region And Coronal Explorer (TRACE) Wide-Field Infrared Explorer (WIRE) Note cut-outs in blankets for heat rejection. Cryostat is not blanketed—runs cold. Note star tracker and shade. Note RF comm antenna. Note safety vent. Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) Fast Auroral Snapshot Explorer (FAST)

44 System Integration Integration is the process of assembling the system from components. Integration begins with the elementary pieces or configuration items (CI’s) of the system. After each CI is tested, components comprising multiple CI’s are tested. This process continues until the entire system is assembled and tested. Interface Specifications and Interface Control are critical to a successful system integration.

45 Work and Resource Management
A Work Breakdown Structure (WBS) is a hierarchical breakdown of the work necessary to complete a project. The WBS should be a product-based, hierarchical division of deliverable items and associated services. The WBS should contain the Product Breakdown Structure (PBS). At the lowest level are products such as hardware items, software items, and information items (documents, databases, etc.) for which there is a cognizant engineer or manager. A project WBS should be carried down to the cost account level appropriate to the risks to be managed.

46 Work Breakdown Structure (WBS)

47 Product Breakdown Structure (PBS)

48 Technical Resource Management
Critical mission resources shall be identified, allocated and managed Acceptable resource margins shall be established A margin management philosophy shall be set up based on design maturity and time Required margins are reduced as the project matures Margins are assessed based on the fidelity of the estimate Care must be taken that margins are not added to margins Stacked margins that do occur simultaneously in real life Lead systems engineer holds the overall system margins Subsystem engineers must be allowed to hold some margin in order to meet their design requirements This hierarchy of margins must be taken into account so that the overall system margins do not drive the design and the cost Margin costs money, so there is always pressure to reduce margin. Use good judgment and the experience of others to judge how much margin is appropriate.

49 Example: Technical Resource Margins
Tracking Estimates (Mass) Allocations defined at SRR for appropriate total margin Estimates tracked monthly Changes to allocation via CCR Estimates over total allocation trigger risk reduction activities

50 Specialty Engineering
Specialty engineers support the systems engineering process by applying specific knowledge and analytic methods from a variety of engineering specialty disciplines to ensure that the resulting system is actually able to perform its mission in its operational environment. For space systems these specialty areas often include: Quality Assurance Reliability Maintainability Producibility Logistics Safety Environment (e.g., radiation, atomic oxygen, atmospheric density, etc.) Contamination Parts Engineering

51 Reliability * Performance
Quality Assurance Performance Providing confidence that the system actually produced and delivered is in accordance with its functional, performance, and design requirements. Quality Cost Time Engineering Efficiency = Reliability * Performance Cost * Time

52 The “Bathtub Curve” Reliability
For many systems, the failure rate function looks like the classic "bathtub curve" illustrated in the graph below. Failures Random Failures Burn-in Period Useful Life Period Wear-out Period Time

53 Maintainability Maintainability is that system design characteristic associated with the ease and rapidity with which the system can be retained in operational status, or safely and economically restored to operational status following a failure.

54 Verification Verification: “Did I build the System Right?”
Each requirement must be verified Verification Methods: Test, Analysis, Inspection and Demonstration Rule #1: “Test wherever possible” Perform Analysis and Inspection, where Test is not possible Pay careful attention to validity of simulators and models Rule #2: “Test the way you fly, fly the way you test” Identify what is not tested in flight configuration Careful review to assure items are properly verified by a combination of Analysis, Inspection or Test. Review of the assumptions and interfaces of element verified in pieces Attention to validity of simulators and simulations Careful review to assure these items are properly verified by a combination of Analysis, Inspection or Test.

55 Verification (Continued)
Rule #3: “Test the system end-to-end” Carefully review the assumptions and interfaces of any elements verified in pieces Rule #4: “Verify Off-Nominal Conditions” Verify Redundancy and Graceful Degradation Modes along with On Board Fault Protection and Ground Contingency Procedures Stress Testing and Negative Testing to find Latent Flaws

56 Validation Validation: “Did I design or build the Right System?”
Validation shows that the Design when used according to the Operations Concept meets the Requirements and the Customers Goals and Objectives and can be produced within the Cost, Schedule and Risk constraints Validation Methods: Analysis, Predictions, Trade Studies, Test The requirements flow is also validated to show that “Parent” requirements have valid “Child” requirements and that “Orphan” requirements are not driving the system design or implementation. Initial Validation during Phase A and B is critical to proceeding into Phase C where detail design occurs Otherwise the detail design proceeds on the “Wrong” system Validation also occurs in parallel with verification where End to End Tests, Mission Simulations show that the “Right System” has been built

57 Summary Systems Engineering addresses the total program lifecycle
Largely a communications activity Consistent Requirements, Design, and Operations Concept Time Phased “Crawl Before You Walk, Walk Before You Run” No Cookbooks or Magic Recipes Multilayered Review, Inspection and Test Process It is the Project Team, the People, that makes projects successful Systems Engineering Techniques Balance Performance, Cost, and Schedule

58 Some Key References Andrew P. Sage and William B. Rouse, Handbook of Systems Engineering and Management, 2nd edition, John Wiley, 2009 ISO/IEC 15288, Systems engineering — System life cycle processes, 2002 Dennis M. Buede, The Engineering Design of Systems: Models and Methods, Wiley, 2000 ANSI/EIA , Processes for Engineering a System, Electronic Industries Alliance, 1999 IEEE 1220, Management of the Systems Engineering Process INCOSE-TP , INCOSE Systems Engineering Handbook v3.1, 2007 SP , NASA Systems Engineering Handbook

59 Homework Assignment In a brief paragraph describe a system of your choosing In another paragraph describe its operation (operations concept) Draw a high-level product breakdown structure (PBS) for that system

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