Principles of Systems Engineering Introduction & Overview

Morgan State University • Systems Engineering Lecture 1

Principles of Systems Engineering

Introduction & Overview

Morgan State University • Systems Engineering Lecture 1 2

Agenda

1. Definitions of system and systems engineer

2. The role of a systems engineer

3. Systems engineering vs. project management

4. 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


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


Definitions (Continued)

What is Systems Engineering?

“Systems Engineering is an interdisciplinary

approach and means to enable the

realization of successful systems.”INCOSE Handbook



Another Definition

“Systems Engineering is a robust approach to the

design, creation, and operations of systems.”NASA Systems Engineering Handbook SP-6105



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



“Engineering of Systems”

Anyone involved in engineering a system should exercise good systems engineering practices.


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

from Sarah A.Sheard (INCOSE proceedings of 1996)


Systems Engineering Project Control

•System Design•Requirement Definition

•Technical Solution Definition

•Product Realization

•Design Realization

•Evaluation•Transition

•Technical Management

•Technical Planning

•Technical Control

•Technical Assessment

•Technical Decision Analysis

• Planning• Risk

Management• Configuration

management• Data

Management• Assessment• Decision

Analysis

• Management Planning

• Integrated Assessment

• Schedule Management

• Configuration management

• Resource Management

• Documentation and Data Management

• Acquisition management

Project Management

Systems Engineering Project Control

•System Design•Requirement Definition

•Technical Solution Definition

•Product Realization

•Design Realization

•Evaluation•Transition

•Technical Management

•Technical Planning

•Technical Control

•Technical Assessment

•Technical Decision Analysis

• Planning• Risk

Management• Configuration

management• Data

Management• Assessment• Decision

Analysis

• Management Planning

• Integrated Assessment

• Schedule Management

• Configuration management

• Resource Management

• Documentation and Data Management

• Acquisition management

Project Management

Systems Engineering vs. Project Management


Key Systems Engineering Functions

Tools help engineers evaluate their

systems more quickly and more efficiently,

but they do not replace the “Art” and

“Creativity” necessary to

conceive them

“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

Project Objectives

and Constraint

s

Requirements

Development and

Management

Architecture and Design

Operations Concept

Verification and Validation

Verification

andValidation

Verification and

Validation

Systems Engineering Management Plan

Project Objectives

Met,Ready for

Operations


Decom

position

&

Defi

nitio

n S

equen

ceIn

tegra

tion

and

Ver

ifica

tion

Seq

uen

ce

Understand UserRequirements, Develop

System Concept andValidation Plan

Demonstrate andValidate System to User Validation Plan

Develop SystemPerformance Specification

and SystemVerification Plan

Expand PerformanceSpecifications Into CI

“Design-to” Specificationsand Inspection Plan

Evolve “Design-to”Specifications into

“Build-to” Documentation and Inspection Plan

Integrate System andPerform SystemVerification to

Performance Specification

Assemble CIs and PerformCI Verification to CI

“Design-to”Specifications

Inspect to“Build-to”

Documentation

Fabricate, Assemble, andCode to “Build-to”

Documentation

CI = Configuration Item

Systems Engineering Process “V”


*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 57 - 65.

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


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.


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

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



• 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



• 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.


What the Proposal Promised Preliminary Design Design Drawings

As Built by ManufacturingFollowing Inspection and Rework What the Customer Wanted

Design Change Specification

After Rework

What Happened toThe Engineering

Team

The Customer’s Swing

The customer requested a new kind of swing that allowed the customer more than one way of swinging.

Communication and Understanding is Key!



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


ID DESCRIPTION REQUIREMENTTRACED FROM

PERFORMANCE MARGIN Comments REF

M1 Mission Orbit 575 +/-15 km Sun-synchronous dawn-dusk orbit S3, S11, P3 Complies NA Pegasus XL with HAPS provides required launch injection dispersion accuracy

F.2.c

M2 Launch Vehicle Pegasus XL with HAPS P2, P4 Complies NA F.2.cM3 Observatory Mass The NEXUS Observatory total mass shall not exceed 241

kg. M1, M2 192.5 kg 25.20% F.5.b

M4 Data Acquisition Quality The NEXUS mission shall deliver 95% data with better than 1 in 100,000 BER.

P1 Complies NA Standard margins and systems baselined, formal system analysis to be completed by PDR

F.7

M5 Communication Band The mission shall use S-band SQPSK at 5 Mbps for spacecraft downlink and 2 kbps uplink.

S12, P4 Complies NA See SC27, SC28 and G1, G2 F.3.f,F.7

M7 Tracking MOC shall use NORAD two line elements for observatory tracking

P4 Complies NA F.7

M8 Data Latency Data Latency shall be less than 72 hours P12 Complies NA F.7M9 Daily Data Volume Accommodate average daily raw science data volume of

10.8 Gbits P1, S12 Complies 12% Marign based on funded ground

contacts F.3.e,

F.7M10 Ground Station The Mission Shall be Compatible With the Rutherford

Appleton Laboratory Ground Station and the Poker Flat Ground Station

P1 Complies NA F.7

M11 Orbital Debris (Casualty Area)

Design NEXUS observatory for demise upon reentry with < 1/10,000 probability of injury

P3 1/51,000 400% See Orbital Debris Analysis in Appendix M-6

F.2.e,App.6

M12 Orbital Debris (Lifetime) Design NEXUS observatory for re-entry <25 years after end of mission

P3 < 10 years 15 years See Orbital Debris Analysis in Appendix M-6

F.2.e,App.6

Table 13

Requirements Management (Continued)


•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

Operations Concept


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


• 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



Image Recording

Inter -Satellite Link

MILITÄRISCHER NUTZER

Dossier

Auftrag

NUTZER-BODENSEGMENT

SATELLITEN-BODENSEGMENT

Command Transmission

Data Download


Control CenterSatellite OperatorsMilitary Planners Request for Data

Data


Decomposition

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


System Requirement

FunctionalRequirement

PerformanceRequirement

PhysicalProperty

Requirement

Imposed DesignRequirement Reference

Requirement

InterfaceRequirement

based on content and allocation

EffectivenessMeasure

User Defined

non-exhaustiveinclusive

Decomposition (Continued)


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


Technology Readiness Levels


•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.

Systems Analysis and Design

Modeling


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.


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”.


Structured Analysis (Continued)

IDEF0StudentRegistration System



“ICOM”

Input Output

Control

Mechanism

Function


Ready Verifying

Do: verify user

[Valid user]

[Invalid user]/Display:”Access Denied”

Validating Options

Do: display user options Do: check option vs access permission

User ID and Password entered(User_ID, Password)/ accept

[Option selected not allowed]/Display error message: “Option not allowed”

Validating ReportRegistering

See superstate diagram

Request for course search

Do: display login pageDo: wait for login

Retrieving

Do: display course search pageDo: retrieve course selections

Request to register (course_nr, user_ID)

Request to register (course_nr, user_ID)

Request to generate report (User type)

Do: display report page Do: validate user vs report selected

[Report not allowed]/Display error message “Option not allowed”

(Report type) [Report allowed]

start

Generating Report

Do: send database request (report parameters)Do: format reportDo: print (report)

Updating Schedule

Do: update student schedule

[No Conflicts] (course_nr)

Drop request (course_nr)

[Registration rejected]

Updating complete/University-updated class roster

Report printed

Behavior Modeling: State Transition Diagram




IDEF1xDATA MODEL


Object-Oriented Analysis and Design

•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.


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.


Domainof Interest

Element

System

Property

StructurePhysicalProperty

Environment

C

C

SystemRequirement

statement of

Interacts with

exhibits

allocated to

Stakeholder Need

Stakeholder

satisfied by

represented by

has

allocated to budgeted to

SystemView

has view

(1)

(3)

(5)

(4)

(6)(7)

(8)

derived from

(9)

(10)

Behavior

C

(12) (14) (13)

ReferenceDocument

(11)

reference for

categorizes

Category

(2)

reference for

Verification

verifies

contained in contained in

C

Cbuilt from

part of

Design View(61)

RealizationView

(62)

FunctionalBreakdown

SystemBreakdown

PhysicalBreakdown

(65)

(64)

(63)


Domainof Interest

(1)

(3)

C

(4)

(22.10)

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 multiplicity1

1

From MDSD Workshop 5 Feb 2003

Unified Modeling Language (UML)


UML vs. SysML


“Concurrent Design”

Integrated Mission Design Center (IMDC) at Goddard Space Flight Center


“Concurrent Design”

Collaborative, Rapid Design Improves Quality of Conceptual Designs

Preliminary design in one week vs. six months


Small Explorers (SMEX) Built at GSFC

Wide-Field InfraredExplorer (WIRE)

Transition Region And Coronal Explorer (TRACE)

Submillimeter Astronomy Satellite (SWAS)

Fast Auroral

SnapshotExplorer

(FAST)

SolarAnomalousand MagnetosphericParticle Explorer(SAMPEX)


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.


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.


Work Breakdown Structure (WBS)


Product Breakdown Structure (PBS)


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


Example: Technical Resource Margins

Margin Factors Estimate Calculated Measured

Mass 20% 15% 3%

Power (solar array, battery, load)

20% 15% 3%

Fuel 10% 5% 3%

Memory 30% 15% 3%

CPU 50% 30% 25%

Telemetry and Commands 20% 15% 10%

RF Link 2dB 1dB .5dB

Estimate

Allocation

Capability

Margin

Contingency

Total Margin

835

750

680

10.3%

11.3%

22.8%

% Margin =Capability

Estimate-1

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


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


Quality

Performance

CostTime

EngineeringEfficiency

= Reliability * Performance

Cost * Time

Quality Assurance

Providing confidence that the system actually produced and delivered is in accordance with its functional, performance, and design requirements.


Reliability

The “Bathtub Curve” For many systems, the failure rate function looks like the

classic "bathtub curve" illustrated in the graph below.

Burn-in Period Useful Life Period Wear-out Period

Fai

lure

s

Time

Random Failures


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.


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.


•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

Verification (Continued)


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


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


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-632-1998, Processes for Engineering a System, Electronic Industries Alliance, 1999

•IEEE 1220, Management of the Systems Engineering Process

•INCOSE-TP-2003-002-03.1, INCOSE Systems Engineering Handbook v3.1, 2007

•SP-2007-6105, NASA Systems Engineering Handbook


Homework Assignment

1. In a brief paragraph describe a system of your choosing

2. In another paragraph describe its operation (operations concept)

3. Draw a high-level product breakdown structure (PBS) for that system

Documents

Principles of Systems Engineering Introduction & Overview