1 Introduction to System Engineering G. Nacouzi ME 155B

2 System Engineering Highlights System Engineering (SE) is an overarching discipline that specifies and brings all the elements of a system together –A system is defined as a collection of HW, SW, related interfaces and operations –SE exists at different levels of a major project, from mission level, i.e., constellation, to payload level, i.e., sensor requirements and integration –SE ensures that all customer requirements, from testing, deployment, operations & maintenance, to disposal (if applicable) are addressed and met by the system

3 System Engineering Highlights In large projects, SE is responsible for –Mission requirements interpretation & analysis, with customer feedback, requirements definition & flowdown to lower levels –Initial Design synthesis: develop a reasonable and achievable conceptual system design (architecture). Trade studies and other tools are used to support this effort –Develop final system design & verify that system meets customer requirements

4 System Engineering Highlights In large projects, SE is also responsible for –Major reviews, including*: System Requirements Review –Starting with customer mission objectives, system level requirements are developed and flowed down to the segment level. Schedules, risks and cost are presented Preliminary Design Review –Preliminary system design is completed. Functions, performance and interfaces are defined Critical Design Review –Review of detailed design before production is initiated *Note: partial list, several other reviews are usually included

5 Basic Project Block Diagram Mission Objectives Customer Based Conceptual Design - Prelim. Trades -Cost/schedule -Architecture -Risk & Tech. Requirements Definition -Reqts Analysis -Reqts flow -Interfaces -Reqts meet Mission obj. Trades & Preliminary Design -System Trades Final -Prelim. System design -Reqts Finalized -Demonstrate System meets reqts -Cost/schedule/risk plan finalized Final Design -Detailed Design -Component build -Demonstrate reqts are met at all levels System Tests -Integrated tests -System ‘sell-off’ Operations & Maintenance -Support customer ops & maintenance -Implement upgrades EOL Disposal -System (or part) disposal ops

6 Trade Studies Basics

7 Trade Studies Purpose Evaluate & compare options Assist in decision making & design selection Develop an ‘optimal’ system for given technologies and project constraints –System includes all the hardware, software, interfaces and operations used in the final product

8 Trade Studies Approach All of us have done some simple trades –New car: VW or Porsche? Actually not a viable trade for most of us, why? Porsche not a practical alternative due to cost, so should not be considered –Trade studies should only consider desirable and practical alternatives.

9 Trade Studies Approach Performed at different levels of project –From system level to component selection –Level of details increases with program maturity –Consider alternatives among: Requirements Technical objectives Design

10 Trade Studies Alternatives (cont’d) Program schedule Functional & program requirements Maintenance and operations Disposal Life cycle costs Make choice using a defined set of criteria: –Results should be unambiguous and repeatable

11 Trade Study Process Step 1 Step 2 Reference: System Engineering Fundamentals, Systems Mgmt College Step 6 Step 5 Step 4 Step 3

12 Trade Study Process: Discussion 1- Defining the problem entails developing a problem statement including any constraints. Problem definition should be done with extreme care. After all, if you don’t have the right problem, you won’t get the right answer 2- Bounding and understanding the problem requires identification of system requirements that apply to the study Reference: System Engineering Fundamentals, Systems Mgmt College

13 3- Establishing the methodology includes choosing the mathematical method of comparison, developing and quantifying the criteria used for comparison, and determining weighting factors (if any). Use of appropriate models will dictate the rationality, objectivity, and repeatability of the study. Trade-off relationships should be relevant and rational. Choice of utility or weights should answer the question, “what is the actual value of the increased performance, based on what rationale?” Trade Study Process Discussion Reference: System Engineering Fundamentals, Systems Mgmt College

14 4- Selecting alternative soltns requires identification of all the potential ways of solving the problem and selecting those that appear viable. The number of alternatives can drive the cost of analysis, so alternatives should normally be limited to clearly viable choices (VW vs Porsche!) Trade Study Process Discussion Reference: System Engineering Fundamentals, Systems Mgmt College

15 5/6- Evaluating the alternatives is the analysis part of the study. It includes the development of a trade-off matrix to compare the alternatives, performance of a sensitivity analysis, selection of a preferred alternative. Since weighting factors and some “quantified” data can have arbitrary aspects, the sensitivity analysis is crucial. If the solution can be changed with relatively minor changes in data input, the study is probably invalid, and the methodology should be reviewed and revised. Once all the tasks are completed, a soltn is selected and documented Trade Study Process Discussion Reference: System Engineering Fundamentals, Systems Mgmt College

16 Cost Effectiveness Analyses Cost effectiveness analyses are a special case trade study that compares system or component performance to its cost. These analyses help determine affordability and relative values of alternate solutions. Specifically, mainly are used to: Support identification of affordable, cost optimized mission and performance requirements Provide criteria for the selection of alternative solutions

17 Decision Matrix Each of the decision factors will also have relative value between them. They are used to establish weighting factors for each decision factor. The weighting factors prioritize the decision factors and allow direct comparison between them. A decision matrix is generated to evaluate the relative value of the alternative solutions. Reference: System Engineering Fundamentals, Systems Mgmt College

18 Trade Studies Summary The purpose of trade studies is to make better and more informed decisions in selecting best alternative solutions. Initial trade studies focus on alternative system concepts and requirements. Later studies assist in selecting component part designs. Cost effectiveness analyses provide assessments of alternative solution performance relative to cost. Reference: System Engineering Fundamentals, Systems Mgmt College