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Alternative system design concepts may be abundantor

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Unformatted text preview: onflicting objectives, negotiated compromises will be required. • Alternative system design concepts may be abundant—or they may require creative genius to develop. Most NASA systems are sufficiently complex that their components are subsystems, which must function in a coordinated way for the system to accomplish its goals. From the point of view of systems engineering, each subsystem is a system in its own right—that is, policies, requirements, objectives, and which costs are relevant are established at the next level up in the hierarchy. Spacecraft systems often have such subsystems as propulsion, attitude control, telecommunications, and power. In a large project, the subsystems are likely to be called "systems". The word system is also used within NASA generically, as defined • A "back-of-the-envelope" computation may be satisfactory for prediction of how well the alternative design concepts would do in achievement of the goals—or credibility may depend upon construction and testing of hardware or software models. • The desired ends usually include an optimization objective, such as "minimize life-cycle cost" or "maximize the value of returned data", so selection of the best design may not be an easy task. Particular projects may need a different sequence of layers— an instrument may not need as many layers, while a broad initiative may need to distinguish more layers. Projects should establish their own terminology. The word system is also used within NASA generically, as defined in the text. In this handbook, "system" is generally used in its generic form. NASA Systems Engineering Handbook Fundamentals of Systems Engineering ject's purpose; its connotations of fervor make it particularly suitable for such political activities, where the emotional content of the term is a desirable factor. In everyday conversation, the terms "project," "mission," and "system" are often used interchangeably; while imprecise, this ra...
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