Unformatted text preview: esult of this step is the discovery and
delineation of the system's goals, which generally
express the desires and requirements of the eventual
users of the system. In the NASA context, the system's
goals should also represent the long term interests of
the taxpaying public.
Identify and Quantify Goals. Before it is possible to
compare the cost-effectiveness of alternative system
design concepts, the mission to be performed by the
system must be delineated. The goals that are
developed should cover all relevant aspects of
effectiveness, cost, schedule, and risk, and should be
traceable to the goals of the supersystem. To make it
easier to choose among alternatives, the goals should
be stated in quantifiable, verifiable terms, insofar as that
is possible and meaningful to do.
It is also desirable to assess the constraints that
may apply. Some constraints are imposed by the state
of technology at the time of creating or modifying
system design concepts. Others may appear to be
inviolate, but can be changed by higher levels of
management. The assumptions and other relevant
information that underlie constraints should always be
recorded so that it is possible to estimate the benefits
that could be obtained from their relaxation.
At each turn of the spiral, higher-level goals are
analyzed. The analysis should identify the subordinate
enabling goals in a way that makes them traceable to
the next higher level. As the systems engineering
process continues, these are documented as functional
requirements (what must be done to achieve the
requirements (quantitative descriptions of how well the
functional requirements must be done). A clear
operations concept often helps to focus the requirements analysis so that both functional and performance
requirements are ultimately related to the original need
or opportunity. In later turns of the spiral, further
elaborations may become documented as detailed
functional and performance specifications.
Create Alternative Design Concepts....
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