Page 274 - Mechanical Engineers' Handbook (Volume 2)

2 The System Life Cycle and Functional Elements of Systems Engineering 265

Figure 4 The phases and steps in one 49-element two-dimensional systems engineering framework
with activities shown sequentially for waterfall implementation of effort.

by Hall in his pioneering efforts in systems engineering. 5,6 The specific methods we need to
use in each of these seven steps are clearly dependent upon the phase of activity that is
being completed, and there are a plethora of systems engineering methods available. 3,4 Using
a seven-phase, seven-step framework raises the number of activity cells to 49 for a single
life cycle. A very large number of systems engineering methods may be needed to fill in
this matrix, especially since more than one method will almost invariably be associated with
many of the entries.
The requirements and specification phase of the systems engineering life cycle has as
its goal the identification of client or stakeholder needs, activities, and objectives for the
functionally operational system. This phase should result in the identification and description
of preliminary conceptual design considerations for the next phase. It is necessary to translate
operational deployment needs into requirement specifications so that these needs may be
addressed by the system design efforts. As a result of the requirement specification phase,
there should exist a clear definition of development issues such that it becomes possible to
make a decision concerning whether to undertake preliminary conceptual design. If the re-
quirement specification effort indicates that client needs can be satisfied in a functionally
satisfactory manner, then documentation is typically prepared concerning system-level spec-
ifications for the preliminary conceptual design phase. Initial specifications for the following
three phases of effort are typically also prepared, and a concept design team is selected to
implement the next phase of the life-cycle effort. This effort is sometimes called system-
level architecting. 7,8 Many 9,10 have discussed technical-level architectures. It is only recently
that the need for major attention to architectures at the systems level has also been identified.
Preliminary conceptual system design typically includes, or results in, an effort to spec-
ify the content and associated architecture and general algorithms for the system product in
question. The desired product of this phase of activity is a set of detailed design and archi-
tectural specifications that should result in a useful system product. There should exist a
high degree of user confidence that a useful product will result from detailed design or the
entire design effort should be redone or possibly abandoned. Another product of this phase
is a refined set of specifications for the evaluation and operational deployment phases of the