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These high-level performance or technical
attributes might represent one of the facets described
above, or they may be only components of one. They
are likely to re quire knowledge or estimates of lower-order
performance or technical attributes. Figure 26 shows
how system effectiveness might look in an hierarchical
tree structure. This figure corresponds, in some sense,
to Figure 25 on life-cycle cost, though rolling up by
simple addition obviously does not apply to system
Lastly, it must be recognized that system
effectiveness, like system cost, is uncertain. This fact is
given a fuller treatment in Section 5.4.
5.3.2 NASA System Effectiveness Measures The facets of system effectiveness in Figure 26
are generic. Not all must apply to a particular system.
The system engineer must determine which
performance or technical attributes make up system
effectiveness, and how they should be combined, on a
system-by-system basis. Table 6 provides examples of
how each facet of system effectiveness could be
interpreted for specific classes of NASA flight systems.
No attempt has been made to enumerate all possible
performance or technical attributes, or NASA Systems Engineering Handbook
Systems Analysis and Modeling Issues to fill in each possible entry in the table; its purpose is
For many of the systems shown in the table,
system effectiveness is largely driven by continual (or
continuous) operations at some level of output over a
period of years. This is in contradistinction to an
Apollo-type project, in which the effectiveness is largely
determined by the successful completion of a single
flight within a clearly specified time horizon. The
measures of effectiveness in these two cases are
correspondingly different. In the former case (with its
lengthy operational phase and continual output), system
effectiveness measures need to incorporate quantitative
measures of availability. The system engineer
accomplishes that through the involvement of the
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