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Unformatted text preview: for use in design optimization. Even without
knowing how to trade effectiveness for cost, designs
that have lower cost and higher effectiveness are
always preferred. NASA Systems Engineering Handbook
Fundamentals of Systems Engineering
tradeoff space between effectiveness and cost. A graph
plotting the maximum achievable effectiveness of
designs available with current technology as a function
of cost would in general yield a curved line such as the
one shown in Figure 1. (In the figure, all the dimensions
of effectiveness are represented by the ordinate and all
the dimensions of cost by the abscissa.) In other words,
the curved line represents the envelope of the currently
available technology in terms of cost -effectiveness.
Points above the line cannot be achieved with
currently available technology e that is, they do not
represent feasible designs. (Some of those points may
be feasible in the future when further technological
advances have been made.) Points inside the envelope
are feasible, but are dominated by designs whose
combined cost and effectiveness lie on the envelope.
Designs represented by points on the envelope are
called cost-effective (or efficient or non-dominated)
Design trade studies, an important part of the
systems engineering process, often attempt to find
designs that provide a better combination of the various
dimensions of cost and effectiveness. When the starting
point for a design trade study is inside the envelope,
there are alternatives that reduce costs without
decreasing any aspect of effectiveness. or increase
some aspect of effectiveness with Figure 1 -- The Enveloping Surface of Non-dominated
out decreasing others and without increasing costs.
Then, the system manager's or system engineer's
decision is easy. Other than in the sizing of subsystems,
such "win-win" design trades are uncommon, but by no
means rare. When the alternatives in a design trade
study, however, require trading cost for effectiveness, or
even one dimension of...
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