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Unformatted text preview: s in such disciplines
as reliability, maintainability, producibility, integrated logistics, software, testing, operations, and costing have
an important supporting role in trade studies. The data
collection activity, however, should be orchestrated by
the system engineer. The results of this step should be a
quantitative description of each alternative to
accompany the qualitative.
Test results on each alternative can be
especially useful. Early in the systems engineering
process, performance and technical attributes are
generally uncertain and must be estimated. Data from
breadboard and brassboard testbeds can provide
additional confidence that the range of values used as
model inputs is correct. Such confidence is also
enhanced by drawing on data collected on related previously developed systems.
The next step in the trade study process is to
quantify the outcome variables by computing estimates
of system effectiveness, its underlying system
performance or technical attributes, and system cost. If
the needed data have been collected, and the
measurement methods (for example, models) are in
place, then this step is, in theory, mechanical. In
practice, considerable skill is often needed to get
In an ideal world, all input values would be precisely known, and models would perfectly predict
outcome variables. This not being the case, the system
engineer should supplement point estimates of the
outcome variables for each alternative with computed or
estimated uncertainty ranges. For each uncertain key
input, a range of values should be estimated. Using this
range of input values, the sensitivity of the outcome
variables can be gauged, and their uncertainty ranges
calculated. The system engineer may be able to obtain
meaningful probability distributions for the outcome
variables using Monte Carlo simulation (see Section
5.4.2), but when this is not feasible, the system engineer
must be content with only ranges and sensitivities.
This essentially completes the analytical portion
of the trade study process. The next steps can be
described as the judgment...
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