Page 216 - Intro to Space Sciences Spacecraft Applications

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Spacecraft Design
each of the solutions considered. It must be realized that none of the pos-
sible solutions may meet all the criteria specified in the desired perfor-
mance function completely or to the level desired, so comparison of the
solutions obtained may be beneficial.

DecisiodOptimization. At this point, the designer must make a decision.
This process is simplified in the systems approach by the fact that only
four courses of action are possible:

One (or more) of the solutions meets an acceptable level of perfor-
mance. The solution which gives the best level is usually the one that
will be passed on as the solution to the next phase of the design
process, though more than one may be passed on as alternative solu-
tions as well.
None of the solutions represents an acceptable solution, but one of the
alternatives exhibits promise if reevaluated or refined within the same
phase of the design. This may involve refining the solution itself in
terms of its configuration or analysis, or may require redefinition of
the evaluation function itself. This process of feeding back to a stage
within the same step of the design process is known as optimization.
None of the solutions are acceptable and a return to an earlier stage is
required.
There is no solution and the program should be dropped.

Communication. The last stage of the design process involves communi-
cation of the results. This must be in a form suitable for use by the follow-
on activities and may involve reports, drawings, specifications, or models.
This represents the end of the design process for a particular step, which
may be simply the end of a single phase of the system’s life cycle, or may
represent the final step in the overall system engineering design. In any
case, the design process is carried out over and over until the program is
terminated or the system reaches the end of its life cycle where, if a need
still exists, the entire process may be started again.

System Life Cycle Phases

Figure 9-2 shows the different phases of the life cycle for a typical
space system development. Each phase of the system life cycle has a def-
inite input which, when subjected to the steps of the systems design
process, leads to the outputs for the phase and ultimately for the period as