Page 214 - Intro to Space Sciences Spacecraft Applications

Spacecraft Design
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with design of the system prior to production. The planning, acquisition,
and use periods represent time-based periods in a system’s life cycle.

System Design Process

While the system life cycle identifies the different periods and phases
in the design of a complex system, the design process defines the funda-
mental sequence of activities used for making design decisions (trade-
offs) during each phase. It is an iterative (repeated) method that results in
a successively more detailed and optimized solution to the problem at
hand. The process is continued repeatedly until either an acceptable solu-
tion is reached or a decision is made to regress to a previous design phase
(or even back to square one!). The process is broken into a number of
stages which are also indicated in Figure 9-1. These stages are discussed
in more detail in the following section, after which the phases in the sys-
tem life cycle will be presented in detail.

Design Process Stages

Gather Information. In the first stage, the designer (or group) gathers all
the information that may be pertinent to the problem. This includes the
inputs to the particular design phase (defined later), as well as overall sys-
tem constraints and purposes, which may be useful in establishing criteria
to which the inputs will be compared and optimized.

Value Model. The next stage uses the information gathered in the first
stage to formulate a function (model) that indicates the desired perfor-
mance of the system or element with respect to all pertinent considera-
tions (such as size, cost, and effectiveness). It is to this model that the
evaluation functions of all the possible approaches will be compared. In
general there are three important areas to consider:

Effectiveness: ability to perform the stated objectives. This mainly
deals with the physical capabilities of the solution.
Cost: resources required by the solution.
Time: when the solution is required or how long it may take to pro-
duce the particular solution.

Many other considerations may be involved such as risk, politics, and
others directly associated with the particular need being addressed. These