Page 212 - Intro to Space Sciences Spacecraft Applications

Spacecraft Design
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approach described herein, or something similar, is the methodology used
to approach the problems encountered by NASA and the aerospace indus-
tries in meeting the needs of the space programs, by AT&T in meeting the
communications needs of millions, and even by urban planners consider-
ing public transportation, pollution, health care, and other needs.
From the above discussion, it should be clear that the prerequisite for
considering the design of a space-based system is that an appropriate mis-
sion need exists. A suitable commercial, military, civil, or scientific need
must be well established to justify the time, effort, and sizable expense
required to warrant the development of a space-based system. The need is
often defined by individuals or groups of potential systems users scattered
all over the world. Sources of demands for satellites originate from mili-
tary or civil government agencies, scientific organizations, and commer-
cial service industries. Some space systems may be sovereign in nature,
providing information and services to a select but important sector of
users. In some cases, international organizations, both scientific and com-
mercial, form shared programs with many entities providing funds and
systems elements. Advisory committees, such as the National Academy
of Sciences and the National Space Council, and universities provide
guidance and play important roles in defining needs for manned and
unmanned satellites. Whatever the source of the initial concept for the
mission or the selection of the specific implementation approach of the
system, further development usually follows a fairly common, relatively
standardized and structured approach, referred to as the systems approach.
As shown in Figure 9-1, the systems approach is a two-dimensional
method which has the design process along one axis and the systems life
cycle along the other. When placed together, the result is a matrix which
delineates a methodical system design process. Each step in this process
is explained in the following sections.

System life Cycle

The system life cycle begins with formalization of the mission need and
terminates when the system is retired or fails. The life cycle may be orig-
inated as a result of a new need, new technology, or as an iteration of a
previous system whose life cycle is nearing completion due to obsoles-
cence. As indicated in Figure 9-1, the system life cycle has three distinct
periods: planning, acquisition, and use. Each of these periods is divided