Page 217 - Intro to Space Sciences Spacecraft Applications

Introduction to Space Sciences and Spacecraft Applications
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well. Each phase is associated with the technical and programmatic (cost,
risk, and schedule considerations) content and level of detail expected at
that stage of mission development. As seen in the figure, a number of for-
mal, documented reviews are used to ensure that the development is pro-
ceeding as expected and that all factors are such that the development can
proceed to the next level. Considering the expense associated with such
missions, and the usual difficulty of retrieving the satellite once placed
into orbit, these factors include budgetary and political as well as quality
assurance and technical considerations. The following sections will
describe the level of detail expected, usual activities, and the reviews
and/or decision gates associated with each phase in the unfolding devel-
opment of a typical satellite mission.

Conceptual Study Phase (Pre-Phase A). This initial conceptual study
phase is usually initiated by the intended users and mission advocates with
the assistance of a spacecraft development organization (Le., a NASA
center, military organization, or spacecraft company). The phase begins
by formulating a clear statement of the mission needs and objectives.
Associated with the mission needs statement is a justification for the mis-
sion describing the scientific benefits that will be achieved, military goals
accomplished, or projected profit to be made. Using descriptions of the

Pre-Phase A Phase A PhaseB Phasem Phase E
Concephlal Mission operations
Study phase Analysis phase Definition Phase Design/Dsvelopment Phase phase
I
Initial Objectives Initial Requirements Design To Detailed Design I Fabrication SpaCW3fl
Requirements Operations
fustificarion/Benefirs Payload Test Models I lnlegration
DefinitiodSelection Reliminary Design Payload
implementation Conceptc * Instruments ' Test Operations
Concept Analysis/ * Spacecraft I
ROM Cost Estimate Selection * Launch Vehicle 1 Launch & Operations Science
Systems Engineering * Ground Systems I Preparation Planning
Announcements of - Operations
3pportunity Updated Cost & Schedule I Data Collectioi
Eitimatcs Scope of Work I Data Reductior
Reasonable Schedule I
I End-of-Life
Expected Costs I
Requests for Proposals I

Figure 9-2. System life cycle. The design of a spacecraft passes through
many phases of evolution and review before becoming reality.