Mil StdB Revisited

This draft standard, discussed in Chapter 2, is rather specific about what it is that constitutes the systems engineering process. Referring to Figure 7.1, we see the four main features of this process, as represented in the standard:

1. Requirements analysis

2. Functional analysis/ allocation

Process Input 3

• Customer needs/objectives/ / requirements / •• Missions / •• Measures of effectiveness /

• Technology base

• Outputs from prior phase 1

• Program decision \ requirements \

• Requirements applied through \ specifications and standards \

Process Output

• Phase dependent •• Decision support data •• System architecture •• Specifications & baselines

Process Output

• Phase dependent •• Decision support data •• System architecture •• Specifications & baselines

Figure 7.1. Military Standard 499B view of systems engineering process.

3. Synthesis

4. System analysis and control

This process requires a variety of inputs, delineated in the figure as ''process input.'' The outputs are also shown under the heading of ''process output.'' The view of systems engineering and its management in this text, however, is considerably broader. As indicated before, it goes beyond architectural design of the system and into detailed subsystem design as well as the physical construction, operation, and maintenance of the system. This broader view can be expressed as a set of some thirty interrelated elements and is the central focus of this chapter. In addition, this view also includes the management of the systems engineering process that is normally the purview of the Chief Systems Engineer (CSE).

7.2.2 The NASA Mission Design Process

NASA's Engineering Management Council has produced an engineering guide to conceptual design, mission analysis, and definition phases of a system [7.12]. NASA tends to build systems by going through a series of formal phases, from Prephase A to Phases C and D. The previously cited engineering guide defines the first three phases as:

1. The conceptual design process: Prephase A

2. The mission analysis process: Phase A

3. The definition process: Phase B

These are well-known by the industry that supports these phases that define the ''front-end'' portion of the system's life cycle. Table 7.1 provides a summary of the mission design activities, reviews, and products for each phase; Table 7.2 shows examples of the required study resources for the phases [7.12].

Two points are especially significant with respect to NASA's approach. The first is that NASA has defined the flow of activities associated with each phase. As examples, Figures 7.2 and 7.3 show these processes for Phase A and Phase B, respectively. These are the systems engineering processes for these early life-cycle phases. The second point is that NASA has implicitly given significant attention to the notion of mission analysis, which has often been overlooked as an integral part of, and indeed key element of, systems engineering. The latter is viewed as an important contribution to a more effective way of ultimately dealing with the significant subject of missions as well as requirements analysis and engineering.

TABLE 7.1 Summary of Mission Design Activities, Reviews, and Products

Prephase A

Phase A

Phase B

Input to Each Phase

Mission Needs and Objectives

Activities

Prephase A Study

Preliminary Mission Requirements Definition

Top-Level Trade Studies

ROM Costs and Schedule Feasibility Assessment

Preliminary Mission Requirements Document

Prephase A Study Report

Evaluation Criteria

System and Subsystem Trade Studies

Analysis of Performance Requirements

Identification of Advanced Technology/Long Lead Items

Risk Analysis

End-to-End System Life-Cycle Cost as a Trade Parameter

Cost and Schedule Development

Top-Down Selection of Study Concepts

Operational Concepts

Phase A Study Report Mission Requirements

Document Operations Concept

Document Project Initiation Agreement Evaluation Criteria Mission Requirements Request (Preliminary) Revalidation of Mission Requirements and System Operations Concept System Decomposition, Requirements Flow-Down, and Verification Risk Analysis

System and Subsystem Studies and Trades Development of the Work Breakdown Structure and Dictionary Updating Cost, Schedule, and

Life-Cycle Cost System and Subsystem Concept Selection and Validation

TABLE 7.1 (Continued)

Prephase A

Phase A

Phase B

Reviews

Peer Reviews

Peer Reviews

Peer Reviews

Mission Concept Review

Mission Design Review

System Requirements Review System Design Review Nonadvocate Review

Products

Prephase A Study Report

Phase A Study Report

Nonadvocate Review Package

Preliminary Mission Require

Mission Requirements Docu

Phase C/D Request for Pro

ments Document

ment (preliminary)

posal Package (s)

Evaluation Criteria

Operations Concept Document

Baseline Systems Description

Science Definition Team

Project Initiation Agreement

Technology Development/

Report

Risk Mitigation

ROM Cost Estimate

Phase B Study Plan

Technology Development Plan

Top-Level System and Mission Architecture Preliminary Cost and Manpower Estimates

Design and Technical

Documents Management and Control Plans

Externally Required Documents and Agreements Mission Cost and Manpower

Estimates Operations Plan

7.3 THE THIRTY ELEMENTS OF SYSTEMS ENGINEERING 191 TABLE 7.2 Examples of Required Study Resources

Duration Funding Staffing

7.3 THE THIRTY ELEMENTS OF SYSTEMS ENGINEERING 191 TABLE 7.2 Examples of Required Study Resources

Duration Funding Staffing

Prephase A

2 to 4 months

$0 to < $100,000

Study Manager/Systems

Engineer Project Scientist Part-time help from others

Phase A

6 months to 1 year

1 to 2% of total system cost

Study Manager Systems Engineer Project Scientist Resource Specialists Discipline Engineers and Specialists

Phase B

1 to 2 years

4 to 8% of total system cost

Project Manager Systems Engineer Project Scientist Resource Specialists Discipline Engineers and Specialists

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