The Systems Engineering Process
Systems engineering, essentially an application of systems analysis to the design and procurement of hardware systems to accomplish specific ends, can be an effective tool of management when well defined and consistently implemented. The essential products of the systems engineering process and their programmatic use are described in this section.
The systems engineering process involves the top-down development of a system's functional and physical requirements from a basic set of mission objectives. The purpose is to organize information and knowledge to assist those who manage, direct, and control the planning, development, and operation of the systems necessary to accomplish the mission (Sage, 1992). The system's physical requirements lead to the specific hardware components that must be acquired or developed to perform the identified functions. The systems engineering process should be conducted in a way that includes consideration of alternative system configurations. The result should be a set of traceable requirements that may be used in design and procurement and in system verification and validation, a baseline description of the physical system, and a baseline description of the operational concept. This should also include a set of documented interfaces to ensure compatibility of different parts of the system as they are developed. The process being used in the Tank Waste Remediation System (TWRS) program at Hanford follows from what is described above; it is illustrated in Figure 1.
Several terms used in systems engineering are defined below for the convenience of the reader. Traceability imposes the conditions that the interdependencies among physical and functional requirements be made explicit and that each requirement be trackable longitudinally through the entire systems engineering process and through the system' s full life cycle (Eisner, 1997). System verification is a two-step process to assure, first, that system design successfully captures the full set of system requirements, and second, that the system hardware and software fully implement the design. System validation is the process of assuring that, once the system is developed, its operational concept will meet the original system requirements (Sage, 1992).
Baseline descriptions, both of design of the physical system and of the functions the system is supposed to perform, once built, are essential to the process of modifying the system as new information or experience is obtained. Configuration management and change control are important quality assurance steps that ensure changes to the baseline occur in a planned manner and are thoroughly documented, so that implications for system performance are understood. The direction of desirable changes is specified through configuration control (Sage, 1992). The system's initial baseline description is also referred to as its conceptual architecture.
The systems engineering process provides value to the development, management, and implementation of a large program by ensuring:
- orderly definition of a system through top-down development of functions and requirements;
- clear distinction between design requirements developed by the program/project (potentially modifiable) and externally imposed constraints (not easily subject to modification);
- top-down consideration and evaluation of alternative solutions and designs, and
- completeness and traceability for design of system elements and interfaces, for configuration and change control, and for the system verification and validation plan(s).
This value of the systems engineering process may be realized in a number of ways, including:
- increased ability to estimate system life-cycle costs,
- reduced redesign due to consideration of the entire system throughout its development,
- increased ability to effect design changes and retrofits due to clear traceability of requirements, design features, and configuration control, and
- increased probability of achieving the best technical de-
Figure 1
The Generic TWRS Systems Engineering Process. From Westinghouse Hanford Company, 1996a (Figure 3.1, p. 3-2), and U.S. Department of Energy, 1994a (Figure 2.3-1).
- sign and operational concept through the iterative consideration of design alternatives, where "best" is defined through decision criteria such as cost, risk, and land use.
Although not necessarily performed for the purpose of reducing program costs, a sound systems engineering approach improves the ability of managers of large engineering programs to deliver a sound design and operational concept with reduced risk of cost growth.
A sound systems engineering approach, appropriately implemented, should result in effective integration of environmental remediation and waste management efforts across the entire Hanford Site. The hallmarks of a well-integrated program are consistency of approach throughout an organization, and a smooth flow of information both up and down the management chain. In such a program, work done by individual units is compatible with the objectives and goals of the larger organization, and individual projects are clearly related to the objectives of the organizational units in which they occur (vertical integration). Within organizational layers, individual units are aware of the efforts of others in related domains and work to assure that their own activity complements that being done by other units (horizontal integration). An additional consideration in the case of programs like DOE/EM, whose ability to go forward is highly dependent on public approval, is the need to assess continually the program objectives with respect to stakeholder values.
