The systems engineering process changes as the program progresses from one phase to the next, as do tools and procedures. The process also changes over the decades, maturing, growing, and evolving from the base established during the conduct of past programs. Systems engineering has a long history. Examples can be found demonstrating application of effective engineering and engineering management, as well as poorly applied, but well-defined processes. Throughout the many decades during which systems engineering has emerged as a discipline, many practices, processes, heuristics, and tools have been developed, documented, and applied.
System requirements are critical to all facets of successful system program development. First, system development must proceed from a well-developed set of requirements. Second, regardless of the evolutionary acquisition approach, the system requirements must flow down to all subsystems and lower-level components. And third, the system requirements must be stable, balanced, and must properly reflect all activities in all intended environments. However, system requirements are not unchangeable. As the system design proceeds, if a requirement or set of requirements is proving excessively expensive to satisfy, the process must rebalance schedule, cost, and performance by changing or modifying the requirements or set of requirements.
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The Department of Defense continues to develop and acquire joint systems and deliver needed capabilities to the warfighter. With a constant objective to improve and mature the acquisi-tion process, it continues to pursue new and creative methodologies to purchase these technically complex systems. A sound systems engineering process, focused explicitly on delivering and sustaining robust, high-quality, affordable products that meet the needs of customers and stake-holders must continue to evolve and mature. Systems engineering is the technical and technical management process that results in delivered products and systems that exhibit the best balance of cost and performance. The process must operate effectively with desired mission-level capabilities, establish system-level requirements, allocate these down to the lowest level of the design, and ensure validation and verification of performance, while meeting the cost and schedule constraints.