Systems Engineering Process

The systems engineering process is based on an iterative, top down, hierarchical decomposition of system requirements, supported by trade studies that record the basis for significant decisions and the options considered. The iterative, top-down, hierarchical decomposition methodology includes the parallel activities of Functional Analysis, Allocation, and Synthesis. The iterative process begins with system-level decomposition and then proceeds through the major subsystem level, the functional subsystem level, to the hardware/software configuration item (CI) or assembly/program level. As each level is developed, the activities of functional analysis, allocation, and synthesis will be completed before proceeding to the next lower level.

Systems engineering with assistance from the other engineering disciplines establishes the baseline system design; allocates system requirements; establishes measures of effectiveness for ranking alternative designs; and integrates the design among the design disciplines. Systems engineering is responsible for verifying that the system developed meets all requirements defined in the system specification and for providing the analysis which assures that all requirements will be met. The following outlines the systems engineering process steps.

During system and mission requirements analysis, systems engineering analyzes and reviews the impact of operational characteristics, environmental factors, and minimum acceptable functional requirements, and develops measures suitable for ranking alternative designs in a consistent and objective manner. These measures should also consider cost and schedule. Each requirement should be periodically examined for validity, consistency, desirability, and attainability. This analysis either verifies that the existing requirements are appropriate or develops new requirements which are more appropriate for the mission/operation.

During functional analysis, systems engineering uses the input of performance requirements developed during mission analysis or operational analysis to progressively identify and analyze system functions and subfunctions in order to identify alternatives to meet system requirements. It is performed in conjunction with Allocation and Synthesis activities. Systems engineering considers all specified modes of operation and support. Systems engineering then establishes performance requirements for each function and sub-function identified. When time is critical to performance of a function, systems engineering also performs a timeline analysis.

During the allocation process, systems engineering allocates performance and design requirements to each system function and sub-function. These derived requirements are stated in sufficient detail to permit allocation to hardware, software, procedural data, or personnel. Systems engineering identifies any special personnel skills or peculiar design requirements. Allocation activities are performed in conjunction with Functional Analysis and Synthesis activities. Traceability of the allocated system requirements should be maintained.

During synthesis, systems engineering together with representatives of hardware, software, and other appropriate engineering specialties develops a system architecture design that is sufficient to specify the performance and design requirements which are allocated in the detailed design. Design of the system architecture occurs simultaneously with the allocation of requirements and analysis of system functions. The design is documented with block and flow diagrams. These diagrams will:

1. Portray the arrangement of items that make up the baseline design
2. Identify each element along with techniques for its test, support, and operation,
3. Identify the internal and external interfaces,
4. Permit traceability to source requirements through each devolution level,
5. And provide a means for comprehensive change control.

This documentation is the primary source of data for developing, updating, and completing the system and subsystem specifications, interface control documentation, specification trees, and test requirements. Interface control requirements and drawings should be established, coordinated, and maintained. Changes to these documents are maintained and disseminated to all appropriate participating engineering groups.

During final configuration item or subsystem requirements definition, systems engineering uses the specifications as a mechanism to transfer information from the systems requirements analysis, system architecture design, and system design tasks. Joint sign-off’s of specifications by the specification author and the detailed designer pertaining to systems engineering and the design engineering disciplines assures understanding and buy-in. The specifications should assure that the requirements are testable and are stated at the appropriate specification level.

Specialty engineering functions participate in the systems engineering process in all phases. They are responsible for reliability, maintainability, testability, producibility, parts control, human factors, safety, and design-to-cost. Specialty engineering shall be involved in the issuing of design criteria, and the monitoring of the progress of the design and performance analysis to assure the design requirements are met.

During requirements verification, systems engineering and test engineering verify the completed system design to assure that all the requirements contained in the requirements specifications have been achieved. Tests conducted to verify requirements are performed using hardware configured to the final design.