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The system lifecycle in systems engineering is an examination of a system or proposed system that addresses all phases of its existence to include system conception, design and development, production and/or construction, distribution, operation, maintenance and support, retirement, phase-out and disposal.
Conceptual design 
The conceptual design stage is where an identified need is examined, requirements for potential solutions are defined, potential solutions are evaluated and a system specification is developed. The system specification represents the technical requirements that will provide overall guidance for system design. Because this document governs all future development, the stage cannot be completed until a conceptual design review has determined that the system specification properly addresses the motivating need.
Key steps within the conceptual design stage include:
- Need identification
- Feasibility analysis
- System requirements analysis
- System specification
- Conceptual design review
Preliminary system design 
During this stage of the system lifecycle, subsystems that perform the desired system functions are designed and specified in compliance with the system specification. Interfaces between subsystems are defined, as well as overall test and evaluation requirements. At the completion of this stage, a development specification is produced that is sufficient to perform detailed design and development.
Key steps within the preliminary design stage include:
- Functional analysis
- Requirements allocation
- Detailed trade-off studies
- Synthesis of system options
- Preliminary design of engineering models
- Development specification
- Preliminary design review
Detail design and development 
This stage includes the development of detailed designs that brings initial design work into a completed with form of specifications. This work includes the specification of interfaces between the system and its intended environment and a comprehensive evaluation of the systems logistical, maintenance and support requirements. The detail design and development is responsible for producing the product, process and material specifications and may result in substantial changes to the development specification.
Key steps within the detail design and development stage include:
- Detailed design
- Detailed synthesis
- Development of engineering and prototype models
- Revision of development specification
- Product, process and material specification
- Critical design review
Production and construction 
During the production and/or construction stage the product is built or assembled in accordance with the requirements specified in the product, process and material specifications and is deployed and tested within the operational target environment. System assessments are conducted in order to correct deficiencies and adapt the system for continued improvement.
Key steps within the product construction stage include:
- Production and/or construction of system components
- Acceptance testing
- System distribution and operation
- Operational testing and evaluation
- System assessment
Utilization and support 
Once fully deployed, the system is used for its intended operational role and maintained within its operational environment.
Key steps within the utilization and support stage include:
- System operation in the user environment
- Change management
- Maintenance and logistics support
- System modifications for improvement
- System assessment
Phase-out and disposal 
Once deployed, the effectiveness and efficiency of the system must be continuously evaluated to determine when the product has met its maximum effective lifecycle. Considerations include: Continued existence of operational need, matching between operational requirements and system performance, feasibility of system phase-out versus maintenance, and availability of alternative systems.
See also 
- Blanchard and Fabrycky (2006). Systems Engineering and Analysis, Fourth Edition. Prentice Hall. p. 19.
- Dr. Joahn Gouws (2007). Introduction to Engineering, System Engineering. Melikon Pty Ltd.
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