System life cycle

System Life Cycle is the sequence of stages and states that a system goes through from the moment a need for it arises until its final decommissioning. The system life cycle is viewed not merely as a time interval of existence, but as a process of sequential transitions of the system from one state to another under the influence of external and internal factors.

Definition

According to standards:

System life cycle - the evolution of the system of interest over time, from conception to retirement (GOST R ISO/IEC 15288 - 2005)
Life cycle — not a time period of existence, but a process of sequential changes in state, caused by the type of actions performed (R 50-605-80-93).

Life Cycle Phases

The system life cycle is typically divided into a series of key phases that reflect the main stages of its development, implementation, and support. The set of phases may vary slightly across different methodologies and standards, but the following general stages are often distinguished:

Needs Definition (Requirements Gathering and Analysis) — Identifying the tasks and conditions that the system must satisfy. At this stage, the system's objectives are formulated, and the customer's requirements and the specifics of its operating environment are clarified.
Concept (Conceptual Design) — Developing the general idea and architectural concept of the system. A conceptual project sketch is created, implementation feasibility is assessed, and preliminary models and diagrams are developed.
Development (Detailed Design) — Elaborating on technical solutions and creating design documentation. At this stage, specifications are refined, and drawings, software code, and other system components are developed.
Production (Manufacturing and Assembly) — Manufacturing, assembling, and testing a prototype or a production model of the system. Here, the finished product is created based on the developed documentation, and acceptance tests are conducted.
Operation — Deploying the system into its working environment and using it for its intended purpose. This includes commissioning, personnel training, and monitoring the system's performance in real-world conditions.
Support (Maintenance) — Performing technical maintenance, updates, and modernization of the system during its operation. This involves repair work, troubleshooting, and implementing new versions and improvements.

Decommissioning (Disposal, Retirement) — Planning and executing the processes for discontinuing the use of the system. This includes dismantling, disposal, or preservation of the system, as well as transferring experience and final data for analysis.

Life Cycle Models

Various modeling approaches are used in systems engineering to describe the life cycle. Among the most well-known models are the Waterfall, V-Model, and Spiral models:

Waterfall Model — A traditional linear approach where development phases follow one another without looping backtechtarget.com. Each stage (requirements analysis, design, development, testing, etc.) is completed before the next one begins. The Waterfall model is well-suited for projects with clearly defined and stable requirements, where a strict sequence of stages is important.
V-Model — An evolution of the Waterfall model, represented in the shape of a "V". In the V-Model, each development phase corresponds to a verification (testing) phase. For example, the "design" phase is paired with the "integration testing" phase, and "coding" with "unit testing." This model emphasizes the importance of verifying and validating results at each stage and is often used in critical domains (aviation, aerospace, and military technology).

Spiral Model — An iterative, risk-oriented approach proposed by Barry Boehm. The project is divided into several cycles ("spirals"), each of which includes planning, risk analysis, implementation, and evaluationen.wikipedia.org. After each iteration, the requirements and results are refined, allowing for flexible responses to uncertainty and mitigation of critical risks. The Spiral model combines elements of the waterfall, iterative, and prototyping models, applying them based on the nature of the project.

NASA Life Cycle Model

According to the NASA approach, the system life cycle is an organized sequence of phases and decision-making control gates aimed at ensuring systematic management of the development, implementation, operation, and decommissioning of a system throughout its existence.

Life Cycle Stages and Phases

Pre-Formulation Stage:

Pre-Phase A (Concept Studies): Generation of a broad range of ideas and alternatives, assessment of feasibility, and preliminary requirements.

Formulation Stage:

Phase A (Concept and Technology Development): Development of the mission concept, technical requirements, and preliminary technology assessment.
Phase B (Preliminary Design and Technology Completion): Preliminary design and completion of necessary technology development, establishing baseline system requirements.

Implementation Stage:

Phase C (Final Design and Fabrication): Final design and fabrication of system components.
Phase D (System Assembly, Integration and Test, Launch): Assembly, integration, and testing of the system, followed by preparation and launch.
Phase E (Operations and Sustainment): Operation and maintenance of the system's functionality during the primary mission.
Phase F (Closeout): Mission completion, system decommissioning, analysis of collected data, and disposal of components

Features of the NASA Approach to Life Cycle Management:

Key Decision Points (KDPs): Reviews and checks are conducted at the boundaries between phases, where decisions are made about the project's continuation or termination.
Technical and Management Processes: In each phase, technical processes (design, verification, validation, etc.) and management processes (risk, configuration, interface, and technical data management) are implemented.
Documents and Plans: At each stage, technical and management documents are created and updated, such as the Systems Engineering Management Plan (SEMP), integration and testing plans, and operation and maintenance manuals