Systems Engineering Life Cycle
Systems engineering activities for a typical project have been discussed by categorizing the timeline cycle into several sections. The time duration of each section depends on the project. Following is a life cycle model proposed in INCOSE SE Handbook:
This phase deals with coming up with the concept for the system. The design begins with understanding the need behind the design, understanding the set objectives and coming up with our expectations of the final product or prototype. The design should start with writing needs into more formal statements known as requirements. Needs are informally, qualitatively expressed expectations from the final design. It is necessary to translate them into formal statements which make more sense from a technical perspective. Requirements are statements which are quantifiable. Concept stage also involves the planning of the project. Various aspects regarding the activities to be performed for the successful execution of the project are laid out.
Development phase deals with coming up with a detailed set of plans for realising the system. Designers have to come up with a number of possible methods which can be utilised in solving the problem at hand. It is possible to explore various new alternatives, some of them could be non-conventional. Various elements of a system are identified. System elements are specified, analyzed and designed. These elements link with each other and form the system. Interfaces between various system elements are understood. These elements are now to be realized. A suitable manufacturing process is to be selected. A detailed plan for manufacturing, integration, verification and validation is made.
The system is realized in this phase. Manufacturers are selected. Vendors are contacted and inventory is procured from them. Required design files like circuit board designs, CAD files etc are to be made for manufacturing. It's necessary to verify these design files before forwarding them to manufacturing. Appropriate tolerances are to be assigned. Once the circuit boards, mechanical parts etc are manufactured, it's important to check whether they have been made as per the requirements. Some tests are performed to test the circuit boards, mechanical parts etc are manufactured as per the specifications.
Utilization and Support
In the case of satellites, this phase is the mission life of the satellite. It has to perform its basic life sustenance activities as well as payload activities for which the mission is designed. Support activities are those which ensure continual service by the system. Some satellite missions require orbit-keeping maneuvers or uplink of certain parameters after regular intervals. Some diagnostic tests may need to be performed, in order to identify an issue, in case the satellite starts deviating from the nominal performance. In the case of a satellite, so far, there are no provisions to have a repair and maintenance mission to be sent up to the satellite. However, there have been such missions to the Hubble Telescope for repair and maintenance.
Over the past few decades, with ever-increasing orbital launches, “space debris” has become a critical issue. We may choose to either retire before its mission life in case of onboard malfunction or extend the mission life based on the system performance towards the end of its stipulated mission life. It may either be automatic or telecommand based. There are various international regulations in place in order to manage and reduce the space debris. Many satellites have dedicated infrastructure onboard for deorbiting.
Vee - Model
All of the major phases of the life cycle model are often visualized with a graphical ‘Vee’ (or V) model representation of the processes and stages of a program development (See figure). Although there might be overlapping stages & processes within the different phases of the system life cycle model, the sequence of processes depicted in the graphical ‘Vee’ model are designed to provide a structured framework for completing the design and verification of a system.
As depicted, the phases begin from the upper left section, and subsequently are worked downward to the center, and then upward again onto the upper right side.
The initial phases of the life cycle model, as mentioned earlier, capture the system-wide requirements, various elements of the system, as well as concepts for realising the system.
As the system matures, the processes of the Vee model proceed towards the center of the Vee, and more details of the system are documented until the production phase begins.
Through the process of functional decomposition, which involves defining a system in functional terms, and then defining lower-level functions and sequencing relationships from these higher level systems functions, the system can be designed as pure functions. Therefore such functions can be reused, or replaced. This allows for the interfaces between blocks to become simple and generic. Such simple interfaces makes it easier to replace a pure function with a related, similar function. By ensuring this methodology, the team is capable of specifying the whole system, its subsystems and/or parts, and their interrelations effectively. Such a top-down approach enables for a thoroughly designed physical assembly.
The subsystems at the intermediate levels are important for managing complex systems, because these activities allow the team to introduce complex details one step at a time. When the team completes the analysis of all the subsystems and their interrelated components, they reach the bottom of the Vee model.
Turning the corner of the Vee model, all the required components/parts are manufactured and assembled according to the system specifications. As the components begin to be tested and brought together into larger subsystems, the stages in the figure are shown moving towards the upper right side of the Vee model.
The model is completed with the complete testing of the system to ensure all of the specified requirements are met - the Verification & Validation of the system.
If there is a need for the project to continue the next version development, the process will start with the Vee again.
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