View source for Life Cycle Model

The Life cycle model is one of two methodical concepts that build the basis for system engineering. Next to the Problem-Solving concept, which deals with the challenge of developing solutions for project management challenges, the Life Cycle Model aims to structure the life of an engineering system.
The model divides the life cycle in four phases, which include development, realisation, utilisation and disposal. 
Each phase is defined by a distinct a set of criteria, purpose and expected results. This allows for evaluation of technical systems according to their current life cycle phase.

== Historic Background ==

The Life Cycle Model can not be clearly attributed to a single author (ref Bonnal). A range of similar models have been presented by A Guide to the Project Management Body of Knowledge (PMBOK® Guide) (PMI Standards Committee 1996) and the Project Management Handbook (Cleland & King, 1988).
This articel is based on the work of Rainer Züst and Peter Troxler (ref), who propose the use of the Life Cycle Model in a Systems Engineering Context.

== The Life Cycle Phases ==

=== Development Phase ===

This early phase is crucial fro the development of any Engineering System. Decisions are taken which will influence the whole life cycle while at the same time the inlfuence on the system itself is decreasing. (ref 5) (maybe add picture)

consists of four steps:
*Proposal for systems design
The proposal for systems design originates at the recognition of a need for change. The change may require an improvement of an Engineering System or its new development. Based on an assessment of the need, the decision wether or not to solve the issue is taken.
*Preliminary study
The preliminary study aims to provide a broad picture of the challenge. It might include elements like stakeholder investigation and system demarcation. The target of the preliminary study are a clear problem description and a set of objectives which shall be addressed by a potential solution. Possible solutions are developed which will be concretised during the main study. 
*Main study
*Detailed study

=== Realisation Phase ===

=== Utilisation Phase ===

=== Disposal Phase ===

== LCM example ==
maybe integrated in phases

== Alternate Use of Life Cycle Models ==

Life Cycle Models are usually featuring similar phases as described above, but as their use-context and perspectives differ, the content of each phase might be subject to change. Following examples make use of the Life Cycle Model but are not related to Systems Engineering.
*Life Cycle Model in a sustainability context. It creates the basis for Life Cycle Sustainability Assessments and Life Cycle Management. Does include the stage of material extraction and is focussed on environment, business and social impacts of a product system (ref 3).
*Product Life Cycle. The life cycle from a business point of view. May include issues such as innovation diffusion, maturity of product/market (ref 2)

== References: ==

how do I make those work?

#Züst, Rainer, and Peter Troxler. “No More Muddling Through: Mastering Complex Projects In Engineering and Management”. No More Muddling Through: Mastering Complex Projects in Engineering and Management (2006): 1-185. Web.
#Klepper, S. (1996). Entry, exit, growth, and innovation over the product life cycle. AMERICAN ECONOMIC REVIEW, 86(3), 562-583.
#UNEP-SETAC. Towards Life Cycle Sustainability Assessment. 2011
#Bonnal, Pierre, Didier Gourc, and Germain Lacoste. “The Life Cycle of Technical Projects.”. Project Management Journal 33.1 (2002): 12. Print.