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Analyzing systems using functional analysis has been the mainstream for systems engineering for five decades. With the advent of object oriented software methods and the object management group's (OMG) Unified Modeling LanguageTM (UML), a number of systems engineers working on software intensive systems began to apply use cases and object oriented analysis and design (OOAD) methods to large scale, complex systems. While the use of these OO methods is still controversial within the systems engineering community, many systems engineers that apply OO methods effectively have used functional analysis and understand the strengths of both methods. FireSAT is a well known fictitious system of systems space mission to provide a space based approach to wildfire detection, monitor and control. This paper will explore the use of OOAD methods to FireSAT for problem definition, concept development, and system architecture development. Using the OMG's recently adopted System Modeling LanguageTM (SysML) and more traditional Systems engineering modeling techniques, this paper will compare and contrast some of the differences between OO and functional methods, showing diagrams from each approach.