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Model-Based Systems Engineering (MBSE) is a key practice to advance systems engineering that can benefit CubeSat missions. MBSE creates a system model that helps integrate other discipline specific engineering models and simulations. The system level model is initiated at the start of a project and evolves throughout development. It provides a cohesive and consistent source of system requirements, design, analysis, and verification. The International Council on Systems Engineering (INCOSE) Space Systems Working Group (SSWG) established the Space Systems MBSE Challenge team in 2007. The SSWG Challenge team has been investigating the applicability of MBSE for designing CubeSats since 2011. Our application of MBSE uses System Modeling Language (SysML), a graphical modeling language. SysML is used to model all aspects of a system either directly or through an interface with another model. SysML diagrams are used to describe requirements, structures, behaviors, and parametrics from the system down to the component level. The first phase of SSWG CubeSat project created a CubeSat reference model that was applied to the Radio Aurora Explorer (RAX), a three-unit CubeSat developed by SRI International and the Michigan Exploration Laboratory at the University of Michigan. The second phase focused on expanding the RAX CubeSat model to include modeling behaviors and interfacing with several Commercial Off the Shelf (COTS) simulation tools. The third phase was comprised of two activities. The first was the development of a CubeSat Enterprise Model to capture cost and product Iifecycle aspects for the mission spacecraft and problem domain. The second activity incorporated additional design and operational characteristics into the RAX model. The modeling effort starts anew in this fourth phase and has two objectives: 1) Develop a CubeSat Reference Model that other projects can use as a starting point for their mission specific CubeSat model. The space and ground systems, subsystems, and components are being modeled throughout the entire project Iifecycle. 2)Develop a CubeSat Project Model that models how CubeSat design and development are to be accomplished. The first objective is in response to: "Model-based systems enj!ineerinj! (MBSE) is the formalized application of modelinj! to support system requirements, desij!n, analysis, verification and validation activities bej!inninj! in the conceptual desij!n phase and continuing throughout development and later life cycle phases." The second objective is in response to: "A MBSE methodology is a collection of related processes, methods, and tools used to support the discipline of systems engineering in a 'modelbased' or 'model-driven' context." The effort to date has been focused on establishing nomenclature; the incorporation of the stakeholders and their needs, objectives, measures of effectiveness; and the architecture down to the logical subsystems. The next step is to determine the level of model definition at each of the Iifecycle stages and to create models for the concept and development phases. The CubeSat Reference Model will be rolled-out in a controlled fashion to make certain that model is understandable and useful. The requests and applications of the model have fallen into two categories: 1) Using the model within an aerospace engineering course and 2) evaluating the application of MBSE within an aerospace program.