Developing a CubeSat Model-Based System Engineering (MBSE) reference model — Interim status #2

Model-Based Systems Engineering (MBSE) is a key practice to advance the systems engineering discipline. The International Council on Systems Engineering (INCOSE) established the MBSE Initiative to promote, advance, and institutionalize the practice of MBSE. As part of this effort, the INCOSE Space Systems Working Group (SSWG) Challenge Team has been investigating the applicability of MBSE for designing CubeSats since 2011. The goal of the team is to provide a sufficiently complete CubeSat Reference Model that can be adapted to any CubeSat project. The INCOSE Systems Engineering Vision 2020 defines MBSE as “the formalized application of modeling to support system requirements, design, analysis, verification and validation activities beginning in the conceptual design phase and continuing throughout development and later life cycle phases.” At the core of MBSE is the development of the system model that helps integrate other discipline-specific engineering models and simulations. The team has been creating this system model by capturing all aspects of a CubeSat project using the Systems Modeling Language (SysML), which is a graphical modeling language for systems engineering. SysML diagrams are used to describe requirements, structures, behaviors, and parametrics from the system level down to the component level. Requirements and design are contained in the model rather than in a series of independent engineering artifacts. In the past three phases of the project, the team has created the initial iteration of the reference model, applied it to the Radio Aurora Explorer (RAX) mission, executed simulations of system behaviors, interfaced with commercial simulation tools, and demonstrated how behaviors and constraint equations can be executed to perform operational trade studies. The modeling effort starts anew in this fourth phase. The CubeSat Reference Model starts with an identification of potential stakeholders. A stakeholder is any entity that has an interest in the system including sponsor, end user, procurer, supplier, and regulatory agencies. The each stakeholder's needs, objectives, constraints, and measures of effectiveness are incorporated in the model. Constraints are those items fixed and not subject to trades such as mission budget and schedule. One of the stakeholders is the Cal Poly CubeSat project. The Cal Poly CubeSat Specification has been populated into its own SysML model to enable the content of the specification to be related to the CubeSat Reference Model. The CubeSat mission enterprise consists of the space system, ground system, launch services, launch vehicle interface system, and communication services. Since the reference model is being developed by a team effort, there is an obligation to protect the investment of time and knowledge of each team member. There also needs to be a licensing environment that is conducive to a user organization supporting the development of and use of the model. There will be a license that allows for non-commercial use and prohibits incorporating the model or model features into a commercial product.