Applying Model-Based Systems Engineering (MBSE) to Develop an Executable Model for the RAX CubeSat Mission

Small satellite missions are becoming increasingly complex, particularly with the emergence of interplanetary and constellation mission architectures. These architectures are challenging to model, design, and optimize because they have ambitious goals, highly contained resources, coupled vehicles and subsystems, and must operate in stochastic environments. There is a need for rigorous and automated analytical system-level modeling and simulation capabilities to support the design and analysis of existing and upcoming mission concepts. Thus, we present an executable Model-Based Systems Engineering (MBSE) representation of a CubeSat mission. The model formally captures the physical and functional elements of a complete spacecraft mission using a standard, modular, and extensible approach to enable the end-to-end execution of realistic mission scenarios. We present a foundational model of a small spacecraft mission in No Magic’s MagicDraw, a visual representation of Systems Modeling Language (SysML), which enables systems engineers to capture, communicate, and analyze designs. The model includes the spacecraft, ground network, external environment, experimental target, and control software; as well as the interactions between these elements. The model represents both physical and logical perspectives of the mission, and model visualization is provided by appropriate SysML diagrams. Spacecraft subsystems required for operational analysis are captured, including the Communication, Power Collection, Power Management, Data Management, Payload, and Bus subsystems. Spacecraft states, such as on-board energy, on-board data, and downloaded data, are modeled in the context of their interaction with the subsystem functions. The SysML model is connected to appropriate simulation tools to achieve high-fidelity analytical modeling of orbital, energetic, and behavioral dynamics. Systems Tool Kit (STK) from Analytical Graphics, Inc. is used to model spacecraft orbits, calculate opportunities to download to ground stations and collect data from targets of interest, and compute the power collected by spacecraft solar panels. Behavioral models describing subsystem functions and state evolution are captured in MagicDraw in activity, state machine, and parametric diagrams. Design requirements are also represented in the modeling environment to ensure traceability of mission requirements and objectives. Model execution is critical to evaluate mission performance throughout an entire planning horizon to verify that mission requirements are satisfied. This ultimately enables accurate analysis and comparison of candidate design solutions. For example, ensuring the minimum science data is successfully collected and downloaded requires a complete end-to-end simulation and accurate modeling of subsystems, states, and opportunities. The SysML model is integrated with analytical orbital models and prediction capabilities from STK, behavioral models, and scheduling capabilities, and executed using No Magic’s Cameo Simulation Toolkit and Phoenix Integration’s ModelCenter. We demonstrate execution of the modeling environment by developing a Radio Aurora Explorer (RAX) CubeSat instance of the model and simulating a realistic mission scenario. Finally, we demonstrate parametric trade studies using the executable model which support the design and optimization of future mission vehicles and operations