# Micro-Satellite Systems Design, Integration, and Flight
## 2 Systems Modeling of the CubeSat  
### Function-Centric Models  
The design process [31; 32] began with a context diagram of the CubeSat nanosatellite. The context diagram shows the external and internal interfaces to track resource usage from start to finish and set clear interface boundaries. The modeling approach followed the systems models created by [PERSON] and [PERSON] in the book \"Principles of Systems Science\" [33].  
A concept diagram, as defined by [PERSON], identifies the sources, sinks, stocks, and interfaces of a system. These were first found externally. Figure 3 presents the \"Black Box\" of the CubeSat system. Here, all of the system inputs and outputs can be easily seen. The inputs are labeled as sources, as shown on the left of the diagram. The sinks are shown going out of the system to the right. In equilibrium, there is conservation of mass and energy across the system. See Figure 3.  
The function that a resource flow goes through is represented by the F values in Figure 3. The M indicates a movement of data inside the function. Table 1 explains what the functions in Figure 3 mean.  
A useful way to analyze the system is to divide it into smaller parts and see how they influence each other. The products that are produced in the \"Black Box\" can be by-products, waste products, catalysts, or reaction intermediates that help achieve the intended functional requirements. By understanding the interactions between subsystems  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variable/Acronym** & **Definition** & **Variable/Acronym** & **Definition** \\ \hline F1 & Solar panel & F3 & Thermistor \\ F2 & Ambient light sensor & F5 & Gyroscope \\ F6 & Malfunctions/damage & F8 & RF transceiver \\ F7 & Torque coils & F9 & Dissipated light \\ F10 & Dissipated heat & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: System top-level black box interfaces.  
Figure 3: Black box diagram ([PERSON] and [PERSON], p. 604 [33]).  
and their products both inside and outside of the system, it was possible to improve the interfaces within the software more effectively. See Figure 4.  
The IMU function that the system uses is shown in Table 2. The IMU location does not depend on any input from the environment, so there is no outside source.  
The model can also be improved to show how energy and information are transferred within the system. The internal interface diagram shows the flow, stocks, buffers, amplifiers, and valves of the model. Moreover, an internal network can map the resources and track the flows from where they begin to where they end. Then, mass and energy continuity can be followed. The internal interfaces show a complete view of every function that the CubeSat needs to do to move from its inputs to it outputs. In the center of Figure 5, S1 is visible. S1 is the buffer memory of the Teensy microcontroller. The data collected are sent to the buffer and then changed into digital data packets that are then moved through the transceiver. See Figure 5.  
Table 3 defines the processes in Figure 5 that are part of the satellite system. They handle the processing and setting up of the data packets.  
These models enabled the representation of the exchanges with the external environment and the movement of resources inside.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Variable/Acronym** & **Definition** \\ \hline F4 & IMU \\ \hline \hline \end{tabular}
\end{table}
Table 2: Immediate subsystem.  
Figure 4: Subsystem black box diagram ([PERSON] [PERSON], p. 607 [33]).