# Agile Stage-Gate Approach for Design, Integration, and Testing of a 1U CubeSat
## 2 Materials and Methods
### Conceptualization and Design  
In product realization, conceptualization allowed the team to extract all performance and mission requirements. Before reaching the first gate, the project had completed the following actions: Project Execution Plan, System Goals, System Model, Communication Diagrams, Verification Requirements, and Validation Requirements. The majority of CubeSats rely on commercial off-the-shelf (COTS) components to meet the required criteria. AztechSat-1 integrates both COTS and self-developed modules. Subsequently, all requirements were defined through Agile methods inside a StageGate model. The success criteria could be rearranged by the team, if necessary, to avoid losses. For the quick development of the AztechSat-1 project, rapid prototyping was also considered as a medium to visualize the results from an initial perspective. Figure 5 shows the design obtained from rapid sprint meetings during the project's early stages. The design process for AztechSat-1 began by defining requirements, as also performed in the traditional approach. Every meeting, each subsystem leader outlined the relevant requirements, advances, and improvements. Some teams developed 3D prototypes to quickly visualize the dimensions, shapes, and methods of integration. All spacecraft and payload modules were printed, starting from the beginning of the project based on a preliminary concept. Because some modules belonged to the COTS category, it was easier to identify mechanical interference. A weekly schedule was established to offer continuous feedback and proposals for improvement. At the end of the design process, all COTS and self-developed modules were already identified. The decisions made during the design process remained for the entirety of the project with only slight variations in the structure selected from a small satellite manufacturer. The following different models were prototyped: a CubeSat Structure, a module for both communications and the on-board computer, an EPS board, a total of five solar panels, and some empty modules. Decisions were based on the perspectives of experts and research proposals. In addition, 3D printing  
Figure 5: AztechSat-1 design obtained from sprints. was advantageous for engineering and other purposes [23]. The AztechSat-1 printed model is visualized in Figure 6.  
FlatSat testing: From the beginning, the AztechSat-1 team sought to mitigate risks by implementing COTS components. However, given their requirements and innovations, core mission modules were designed completely by the team. To test the self-developed subsystems, a FlatSat model was implemented. A FlatSat unit was used to reduce time and allow students to test their capabilities and training. Before wiring and assembling the modules, all participants from the AztechSat-1 team dealing with technical responsibilities were trained using empty modules in which only connectors were assembled. Verification tests were carried out to achieve communications between the intersatellite communication module and the communication module. The Agile Stage-Gate methodology was integrated into the FlatSat testing methodology so that all teams were notified of success or failure in the development of the core modules as soon as possible. AztechSat-1's mission is to allow intersatellite communication between a nanosatellite and a satellite constellation; therefore, most of the prototyping and testing relied on communication. Figure 7 highlights the implementation and use of the FlatSat unit. FlatSat testing resulted in the verification of data packet transmissions from different sizes for both intersatellite and satellite communications as well as testing of the temperature, sun, and magnetic sensors; reports on housekeeping information; and communication  
Figure 6: 3D printed version of AztechSat-1. Figure 7: AztechSat-1 FlatSat. between different modules. AztechSat-1 integrated magnetorquer actuators to work as the attitude determination and control subsystem.