# Agile Stage-Gate Approach for Design, Integration, and Testing of a 1U CubeSat
## 1 Introduction
Even though many results highlight the weaknesses and risks in the model, as requirements can change during the execution of the project, this pragmatic approach, in practice, facilitates communication among team members [8]. When requirements are not clear, iterative methods are a better option for handling a project. In these methods, the designs are constantly assessed, and, therefore, new additions can be integrated, producing a better match according to evolving requirements. The iterative approach is useful for simple systems. One of the most dominant iterative models is the V model, which improves over time from requirement identification to conceptualization, design, integration, and testing because this model allows for iteration and recursion. The main disadvantage of the V model is its inability to respond to changes \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Number of satellites & 48 \\ Orbital altitude (km) & 1414 \\ Orbital inclination (\({}^{\circ}\)) & 52\({}^{\circ}\) \\ Orbital planes & 8 \\ Satellite by orbital plane & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of the first-generation GlobalStar constellation. during the life cycle. Thus, an issue in the design discovered during implementation can lead to a setback. Unlike Stage-Gate projects, the V model encourages activities in parallel but can be rigid and not as flexible as desired [9]. On the other hand, Agile methods taken from the software industry are now used in some manufacturing industries. In many projects, definitions and actions change as the project proceeds. Stage-Gates do not offer adaptability as the nature of the method is simple and linear. Agile methods address collaboration, responses to changes, and working products. An Agile methodology starts with a design and adds capabilities through iterations, thereby facilitating changes and feedback. The Agile Stage-Gate combines both the Stage-Gate and Agile approaches. This approach is considered a hybrid model that offers the best of both systems [10]. A general development process approach is usually focused on design, integration, and verification through testing or analysis. Some case studies have been applied to CubeSat projects. One such study was developed by the University of Patras. The Patras team successfully manufactured a CubeSat structure that was later verified by testing and analysis [11]. After testing the new structure, the researchers were able to meet the requirements imposed by the EU-funded FP7-QB50 project. The AztechSat-1 model also utilized sequential verification though its various stages. However, development of this model also involved iterative reviews by experts from NASA and members of the team to make improvements that could help in the development of the nanosatellite in the early stages with no great changes. AztechSat-1's verification via testing and analysis was accomplished only after applying an Agile Stage-Gate approach to ensure a higher rate of success. However, some authors have taken a different approach and proposed the creation of an integration and validation method for nanosatellites. The nanosatellite ISTSat-1 was also developed following an iterative approach, offering verification of unfinished prototypes and proving highly useful for educational projects. However, no flight results are yet available [12]. AztechSat-1 was already tested and verified, and its mission was proven to be successful. As stated in research on the ISTSat-1 nanosatellite, it is possible to implement an iterative model for a development process. AztechSat-1 uses a hybrid model for both sequential and iterative approaches in the same model for product development. Our literature review of the development of CubeSat missions also underscored the idea of presenting a hybrid framework for software development in academic nanosatellite missions whose results highlighted the simplification of processes and documentation for the Libertad-2 nanosatellite [13].