## 4 Preliminary Design of the 3 ColStar KiboCUBE mission. ### 3 ColStar KiboCUBE Agile Methodology Implementation  
Since the Manifesto for Agile Software Development was introduced in 2001, Agile practices have transformed how software teams create products. The Manifesto outlines a series of core values and principles aimed at enhancing software development [17]. It has led to various methodologies and frameworks like Scrum, Kanban, and Lean, along with other terms and techniques [108]. Hardware and software development involve distinct developmental tasks. While Scrum, an Agile process commonly applied to software development, might not initially appear suitable for hardware development, the apparent disparities mainly revolve around the nature and order of deliverables, rather than fundamental constraints on the process itself. Some differences in the hardware development with software development are as follows [109]:  
* Software is more malleable (easier to change) than hardware. The cost of change is much higher for hardware than for software. * Specialized hardware parts may take significantly longer to procure as compared to software. * Software products develop over time with successive releases, involving the addition of new features and the refinement of existing ones. In contrast, hardware products primarily comprise physical components that cannot be easily altered after manufacturing like software. They cannot gain new capabilities through simple modifications. * Architectural decisions heavily influence the design of a hardware product, needing a higher upfront investment in architectural planning due to the high cost of making changes later, unlike in software products. Although Agile adoption is relatively new for hardware, there are already some proposed frameworks, such as Modified Agile for Hardware Development (MAHD) [110], in which there is a section of upfront work called MAHD on ramp and then it moves on to sprints. Likewise, MAHD is not based on incremental development, but on iterative design and early validation. Another difference is that this framework uses a focus matrix to prioritize product attributes. There are several aerospace-based development projects in which the scrum methodology has been applied [111]. Other works include manufacturing and launching a cubesat [112; 113; 114]. As a result of works such as this one, a slightly deeper understanding has been gained as to whether Agile methodologies and practices are compatible with space development, given the unique characteristics of hardware development and key aspects of the space sector. As a way to shed some light on the use of Agile methods in the space systems engineering domain, we adopted Agile practices during two critical phases of the \({}^{3}\)ColStar project: the proposal structuring and preliminary design stages. The development team incorporated several general practices from Agile methodologies, including the use of weekly sprints. These weekly sprints facilitated iterative development, allowing for regular reassessment of progress, prompt identification of issues, and integration of feedback. At the end of each sprint, sprint meetings were conducted to evaluate progress, address challenges, and realign goals as necessary. Additionally, the project utilized a team-based approach with specific objectives, with sub-teams organized around different CubeSat subsystems, such as ADCS, Thermal, OBC, and Systems Engineering (SE), as illustrated in Figure 15.  
Concerning the implementation and testing stages of the \({}^{3}\)ColStar project, the development team will adopt a Scrum-inspired methodology, tailored to suit their specific needs. This approach, depicted in Figure 16a, differs slightly from the original Scrum framework. Sprints will be conducted on a weekly basis, with each team maintaining its own product backlog. Additionally, weekly scrum meetings should be held within each team to ensure effective communication and progress tracking.