In human spaceflight, the Environmental Control and Life Support System (ECLSS) is an essential part of a mission, as it provides the necessary conditions for sustaining life within space habitats. Designing a long-duration human spaceflight mission requires developing a highly reliable and complex ECLSS, which must be integrated into the overall mission architecture. The traditional document-centric systems engineering approach might be inadequate for managing this level of complexity. In contrast, a Model-Based Systems Engineering (MBSE) methodology could significantly improve the design, management, and traceability of such a complex system. The ECLSS design process is highly iterative and recursive, involving the evaluation of technologies and system configurations through simulations, analysis tools, and hardware/software testing.