The increasing complexity of modern space systems and stricter performance and safety requirements have highlighted the limitations of traditional document-based systems engineering, particularly in early design phases, motivating the adoption of Model-Based Systems Engineering (MBSE) as a model-centric approach. This thesis investigates the potential of MBSE for space system conceptual and early-stage design, in particular examining System Composer comparing it with other MBSE tools to assess its capability to support the standardisation and scalability of system architectures across multiple levels of abstraction, and demonstrate its effectiveness through realistic space engineering case studies. A comprehensive literature review of MBSE practices and tools has been performed together with practical modelling activities implemented in System Composer and Simulink.