The development and validation of a capability to perform quantitative, physics-based analysis of alternatives of conceptual unmanned, reusable lunar cargo lander architectures is discussed. The lander is conceptualized as a suite of disciplines that need to be sized, synthesized, and optimized for a mission. As such, models of these disciplines were developed and integrated in a recently-developed multi-disciplinary analysis and optimization framework for space systems. The development of the disciplines, as well as how they are integrated into the framework, is discussed. Additionally, validation studies were performed against the Descent Module of the Altair lunar lander.