AMA performs physics-based spacecraft vehicle design and analysis to develop concept-level and preliminary designs tailored to mission requirements. We size all major spacecraft subsystems using first-principles engineering models, empirical mass estimating relationships, and custom analysis tools to produce accurate vehicle mass and performance estimates. Our integrated Python-based modeling environment enables seamless coupling with mission design and trajectory analyses in Copernicus, allowing rapid iteration between vehicle design and mission performance. For unique or emerging technologies, we develop new physics-based subsystem models as needed, and structural sizing is performed using analytical methods or higher-fidelity finite element analyses with NASTRAN/Femap and Hypersizer when appropriate.