This paper describes a computational engineering level assessment tool developed for the design and optimization of thermal management systems for advanced hypersonic and supersonic aircraft. The tool, entitled Vehicle Integrated Thermal MAnagement Code (VITMAC), simulates the coupled thermal response of the aircraft's active cooling systems, structures, fuel tanks, and engines.The tool simulates either the steady-state or transient thermal-hydraulics along coolant flow paths (distributions of mass flow rate, pressure, and temperature) together with the temperature of surrounding airframe and engine structures. A homogeneous multiphase model with a binary gas phase mixture simulates slush hydrogen in the cryotank, and includes the use of a secondary-gas ullage pressure control. A graphical user interface which enables the user to quickly construct and analyze various thermal management schemes has also been developed and incorporated into VITMAC.Sample results are discussed illustrating selected features of the code, along with comparisons to experimental data. An overview of the graphical user interface is also provided.