The betterment of Space Shuttle Environmental System Consumables Analysis Program (ESCAP) has been in progress by the determination and incorporation of a newly' developed structural heat loss model. Heat exchange apparently exists among components, orbiter structure, and space/sun/earth. This results in a net heat loss from the orbiter to space for most cases. The heat losses have been correlated to flight parameters in attitude and duration, beta-angle, altitude, and power level. This has corrected a long-standing over-estimation of ATCS heat rejection and heat sink inlet temperatures. It also improves performance prediction of radiators and the subsequent supply water management. Therefore, this work is regarded as a major breakthrough that enables the STS community to perform pre-flight and post-flight studies, thermal analysis tasks, and real-time console support with high fidelity for Space Shuttle missions.