The ENVISAT ASAR antenna is 10 meters in length in the deployed configuration and consequently thermal balance testing was impossible due to TVAC chamber size and MGSE limitations. Therefore the verification of the ASAR active antenna thermal design was based mainly on analysis complemented, when necessary, by thermal balance tests at subsystem level on key components. This approach called up for extensive sensitivity analyses, taking into account the fact that all of the design, orbital parameters, operational scenario and mathematical simulation are subject to uncertainties. Special emphasis was put on assessing the impact of uncertainties on albedo and earthshine for low time constant components of the ASAR antenna which is facing the Earth. Predictions of temperatures and heater power needs were based on a chain of thermal mathematical models starting at components level and ending up at system level, relying upon reduced models integrated into upper level detailed models and built from various software packages, viz. ESATAN, TMG, ESABASE, THERMICA. This heterogeneous chain led to systematic uncertainties on model predictions which were carefully assessed.