Abstract: The silicon Tracker, a charge particle core detector in the Alpha Magneto- spectrometer, requires a cooling system to provide a working condition. This cooling system must be small in size, strong for its cooling ability and temperature control precision, even in the complex thermal, and microgravity environments on the international space
station. In this paper, the attempt of design optimization of the condenser in the CO$_2$ two-phase thermal control system for such purpose is introduced, by employing thermal simulation analysis with SINDA/FLUINT. Because of the specific radiator, different design of the configurations of condenser inlet are investigated, by contacting the inlet at 1st, 2nd, 5th heat pipe and out of all heat pipes on the radiator. The result shows that with different configurations, the inlet part will have different effect on the heat transfer part of the condenser, which will cause the outlet temperature of the condenser different. It also tells that contacting the inlet at the 2nd heat pipes shows a best result for either reducing the anti-freezing power in cold case or guaranteeing enough subcooling of the pump inlet in the hot case.