A U.S. Laboratory-A (U.S. Lab-A) payload rack has two primary thermal control systems designed for cooling payloads: a water cooling system and a distributed avionics air cooling system. This paper gives an overview of the rack-level thermal control systems available in a U.S.Lab-Arack. This paper also presents an analysis of the existing sensible payload heat removal capability of the laboratory module cooling system.In the U.S. Lab-A, all payload rack locations are configured as per the international Standard Payload Rack (ISPR) configuration. This paper begins with an overview of the ISPR with emphasis on the liquid and air cooling interfaces. An overview of both the liquid and air cooling systems is presented, showing general capability and limitations, payload rack flow control modes and optional payload rack thermal configurations.Performance data showing a sample overall system-level thermal energy balance is presented. An important result of this energy balance is the determination of the net sensible heat load on the U.S. Lab-A module's cabin air heat exchanger. The cabin air heat exchanger, while it functions as the primary heat removal system for cabin sensible and latent heat loads, also functions as a secondary heat removal system for payloads.