Because of the high cost of electric power and other consumables, new technologies are being considered for manned Space Station heat transport. At the same time, continuing use of safe, well understood, and reliable cooling system technology, which has been developed for STS, Skylab, and Spacelab manned compartments, is recognized as the benchmark for evaluation of this new technology.This paper describes trade studies comparing advanced technology two-phase thermal transport concepts with presently used pumped liquid concepts. Systems meeting equal design requirements, with each suboptimized for minimum effective launch weight, are compared. Two-phase heat transport shows significant, but not overwhelming, potential for savings in launch weight.The two-phase heat transport concept has been further investigated by developing a preliminary flight design. The heat loads and thermal bus layout, heat exchanger conceptual designs, and general schematic diagram for such a system are described herein.