A study is being conducted to design, develop, fabricate, integrate, and test a preprototype coolant loop subsystem for an advanced extravehicular mobility unit portable life support system for Space Station Freedom. The overall function of the coolant loop is to remove metabolic and equipment heat loads and provide a comfortable thermal environment for a crewperson during extravehicular activity. The heat loads are transported by water circulating through a liquid-cooled ventilation garment. The thermal environment is regulated using thermal capacitive and/or radiative control. After use, the system must be capable of regenerating relatively rapidly. The key component in the coolant loop is the thermal sink, which is a completely nonventing unit comprising cold-plate heat exchangers, a radiator to reject a fraction of the generated heat load, and a regenerable thermal storage unit to absorb the remaining heat load. No embedded thermoelectric devices are required.