At present, both the astronaut's metabolic heat and that produced by the Portable Life Support System are rejected to space by a sublimator that consumes up to 8 pounds of water per use; the single largest expendable during an eight-hour EVA. Unfortunately, this will not be acceptable for lunar and interplanetary missions where resupply is difficult. We can greatly reduce the water consumption by radiating most of the heat load to space. However, a radiator rejects heat at a relatively constant rate, whereas the heat generation rate depends on the workload. Without a way to match the heat removal rate, the astronaut could alternately suffer both heat exhaustion and frostbite. Therefore, TDA Research, Inc. proposes to regulate the heat rejection rate with a freezable heat exchanger. In Phase I we will conduct tests to show that the heat transfer rate can be self-regulated from high to low heat loads and vice-versa. Our research institute partner, Portland State University, will design zero-g loop heat pipes to transfer heat from the heat exchanger to the radiator. In Phase II we will design and build a full-scale freezable heat exchanger and lightweight radiator and evaluate its performance in an environmental vacuum chamber.