2008-01-2111 A Freezable Heat Exchanger for Space Suit Radiator Systems James A. Nabity, Georgia R. Mason and Robert J. Copeland TDA Research, Inc Luis A. Trevino NASA Johnson Space Center Copyright © 2008 SAE International ABSTRACT During an ExtraVehicular Activity (EVA), both the heat generated by the astronaut’s metabolism and that produced by the Portable Life Support System (PLSS) must be rejected to space. The heat sources include the heat of adsorption of metabolic CO 2 , the heat of condensation of water, the heat removed from the body by the liquid cooling garment, the load from the electrical components and incident radiation. Although the sublimator hardware to reject this load weighs only 1.58 kg (3.48 lbm), an additional 3.6 kg (8 lbm) of water are loaded into the unit, most of which is sublimated and lost to space, thus becoming the single largest expendable during an eight-hour EVA. Using a radiator to reject heat from the astronaut during an EVA can reduce the amount of expendable water consumed in the sublimator. Radiators have no moving parts and are thus simple and highly reliable. However, past freezable radiators have been too heavy. The weight can be greatly reduced by placing a small and freeze tolerant heat exchanger between the astronaut and radiator, instead of making the very large radiator freeze tolerant. Therefore, the key technological innovation to improve space suit radiator performance was the development of a lightweight and freezable heat exchanger that accommodates the variable heat load generated by the astronaut. Herein, we present the heat transfer performance of a newly designed heat exchanger that endured several freeze / thaw cycles without any apparent damage. The heat exchanger was also able to continuously turn down or turn up the heat rejection to follow the variable load. INTRODUCTION At present, both the astronaut’s metabolic heat and that produced by the Portable Life Support System (PLSS) are rejected to space by a sublimator that consumes up to 3.6 kg (8 lbm) of water [1]; the single largest expendable during an eight-hour extravehicular activity (EVA) [2]. This will not be acceptable for long duration Lunar and interplanetary missions where resupply is difficult. The amount of water lost to sublimation can be greatly reduced by radiating most of the heat load to the ambient environment. MISSION NEED FOR SPACE SUIT RADIATORS A space suit radiator can replace the PLSS covering with very little net increase in weight and yet will cut the amount of water needed to cool the astronaut during an EVA by up to 2.7 KG (6 lbs). This will represent a significant cost savings to future missions. As an example, the assembly of the International Space Station (ISS) has required approximately 1920 EVA hrs so far [3]. The cost to transport the cooling water needed during EVAs was about $20M assuming a cooling water consumption rate of 0.45 kg/h and an approximate launch cost of $22,000/kg to transport the water to the ISS. A space suit radiator would have lowered this cost by $15M. However, the costs to transport cooling water increase by about 12X for Lunar and 26X for Mars surface EVAs [4], which will make it prohibitively expensive to carry water just for cooling. In- situ sources of water may be available, but the costs to recover are not known. For Lunar and Mars EVA missions the reduction in water loss is not merely nice, it is essential. Current plans for Lunar exploration place an outpost and the majority of EVA missions at the poles, which has an ideal environment for the use of a radiator. It will be highly effective, since the sink temperatures of space and the Lunar surface are both cold and not subject to large fluctuations in temperature. Incident solar energy will not heat the radiator surface due its low absorption in the visible spectrum. FREEZABLE SPACE SUIT RADIATORS While the advantages of radiators have long been recognized (they can operate effectively in Earth orbit, trans-Lunar, trans-Martian, and in most Lunar and Mars environments), they have a problem that has so far prevented their use on space suits: current simple