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We have completed preliminary tests that show the feasibility of an innovative concept for a spacesuit thermal control system using a lightweight, flexible heat pump/radiator. The heat pump/radiator is part of a regenerable LiCI/water absorption cooling device that absorbs an astronaut's metabolic heat and rejects it to the environment via thermal radiation at a relatively high temperature. We identified key design specifications for the system, demonstrated that it is feasible to fabricate the flexible radiator, measured the heat rejection capability of the radiator, and assessed the effects on overall mass of the PLSS. We specified system design features that will enable the flexible absorber/radiator to operate in a wide range of space exploration environments. The materials used to fabricate the flexible absorber/radiator samples were all found to be low off-gassing and many have already been qualified for use in space.

Refrigeration systems with parallel evaporators are prone to systemic instabilities and thermal excursions, particularly under variable loading conditions. Conventional vapor compression systems require evaporators to discharge at very high vapor qualities to prevent liquid ingress to the compressor. This requires active control algorithms to regulate the flow to individual evaporators. This paper introduces a novel liquid recirculation loop that minimizes the effects of flow maldistribution and prevents dryout using passive components. The loop utilizes a refrigerant phase separator, in conjunction with passive inlet restrictions, to mitigate flow maldistribution and support larger evaporator mass flow rates corresponding to low-to-moderate exit qualities. With greater margin in exit quality before dryout occurs, thermal excursions at the evaporator outlets are readily avoided.

Future electronics and photonics systems, weapons systems, and environmental control systems in aircraft will require advanced thermal management technology to control the temperature of critical components. Two-phase Thermal Management Systems (TMS) are attractive because they are compact, lightweight, and efficient. However, maintaining stable and reliable cooling in a two-phase flow system presents unique design challenges, particularly for systems with parallel evaporators during thermal transients. Furthermore, preventing ingress of liquid into a vapor compressor during variable-gravity operation is critical for long-term reliability and life. To enable stable and reliable cooling, a highly stable two-phase system is being developed that can effectively suppress flow instability in a system with parallel evaporators. Flow stability is achieved by ensuring that only single-phase liquid enters the evaporators.