Thermal Control for Exploration Study (TC-Explore-STUDY)

Two-phase heat transfer thermal control refers to the method of managing and controlling temperature in a system by utilizing the heat transfer properties of two-phase fluids. A two-phase fluid involves both liquid and vapor phases, such as when a liquid boils and forms a vapor. This type of thermal control system is particularly effective in applications requiring efficient heat removal, as it can handle large amounts of heat with relatively small temperature changes. Two-phase heat transfer thermal control offers the ability to transfer more heat, with smaller temperature drops and less pump power, and offers potential freeze tolerance and higher heat rejection turn down. However, managing the balance between liquid and vapor phases can be difficult. Factors like pressure, temperature, and the working fluid properties must be carefully controlled to ensure optimal performance since managing the balance between fluid and vapor phases, especially in microgravity, can be difficult. Passive two-phase thermal control (heat pipes, etc.) has been routinely used on flight systems at a tactical level.  However, a quantitative assessment of how active (mechanically pumped) and advanced passive two-phase systems can be leveraged at the architectural scale for a spacecraft-level “thermal bus" has been lacking since pre-ISS days. The abilities to share and re-use heat dissipations across the spacecraft and efficiently reject or conserve such heat when the mission phase calls for it can result in mission-enabling savings in resources.  Such claims depend on the mission parameters, and given the substantial advances made and the key role that thermal management plays in future missions, a focused study is needed to assess that applicability to identified shortfalls and to determine the possibilities, metrics, and areas for future focus.

Advantages of Two-Phase Heat Transfer: High Efficiency: The phase change allows large amounts of heat to be transferred with relatively small temperature changes, making it highly efficient. Compactness: Two-phase systems can be designed to be more compact compared to single-phase cooling systems because they can remove heat more effectively per unit of fluid. Heat Transfer Enhancement: Boiling and condensation provide significant enhancement in heat transfer rates compared to single-phase heat transfer mechanisms.This study task examines active and passive two-phase thermal control systems (TCS) relative to the state-of-the-practice and will specifically target nuclear heat rejection, habitat thermal control, surface rovers surviving the lunar day/night, and ISRU and science platforms.  Because of the system-wide nature of TCS that can realize cascading benefits, the study will include effects to/from other subsystems to assess resource impacts. From this effort, an appropriate, i.e., widely applicable, point-design can be formulated for use in a concurrent engineering environment (e.g., GSFC's Integrated Design Center or JPL's Team-X) as an independent assessment of benefits.

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