Both future space exploration, such as the Artemis program and journeys to Mars, and future lander missions will require thermal control systems (TCSs) with the ability to adapt to a wide range of thermal loads due to vastly fluctuating external temperatures. Current TCSs that employ radiators can achieve a turndown ratio (defined as the ratio of the maximum to minimum heat rejection rates) of 12:1 by utilizing regenerative heat exchangers and a two-loop fluid system, both of which are heavy and complex. However, future missions will demand radiators that can provide turndown ratios of 12:1 while remaining light, functionally passive, and simply designed. Previous work has investigated using shape memory alloy (SMA) components in single-loop, single phase radiator prototypes to achieve efficient designs. Preliminary analysis shows that torque-tube based radiators can enable turndown ratios as high as 40:1. 

In this paper, the design, fabrication, and testing of an SMA torque tube-driven radiator prototype is discussed. The SMA torque tube is attached to a heat rejecting panel that resembles current flat radiator panels seen on the International Space Station. As the temperature of the fluid increases, indicative of an adverse change in thermal environment, heat rejection load, or both, the SMA torque tube actuates and rotates the panel, modifying its radiative performance features and allowing for more radiative heat rejection to occur. This new design matures the concept past a previous prototype that merely demonstrated actuation under single-phase (e.g. liquid water) flow. The current radiator prototype has been designed to function not only with closed-loop single phase fluid flow, but also in conjunction with a two-phase TCS and even as a thermosiphon. Both approaches take advantage of phase transformation to improve overall TCS efficiency and decrease complexity. During testing, a heated two-phase working fluid was circulated through the system, resulting in a maximum angular actuation of  67 degrees, thus demonstrating two-phase operation for the first time.  These results give confidence that an SMA torque tube-driven radiator can outperform current radiators as development continues. 


Development and Experimental Demonstration of a Shape Memory Alloy-Based Adaptive Two-Phase Radiator for Space Applications

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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