Thermal control is an important aspect of spacecraft design, particularly in the case of crewed vehicles, which must maintain a precise internal temperature at all times in spite of significant variations in the external thermal environment and internal heat loads. Future missions beyond low Earth orbit will require radiator systems with high turndown ratios, defined as the ratio between the maximum and minimum heat rejection rates achievable by the radiator system. Current radiators are only able to achieve turndown ratios of 3:1, far less than the 12:1 turndown ratio requirement expected for future missions. An innovative morphing radiator concept uses the temperature-induced phase transformation of shape memory alloy (SMA) materials to achieve turndown ratios that are predicted to exceed 12:1 via substantial geometric reconfiguration. Developing mathematical and computational models of these morphing radiators is challenging due to the strong two-way thermomechanical coupling not present in traditional fixed-geometry radiators and not widely considered in the literature. Although existing simulation tools are capable of analyzing the behavior of some thermomechanically coupled structures, general problems involving radiation and deformation cannot be modeled using publicly available codes due to the complexity of modeling spatially evolving boundary fields. This paper provides important insight into the operational response of SMA-based morphing radiators by employing computational tools developed to overcome previous shortcomings. Several example problems are used to demonstrate the novel radiator concept. Additionally, a prototype morphing radiator was designed, fabricated, and tested in a thermal environment compatible with mission operations. An associated finite element model of the prototype was developed and executed. Model predictions of radiator performance generally agree with the experimental data, giving confidence that the tools developed are able to accurately represent the thermomechanical coupling present in morphing radiators and that such tools will be useful in future designs.

The addition of metallic nanoparticles to a base heat transfer fluid can dramatically increase its thermal conductivity. These nanofluids have been shown to have advantages in some heat transport systems. Their enhanced properties can allow lower system volumetric flow rates and can reduce the required pumping power. Nanofluids have been suggested for use as working fluids for spacecraft Active Thermal Control Systems (ATCSs). However, there are no studies showing the end-to-end effect of nanofluids on the design and performance of spacecraft ATCSs.In the present work, a parametric study is performed to assess the use of nanofluids in a spacecraft ATCSs. The design parameters of the current Orion capsule and the tabulated thermophysical properties of nanofluids are used to assess the possible benefits of nanofluids and how their incorporation affects the overall design of a spacecraft ATCS. The study shows that the unique system and component-level design parameters of spacecraft ATCSs render them best suited for pure working fluids. The addition of nanoparticles to typical spacecraft thermal control working fluids actually results in an increase in the system mass and required pumping power. The addition of metallic nanoparticles to a base heat transfer fluid can substantially increase its thermal conductivity. These nanofluids have been shown to have advantages in some heat transport systems. Their thermal properties allow the system volumetric flow rate to be reduced, thus reducing the required pumping power. Nanofluids have been suggested as working fluids in spacecraft Active Thermal Control Systems (ATCSs). However, spacecraft ATCSs are unique in that they have stringent temperature control requirements and use specialized heat transfer devices. In the present work, a parametric study was performed to assess the use of nanofluids in spacecraft ATCSs. The tabulated thermophysical properties of various nanofluids, the design requirements of NASA's Orion ATCS and the performance parameters of its key heat transfer components were used to assess the effects of the incorporation of nanofluids. The study shows that the unique system and component-level design parameters of spacecraft ATCSs do not lend themselves to the use of nanofluids. The addition of nanoparticles to typical spacecraft internal flow loop working fluids actually results in an increase in either the system mass or the required pumping power, the opposite of the hoped-for effect. The intermediate results obtained in the study also suggest that that the addition of nanoparticles to an external ATCS loop is not likely to result in a significant overall system benefit.

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