Design Description and Initial Characterization Testing of an Active Heat Rejection Radiator with Digital Turn-Down Capability

Ganapathi, Gani B.; Sunada, Eric; Birur, Gajanana C.; Miller, Jennifer R.; Stephan, Ryan A.

doi:10.4271/2009-01-2419

Cited by 11 publications

(6 citation statements)

References 4 publications

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“…This morphing behavior is fully reversible; a subsequent decrease in temperature will cause the radiator to return to the minimum heat rejection shape. To maximize heat rejection in the open shape and minimize heat rejection in the closed shape, the panel is given a high-emissivity coating on the inner (concave) surface, shown with dark shading, and low-emissivity coating on the outer (convex) surface, shown with light shading 4 .…”

Section: Introductionmentioning

confidence: 99%

Coupled behavior of shape memory alloy-based morphing spacecraft radiators: experimental assessment and analysis

Bertagne

Walgren

Erickson

et al. 2018

Smart Mater. Struct.

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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.

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Section: Introductionmentioning

confidence: 99%

Coupled behavior of shape memory alloy-based morphing spacecraft radiators: experimental assessment and analysis

Bertagne

Walgren

Erickson

et al. 2018

Smart Mater. Struct.

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“…Several efforts have been undertaken to improve TCS performance through the development of variable heat rejection radiators. 5 Examples include roll-out fin radiators , 6 freezable radiators , 2 digital radiators , 7 and variableemissivity radiators . [8][9][10][11] This work supports the development of a novel type of radiator, known as a variable-geometry or morphing radiator , 12 and provides details regarding the thermal characterization of various prototypes that were built.…”

Section: Introductionmentioning

confidence: 99%

Experimental Characterization of a Composite Morphing Radiator Prototype in a Relevant Thermal Environment

Bertagne

Chong

Whitcomb

et al. 2017

25th AIAA/AHS Adaptive Structures Conference

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For future long duration space missions, crewed vehicles will require advanced thermal control systems to maintain a desired internal environment temperature in spite of a large range of internal and external heat loads. Current radiators are only able to achieve turndown ratios (i.e. the ratio between the radiator's maximum and minimum heat rejection rates) of approximately 3:1. Upcoming missions will require radiators capable of 12:1 turndown ratios. A radiator with the ability to alter shape could significantly increase turndown capacity. Shape memory alloys (SMAs) offer promising qualities for this endeavor, namely their temperature-dependent phase change and capacity for work. In 2015, the first ever morphing radiator prototype was constructed in which SMA actuators passively altered the radiator shape in response to a thermal load. This work describes a follow-on endeavor to demonstrate a similar concept using highly thermally conductive composite materials. Numerous versions of this new concept were tested in a thermal vacuum environment and successfully demonstrated morphing behavior and variable heat rejection, achieving a turndown ratio of 4.84:1. A summary of these thermal experiments and their results are provided herein.

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“…As a consequence, converting or allowing the entire suit surface to act as a radiator has been suggested as a potential means of leveraging the local environment for thermal control, and thereby reducing water mass loss associated with EVAs [19][20][21]. In addition, concepts for terraced radiators [22], shielded radiators [23,24], or selectable branch flow radiators [25] have also been proposed. A full suit radiator concept was also extended to include the use of variable infrared (IR) electrochromic materials as radiator surface coatings to achieve active control of variable heat rejection rates [26].…”

Section: Introductionmentioning

confidence: 99%

Characterizing a Transient Heat Flux Envelope for Lunar-Surface Spacesuit Thermal Control Applications

Hager¹,

Walter²,

Massina³

et al. 2015

Journal of Spacecraft and Rockets

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In this paper, a transient thermal simulation approach is used to characterize the heat flux and heat flux rates between the lunar surface and a moving spacesuit model. Five different lunar-surface settings are simulated with craters and boulders at three solar elevation angles (θ 2, 10, 90 deg). Heat fluxes and rates are evaluated for different parts of the suit and different characteristic tasks along a given path. The simulated paths are based on Apollo mobility studies. The results indicate that, at lower solar elevation angles, which imply lower lunar-surface temperatures, the thermal impact of surface features becomes more pronounced. In all simulated cases, and for more than 85% of the time, the infrared heat fluxes vary at rates below 20 W · m −2 · s −1 . The incidence versus magnitude of infrared heat flux rates follows a power law with a negative exponent. Smaller heat flux rates have a higher occurrence at lower surface temperatures, and vice versa. The created lookup tables with task, solar elevation angle, and incident heat fluxes can be used as a baseline in the design and sizing of thermal control hardware for moving objects on the surface of the Moon. Nomenclature

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Design Description and Initial Characterization Testing of an Active Heat Rejection Radiator with Digital Turn-Down Capability

Cited by 11 publications

References 4 publications

Coupled behavior of shape memory alloy-based morphing spacecraft radiators: experimental assessment and analysis

Coupled behavior of shape memory alloy-based morphing spacecraft radiators: experimental assessment and analysis

Experimental Characterization of a Composite Morphing Radiator Prototype in a Relevant Thermal Environment

Characterizing a Transient Heat Flux Envelope for Lunar-Surface Spacesuit Thermal Control Applications

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