Variable Geometry Radiators Using Shape Memory Alloys

The primary goal of this research investigation was to advance a novel and innovative radiator technology known as a variable geometry or morphing radiator. Such a device would employ the temperature-dependent phase change of shape memory alloy (SMA) materials in order to passively reconfigure radiator shape and thus adapt the rate of heat rejection to evolving vehicle requirements. Preliminary analytical studies have shown that morphing radiators have the potential to achieve system-level turndown ratios of at least 12:1, which far exceeds the 3:1 turndown ratio of current state of the art radiator technology and enables a single-loop thermal control system (TCS) to be used in lieu of the traditional two-loop system; adopting a single-loop TCS with a morphing radiator system could reduce TCS mass by as much as 25%. Thus, the SMA morphing radiator concept is truly revolutionary in its potential to improve several performance metrics simultaneously, including increases in system versatility and reliability as well as decreases in system mass and complexity. The research investigation was divided into two phases. Phase I focused on developing new analysis and design tools to support future design, development, and deployment of morphing radiator systems. Morphing radiators that use thermally activated smart materials (e.g. SMAs) for actuation exhibit a complex coupling between geometry and temperature which has not been widely addressed in the archival literature. Further, existing simulation tools are generally unable to model this type of coupling. A number of new analysis tools were developed during Phase I, including mathematical and finite element models at various levels of fidelity as well a custom analysis framework which can be used to simulate general problems involving morphing radiators. The resulting tools were demonstrated through several realistic example problems, including component- and system-level simulations of various morphing radiator conceptual designs. Phase II involved the design, fabrication, and testing of a morphing radiator prototype, subsequent experimental validation of the analysis tools developed during Phase I, and design studies to explore the effects of various design parameters (e.g. geometry, material selection) on the thermal and structural response of a representative morphing radiator system. The morphing radiator prototype, known as Prototype A, successfully demonstrated the desired temperatureinduced morphing behavior in a thermal vacuum chamber at NASA JSC, which represents the first known experimental testing of an SMA-actuated morphing component in a purely radiative environment. Following these experiments, two finite element models of Prototype A were developed: a thermal model capable of predicting its thermal response and a fully coupled thermomechanical model capable of predicting both its thermal and structural response. The thermal model was used to validate the implementation of radiation boundary conditions in Abaqus and to predict the turndown ratio of Prototype A: 6.4:1. The fully coupled model was used to validate the analysis framework developed during Phase I, giving additional confidence in the approach taken. In addition, parallel development of a high-conductivity composite morphing radiator panel via a NASA JSC IR&D grant enabled three additional prototypes (Prototypes B, C, and D) to be designed, fabricated, and tested in a thermal vacuum chamber at NASA JSC and also successfully demonstrated the desired morphing behavior and variable heat rejection. These tests represent an additional milestone: namely, the first successful experimental demonstration of a flexible yet highly conductive radiator panel.