A thermal switch is a passive variable conductance device used to regulate the temperature of spacecraft components in the highly fluctuating thermal environment of space. Current commercially-off-the-shelf (COTS) thermal switch solutions do not exist and custom products that are offered are expensive with long lead times. It has been suggested that Shape Memory Alloys (SMAs) could be utilized in a thermal switch to make them less expensive and simpler to create. Recognizing the opportunity to fill this technology gap, the SMA Thermal Switch Technical Investigation at MIT Lincoln Laboratory aims to create a low size, weight, and cost thermal switch with shorter lead times compared to the current state of the art solutions offered in the market. The general space application selected to demonstrate this technology is to regulate the lithium-ion battery pack of a CubeSat operating in low-earth orbit (LEO), though it could easily be adapted to lunar or deep space environments. This paper describes the design of parameters desired for ordering a custom SMA, a survey of providers, and the selection process of a two-way SMA for space application. Models were created to estimate the conductivity changes in the switch, estimating a 118:1 turndown (on:off) ratio. For the given application, this results in a reduction of heater duty cycle from 48.6% to 2.2%. Additionally, an introduction to a novel test setup for characterizing the dimensional change of a two-way SMA in Belleville washer form is provided, along with accuracy calculations, and results of the characterization testing.
Lopez et al. (Sun,) studied this question.