Freeze Tolerant Water Heat Pipe and Thermal Switch

unar night poses a significant thermal challenge to small, low power payloads, rovers and landers. Due to the slow rotation of the lunar surface, the environmental temperature drops to below 100K for approximately 14 earth days. In order to enable long duration science missions on the lunar surface it is necessary to maintain the electronics above survival temperature during the lunar night. This requires thermal management technology with high turndown ratios, capable of rejecting waste heat during the hot lunar day and minimizing heat leaks during the lunar night. Other key features include passive operation, high reliability, and lightweight. Variable conductance heat pies (VCHP) and thermal switches can achieve many of these goals but come with drawbacks. For example, ammonia VCHPs require bulky reservoirs of gas and stainless-steel envelopes to achieve the high turndown ratio, and many thermal switches are limited in how much power they can transport. In this SBIR program, Advanced Cooling Technologies will develop a freeze-tolerant water-based heat pipe that uses freezing of the working fluid as a thermal switching mechanism to provide a high turndown ratio (>1000:1). ACT’s innovative approach to freeze tolerance will enable the heat pipe to survive an indefinite number of freeze/thaw cycles without experiencing damage due to the expansion of freezing water. The thermal switching feature enabled by freezing the working fluid results in a highly versatile thermal management device with many advantages for lunar applications as well as other space missions and terrestrial uses.