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Completed TRL 3 (started at 3, targeting 6)
Project Objective
The objective is to design, build, test, and optimize a thermal switch for passive thermal management of avionics.
Project Description
The long-term goal of this project is to create a technology that will allow the operation of electronics in extreme thermal environments while minimizing power consumption. In order to do this, a thermal switch will be developed and optimized through thermal vacuum testing. By isolating variables and variation of the design, we can achieve a high turndown ratio. The turndown ratio is the ratio of conductivity of the switch in its open and closed state.
Once this design is optimized and understood, a test article will be sent to operate outside the international space station as a proof of concept.
With a proof-of-concept and operational parameters, an energy savings for a given mission can be calculated. That energy savings can then be converted to a mass savings for a given battery system.
Project Results and Conclusions
The project was a great success. All objectives for the period of performance were met or exceeded.
Two different designs were tested, a design that used a wax motor and a design that used coefficients of expansion. In addition, multiple heat pipe designs and thermal interface materials were tested. By combining the best design characteristics, a turndown ratio about 70:1 was achieved.
After the design was optimized, a test electronics box and enclosure were designed, built, and tested to represent the box that would be sent to the international space station. The testing of the full electronics enclosure with the switch on the printed circuit board showed that the turndown ratio drops significantly due to the circuit board mounting and electrical wiring. In the full enclosure, the ratio dropped to 10:1.
Going forward, a new enclosure will be designed to maximize insulation and increase the turndown ratio.
This investment is for the further development of an innovative passive thermal switch mechanism which helps to regulate the temperature of printed circuit boards (PCBs) in extreme thermal environments via variable heat rejection capabilities. There are multiple STMD capability gaps addressed by this project. In the category of Advanced Avionics Systems, this project addresses STMD gap ID AV 447. This technology will help to create electronics that can operate over a wide temperature range. The technology will reduce the amount of energy needed to keep the electronics warm during lunar night. In the category of Advanced Thermal, this project addresses STMD gap ID THERMAL 483, 604, 1132. The ability to have variable heat rejection on small independent payloads with high efficiency heat pipes will allow for better power management. The technology can make each avionics box easier to manage thermally as it can isolate or conduct as needed.
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