Active Thermal Switching OHP Radiator for Lunar Science

The number one shortfall identified by NASA technology is the ability to survive and operate through the lunar night. ThermAvant Technologies (TAT) proposes a freeze-tolerant thermal switching Oscillating Heat Pipe (OHP) assembly using a low toxicity working fluid and freeze tolerant azeotrope working fluid to address the challenge posed by S16.05. NASA SBIR S16.05 calls for new capabilities in thermal management for long-duration lunar science, especially focused on surviving the lunar night with temperature excursions as low as -213°C for as long as 14 days, with low toxicity radiator working fluids, and gravity independent performance. TAT proposes to demonstrate the following capabilities not found in State of the Art (SOTA) radiator systems: Thermal conductance ratio of ON to OFF (or turn down ratio) in excess of 600:1. 240:1 has been demonstrated by TAT under a privately funded effort. TAT radiator panels will have a reservoir into which working fluid may be condensed (emptying the OHP and lower conductance) when an OFF condition is desired. This fluid reservoir will be managed with low power heaters to ensure reservoir stays warmer than the OHP when an ON condition is required and by turning the heaters off to allow reservoir to cool below radiator temperature and begin condensing fluid into the reservoir when OFF condition is desired. Calculated conductance in case study (ref Fig 1), is 2.27 W/K when the OHP is ON and 0.0033 W/K when OFF resulting in 688:1 predicted turn down ratio. This will be achieved with a 58% reduction in specific mass and 62% reduction in areal density compared with SOA radiator systems increasing lunar science SWaP-C as reduced mass reduces launch costs.

Key target of the proposal is to address lunar missions, especially to survive the lunar night with excursion temperatures as low as -213C. I.e. related to Civil Space Shortfalls 1618: Survive and Operate Through the Lunar Night. The proposed solution will also enable many other missions by addressing Civil Shortfalls 1622 and 1624. Specifically, Kilowatt Class Fission Power Systems for surface missions to the moon and Mars. Kilowatt-class Energy Conversion for Small Fission Reactors. ThermAvant worked with NASA, in 2020, on High-Efficiency Electrified Aircraft Thermal Research (HEATheR) demonstrating a thermal skin for heat dissipation from high power electronics. Any spacecraft in process (e.g. Orion Spacecraft, Lunar Gateway) which plans to leverage thermal radiators could benefit from improved efficiency and reduced parasitic losses of herein proposed solution. The most likely near-term, non-NASA end uses of the proposed large-format, high-temperature (and high heat transfer capacity) panels are within the Department of Defense (DoD). ThermAvant is currently supplying leading DoD agencies and prime contractors with OHP-based heat sinks and heatspreaders. DoD agencies and contractors are keenly interested in higher temperature radiators and large format heat sinks to take advantage of GaN-based power amplifier technology in airborne and space-based platforms without size, weight or power (not to mention performance) drawbacks of status quo thermal management approaches that rely on either actively pumped coolant or relatively low heat flux, low capacity CCHPs. Specific military applications for OHP radiators for GaN-based power electronics include radar, electronic warfare systems seeking greater RF or microwave power insmaller packages that can operate at interface temperatures above 400 K without the efficiency or reliability risks associated with conventional GaAs-based power electronics. ThermAvant is presently engaged on several Active Electronically Scanned Arrays (AESA) projects for both military and commercial applications with multiple OHPs on-orbit and many more in production through 2026. These current high TRL and MRL solutions do not involve freeze tolerant, non-toxic working fluids, nor do they include thermal switching to reduce parasitic losses. This proposed Phase I will enable these increased capabilities and expand the market opportunity for Oscillating Heat Pipe Radiators with these commercial and military applications as well as with NASA.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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