Speaker
Description
NASA seeks new technologies that will facilitate low-mass and highly reliable thermal control systems for the solar system. There is interest in developing thermal control technologies that will enable crewed habitats to survive and operate through the lunar night for extended periods of time on the lunar surface where temperatures range from -193 °C or lower in shadowed regions (including night) to 120 °C at the equator. In addition, these technologies would allow habitats or pressurized rovers to operate in all these environments, transit from Earth to the Moon as well as Deep Space while meeting requirements like reduced mass, volume, and power usage, avoiding thermal control heaters, micrometeoroid and orbital debris (MMOD) robustness and protection potential, high heat rejection turndown ratio, freeze tolerance and low toxicity.
In response to the above stated requirements, Advanced Cooling Technologies, Inc (ACT) develops a high turndown ratio, freeze-tolerant and passive Variable Heat Rejection Radiator for Planetary Surface and Space Habitats based on multiple Non-Integrated Hot Reservoir Variable Conductance Heat Pipes (HR-VCHPs). Figure 1 shows a CAD design of the proof-of-concept prototype that is currently in development. Habitat waste heat is acquired by a single-phase pumped loop (SPL) using a benign fluid and further transferred to a series of these VCHPs charged with ammonia (or propylene depending on freezing and toxicity requirements) and argon (or neon, again, depending on the freezing requirements) that in turn transfer the heat (with self-adjusting resistance) to the radiators for ultimate rejection. In addition, the HR-VCHPs, which mainly consist of aluminum extrusions, will be flexible/deployable because of stainless steel bellows inserted as adiabatic sections that would also act as thermal barriers during survival. Therefore, the passive high turndown ratio of the system is provided by the following three components:
1. The hot biased reservoir that, by its nature, provides high sensitivity to the NCG front motion to modulate the conductance.
2. The fact that ammonia freezes relatively early during sink temperature decay (especially during the Lunar night)
3. The bimetallic section/bellows that, in addition to flexibility, acts as thermal barrier significantly reducing the parasitic dry conductance of the HR-VCHPs during low sink temperatures/survival.
An additional feature that would significantly contribute to control and survival power savings is the use of the Non-Integrated HR-VCHPs. It means that the VCHP reservoirs are installed inside the habitat on the SPL upstream of each corresponding evaporator. During survival conditions, to minimize parasitic conduction, the reservoir may need to be heated with a low control power to further push the NCG front all the way into the evaporator. This control power/energy will remain inside the habitat, and, at most, will count as habitat survival power to compensate for the already minimized conduction based parasitic leaks.