Robust Two-Phase Cooling Technology for Megawatt Space-Based Systems

After 20 years serving the American space thermal control systems amicably, the leading capillary-pumped heat transport technology - Loop Heat Pipes (LHPs) - has finally run out of capacity to offer the ever-increasing demand for spacecraftpower. LHPs contained no mechanical moving part to wear out or break down, hence, highly reliable for space applications. The simplest and most rational approach was to employea mechanical pump to augment the capillary pumping head of the LHP. In fact, NASA Goddard had tried in in the 1980s time frame and the results were not very well-received simply because the mechanical pumps especially the gear-type were notoriously unreliable, lasting no more than 1,000 hours of service. In 2004-2005, TTH Research Inc. introduced an Advanced concept of LHP - called Advanced LHP or A-LHP - in which any pumping device could be utilized to assist the capillary pumping. One variant of the A-LHP called for a bearingless pumpto be added in-line to the LHP liquid return line. Since the bearingless pump was originally developed for the bio-medical technology as a blood pump, it could not withstand the high fluid pressure of Ammonia. Nevertheless, a Freon 11 breadboard test unit was constructed and performance tested and the results were very encouraging. Subsequent efforts to design an Ammonia version of the Freon 11 pump ended up in a complete failure and the researched had to be put a shelf for 10 years. In 2015, by sheer serendipity, another type of bearingless pump manufactured by Levitronix was discovered. The pump was of centrifugal (impeller) type having a single impeller embedded with permanent magnets to (i) employ magnetic levitation (MagLev)to suspend itself in the fluid while inside a hermetically-sealed casing AND (ii) be magnetically driven by an external electro-manetic motor. The MagLev allowed liquid to flow through without impedance. More importantly, more than one unit can be used for redunancy or enhanced capacity. After serving the space thermal control systems amicably for the last 20 years, the current leading heat transport technology - Loop Heat Pipes - may finally runs out of capacity to continue as the ever-increasing demand for spacecraft power.  Now that with the NASA Artemis program planned a base camp for humanity on the Moon, the transport requirement all of the sudden jumps at least one order-of-magnitude higher.  The simplest and most logical approach is to add a mechanical pump to an existing LHP to augment the capillary pumping head.  Unfortunately, attempted was made in the 1980s to flight qualified a mechanical-pumped two-phase loop (TEMP2A3 flight experiment).  Unfortunately, the mechanical pumps at the time were notoriously unreliable for space use.  A type of bearingless pump based on magnetic levitation (MagLev) to "float" a lone impeller in the fluid withing the confine of the hermetically-sealed housing.  The result is is very reliable, durable even without matintenance. To design and construct a demonstration test unit to verify the functionalities of the proposed concept of Hybrid Loop. The final deliverables shall be the Phase I test unit, test data and all other documentation.

Every NASA space missions would require some amount of thermal control and management of the onboard payloads.  The LHP provided that service to NASA since the early 2000s for the transport requirements of 1 few hundreds Watt-meters to more than 10kW-m.  But now with NASA Artemis program planned to establish a base camp for humanity on the surface of the Moon, requiring at least one-order-of-magnitude enhancement of heat transport over the existing LHP.  The Hybrid Loop was proposed for that purpose as a consequence. Besides NASA, the U.S. Departments of the Air Force and the Navy maintain their own fleet of satellites.  They have the same needs as NASA as far as space missions are concerned.  In addition, with the All-Electric initiative, high power electronics as well as electric vehicles (EV), surface ships, even air planes are need the heat transport capacity of systems like the Hybrid Loop.

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