Lunar Water Extraction Using Cryogenic Feedstock as a Cold-Trap Heat Sink

Thermal extraction of water from lunar polar regolith requires heating large masses of cryogenic soil and then removing the same latent heat again at a cold trap. Published system designs reject that condensation heat to radiators or chillers. This article proposes routing it instead into the incoming feedstock through an indirect heat exchanger. Because regolith excavated from permanently shadowed regions arrives near 40 K, well below a typical cold-trap temperature of 200–220 K, the transfer is spontaneous and needs no heat pump. A steady-state heat balance using the temperature-dependent heat capacity of Apollo soils shows that condenser-to-feed integration alone reduces the ideal extraction heat by 17–38% across ice contents of 1–10% by mass. Combined with conventional recuperation from spent regolith, the reduction is 21–59%. Integration also compresses the energy penalty of low-grade deposits: ideal heat varies by a factor of 1.6 between 1% and 10% ice, against 3.0 without heat recovery. Below about 1.4–2.4% ice, depending on cold-trap temperature, the feed can absorb all condensation heat and the cold-trap radiator can be eliminated. A targeted review of the literature found no prior description of the concept. A bench experiment to measure the governing heat-transfer coefficient is proposed.