Distillation of H2O from hard-frozen Martian permafrost
The authors present a method for distillation of hard-frozen Martian permafrost. A cable-tool is drilled into hard frozem permafrost to a depth of 10 to 20 m. They calculate that a 10 m hole could be drilled in a few days. A 10 m shaft with a diameter equal to the bore is inserted into the hole, and a air tight tent-like structure is erected over the borehole. Photovoltaic cells mounted on the tent supply electrical energy that is dissipated in the shaft. Drilling power can be supplied by other sources. With 1000 watts, the shaft can be heated to near 350 K, producing relatively high temperatures in the vicinity of the borehole. Surrounding H2O is vaporized and diffuses up through the regolith. The authors calculate that a tent of a radius of no more than a few meters would intercept most of the H2O as it diffused to the surface. Calculations suggest that it would require perhaps 30 days to extract H2O from most of the volume drained by this technique. Assuming that the hard frozen regolith is no more than 10 percent ice, the author's calculate that that about 2890 kg of H2O could be extracted in 30 days. Since the nominal requirement for each crew member is about 5 kg/day, one such borehole might be expected to supply enough H2O to maintain a crew of 5 for perhaps 100 days. Additional engineering studies will be done to attempt to improve the capacity or efficiency of this method.