For what it’s worth, I just redid my calculations with the best figures I could find.
The comparison of energy density to lignite was just about the same as the calculations I remembered doing a year or two ago—average thermal energy density assuming complete fusion of the He3 present in lunar soil of about 6 megajoules per kilogram, as compared to 15 or so for average lignite. I found references to speculation that at the edges of cold traps where sunlight never falls near where the sunlight makes it you might have levels six or seven times that.
Something was apparently wrong with my old heat capacity calculations, though. The heating of crustal minerals by 300 kelvin or so would only take about a quarter of a megajoule per kilogram. Though that’s still a twelfth the thermal energy used in ONE step at point-of-intake assuming perfect capture and efficiency, and at least a quarter of the extractable energy you could get out of a heat engine driven by such a reaction. Regardless of the particular numbers, the mere fact that it’s going after an energy source several times less dense than the worst of the fossil fuels on another planet, requiring infrastructure that has not been invented for both extraction and energy-production, has often made me wonder why the meme persists.
For what it’s worth, I just redid my calculations with the best figures I could find.
The comparison of energy density to lignite was just about the same as the calculations I remembered doing a year or two ago—average thermal energy density assuming complete fusion of the He3 present in lunar soil of about 6 megajoules per kilogram, as compared to 15 or so for average lignite. I found references to speculation that at the edges of cold traps where sunlight never falls near where the sunlight makes it you might have levels six or seven times that.
Something was apparently wrong with my old heat capacity calculations, though. The heating of crustal minerals by 300 kelvin or so would only take about a quarter of a megajoule per kilogram. Though that’s still a twelfth the thermal energy used in ONE step at point-of-intake assuming perfect capture and efficiency, and at least a quarter of the extractable energy you could get out of a heat engine driven by such a reaction. Regardless of the particular numbers, the mere fact that it’s going after an energy source several times less dense than the worst of the fossil fuels on another planet, requiring infrastructure that has not been invented for both extraction and energy-production, has often made me wonder why the meme persists.
Lalartu has a good response below.