The fact that bombarding lithium with neutrons produces tritium that decays into helium 3 (this reaction is actually responsible for a good fraction of the yield of many fusion warheads, see Castle Bravo). And the helium 3 on the moon is A—on the moon, B—of such a low concentration that the total thermal energy possible to get from fusion of absolutely all the He3 present per cubic meter of the top foot or so of lunar soil is about a quarter that of the worst lignite coal on Earth. And lignite requires a hell of a lot less energy and infrastructure per unit mass to process. By my calculations, given the heat capacity of the minerals it has been blasted into by the solar wind, you need to use at least half that energy on site just to heat the rocks to the point it gets driven off as a vapor. Then there’s all the movement of mass, purifying it down non-terrestrially from all kinds of other vapor, ridiculous launch costs… its not happening.
I’ve seen claims in several internet sources, a video documentary and the Wikipedia article that some countries have had plans to mine helium-3 on the moon. I wonder if the reporting is incompetent or if the plans are made by incompetent optimists if what you’re saying is true. How did this meme originate?
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.
Nobody has plans (in business meaning of term) to mine helium-3 on Moon. This idea was first proposed by Gerald Kulcinski in 1989. He gave very optimistic predictions regarging D-He3 fusion, underestimated cost of lunar mining and ignored possibility of specialized reactors for producing He3. Since then idea is pushed by space advocates.
The fact that bombarding lithium with neutrons produces tritium that decays into helium 3 (this reaction is actually responsible for a good fraction of the yield of many fusion warheads, see Castle Bravo). And the helium 3 on the moon is A—on the moon, B—of such a low concentration that the total thermal energy possible to get from fusion of absolutely all the He3 present per cubic meter of the top foot or so of lunar soil is about a quarter that of the worst lignite coal on Earth. And lignite requires a hell of a lot less energy and infrastructure per unit mass to process. By my calculations, given the heat capacity of the minerals it has been blasted into by the solar wind, you need to use at least half that energy on site just to heat the rocks to the point it gets driven off as a vapor. Then there’s all the movement of mass, purifying it down non-terrestrially from all kinds of other vapor, ridiculous launch costs… its not happening.
I’ve seen claims in several internet sources, a video documentary and the Wikipedia article that some countries have had plans to mine helium-3 on the moon. I wonder if the reporting is incompetent or if the plans are made by incompetent optimists if what you’re saying is true. How did this meme originate?
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.
Nobody has plans (in business meaning of term) to mine helium-3 on Moon. This idea was first proposed by Gerald Kulcinski in 1989. He gave very optimistic predictions regarging D-He3 fusion, underestimated cost of lunar mining and ignored possibility of specialized reactors for producing He3. Since then idea is pushed by space advocates.