Globally distributed in surface regolith; higher concentrations in mature regolith on the lunar maria
Solar-wind-implanted isotope unique to airless bodies. Theoretical fusion fuel that produces no neutrons (clean aneutronic fusion). Interlune (US) and others have raised funds on the thesis. Current applications: medical imaging (MRI), neutron detection, cryogenics — all served adequately by Earth-sourced ³He from tritium decay or natural-gas fields.
No commercial fusion reactor exists. D-³He fusion has higher ignition temperature than D-T fusion, and D-T fusion has not yet achieved commercial breakeven. At 4 ppb average concentration, extracting 1 kg of ³He requires processing ~250,000 tonnes of regolith. Earth-side ³He from tritium decay costs ~$20M/kg today — substantial but not 'unobtainable.' SpaceNews has called helium-3 marketing 'separating market from marketing.'
“The scientific and technological promise of helium-3 fusion is undeniably compelling, yet the economic feasibility of lunar mining remains a formidable challenge, requiring advanced excavation, processing, and transportation infrastructure. The vision of a self-sustaining lunar economy is concrete for well-characterized resources like solar energy and regolith for construction, but the picture gets murkier with helium-3.”