Nobody has yet mentioned Helium-3, though it's related to your asteroid mining point. Helium-3 is used in fusion and seems to be the "free energy" replacement f

Nobody has yet mentioned Helium-3, though it's related to your asteroid mining point. Helium-3 is used in fusion and seems to be the "free energy" replacement for petrochemicals that we need. China and the USA have both stated that they have sights set on Helium-3 mining on the Earth's moon, though China appears to be much more serious about it than the United States. I personally believe that Helium-3 will be the thing that causes a gold rush into space.