<p><br />I think a critical mistake we're making here is assuming we only want to mine asteroids for Earth. It seems to me that we've got plenty of material to support whatever we may need (in terms of bulk cheap/recycleable materials such as aluminum or iron at least; rare minerals may have some demand), but these things are grossly expensive to move <font style=""> from Earth to Space</font>. <br /><p><br />If our interest in space continues to expand, if we begin to make a permanent presence there with a significant population, we are going to need a lot of the cheap crap (al, fe) for structures. This is where it will become cost effective to mine asteroids because doing so will (could, i should say) be more cost effective than moving it up from Earth. In essence, I believe that the materials industry in space will exist to support our other industries in space, our orbital "drydocks" and habitats, our oxygen and water, all of these things will be brought from the surrounding space rather than hefted on the backs of heavy boosters.</p></p>