There's a lot of valuable Helium-3 on the lunar surface. It's very impractical today to contemplate using it, but if materials science ever advanced enough that

There's a lot of valuable Helium-3 on the lunar surface. It's very impractical today to contemplate using it, but if materials science ever advanced enough that we could construct a space elevator, it might be feasible to do exactly that because 1 ton of Helium-3 can apparently generate 1.5x the energy of a Tsar Bomba.