Helium-3

Helium-3 is rare on Earth. To ignite the potential of nuclear fusion, Washington-based Helion states it will produce helium-3 by fusing deuterium, which can be sourced from water.

Helium-3 can also mined since it's abundant on the Moon. Interlune, based in Seattle, is one such company working towards harvesting helium-3 and other natural resources from space.