Figure 4. The original fusion reactor.

1. Helium is created in the sun. In space, helium is struck by cosmic rays. Cosmic rays knock out neutrons from helium, turning it into helium-3. Stray neutrons strike other helium atoms, creating more helium-3. 2. Diverted by Earth’s magnetic field, helium-3 collects on the moon.  3. Heating rock and soil releases helium and helium-3.