This non-radioactive fuel is well sought after in fusion energy because it provides a cleaner and safer means of generating a lot of energy. However, there’s a catch: helium-3 is rare on Earth, though it has been found on the surface of the Moon, accumulated over billions of years by the solar wind.
Extraction of helium-3 from the lunar surface is not an easy task, and it is expensive. According to the lunar rock samples, helium-3 is present in the lunar soil, or regolith, in an amount of only 10 ppb. To obtain usable quantities would mean having to mine large swaths of the lunar surface and inventing exotic equipment to extract the isotope from the moon dust.