Researchers and space enthusiasts see helium-3 as a perfect fuel source
"Fusion research began in 1951 in the United States under military auspices. After its declassification in 1957 scientists began looking for a candidate fuel source that wouldn't produce neutrons. Although Louie Alvarez and Robert Cornog discovered helium 3 in 1939, only a few hundred pounds (kilograms) were known to exist on Earth, most the by-product of nuclear-weapon production.
Apollo astronauts found helium 3 on the moon in 1969, but the link between the isotope and lunar resources was not made until 1986. 'It took 15 years for us [lunar geologists and fusion pioneers] to stumble across each other,' said Schmitt, the last astronaut to leave footprints on the moon. "