Helium3

³He (a.k.a. Helium 3) provides clean and effective fuel for nuclear fusion engines. It is usually mined from the upper layers of gas giants.

Helium3 mining
Extracting 3He from the upper layers of a gas giant (the only commecial source available) was done using skimming aerostats in 2062-2090. Afterwards these were replaced by the more effective cloudscoops, aspiration facilities anchored to an asteroid in very low orbit.

Helium3 mining is typically done by Edenists, attended by a proportional number of bitek habitats, but the Kulu Kingdom and some of the independent habitats have their own operations.

The books use the spelling "He₃", but this is an incorrect way to symbolize the isotope of helium with two protons and one neutron, as indended. "He₃" would be a molecule composed of three Helium atoms (just like well known O₃, ozone, or O₂, regular oxygen), which is not even possible in practice.