Promethium

Promethium is a refined combination of highly volatile hydrocarbons and a thickening agent. It is highly efficient for its use-case, and has largely entirely replaced the crude and ineffective fossil fuel that powered Earth thousands of years ago. 
Promethium is used to power anything from sublight engines to the missiles used for GOMP launchers. Along with being highly efficient, Promethium is also cheap and widespread throughout the entire orion arm. While some planets might lack the hydrocarbons neccessary for its production, there are many, like Ignis, that are rich in the neccessary ingredients.
Promethium does have the downside of being a polluter, especially when it is burned in great amounts planetside. Industrial or city planets usually avoid using promethium as a power source for this reason, though some still do like Kalvus, causing a thick smog to hang in the atmosphere.

Type

Metamaterial