View source for Chemical Drive Spacecraft

Chemical reaction drives work much like modern rockets. A fuel is mixed with an oxidizer, ignited, and expelled at high speed through a nozzle to create thrust.

The efficiency of a rocket fuel is measured by its '''specific impulse''' (usually abbreviated '''Isp'''). Higher Isp generally means that the engine can produce more change in velocity from a given amount of propellant.

By 2158, three fuel combinations dominate:

* '''Methalox''' (liquid methane and liquid oxygen). Reliable, inexpensive and widely available.
* '''Hydrolox''' (liquid hydrogen and liquid oxygen). Higher performance but considerably more difficult to store and handle.
* '''Alulox''' (aluminum and liquid oxygen). Lower performance than either methalox or hydrolox, but well suited to lunar industry because aluminum is abundant on Luna and the lower gravity makes extreme thrust less important.

Every launch vehicle uses chemical propulsion. Orbital vehicles almost always do as well. The technology is mature, dependable, and supported by nearly two centuries of industrial development.