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. But you don't have to worry about that unless you want to; the game is organized around a simpler concept called 'burns.'

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.

The technology is mature, dependable, and supported by nearly two centuries of industrial development.

Chemical Drive Spacecraft by Function

Launch Vehicles

Launch vehicles exist for one purpose: escaping a planetary gravity well. They produce enormous thrust for a very short period of time and consume tremendous amounts of fuel in the process.

Examples include the Apollo Saturn V, modern SpaceX launch vehicles, and the MAV from The Martian.

Typical characteristics include:

• immense thrust
• enormous fuel consumption
• short operational life
• rarely travel beyond Low Earth Orbit

Once their job is finished, launch vehicles have usually delivered either cargo or another spacecraft into orbit.

Orbital Vehicles

Orbital vehicles move people and cargo between stations, moons and colonies. Since they never have to fight Earth's gravity, they can carry enough propellant for repeated trips without becoming excessively large.

Typical characteristics include:

• chemical propulsion
• moderate fuel capacity
• relatively inexpensive
• the workhorses of the Earth-Moon system

The Long Beach Transfer Shuttle is a typical orbital vehicle. It routinely carries passengers between Luna and the Lagrange colonies.

Fans of The Expanse can think of Uncle Mateo's ice miner or the crowded Belt Transit Ferry that Detective Miller uses between Ceres and Eros. Those vessels are somewhat more advanced than those found in the In-System setting, but they fill a similar role.