There are 3 types of drives that can be mounted on a ship hull.

Small vessel drives are usually mounted onto the fighter and bomber. They are light and cheap.

Capital Ship Drives are mounted onto the freighter, colonizer, destroyer, corvette, carrier, battleship, probe, and space station. They are large and heavy, but needed to move the bigger ships around.

An experimental drive which can only be mounted to a corvette or space station. They are even larger than a capital ship drive, and sacrifice maximum range for much greater speed. Useful for interception, or pushing a station into position a little more quickly.

There are two key metrics in the drive specifications that determine a drive's base level of performance.
* Meganewtons of thrust - This determines how much power is available to drive a ship of a given mass (more thrust more speed)
* Endurance - simply a relative number in the thousands that can be used to compare how much range a given drive has compared to other drives for a given ship mass (the higher the endurance number, the further a ship can go)