To explore strange new worlds...
The Electric Thruster is the game's first thruster.
It costs 3 
Hydrogen Tank to build and takes up only one tile.
It needs 3 
Power to run at full efficiency and produces 600 units of thrust.
Its tiny footprint, negligible build cost, and low power requirement make it easy to place in large numbers. A mere 4 electric thrusters will provide more speed than a single Plasma Thruster, consume less power, and take up half the space (including the wires). These same traits also make it ideal for planetoid disposal builds.
A single Magnetoplasma Thruster, however, will outperform a bank of Electric Thrusters of the same volume in terms of both power and performance.