One of the oldest propulsion systems to be used in outer space, a combustion-based thrust system involves the burning of liquid propellant (fuel, in other words. Older variants of this system use gasoline, newer ones use a combination of gasoline, liquid oxygen and liquid nitrogen). The burning propellant is expelled at extreme speed from engine, producing thrust. The CTD is essentially rocket technology. Top speeds in deep space may reach up to 55,000 kilometers/hour, significantly faster than Ion-based drives. However, the CTD requires a far more demanding source of fuel than Ion Drives do, and as such, is suitable only for use with starfighter-sized craft - anything larger would use far too much fuel to be even remotely cost-efficient. The exhaust from combustion drives has also shown to have a corrosive effect on the ozone layer of planets, meaning that it is best used in outer space only.