Many of the interstellar spaceships that leave Earth in science-fiction literature and reach out to explore the unknown make use of a fusion-drive propulsion system. The fusion drive, also known as impulse drive, is a propulsion system that works on the classical Newtonian reaction principle and is used for subphotonic flight (i.e. velocities less than the speed of light). The propulsive medium is composed of electrically charged particles, which are compressed and accelerated to the speed of light before they leave the spaceship’s propulsion system.

The term fusion drive arises because the particles being accelerated are a byproduct of the fusion reactors, which are used to produce the energy for the spaceship. As the “fuel output” of the fusion reactors is limited, additional "fuel" – often in the form of Bismuth atoms – can be injected into the propulsion system if more thrust is required. This system is then often introduced as the spaceship’s “afterburner”. Fusion drives are used in the “Star Trek” series, “Star Wars” movies, “Perry Rhodan” novels, and in many other science-fiction books, computer games and films.

Although humanity has not been able to utilise the enormous power of the fusion reaction for energy generation, a fusion-drive system might not be so far off. Fusion reactors have one major problem: they have to hold the plasma particles together long enough for several fusion reactions to be established, generating enough energy to sustain the heating and confinement of the plasma. A fusion drive would also need to support several fusion reactions, but it does not need to be as efficient as a fusion reactor, as the main purpose of the fusion reaction is to heat up the plasma particles to extremely high temperatures. As the temperature of the plasma particles increases, the velocity with which they are streaming out of a magnetic nozzle increases also, thus creating a very effective propulsion system.

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