7 - Interstellar Propulsion Systems

Summary

There is no lack of propulsion systems available to any creatures which possess some technical competence and a desire to travel around in the galaxy. The following is an incomplete list of propulsion systems which have been suggested and studied by members of our own species.

Group A: Systems which are certainly feasible but are limited to mission velocities of the order of 10^–2c.

1. Nuclear-electric. Uses a fission reactor as energy source, and ion-beam or magnetohydrodynamic plasma jet for propulsion. One can imagine a ‘minimal starship’ using nuclear-electric propulsion, with 10^–6 g acceleration, a mass of 5 kg/kW (electric) for reactor and radiator, and a mission duration of 104 yr for voyages of the order of 10 pc.

2. Old-fashioned Orion nuclear pulse propulsion, using full-sized fission or fusion bombs. This is also limited to velocities of the order of 10^-2c but can have acceleration of the order of 1g, giving it much better performance in local maneuvers (see Dyson, 1968; Martin & Bond, 1979).

Group B: Systems which are probably feasible but require very demanding new technology. These systems should be capable of mission velocities of the order of 0.5c, and mission durations of a few decades for distances of a few parsecs.

1. 3. Laser-driven sails (see Norem, 1969).

2. 4. Microwave-driven sails (see Forward, 1985).

3. 5. Pellet-stream propulsion (see Singer, 1980).

4. 6. Direct electromagnetic launch (see Clarke, 1950).