Advanced propulsion concepts represent “bridge” solutions to achieve the goals of interstellar space exploration while breakthrough propulsion concepts are not yet ready. If humankind wants to become an actual space faring species, then it needs to pursue advanced propulsion now. And this is not only true for the goals of interstellar flight, but also for reaching destinations which are much closer to the solar system. In a sense, it could be stated that advanced propulsion is more important to travel within or near the outer boundaries of the solar system than to achieve the primary goals of interstellar flight, as it falls short for the latter. The development of advanced propulsion will stimulate those studies which will in the future lead to newer ways of moving through space, perhaps without propellant or in ways which at present cannot be predicted. For this a breakthrough in propulsion physics is needed, and it is actually needed if what has been proposed under the heading of long term interstellar travel will be implemented. A breakthrough may arrive, but in the meantime there is much room for improvement in advanced (conventional physics) propulsion: solar and magnetic sails; nuclear electric propulsion; nuclear fission or fusion propulsion; matter-antimatter annihilation or hybrid antimatter-augmented fission/fusion propulsion; beamed energy propulsion (sails, Lightcraft, thermal rockets), etc. All these options represent near-to-medium term viable solutions.
Marc G. Millis, “Energy, incessant obsolescence, and the first interstellar missions,” January 2011.
This page is a quick introduction to the subject and is under construction. There were soon be menu links on the left for various topics including sails, nuclear propulsion, antimatter annihilation, and beamed energy propulsion.