© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

17.3  Conventional Interstellar Propulsion Systems

Three fundamental requirements must be satisfied if starflight is to be considered plausible for alien or human civilizations. First, the kinematics must be right. Second, the energy available for the mission must be sufficient. Third, there must exist an astronautic technology capable of performing the requisite kinematics using the available energy. In the preceding section we saw that the kinematic and energetic requirements are satisfied by Type II and Type III civilizations operating within the bounds of Einsteinian Relativity theory. For the remainder of this chapter the third requirement is examined in more detail -- the technological aspects of interstellar voyaging.

Consider the nature of technical progress. There is an orderly progression from the emergence of new ideas, further research and development, then finally a reduction to practice and economic exploitation. Thus, the realization of new technology normally proceeds in four stages:

1. IDEA -- the basic philosophical idea, discovery of a new physical law, a new branch of mathematics, a new possibility within the existing framework of science. (See Hogan²⁹¹⁶ for an excellent example of this in science fiction.)

2. THEORY -- development of the mathematical/physical theoretical framework which ties the new idea to other known phenomena.

3. PRACTICE -- research and engineering; building a device which utilizes the new idea in its manufacture or operation.

4. PROFIT -- social, political, and economic acceptance and exploitation; who pays for it, is it worth the effort, who will benefit, etc.?

Matching this progression against current human achievements, we find that radio, television, computers, automobiles, and chemical rockets all have arrived at the profit stage here on Earth. Such advanced technologies as nuclear power planets, SSTs, and fission propulsion rockets are at the practice stage, awaiting full societal and economic commitment to move them into the profit stage. Laser fusion and satellite solar power stations are presently in transition from theory to practice.

The five conventional interstellar propulsion systems described in this section are all at the theory stage in human technological development. Each has received sufficient study to tell us that they have the basic physical and energetic feasibility to be considered for missions to the stars. All retain a number of technical uncertainties which will require significant engineering effort to overcome. Nevertheless, xenologists expect that all five propulsion systems are likely to advance at least to the practice stage within a century or less on this planet. So it is likely that these same systems also accurately represent the interstellar transport technologies of many extraterrestrial sentient races in the universe.

A sixth conventional interstellar propulsion system employing paired high-energy mass drivers for efficiently transporting massive cargoes between distant stars is briefly described in Section 21.4.1.

Last updated on 6 July 2013