The following item is an excerpt from the Settlers' Sentinel, issue 4, (incorpating issue 25 of Free Space News)

November-December 1988, & January 1989.

INTERSTELLAR RAMJETS

Andrew, after being caught at the Interstellar Ramjet fuel again !!!
(It's the lack of oxygen that does it)

by Andrew Collin B.Sc., Ph.D.

Until now, we've frequently considered many serious methods of spaceflight, but all have been concerned with flight within our Solar System. Now, we venture tentatively beyond, and among other things, Andrew teaches us how to blow bubbles of magnetism - Andy.

1 INTRODUCTION

The interstellar ramjet is a familiar concept in science fiction (e.g. Niven 1970) but the capabilities and limitations of this unique form of transport are less well known. "Interstellar Ramjets" presents a brief overview of some of the concepts involved in the successful design and construction of a ramjet (or ram scoop) spacecraft capable of travelling over interstellar distances. The article concludes with an outline for the design of one such vehicle.

It's useful to begin by looking at some of the technical problems inherent in building a workable interstellar spacecraft. These can be broadly summarized as Weight, and Speed.

For travel over interstellar distances the traditional approach in which a rocket carries all its fuel and reaction mass at launch, presents serious difficulties. Even using the most energetic thermonuclear reactions, the maximum speed that any spacecraft can attain is about 0.1c, where 'c' is the speed of light, and maximum acceleration attainable is about 0.001g, where 'g' is the acceleration due to gravity at the surface of the Earth. With such a low acceleration, these figures imply flight times to the nearest stars of hundreds of years' duration, and so such a mission would be unlikely to return any useful results to the society that launched the craft. This is the speed problem.

Going further and assuming total conversion of matter to radiative energy, then an acceleration of 1g is possible. Unfortunately it may then be proven that a mass ratio of about 10¹⁰ is needed (a mass ratio is the ratio of fuel mass to payload mass). In this case the transport of 1 ton of payload would need 1,000,000,000 tons of reaction material, which is comparable to a sizeable asteroid! Enormous inefficiency forms the weight side of the problem.

Other forms of interstellar transport have been suggested by various authors. Light sails powered by laser cannon are too slow as is the "space ark" concept, in which a self-sufficient colony embarks on a flight of several hundred years; and besides some preliminary exploration of the destination is surely indicated! More speculative means of transport still ("warp" drive, "wormholes") are not considered here since they are too far beyond current technology for this author to make any reasonable comments on their practicality.

Feel free to contact our president direct at: andy-nimmo@ntlworld.com
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