An Interstellar Propulsion System

 Kevin Langdon

 published in Noesis , the journal of the Mega Society, #183, December 2006

We have now conducted a preliminary exploration, by means of robotic spacecraft, of our own solar system, but we know almost nothing of the worlds around nearby stars. Clearly, these other planetary systems are of great interest but conducting an exploration of them poses great technical challenges, because of the great distances involved and because we know so little about conditions in the vicinity of stars other than the sun.

 The primary challenges are accelerating spacecraft to speeds which will make it possible to reach the stars in years or decades rather than centuries or millennia, miniaturization to minimize the energy requirements for propelling them, protecting them against the hazards of long space voyages and radiation and debris in the target star systems, and developing communication technology capable of sending (from the spacecraft) and receiving (on earth) data from the brief reconnaissance possible by means of flybys of distant stars (deceleration of spacecraft for more prolonged investigation of other star systems is a much more difficult problem requiring much more advanced technology; the first interstellar missions will, of necessity, be flybys).

 This paper addresses the first challenge mentioned above (speed); it assumes that it will be possible to construct fairly small probes to minimize the energy required. While designers of interstellar probes will need to think seriously about various hazards, exploration of new worlds is always risky and there is no guarantee that the first few attempts will be successful. The communication problem is within the reach of present technology and is not likely to be the most critical factor in such missions, but it also poses a challenge. A number of spacecraft within the solar system have been lost because of failed communications.

 The idea proposed here would require a massive macrotechnology initiative but it is doable in principle through scaling up existing technology.

 I propose a spacecraft accelerator consisting of a ring of satellites in a close orbit around the sun (at a distance of about .05 to .2 A.U., depending on the tradeoff between the availability of a large amount of solar energy and the technical difficulty of protecting the spacecraft and the satellite stations from solar radiation).

 Each station would consist of four principal parts:  

1.      Massive arrays of solar panels to capture the very large amount of energy that would be required.

2.      A very robust cooling system to dissipate the very large amount of heat that would accumulate.

3.      Very powerful magnets to tweak the trajectory of a spacecraft as it circulates around the accelerator. Most of the force would be required to keep the spacecraft from flying outward before it’s built up sufficient velocity, or in the wrong direction.

4.      Advanced sensing instrumentation and computing to control the spacecraft during the process of acceleration.

 After the spacecraft reaches its target velocity it would be released in the direction of a star of interest.

 The spacecraft would be equipped with advanced imaging systems and other instruments, similar to the instrumentation of the Voyager spacecraft, which gathered valuable data as they passed through the satellite systems of the outer planets of the solar system, but far more sophisticated—and much greater sophistication would be needed, because, in addition to the much greater distances involved in reaching another planetary system, the spacecraft wouldn’t necessarily approach such a system in the plane containing most of the orbits of major bodies in the system. (However, it might well be possible to target a nearby star with planets in a plane closely aligned with our solar system.)

 How many stations would be required and how closely they’d be spaced, and their exact orbital distance, are engineering questions which could only be answered after detailed studies, but there would undoubtedly have to be many of them. One advantage of this design is that if something went wrong a circulating spacecraft could only take out one station.

 This system would make it possible to reach the high velocities which will be needed for interstellar exploration.

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