A mission to another star is quite a jump for today’s technologies and will be for some time to come. But if you’re thinking of robotic payloads rather than human, it’s at least in the range of possibility. Fast ‘Sun-diver’ trajectories that could get a fly-by probe to Alpha Centauri in something on the order of a thousand years are not beyond question, and Robert Forward-style lightsails, pushed by gigantic lasers, might reduce that time to a century or less, using a Solar System-wide infrastructure we might be able to build with the help of nanotechnology in the next century.

Human crews, though, are quite another matter. The problem seems to demand breakthrough technologies, one of which could be the propellantless propulsion being investigated by James Woodward (California State University, Fullerton). The vast amounts of propellant needed for chemical or even nuclear missions seem to rule out their use in practical crewed spacecraft. A propellantless thruster would resolve the issue, but most theorists think that producing acccelerating forces without expelling some kind of propellant mass from the vehicle is an idle dream.

On the other hand, we learn things by finding out just what the problems are — in this case, the distances to be traversed, and the time involved — and then asking what breakthroughs would be needed to surmount them. Our experiments to probe breakthrough concepts may lead to further solutions we hadn’t ever thought of. And if the work of a James Woodward, recently considered in these pages, ultimately fails, it will still offer the chance to confirm our existing understanding of physical laws and perhaps broaden our views of what is and is not possible.

Those who have asked for more information about Woodward will also want to know about the investigations of Hector Brito (Instituto Universitario Aeronautico, Cordoba, Argentina) and colleague Sergio Elaskar (CONICET, Universidad Nacional de Cordoba). In a recent paper, the researchers describe their experiments with what they call an electromagnetic inertia manipulation (EMIM) thruster, producing what they believe is experimental evidence of sustained thrust using concepts not dissimilar to those championed by Woodward.

After describing their device, the authors present the principle behind it:

By Minkowski’s formalism, a nonvanishing momentum of electromagnetic origin is shown to arise for the particular device… It follows that the EM field can modify the inertial properties of the generating device, their variation producing forces on the device without any exchange of mass-energy with the surrounding medium. A propulsion concept based upon this kind of inertia manipulation mechanism was subsequently drawn; an electromagnetic inertia manipulation (EMIM) thruster was engineered up to the “proof of concept” level. Experiments were designed and performed, yielding by spectral analysis techniques, in an exploratory phase, indirect evidence of Minkowski’s approach being valid.

Brito and Elaskar then go on to modify the experiment, producing what they call “…sharper and clearer evidence of sustained thrust…” Work like this depends crucially on filtering out the signal from the noise, so that tiny effects that might be construed as thrust aren’t confused with myriad side-effects caused by the apparatus itself. The paper studies such effects in a series of experiments, with results the authors consider provocative:

Tests performed during an exploratory phase produced results, which after intensive data processing gave indirect evidence of matter-electromagnetic field momentum exchange, as predicted by Minkowski’s formalism; direct detection of the sought effect could not be achieved due to interfering effects leading to very low S/N ratios. Sustained thrust experiments based on an alternative formulation of the EM force densities were devised and performed, aiming at getting rid of most of the identified spurious effects. They yield sharp and clear evidence of force-producing effects as predicted by that formulation, albeit in contradiction with null results predicted by the standard formulation.

Are Brito and Elaskar (and, by extension, Woodward) on to something, or are they mistaking mechanical noise for thrust? I tend to agree with Bob Shaw that there is no such thing as a free launch, but we’ll see. The uncertainties are numerous, with the researchers noting how extensive is the work necessary to confirm their results, including (one day) in-orbit testing. Right now we’re a long way from that, or from understanding the principles underlying such anomalous effects, if they are indeed genuine.

The paper is Brito and Elaskar, “Direct Experimental Evidence of Electromagnetic Inertia Manipulation Thrusting,” Journal of Propulsion and Power Vol. 23, No. 2 (March/April 2007), pp. 487-494. Many thanks to Joseph Mahaney for getting a copy of this paper to me.