Martin Tajmar’s presentation at the American Institute of Aeronautics and Astronautics’ Propulsion and Energy Forum and Exposition in Orlando yesterday has been getting plenty of press. Tajmar is looking at the device now commonly called an EmDrive, studied by Sonny White’s team at Eagleworks (Johnson Space Center) and advocated by Roger Shawyer, Guido Fetta and Chinese experimenters as a way of producing thrust in a way that seemingly violates conservation of momentum.


Tajmar (Dresden University of Technology) offers a paper entitled “Direct Thrust Measurements of an EmDrive and Evaluation of Possible Side-Effects” in his presentation on apparent thrust produced by the test device. As he told WIRED (which announced that The ‘impossible’ EmDrive could reach Pluto in 18 months), the current work will not close the story. From the paper itself:

The nature of the thrusts observed is still unclear… Our test campaign can not confirm or refute the claims of the EmDrive but intends to independently assess possible side-effects in the measurements methods used so far. Nevertheless, we do observe thrusts close to the magnitude of the actual predictions after eliminating many possible error sources that should warrant further investigation into the phenomena. Next steps include better magnetic shielding, further vacuum tests and improved EmDrive models with higher Q factors and electronics that allow tuning for optimal operation. As a worst case we may find how to effectively shield thrust balances from magnetic fields.

Image: Physicist Martin Tajmar. Credit: Dresden University of Technology.

An example of something needing attention is that the thrust measurements linger even after the power is turned off. Such behavior is indicative of thermal effects, but it is premature to reach that conclusion.

A thruster that operates through methods we do not understand naturally seizes the attention, because we seem to do away with the need for a propellant, which would make all manner of missions possible that would otherwise be achieved only through more costly chemical rocket methods. And if we are uncovering something that gets at ‘new physics,’ so much the better, as productive things happen when we find anomalies that lead to deeper investigation and, if we are lucky, a formulation of new principles.

Will that happen here? What needs to be emphasized is that this is work in progress, as Tajmar himself points out, so we cannot draw premature conclusions. We’re at the beginning of a process that includes peer review analysis and publication of papers widely disseminated in the physics community, as well as replication of experimental results examined in those papers. Finding out that momentum is not necessarily conserved would be a result so startling that it would demand the highest level of scrutiny, especially in terms of possible systematic errors — i.e., are there effects being registered which we can account for through the experimental apparatus itself? Tajmar knows this and says as much in his paper.

A bit of background: If you’ll check our book Frontiers of Propulsion Science, you’ll see that Martin Tajmar did an independent series of replication experiments on work performed by James Woodward (the ‘Woodward effect’), while working at the Austrian Research Center’s department of electric propulsion physics. While that work produced a null result, Tajmar went on to pursue experiments with rotating superconductors and, for a time, believed his apparatus was producing anomalous gravitomagnetic forces. Replication experiments that researchers at EarthTech in Austin planned to perform were abandoned because of what they believed to be flaws in the experimental apparatus Tajmar was using, including issues with the laser ring gyro Tajmar used that produced systematic noise that was being misinterpreted as a positive anomalous force signal. Tajmar continued the work for a time but eventually ended the experiment.

Does a similar fate await the EmDrive? We learn as we go, and if we can find ways to reduce or eliminate the problem of onboard propellant, we will utterly change the game of deep space. So, as experiments continue, let’s look for analysis in the journals as the work is subjected to peer review, and let’s insist on the same degree of caution we would use with any result that seems to contradict known physical law. If the effect Tajmar is studying is genuine, science will ferret it out, a process that is usually time-consuming and often subject to misinterpretation.

Addendum: George Dvorsky’s piece No, German Scientists Have Not Confirmed the Impossible EMDrive cites Eric Davis, Tau Zero founder Marc Millis and physicist Sean Carroll (Caltech), and is well worth your time.

An article that brings a determinedly neutral perspective to the matter is Suggestion: The EM Drive Is Getting the Appropriate Level of Attention from the Science Community. Thanks to Sonny White (NASA JSC) for the link to this one.