EMDRIVE ANOMALIES

It may violate the laws of phsyics, but does that matter if engineer Roger shawyer’s propellantless space drive actually works? DAVID HAMBLING provides the latest news.

First they ignore you, then they laugh at you, then they attack you, then you win,” said Mahatma Gandhi. Allegedly – the quote has never been conclusively proven. The quip might apply to that most unlikely of technologies, a propellantless space drive invented by British engineer Roger Shawyer. First described in these pages back in 2005 [ FT201:14], the EmDrive is a sealed cavity in the shape of a truncated cone filled with resonant microwaves shuttling back and forth. Classical physics says that no closed system can produce thrust – it would violate the law of conservation of momentum – but whatever the theory, the real issue is whether the EmDrive actually works.

Or at least, it would be if science worked like that. In practice, the weight of established physics presses down on anyone wishing to make this sort of claim, and the EmDrive was initially ignored just as the myriad of alleged perpetual-motion contraptions are ignored. If someone tells you there is a nest of fire-breathing, flying dragons at the bottom of his garden, you would not trouble to check it out either.

However, as recounted last year [ FT320:12], Shaywer’s continued claims inspired a Chinese team led by Juan Yang at Xi’an Northwest Polytechnic University to replicate his apparatus. They found that the EmDrive produced thrust, and published results from 2008 onwards which were steadfastly ignored in the West. Then a maverick team at NASA – the so-called Eagleworks, based at Johnson Space Center in Houston – built their own version. That apparently worked too.

The NASA result was received with scorn and ridicule. Although they simply labelled their results as ‘anomalous thrust’ and did not attempt to explain how it worked, they were criticised for ignoring the laws of physics. Many uninformed suggestions were made as to what errors they might have made in their measurement.

NASA management were understandably cool about the results. It might be the greatest discovery of the age, but it still looked impossible, and they declined to make any comment at all on the heretical EmDrive research until the growing amount of news coverage inspired them to make this formal statement to Space.com: “While conceptual research into novel propulsion methods by a team at NASA’s Johnson Space Center in Houston has created headlines, this is a small effort that has not yet shown any tangible results.”

Since then, there seems to have been a media blackout from NASA. The Eagleworks continues work on the EmDrive, and according to leaks earlier this year their results continued to be positive, but funding for the project will reportedly end in September. NASA, an organisation that has to fight hard for its budget, would attract a storm of abuse if they allowed the Eagleworks to publish anything positive. If the Eagleworks build a robust EmDrive that produces enough thrust to be useful, it might just survive; mildly positive results that would be instantly picked to pieces as evidence of NASA craziness with public money would not be worthwhile.

The UK Space Agency says that “Funding from the UK Space Agency is made available in fair competition in line with our technology priorities, and EmDrive may be eligible to apply for such funding.” Shawyer says that in practice they have never shown much enthusiasm.

In the meantime another player has emerged. Martin Tajmar, Professor and Chair for Space Systems at the Dresden University of Technology, is something of an expert on testing exotic space drives. He presented his results on the EmDrive at the American Institute of Aeronautics and Astronautics in July. He clearly didn’t start as a believer in the EmDrive, but his position may have shifted. The first test was simply to point the drive in different directions and see if it made any difference.

“Remarkably, we can indeed see a fairly large difference between thrust directions. The difference between upwards and downwards measurements was 229 microNewtons and therefore close to our expectation of 2x98 MicroNewtons.”

The EmDrive was also tested in a vacuum chamber to ensure that air currents or ionisation was not producing thrust – an effect that fooled experimenters playing with ‘Lifters’ a few years ago. “Surprisingly we could still observe thrusts that are indeed reversing with thruster orientation,” Tajmar noted. The experiments could not rule out every single possible source of error, and Tajmar is cautious in his conclusion:

“Our test campaign can not confirm or refute the claims of the EmDrive but intends to independently assess possible side-effects in the measurement 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.”

Like the Eagleworks results – which one British tabloid interpreted as a Star Trek-style Warp Drive – Tajmar’s were distorted by the media. But they do represent another hurdle passed, the set of possible errors whittled down, another replication of the effect by an independent researcher.

One of the big criticisms of the EmDrive is the lack of peerreviewed research, but Shawyer himself has now published a peerreviewed paper in Ars Astronautica detailing his concepts for an EmDrive-powered spaceplane and deep-space probe. The spaceplane is based on the existing X-37 airframe and could provide cheap, ecologically friendly access to orbit, making Virgin Galactic look like a horse-drawn buggy. The space probe could reach a star four light years away in 10 years – roughly the same time it took for Deep Horizons to reach Pluto. Peer review pushes these concepts a step away from fantasy and towards fact.

NASA and the UK may find the whole idea too radical, and the Chinese work is now veiled in secrecy, but Industry rumours suggest there are more labs around the world exploring the EmDrive effect. The eras of ignoring the EmDrive and laughing at it are over. The fight is on between those who want to dismiss the EmDrive and those who want further research to find out if the astonishing claims are true.

NASA DECLINED TO COMMENT ON THE HERETICAL RESEARCH