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Nasa is a major player in space science, so when a team from the agency this week presents evidence that "impossible" microwave thrusters seem to work, something strange is definitely going on.

Either the results are completely wrong, or Nasa has confirmed a major breakthrough in space propulsion.


British scientist Roger Shawyer has been trying to interest people in his EmDrive for some years through his company SPR Ltd. Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.

According to good scientific practice, an independent third party needed to replicate Shawyer's results. As Wired.co.uk reported, this happened last year when a Chinese team built its own EmDrive and confirmed that it produced 720 mN (about 72 grams) of thrust, enough for a practical satellite thruster. Such a thruster could be powered by solar electricity, eliminating the need for the supply of propellant that occupies up to half the launch mass of many satellites. The Chinese work attracted little attention; it seems that nobody in the West believed in it.

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However, a US scientist, Guido Fetta, has built his own propellant-less microwave thruster, and managed to persuade Nasa to test it out. The test results were presented on July 30 at the 50th Joint Propulsion Conference in Cleveland, Ohio. Astonishingly enough, they are positive.

The Nasa team based at the Johnson Space Centre gave its paper the title "Anomalous Thrust Production from an RF [radio frequency] Test Device Measured on a Low-Thrust Torsion Pendulum". The five researchers spent six days setting up test equipment followed by two days of experiments with various configurations. These tests included using a "null drive" similar to the live version but modified so it would not work, and using a device which would produce the same load on the apparatus to establish whether the effect might be produced by some effect unrelated to the actual drive. They also turned the drive around the other way to check whether that had any effect.


Back in the 90s, Nasa tested what was claimed to be an antigravity device based on spinning superconducting discs. That was reported to give good test results, until researchers realised that interference from the device was affecting their measuring instruments. They have probably learned a lot since then.

The torsion balance they used to test the thrust was sensitive enough to detect a thrust of less than ten micronewtons, but the drive actually produced 30 to 50 micronewtons -- less than a thousandth of the Chinese results, but emphatically a positive result, in spite of the law of conservation of momentum: "Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma."

This last line implies that the drive may work by pushing against the ghostly cloud of particles and anti-particles that are constantly popping into being and disappearing again in empty space. But the Nasa team has avoided trying to explain its results in favour of simply reporting what it found: "This paper will not address the physics of the quantum vacuum plasma thruster, but instead will describe the test integration, test operations, and the results obtained from the test campaign."

The drive's inventor, Guido Fetta calls it the "Cannae Drive", which he explains as a reference to the Battle of Cannae in which Hannibal decisively defeated a much stronger Roman army: you're at your best when you are in a tight corner. However, it's hard not to suspect that Star Trek's Engineer Scott -- "I cannae change the laws of physics" -- might also be an influence. (It was formerly known as the Q-Drive.)

Fetta also presented a paper at AIAA on his drive, "Numerical and Experimental Results for a Novel Propulsion Technology Requiring no On-Board Propellant". His underlying theory is very different to that of the EmDrive, but like Shawyer he has spent years trying to persuade sceptics simply to look at it. He seems to have succeeded at last.


Shawyer himself, who sent test examples of the EmDrive to the US in 2009, sees the similarity between the two. "From what I understand of the Nasa and Cannae work -- their RF thruster actually operates along similar lines to EmDrive, except that the asymmetric force derives from a reduced reflection coefficient at one end plate," he says. He believes the design accounts for the Cannae Drive's comparatively low thrust: "Of course this degrades the Q and hence the specific thrust that can be obtained."

Fetta is working on a number of projects which he is not able to discuss at present, and Nasa's PR team was not able to get any comments from the research team. However, it's fair to assume that the results will be picked over very closely indeed, like CERN's anomalous faster-than-light neutrinos. The neutrino issue was cleared up fairly quickly, but given that this appears to be at least the third independent propellant-less thruster to work in tests, the anomalous thrust may prove much harder to explain away.

A working microwave thruster would radically cut the cost of satellites and space stations and extend their working life, drive deep-space missions, and take astronauts to Mars in weeks rather than months. In hindsight, it may turn out to be another great British invention that someone else turned into a success.