There's been a whole lot of hype, controversy, and debate the past few months about the EM Drive – an "impossible" engine that, if functional, could supposedly power a spacecraft to Mars in just 10 weeks, without any rocket fuel.

It's pretty easy to understand the appeal. Science can't explain how the engine could possibly work and yet, somehow, throughout a range of tests at NASA's Eagleworks Laboratory, the engine reportedly continues to produce thrust. But here's the catch – so far none of these results have been peer-reviewed, and it can't be ruled out that the thrust isn't the result of some type of experimental error. So for now, we remain skeptical.

But in the meantime, Paul Mach, one of the principal investigators at the Eagleworks Lab, has provided the first public update about their tests on the EM Drive in months, and has admitted that the team has upgraded their experimental protocol and mitigated some of the errors that people were concerned about in prior tests.

"And yet the anomalous thrust signals remain..." Mach wrote on the NASASpaceFlight forums.

His comment was in response to an unpublished paper, which claimed that the propulsion seen in earlier trials of the EM Drive were a result of Lorentz force – which means the force generated by interactions between the EM Drive and the Earth's magnetic field.

An EM Drive prototype. Image: Science 2.0

Mach explains that he can't comment on this work in detail or provide any photos, as his lab is in the process of getting a peer-reviewed paper published, but that he can shed some light on the issue.

“I will tell you that we first built and installed a 2nd generation, closed face magnetic damper that reduced the stray magnetic fields in the vacuum chamber by at least an order of magnitude and any Lorentz force interactions it could produce,” wrote Mach.

He also admits that there are still traces of contamination caused by thermal expansion in the system, and the team is now developing an advanced analytics tool to try to work out where this is coming from.

The Em Drive stands for electromagnetic propulsion drive, and the reason it's so controversial is that it defies one of the fundamental concepts of physics – the conservation of momentum, which states that for something to be propelled forward (like a spacecraft), some kind of propellant (like fuel) needs to be pushed out in the opposite direction.

But the EM Drive, which was invented by English researcher Roger Shawyer in the early 2000s, works in theory by bouncing microwaves back and forth inside an enclosed chamber in order to generate thrust.

And so far a range of scientists, including the NASA team, have shown that the engine "is producing a force that is not attributable to any classical electromagnetic phenomenon," as the Eagleworks researchers wrote in an unpublished paper last year. In other words, it seems to work, but they can't explain why.

So far, this thrust has only been produced in incredibly small amounts, but given the fact that the theoretical system – once scaled up – would be able to power a spacecraft without the need for heavy rocket fuel on board, that's not an issue. The EM Drive is still predicted to be able to carry humans great distances in incredibly short periods of time.

Of course, that's all dependent on the thrust the scientists are detecting being an actual result of the EM Drive's bouncing microwaves, and not an experimental artefact. And despite reports that more and more stringent testing is being conducted to rule this out, we still need to see some results in peer review.

So please, Eagleworks scientists, while we love your interaction on the forums and the feedback, get cracking with the journal articles and those replicable results, we beg of you, because we really would love something concrete to go on sometime soon!