Researchers at Nasa's Eagleworks Laboratories say that they are still discovering signals of thrust which cannot be explained in their latest tests of the highly controversial electromagnetic space propulsion technology EmDrive.

The EmDrive is the invention of British scientist Roger Shawyer, who proposed in 1999 that based on the theory of special relativity, electricity converted into microwaves and fired within a closed cone-shaped cavity causes the microwave particles to exert more force on the flat surface at the large end of the cone (i.e. there is less combined particle momentum at the narrow end due to a reduction in group particle velocity), thereby generating thrust.

His critics say that according to the law of conservation of momentum, his theory cannot work as in order for a thruster to gain momentum in one direction, a propellant must be expelled in the opposite direction, and the EmDrive is a closed system. However, Shawyer claims that following fundamental physics involving the theory of special relativity, the EmDrive does in fact preserve the law of conservation of momentum and energy.

According to Eagleworks engineer Paul March, who explained the lab's findings on the Nasa Spaceflight forum on 31 October, the researchers built a second generation version of the EmDrive and took steps to reduce and mitigate any possible magnetic or thermal interference, in order to try to discover just where the unexplained, anomalous thrust signals were coming from.

"And yet the anomalous thrust signals remain..."

To that end, the researchers added a second generation magnetic damper to the EmDrive to help reduce any stray magnetic fields in the vacuum chamber by an order of magnitude.

Despite this the researchers still noted that the thrust signals were being contaminated by thermal expansion of the copper frustum and aluminium radio frequency (RF) amp.

Unfortunately, the thermal expansion was even worse when the EmDrive was tested in a vacuum, which simulated outer space, largely because the vacuum had strong insulation properties.

So March and his team of researchers went back to the drawing board: "We have now developed an analytical tool to help separate the EmDrive thrust pulse waveform contributions from the thermal expansion [interference].

"Not being satisfied with just this analytical impulsive vs thermal signal separation approach, we are now working on a new integrated test...that should mitigate this...problem once and for-all," March wrote on the forum. He ended his post by saying: "And yet the anomalous thrust signals remain..."

Nasa Eagleworks working on a peer-reviewed lab paper

March hinted that more information about their EmDrive tests will be made available when an Eagleworks Lab paper is peer-reviewed and published.

In April, a Nasa Spaceflight report thrust the EmDrive back into the media spotlight. March now states that Nasa is restricting the Eagleworks Laboratory from issuing press releases, and perhaps this is in part due to the intense furore in the media and on the internet that followed the report. The subject of EmDrive is still quite a touchy one and there are many detractors who still don't believe that the technology is viable.

As for Shawyer, who endured years of having his technology ridiculed by the international space science research community and was accused of being a fraud, he has long since come to terms with the situation and told IBTimes UK that Nasa is still far behind in its research of the technology, and that private companies are all quietly competing to bring it to market commercially first.

Following the Nasa Eagleworks furore, in July Dr Martin Tajmar, Chair for Space Systems at the Dresden University of Technology's Institute of Aerospace Engineering, who is well known for debunking space propulsion systems, presented a paper showing that he and his researchers were able to measure effects similar to the EmDrive. However, the researchers were not able to establish the nature of the thrust measurement, or define if there were any other factors obscuring their results.

Nasa lagging behind private space industry's efforts

Also in July, Shawyer exclusively revealed to IBTimes UK that he had finally had a paper on the second generation of the EmDrive peer-reviewed and accepted by the International Academy of Astronautics (IAA).

He continues to feel that people who don't believe in EmDrive need to "do the maths" for themselves first: "If you don't understand something and it's a difficult something, then what you should do is go away and listen, and read, and then you should go away, and if you're capable of it, you should do the maths. That's the key to it.

"Once you've done that, and you're really serious, then you go and do your experiments, and then think about it for one to two years. Because that is what real scientists do, and they're seeing that EmDrive does work."