An 'impossible' fuel-free engine, which could take a humans to Mars in just 10 weeks, is still defying science after another batch of tests by Nasa suggested the thruster does work.

The so-called EM Drive creates thrust by bouncing microwaves around in an enclosed chamber, and uses only solar power.

When the concept was first proposed, it was considered implausible because it went against the laws of physics - and subsequent tests of the engine have shown that the idea could revolutionise space travel.

Now Nasa has provided the first update on the test in months, and it seems to suggest that the futuristic engine does, in fact, work.

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A prototype of the 'impossible' fuel-free engine that could power a spacecraft to Mars in just 10 weeks

WHAT IS AN EM DRIVE? The concept of an EM Drive engine is relatively simple. It provides thrust to a spacecraft by bouncing microwaves around in a closed container. Solar energy provides the electricity to power the microwaves, which means that no propellant is needed. The implications for this could be huge. For instance, current satellites could be half the size they are today without the need to carry fuel. Humans could also travel further into space, generating their own propulsion on the way. But when the concept was first proposed it was considered implausible because it went against the laws of physics. Its allegedly fuel-free nature also means that the drive may directly contradict the law of conservation of momentum. It suggests it would produce a forward-facing force without an equal and opposite force acting in the other direction. Advertisement

Scientists, however, still don't know why.

The update was given by Paul March, one of the top engineers working the EM Drive thruster at the Eagleworks Laboratory at the Johnson Space Center in Texas.

He said Nasa has managed to remove some of the errors from earlier tests - but still found signals of unexplained thrust.

Among the criticisms of previous experiments were that the tests were not carried out in a vacuum, thereby mirroring the conditions in space.

But the latest Nasa test appears to have addressed these concerns.

March's announcement is the first direct announcement in months, with the space agency largely remaining silent about any developments on the controversial project.

March posted on the Nasa Spaceflight forum in reply to an unpublished paper that claims the unaccounted thrust is generated by something known as the Lorentz force.

The Lorentz force is the force that is exerted by a magnetic field on a moving electric charge.

But March says his tests prove this is not true.

'I will tell you that we first built and installed a second 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,' he said

'And yet the anomalous thrust signals remain.'

March also says that in the latest developments, thermal expansion of the thruster is taken into account to reduce all possible sources of error.

But the thrust can still be seen, and engineers still can't explain what's causing it.

If it becomes operatonal, the EM Drive propulsion system would permit travel at speeds until now only seen in science fiction and have other implications for space exploration.

The fact that it's a recurring phenomenon now makes the EM Drive appear less of a ridiculous concept and more of real solution to deep space travel.

One of the images from an as-yet unpublished paper on the EMDrive, revealing the magnetic fields of the device

WHAT IS THE LAW OF CONSERVATION OF MOMENTUM? The basic laws that are applied in the theory of the EmDrive include Newton’s laws including the law of conservation of momentum and the law of conservation of energy. At its most simple, the law of conservation of momentum can be explained by studying collisions. During a collision between two objects - object 1 and object 2 - the forces acting on and between the two objects are equal, and opposite in direction. These forces act for a set amount of time depending on the strength of the force and the shape and size of the objects, but regardless of how long this lasts, the time on each object is the same. The EmDrive appears to violate this law because it seemingly produces a forward-facing force that powers it through space without an equal and opposite force acting in the other direction. However, the electromagnetic wave momentum that is created in the resonating cavity travels to the end walls. At this point, the momentum gained and the momentum lost by the electromagnetic wave is equal, which suggests it complies with the law. Advertisement

Researchers say the new drive could carry passengers and their equipment to the moon in as little as four hours, or to Mars in 10 weeks.

A trip to Alpha Centauri, which would take tens of thousands of years to reach under current methods, could be reached in just 100 years. And as the thrusters are solar powered, propulsion would be generated along the way.

The system is based on electromagnetic drive, or EM Drive, which converts electrical energy into thrust without the need for rocket fuel.

While there has been some scepticism surrounding the EM Drive, in April Nasa released results of their own test which showed that the EM Drive did in fact create thrust.

Nasa's test set-up for the futuristic EM Drive in its 'Eagleworks' lab

'Thrust measurements of the EM Drive defy classical physics' expectations that such a closed (microwave) cavity should be unusable for space propulsion because of the law of conservation of momentum,' announced NasaSpaceFlight.com in April

The site has become an unofficial source of EM Drive news, with Nasa engineers reportedly posting on its forum.

While there has been some scepticism around the EMDrive, in April Nasa released results of its own test which showed that the EMDrive did in fact create thrust. Pictured is an experimental set-up to test the system

Earlier this year, German scientists also backed Nasa's claim that the engines do work.

Martin Tajmar, professor and chair for Space Systems at the Dresden University of Technology, presented a paper to the American Institute for Aeronautics and Astronautics' Propulsion and Energy Forum in July.

Tajmar wrote: 'Additional tests need to be carried out to study the magnetic interaction of the power feeding lines used for the liquid metal contacts.'

'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 EM Drive models with higher Q factors and electronics that allow tuning for optimal operation.'

According to classical physics, the EM Drive should be impossible because it seems to violate the law of conservation of momentum.

The law states that the momentum of a system is constant if there are no external forces acting on the system – which is why propellant is required in traditional rockets.

Researchers from the US, UK and China have demonstrated EM Drives over the past few decades, but their results have been controversial as no one has been exactly sure how it works.

The concept of an EmDrive engine is relatively simple. It provides thrust to a spacecraft by bouncing microwaves around in a closed container. Solar energy provides the electricity to power the microwaves, which means that no propellant is needed

The propulsion system may make deep space travel as in Star Trek a realistic possibility

When London-based Roger Sawyer came up with concept in 2000, the only team that took him seriously was a group of Chinese scientists.

In 2009, the team allegedly produced 720 millinewton (or 72g) of thrust, enough to build a satellite thruster. But still, nobody believed they had achieved this.

Last year, Pennsylvania-based scientist Guido Fetta and his team at Nasa Eagleworks published a paper that demonstrates that a similar engine works on the same principles.

Their model, dubbed Cannae Drive, produces much less thrust at 30 to 50 micronewtons - less than a thousandth of the output of some relatively low-powered ion thrusters used today.

On the NasaSpaceFlight.com, those allegedly involved in the project claim that the reason previous EM Drive models were criticised were that none of the tests had been carried out in a vacuum.

Physics says particles in the quantum vacuum cannot be ionised, so therefore you cannot push against it. But Nasa's latest test claims to have shown otherwise.

'Nasa has successfully tested their EmDrive in a hard vacuum – the first time any organisation has reported such a successful test,' the researchers wrote.

'To this end, Nasa Eagleworks has now nullified the prevailing hypothesis that thrust measurements were due to thermal convection.'

However, Nasa's official site said earlier this year: 'There are many "absurd" theories that have become reality over the years of scientific research.