Voice from the Deep!

EM Drive Takes Shape

It seems from the outset to be something out of a StarWars novel.

A propulsion system that emits nothing at all! It just works… all it needs is electricity.

EMdrive prototype thruster

The EMdrive (ElectroMagnetic Drive) is the brain child of UK scientist, Roger Shawyer.

He worked his way up through the aerospace industry, designing and building navigation and communications equipment for military and commercial satellites, before becoming a senior aerospace engineer at Matra Marconi Space (later part of EADS Astrium) in Portsmouth, near where he now lives. He was also a consultant to the Galileo project, Europe’s satellite navigation system, which engineers are now testing in orbit and for which he negotiated the use of the radio frequencies it needed.

With that pedigree, you’d imagine Shawyer would be someone the space industry would have listened to. Far from it. While working at Astrium, Shawyer proposed that the company develop his idea. “I was told in no uncertain terms to drop it,” he says. “This came from the very top.”

What he had in mind was a replacement for reaction thrusters for satellites… So why the problem? 

Shawyer argues that for companies investing billions in rockets and launch sites, a new technology that leads to fewer launches and longer-lasting satellites has little commercial appeal. By the same token, a company that offers more for less usually wins in the end, so Shawyer’s idea may have been seen as too speculative. Whatever the reason, in 2000, he resigned to go it alone.

What is it ?
It’s an enclosed waveguide cavity that is filled with microwaves from an emitter at one end.The microwaves are “shaped” by the internal structure of the cavity and are caused to impact a force on the far end.

Now it would seem that equal and opposite forces would cancel each other out…  well that’s where the internal design and shape of the waveguide cavity comes into it. The microwaves bounce back and forth (much like a microwave laser MASER”) and due to the internal design a force is generated on the far side.

The inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having
separate frames of reference.

A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device.

Currently the force generated is very small. The 1st prototype, shown above, only produced a thrust of 16 millinewtons (mN). All this with an input power of 1 Kilowatt! It had a Q rating, which is a measure of efficiency, of 5,900. The higher the Q the better!

The 2nd prototype had a much better Q of 50,000 and that generated a thrust of 300 mN. Still not much…
But NASA have used a thruster with a lot less push, Deep Space 1 was launched with only a 100mN thruster onboard.

This looks more promising and you can see a video of it inaction here, it’s slow but in space that really doesn’t matter too much.

Why haven’t physicists stumbled across the effect before?
“They have” says Shawyer, and they design their cavities to counteract it. The forces inside the latest accelerator cavities are so large that they stretch the chambers like plasticine! To counteract this, engineers use piezoelectric actuators to squeeze the cavities back into shape. “I doubt they’ve ever thought of turning the force to other uses,” he says.

The key, says Shawyer, is to make the cavity superconducting. Without electrical resistance, currents in the cavity walls will not generate heat. Engineers in Germany working on the next generation of particle accelerators have achieved a Q of several billion using superconducting cavities. If Shawyer can match that performance, he calculates that the thrust from a microwave engine could be as high as 30,000 Newton’s per kilowatt, enough to lift a large car.

Shawyer’s company has received £250,000 from the UK Department of Trade and Industry to continue his work…

One of the conditions of Shawyer’s funding is that his research be independently reviewed, and he has been meticulous in cataloguing his work and in measuring the forces involved. “It’s not easy because the forces are tiny compared to the weight of the equipment,” he says.

Optimising the cavity is crucial, and it’s as much art as science. Energy leaks out in all kinds of ways: microwaves heat the cavity, for example, changing its electrical characteristics so that it no longer resonates. At very high powers, microwaves can rip electrons out of the metal, causing sparks and a dramatic loss of power. “It can be a very fine balancing act,” says Shawyer.

The next step ?

No doubt his superconducting cavities will be hard to build, and Shawyer is realistic about the problems he is likely to meet. Particle accelerators made out of niobium become superconducting at the temperature of liquid helium only a few degrees above absolute zero. That would be impractical for a motor, Shawyer believes, so he wants to find a material that superconducts at a slightly higher temperature, and use liquid hydrogen, which boils at 20 Kelvin, as the coolant. Hydrogen could also power a fuel cell or turbine to generate electricity for the emdrive.

Then there is the issue of acceleration. Shawyer has calculated that as soon as the thruster starts to move, it will use up energy stored in the cavity, draining energy faster than it can be replaced. So while the thrust of a motionless emdrive is high, the faster the engine moves, the more the thrust falls. Shawyer now reckons the emdrive will be better suited to powering vehicles that hover rather than accelerate rapidly. A fan or turbine attached to the back of the vehicle could
then be used to move it forward without friction. He hopes to demonstrate his first superconducting thruster within two years.

In the meantime, he wants to test the device with liquid nitrogen, which is easier to handle. It boils at 77 Kelvin, a temperature that will require the latest generation of high-temperature ceramic superconductors. Shawyer hasn’t yet settled on the exact material, but he admits that any ceramic will be tricky to incorporate into the design because of its fragility. It will have to be reliably bonded to the inside of a cavity and mustn’t crack or flake when cooled. There are other
problems too. The inside of the cavity will still be heated by the microwaves, and this will possibly quench the superconducting effect. “Nobody has done this kind of work,” Shawyer says. “I’m not expecting it to be easy.”

Shawyer suggested that a hover car with an emdrive thruster array, cooled and powered by hydrogen, could be a major factor in converting our society from a petrol-based one to one based on hydrogen. “You need something different to persuade people to make the switch. Perhaps being able to move in three dimensions rather than two would do the trick.”

Think about it, this could replace the need for wheels on trains, cars, even the wings of planes !!.
A nearly frictionless drive system that can move in 3 dimensions.