Breaking News
Get 4 extra free issues and unlimited free access to
New Scientist is now partnered with Approved Index. Visit the site to get free quotes from website designers and a range of web, IT and marketing services in the UK.

The World's No.1 Science & Technology News Service


Relativity drive: The end of wings and wheels?

  • 08 September 2006
  • Exclusive from New Scientist Print Edition. Subscribe and get 4 free issues.
  • Justin Mullins
Printable versionEmail to a friendRSS FeedSyndicate
Messenger finds web of debris on Mercury

Mercury's web

Movie Camera
The Messenger probe has imaged new regions of the planet, revealing trails of impact debris
Chemistry Nobel for green jellyfish protein

Protein prize

Movie Camera

The Nobel prize for chemistry goes to the scientists behind a green jellyfish protein.

See a gallery of it in action

Gallery: Wildlife photographers of the year

Wild images

Movie Camera
See some of the best pictures from the Wildlife Photographer of the Year competition
Native people reject palm-oil offer

No to palm oil

Indigenous people in Borneo vote not to sell their land
map of a building

Transparent car

Look straight through the dashboard to see hidden hazards with a new display
The electromagnetic drive
The electromagnetic drive
Look, no wings!
Look, no wings!

Note: You can read debates on the article and make comments here, and read Shawyerís theory paper here (pdf format).

The trip from London to Havant on the south coast of England is like travelling through time. I sit in an air-conditioned train, on tracks first laid 150 years ago, passing roads that were known to the Romans. At one point, I pick out a canal boat, queues of cars and the trail from a high-flying jet - the evolution of mechanised travel in a single glance.

But evolution has a habit of springing surprises. Waiting at my destination is a man who would put an end to mechanised travel. Roger Shawyer has developed an engine with no moving parts that he believes can replace rockets and make trains, planes and automobiles obsolete. "The end of wings and wheels" is how he puts it. It's a bold claim. (Too bold? See the later feedback here and here)

Of course, any crackpot can rough out plans for a warp drive. What they never show you is evidence that it works. Shawyer is different. He has built a working prototype to test his ideas, and as a respected spacecraft engineer he has persuaded the British government to fund his work. Now organisations from other parts of the world, including the US air force and the Chinese government, are beating a path to his tiny company.

The device that has sparked their interest is an engine that generates thrust purely from electromagnetic radiation - microwaves to be precise - by exploiting the strange properties of relativity. It has no moving parts, and releases no exhaust or noxious emissions. Potentially, it could pack the punch of a rocket in a box the size of a suitcase. It could one day replace the engines on almost any spacecraft. More advanced versions might allow cars to lift from the ground and hover. It could even lead to aircraft that will not need wings at all. I can't help thinking that it sounds too good to be true.

When I meet Shawyer, he turns out to be reassuringly normal. His credentials are certainly impressive. 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.

Dangerous idea

With that pedigree, you'd imagine Shawyer would be someone the space industry would have listened to. Far from it. While 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 Shawyer had in mind was a replacement for the small thrusters conventional satellites use to stay in orbit. The fuel they need makes up about half their launch weight, and also limits a satellite's life: once it runs out, the vehicle drifts out of position and must be replaced. Shawyer's engine, by contrast, would be propelled by microwaves generated from solar energy. The photovoltaic cells would eliminate the fuel, and with the launch weight halved, satellite manufacturers could send up two craft for the price of one, so you would only need half as many launches.

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.

Surprisingly, Shawyer's disruptive technology rests on an idea that goes back more than a century. In 1871 the physicist James Clerk Maxwell worked out that light should exert a force on any surface it hits, like the wind on a sail. This so-called radiation pressure is extremely weak, though. Last year, a group called The Planetary Society attempted to launch a solar sail called Cosmos 1 into orbit. The sail had a surface area of about 600 square metres. Despite this large area, about the size of two tennis courts, its developers calculated that sunlight striking it would produce a force of 3 millinewtons, barely enough to lift a feather on the surface of the Earth. Still, it would be enough to accelerate a craft in the weightlessness of space, though unfortunately the sail was lost after launch. NASA is also interested in solar sails, but has never launched one. Perhaps that shouldn't be a surprise, as a few millinewtons isn't enough for serious work in space.

But what if you could amplify the effect? That's exactly the idea that Shawyer stumbled on in the 1970s while working for a British military technology company called Sperry Gyroscope. Shawyer's expertise is in microwaves, and when he was asked to come up with a gyroscopic device for a guidance system he instead came up with the idea for an electromagnetic engine. He even unearthed a 1950s paper by Alex Cullen, an electrical engineer at University College London, describing how electromagnetic energy might create a force. "It came to nothing at the time, but the idea stuck in my head," he says.

In his workshop, Shawyer explains how this led him to a way of producing thrust. For years he has explored ways to confine microwaves inside waveguides, hollow tubes that trap radiation and direct it along their length. Take a standard copper waveguide and close off both ends. Now create microwaves using a magnetron, a device found in every microwave oven. If you inject these microwaves into the cavity, the microwaves will bounce from one end of the cavity to the other. According to the principles outlined by Maxwell, this will produce a tiny force on the end walls. Now carefully match the size of the cavity to the wavelength of the microwaves and you create a chamber in which the microwaves resonate, allowing it to store large amounts of energy.

What's crucial here is the Q-value of the cavity - a measure of how well a vibrating system prevents its energy dissipating into heat, or how slowly the oscillations are damped down. For example, a pendulum swinging in air would have a high Q, while a pendulum immersed in oil would have a low one. If microwaves leak out of the cavity, the Q will be low. A cavity with a high Q-value can store large amounts of microwave energy with few losses, and this means the radiation will exert relatively large forces on the ends of the cavity. You might think the forces on the end walls will cancel each other out, but Shawyer worked out that with a suitably shaped resonant cavity, wider at one end than the other, the radiation pressure exerted by the microwaves at the wide end would be higher than at the narrow one.

Key is the fact that the diameter of a tubular cavity alters the path - and hence the effective velocity - of the microwaves travelling through it. Microwaves moving along a relatively wide tube follow a more or less uninterrupted path from end to end, while microwaves in a narrow tube move along it by reflecting off the walls. The narrower the tube gets, the more the microwaves get reflected and the slower their effective velocity along the tube becomes. Shawyer calculates the microwaves striking the end wall at the narrow end of his cavity will transfer less momentum to the cavity than those striking the wider end (see Diagram). The result is a net force that pushes the cavity in one direction. And that's it, Shawyer says.

Hang on a minute, though. If the cavity is to move, it must be pushed by something. A rocket engine, for example, is propelled by hot exhaust gases pushing on the rear of the rocket. How can photons confined inside a cavity make the cavity move? This is where relativity and the strange nature of light come in. Since the microwave photons in the waveguide are travelling close to the speed of light, any attempt to resolve the forces they generate must take account of Einstein's special theory of relativity. This says that the microwaves move in their own frame of reference. In other words they move independently of the cavity - as if they are outside it. As a result, the microwaves themselves exert a push on the cavity.

How can photons confined inside a cavity make the cavity move? This is where relativity and the strange nature of light come in

Each photon that a magnetron fires into the cavity creates an equal and opposite reaction - like the recoil force on a gun as it fires a bullet. With Shawyer's design, however, this force is minuscule compared with the forces generated in the resonant cavity, because the photons reflect back and forth up to 50,000 times. With each reflection, a reaction occurs between the cavity and the photon, each operating in its own frame of reference. This generates a tiny force, which for a powerful microwave beam confined in the cavity adds up to produce a perceptible thrust on the cavity itself.

Shawyer's calculations have not convinced everyone. Depending on who you talk to Shawyer is either a genius or a purveyor of snake oil. David Jefferies, a microwave engineer at the University of Surrey in the UK, is adamant that there is an error in Shawyer's thinking. "It's a load of bloody rubbish," he says. At the other end of the scale is Stepan Lucyszyn, a microwave engineer at Imperial College London. "I think it's outstanding science," he says. Marc Millis, the engineer behind NASA's programme to assess revolutionary propulsion technology accepts that the net forces inside the cavity will be unequal, but as for the thrust it generates, he wants to see the hard evidence before making a judgement.

Thrust from a box

Shawyer's electromagnetic drive - emdrive for short - consists in essence of a microwave generator attached to what looks like a large copper cake tin. It needs a power supply for the magnetron, but there are no moving parts and no fuel - just a cord to plug it into the mains. Various pipes add complexity, but they are just there to keep the chamber cool. And the device seems to work: by mounting it on a sensitive balance, he has shown that it generates about 16 millinewtons of thrust, using 1 kilowatt of electrical power. Shawyer calculated that his first prototype had a Q of 5900. With his second thruster, he managed to raise the Q to 50,000 allowing it to generate a force of about 300 millinewtons - 100 times what Cosmos 1 could achieve. It's not enough for Earth-based use, but it's revolutionary for spacecraft.

One of the conditions of Shawyer's £250,000 funding from the UK's Department of Trade and Industry 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.

To review the project, the UK government hired John Spiller, an independent space engineer. He was impressed. He says the thruster's design is practical and could be adapted fairly easily to operate in space. He points out, though, that the drive needs to be developed further and tested by an independent group with its own equipment. "It certainly needs to be flown experimentally," he says.

Armed with his prototypes, the test measurements and Spiller's review, Shawyer is now presenting his design to the space industry. The reaction in China and the US has been markedly more enthusiastic than that in Europe. "The European Space Agency knows about it but has not shown any interest," he says. The US air force has already paid him a visit, and a Chinese company has attempted to buy the intellectual property associated with the thruster. This month, he will be travelling to both countries to visit interested parties, including NASA.

A Chinese company has tried to buy rights to the microwave thruster
To space and beyond

His plan is to license the technology to a major player in the space industry who can adapt the design and send up a test satellite to prove that it works. If all goes to plan, Shawyer believes he could see the engine tested in space within two years. He estimates that his thruster could save the space industry $15 billion over the next 10 years. Spiller is more cautious. While the engine could certainly reduce the launch weight of a satellite, he doubts it will significantly increase its lifetime since other parts will still wear out. The space industry might not need to worry after all.

Meanwhile Shawyer is looking ahead to the next stage of his project. He wants to make the thrusters so powerful that they could make combustion engines obsolete, and that means addressing the big problem with conventional microwave cavities - the amount of energy they leak. The biggest losses come from currents induced in the metal walls by the microwaves, which generate heat when they encounter electrical resistance. This uses up energy stored in the cavity, reduces the Q, and the thrust generated by the engine drops.

Fortunately particle accelerators use microwave cavities too, so physicists have done a lot of work on reducing Q losses inside them. 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 newtons per kilowatt - enough to lift a large car.

This raises another question. Why haven't physicists stumbled across the effect before? They have, says Shawyer, and they design their cavities to counter 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.

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.

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."

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.

What of the impact of such a device? On my journey home I have plenty of time to speculate. No need for wheels, no friction. Shawyer suggested to me before I left that a hover car with an emdrive thruster 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."

What about aircraft without wings? I'm aware that my feeling of scepticism is being replaced by a more dangerous one of unbounded optimism. In five minutes of blue-sky thinking you can dream up a dozen ways in which the emdrive could change the world. I have an hour ahead of me. The end of wings and wheels. Now there's a thought.

From issue 2568 of New Scientist magazine, 08 September 2006, page 30-34
Comment subject
No HTML except lower case italic tags or lower case bold tags, please:
<i> or <b>
Your name
Your email

We need your email in case we need to contact you about the comment. We will not use it for any other purpose.

There are 53 comments on 7 pages
1  | 
2  | 
3  | 
4  | 
5  | 
 | Next
 | Most Recent
 | See all

As Physics Research

By Nadine Kalmoni

Mon Nov 26 09:15:15 GMT 2007

This comment has been found to be in breach of our terms of use and has been removed.


What Has Happened To Date.

By J. Richard Niemela, Col. Usaf (ret)

Sat Dec 29 19:04:56 GMT 2007

This "discovery" appear to have validity, yet nothing further has been heard as to its future use and applicaton..Is there more to this or has it gone the way of other "inventions" that run afoul of the Oil Interests?


What Has Happened To Date.

By Atto

Fri Sep 26 02:55:23 BST 2008

http://Http:// has had a piece of this for a long time.


By Axemaster

Sun Dec 30 07:59:48 GMT 2007

Uh... I hate to say it, but this article looks really dumb. I seriously doubt the reporter did any homework before looking this nut up.

"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."

Is it just me, or are these guys on life support? Nothing in this paragraph makes even marginal sense, and it massively violates relativity.

Anybody here know flux, or Gause's Law? Because this violates it. Badly. Force flux isn't just going to dissappear, which is exactly the same as saying that this engine cannot possibly work, not if we've done any science at all in the past 500 years.



By Oscar

Tue Jun 10 12:57:27 BST 2008

Could you expalain to me about Flux or Gause's law as I would like to understand why you beleive this to be rubbish, although in many respects I agree.



By Brian

Wed Aug 20 20:26:30 BST 2008

Gause's law states that the niche occupied by brown squirrels in new york's central park is occupied by lizards in brisbane australia's kodak park. Gauss on the other hand came up with the gravitational constant-- a reference used when talking about anything gravitational. Flux has to do with integral magnetic stability. Rubbish or not, it's clever. People love clever. That is why there is popular science magazine. ;)



By Vendicar Decarian

Mon Sep 29 15:48:57 BST 2008

Relativity is formulated such that momentum is concerved, and momentum is re-formulated so that photons carry momentum.

As soon as you open the cavity, and radiation begins to be emitted in a direction, the cavity will experience a force in the opposite direction.

The pressure on the closed side of the cavity is produced by the reflection of the cavity photons back toward the open side.

The photon in the cavity won't change their frequency until they intereact with the cavity walls however. To an observer accelerating with the cavity, they will be doppler shifted downward at the back end of the cavity and forward with reflection from the front (open) end.

Any new photons entering the cavity will enter as if the cavity was intially not-moving.

The inner reactions between the photons and the cavity are not relevant however. What matters is the momentum carried from the system by the photons emitted from output end of the cavity.

I presume microwaves are used because more raw energy can be dumped though a maser than a laser, but the principle is the same.

Nothing new here.



By Ivan Dreiss

Wed Sep 24 17:09:23 BST 2008

Gauss and relativity are oil and water. Gauss frame of reference makes no account of relativistic effects - any sophomore will understand that!

Shawyer has hit upon the most brilliant innovation of the 21st century and, like many innovators, is meeting with scorn from the drab scientific establishment.



By Reality Check

Sat Sep 27 13:28:55 BST 2008

Why comment on things you clearly don't understand the first thing about?

Maxwell's equations are explicitly Lorentz invariant - in fact, they were one of Einstein's primary motivations for special relativity. Gauss' law is one of Maxwell's equations.

The "drive" described in the article is obviously impossible. It violates more or less every law of physics. It will not work. If you don't believe me, prepare to be disappointed.



By Space-modulater

Sat Sep 27 20:02:14 BST 2008

Law of blah blah blah nothing is imposible it's all bout turing the thoery into hardware and gauss law he did not create anthing nor did einstin if u ask me there all me there more like things he could not explain so he put he own laws and notions on them i think he's on trark so stop haten...



By Jim

Sun Sep 28 20:36:36 BST 2008

You say impossible but he says hes measured the force it produces. Assuming hes done this correctly that means it works. So either hes wrong or gauss is wrong, and lets face it, it certainly wouldnt be the first time practice has proved theory wrong.

Also wouldnt be the first time an amazing new technology has turned out to be a load of rubbish.

But if makes one on a satellite work pack up the nobel prizes cos you wont top that



By Vendicar Decarian

Mon Sep 29 16:03:34 BST 2008

"The "drive" described in the article is obviously impossible. It violates more or less every law of physics. It will not work. If you don't believe me, prepare to be disappointed. " - Reality check

Don't be silly. Remove the cavity and point the microwave emitter in any direction, there will be a force imparted on the emitter in the opposite direction.

The cavity is irrelivant tothe average thrust, but can be used to store EM radiation for smaller periods of higher thrust.


There are 53 comments on 7 pages
1  | 
2  | 
3  | 
4  | 
5  | 
 | Next
 | Most Recent
 | See all

All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.

If you are having a technical problem posting a comment, please contact technical support.

Cover of latest issue of New Scientist magazine
  • For exclusive news and expert analysis every week subscribe to New Scientist Print Edition
  • For what's in New Scientist magazine this week see contents
  • Search all stories
  • Contact us about this story
  • Sign up for our free newsletter
Subscribe to New Scientist magazine