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Fly byWings and wheels are so last century.Justin Mullins meets the man whowould replace them with pure radiation

THE trip from London to Havant onthe south coast of England is liketravelling through time. I sit in an

air-conditioned train, on tracks first laid150 years ago, passing roads that were knownto the Romans. At one point, I pick out a canalboat, queues of cars and the trail from ahigh-flying jet -the evolution of mechanisedtravel in a single glance.

But evolution has a habit of springingsurprises. Waiting at my destination is a manwho would put an end to mechanised travel.Roger Shawyer has developed an engine withno moving parts that he believes can replacerockets and make trains, planes andautomobiles obsolete. "The end of wings andwheels" is how he puts it. It's a bold claim.

Of course, any crackpot can rough out plansfor a warp drive. What they never show youis evidence that it works. Shawyer is different.He has built a working prototype to test hisideas, and as a respected spacecraft engineerhe has persuaded the British government tofund his work. Now organisations from otherparts of the world, including the US air forceand the Chinese government, are beating apath to his tiny company.

The device that has sparked their interestis an engine that generates thrust purely fromelectromagnetic radiation - microwaves to beprecise - by exploiting the strange propertiesof relativity. It has no moving parts, and

releases no exhaust or noxious emissions.Potentially, it could pack the punch of a rocketin a box the size of a suitcase. It could one dayreplace the engines on almost any spacecraft.More advanced versions might allow cars to liftfrom the ground and hover. It could even leadto aircraft that will not need wings at all. I can'thelp thinking that it sounds too good to be true.

When I meet Shawyer, he turns out to bereassuringly normal. His credentials arecertainly impressive. He worked his way upthrough the aerospace industry, designingand building navigation and communicationsequipment for military and commercialsatellites, before becoming a senior aerospaceengineer at Matra Marconi Space (later partof EADS Astrium) in Portsmouth, near wherehe now lives. He was also a consultant to theGalileo project, Europe's satellite navigationsystem, which engineers are now testing inorbit and for which he negotiated the use ofthe radio frequencies it needed.

Dangerous ideaWith that pedigree, you'd imagine Shawyerwould be someone the space industry wouldhave listened to. Far from it. While at Astrium,Shawyer proposed that the company develophis idea. "I was told in no uncertain terms todrop it," he says. "This came from the very top."

What Shawyer had in mind was a

30 New Scientist 9 September 2006

With the thruster and itspower supply balanced onan air bearing, the entireassembly (left) shouldspin horizontally undermicrowave power

replacement for the small thrustersconventional satellites use to stay in orbit. Thefuel they need makes up about half their launchweight, and also limits a satellite's life: once itruns out, the vehicle drifts out of position andmust be replaced. Shawyer's engine, by contrastwould be propelled by microwaves generatedfrom solar energy. The photovoltaic cellswould eliminate the fuel, and with the launchweight halved, satellite manufacturers couldsend up two craft for the price of one, so youwould only need half as many launches.

"How can photons confined inside a cavitymake the cavity move? This is where relativityand the strange nature of light come in"

So why the problem? Shawyer argues thatfor companies investing billions in rocketsand launch sites, a new technology that leadsto fewer launches and longer-lasting satelliteshas little commercial appeal. By the sametoken, a company that offers more for lessusually wins in the end, so Shawyer's idea mayhave been seen as too speculative. Whateverthe reason, in 2000, he resigned to go it alone

Surprisingly, Shawyer's disruptivetechnology rests on an idea that goes backmore than a century. In 1871 the physicist

James Clerk Maxwell worked out that lightshould exert a force on any surface it hits, likethe wind on a sail. This so-called radiationpressure is extremely weak, though. Last year,a group called The Planetary Societyattempted to launch a solar sail called Cosmos1 into orbit. The sail had a surface area of about600 square metres. Despite this large area,about the size of two tennis courts, itsdevelopers calculated that sunlight striking itwould produce a force of 3 millinewtons,barely enough to lift a feather on the surface

of the Earth. Still, it would be enough toaccelerate a craft in the weightlessness ofspace, though unfortunately the sail was lostafter launch. NASA is also interested in solarsails, but has never launched one. Perhaps thatshouldn't be a surprise, as a few millinewtonsisn't enough for serious work in space.

But what if you could amplify the effect?That's exactly the idea that Shawyer stumbledon in the 1970s while working for a Britishmilitary technology company calledSperry Gyroscope. Shawyer's expertise is in

microwaves, and when he was asked to comeup with a gyroscopic device for a guidancesystem he instead came up with the ideafor an electromagnetic engine. He evenunearthed a 1950s paper by Alex Cullen,an electrical engineer at University CollegeLondon, describing how electromagneticenergy might create a force. "It came tonothing at the time, but the idea stuck inmy head," he says.

In his workshop, Shawyer explains howthis led him to a way of producing thrust.For years he has explored ways to confinemicrowaves inside waveguides, hollow tubesthat trap radiation and direct it along theirlength. Take a standard copper waveguide andclose off both ends. Now create microwavesusing a magnetron, a device found in everymicrowave oven. If you inject thesemicrowaves into the cavity, the microwaveswill bounce from one end of the cavity to theother. According to the principles outlined byMaxwell, this will produce a tiny force on theend walls. Now carefully match the size of thecavity to the wavelength of the microwavesand you create a chamber in which themicrowaves resonate, allowing it to storelarge amounts of energy.

What's crucial here is the Q-value of thecavity - a measure of how well a vibratingsystem prevents its energy dissipating intoheat, or how slowly the oscillations are

32 New Scientist 9 September 2006

damped down. For example, a pendulumswinging in air would have a high Q, while apendulum immersed in oil would have a lowone. If microwaves leak out of the cavity, the Qwill be low. A cavity with a high Q-value canstore large amounts of microwave energy withfew losses, and this means the radiation willexert relatively large forces on the ends of thecavity. You might think the forces on the endwalls will cancel each other out, but Shawyerworked out that with a suitably shapedresonant cavity, wider at one end than theother, the radiation pressure exerted by themicrowaves at the wide end would be higherthan at the narrow one.

Key is the fact that the diameter of atubular cavity alters the path - and hence theeffective velocity - of the microwavestravelling through it. Microwaves movingalong a relatively wide tube follow a more orless uninterrupted path from end to end,while microwaves in a narrow tube movealong it by reflecting off the walls. Thenarrower the tube gets, the more themicrowaves get reflected and the slowertheir effective velocity along the tubebecomes. Shawyer calculates the microwavesstriking the end wall at the narrow end of hiscavity will transfer less momentum to thecavity than those striking the wider end

(see Diagram, below). The result is a netforce that pushes the cavity in one direction.And that's it, Shawyer says.

Hang on a minute, though. If the cavity isto move, it must be pushed by something.A rocket engine, for example, is propelled byhot exhaust gases pushing on the rear of therocket. How can photons confined inside acavity make the cavity move? This is whererelativity and the strange nature of light comein. Since the microwave photons in thewaveguide are travelling close to the speed oflight, any attempt to resolve the forces theygenerate must take account of Einstein'sspecial theory of relativity. This says that themicrowaves move in their own frame ofreference. In other words they moveindependently of the cavity - as if they areoutside it. As a result, the microwavesthemselves exert a push on the cavity.

Each photon that a magnetron fires intothe cavity creates an equal and oppositereaction - like the recoil force on a gun as itfires a bullet. With Shawyer's design, however,this force is minuscule compared with theforces generated in the resonant cavity,because the photons reflect back and forth upto 50,000 times. With each reflection, areaction occurs between the cavity and thephoton, each operating in its own frame of

reference. This generates a tiny force, whichfor a powerful microwave beam confined inthe cavity adds up to produce a perceptiblethrust on the cavity itself.

Shawyer's calculations have not convincedeveryone. Depending on who you talk toShawyer is either a genius or a purveyor ofsnake oil. David Jefferies, a microwaveengineer at the University of Surrey in the UK,is adamant that there is an error in Shawyer'sthinking. "It's a load of bloody rubbish,"he says. At the other end of the scale is StepanLucyszyn, a microwave engineer at ImperialCollege London. "I think it's outstandingscience," he says. Marc Millis, the engineerbehind NASA's programme to assessrevolutionary propulsion technology acceptsthat the net forces inside the cavity will beunequal, but as for the thrust it generates,he wants to see the hard evidence beforemaking a judgement.

Thrust from a boxShawyer's electromagnetic drive - emdrive forshort - consists in essence of a microwavegenerator attached to what looks like a largecopper cake tin. It needs a power supply forthe magnetron, but there are no moving partsand no fuel - just a cord to plug it into themains. Various pipes add complexity, but theyare just there to keep the chamber cool.And the device seems to work: by mounting iton a sensitive balance, he has shown that itgenerates about 16 millinewtons of thrust,using 1 kilowatt of electrical power.Shawyer calculated that his first prototypehad a Q of 5900. With his second thruster,he managed to raise the Q to 50,000allowing it to generate a force of about 300millinewtons -100 times what Cosmos 1could achieve. It's not enough for Earth-baseduse, but it's revolutionary for spacecraft.

One of the conditions of Shawyer's250,000 funding from the UK's Departmentof Trade and Industry is that his research beindependently reviewed, and he has beenmeticulous in cataloguing his work and inmeasuring the forces involved. "It's not easybecause the forces are tiny compared to theweight of the equipment," he says.

Optimising the cavity is crucial, and it's asmuch art as science. Energy leaks out in allkinds of ways: microwaves heat the cavity, forexample, changing its electricalcharacteristics so that it no longer resonates.At very high powers, microwaves can ripelectrons out of the metal, causing sparks anda dramatic loss of power. "It can be a very finebalancing act," says Shawyer.

To review the project, the UK governmenthired John Spiller, an independent spaceengineer. He was impressed. He says the

THE ELECTROMACNETIC DRIVEMicrowaves trapped in a cavity exert a force on the end walls. By making the area of one endgreater than the other, Roger Shawyer says he can tailor this force so his device generates thrust

9 September 2006 New Scientist 33

LOOK, NO WINGS!If Roger Shawyer's electromagnetic drive performs as he hopes, it might be possible to build vehicles that hover. Liquid hydrogencould cool the drives and fuel a turbine to propel the craft forwards

thruster's design is practical and could beadapted fairly easily to operate in space.He points out, though, that the drive needsto be developed further and tested by anindependent group with its own equipment."It certainly needs to be flownexperimentally," he says.

Armed with his prototypes, the testmeasurements and Spiller's review, Shawyeris now presenting his design to the spaceindustry. The reaction in China and the US hasbeen markedly more enthusiastic than that inEurope. "The European Space Agency knowsabout it but has not shown any interest,"he says. The US air force has already paid hima visit, and a Chinese company has attemptedto buy the intellectual property associatedwith the thruster. This month, he will betravelling to both countries to visit interestedparties, including NASA.

To space and beyondHis plan is to license the technology to a majorplayer in the space industry who can adaptthe design and send up a test satellite to provethat it works. If all goes to plan, Shawyerbelieves he could see the engine tested inspace within two years. He estimates that histhruster could save the space industry $15billion over the next 10 years. Spiller is morecautious. While the engine could certainlyreduce the launch weight of a satellite, hedoubts it will significantly increase its lifetimesince other parts will still wear out. The spaceindustry might not need to worry after all.

Meanwhile Shawyer is looking ahead to thenext stage of his project. He wants to make thethrusters so powerful that they could makecombustion engines obsolete, and that meansaddressing the big problem with conventionalmicrowave cavities - the amount of energythey leak. The biggest losses come fromcurrents induced in the metal walls by the

"A Chinese company hastried to buy rights to themicrowave thruster"microwaves, which generate heat when theyencounter electrical resistance. This uses upenergy stored in the cavity, reduces the Qand the thrust generated by the engine drops.

Fortunately particle accelerators usemicrowave cavities too, so physicists havedone a lot of work on reducing Q losses insidethem. The key, says Shawyer, is to make thecavity superconducting. Without electricalresistance, currents in the cavity walls will notgenerate heat. Engineers in Germany workingon the next generation of particle acceleratorshave achieved a Q of several billion usingsuperconducting cavities. If Shawyer canmatch that performance, he calculates thatthe thrust from a microwave engine could beas high as 30,000 newtons per kilowatt -enough to lift a large car.

This raises another question. Why haven'tphysicists stumbled across the effect before?They have, says Shawyer, and they designtheir cavities to counter it. The forces insidethe latest accelerator cavities are so large thatthey stretch the chambers like plasticine. Tocounteract this, engineers use piezoelectricactuators to squeeze the cavities back intoshape. "I doubt they've ever thought ofturning the force to other uses," he says.

No doubt his superconducting cavities willbe hard to build, and Shawyer is realistic aboutthe problems he is likely to meet. Particleaccelerators made out of niobium becomesuperconducting at the temperature of liquidhelium - only a few degrees above absolutezero. That would be impractical for a motor,Shawyer believes, so he wants to find amaterial 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 orturbine to generate electricity for the emdrive.

In the meantime, he wants to test thedevice with liquid nitrogen, which is easier tohandle. It boils at 77 kelvin, a temperature thatwill require the latest generation of high-temperature ceramic superconductors.Shawyer hasn't yet settled on the exactmaterial, but he admits that any ceramicwill be tricky to incorporate into the designbecause of its fragility. It will have to bereliably bonded to the inside of a cavity andmustn't crack or flake when cooled. There areother problems too. The inside of the cavitywill still be heated by the microwaves, and thiswill possibly quench the superconductingeffect. "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 thethruster starts to move, it will use up energystored in the cavity, draining energy fasterthan it can be replaced. So while the thrustof a motionless emdrive is high, the fasterthe engine moves, the more the thrust falls.Shawyer now reckons the emdrive will bebetter suited to powering vehicles that hoverrather than accelerate rapidly. A fan or turbineattached to the back of the vehicle could thenbe used to move it forward without friction.He hopes to demonstrate his firstsuperconducting thruster within two years.

What of the impact of such a device?On my journey home I have plenty of timeto speculate. No need for wheels, no friction.Shawyer suggested to me before I left that ahover car with an emdrive thruster cooled andpowered by hydrogen could be a major factorin converting our society from a petrol-basedone to one based on hydrogen. "You needsomething different to persuade people tomake the switch. Perhaps being able to movein three dimensions rather than two woulddo the trick."

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

Further Reading: "The development of a microwaveengine for spacecraft propulsion" by Roger Shawyer,Space Chronicle Journal of the British InterplanetarySociety, vol 58, p 26

Read previous issues of New Scientist athttp://archive.newscientist.com

34 New Scientist 9 September 2006