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Cover story
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
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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
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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
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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