[FoRK] Relativity drive: The end of wings and wheels?
Stephen D. Williams <
sdw at lig.net
> on >
Sat Sep 23 17:51:47 PDT 2006
Umm. Wow. Self-contained, non-Newtonian (or semi-Newtonian?) force. If
this is confirmed and analyzed it will be very interesting.
If true, it's a matter of physics and material research to optimize,
pretty straightforward it seems.
It seems that with a microwave oven, welder, some metal, and a scale you
could duplicate the prototype.
Magnetrons produce photons? Microwave energy is photon based? Reporter
* 08 September 2006
* Exclusive from New Scientist Print Edition. Subscribe and get 4 free
* Justin Mullins
* Shawyer's theory paper (pdf)
The electromagnetic drive
The electromagnetic drive
Look, no wings!
Look, no wings!
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. Read
Shawyer’s theory paper here (pdf format).
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
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.
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
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
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