Tom Shelley reports on progress with the controversial Emdrive and its potential applications in space and on the ground
The Emdrive - originally revealed in Eureka's December 2002
edition as a way of driving satellites and spacecraft using
microwaves - is now demonstrating its ability to produce thrust
on a consistent basis and is scheduled to be ready for space use
by May 2009.
Meanwhile studies are underway into the design of a
superconducting version, with a possible thrust of more than
30kN/kW. While it couldn't be used to accelerate a rocket, it
might well be able to provide enough static lift for a flying
vehicle propelled forward by other means.
Despite massive controversy, the project continues to be backed
by DTI and private investors, and has now been shown to work.
Roger Shawyer, who spent 20 years at Marconi Space Systems (now
EADS Astrium), revealed details of the prototype engine and its
development plans to an IEE chapter meeting in Portsmouth, where
the audience included many ex-colleagues from his former company.
Shawyer stated that many of the claims he is alleged to have made
about the Emdrive are untrue, particularly suggestions that it
defies the principles of conservation of momentum, or Newton's
Laws of Motion.
The crucial part, as he explained, is that it is a relativistic
effect that arises because the waves being reflected at the two
ends of the conical cavity into which the microwaves are injected
have different effective velocities, and thus different frames of
reference, and that a closed microwave wave guide is an 'open
system' in terms of relativity. According to Einstein, all moving
frames of reference are equivalent. Why this should be so,
whether one is standing still or going at half the speed of
light, nobody knows, and in effect Shawyer's engine could be
chucking Dark Energy out of the back of it and functioning as a
conventional rocket. On the other hand, there may be no such
thing as Dark Energy, and Shawyer may have stumbled on what is
really driving the galaxies apart.
But as he pointed out: "I am just a microwave engineer and
all that matters is that it works."
In the present experimental engine and its immediate predecessor,
the cavity is made in the form of a copper cone closed off by
flat plates at the wide and narrow ends. The net thrust is
proportional to the Q value of the cavity, where Q is the ratio
of the amount of stored energy to the amount of energy lost per
cycle. Acceleration extracts energy from the system and Q
decreases. The development engine has a Q value of 50,000 and
produces a specific thrust of 0.315N/kW. The original engine
produced a thrust of 1.6 grammes, but could only run for tens of
seconds at a time before the magnetron overheated and burned out.
The present engine produces 9 grammes of thrust from 300W of
microwave power and is continually water-cooled. The internal
power density is about 17MW.
A video of the demonstration of the engine in its test cell
involved mounting the engine and its cooling system on a beam,
and supporting it on an air bearing. The test was undertaken in
October last year, producing a thrust of 9.8 grammes, maximum
speed of 2 cm/s and a movement distance of 185cm. According to
Shawyer, the tests had involved accelerating from rest,
deceleration to rest, forward and reverse engine mounting,
energising at different start angles and using different input
powers.
While 9.8 grammes of thrust from a 100kg of machinery may not
sound very much, it is a much better power-to-weight ratio than
the best competitive satellite and spacecraft propulsion
technology, which involves using an ion engine.
For a 1500W DC input power, an ion drive produces 92mN thrust,
whereas an Emdrive, based on current technology, should produce
330mN thrust. Furthermore, an ion engine of this size would weigh
112.5kg plus propellant, whereas an Emdrive would weigh 9kg. And
while life under power for an ion engine is about six months, an
Emdrive should run for 15 years - or virtually forever, if the
microwaves were generated by some solid state device.
The big application is for commercial communication satellites -
where 'Hotbirds' have a take-off weight of 3 tonnes, of which 1.7
tonnes is propellant - both to get them from Low Earth Orbit to
Geostationary and to keep them pointing the right way once they
get there. Using Emdrives, says Shawyer, should save £15 billion
in launch costs over 10 years. While the thrust from the Emdrive
would be small, it should get the satellite from Low Earth to
Geostationary orbit in 36 days. Power would be from 6kW of solar
cells fed to Travelling Wave Tube Amplifiers.
But what really captivated the audience was Shawyer's proposal
for the next stage, which would be to use a superconducting
cavity with a Q value of 5 billion and a thrust of 3 tonnes/kW.
Unfortunately, one could not use the device accelerate without
"causing the Q value to collapse, losing thrust in that
vector", he conceded.
One serious consideration is to develop the technology so that it
could be used gently to divert a large asteroid in danger of
colliding with the Earth. In fact, prior to Shawyer's address,
David Hall from EADS Astrium had discussed the use of microwave
technology to study the internals of Near Earth Object asteroids.
He said blowing up such a threat, Hollywood-style, was not really
practical - the parts would still be likely to hit the Earth.
Current ideas were mostly about finding ways of nudging asteroids
into a safe trajectory. As acceleration would be so low, a
superconducting Emdrive would be a possible option. A 1kW engine
would require 24kW to keep it cool and shifting the asteroid
would take somewhere in the order of 10 years, depending on its
size.
Shawyer said his team was thinking of using superconducting
cavities of a type already being developed and manufactured for a
major accelerator project, and cooling them with hydrogen. If
applied to lifting a vehicle, the boiling off hydrogen could be
used to provide horizontal motion by feeding it to conventional
turbofan engines, if in the atmosphere, or to rocket engines for
use in space. Whether the technology will ever be used to produce
hydrogen-propelled air cars or other wonders, only time will
tell.
A full theoretical paper on the technology is available on the
Emdrive web site ( www.emdrive.com
)
Pointers
* Novel non-propellant microwave drive has reached the point
where it can be run continuously
* Demonstration engine and cooling system weighs about 100kg and
produces just under 10 grammes of thrust
* Next engine for satellite propulsion should weigh a little less
than 10kg and produce 330mN thrust
* A superconducting design able to deliver tonnes of lift thrust
(but no acceleration) is being studied
For more technical
developments see www.eurekamagazine.co.uk