His engine works with no moving parts, using only microwaves and esoteric physics. He uses a principle discovered by Maxwell nearly 150 years ago, and the same one behind solar sails: that light exerts a force on any surface it hits. Shawyer uses resonant cavities, (those with lengths in integer multiples of the wavelength of light being used) to produce the force. Unfortunately, with cylindrical cavities the forces on both ends are the same, canceling any force.
Continue reading...However, by making a conically shaped resonant cavity, the waves will travel more slowly in the narrow end, producing an uneven force that results in thrust. According to Shawyer, it’s that simple.
But what actually makes the thrust? That’s where relativity comes in. Because the microwaves are moving close to (or at) the speed of light, relativistic effects must be taken into account. This means “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.” Very strange indeed.
The chief engineering difficulty is that the cavity tends to release energy, which diminishes the effectiveness of the engine. Shawyer has two prototypes, the better of the two produces about 300 miliNewtons, or 0.067 pounds of thrust. More efficient containers, like those used in particle accelerators and made of superconductors, could vastly improve performance.
One big drawback is that the faster these engines go, the less effective they become. That’s why Shawyer wants to use them to make hover-cars, freeing them from the ground while using conventional propulsion to move them.
As is usually the case with a new, untested technology, some people think it’s meaningless crank science, and others think it’s the wave of the future. However, Shawyer has been meticulous in documenting his research, and independent analysts have been impressed.
It’s hard to say what might come of this, there are many technological hurdles still to be crossed, and .067 pounds of thrust, while a good start, is nowhere near enough to be used in anything practical. Maybe one day when we’re all driving hover-cars around Shawyer will be looked upon as the man who gave us the relativity-drive; but he may also fade into obscurity. It’ll be a few years before we can tell for sure. I’ll be waiting to hear more, that’s for sure.
(From New Scientist, Sept. 08 2006, Reltivity Drive: the End of Wings and Wheels? Subscription required)