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NEWSCIENCENEWSCIENCENEWSCIENCE RELATIVITY DRIVE: THE END OF WINGS AND WHEELS? 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 the British military technology company 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. It led him to a way of producing thrust. cavity. 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 oger Shawyer has developed an Ree with no moving parts that he believes can replace rockets and make trains, planes and automobiles obsolete. 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 are beating a path to his tiny company. 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! Shawyer 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, UK. 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. 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." Shawyer's technology rests on an idea that goes back to the physicist James Clerk Maxwell, who in 1871 worked out that light should exert a force on any surface it hits, like the wind ona sail. This so-called radiation pressure is extremely weak. In 2005, a group called The Planetary Society attempted to launch a solar sail called Cosmos I into orbit. The sail had a surface area of about 600 square metres. Despite this large area, its developers calculated that sunlight striking it would produce a force of three 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. Unfortunately, But what if you could amplify the effect? narrow one. That's exactly the idea that Shawyer Key is the fact that the diameter of a stumbled on in the 1970s while working for _ tubular cavity alters the path—and hence the British military technology company __ the effective velocity—of the microwaves Sperry Gyroscope. Shawyer's expertise is travelling through it. Microwaves moving in microwaves, and when he was asked to along a relatively wide tube follow a more come up with a gyroscopic device fora __ or less uninterrupted path from end to end, guidance system he instead came up with while microwaves in a narrow tube move the idea for an electromagnetic engine. He along it by reflecting off the walls. The even unearthed a 1950s paper by Alex narrower the tube gets, the more the Cullen, an electrical engineer at University microwaves get reflected and the slower College, London, describing how their effective velocity along the tube electromagnetic energy might create a becomes. Shawyer calculates that the force. "It came to nothing at the time, but microwaves striking the end wall at the the idea stuck in my head," he says. It led narrow end of his cavity will transfer less him to a way of producing thrust. momentum to the cavity than those striking the wider end. The result is a net force that pushes the cavity in one direction. Since the microwave photons in the waveguide are travelling close to the speed It has no moving parts, of light, any attempt to resolve the forces and releases no exhaust they generate must take into account . oe Einstein's special theory of relativity, i.e., or noxious emissions. that 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. For years, Shawyer has explored ways to Armed with his prototypes, the test confine microwaves inside waveguides— measurements and the positive review by hollow tubes that trap radiation and direct it | UK government-hired independent space along their length. Take a standard copper engineer John Spiller, Shawyer is now waveguide and close off both ends. Now presenting his design to the space industry. create microwaves using a magnetron, a__ The reaction in China and the US has been device found in every microwave oven. If markedly more enthusiastic than in Europe. you inject these microwaves into the "The European Space Agency knows about cavity, the microwaves will bounce from _ it but has not shown any interest," he says. one end of the cavity to the other. The US Air Force has already paid him a According to the principles outlined by __ visit, and a Chinese company has attempted Maxwell, this will produce a tiny force on to buy the intellectual property rights the end walls. Now carefully match the associated with the thruster. size of the cavity to the wavelength of the Shawyer's plan is to license the microwaves and you create a chamber in _ technology to a major player in the space which the microwaves resonate, allowing it industry who can adapt the design and send to store large amounts of energy. up a test satellite to prove that it works. If What's crucial here is the Q-value of the all goes to plan, Shawyer believes he could cavity—a measure of how well a vibrating see the engine tested in space within two system prevents its energy dissipating into years. He estimates that his thruster could heat, or how slowly the oscillations are save the space industry US$15 billion over damped down. If microwaves leak out of _ the next 10 years. oo the cavity, the Q will be low. A cavity (Source: Edited from New Scientist, with a high Q-value can store large issue 2568, 8 September 2006, pp. 30- amounts of microwave energy with few 34; Shawyer's theory paper is available losses, which means the radiation will exert at http://www.newscientist.com/data/ relatively large forces on the ends of the —_images/ns/av/shawyertheory.pdf) It has no moving parts, and releases no exhaust or noxious emissions. NEXUS = 51 by Justin Mullins © 2006 or noxious emissions. FEBRUARY — MARCH 2007 www.nexusmagazine.com