Defying gravity

A UK company has obtained government backing to build a propellant-less engine based on microwaves that could lead to anti-gravity transport, and revolutionise spacecraft propulsion.

The Emdrive engine works by the relative movement of microwaves exerting a force within the engine, and the application of Einstein’s law of relativity, its developer SPR (Satellite Propulsion Research) claims.

SPR researchers said that the engine could position satellites in orbit, so launch weight could be halved and satellite lifetime significantly increased. The company’s bold claims also include using the engine as a means to divert an asteroid or to power a reusable launch vehicle into space.

Managing director Roger Shawyer said the engine could even lead to earth vehicles equipped with anti-gravity devices. ’It offers a potential transport infrastructure based on moving in 3D, no longer dependent on wings and wheels,’ said Shawyer. ’It would provide a static thrust that counteracts gravity, and conventional propulsion such as rocket or fan engines could then provide acceleration. It would be like a hot air balloon.’

Shawyer acknowledged that despite the engine’s potential, SPR has struggled to convince sceptics. ’It’s the first time there has been a demonstration of propulsion without propellant. It’s unique,’ he said. ’Nobody who has seen the technology has identified any flaw in the physics or maths.’

The team claims to have undergone seven independent reviews from experts at BAE Systems, EADS Astrium, Siemens and the IEE. The DTI has awarded the company £125,000 to develop a prototype engine as part of a three-year, £250,000 programme.

’This will be a complete engine to demonstrate the sort of performance needed to get a satellite from low-earth to geostationary orbit,’ he said.

The team claims that in over 450 tests the engine mass dropped by two grams when the device was running on a static platform.

The engine uses the effects of microwave propagation at the speed of light, according to Shawyer. A water-cooled magnetron feeds microwaves into a tuned tapered cylindrical waveguide, a hollow copper cone that transmits the waves back and forth between the two ends. At the wider end of the cone the wave travels at the speed of light, while at the other the wave travels at one tenth of that speed, due to the geometry of the waveguide.

This creates higher radiation pressure at the wider end of the waveguide because the rate of change of momentum of the waves is different. Newton’s second law defines force as the rate of change of momentum.

Shawyer explained that if these forces were the result of a working fluid, there would merely be a mechanical strain in the waveguide walls. But as the working fluid is replaced by an electromagnetic wave at close to the speed of light, Newtonian mechanics are replaced with the special theory of relativity.

’The electromagnetic wave is going at very high velocities, so you have to apply two different reference planes,’ he said. ’It can no longer be considered a closed system. As soon as you approach the speed of light the wave can be considered completely independent of the waveguide.’ Shawyer compared the engine to a laser gyroscope, which also relies on Einstein’s laws, where attitude information is obtained from an apparently closed system.

The team claims its experimental thruster proved their calculations that thrust can be produced by momentum transfer, and eliminated any spurious thermal or electromagnetic effects, although the evidence has yet to be peer-reviewed. Shawyer said that aerospace companies outside the UK are interested in the technology, but declined to reveal details.

The team eventually plans to build the engine using superconducting material, as this could allow the thrust to be massively increased. Superconducting waveguides would have significantly higher ’Q-values’.

A resonant waveguide has a Q-value, which is essentially a measure of the number of times a wave will bounce up and down before it loses energy, and this is related to the thrust, said Shawyer. ’Instead of getting grams of thrust, you could get tonnes out of the engine,’ he said. ’The big problem to overcome with this is that the internal radiation would distort the cavity and it would detune.’

Some experts remain sceptical about the SPR’s claim’s however. Professor Corin Segal, a University of Florida space propulsion expert and executive director of the NASA-backed Institute for Future Space Transport, said it is unclear whether the engine can exert any thrust.

’Theoretically a force may be generated, but it has to act on the surroundings to generate a reaction,’ he said. ’The device appears to generate a flux that remains within the system with no action on the surroundings. I’m sceptical that thrust can be obtained by the oscillatory motion in the cavity.’