Microwave engine gets a boost

1 September 2006

UK research into a propellant-free microwave engine designed for spacecraft propulsion is stirring interest from US and Chinese aerospace companies, its developer has claimed.

Despite sounding like the stuff of science-fiction, SPR (Satellite Propulsion Research), the company behind the EmDrive – which was first reported by The Engineer in November 2004 – insists its technology is gathering momentum in the international aerospace community.

According to the managing director of Roger Shawyer, the engine takes microwave radiation produced by a magnetron and feeds it into a specially shaped resonant cavity. The waves push against the end wall. Because of the difference in wave velocity, being higher at one end that the other, there is a momentum transfer. The result is a measurable net force from the cavity against its surroundings.

The EmDrive is just entering the third of three development phases. The first was an experimental thruster, which Shawyer claims provided a thrust of 2g in over 240 tests, shown as a drop in the engine mass.

The second phase produced a demonstrator engine which has recently completed its own set of independently reviewed static thrust tests.

‘These first two models were prototypes,’ said Shawyer. ‘As they operate at room temperature, the Q value, or the stored energy divided by losses, was restricted.

‘The next stage would ideally use technology employed by high-energy physics. If we approach a condition where we use the same shape cavity but at absolute zero and made from Niobium, the resistance drops to near zero and the Q value increases by several orders of magnitude.’

Shawyer cautions that the calculations only work for static thrusts. ‘You can’t beat the laws of physics. If it is used to accelerate, the Q value drops. It is best used to lift a body and oppose a force, for instance to counteract gravity. It cannot be used to accelerate further.’

Shawyer said the most practical application of the first generation is for thrusters used to lift a satellite into geostationary orbit form low-earth orbit. ‘The dramatic drop-off in Q doesn’t happen as quickly, so it makes little difference. It tends not to accelerate in the main velocity vector, only for thrusts up and down. It beats ion engines.’

The third stage of development will product a new generation of EmDrive, which Shawyer envisages coming into its own in 10 years or so and being used in a variety of terrestrial transport.

Shawyer is looking to US and Chinese aerospace industry to fund the next phase of development. The company hopes to license the first generation technology to one or more aerospace companies while they concentrate on the next phase, which will include experimental superconducting thrusters.

‘We are expanding the company, but we want to offload the marketing so we can concentrate on research,’ said Shawyer.