Scientists in China have built and tested a radical new space drive. Although the thrust it produces may not be enough to lift your mobile phone, it looks like it could radically change the satellite industry. Satellites are just the start: with superconducting components, this technology could generate the thrust to drive everything from deep space probes to flying cars. And it all started with a British engineer whose invention was ignored and ridiculed in his home country.
The latest research comes from a team headed by Yang Juan, Professor of Propulsion Theory and Engineering of Aeronautics and Astronautics at the Northwestern Polytechnic University in Xi’an. Titled “Net thrust measurement of propellantless microwave thruster,” it was published last year in the academic journal Acta Physica Sinica, now translated into English.
The technology is controversial because of that key word “propellantless”. Space drives rely on Newton’s laws of motion: all are based on the principle of firing propellant out the back at high speed, pushing the spacecraft forward. Even with endless power from solar cells, thrust is still limited by the supply of propellant, even with high-velocity ion drives. Numerous attempts have been made to overcome this, from the infamous Dean Drive of the 1950’s to Nasa’s experiments with antigravity from spinning superconductors in the 1990’s. All have failed, and the efforts of pseudoscientific cranks and scammers have left the field thoroughly discredited.
British engineer Roger Shaywer stepped into this dangerous field in 2001, after twenty years with European satellite firm EADS Astrium. He set up his own company, Satellite Propulsion Research (SPR) Ltd, with the aid of a modest grant from the UK’s Department of Trade and Industry.
Shawyer aimed to develop an EmDrive: a closed, conical container which, when filled with resonating microwaves, experiences a net thrust towards the wide end. It seems to violate of the law of conservation of momentum, implied by Newton, which says that no closed system can have a net thrust. However, Shawyer says net thrust occurs because the microwaves have a group velocity which is greater in one direction than the other and Einstein’s relativity comes into play. Group velocity, the speed of a collection of electromagnetic waves, is a tricky business — a pulse of light can even have a group velocity which is greater than the speed of light — but can it really cause net thrust?
Shawyer built a demonstration thruster to test the theory in 2003. The thrust was tiny — 16 mN, equal to the weight of a couple of peanuts — but enough to validate the concept. However, sceptics were quick to attack. None of them actually inspected the apparatus, but Shawyer was assailed from all sides online and in the science press. Criticism was unsophisticated: Newton said it was impossible, therefore he must be a fraud. Even the most advanced theoretical critique, produced by John Costella, a PhD in relativistic electrodynamics, amounted to arguing about the direction of an arrow on one of Shawyer’s diagrams.
Shawyer continued to produce and test more advanced demonstrators, working out elaborate ways of ensuring that the test results are valid and not the result of air currents, friction, ionization, interference or electromagnetic effects.