A Nasa test has yielded results seemingly favourable to a British scientist’s idea of propelling rockets without fuel, but many experts are still sceptical.
Roger Shawyer’s electromagnetic (EM)-drive theory of generating thrust without expending fuel, propounded over 15 years ago, was so revolutionary that one physicist labelled it “rubbish” in 2006.
Now, scientists at Nasa’s Johnson Space Centre in Houston, Texas, have described the results of a fresh experiment in which they observed thrust by bouncing microwaves inside a cone-shaped cavity.
The EM-drive has spawned visions of flying cars and easy space travel. But it remains controversial because, some physicists say, it appears to violate a cardinal principle of physics, the conservation of momentum, linked to Newton’s third law.
Shawyer disagrees. “EM-drive is based on standard physics and has been proved by experiment,” he said in a presentation on the website of Space Propulsion Research, a UK-based company that is studying EM-drive technology alongside research groups in China, Germany and the US.
“It is now up to the space and the defence world to demonstrate the many possible EM-drive applications and for the commercial industry to capitalise on this technology,” Shawyer said.
In their new study, just published in the Journal of Propulsion and Power, Harold White and his colleagues at the Nasa centre reported tiny levels of thrust, but about 100 times greater than other forms of “zero-propellant” thrust such as light sails, laser propulsion, or photon rockets.
The Nasa scientists, who had presented earlier experimental results at scientific conferences in 2014 and 2015, said their latest test campaign was not focused on “optimising performance” but was more an “exercise in existence proof”.
The EM-drive concept is controversial because it appears to defy the basic principle of physics that every action has an equal and opposite reaction, or Newton’s third law.
Shawyer has in interviews suggested that the EM-drive technology may be used for many applications, from unmanned aerial vehicles to small flying vehicles and space planes that can ferry giant payloads into space at a fraction of the current cost.
In one interview, he had said it might give rise to “flying cars” and solve city traffic jams.
An Australia-based physicist, John Costella, however, wrote in a 2006 paper that the proposal for the EM-drive was “rubbish” and the EM-drive itself “impossible”.
Costella had said that Shawyer’s proposal for the EM-drive contained a “fundamental blunder” that rendered it “meaningless”.
Despite such criticism, some scientists have persisted. Last year, physicist Martin Tajmar at the Institute of Aerospace Engineering at the Technical University of Dresden, Germany, built and tested an EM-drive and studied the thrust generated.
But Tajmar also cautioned that his experiments “cannot confirm or refute the claims of the EM-drive but (were intended) to independently assess possible side-effects in measurement methods so far”.
The latest paper from the Nasa researchers hasn’t shaken the physics community, either.
Chris Lee, a physicist at the University of Twente in The Netherlands, has in a commentary published on Tuesday in Ars Technica, a technology news and information website, said that holes in the paper had left him “sceptical and exasperated”.
Lee has suggested that the observed thrust may be the result of unaccounted for thermal effects.
“There is no theory that makes any numerical predictions about the EM-drive,” Lee told this newspaper via email.
“The effort to eliminate or estimate instrumental uncertainty is misplaced now, the spread in the data suggest that they need to look deeper into possible systematic that are influencing their results.
Source: The Telegraph