Controversial research into ‘propellantless propulsion’ is ongoing in Europe, China and North America. Despite claims that there should be no thrust laboratories, including NASA’s, are measuring a force at work. ROB COPPINGER investigates the claims.

British Roger Shawyer's 'Impossible engine' EmDrive received a boost last year after a NASA paper backed up claims of propellantless thrust- but does it really work? (Roger Shawyer).

After decades of conjecture that the concepts cannot work, demonstrations of propellantless propulsion are being promised in the next few years with in-orbit satellite tests and a demonstrator flying vehicle. In 2016, some of the latest research challenging the mainstream view that it is all impossible was published by the American Institute of Aeronautics and Astronautics’ (AIAA).

The AIAA’s peer reviewed Journal of Propulsion and Power published the paper, ‘Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum’, from NASA’s Eagleworks Laboratory. The laboratory is based at NASA’s Johnson Space Flight Center in Houston, Texas. The paper’s abstract states that: ‘Thrust data ... suggested that the system was consistently performing with a thrust-to-power ratio of 1.2 plus or minus 0.1 milliNewtons per kiloWatt.’

Since 2013, the Eagleworks team has been examining two concepts: the EmDrive, which the NASA researchers refer to as the tapered cavity, and the Cannae Drive. A Guido Fetta is the originator of the Cannae Drive. His company, Cannae LLC, is based in the US. The EmDrive inventor is Roger Shawyer, founder of Satellite Propulsion Research (SPR), based in the UK. It was the tapered cavity concept cited in the AIAA paper that achieved the thrust-to-power ratio of 1.2 during Eagleworks’ experiments.

A published SPR EmDrive timetable from 2014 gives 2019 as the date for a demonstrator flying vehicle. Fetta’s Cannae Drive is planned to be launched into orbit in a cubesat before late July 2018. A Cannae press release dated 20 July 2016 says the cubesat would be launched within 24 months. In December 2016, the China Academy of Space Technology (CAST), the Chinese Government’s satellite manufacturer, announced that it had a development programme to test a propellentless drive in orbit.

A claim by the online news publication, International Business Times, in November 2016 that EmDrive type propellantless drives have been flown on China’s Tiangong-2 space laboratory and the US Air Force’s X-37B spaceplane could not be verified by Aerospace. Tiangong-2 was launched in September last year. This space laboratory programme is run by the China Manned Space Program (CMSP) but the CMSP did not respond to email contact.

In May 2015, the USAF’s Boeing X-37B spaceplane was launched for its fourth mission. At the time the USAF said that the X-37B would test an ‘electric propulsion thruster,’ while it was in orbit, which could be for two or three years. Previous X-37B flights have lasted for more than a year. AEROSPACE contacted the USAF’s Rapid Capabilities Office (RCO), which manages the X-37B programme, and asked if the electric thruster was an EmDrive and the RCO said it was not. A report by the space news site, Spaceflightnow.com, on 6 May 2015 stated that US military officials told the website that it was a new Hall Effect thruster.

Boeing’s interest

The Boeing X-37 spaceplane has not bee testing the EmDrive, according to the USAF. (USAF)

Boeing is the prime contractor for the X-37B and the US aerospace giant has assessed Shawyer’s EmDrive technology; it confirmed this to AEROSPACE. “Boeing has no current plans for EmDrive technology. Boeing will continue to monitor [propellantless drive] development and proof of concept testing by other entities, including NASA,” Boeing told AEROSPACE.

Shawyer, a RAeS Fellow, told AEROSPACE that his first contact with Boeing was in 2006. EmDrive had received some trade press media coverage in the early 2000s because of the UK Government funding Shawyer had received. But it was the 6 September 2006 New Scientist magazine cover story about EmDrive that raised the concept’s profile and led to the backlash by physicists and others.

Shawyer was still invited to visit Boeing’s Phantom Works and, later in 2008, the USAF contacted him and a meeting took place on 10 December at the Department of Defense’s (DoD) Pentagon building. He gave a presentation on the EmDrive at this meeting, which was chaired by the Director of the National Security Space Office and had representatives from USAF, the DoD’s Defense Advanced Research Projects Agency (DARPA) and NASA in attendance.

In 2009, government-to-government agreements enabled Shawyer’s firm SPR to work with Boeing. In a UK Government Department of Trade and Industry end-user undertaking seen by Aerospace, Boeing was to receive an SPR built EmDrive flight thruster for work to take place at the company’s Huntingdon Beach, California facility. It was Boeing’s Phantom Works that assessed the EmDrive.

Following the Pentagon meeting, Shawyer had a further meeting with DARPA. The defence research agency acknowledged to AEROSPACE that it had been in ‘discussions’ about EmDrive, but would not disclose any more information.

EmDrive development

EmDrive hybrid spaceplane propulsion system concept. (Roger Shawyer)

Shawyer has continued to develop his EmDrive and is bemused by the strength of feeling directed at it. The EmDrive emits microwaves into a cavity with one end larger than the other; it is tapered. His hypothesis is that radiation pressure at one end of the cavity is greater than the other, generating thrust. Today, he is working with the UK aerospace company Gilo Industries. “We envisage a wide range of aeronautical, astronautical and terrestrial applications once these engines become available to commercial industry. A flying car is one of the more obvious applications,” Shawyer told AEROSPACE.

He declined to give details about the work with Gilo, due to ‘commercial and government imposed restrictions.’ However, Shawyer does confirm he is working on a superconducting EmDrive thruster. A 2014 published timetable of his estimated that, by 2016, he would have a 3kW thruster producing 3kN of thrust. He declined to confirm if he and Gilo has achieved that, saying that he is unable to talk about, ‘current test data’.

The timetable also states that a vehicle demonstrator would be tested in 2019. While Shawyer also declines to comment on if this will also occur on time, he does explain how such a vehicle would be powered. A flying vehicle, atmospheric or exo-atmospheric, would cool its many EmDrive thrusters with liquid hydrogen. As the liquid hydrogen boils off, that gas is used that to cool down the high-power microwave sources and is then pumped into a fuel cell to generate the electricity needed to power the vehicle’s systems, including the EmDrive’s microwave input.

China’s work

Unsubstantiated news reports have speculated that a Chinese propellentless drive has been tested on the Tiangong-2 space station. (CATC)

The announcement in December 2016 that China plans to launch a test satellite with a propellantless drive on-board follows at least a decade of Chinese research. The Chinese science and technology publication, STDaily.com, reported on 10 December on press conference comments by CAST’s Institute of Communication Satellite division’s Dr Chen Yue. However, no date for the propellantless propulsion test satellite has been given. Yue was not available for comment when emailed by AEROSPACE.

In 2008, a professor Juan Yang and her scientists studying the EmDrive concept at Northwestern Polytechnical University (NWPU) in Xi’an, China invited Shawyer to visit and give lectures. Yang and her team had been studying propellantless drives and the EmDrive. Shawyer told AEROSPACE, he was shown their thermal vacuum test chambers for flight thrusters and other facilities.

Yang is a Professor of Aerospace Propulsion Theory and Engineering at NWPU. In 2011, her team submitted their first paper claiming a measured thrust output of 270milliNewtons (mN). It was in 2013 that Yang’s team published another paper in the Chinese Physics B Journal, an international journal produced by the Institute of Physics’ publishing arm, showing a dramatic thrust increase to 720mN. Yang has not responded to AEROSPACE’s emails.

Shawyer told AEROSPACE that 720mN is the highest published EmDrive thrust. The NPWU team published again early in 2016 but it was only in Chinese with an English abstract, professor Martin Tajmar told Aerospace. Tajmar is a director of the Technical University of Dresden’s Institute of Aerospace Engineering and Head of Space Systems.

Tajmar’s Institute has been studying propellantless drives. One of Tajmar’s graduate students built an EmDrive and Tajmar published the results in 2015. “What I reported was inconclusive. We built the thruster, according to the [EmDrive] specification, and we could measure thrust that was according to what we should have measured, but I couldn’t get a null measurement,” he told AEROSPACE. A null measurement is when a test or experiment is set up in such a way that it should not produce anything that can be measured.

On the controversy, Tajmar’s view is that good science needs to be done to either disprove or prove something. He rejects Shawyer’s radiation pressure hypothesis. “[First], is there an experimental case or not? There is no settled case here,” Tajmar commented. Another graduate student is to continue the EmDrive work this year and likely into 2018 to eliminate the possible experimental errors identified.

Tajmar has also tested a propellantless drive designed by Dr James Woodward, Emeritus Adjunct Professor of Physics at the State University of California Fullerton. Woodward’s approach is very different to Shawyer’s. Woodward’s concept is based on the hypotheses of Ernst Mach, whose ideas influenced Albert Einstein. Mach also gave his name to the measurement of the speed of sound.

Woodward told AEROSPACE that Mach’s principle is that all inertial forces, the forces of reaction in Newton’s third law, are produced by the gravitational action of all the matter in the universe. When that universal gravity action on an object is analysed, it is found that the object’s mass changes, fluctuates if it is subject to forces that cause it to be deformed, changing its, ‘internal energy’ as it is accelerated. If a second periodic force is brought to bear on the object whose mass is fluctuating, by pushing heavily and pulling lightly on said object, a steady thrust is produced in the direction of the heavy push.

Tajmar’s work on a Mach Effect Drive is ongoing. He told AEROSPACE that his team is detecting thrust but the test campaign is not completed, they have not finished their calibration checks and the laboratory has many error sources to check.

Eagleworks’ thruster

Harold Sonny White from NASA said that tests of the EmDrive tapered cavity concept had only detected small levels of milliNewtons of thrust because their power input has been small. (NASA Ames)

Of the different laboratories researching propellantless drives, the most well-known is NASA’s Eagleworks. Its peer-reviewed paper follows an AIAA conference presentation by the Eagleworks team in 2014 at the 50th AIAA Joint Propulsion Conference, held in Cleveland, Ohio. Then and with the 2016 AIAA publication, Harold Sonny White’s team has only reported small levels of milliNewtons of thrust because their power input has been small.

His Eagleworks’ AIAA Journal paper proposes a hypothesis that the quantum vacuum is a dynamic medium that could provide the detected thrust. Professor Lawrence Krauss, a theoretical physicist at the State University of Arizona, has written a book about the nature of the vacuum and how a universe can be spawned from it, entitled A Universe from Nothing. Krauss told AEROSPACE that the dynamic medium “idea won’t work”. White was not available for an interview about Eaglework’s experiments.

" Much time has been spent by many parties reviewing the claims of propellantless propulsion despite an apparent lack of reproducible results. The issue with all of these ‘thrusters’ is the lack of theoretical background to them"

With such widespread mainstream scepticism, it may seem strange that an organisation like the AIAA would publish such research. The AIAA has what it calls publishing principles and, under its principle for the evaluation of manuscripts and acceptance procedure for AIAA Journals, the Institute states: ‘It is the policy of the Editors to give unbiased and impartial consideration to all manuscripts offered for publication and to make sure that no unconventional hypothesis or original idea is throttled if there is a chance that such a paper might stimulate either progress or constructive controversy on a technical point.”

However, the AIAA paper is not the only peer-reviewed paper to be published in 2016. In June, last year, the American Institute of Physics’ (AIP) AIP Advances publication published a paper from University of Helsinki and University of Jyväskylä researchers entitled ‘On the exhaust of electromagnetic drive’. That paper sets out a theoretical exploration of a possible hypothesis for why EmDrive appears to work. The idea is that photon pairing is generating thrust.

The paper’s correspondence author, Professor Arto Annali, one of its three authors, told AEROSPACE in an email that: “When it comes to the EmDrive, we reason that the photons that are fed into the cavity will bounce back and forth, and eventually will pair with each other at the opposite phase. Since the pair is without electromagnetic fields, it can escape from the metal cavity. If the escaping from one end differs from the other end, there will be thrust.” As they escape the cavity, they conserve momentum – not violating Newton’s third law of motion.

In a phone interview, Annali added that the AIP peer-review feedback he and his colleagues were given was that the ideas in their paper have been around since the 1920s or 1930s. Annali added that only experimentation would confirm the paired-photon idea but his university would not be conducting experiments. Their theoretical study used physics simulation software from the COMSOL company and one of the three authors was from the firm.

Another ‘impossible drive’

A Helsinki-based team has put forward a paired-photon hypothesis of why the EmDrrive appears to work. (Professor Arto Annali)

As well as the Eagleworks lab, NASA is funding another propellantless drive, which, like the Helsinki, Jyväskylä team, has a photon hypothesis for how it works; but, using lasers not microwaves. In October 2013, the space agency awarded the California based Y.K. Bae Corporation (named after its founder Dr Young K Bae) a NASA Innovative Advance Concepts (NIAC) phase two grant sto investigate, ‘innovative spacecraft manoeuvring and formation flying,’ with what Bae calls a Photonic Laser Thruster (PLT).



Bae states on its website that the PLT works by amplifying photon power by bouncing photons, lasers, several hundred times between two laser mirrors to achieve useful thrust. In May 2015, Bae announced it had achieved a thrust of up to 1.1milliNewtons and accelerated a 450gram object, a ‘spacecraft simulator,’ on a gliding platform along a two-metre frictionless air track, simulating zero-gravity. In the same announcement, Bae’s founder stated that the company’s next milestone was a low Earth orbit flight to prove that PLT could enable precision formation flying and station keeping for small satellites.

Cannae cubesat

Artist’s impression of a cubesat to be launched in 2018 which will use Cannae propellantless thruster technology to maintain orbit around the Earth. (Cannae)

Meanwhile, Fetta’s cubesat borne Cannae Drive is expected to be launched into low Earth orbit at about 150miles (240km) altitude by July 2018. Fetta was not available for interview but he has publicly stated on his website that his company has, “demonstrated two separate prototypes of a superconducting thruster,” at the company’s Pennsylvania test facility. Cannae’s website also explains that the drive works by using, “the Lorentz force imbalances generated by our thrusters to generate thrust without requiring on-board propellant.” The Lorentz force describes electric and magnetic forces acting on a charged particle.

Despite all the corporate and government interest, Fetta, Woodward and Shawyer still have a long way to convince the scientific and technical communities. Brian Koberlein is a computational astrophysicist specialising in phenomena such as blackholes. He criticised the propellantless drive concepts in his 19 November 2016 article for business magazine Forbes’ online site. “The biggest problem with both of those [EmDrive and Mach Effect] is that their explanations don’t get around the fact that they violate Newton’s third law,” Koberlein told AEROSPACE.

“They are trying to come with an explanation that will allow this thing to work. And their doing that without any clear evidence that it does work. If we had a device that truly accelerated without any reaction we would turn around and say ok how do we explain this.” He expects that the Eagleworks team will not be able to eliminate the sources of error and in the, “long run, it won’t work out”.

‘Far stronger evidential basis needed’, says RAeS

Will the EmDrive allow next-generation spaceplanes like the one above? Or are they the propulsion equivalent of 'cold fusion' hype in the 1990s? (Roger Shawyer).

The Committee of the Royal Aeronautical Society’s Space Group (chairman: Philip Davies FRAeS) has followed the controversy since at least 2005 when Roger Shawyer sought to publish an EmDrive paper in the Society’s The Aeronautical Journal. The Committee responded to the current situation with the following statement:

“Much time has been spent by many parties reviewing the claims of propellantless propulsion despite an apparent lack of reproducible results. The issue with all of these ‘thrusters’ is the lack of theoretical background to them, with each proponent claiming their own to be obvious and sound, yet with none of them agreeing. This was not how the jet engine was developed and is not how the Sabre hypersonic air-breathing engine is being developed by Reaction Engines (see AEROSPACE September 2013, p 39).

If the developers of such devices want to be taken more seriously, it’s incumbent upon them to allow greater scrutiny of their experiments or to prove, beyond reasonable doubt, that they have something that works. We note the reluctance of the proponents to publish detailed results which is a barrier to acceptance by the scientific community and we support the AIAA in publishing a peer-reviewed paper on the subject. The lack of acceptance by the mainstream propulsion community will not change without a more open sharing of results and proofs, as well as a rigorous theoretical underpinning. We therefore encourage the inventors to facilitate the creation of a far stronger evidential basis – perhaps with the Society providing an impartial forum for this.”

Rob Coppinger

