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{{short description|Device claimed to be a propellantless spacecraft thruster}}
{{pp-vandalism|small=yes}}
{{Use dmy dates|date=August 2018}}
{{multiple issues|
{{About||thrusters that use electrical power to change the velocity of spacecraft|Electrically-powered spacecraft propulsion| rocket that uses thrust from the momentum of emitted photons|Photon rocket}}
{{Technical|date=August 2014}}
{{Infobox rocket engine
{{POV|date=August 2014}}
|name = EmDrive
|image = EmDrive built by Eagleworks inside the test chamber.jpg
|caption = EmDrive experiment built by NASA Eagleworks laboratory in 2013
|country_of_origin= United States
|date = 2001
|purpose = ]
|status = Device concept
|thrust(SL) = {{cvt|0|N|ozf|lk=on}}<ref name=Delbert2021/>
}} }}


The '''EmDrive''' is a concept for a thruster for ], first written about in 2001.<ref name="Powell" /><ref name="JBIS 2016a" /><ref name="shawyertheory 9.3" /><ref name="Shawyer interview">{{cite web|last1=Breeze|first1=Nick|date=29 July 2015|title=Roger Shawyer, EmDrive Interview, 2015|url=http://envisionation.co.uk/index.php/roger-shawyer-emdrive/138-roger-shawyer-emdrive-interview-2015|publisher=Envisionation UK}}</ref> It is purported to generate thrust by reflecting microwaves inside the device, in a way that would violate the law of ] and other ].<ref name="NASA AIAA 2014" /><ref>{{cite web|url=http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-cubesat-reactionless/|title=The Impossible Propulsion Drive Is Heading to Space|date=2 September 2016|website=popularmechanics.com|access-date=9 October 2017}}</ref><ref>{{cite web|url=https://www.sciencealert.com/the-impossible-em-drive-is-about-to-be-tested-in-space|title=The 'Impossible' EM Drive Is About to Be Tested in Space|last=Crew|first=Bec|website=sciencealert.com|date=6 September 2016 |access-date=9 October 2017}}</ref><ref>{{cite web|url=http://news.nationalgeographic.com/2016/11/nasa-impossible-emdrive-physics-peer-review-space-science/|archive-url=https://web.archive.org/web/20161122020601/http://news.nationalgeographic.com/2016/11/nasa%2Dimpossible%2Demdrive%2Dphysics%2Dpeer%2Dreview%2Dspace%2Dscience/|url-status=dead|archive-date=22 November 2016|title=NASA Team Claims 'Impossible' Space Engine Works—Get the Facts|date=21 November 2016|website=National Geographic|access-date=9 October 2017}}</ref><ref>{{cite web|url=https://phys.org/news/2016-12-mars-days-expert-discusses-nasa.html|title=To Mars in 70 days: Expert discusses NASA's study of paradoxical EM propulsion drive|last1=Poitras|first1=Colin|date=7 December 2016|website=Phys.org|access-date=1 May 2018}}</ref> The concept has at times been referred to as a '''resonant cavity thruster'''.<ref>{{cite news
{{Use dmy dates|date=July 2013}}
| url = https://www.extremetech.com/extreme/235566-can-the-impossible-space-drive-survive-falsification-in-orbit
{{Infobox controversial invention
| title = Can the 'impossible' space drive survive falsification in orbit? – ExtremeTech
| name = EmDrive
| date = 16 September 2016
| inventor = ]
| newspaper = Extremetech
| lawviolation = ], ]
| access-date = 1 November 2017
}}
| last1 = Templeton
'''EmDrive''' (also '''RF resonant cavity thruster''') is a proposed ] device invented by British ] ], who develops prototypes at ''Satellite Propulsion Research Ltd'' (SPR),<ref name="SPR">{{cite web
| first1 = Graham
|title=EmDrive.com
}}</ref><ref>{{cite magazine
|publisher=Roger Shawyer / SPR Ltd
| url = https://www.wired.co.uk/article/10-qs-about-nasa-impossible-drive
|website=Satellite Propulsion Research Ltd (SPR) web site
| title = 10 questions about Nasa's 'impossible' space drive answered
|author=<!--Staff writer(s); no by-line.-->
| first = David
|url=http://www.emdrive.com
| last = Hambling
}}</ref> the company he created for that purpose in 2000.<ref name="SPR ADS">{{cite web
| magazine = Wired UK
|title=Satellite Propulsion Research
| access-date = 1 November 2017
|author=<!--Staff writer(s); no by-line.-->
| date = 2014-08-07
|website=Aerospace Member Directory
}}</ref>
|publisher=]
|url=http://om.adsgroup.org.uk/directorydetail.aspx?OrganisationId=103505&directorycode=6561&infocode=UKSPACE_DIR
}}</ref> The device uses a ] to produce ]s which are directed into a metallic, fully enclosed conically tapered ] ] with a greater area at one end of the device, and a ] in front of the narrower end. The inventor claims that the device generates a directional ] toward the narrow end of the tapered cavity. The device (engine) requires an electrical power source to produce its reflecting internal microwaves but does not have any moving parts or require any ] as fuel. If proven to work as claimed, this technology could be used to propel vehicles intended for all forms of travel including ground travel, marine travel, sub-marine travel, ] and ].<ref name ="Wired 2008">{{cite web |last=Hambling |first=David |title=Chinese Say They're Building 'Impossible' Space Drive |date=24 September 2008 |website=Wired |publisher=] |url=http://www.wired.com/2008/09/chinese-buildin/}}</ref><ref name ="Wired 2008 video">{{cite web |last=Hambling |first=David |title=Video: 'Impossible' Space Drive In Action? |date=2 October 2008 |website=Wired |publisher=] |url=http://www.wired.com/2008/10/video-impossibl/}}</ref><ref name ="Wired 2009">{{cite web |last=Hambling |first=David |title='Impossible' Device Could Propel Flying Cars, Stealth Missiles |date=29 October 2009 |website=WIred |publisher=] |url=http://www.wired.com/2009/10/impossible-drive-designers-dream-flying-cars-stealth-missiles/}}</ref><ref name="AW&ST 2012">{{cite web |last=Hambling |first=David |title=Propellentless Space Propulsion Research Continues |date=5 November 2012 |publisher=] |url=http://aviationweek.com/awin/propellentless-space-propulsion-research-continues}}</ref><ref name="Wired 2013">{{cite web |last=Hambling |first=David |title=EmDrive: China's radical new space drive |date=6 February 2013 |website=Wired UK |publisher=] |url=http://www.wired.co.uk/news/archive/2013-02/06/emdrive-and-cold-fusion}}</ref><ref name="Wired 2014">{{cite web |last=Hambling |first=David |title=Nasa validates 'impossible' space drive |url=http://www.wired.co.uk/news/archive/2014-07/31/nasa-validates-impossible-space-drive |accessdate=31 July 2014 |website=Wired UK |publisher=] |date=31 July 2014}}</ref>


There is no official design for this device. Neither person who claims to have invented it has committed to an explanation for how it could operate as a thruster or what elements define it, making it hard to say definitively whether a given object is an example of an EmDrive. However, over the years, prototypes based on its public descriptions have been constructed and tested.
The device, its mode of operation, and theories attempting to explain it are all controversial. {{As of|2015}}, there are still arguments about whether the EmDrive is genuinely a new propulsion device, or whether its experimental results are simply misinterpretations of spurious effects mixed with experimental errors. The proposed theories of its operation have all been criticized because they seem to violate the ], a fundamental ], though Shawyer asserts that EmDrive does not.<ref name="faq" />


In 2016, ]'s group at ] observed a small apparent thrust from one such test,<ref name="Nat Geo Peer review" /> however subsequent studies suggested this was a measurement error caused by thermal gradients.<ref name="tajmar20180514" /><ref name="tajmar20210401" /> In 2021, ]'s group at the ] replicated White's test, observing apparent thrusts similar to those measured by the NASA team, and then made them disappear again when measured using point suspension.<ref name=Delbert2021/>
Chinese researchers from the ] (NWPU) in ] in 2010, built and tested their own device based upon Shawyer's design, claiming to have replicated Shawyer's experiments, recording better results than Shawyer had claimed at even higher power levels,<ref name="AW&ST 2012" /><ref name="Yang 2010" /><ref name="Yang 2012" /><ref name="Yang 2013" /><ref name="Yang 2014" /> though they were also clear that their work was still preliminary. Then at the ] in 2014 a ] evaluation group also claimed replication at low power levels, measuring a directional thrust level in accord with Shawyer's experiments and claims.<ref name="Wired 2014" /><ref name="NASA AIAA 2014">{{cite conference |last1=Brady |first1=David A. |last2=White |first2=Harold G. |last3=March |first3=Paul |last4=Lawrence |first4=James T. |last5=Davies |first5=Franck J. |title=Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum |conference=50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference |publisher=] |date=30 July 2014 |url=http://arc.aiaa.org/doi/abs/10.2514/6.2014-4029 |doi=10.2514/6.2014-4029 |accessdate=31 July 2014 |layurl=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140006052.pdf |laysource=NASA |laydate=30 July 2014}}</ref>


No other published experiment has measured apparent thrust greater than the experiment's margin of error.<ref>{{Cite news|url=https://www.space.com/40682-em-drive-impossible-space-thruster-test.html|title='Impossible' EmDrive Space Thruster May Really Be Impossible|work=Space.com|access-date=2018-09-03}}</ref> Tajmar's group published three papers in 2021 claiming that all published results showing thrust had been false positives, explaining each by outside forces. They concluded, "Our measurements refute all EmDrive claims by at least 3 orders of magnitude."<ref name="Delbert2021">{{cite web
== Theory ==
|url=https://www.popularmechanics.com/science/a35991457/emdrive-thruster-fails-tests/
|access-date=29 June 2021
|title=Scientists Just Killed the EmDrive
|last1=Delbert
|first1=Caroline
|date=31 March 2021
|website=popularmechanics.com
|publisher=]
}}</ref>


{{toclimit|3}}
Any apparently ] is treated with skepticism by the physics community because a truly reactionless drive would violate the law of ]. Shawyer claims that his drive does not violate conservation of momentum and is not reactionless.<ref name=faq>
{{cite web
| url = http://emdrive.com/faq.html
| title = EmDrive FAQ
| publisher = SPR Ltd
| accessdate = 2011-07-24
}}</ref> Shawyer has posted an updated theory paper (version 9.4) for the EmDrive.<ref name="shawyertheory 9.4">
{{cite web
|last=Shawyer
|first=Roger
|title=A Theory of Microwave Propulsion for Spacecraft (Theory paper v.9.4)
|publisher=SPR Ltd
|date=March 2007
|url=http://www.emdrive.com/theorypaper9-4.pdf
|format=PDF
}}</ref> Shawyer's paper includes the fundamental assertion underlying the theory: "his force difference is supported by inspection of the classical Lorentz force equation F = q(E + νB). (1) If ν is replaced with the group velocity ν<sub>g</sub> of the electromagnetic wave, then equation 1 illustrates that if v<sub>g1</sub> is greater than v<sub>g2</sub>, then F<sub>g1</sub> should be expected to be greater than F<sub>g2</sub>." This statement makes two assumptions which Shawyer does not substantiate and which may explain the discrepancy between Shawyer's predictions and those of conventional physics. First, Shawyer assumes that ] is the result of the ] acting on charged particles in the reflecting material. This is analyzed by Rothman and Boughn<ref name=rothman2008>{{cite web|last1=Rothman|first1=Tony|last2=Boughn|first2=Stephen|title=The Lorentz force and the radiation pressure of light|url=http://arxiv.org/pdf/0807.1310v5.pdf}}</ref> who point out that the standard theory of radiation pressure is somewhat more complicated than the simplified analysis suggests. Second, Shawyer asserts that quantum energy is transferred at the '']'', and thus momentum of the photon and the consequent radiation pressure must vary with group velocity. Photon momentum varies with ]. Group velocity measures the rate of propagation of information. The phase velocity is constant throughout the frustum resonator, consequently radiation pressure would not be expected to produce unbalanced forces.


== History and controversy ==
Various hypotheses and theories have been proposed explaining the underlying physics for how the EmDrive and related designs might be producing thrust. Shawyer claims that thrust is caused by a radiation pressure imbalance between the two faces of the cavity caused by the action of group velocity in different ] within the framework of ].<ref name="IAC 2008">
{{cite conference
|last=Shawyer
|first=Roger
|title=Microwave Propulsion - Progress in the EmDrive Programme
|date=29 September – 3 October 2008
|conference=59th International Astronautical Congress (IAC 2008)
|location=Glasgow, U.K.
|publisher=International Astronautical Federation
|url=http://www.emdrive.com/IAC-08-C4-4-7.pdf
|format=PDF
}}</ref> Yang from NWPU calculated the net force/thrust using ].<ref name="Yang 2013" /> ], who investigates ] at Eagleworks, NASA's Advanced Propulsion Physics Laboratory, speculated that such resonant cavities may operate by creating a virtual ] ] that could realize net thrust using ] forces acting upon ].<ref>{{cite web |author=Harold "Sonny" White |title=Eagleworks Laboratories WARP FIELD PHYSICS |website=NASA Technical Reports Server (NTRS) |publisher=NASA |year=2013 |url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140000851.pdf |format=PDF}}</ref> Likewise, the paper describing the Eagleworks test of the Cannae drive referred to a possible interaction with a so-called "quantum vacuum virtual plasma".<ref name="NASA AIAA 2014" /> This reference has been criticized by mathematical physicists ] and ] because in the standard description of vacuum fluctuations, ]s do not behave as a plasma.<ref name=Powell /><ref>{{cite web|last1=Baez|first1=John|title=The incredible shrinking force|url=https://plus.google.com/117663015413546257905/posts/WfFtJ8bYVya|website=Google Plus|accessdate=6 August 2014}}</ref><ref>{{cite web|last1=Gonzalez|first1=Robert T.|title=Don't Get Too Excited About NASA's New Miracle Engine|url=http://space.io9.com/a-new-thruster-pushes-against-virtual-particles-or-1615361369/1615513781|publisher=io9|accessdate=6 August 2014|quote=The business about "quantum vacuum virtual plasma" (the physics of which they "won't address" in this paper) is complete bullshit. There is a quantum vacuum, but it's nothing like a plasma.}}</ref>


]s operate by expelling ], which acts as a ] and which produces thrust per ]. All designs for ] operate on the principle of reaction mass. A hypothetical drive which did not expel propellant in order to produce a ], providing thrust while being a ] with no external interaction, would be a ], violating the ] and ].<ref name="Wired 2013">{{cite magazine|last=Hambling|first=David|date=6 February 2013|title=EmDrive: China's radical new space drive|url=https://www.wired.co.uk/news/archive/2013-02/06/emdrive-and-cold-fusion|magazine=Wired UK}}</ref> Claims that a drive is reactionless are generally considered by physicists to be ].<ref name="Nat Geo Peer review"/>
== Testing and replication claims ==
=== Static thrust tests ===


The first design of a resonant cavity thruster claiming to be a reactionless drive was by Roger Shawyer in 2001. He called his conical design an "EmDrive", and claimed that it produced thrust in the direction of the base of the cone. Guido Fetta later built a "Cannae Drive", based in part on Shawyer's concept,<ref name="AW&ST 2012">{{cite web|url=http://aviationweek.com/awin/propellentless-space-propulsion-research-continues|title=Propellentless Space Propulsion Research Continues|last=Hambling|first=David|date=5 November 2012|work=]}}</ref><ref name="Wired 2013" /> using a pillbox-shaped cavity.
Shawyer has reported seven independent positive reviews from experts at ], ], ] and the ].<ref name="The Engineer 2004">{{cite journal|title=Defying gravity: UK team claims engine based on microwaves could revolutionise spacecraft propulsion|last=Fisher|first=Richard|magazine=]|location=London|volume=293|issue=7663|page=8|date=5 November 2004|url=http://www.theengineer.co.uk/news/defying-gravity/266633.article}}</ref> As of 2015, no EmDrive has been tested in ].


Since 2008, a few physicists have tested their own models, trying to reproduce the results claimed by Shawyer and Fetta. Juan Yang at ]'s ] (NWPU) was unable to reproducibly measure thrust from their models, over the course of 4 years.<ref name="Wired 2008">{{cite magazine|last=Hambling|first=David|date=24 September 2008|title=Chinese Say They're Building 'Impossible' Space Drive|url=https://www.wired.com/2008/09/chinese-buildin/|magazine=]}}</ref><ref name="Yang 2016">{{cite journal|last1=Yang|first1=J.|last2=Liu|first2=X.-C.|last3=Wang|first3=Y.-G.|last4=Tang|first4=M.-J.|last5=Luo|first5=L.-T.|last6=Jin|first6=Y.-Z.|last7=Ning|first7=Z.-X.|date=February 2016|title=Thrust Measurement of an Independent Microwave Thruster Propulsion Device with Three-Wire Torsion Pendulum Thrust Measurement System|url=http://www.tjjs.casic.cn/ch/reader/create_pdf.aspx?file_no=20160220&flag=1&journal_id=tjjs&year_id=2016|journal=Journal of Propulsion Technology|language=zh|volume=37|issue=2|pages=362–371|access-date=1 May 2016|archive-date=28 January 2018|archive-url=https://web.archive.org/web/20180128115752/http://www.tjjs.casic.cn/ch/reader/create_pdf.aspx?file_no=20160220&flag=1&journal_id=tjjs&year_id=2016|url-status=dead}}</ref><ref>{{Cite web|url=https://forum.nasaspaceflight.com/index.php?topic=39772.1820|title=EM Drive Developments, NASA spaceflight forums, discussion of Yang's 2016 paper|website=forum.nasaspaceflight.com|access-date=14 September 2016}}</ref> In 2016, ]'s group at NASA's ] reported in the '']'' that a test of their own model had observed a small thrust.<ref name="Eagleworks AIAA 2016">{{cite journal|last1=White|first1=Harold|last2=March|first2=Paul|last3=Lawrence|first3=James|last4=Vera|first4=Jerry|last5=Sylvester|first5=Andre|last6=Brady|first6=Davi|last7=Bailey|first7=Paul|date=17 November 2016|title=Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum|journal=]|volume=33|issue=4|pages=830–841|doi=10.2514/1.B36120|hdl=2060/20170000277|s2cid=126303009 |hdl-access=free}}</ref> In late 2016, Yue Chen of the communication satellite division of the ] (CAST), said his team had tested prototypes, and would conduct in-orbit tests to determine if they could observe thrust.<ref>{{cite web|url=http://www.ibtimes.co.uk/emdrive-chinese-space-agency-put-controversial-tech-onto-satellites-soon-possible-1596328|title=EmDrive: Chinese space agency to put controversial tech onto satellites 'as soon as possible'|last1=Russon|first1=Mary-Ann|date=13 December 2016|work=International Business Times|access-date=15 December 2016}}</ref><ref>{{cite web|url=http://www.ibtimes.co.uk/emdrive-these-are-problems-china-must-fix-make-microwave-thrusters-work-satellites-1596487|title=EmDrive: These are the problems China must fix to make microwave thrusters work on satellites|last1=Russon|first1=Mary-Ann|date=14 December 2016|work=International Business Times|access-date=15 December 2016}}</ref><ref>{{cite web|url=http://digitalpaper.stdaily.com/http_www.kjrb.com/kjrb/html/2016-12/11/content_357004.htm|title=电磁驱动:天方夜谭还是重大突破 我国正开展关键技术攻关,争取5年内实现工程应用|author1=操秀英|date=11 December 2016|website=Science and Technology Daily|publisher=Ministry of Science and Technology of the People's Republic of China|language=zh|trans-title=EmDrive: Fantasy or major breakthrough|access-date=15 December 2016|archive-date=16 December 2016|archive-url=https://web.archive.org/web/20161216144000/http://digitalpaper.stdaily.com/http_www.kjrb.com/kjrb/html/2016-12/11/content_357004.htm|url-status=dead}}</ref><ref>{{Cite web|url=http://www.techtimes.com/articles/190067/20161226/china-confirms-emdrive-research-plans-to-use-the-technology-on-chinese-satellites-as-soon-as-possible.htm|title=China Confirms EmDrive Research, Plans To Use The Technology On Chinese Satellites As Soon As Possible|last=Kumar|first=Kalyan|date=26 December 2016|access-date=28 December 2016}}</ref><ref name="CCTV">{{cite news|url=http://www.huffingtonpost.co.uk/entry/china-built-em-engine-nasa-mars-in-ten-weeks_uk_59b8efb9e4b0edff971798cf|title=China Claims To Have Built A Version Of NASA's 'Impossible Engine' That Uses NO Fuel|last1=Gallagher|first1=Sophie|date=13 September 2017|website=The Huffington Post UK}}</ref> ]'s group at the ] started testing prototypes in 2015, and by 2021 concluded that observations of thrust were false positives, reporting in the CEAS Space Journal they had refuted all EmDrive claims by "at least 3 orders of magnitude."<ref name="Delbert2021"/><ref>{{Cite journal |last1=Tajmar |first1=M. |last2=Neunzig |first2=O. |last3=Weikert |first3=M. |date=2022-01-01 |title=High-accuracy thrust measurements of the EMDrive and elimination of false-positive effects |journal=CEAS Space Journal |language=en |volume=14 |issue=1 |pages=31–44 |doi=10.1007/s12567-021-00385-1 |bibcode=2022CEAS...14...31T |s2cid=237650091 |issn=1868-2510|doi-access=free }}</ref>
Shawyer speculated in 2006 that, with adequate funding, commercial terrestrial aircraft incorporating EmDrives as lift engines could be ready by 2020.<ref name="The Engineer 2006">{{cite news|title=Microwave engine gets a boost|last=Fisher|first=Richard|date=1 September 2006|url=http://www.theengineer.co.uk/news/microwave-engine-gets-a-boost/295931.article|location=London|website=]}}</ref><ref name="BTE 2013 interview">{{cite web |title=80 Ton Lifter Possible in 6 Years: Interview with EmDrive Inventor |date=27 February 2013 |author=<!--Staff writer(s); no by-line.--> |website=BTE Blog |publisher=BuildTheEnterprise |url=http://www.buildtheenterprise.org/80-ton-lifter-possible-in-6-years-interview-with-emdrive-inventor}}</ref> He proposed that very high ''Q'' ] resonant cavities could produce static specific thrusts of about 30&nbsp;N/W, which is 3 tonnes-force of thrust per kilowatt of input power − "enough to lift a large car".<ref name="TMCnet">{{cite web |title=Fly by light |author=<!--Staff writer(s); no by-line.--> |date=8 September 2006 |website=Contact Center Solutions, TMCnet |publisher=Technology Marketing Corporation (TMC) |url=http://callcenterinfo.tmcnet.com/news/2006/09/08/1874074.htm}}</ref>{{dubious|date=April 2015}}


=== Media coverage and responses ===
=== Chinese Northwestern Polytechnical University (NWPU) ===
Media coverage of experiments using these designs has been polarized. The EmDrive first drew attention, both credulous and dismissive, when '']'' wrote about it as an "impossible" drive in 2006.<ref name="New Scientist blog" /> Media outlets were later criticized for misleading claims that a resonant cavity thruster had been "validated by NASA"<ref>{{cite magazine
In 2008, '']'' magazine reported that a team of Chinese researchers led by Juan Yang (杨涓), professor of propulsion theory and engineering of aeronautics and astronautics at ] (NWPU) in ], claimed to have developed a valid electro-magnetic theory behind the Emdrive.<ref name="Wired 2008"/><ref name="Yang 2008">
| url = https://www.wired.co.uk/article/nasa-validates-impossible-space-drive
{{cite journal
| title = Nasa validates 'impossible' space drive
|last1=ZHU |first1=Yu
| date = 31 July 2014
|last2=YANG |first2=Juan
| magazine = Wired
|last3=MA |first3=Nan
| author = David Hambling
|title=The Performance Analysis of Microwave Thrust Without Propellant Based On The Quantum Theory
|date=September 2008 | access-date = 6 September 2016
}}</ref> following White's first tentative test reports in 2014.<ref name="powell-no">{{cite news
|journal=]
|url = http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-validate-imposible-space-drive-word/
|volume=29
|title = Did NASA Validate an "Impossible" Space Drive? In a Word, No.
|issue=5
|work = Discover magazine
|pages=1612–1615
|date = 6 August 2014
|language=Chinese
|access-date = 16 February 2016
|url=http://en.cnki.com.cn/Article_en/CJFDTOTAL-YHXB200805027.htm
|author = Powell, Corey S.
}}</ref> A demonstration version of the drive was built and tested under different cavity shapes and at higher power levels in 2010.<ref name="Yang 2010">
|archive-date = 8 August 2014
{{cite journal
|archive-url = https://web.archive.org/web/20140808210746/http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-validate-imposible-space-drive-word/
|last1=YANG |first1=Juan
|url-status = dead
|last2=YANG |first2=Le
}}</ref> Scientists have continued to note the lack of unbiased coverage.<ref name="Tau Zero">{{Cite web
|last3=ZHU |first3=Yu
| url = http://www.centauri-dreams.org/?p=36830
|last4=MA |first4=Nan
| title = Uncertain Propulsion Breakthroughs?
|date=6 December 2010
| date = 30 December 2016
|title=Applying Method of Reference 2 to Effectively Calculating Performance of Microwave Radiation Thruster
| last1 = Millis
|journal=]
| first1 = Marc
|volume=28
| last2 = Hathaway
|issue=6
| first2 = George
|pages=807–813
| editor-last = Gilster
|url=http://www.emdrive.com/NWPU2010translation.pdf
| editor-first = Paul
|format=PDF
| website = Centauri Dreams
}}</ref> A maximum thrust of 720&nbsp;mN was reported at 2,500&nbsp;W of input power on an aerospace ] usually used to precisely test spacecraft engines like ]s.<ref name="Wired 2013" /><ref name="Yang 2012">{{cite doi|10.7498/aps.61.110301}}</ref><ref name="Yang 2013" >{{cite doi|10.1088/1674-1056/22/5/050301}}</ref><ref name="Yang 2014">{{cite doi|10.7498/aps.63.154103}}</ref><ref name="Yang thrust">
| last3 = Tajmar
{{cite web
| first3 = Martin
|author=YANG, Juan ''et al.''
| last4 = Davis
|title=Figure 4: Different microwave output power range thrust measurement results. Output power ranging from 300-2500W.
| first4 = Eric
|url=http://www.emdrive.com/NWPU2010testresults.pdf
| last5 = Maclay
}}</ref>
| first5 = Jordan
}}</ref>


In 2006, responding to the ''New Scientist'' piece, mathematical physicist ] at the ], and Australian science-fiction writer ], said the positive results reported by Shawyer were likely misinterpretations of experimental errors.<ref name="egan" />
The editor of ''Wired'' magazine who covered the experimental results relating to reactionless drives reported that he received some comments from the Chinese researchers stating "the publicity was very unwelcome, especially any suggestion that there might be a military application"<ref name="Wired 2009" /> and that Yang told him that "she is not able to discuss her work until more results are published".<ref name="Wired 2013" />


In 2014, White's first conference paper suggested that resonant cavity thrusters could work by transferring momentum to the "quantum vacuum virtual plasma", a new term he coined.<ref name="NASA AIAA 2014">{{cite conference
=== NASA/JSC Advanced Propulsion Physics Laboratory (Eagleworks) ===
|last1 = Brady
|first1 = David A.
|last2 = White
|first2 = Harold G.
|last3 = March
|first3 = Paul
|last4 = Lawrence
|first4 = James T.
|last5 = Davies
|first5 = Franck J.
|title = 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
|chapter = Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum
|conference = 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
|publisher = ]
|date = 30 July 2014
|chapter-url = http://www.libertariannews.org/wp-content/uploads/2014/07/AnomalousThrustProductionFromanRFTestDevice-BradyEtAl.pdf
|doi = 10.2514/6.2014-4029
|access-date = 31 July 2014
|hdl = 2060/20140009930
|isbn = 978-1-62410-303-2
|hdl-access = free
|archive-date = 18 February 2015
|archive-url = https://web.archive.org/web/20150218162819/http://www.libertariannews.org/wp-content/uploads/2014/07/AnomalousThrustProductionFromanRFTestDevice-BradyEtAl.pdf
|url-status = dead
}}</ref> ] and ] criticized this explanation, because in the standard description of vacuum fluctuations, ]s do not behave as a plasma; Carroll also noted that the quantum vacuum has no "rest frame", providing nothing to push against, so it cannot be used for propulsion.<ref name="Powell" /><ref>{{cite web
| last1 = Baez
| first1 = John
| title = The incredible shrinking force
| url = https://plus.google.com/117663015413546257905/posts/WfFtJ8bYVya
| website = Google Plus
| access-date = 6 August 2014
}}</ref> In the same way, physicists ] and Heidi Fearn published two papers showing that ]−] ] of the quantum vacuum, discussed by White as a potential virtual plasma propellant, could not account for thrust in any isolated, closed electromagnetic system such as a ].<ref name="JBIS 2016a">{{cite journal
|last1 = Fearn
|first1 = H.
|last2 = Woodward
|first2 = J. F.
|title = Breakthrough Propulsion I: The Quantum Vacuum
|date = May 2016
|journal = Journal of the British Interplanetary Society
|volume = 59
|issue = 5
|pages = 155–162
|url = http://www.ayuba.fr/images/emdrive/JBIS-69-05.pdf
|bibcode = 2016JBIS...69..155F
|access-date = 12 February 2017
|archive-date = 29 December 2016
|archive-url = https://web.archive.org/web/20161229032249/http://www.ayuba.fr/images/emdrive/JBIS-69-05.pdf
|url-status = dead
}}</ref><ref name="JBIS 2016b">{{cite journal
|last1 = Fearn
|first1 = H.
|last2 = Woodward
|first2 = J. F.
|title = Breakthrough Propulsion II: A Mass Change Experiment
|date = October 2016
|journal = Journal of the British Interplanetary Society
|volume = 59
|issue = 10
|pages = 331–339
|url = http://www.jbis.org.uk/paper.php?p=2016.69.331
|bibcode = 2016JBIS...69..331F
|access-date = 13 September 2017
|archive-date = 10 September 2017
|archive-url = https://web.archive.org/web/20170910173944/http://www.jbis.org.uk/paper.php?p=2016.69.331
|url-status = dead
}}</ref>


In 2015, physicists Eric W. Davis at the Institute for Advanced Studies in Austin and ] at the ] concluded that the thrust measurements reported in papers by both ] and White were indicative of thermal effect errors.<ref name=":0">{{cite web
A NASA team at the Advanced Propulsion Physics Laboratory (informally known as ''Eagleworks'')<ref name="Eagleworks">
| last = Dvorsky
{{cite techreport
| first = George
|last1=White
| title = No, German Scientists Have Not Confirmed the "Impossible" EMDrive
|first1=Harold
| date = 28 July 2015
|last2=March
| website = io9
|first2=Paul
| url = http://io9.com/no-german-scientists-have-not-confirmed-the-impossibl-1720573809
|last3=Nehemiah
}}</ref>
|first3=Williams
|last4=O'Neill
|first4=William
|title=Eagleworks Laboratories: Advanced Propulsion Physics Research
|url=http://ntrs.nasa.gov/search.jsp?R=20110023492
|publisher=NASA
|website=NASA Technical Reports Server (NTRS)
|number=JSC-CN-25207
|date=5 December 2011
}}</ref> located at the ] (JSC) under the guidance of physicist ] is devoted to studying advanced propulsion systems that they hope to develop using quantum vacuum and spacetime engineering. The group has investigated a wide range of ] including the EmDrive, and related concepts listed below.


In May 2018, researchers from the Institute of Aerospace Engineering at ], ], concluded that the dominant effect underlying the apparent thrust could be clearly identified as an artifact caused by Earth's magnetic field interacting with power cables in the chamber, a result that other experts agree with.<ref>. ], ''National Geographic''. 22 May 2018.</ref><ref>. Mike Wall, Space.com. May 23, 2018,</ref><ref name=tajmar20180514>. (PDF) Martin Tajmar, Matthias Kößling, Marcel Weikert, and Maxime Monette. ''Technische Universität Dresden'', Germany. Presented at Barcelo Renacimiento Hotel, Seville, Spain 14 – 18 MAY 2018.</ref>
==== RF resonant tapered cavity thruster (EmDrive) ====


In March 2021, Tajmar's group published a definitive analysis of their own past experiments and those of others, showing that all could be explained by and reproduced via outside forces, refuting all EmDrive claims.<blockquote>When power flows into the EmDrive, the engine warms up. This also causes the fastening elements on the scale to warp, causing the scale to move to a new zero point. We were able to prevent that in an improved structure. Our measurements refute all EmDrive claims by at least 3 orders of magnitude.<ref name="Delbert2021" /></blockquote>
In July 2014, the group reported positive results for an evaluation of a RF resonant tapered cavity similar to Shawyer's EmDrive.<ref name="NASA AIAA 2014" /> Testing was performed using a low-thrust ] capable of detecting force at the micronewton level within a sealed but not evacuated ]; the ] used an ] not capable of operating in a hard vacuum.<ref name="NASA AIAA 2014"/> The experimenters recorded directional thrust immediately upon application of power.


== Designs and prototypes ==
NASA's tests of this tapered RF resonant cavity were conducted at very low power (2% of Shawyer's 2002 experiment and 0.7% of the Chinese 2010 experiment), but a net mean thrust over five runs was measured at 91.2&nbsp;µN at 17&nbsp;W of input power. A net peak thrust was recorded at 116&nbsp;µN at the same power level.<ref name="NASA AIAA 2014" />
]


=== EmDrive ===
The experiment was criticized for not having been conducted under vacuum, which would have eliminated thermal air currents. The researchers plan to replace vacuum-incompatible components.<ref name=Astronotes>
In 2001, Shawyer founded ''Satellite Propulsion Research Ltd'', to work on the EmDrive, which he said used a resonant cavity to produce thrust without propellant. The company was backed by a ] award grant from the ].<ref name="Wired 2013" /><ref name="UK House of Commons">{{cite news
{{cite web
| last = Margaret
| url = http://www.armaghplanet.com/blog/no-nasa-has-not-verified-an-impossible-space-drive.html
| first = Hodge
| title = No, NASA has not verified an impossible space drive!
| title = Answer about the Electromagnetic Relativity Drive
| publisher = Armagh Planetarium
| department = Column 346W
| accessdate = 2014-08-07
| date = 5 December 2006
| journal = Daily Hansard Official Report
| publisher = ]
| location = London
| url = https://publications.parliament.uk/pa/cm200607/cmhansrd/cm061205/text/61205w0031.htm
}}</ref> In December 2002, he loosely described a prototype which he alleged had produced a thrust of {{convert|0.02|N|ozf|lk=on}} powered by an 850 W ]. The device could operate for only a few dozen seconds before the magnetron failed from overheating.<ref>{{cite web
| url = http://rexresearch.com/shawyer/shawyer.htm
| title = Roger Shawyer – EM Space Drive – Articles & Patent
}}</ref> Details were never published or replicated.

==== Second device and ''New Scientist'' article ====
In October 2006, Shawyer claimed to have conducted tests on a new water-cooled prototype with increased thrust.<ref name=Eureka2007>{{cite web
| url = http://www.eurekamagazine.co.uk/design-engineering-features/technology/no-propellant-drive-prepares-for-space-and-beyond/9657/
| title = No-propellant drive prepares for space and beyond
| work = Eureka Magazine
| author = Tom Shelley
| date = 14 May 2007
| access-date = 4 May 2015
}}</ref> He reported plans to have the device ready to use in space by May 2009 and to make the resonant cavity a superconductor,<ref name=Eureka2007 /> neither of which materialized.

'']'' magazine<ref name="shawyertheory 9.3">{{cite journal
| last = Shawyer
| first = Roger
| title = A Theory of Microwave Propulsion for Spacecraft (Theory paper v.9.3)
| journal = ]
| date = September 2006
| url = https://www.newscientist.com/data/images/ns/av/shawyertheory.pdf
| url-status = dead
| archive-url = https://web.archive.org/web/20180526051221/https://www.newscientist.com/data/images/ns/av/shawyertheory.pdf
| archive-date = 26 May 2018
}}</ref> featured the EmDrive on the cover of 8 September 2006 issue. The article portrayed the device as plausible and emphasized the arguments of those who held that point of view. ], a popular ] author, distributed a public letter stating that "a sensationalist bent and a lack of basic knowledge by its writers" made the magazine's coverage unreliable, sufficient "to constitute a real threat to the public understanding of science". Especially, Egan said he was "gobsmacked by the level of scientific illiteracy" in the magazine's coverage, alleging that it used "meaningless double-talk" to obfuscate the problem of conservation of momentum. The letter was endorsed by Baez and posted on his blog.<ref name="egan">{{cite web
| last = Egan
| first = Greg
| editor-last = Baez
| editor-first = John C.
| title = A Plea to Save ''New Scientist''
| date = 19 September 2006
| url = http://golem.ph.utexas.edu/category/2006/09/a_plea_to_save_new_scientist.html
| publisher = The n-Category Café (a group blog on math, physics and philosophy)
}}</ref><ref name="Powell">{{cite web
|url = http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-validate-imposible-space-drive-word/
|title = Did NASA Validate an "Impossible" Space Drive? In a Word, No.
|publisher = Discover
|date = 6 August 2014
|access-date = 6 August 2014
|author = Powell, Corey S.
|archive-date = 8 August 2014
|archive-url = https://web.archive.org/web/20140808210746/http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-validate-imposible-space-drive-word/
|url-status = dead
}}</ref> ''New Scientist'' editor Jeremy Webb responded to critics:{{quote|It is a fair criticism that ''New Scientist'' did not make clear enough how controversial Roger Shawyer's engine is. We should have made more explicit where it apparently contravenes the laws of nature and reported that several physicists declined to comment on the device because they thought it too contentious{{nbsp}}... The great thing is that Shawyer's ideas are testable. If he succeeds in getting his machine flown in space, we will know soon enough if it is ground-breaking device or a mere flight of fancy.<ref name="New Scientist blog">{{cite web
| title = Emdrive on trial
| last = Webb
| first = Jeremy
| date = 3 October 2006
| website = New Scientist Publisher's blog
| url = https://www.newscientist.com/blog/fromthepublisher/2006/10/emdrive-on-trial.html
}}</ref>}} ''New Scientist'' also published a letter from the former technical director of ]: {{quote|I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger was advised that the company had no interest in the device, did not wish to seek patent coverage and in fact did not wish to be associated with it in any way.<ref name="newscientist-astrium-debunk">{{cite web
| url = https://www.newscientist.com/letter/mg19225740-300-emdrive-no-thanks/
| title = Emdrive? No thanks
| author = Alvin Wilby
| work = New Scientist
}}</ref>}} A letter from physicist Paul Friedlander: {{quote|As I read it, I, like the thousands of other physicists who will have read it, immediately realised that this was impossible as described. Physicists are trained to use certain fundamental principles to analyse a problem and this claim clearly flouted one of them{{nbsp}}... The Shawyer drive is as impossible as perpetual motion. Relativistic conservation of momentum has been understood for a century and dictates that if nothing emerges from Shawyer's device then its centre of mass will not accelerate. It is likely that Shawyer has used an approximation somewhere in his calculations that would have been reasonable if he hadn't then multiplied the result by 50,000. The reason physicists value principles such as conservation of momentum is that they act as a reality check against errors of this kind.<ref>{{cite web
| url = https://www.newscientist.com/letter/mg19225720-700-emdrive-on-trial/
| title = Emdrive on trial
| author = Paul Friedlander
| work = New Scientist
}}</ref>}}

==== Later work ====
In 2007, the UK ] granted SPR an export license to ] in the US.<ref>{{cite web
| url = https://drive.google.com/file/d/0B7kgKijo-p0idV9tcmVIVzZrdTQ/view
| title = End User Undertaking.pdf
| access-date = 9 October 2017
}}</ref> According to Shawyer, in December 2008 he was invited to present on the EmDrive, and in 2009 ] expressed interest in it,<ref name="Shawyer2015">{{cite journal
| last = Shawyer
| first = Roger
| date = November–December 2015
| title = Second generation EmDrive propulsion applied to SSTO launcher and interstellar probe
| url = http://www.emdrive.com/IAC14publishedpaper.pdf
| journal = Acta Astronautica
| volume = 116
| pages = 166–174
| doi = 10.1016/j.actaastro.2015.07.002
}}</ref> at which point he stated that SPR built a thruster which produced 18 grams{{val}} of thrust, and sent it to Boeing. Boeing did not license the technology and communication stopped.<ref name="IBT14102016">{{cite web
| title = EmDrive exclusive: Roger Shawyer confirms MoD and DoD interested in controversial space propulsion tech
| author = Mary-Ann Russon
| date = 14 October 2016
| website = International Business Times
| url = http://www.ibtimes.co.uk/emdrive-exclusive-roger-shawyer-confirms-mod-dod-interested-controversial-space-propulsion-tech-1586392
}}</ref> In 2012, a Boeing representative confirmed that ] used to explore exotic forms of space propulsion, including Shawyer's drive, but such work later ceased. They confirmed that "Phantom Works is not working with Mr. Shawyer," nor pursuing those explorations.<ref name="AW&ST 2012" />

In 2014, Shawyer presented ideas for 'second-generation' EmDrive designs and applications at the annual ]. A paper based on his presentation was published in '']'' in 2015.<ref name="Shawyer Acta Astronautica">{{Cite journal
| title = Second generation EmDrive propulsion applied to SSTO launcher and interstellar probe
| url = http://www.emdrive.com/IAC14publishedpaper.pdf
| journal = Acta Astronautica
| date = 1 November 2015
| pages = 166–174
| volume = 116
| doi = 10.1016/j.actaastro.2015.07.002
| first = Roger
| last = Shawyer
}}</ref> While no functional prototype of the first-generation drive had yet been produced, it described a model for a superconducting resonant cavity and three models for thrusters with multiple cavities.

In 2016, Shawyer filed further patents<ref name="IBT12102016">{{cite web
| title = EmDrive: Roger Shawyer is patenting a new design for next-gen superconducting thruster
| author = Mary-Ann Russon
| date = 12 October 2016
| website = International Business Times
| url = http://www.ibtimes.co.uk/emdrive-roger-shawyer-patenting-new-design-next-gen-superconducting-thruster-1585982
}}</ref><ref name="international patent">{{cite patent
| country = WO
| number = 2016162676
| status = application
| title = Superconducting Microwave Radiation Thruster
| pubdate = 2016-10-16
| fdate = 2016-04-07
| pridate = 2015-04-07
| invent1 = SHAWYER, Roger John
| invent2 = CARDOZO, Gilo
| assign1 = Satellite Propulsion Research Ltd.
| class =
| url = https://patentscope.wipo.int/search/docservicepdf_pct/id00000035187289/PAMPH/WO2016162676.pdf
}} {{Webarchive|url=https://web.archive.org/web/20161117213016/https://patentscope.wipo.int/search/docservicepdf_pct/id00000035187289/PAMPH/WO2016162676.pdf |date=17 November 2016 }}</ref> and launched a new company, ''Universal Propulsion Ltd.'', as a ] with ''Gilo Industries Group'', a small UK aerospace company.<ref name="IBT14102016" />

=== Cannae and other drives{{anchor|Cannae_drive}} ===
The Cannae Drive (formerly Q-drive),<ref name="Cannae patent 1" /> is another implementation of this idea, with a relatively flat cavity rather than a truncated cone. It was designed by Guido Fetta in 2006 and promoted within the US through his company, Cannae LLC, since 2011.<ref name="Cannae patent 1">{{cite patent
| country = WO
| number = 2007089284
| status = application
| title =
| pubdate = 2007-11-15
| fdate = 2006-09-12
| pridate = 2005-09-12
| invent1 = Fetta, Guido Paul
| assign1 = Fetta, Guido Paul
}}</ref><ref name="Cannae LLC">{{cite web
| title = Cannae Drive
| url = http://www.cannae.com/
| website = Cannae LLC website
| access-date = 31 July 2014
}}</ref><ref name="Cannae patent 2">{{cite patent
| country = US
| number = 2014013724
| status = application
| title =
| pubdate = 2014-01-16
| fdate = 2012-03-22
| pridate = 2011-03-25
| invent1 = Fetta, Guido P.
| assign1 = Cannae LLC
}}</ref><ref name="Cannae AIAA 2014">{{cite conference
| last1 = Fetta
| first1 = Guido P.
| title = 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
| chapter = Numerical and Experimental Results for a Novel Propulsion Technology Requiring no On-Board Propellant
| conference = 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
| publisher = ]
| date = 30 August 2014
| doi = 10.2514/6.2014-3853
| isbn = 978-1-62410-303-2
}}</ref><ref name="Cannae patent 3">{{cite patent
| country = WO
| number = 2016004044
| status = application
| title =
| pubdate = 2016-01-07
| fdate = 2015-06-30
| pridate = 2014-06-30
| invent1 = Fetta, Guido P.
| assign1 = Cannae LLC
}}</ref> In 2016, Fetta announced plans to eventually launch a ] satellite containing a version of the Cannae Drive, which would run for 6 months to observe how it functions in space.<ref name="popularmechanics.com">{{Cite web
| url = http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-cubesat-reactionless/
| title = The Impossible Propulsion Drive Is Heading to Space
| date = 2 September 2016
| access-date = 14 September 2016
}}</ref> No followup was published.

In China, researchers working under Yang at NWPU built a resonant cavity thruster in 2008, and tested it for a number of years. A 2012 report claimed they had observed thrust, but in 2014 they found it to have been an experimental error. A second, improved prototype did not produce any measured thrust.<ref name="AW&ST 2012" /><ref name="Yang 2013" /><ref name="Yang 2014" />

At the ], Yue Chen filed several patent applications in 2016 describing various radio frequency (RF) resonant cavity thruster designs. These included a method for stacking several short resonant cavities to improve thrust,<ref name="CN105781921A">{{cite patent
| country = CN
| number = 105781921A
| status = application
| title = Electromagnetic thruster cavity based on periodic structure
| pubdate = 2016-07-20
| fdate = 2016-03-16
| pridate = 2016-03-16
| invent1 = Chen, Yue
| invent2 = Peng Weifeng
| invent3 = Bai Guangming
| invent4 = Yaxing Cai, Liu Yang, Yin Jiacong, Zhang Faren
| assign1 = China Academy of Space Technology
| url = https://www.google.com/patents/CN105781921A?cl=en
}}</ref> and a design with a cavity that was a semicylinder instead of a frustum.<ref name="CN105947224A">{{cite patent
| country = CN
| number = 105947224A
| status = application
| title = An electromagnetic propulsion system and method
| pubdate = 2016-09-21
| fdate = 2016-06-20
| pridate = 2016-06-20
| invent1 = Chen, Yue
| invent2 = Peng Weifeng
| invent3 = Bai Guangming
| assign1 = China Academy of Space Technology
| url = https://www.google.com/patents/CN105947224A?cl=en
}}</ref> That December, Chen announced that CAST would conduct tests on a resonant cavity thruster in orbit,<ref name="PopSci 20161220" /> without specifying what design was used. In an interview on CCTV in September 2017, Chen showed some testing of a flat cylindrical device, corresponding to the patent describing stacked short cavities with internal diaphragms.<ref name="CCTV-YouTube">{{YouTube|id=Mdcer1QQLrA|title=Propellantless propulsion: The Chinese EmDrive by CAST scientist Dr Chen Yue, China's Space Agency}}</ref><ref name="CN105781921A" />

== Theoretical inconsistencies ==
All proposed theories for how the EmDrive works violate the ], which states any interaction cannot have a net force; a consequence of the conservation of momentum is Newton's third law, where for every action there is an equal and opposite reaction.<ref name="Nat Geo Peer review" /> Also, because force·velocity = power, any such device would violate conservation of energy when moving at a high enough velocity. The conservation of momentum is a ].<ref name="Lee 2013">{{cite web
| last1 = Lee
| first1 = C.
| title = Generating Thrust Without Fuel Relies on Missing Details
| url = https://arstechnica.com/science/2013/02/generating-thrust-without-fuel-relies-on-missing-details/
| website = arstechnica.com
| archive-url = https://archive.today/20170511132235/https://arstechnica.com/science/2013/02/generating-thrust-without-fuel-relies-on-missing-details/
| archive-date = 11 May 2017
| date = 8 February 2013
| url-status = dead
}}</ref> }}</ref>


An often-cited example of apparent nonconservation of momentum is the ];<ref name=Maxey>{{cite web
In the paper, Eagleworks announced a plan to upgrade their equipment to higher power levels, use vacuum-capable RF amplifiers with power ranges of up to 125&nbsp;W, and design a new tapered cavity analytically determined to be in the 0.1&nbsp;N/kW region. The test article will be subjected to ] at ], the ], and the Johns Hopkins University ].<ref name="NASA AIAA 2014" />
| last1 = Maxey
| first1 = K.
| title = Propulsion on an Interstellar Scale – the Quantum Vacuum Plasma Thruster
| url = http://www.engineering.com/DesignerEdge/DesignerEdgeArticles/ArticleID/5058/Propulsion-on-an-Interstellar-Scale-the-Quantum-Vacuum-Plasma-Thruster.aspx
| website = engineering.com
| archive-url = https://archive.today/20130215224220/http://www.engineering.com/DesignerEdge/DesignerEdgeArticles/ArticleID/5058/Propulsion-on-an-Interstellar-Scale-the-Quantum-Vacuum-Plasma-Thruster.aspx
| archive-date = 15 February 2013
| url-status = dead
}}</ref> in the standard case where two parallel plates are attracted to each other. However the plates move in opposite directions, so no net momentum is extracted from the vacuum and, moreover, energy must be put into the system to take the plates apart again.<ref name="Lafleur" />


Assuming homogeneous electric and magnetic fields, it is impossible for the EmDrive, or any other device, to extract a net momentum transfer from either a classical or ].<ref name="Lafleur" />
Six months later, early 2015, Paul March from Eagleworks made new results public, claiming positive experimental force measurements with a torsional pendulum in a hard vacuum: about 50&nbsp;µN with 50&nbsp;W of input power at 5.0×10<sup>−6</sup>&nbsp;], and new null-thrust tests.<ref name="NBF_20150206">
Extraction of a net momentum "from nothing"<ref>{{cite magazine
{{cite web
| last1 = Cho
|title=Update on EMDrive work at NASA Eagleworks
| first1 = A.
|website=NextBigFuture
| title = Momentum From Nothing
|author=Wang, Brian
| magazine = Physical Review Focus
|date=6 February 2015
| volume = 13
|url=http://nextbigfuture.com/2015/02/update-on-emdrive-work-at-nasa.html
| date = 23 January 2004
}}</ref> The new RF power amplifiers were said to be made for hard vacuum, but still fail rapidly due to internal ]s, with not enough funding to replace or upgrade them, so measurements are still scarce and need improvement before a new report can be published.<ref name="NBF_20150207">
| issn = 1539-0748
{{cite web
| doi = 10.1103/PhysRevFocus.13.3
|title=NASA Emdrive experiments have force measurements while the device is in a hard vacuum
}}</ref><ref>{{cite journal
|website=NextBigFuture
| last1 = Ball
|author=Wang, Brian
| first1 = P.
|date=7 February 2015
| title = Movement From Nothing
|url=http://nextbigfuture.com/2015/02/more-emdrive-experiment-information.html
| url = http://www.nature.com/news/2003/030202/full/news040126-19.html
| journal = Nature
| archive-url = https://archive.today/20170201170321/http://www.nature.com/news/2003/030202/full/news040126-19.html
| archive-date = 1 February 2017
| doi = 10.1038/news040126-19
| date = 2 February 2003
| url-status = dead
}}</ref>
has been postulated in an inhomogeneous vacuum, but this remains highly controversial as it will violate ].<ref name="Lafleur">{{cite arXiv
| last1 = Lafleur
| first1 = T.
| title = Can the Quantum Vacuum be Used as a Reaction Medium to Generate Thrust?
| year = 2014
| eprint = 1411.5359
| class = quant-ph
}}</ref> }}</ref>


Both Harold White's<ref>{{cite web
Glenn Research Center offered to replicate the experiment in a hard vacuum when Eagleworks manage to reach 100&nbsp;µN of thrust, because the GRC thrust stand can only measure down to 50&nbsp;µN.<ref name="NBF_20150206" />
| last1 = White
| first1 = H.
| last2 = March
| first2 = P.
| last3 = Williams
| first3 = N.
| last4 = O'Neill
| first4 = W.
| url = https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023492_2011024705.pdf
| title = Eagleworks Laboratories: Advanced Propulsion Physics Research
| year = 2011
| publisher = NASA
}}</ref><ref>{{cite journal
| last1 = White
| first1 = H.
| last2 = March
| first2 = P.
| title = Advanced Propulsion Physics: Harnessing the Quantum Vacuum
| journal = Nuclear and Emerging Technologies for Space
| year = 2012
| url = http://www.lpi.usra.edu/meetings/nets2012/pdf/3082.pdf
}}</ref><ref>{{cite web
| last1 = White
| first1 = H.
| title = NASA Ames Research Director's Colloquium: Eagleworks Laboratories: Advanced Propulsion
| url = https://www.youtube.com/watch?v=Wokn7crjBbA&t=55m45s
| via = YouTube
| publisher = NASA's Ames Research Center
| date = 5 November 2014
| quote = 56m:21s That test article is trying to establish more accurately the requirements as required by the mathematics – working with negative vacuum energy – the Casimir force.
}}</ref><ref name=Maxey />
and Mike McCulloch's<ref>{{cite journal
| last1 = McCulloch
| first1 = M. E.
| title = Inertia From an Asymmetric Casimir Effect
| journal = EPL
| volume = 101
| issue = 5
| year = 2013
| pages = 59001
| issn = 0295-5075
| doi = 10.1209/0295-5075/101/59001
| bibcode = 2013EL....10159001M
| arxiv = 1302.2775
| s2cid = 118357836
}}</ref> theories of how the EmDrive could work rely on these asymmetric or ]. However, if these vacuum forces are present, they are expected to be exceptionally tiny based on our current understanding, too small to explain the level of observed thrust.<ref name="Lafleur" /><ref name="Freeman 2015">{{cite web
| last1 = Freeman
| first1 = D.
| title = Warp Drives and Science Fictions
| url = http://berkeleysciencereview.com/warp-drives-and-science-fictions/
| website = berkeleysciencereview.com
| publisher = UC Berkeley
| archive-url = https://archive.today/20170612124308/http://berkeleysciencereview.com/warp-drives-and-science-fictions/
| archive-date = 12 June 2017
| year = 2015
}}</ref><ref>{{cite web
| last1 = Marcus
| first1 = A.
| title = Research in a Vacuum: DARPA Tries to Tap Elusive Casimir Effect for Breakthrough Technology
| url = https://www.scientificamerican.com/article/darpa-casimir-effect-research/
| work = Scientific American
| archive-url = https://archive.today/20150302015744/http://www.scientificamerican.com/article/darpa-casimir-effect-research/
| archive-date = 2 March 2015
| date = 12 October 2009
| url-status = dead
}}</ref>
In the event that observed thrust is not due to experimental error, a positive result could indicate new physics.<ref name="TZF 2016">{{cite web
| url = https://www.centauri-dreams.org/?p=36830
| title = Uncertain Propulsion Breakthroughs?
| last2 = Hathaway
| first2 = G.
| date = 30 December 2016
| website = centauri-dreams.org
| publisher = Tau Zero Foundation
| last3 = Tajmar
| first3 = M.
| last4 = Davis
| first4 = E.
| last5 = Maclay
| first5 = J.
| last1 = Millis
| first1 = M.
| archive-url = https://archive.today/20161230172536/http://www.centauri-dreams.org/?p=36830
| archive-date = 30 December 2016
| url-status = dead
}}</ref><ref name="Poitras 2016">{{cite web|url=http://today.uconn.edu/2016/12/the-em-drive-science-fact-or-science-fiction/|title=To Mars in 70 Days. Science Fiction or Fact?|last1=Poitras|first1=C.|date=6 December 2016|website=today.uconn.edu|publisher=University of Connecticut|url-status=dead|archive-url=https://archive.today/20170305105905/http://today.uconn.edu/2016/12/the-em-drive-science-fact-or-science-fiction/|archive-date=5 March 2017}}</ref>


== Tests and experiments ==
Paul March, an engineer at NASA Eagleworks, recently reported in NASASpaceFlight.com’s forum that NASA has successfully tested their EM Drive in a hard vacuum – the first time any organization has reported such a successful test. <ref> http://www.nasaspaceflight.com/2015/04/evaluating-nasas-futuristic-em-drive/ Evaluating NASA’s Futuristic EM Drive</ref>
=== Tests by inventors ===
In 2004, Shawyer claimed to have received seven independent positive reviews from experts at ], ], ] and the ].<ref name="The Engineer 2004">{{cite journal
|title = Defying gravity: UK team claims engine based on microwaves could revolutionise spacecraft propulsion
|last = Fisher
|first = Richard
|journal = ]
|volume = 293
|issue = 7663
|page = 8
|date = 5 November 2004
|url = http://www.theengineer.co.uk/news/defying-gravity/266633.article
|access-date = 9 July 2014
|archive-date = 9 January 2015
|archive-url = https://web.archive.org/web/20150109002553/http://www.theengineer.co.uk/news/defying-gravity/266633.article
|url-status = dead
}}</ref> The technical director of EADS Astrium (Shawyer's former employer) denied this in the strongest terms, stating:
{{quote|I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger was advised that the company had no interest in the device, did not wish to seek patent coverage and in fact did not wish to be associated with it in any way.<ref name="newscientist-astrium-debunk" />}}


None of the other alleged independent experts published a positive review publicly.
Measurements of the EmDrive experimental engine suggest that ] space travel might be a possibility.<ref>{{cite web|url=http://www.wired.co.uk/news/archive/2014-07/31/nasa-validates-impossible-space-drive|title=Nasa validates "impossible"space drive|accessdate=2015-05-01}}</ref> (]).


In 2011, Fetta tested a ] version of the Cannae drive, suspended inside a liquid-helium-filled ], with inconclusive results.
==== Cannae drive ====


None of these results were published in the scientific literature, replicated by independent researchers, or replicated consistently by the inventors. In a few cases details were posted for a time on the inventors' websites, but no such documents remain online as of 2019.<ref>Fetta's experimental notes are no longer available, but an archived version as of 2 November 2012 is on archive.org: (retrieved 11 February 2015)</ref>
The same NASA test campaign evaluated a similar unconventional test device known as the Cannae drive (formerly Q-drive)<ref name="NASA AIAA 2014" /> invented by Guido P. Fetta. Its cavity is also asymmetric, but is flatter than that of the EmDrive. Fetta is the CEO of Cannae LLC,<ref name="Cannae LLC">{{cite web |title=Cannae Drive|url=http://www.cannae.com/ |website=Cannae LLC website |accessdate=31 July 2014}}</ref> a company located in Pennsylvania, has filed two patent applications,<ref name="Cannae patent 1">
{{cite patent
|country=WO
|number=2007089284
|status=application
|title=
|pubdate=2007-11-15
|fdate=2006-09-12
|pridate=2005-09-12
|invent1=Fetta, Guido Paul
|assign1=Fetta, Guido Paul
}}</ref><ref name="Cannae patent 2">
{{cite patent
|country=US
|number=2014013724
|status=application
|title=
|pubdate=2014-01-16
|fdate=2012-03-22
|pridate=2011-03-25
|invent1=Fetta, Guido P.
|assign1=Cannae LLC
}}</ref> and presented a paper at the same conference.<ref name="Cannae AIAA 2014">
{{cite conference
|last1=Fetta |first1=Guido P.
|title=Numerical and Experimental Results for a Novel Propulsion Technology Requiring no On-Board Propellant
|conference=50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
|publisher=]
|date=30 August 2014
|url=http://arc.aiaa.org/doi/abs/10.2514/6.2014-3853
|doi=10.2514/6.2014-3853
|accessdate=31 July 2014
}}</ref> Shawyer stated that the Cannae drive "operates along similar lines to EmDrive, except that its thrust is derived from a reduced reflection coefficient at one end plate," which he says "degrades the ''Q'' resonance factor of the device and hence the level of thrust that can be obtained".<ref name="Wired 2014" />


In 2015, Shawyer published an article in '']'', summarising seven existing tests on the EmDrive. Of these, four produced a measured force in the intended direction, three produced thrust in the opposite direction, and in one test thrust could be produced in ''either'' direction by varying the spring constants in the measuring apparatus.<ref>{{Cite journal
Eagleworks tested two versions of the Cannae drive: one device with radial slots engraved along the bottom rim of the resonant cavity interior, as required by Fetta's theory to produce thrust;<ref name="Cannae LLC" /> and a "null" test article lacking those radial slots. Both drives were equipped with an internal ].<ref name="NASA AIAA 2014" /> The null test device was not intended to be the experimental control. The control device was a third test article involving an RF load but without the resonant cavity interior.<ref name="Astronotes" /> Like the EmDrive tests, these took place at atmospheric pressure, not in a vacuum.
| last = Shawyer
| first = Roger
| date = 1 November 2015
| title = Second generation EmDrive propulsion applied to SSTO launcher and interstellar probe
| journal = Acta Astronautica
| volume = 116
| pages = 166–174
| doi = 10.1016/j.actaastro.2015.07.002
}}</ref>


=== Northwestern Polytechnical University ===
About the same net thrust was reported for both the standard and the null test devices. The experimental control without a resonant cavity interior measured zero thrust as expected.<ref name="Astronotes" /> Some considered the positive result for the non-slotted article as indicating a possible flaw in the experiment, as the null test device had been expected to produce less or no thrust based upon Fetta's theory of the designed mechanics.<ref name="Astronotes" /><ref>{{cite web |last1=Nelsen |first1=Eleanor |title=Improbable Thruster Seems to Work by Violating Known Laws of Physics |url=http://www.pbs.org/wgbh/nova/next/space/improbable-thruster-seems-work-violating-known-laws-physics/ |website=Nova |publisher=] |date=31 July 2014 |accessdate=1 August 2014}}</ref><ref name=Ars>{{cite web |last1=Timmer |first1=John |title=Don’t buy stock in impossible space drives just yet |url=http://arstechnica.com/science/2014/08/dont-buy-stock-in-impossible-space-drives-just-yet/ |website=Ars Technica |publisher=]|date=1 August 2014 |accessdate=2 August 2014}}</ref> In the complete paper, Eagleworks concluded, however, that the test results proved that "thrust production was not dependent upon slotting".<ref name="NASA AIAA 2014" /> As pointed out by Baez, the fact that the results were not dependent of the slotting, which was claimed to be necessary for thrust according to the inventor, should be seen as an invalidation of the device.<ref name=Powell />
In 2008, a team of Chinese researchers led by Juan Yang (杨涓), professor of propulsion theory and engineering of aeronautics and astronautics at ] (NWPU) in ], ], said that they had developed a valid electro-magnetic theory behind a microwave resonant cavity thruster.<ref name="Wired 2008" /><ref name="Yang 2008">{{cite journal
|last1 = ZHU
|first1 = Yu
|last2 = YANG
|first2 = Juan
|last3 = MA
|first3 = Nan
|title = The Performance Analysis of Microwave Thrust Without Propellant Based on the Quantum Theory
|date = September 2008
|journal = ]
|volume = 29
|issue = 5
|pages = 1612–1615
|language = zh
|url = http://en.cnki.com.cn/Article_en/CJFDTOTAL-YHXB200805027.htm
|access-date = 4 July 2014
|archive-date = 14 July 2014
|archive-url = https://web.archive.org/web/20140714225420/http://en.cnki.com.cn/Article_en/CJFDTOTAL-YHXB200805027.htm
|url-status = dead
}}</ref> A demonstration version of the drive was built and tested with different cavity shapes and at higher power levels in 2010. Using an aerospace ] usually used to precisely test spacecraft engines like ]s,<ref name="Wired 2013" /><ref name="Yang 2013">{{Cite journal
| last1 = Yang
| first1 = Juan
| last2 = Wang
| first2 = Yu-Quan
| last3 = Ma
| first3 = Yan-Jie
| last4 = Li
| first4 = Peng-Fei
| last5 = Yang
| first5 = Le
| last6 = Wang
| first6 = Yang
| last7 = He
| first7 = Guo-Qiang
| date = May 2013
| title = Prediction and experimental measurement of the electromagnetic thrust generated by a microwave thruster system
| journal = Chinese Physics B
| volume = 22
| issue = 5
| pages = 050301
| doi = 10.1088/1674-1056/22/5/050301
| url = http://cpb.iphy.ac.cn/EN/article/downloadArticleFile.do?attachType=PDF&id=53411
| format = PDF
| bibcode = 2013ChPhB..22e0301Y
| s2cid = 250763558
}}</ref><ref name="Yang 2014">{{Cite journal
| last1 = Shi
| first1 = Feng
| last2 = Yang
| first2 = Juan
| last3 = Tang
| first3 = Ming-Jie
| last4 = Luo
| first4 = Li-Tao
| last5 = Wang
| first5 = Yu-Quan
| date = September 2014
| title = Resonance experiment on a microwave resonator system
| journal = Acta Physica Sinica
| volume = 63
| issue = 15
| page = 154103
| doi = 10.7498/aps.63.154103
| url = http://wulixb.iphy.ac.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=60316
| format = PDF
| language = zh
| doi-access= free
}}</ref> they reported a maximum thrust of 720&nbsp;mN at 2,500&nbsp;W of input power.<ref name="Yang 2014" /> Yang noted that her results were tentative, and said she " not able to discuss her work until more results are published".<ref name="Wired 2013" />


In a 2014 follow-up experiment (published in 2016), Yang could not reproduce the 2010 observation and suggested it was due to experimental error.<ref name="Yang 2016" /> They had refined their experimental setup, using a three-wire torsion pendulum to measure thrust, and tested two different power setups. They concluded that they were unable to measure significant thrust; that "thrust" measured when using external power sources (as in their 2010 experiment) could be noise; and that it was important to use self-contained power systems for these experiments, and more sensitive pendulums with lower ] ].<ref name="Yang 2016" />
Fetta had tested a ] version of the "Q-drive" or Cannae drive on 13 January 2011 several years prior to the Eagleworks test campaign. The RF resonant cavity was suspended inside a liquid helium-filled ]. The weight of the cavity was monitored by ]s. Fetta theorized that when the device was activated and produced upward thrust, the load cells would detect the thrust as change in weight. When the Cannae drive was energized by sending 10.5&nbsp;watt power pulses of 1047.335&nbsp;MHz RF power into the resonant cavity there was a reduction in compressive force on the load cells consistent with thrust of 8-10&nbsp;mN. The results have not been published in the scientific literature, but were posted on Cannae LLC's website.<ref>Page is no longer available, but an archived version as of 2 November 2012 is available at archive.org: (retrieved 11 February 2015)</ref>


== ''New Scientist'' article == === NASA Eagleworks ===
After receiving criticism that no ]ed publications on the subject had been made, Shawyer submitted a theory paper to '']'', a weekly ] consumer magazine.<ref name="shawyertheory 9.3">
{{cite journal
|last=Shawyer
|first=Roger
|title=A Theory of Microwave Propulsion for Spacecraft (Theory paper v.9.3)
|magazine=]
|date=September 2006
|url=http://www.newscientist.com/data/images/ns/av/shawyertheory.pdf
|format=PDF
}}</ref> The EmDrive was featured on the cover of the 8 September 2006 issue of the magazine. The article portrayed the device as plausible, and emphasized the arguments of those who held that point of view.


Since 2011, White had a team at NASA known as the ], or Eagleworks Laboratories, devoted to studying exotic propulsion concepts.<ref name="Eagleworks">{{cite tech report
] author ], who holds a Bachelor of Science degree in Mathematics from the University of Western Australia, distributed a public letter stating that "a sensationalist bent and a lack of basic knowledge by its writers" made the magazine's coverage unreliable, sufficient "to constitute a real threat to the public understanding of science". In particular, Egan found himself "gobsmacked by the level of scientific illiteracy" in the magazine's coverage of the EmDrive, stating that ''New Scientist'' employed "meaningless double-talk" to obfuscate the relation of Shawyer's proposed space drive to the principle of ]. Egan urged those reading his letter to write to ''New Scientist'' and pressure the magazine to raise its standards, instead of "squandering the opportunity that the magazine's circulation and prestige provides" for genuine science education. The letter was endorsed by ] ] and posted on his blog.<ref name="egan">{{cite web
| last1 = White
|last=Egan |first=Greg |editor-last=Baez |editor-first=John C. |title=A Plea to Save ''New Scientist'' |date=19 September 2006 |url=http://golem.ph.utexas.edu/category/2006/09/a_plea_to_save_new_scientist.html |publisher=The n-Category Café (a group blog on math, physics and philosophy)}}</ref><ref name=Powell>{{cite web | url=http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-validate-imposible-space-drive-word/ | title=Did NASA Validate an "Impossible" Space Drive? In a Word, No. | publisher=''Discover'' | date=6 August 2014 | accessdate=6 August 2014 | author=Powell, Corey S.}}</ref> Egan also recommended<ref name="egan"/> that ''New Scientist'' publish a refutation penned by John P. Costella (a data scientist with a PhD in theoretical physics)<ref name="costella">
| first1 = Harold
{{cite web
| last2 = March
|last=Costella
| first2 = Paul
|first=John P.
| last3 = Nehemiah
|title=Why Shawyer's 'electromagnetic relativity drive' is a fraud
| first3 = Williams
|date=2006
| last4 = O'Neill
|website=John Costella’s home page
| first4 = William
|url=http://johncostella.webs.com/shawyerfraud.pdf
| title = Eagleworks Laboratories: Advanced Propulsion Physics Research
|format=PDF
| url = https://ntrs.nasa.gov/search.jsp?R=20110023492
}}</ref> of Shawyer's paper.<ref name="shawyertheory 9.3"/>
| website = NASA Technical Reports Server (NTRS)
| publisher = NASA
| number = JSC-CN-25207
| date = 5 December 2011
}}</ref> The group investigated ideas for a wide range of untested and ], including ]s, drives that interact with the ], and RF resonant cavity thrusters. In 2014, the group began testing resonant cavity thrusters, and in November 2016 they published a peer-reviewed paper on this work, in the '']''.<ref name="Eagleworks AIAA 2016" /><ref name="Wired Peer review">{{Cite magazine
| url = https://www.wired.co.uk/article/emdrive-peer-review-paper-science
| title = Nasa's 'impossible' EmDrive could work, study says
| last = Burgess
| first = Matt
| magazine = Wired
| location = Wired.com
| date = 21 November 2016
| access-date = 22 November 2016
}}</ref><ref name="Motherboard Peer Review">{{Cite web
| url = http://motherboard.vice.com/read/nasas-peer-reviewed-paper-on-the-emdrive-is-now-online
| title = NASA's Peer-Reviewed Paper on the EmDrive Is Now Online
| last = Johnson
| first = Lief
| date = 19 November 2016
| website = Motherboard.com
| publication-date = 19 November 2016
| access-date = 22 November 2016
}}</ref>

==== EmDrive and tapered cavities ====

In July 2014, White reported tentative positive results for evaluating a tapered RF resonant cavity.<ref name="NASA AIAA 2014" /> Their first tests of this tapered cavity were conducted at very low power (2% of Shawyer's 2002 experiment). A net mean thrust over five runs was measured at 91.2&nbsp;μN at 17&nbsp;W of input power.<ref name="NASA AIAA 2014" /> The experiment was criticized for its low power, small data set, and for not having been conducted in vacuum, to eliminate thermal air currents.

The group announced a plan to upgrade their equipment to higher power levels, and to use a test framework subject to independent ] at one or more major research centers.<ref name="NASA AIAA 2014" /><ref name="NBF_20150206">
{{cite web|author=Wang, Brian|date=6 February 2015|title=Update on EMDrive work at NASA Eagleworks|url=http://nextbigfuture.com/2015/02/update-on-emdrive-work-at-nasa.html|url-status=dead|archive-url=https://web.archive.org/web/20160315230923/http://nextbigfuture.com/2015/02/update-on-emdrive-work-at-nasa.html|archive-date=15 March 2016|access-date=8 February 2015|website=NextBigFuture|df=dmy-all}}
</ref> This did not happen.<ref>, Nasa Spaceflight Forum, posts by Paul March, 26 November 2016.</ref>

They later conducted experiments in vacuum at 40-80W of input power, publishing the results in 2016 in the '']'', under the title "Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum".<ref name="Eagleworks AIAA 2016" /><ref name="Wired Peer review" /><ref name="Motherboard Peer Review" /> The study said their system was "consistently performing with a thrust-to-power ratio of 1.2±0.1mN/kW", but also enumerated many potential sources of error.<ref name="Eagleworks AIAA 2016" /> This was the first such paper published in a peer-reviewed journal, however the experiment was again criticized for its small dataset and missing details about the experimental setup, which was again not independently validated.<ref name="Nat Geo Peer review">{{Cite web
| url = http://news.nationalgeographic.com/2016/11/nasa-impossible-emdrive-physics-peer-review-space-science/
| archive-url = https://web.archive.org/web/20161122020601/http://news.nationalgeographic.com/2016/11/nasa%2Dimpossible%2Demdrive%2Dphysics%2Dpeer%2Dreview%2Dspace%2Dscience/
| url-status = dead
| archive-date = 22 November 2016
| title = NASA Team Claims 'Impossible' Space Engine Works—Get the Facts
| last1 = Drake
| first1 = Nadia
| author1-link = Nadia Drake
| last2 = Greshko
| first2 = Michael
| work = National Geographic
| location = Nationalgeographic.com
| date = 21 November 2016
| access-date = 23 November 2016
}}</ref><ref name="Chris Lee Ars Technica">{{Cite web
| url = http://arstechnica.co.uk/science/2016/11/nasas-em-drive-still-a-wtf-thruster/
| title = NASA's EM-drive still a WTF-thruster
| last = Lee
| first = Chris
| website = arstechnica.co.uk
| date = 23 November 2016
| access-date = 23 November 2016
}}</ref><ref name="Tau Zero 2">{{Cite web
| url = http://www.centauri-dreams.org/?p=36890
| title = Close Look at Recent EmDrive Paper
| date = 3 January 2017
| last = Hathaway
| first = George
| editor-last = Gilster
| editor-first = Paul
| website = Centauri Dreams
}}</ref>

=== Dresden University of Technology ===

In July 2015, an aerospace research group at the ] (TUD) under ] reported results for an evaluation of an RF resonant tapered cavity similar to the EmDrive.<ref name="Tajmar2015">{{cite conference|last1=Tajmar|first1=Martin|last2=Fiedler|first2=Georg|date=July 2015|title=Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects|chapter=Direct Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects |url=http://tu-dresden.de/die_tu_dresden/fakultaeten/fakultaet_maschinenwesen/ilr/rfs/forschung/folder.2007-08-21.5231434330/ag_raumfahrtantriebe/JPC%20-%20Direct%20Thrust%20Measurements%20of%20an%20EM%20Drive%20and%20Evaluation%20of%20Possible%20Side-Effects.pdf|conference=51st AIAA/SAE/ASEE Joint Propulsion Conference|publisher=]|doi=10.2514/6.2015-4083|isbn=978-1-62410-321-6 |access-date=26 July 2015}}</ref> Testing was performed first on a knife-edge ] able to detect force at the micronewton level, atop an antivibration granite table at ambient air pressure; then on a torsion pendulum with a force resolution of 0.1&nbsp;mN, inside a vacuum chamber at ambient air pressure and in a hard vacuum at {{convert|4e-6|mbar|uPa|abbr=on|order=flip}}.

They used a conventional ] 2.45&nbsp;GHz 700 W oven magnetron, and a small cavity with a low Q factor (20 in vacuum tests). They observed small positive thrusts in the positive direction and negative thrusts in the negative direction, of about 20&nbsp;μN in a hard vacuum. However, when they rotated the cavity upwards as a "null" configuration, they observed an anomalous thrust of hundreds of micronewtons, much larger than the expected result of zero thrust. This indicated a strong source of noise which they could not identify. This led them to conclude that they could not confirm or refute claims about the device.

In 2018, they published results from an improved test rig, which showed that their measured thrust had been a result of experimental error from insufficiently shielded components interacting with the Earth's magnetic field.<ref name=newscientist2018>{{cite news
| title = 'Impossible' EM drive doesn't seem to work after all
| url = https://www.newscientist.com/article/2169809-impossible-em-drive-doesnt-seem-to-work-after-all/
| access-date = 25 May 2018
| work = New Scientist
}}</ref> In new experiments, they measured thrust values consistent with previous experiments and again measured thrust perpendicular to the expected direction when the thruster was rotated by 90°. Moreover, they did not measure a reduction in thrust when an ] was used to reduce the power that actually entered the resonant cavity by a factor of 10,000, which they said "clearly indicates that the "thrust" is not coming from the EMDrive but from some electromagnetic interaction." They concluded that "magnetic interaction from not sufficiently shielded cables or thrusters are a major factor that needs to be taken into account for proper μN thrust measurements for these type of devices," and they planned on conducting future tests at higher power and at different frequencies, and with improved shielding and cavity geometry.<ref name=tajmar2018>{{Cite conference
| last1 = Tajmar
| first1 = Martin
| last2 = Kößling
| first2 = Matthias
| last3 = Weikert
| first3 = Marcel
| last4 = Monette
| first4 = Maxime
| date = 16 May 2018
| title = The SpaceDrive Project – First Results on EMDrive and Mach-Effect Thrusters
| url = https://www.researchgate.net/publication/325177082
| conference = Space Propulsion Conference, at Seville, Spain
}}</ref><ref name=newscientist2018 />

In 2021, they revisited these experiments again and ran more precise tests. They reported with high confidence that the forces previously measured could be completely explained by experimental error, and that there was no evidence for any measurable thrust once these errors were taken into account.<ref>{{Cite web
|date = 2021-03-21
|title = Latest EmDrive tests at Dresden University shows "impossible Engine" does not develop any thrust
|url = https://www.grenzwissenschaft-aktuell.de/latest-emdrive-tests-at-dresden-university-shows-impossible-engine-does-not-develop-any-thrust20210321/
|access-date = 2021-04-01
|website = grenzwissenschaft-aktuell.de
}}</ref><ref>{{Cite web|last=Delbert|first=Caroline|date=2021-03-31|title=Scientists Just Killed the EmDrive|url=https://www.popularmechanics.com/science/a35991457/emdrive-thruster-fails-tests/|access-date=2021-04-01|website=Popular Mechanics|language=en-US}}</ref><ref name=tajmar20210401>{{Cite web
|title = High-Accuracy Thrust Measurements of the EMDrive and Elimination of False-Positive Effects
|last1= Tajmar |first1=Martin |last2=Neunzig |first2=Oliver|last3=Weikert |first3=Marcel
|url = https://www.researchgate.net/publication/350108418
|access-date = 2021-04-01
|website = ResearchGate
|language=en}}</ref> They were able to run the experiment and show no thrust in any direction, and to reintroduce the previous sources of experimental error to replicate the earlier results. They also replicated White's setup, showing that thermal effects could replicate the apparent thrust his team had observed, and that this thrust went away when measured with a more precise suspension. They went on to publish two further papers, showing similar negative results for the laser-based ] variant and Woodward's ].<ref>{{Cite web
|title = Thrust Measurements and Evaluation of Asymmetric Infrared Laser Resonators for Space Propulsion
|url=https://www.researchgate.net/publication/350108417
|access-date = 2021-04-01|website=ResearchGate
|language = en}}</ref><ref>{{Cite web
|title = The SpaceDrive Project – Mach-Effect Thruster Experiments on High-Precision Balances in Vacuum
|url = https://www.researchgate.net/publication/350108329
|access-date = 2021-04-01
|website = ResearchGate
|language = en}}</ref>

=== Tests in space ===
In August 2016, Cannae announced plans to launch its thruster on a 6U ] which they would run for 6 months to observe how it functions in space. Cannae formed a company called Theseus for the venture and partnered with LAI International and SpaceQuest Ltd. to launch the satellite. As of 2022, no launch date has yet been announced.<ref name="popularmechanics.com" />

In December 2016, Yue Chen told a reporter at China's '']'' that his team would test an EmDrive in orbit. Chen claimed their prototype's thrust was at the "micronewton to millinewton level", which would have to be scaled up to at least 100–1000 millinewtons for a chance of conclusive experimental results. Despite this, he said his goal was to validate the drive if possible, and make such technology available for satellite engineering "as quickly as possible".<ref name="ibtimes20161213">{{cite news
| url = http://www.ibtimes.co.uk/emdrive-chinese-space-agency-put-controversial-tech-onto-satellites-soon-possible-1596328
| title = EmDrive: Chinese space agency to put controversial tech onto satellites 'as soon as possible'
| work = International Business Times
| first = Mary-Ann
| last = Russon
| date = 13 December 2016
| access-date = 15 December 2016
}}</ref><ref name="ibtimes20161214">{{cite news
| url = http://www.ibtimes.co.uk/emdrive-these-are-problems-china-must-fix-make-microwave-thrusters-work-satellites-1596487
| title = EmDrive: These are the problems China must fix to make microwave thrusters work on satellites
| work = International Business Times
| first = Mary-Ann
| last = Russon
| date = 14 December 2016
| access-date = 15 December 2016
}}</ref><ref name="stdaily20161211">{{citation |url=http://digitalpaper.stdaily.com/http_www.kjrb.com/kjrb/html/2016-12/11/content_357004.htm |title=电磁驱动:天方夜谭还是重大突破 我国正开展关键技术攻关,争取5年内实现工程应用 |trans-title=EmDrive: Fantasy or major breakthrough |work=Science and Technology Daily |language=zh |author=操秀英 |date=11 December 2016 |access-date=15 December 2016 |archive-date=16 December 2016 |archive-url=https://web.archive.org/web/20161216144000/http://digitalpaper.stdaily.com/http_www.kjrb.com/kjrb/html/2016-12/11/content_357004.htm |url-status=dead }}</ref><ref>{{cite news
| last1 = Yan
| first1 = Li
| title = Mars could be getting closer and closer, if this science isn't m
| url = http://www.ecns.cn/2016/12-21/238503.shtml
| access-date = 21 December 2016
| agency = China News Service (中国新闻社)
| date = 21 December 2016
}}</ref><ref name="PopSci 20161220">{{cite web
| last1 = Lin
| first1 = Jeffrey
| last2 = Singer
| first2 = P. W.
| title = EmDrive: China Claims Success With This "Reactionless" Engine for Space Travel
| url = http://www.popsci.com/emdrive-engine-space-travel-china-success
| website = popsci.com
| publisher = Popular Science
| access-date = 21 December 2016
| date = 20 December 2016
}}</ref> After 2017, no further updates were announced.

==== BARRY 1 Cubesat ====

On 11 November 2023, the BARRY-1 satellite, a 3U ], was launched as part of the SpaceX ]. Produced by Rogue Space Systems, BARRY-1's primary objective is to test the company's hardware and software, with a future goal of offering ] services. Rogue Space Systems announced that the satellite is equipped with an "experimental propulsion" system, referred to as a "quantum drive," developed by IVO Limited.

The satellite's testing program includes a 60-day resting period post-launch to stabilize its orbit, accounting for initial perturbations such as ]. Subsequently, the experimental drive is planned to be activated, with its effects observable through public satellite tracking services.<ref>{{cite web
|last1=Hambling
|first1=David
|title=Controversial Quantum Space Drive In Orbital Test, Others To Follow
|url=https://www.forbes.com/sites/davidhambling/2023/11/17/controversial-quantum-space-drive-in-orbital-test-others-to-follow/
|work=Forbes
|date=17 November 2023
|accessdate=19 January 2024}}</ref>

{{As of|2024|01|16}}, Richard Mansell, the creator of the Quantum Drive, has said that initial operations of Barry-1 are taking longer than expected and there is no set date for activating the drive, which will wait until the satellite's primary mission is complete.<ref>{{Cite web |last=Mansell |first=Richard |date=Jan 16, 2024 |title=@RaMansell |url=https://twitter.com/RaMansell/status/1747321369732567117?t=jfi2CUHlK5Tnu4OtaSn3zQ&s=19 |website=X}}</ref> Independent analysis of the satellite's ] data indicates a gradual decay in its orbital altitude.<ref>{{cite web
|last1=Anne
|first1=Erin
|title=How is the Quantum Drive functioning on board the BARRY-1 satellite?
|url=https://space.stackexchange.com/a/65268/21538
|website=Space Exploration Stack Exchange
|publisher=Stack Exchange
|date=19 January 2024
|accessdate=19 January 2024}}</ref>

On the 9th of February 2024, Rogue Space Systems announced the end of the mission with the loss of communication to BARRY-1. For Rogue, this mission was mostly characterized as a success, however due to "ongoing power-system issues" the experimental drive provided by IVO was never tested in space. According to Rogue's CEO, the company is in discussion about including a new payload from IVO on a future launch.<ref>{{cite web
|title=Rogue Space Systems operations team is announcing the suspension of the active phase of a partially successful mission.
|url=https://rogue.space/suspension_of_barry1_operations/
|website=Rogue Space Systems
|date=9 February 2024
|accessdate=20 March 2024}}</ref>

== Experimental errors ==
The strongest early result, from Yang's group in China, was later reported to be caused by an experimental error.<ref name="Yang 2016" /> Tajmar published an explanation of how all reports of apparent thrust could have been caused entirely by failing to account for all sources of error or noise.

Experimental errors in the testing of the prototypes generally fall into four categories<ref name="discover_hurdle">{{cite news|url=http://blogs.discovermagazine.com/d-brief/2016/11/21/impossible-emdrive-thruster-cleared-first-hurdle/#.WDUr2R_6zCI|title=The Impossible' EmDrive Thruster Has Cleared Its First Credibility Hurdle – D-brief|date=21 November 2016|work=D-brief (])|access-date=23 November 2016|archive-date=22 November 2016|archive-url=https://web.archive.org/web/20161122110859/http://blogs.discovermagazine.com/d-brief/2016/11/21/impossible-emdrive-thruster-cleared-first-hurdle/#.WDUr2R_6zCI|url-status=dead}}</ref>

* Measurement error and noise. Most theoretical scientists who have looked at the EmDrive believe this to be the likely case.
* Thermal effects.
* Electromagnetic effects, including interaction with ambient magnetic fields and Lorentz forces from power leads.
Other potential sources of error include confirmation bias and publication bias (discarding negative results).

=== Measurement errors ===
{{Main|Observational error}}
The simplest and most likely explanation is that any thrust detected is due to ] or noise. In all of the experiments set up, a very large amount of energy goes into generating a tiny amount of thrust. When attempting to measure a small signal superimposed on a large signal, the noise from the large signal can obscure the small signal and give incorrect results.

=== Shift in center of gravity due to thermal effects ===
]
The largest error source is believed to come from the ] of the thruster's ]; as it expands this would lead to a change in the centre of gravity causing the resonant cavity to move. White's team attempted to model the thermal effect on the overall displacement by using a superposition of the displacements caused by "thermal effects" and "impulsive thrust" with White saying "That was the thing we worked the hardest to understand and put in a box". Despite these efforts, White's team were unable to fully account for the thermal expansion. In an interview with ''Aerospace America'', White comments that "although maybe we put a little bit of a pencil mark through ... they are certainly not black-Sharpie-crossed-out."<ref name="Hadhazy 2016">{{cite journal|last1=Hadhazy|first1=A.|year=2016|title=Fuel Free Space Travel|url=https://aerospaceamerica.aiaa.org/features/fuel-free-space-travel/|journal=Aerospace America|volume=February 2017|access-date=January 11, 2023}}</ref>

Their method of accounting for thermal effects has been criticized by Millis and Davies, who highlight that there is a lack of both mathematical and empirical detail to justify the assumptions made about those effects. For example, they do not provide data on temperature measurement over time compared to device displacement. The paper includes a graphical chart, but it is based on ] assumptions about what the shapes of the "impulsive thrust" and "thermal effects" should be, and how those signals will superimpose. The model further assumes all noise to be thermal and does not include other effects such as interaction with the chamber wall, power lead forces, and tilting. Because the Eagleworks paper has no explicit model for thrust to compare with the observations, it is ultimately subjective, and its data can be interpreted in more than one way. The Eagleworks test, therefore, does not conclusively show a thrust effect, but cannot rule it out either.<ref name="TZF 2016" />

White suggested future experiments could run on a ]. In such a setup, the thruster could rotate out to much larger angular displacements, letting a thrust (if present) dominate any possible thermal effects. Testing a device in space would also eliminate the center-of-gravity issue. Tajmar's team later used such a setup to show that past results had all been artefacts of thermal effects.<ref name="Hadhazy 2016" />

=== Electromagnetic interactions ===
These experiments used relatively large electromagnetic inputs to generate small amounts of thrust. As a result, electromagnetic interactions between power leads, between power lines and ambient magnetic fields, or between the apparatus and walls of a test chamber, could all have significant effects.


Yang reported in 2016 that an interaction with the Earth's magnetic field had caused the fairly large apparent thrust in their 2012 paper. Tajmar looked for potential Lorentz force interactions between power leads in trying to replicate White's experimental setup. Another source of error could have arisen from electromagnetic interaction with the walls of the vacuum chamber.<ref name="Hadhazy 2016" /> White argued that any wall interaction could only be the result of a well-formed resonance coupling between the device and wall and that the high frequency used imply the chances of this would be highly dependent on the device's geometry. As components get warmer due to thermal expansion, the device's geometry changes, shifting the resonance of the cavity. In order to counter this effect and keep the system in optimal resonance conditions, White used a ] system (PLL). Their analysis assumed that using a PLL ruled out significant electromagnetic interaction with the wall.<ref name="Eagleworks AIAA 2016" />
The following month, the ''New Scientist'' editor addressed the ensuing controversy over the article stating that "e should have made more explicit where it apparently contravenes the laws of nature and reported that several physicists declined to comment on the device because they thought it too contentious."<ref name="New Scientist blog">{{cite web |title=Emdrive on trial|last=Webb|first=Jeremy|date=3 October 2006|website=New Scientist Publisher's blog|url=http://www.newscientist.com/blog/fromthepublisher/2006/10/emdrive-on-trial.html}}</ref>


== See also == == See also ==
{{Columns-list|colwidth=22em|
* ] * ]
* ] * ]
* ] * ]
* ] * ]
* ]
* ]
* ] *]
* ]
* ]
* ]
* ]
* ] * ]
}}
*]


== References == == References ==
{{Reflist|30em}} {{Reflist}}

== External links ==
*{{Official website|cannae.com}}, Cannae
*{{Official website|emdrive.com}}, EmDrive
*{{cite magazine |last=Oberhaus |first=Daniel|title=A Mythical Form of Space Propulsion Finally Gets a Real Test |magazine=WIRED |date=2019-06-05 |url=https://www.wired.com/story/a-mythical-form-of-space-propulsion-finally-gets-a-real-test/ |access-date=2019-06-07}}
* @ '']''
* @ Space Studies Institute YouTube Playlist
* {{Webarchive|url=https://web.archive.org/web/20161008202307/https://www.tmro.tv/2016/05/09/the-empossibledrive/ |date=8 October 2016 }} @25 minutes in
*


{{Pseudoscience}}
]
{{Spacecraft propulsion}}
]
] ]
] ]
] ]
]
]

Latest revision as of 18:56, 11 November 2024

Device claimed to be a propellantless spacecraft thruster

For thrusters that use electrical power to change the velocity of spacecraft, see Electrically-powered spacecraft propulsion. For rocket that uses thrust from the momentum of emitted photons, see Photon rocket.
EmDrive
EmDrive experiment built by NASA Eagleworks laboratory in 2013
Country of originUnited States
Date2001
ApplicationSpacecraft thruster
StatusDevice concept
Performance
Thrust, sea-levelN (0 ozf)

The EmDrive is a concept for a thruster for spacecraft, first written about in 2001. It is purported to generate thrust by reflecting microwaves inside the device, in a way that would violate the law of conservation of momentum and other laws of physics. The concept has at times been referred to as a resonant cavity thruster.

There is no official design for this device. Neither person who claims to have invented it has committed to an explanation for how it could operate as a thruster or what elements define it, making it hard to say definitively whether a given object is an example of an EmDrive. However, over the years, prototypes based on its public descriptions have been constructed and tested.

In 2016, Harold White's group at NASA observed a small apparent thrust from one such test, however subsequent studies suggested this was a measurement error caused by thermal gradients. In 2021, Martin Tajmar's group at the Dresden University of Technology replicated White's test, observing apparent thrusts similar to those measured by the NASA team, and then made them disappear again when measured using point suspension.

No other published experiment has measured apparent thrust greater than the experiment's margin of error. Tajmar's group published three papers in 2021 claiming that all published results showing thrust had been false positives, explaining each by outside forces. They concluded, "Our measurements refute all EmDrive claims by at least 3 orders of magnitude."

History and controversy

Rocket engines operate by expelling propellant, which acts as a reaction mass and which produces thrust per Newton's third law of motion. All designs for electromagnetic propulsion operate on the principle of reaction mass. A hypothetical drive which did not expel propellant in order to produce a reaction force, providing thrust while being a closed system with no external interaction, would be a reactionless drive, violating the conservation of momentum and Newton's third law. Claims that a drive is reactionless are generally considered by physicists to be pseudoscience.

The first design of a resonant cavity thruster claiming to be a reactionless drive was by Roger Shawyer in 2001. He called his conical design an "EmDrive", and claimed that it produced thrust in the direction of the base of the cone. Guido Fetta later built a "Cannae Drive", based in part on Shawyer's concept, using a pillbox-shaped cavity.

Since 2008, a few physicists have tested their own models, trying to reproduce the results claimed by Shawyer and Fetta. Juan Yang at Xi'an's Northwestern Polytechnical University (NWPU) was unable to reproducibly measure thrust from their models, over the course of 4 years. In 2016, Harold White's group at NASA's Advanced Propulsion Physics Laboratory reported in the Journal of Propulsion and Power that a test of their own model had observed a small thrust. In late 2016, Yue Chen of the communication satellite division of the China Academy of Space Technology (CAST), said his team had tested prototypes, and would conduct in-orbit tests to determine if they could observe thrust. Martin Tajmar's group at the Dresden University of Technology started testing prototypes in 2015, and by 2021 concluded that observations of thrust were false positives, reporting in the CEAS Space Journal they had refuted all EmDrive claims by "at least 3 orders of magnitude."

Media coverage and responses

Media coverage of experiments using these designs has been polarized. The EmDrive first drew attention, both credulous and dismissive, when New Scientist wrote about it as an "impossible" drive in 2006. Media outlets were later criticized for misleading claims that a resonant cavity thruster had been "validated by NASA" following White's first tentative test reports in 2014. Scientists have continued to note the lack of unbiased coverage.

In 2006, responding to the New Scientist piece, mathematical physicist John C. Baez at the University of California, Riverside, and Australian science-fiction writer Greg Egan, said the positive results reported by Shawyer were likely misinterpretations of experimental errors.

In 2014, White's first conference paper suggested that resonant cavity thrusters could work by transferring momentum to the "quantum vacuum virtual plasma", a new term he coined. Baez and Carroll criticized this explanation, because in the standard description of vacuum fluctuations, virtual particles do not behave as a plasma; Carroll also noted that the quantum vacuum has no "rest frame", providing nothing to push against, so it cannot be used for propulsion. In the same way, physicists James F. Woodward and Heidi Fearn published two papers showing that electronpositron virtual pairs of the quantum vacuum, discussed by White as a potential virtual plasma propellant, could not account for thrust in any isolated, closed electromagnetic system such as a quantum vacuum thruster.

In 2015, physicists Eric W. Davis at the Institute for Advanced Studies in Austin and Sean M. Carroll at the California Institute of Technology concluded that the thrust measurements reported in papers by both Tajmar and White were indicative of thermal effect errors.

In May 2018, researchers from the Institute of Aerospace Engineering at Technische Universität Dresden, Germany, concluded that the dominant effect underlying the apparent thrust could be clearly identified as an artifact caused by Earth's magnetic field interacting with power cables in the chamber, a result that other experts agree with.

In March 2021, Tajmar's group published a definitive analysis of their own past experiments and those of others, showing that all could be explained by and reproduced via outside forces, refuting all EmDrive claims.

When power flows into the EmDrive, the engine warms up. This also causes the fastening elements on the scale to warp, causing the scale to move to a new zero point. We were able to prevent that in an improved structure. Our measurements refute all EmDrive claims by at least 3 orders of magnitude.

Designs and prototypes

Simplified schematic drawing of an EmDrive prototype by Tajmar and Fiedler

EmDrive

In 2001, Shawyer founded Satellite Propulsion Research Ltd, to work on the EmDrive, which he said used a resonant cavity to produce thrust without propellant. The company was backed by a SMART award grant from the UK Department of Trade and Industry. In December 2002, he loosely described a prototype which he alleged had produced a thrust of 0.02 newtons (0.072 ozf) powered by an 850 W cavity magnetron. The device could operate for only a few dozen seconds before the magnetron failed from overheating. Details were never published or replicated.

Second device and New Scientist article

In October 2006, Shawyer claimed to have conducted tests on a new water-cooled prototype with increased thrust. He reported plans to have the device ready to use in space by May 2009 and to make the resonant cavity a superconductor, neither of which materialized.

New Scientist magazine featured the EmDrive on the cover of 8 September 2006 issue. The article portrayed the device as plausible and emphasized the arguments of those who held that point of view. Egan, a popular science fiction author, distributed a public letter stating that "a sensationalist bent and a lack of basic knowledge by its writers" made the magazine's coverage unreliable, sufficient "to constitute a real threat to the public understanding of science". Especially, Egan said he was "gobsmacked by the level of scientific illiteracy" in the magazine's coverage, alleging that it used "meaningless double-talk" to obfuscate the problem of conservation of momentum. The letter was endorsed by Baez and posted on his blog. New Scientist editor Jeremy Webb responded to critics:

It is a fair criticism that New Scientist did not make clear enough how controversial Roger Shawyer's engine is. We should have made more explicit where it apparently contravenes the laws of nature and reported that several physicists declined to comment on the device because they thought it too contentious ... The great thing is that Shawyer's ideas are testable. If he succeeds in getting his machine flown in space, we will know soon enough if it is ground-breaking device or a mere flight of fancy.

New Scientist also published a letter from the former technical director of EADS Astrium:

I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger was advised that the company had no interest in the device, did not wish to seek patent coverage and in fact did not wish to be associated with it in any way.

A letter from physicist Paul Friedlander:

As I read it, I, like the thousands of other physicists who will have read it, immediately realised that this was impossible as described. Physicists are trained to use certain fundamental principles to analyse a problem and this claim clearly flouted one of them ... The Shawyer drive is as impossible as perpetual motion. Relativistic conservation of momentum has been understood for a century and dictates that if nothing emerges from Shawyer's device then its centre of mass will not accelerate. It is likely that Shawyer has used an approximation somewhere in his calculations that would have been reasonable if he hadn't then multiplied the result by 50,000. The reason physicists value principles such as conservation of momentum is that they act as a reality check against errors of this kind.

Later work

In 2007, the UK Department of Trade and Industry granted SPR an export license to Boeing in the US. According to Shawyer, in December 2008 he was invited to present on the EmDrive, and in 2009 Boeing expressed interest in it, at which point he stated that SPR built a thruster which produced 18 grams of thrust, and sent it to Boeing. Boeing did not license the technology and communication stopped. In 2012, a Boeing representative confirmed that Boeing Phantom Works used to explore exotic forms of space propulsion, including Shawyer's drive, but such work later ceased. They confirmed that "Phantom Works is not working with Mr. Shawyer," nor pursuing those explorations.

In 2014, Shawyer presented ideas for 'second-generation' EmDrive designs and applications at the annual International Astronautical Congress. A paper based on his presentation was published in Acta Astronautica in 2015. While no functional prototype of the first-generation drive had yet been produced, it described a model for a superconducting resonant cavity and three models for thrusters with multiple cavities.

In 2016, Shawyer filed further patents and launched a new company, Universal Propulsion Ltd., as a joint venture with Gilo Industries Group, a small UK aerospace company.

Cannae and other drives

The Cannae Drive (formerly Q-drive), is another implementation of this idea, with a relatively flat cavity rather than a truncated cone. It was designed by Guido Fetta in 2006 and promoted within the US through his company, Cannae LLC, since 2011. In 2016, Fetta announced plans to eventually launch a CubeSat satellite containing a version of the Cannae Drive, which would run for 6 months to observe how it functions in space. No followup was published.

In China, researchers working under Yang at NWPU built a resonant cavity thruster in 2008, and tested it for a number of years. A 2012 report claimed they had observed thrust, but in 2014 they found it to have been an experimental error. A second, improved prototype did not produce any measured thrust.

At the China Academy of Space Technology, Yue Chen filed several patent applications in 2016 describing various radio frequency (RF) resonant cavity thruster designs. These included a method for stacking several short resonant cavities to improve thrust, and a design with a cavity that was a semicylinder instead of a frustum. That December, Chen announced that CAST would conduct tests on a resonant cavity thruster in orbit, without specifying what design was used. In an interview on CCTV in September 2017, Chen showed some testing of a flat cylindrical device, corresponding to the patent describing stacked short cavities with internal diaphragms.

Theoretical inconsistencies

All proposed theories for how the EmDrive works violate the conservation of momentum, which states any interaction cannot have a net force; a consequence of the conservation of momentum is Newton's third law, where for every action there is an equal and opposite reaction. Also, because force·velocity = power, any such device would violate conservation of energy when moving at a high enough velocity. The conservation of momentum is a symmetry of nature.

An often-cited example of apparent nonconservation of momentum is the Casimir effect; in the standard case where two parallel plates are attracted to each other. However the plates move in opposite directions, so no net momentum is extracted from the vacuum and, moreover, energy must be put into the system to take the plates apart again.

Assuming homogeneous electric and magnetic fields, it is impossible for the EmDrive, or any other device, to extract a net momentum transfer from either a classical or quantum vacuum. Extraction of a net momentum "from nothing" has been postulated in an inhomogeneous vacuum, but this remains highly controversial as it will violate Lorentz invariance.

Both Harold White's and Mike McCulloch's theories of how the EmDrive could work rely on these asymmetric or dynamical Casimir effects. However, if these vacuum forces are present, they are expected to be exceptionally tiny based on our current understanding, too small to explain the level of observed thrust. In the event that observed thrust is not due to experimental error, a positive result could indicate new physics.

Tests and experiments

Tests by inventors

In 2004, Shawyer claimed to have received seven independent positive reviews from experts at BAE Systems, EADS Astrium, Siemens and the IEE. The technical director of EADS Astrium (Shawyer's former employer) denied this in the strongest terms, stating:

I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger was advised that the company had no interest in the device, did not wish to seek patent coverage and in fact did not wish to be associated with it in any way.

None of the other alleged independent experts published a positive review publicly.

In 2011, Fetta tested a superconducting version of the Cannae drive, suspended inside a liquid-helium-filled dewar, with inconclusive results.

None of these results were published in the scientific literature, replicated by independent researchers, or replicated consistently by the inventors. In a few cases details were posted for a time on the inventors' websites, but no such documents remain online as of 2019.

In 2015, Shawyer published an article in Acta Astronautica, summarising seven existing tests on the EmDrive. Of these, four produced a measured force in the intended direction, three produced thrust in the opposite direction, and in one test thrust could be produced in either direction by varying the spring constants in the measuring apparatus.

Northwestern Polytechnical University

In 2008, a team of Chinese researchers led by Juan Yang (杨涓), professor of propulsion theory and engineering of aeronautics and astronautics at Northwestern Polytechnical University (NWPU) in Xi'an, China, said that they had developed a valid electro-magnetic theory behind a microwave resonant cavity thruster. A demonstration version of the drive was built and tested with different cavity shapes and at higher power levels in 2010. Using an aerospace engine test stand usually used to precisely test spacecraft engines like ion drives, they reported a maximum thrust of 720 mN at 2,500 W of input power. Yang noted that her results were tentative, and said she " not able to discuss her work until more results are published".

In a 2014 follow-up experiment (published in 2016), Yang could not reproduce the 2010 observation and suggested it was due to experimental error. They had refined their experimental setup, using a three-wire torsion pendulum to measure thrust, and tested two different power setups. They concluded that they were unable to measure significant thrust; that "thrust" measured when using external power sources (as in their 2010 experiment) could be noise; and that it was important to use self-contained power systems for these experiments, and more sensitive pendulums with lower torsional stiffness.

NASA Eagleworks

Since 2011, White had a team at NASA known as the Advanced Propulsion Physics Laboratory, or Eagleworks Laboratories, devoted to studying exotic propulsion concepts. The group investigated ideas for a wide range of untested and fringe proposals, including Alcubierre drives, drives that interact with the quantum vacuum, and RF resonant cavity thrusters. In 2014, the group began testing resonant cavity thrusters, and in November 2016 they published a peer-reviewed paper on this work, in the Journal of Propulsion and Power.

EmDrive and tapered cavities

In July 2014, White reported tentative positive results for evaluating a tapered RF resonant cavity. Their first tests of this tapered cavity were conducted at very low power (2% of Shawyer's 2002 experiment). A net mean thrust over five runs was measured at 91.2 μN at 17 W of input power. The experiment was criticized for its low power, small data set, and for not having been conducted in vacuum, to eliminate thermal air currents.

The group announced a plan to upgrade their equipment to higher power levels, and to use a test framework subject to independent verification and validation at one or more major research centers. This did not happen.

They later conducted experiments in vacuum at 40-80W of input power, publishing the results in 2016 in the Journal of Propulsion and Power, under the title "Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum". The study said their system was "consistently performing with a thrust-to-power ratio of 1.2±0.1mN/kW", but also enumerated many potential sources of error. This was the first such paper published in a peer-reviewed journal, however the experiment was again criticized for its small dataset and missing details about the experimental setup, which was again not independently validated.

Dresden University of Technology

In July 2015, an aerospace research group at the Dresden University of Technology (TUD) under Martin Tajmar reported results for an evaluation of an RF resonant tapered cavity similar to the EmDrive. Testing was performed first on a knife-edge beam balance able to detect force at the micronewton level, atop an antivibration granite table at ambient air pressure; then on a torsion pendulum with a force resolution of 0.1 mN, inside a vacuum chamber at ambient air pressure and in a hard vacuum at 400 μPa (4×10 mbar).

They used a conventional ISM band 2.45 GHz 700 W oven magnetron, and a small cavity with a low Q factor (20 in vacuum tests). They observed small positive thrusts in the positive direction and negative thrusts in the negative direction, of about 20 μN in a hard vacuum. However, when they rotated the cavity upwards as a "null" configuration, they observed an anomalous thrust of hundreds of micronewtons, much larger than the expected result of zero thrust. This indicated a strong source of noise which they could not identify. This led them to conclude that they could not confirm or refute claims about the device.

In 2018, they published results from an improved test rig, which showed that their measured thrust had been a result of experimental error from insufficiently shielded components interacting with the Earth's magnetic field. In new experiments, they measured thrust values consistent with previous experiments and again measured thrust perpendicular to the expected direction when the thruster was rotated by 90°. Moreover, they did not measure a reduction in thrust when an attenuator was used to reduce the power that actually entered the resonant cavity by a factor of 10,000, which they said "clearly indicates that the "thrust" is not coming from the EMDrive but from some electromagnetic interaction." They concluded that "magnetic interaction from not sufficiently shielded cables or thrusters are a major factor that needs to be taken into account for proper μN thrust measurements for these type of devices," and they planned on conducting future tests at higher power and at different frequencies, and with improved shielding and cavity geometry.

In 2021, they revisited these experiments again and ran more precise tests. They reported with high confidence that the forces previously measured could be completely explained by experimental error, and that there was no evidence for any measurable thrust once these errors were taken into account. They were able to run the experiment and show no thrust in any direction, and to reintroduce the previous sources of experimental error to replicate the earlier results. They also replicated White's setup, showing that thermal effects could replicate the apparent thrust his team had observed, and that this thrust went away when measured with a more precise suspension. They went on to publish two further papers, showing similar negative results for the laser-based LemDrive variant and Woodward's Mach-Effect thruster.

Tests in space

In August 2016, Cannae announced plans to launch its thruster on a 6U cubesat which they would run for 6 months to observe how it functions in space. Cannae formed a company called Theseus for the venture and partnered with LAI International and SpaceQuest Ltd. to launch the satellite. As of 2022, no launch date has yet been announced.

In December 2016, Yue Chen told a reporter at China's Science and Technology Daily that his team would test an EmDrive in orbit. Chen claimed their prototype's thrust was at the "micronewton to millinewton level", which would have to be scaled up to at least 100–1000 millinewtons for a chance of conclusive experimental results. Despite this, he said his goal was to validate the drive if possible, and make such technology available for satellite engineering "as quickly as possible". After 2017, no further updates were announced.

BARRY 1 Cubesat

On 11 November 2023, the BARRY-1 satellite, a 3U cubesat, was launched as part of the SpaceX Transporter 9 Rideshare mission. Produced by Rogue Space Systems, BARRY-1's primary objective is to test the company's hardware and software, with a future goal of offering hosted payload services. Rogue Space Systems announced that the satellite is equipped with an "experimental propulsion" system, referred to as a "quantum drive," developed by IVO Limited.

The satellite's testing program includes a 60-day resting period post-launch to stabilize its orbit, accounting for initial perturbations such as outgassing. Subsequently, the experimental drive is planned to be activated, with its effects observable through public satellite tracking services.

As of 16 January 2024, Richard Mansell, the creator of the Quantum Drive, has said that initial operations of Barry-1 are taking longer than expected and there is no set date for activating the drive, which will wait until the satellite's primary mission is complete. Independent analysis of the satellite's TLE data indicates a gradual decay in its orbital altitude.

On the 9th of February 2024, Rogue Space Systems announced the end of the mission with the loss of communication to BARRY-1. For Rogue, this mission was mostly characterized as a success, however due to "ongoing power-system issues" the experimental drive provided by IVO was never tested in space. According to Rogue's CEO, the company is in discussion about including a new payload from IVO on a future launch.

Experimental errors

The strongest early result, from Yang's group in China, was later reported to be caused by an experimental error. Tajmar published an explanation of how all reports of apparent thrust could have been caused entirely by failing to account for all sources of error or noise.

Experimental errors in the testing of the prototypes generally fall into four categories

  • Measurement error and noise. Most theoretical scientists who have looked at the EmDrive believe this to be the likely case.
  • Thermal effects.
  • Electromagnetic effects, including interaction with ambient magnetic fields and Lorentz forces from power leads.

Other potential sources of error include confirmation bias and publication bias (discarding negative results).

Measurement errors

Main article: Observational error

The simplest and most likely explanation is that any thrust detected is due to experimental error or noise. In all of the experiments set up, a very large amount of energy goes into generating a tiny amount of thrust. When attempting to measure a small signal superimposed on a large signal, the noise from the large signal can obscure the small signal and give incorrect results.

Shift in center of gravity due to thermal effects

Infrared image showing heating of the heat sink

The largest error source is believed to come from the thermal expansion of the thruster's heat sink; as it expands this would lead to a change in the centre of gravity causing the resonant cavity to move. White's team attempted to model the thermal effect on the overall displacement by using a superposition of the displacements caused by "thermal effects" and "impulsive thrust" with White saying "That was the thing we worked the hardest to understand and put in a box". Despite these efforts, White's team were unable to fully account for the thermal expansion. In an interview with Aerospace America, White comments that "although maybe we put a little bit of a pencil mark through ... they are certainly not black-Sharpie-crossed-out."

Their method of accounting for thermal effects has been criticized by Millis and Davies, who highlight that there is a lack of both mathematical and empirical detail to justify the assumptions made about those effects. For example, they do not provide data on temperature measurement over time compared to device displacement. The paper includes a graphical chart, but it is based on a priori assumptions about what the shapes of the "impulsive thrust" and "thermal effects" should be, and how those signals will superimpose. The model further assumes all noise to be thermal and does not include other effects such as interaction with the chamber wall, power lead forces, and tilting. Because the Eagleworks paper has no explicit model for thrust to compare with the observations, it is ultimately subjective, and its data can be interpreted in more than one way. The Eagleworks test, therefore, does not conclusively show a thrust effect, but cannot rule it out either.

White suggested future experiments could run on a Cavendish balance. In such a setup, the thruster could rotate out to much larger angular displacements, letting a thrust (if present) dominate any possible thermal effects. Testing a device in space would also eliminate the center-of-gravity issue. Tajmar's team later used such a setup to show that past results had all been artefacts of thermal effects.

Electromagnetic interactions

These experiments used relatively large electromagnetic inputs to generate small amounts of thrust. As a result, electromagnetic interactions between power leads, between power lines and ambient magnetic fields, or between the apparatus and walls of a test chamber, could all have significant effects.

Yang reported in 2016 that an interaction with the Earth's magnetic field had caused the fairly large apparent thrust in their 2012 paper. Tajmar looked for potential Lorentz force interactions between power leads in trying to replicate White's experimental setup. Another source of error could have arisen from electromagnetic interaction with the walls of the vacuum chamber. White argued that any wall interaction could only be the result of a well-formed resonance coupling between the device and wall and that the high frequency used imply the chances of this would be highly dependent on the device's geometry. As components get warmer due to thermal expansion, the device's geometry changes, shifting the resonance of the cavity. In order to counter this effect and keep the system in optimal resonance conditions, White used a phase-locked loop system (PLL). Their analysis assumed that using a PLL ruled out significant electromagnetic interaction with the wall.

See also

References

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