Jump to content

EmDrive

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by PeterNLewis (talk | contribs) at 06:39, 6 August 2014 (missing [). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

EmDrive (also RF resonant cavity thruster) is a spacecraft propulsion system proposed by British aerospace engineer Roger J. Shawyer, who develops prototypes at Satellite Propulsion Research Ltd (SPR),[1] the company he created for that purpose in 2000.[2] New Scientist ran a cover story on EmDrive in its 8 September 2006 issue.[3] The device uses a magnetron producing microwaves directed inside a specially shaped, fully enclosed tapering high Q resonant cavity whose area is greater at one end. The inventor claims that the device generates a thrust even though no detectable energy leaves the device. The engine does not require any reaction mass although an outside energy input (fuel, solar or nuclear) is still required. If proven to work as claimed, it would be a breakthrough in airflight and spaceflight.[4][5][6][7][8][9]

The device, its mode of operation, and theories attempting to explain it are all highly controversial. As of 2014, there are still arguments about whether the EmDrive is a genuinely new propulsion method, or a misinterpretation of spurious effects mixed with mathematical errors. The proposed theory immediately received virulent criticism because it seems to violate a basic law of physics, namely conservation of momentum, though the inventor insists on the contrary.[10] Chinese researchers from the Northwestern Polytechnical University (NWPU) in Xi'an first repeated the experiment in 2010,[7][11][12][13] then NASA at the Johnson Space Center in 2014.[9][14]

Static thrust tests

Shawyer claims to have undergone seven independent positive reviews from experts at BAE Systems, EADS Astrium, Siemens and the IEE.[15]As of 2014, no EmDrive has been tested in microgravity.

Shawyer, in 2006, claimed that commercial terrestrial aircrafts incorporating EmDrives as lift engines could be ready by 2020,[16][17] through very high Q superconducting resonant cavities that would allow static specific thrusts of about 30 kN/kW, that is 3 tonnes of thrust per kilowatt of input power, "enough to lift a large car".[18]

New Scientist article

After receiving criticism that no peer-reviewed publications on the subject had been made, Shawyer submitted a theory paper to New Scientist, a weekly science magazine which is not a peer-reviewed scientific journal.[19] The EmDrive was consequently 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.

The following month, the editor addressed the apparent credulity of the publication stating that "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."[20]

Science fiction writer Greg Egan 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, and alleged that New Scientist employed "meaningless double-talk" to obfuscate the relation of Shawyer's proposed space drive to the principle of conservation of momentum. 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 mathematical physicist John C. Baez and posted on his blog.[21] Egan has also recommended[21] that New Scientist publish Costella's refutation[22] of Shawyer's paper.[19]

Replication claims

Chinese Northwestern Polytechnical University (NWPU)

In 2008, Wired 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 Northwestern Polytechnical University (NWPU) in Xi'an, claimed to have confirmed the theory behind the drive.[4][23] Their demonstration version of the drive was built and tested at high power in 2010.[11] A maximum thrust of 720 mN was measured at 2500 W of input power on an aerospace engine test stand usually used to precisely test spacecraft engines like ion drives.[8][24][12][13]

It is claimed[according to whom?] that the EmDrive, because it does not rely on reaction mass, would work indefinitely without any fuel other than that which might be required to generate electricity. Because the reaction mass typically forms 90% or more of the total weight of a spacecraft, a thruster that did not require reaction mass would represent a fundamental breakthrough in spacecraft design and propulsion.

The editor of Wired magazine who regularly covered the experimental results in the news declared he received some comments from the Chinese stating "the publicity was very unwelcome, especially any suggestion that there might be a military application"[6] and that Yang told him that "she is not able to discuss her work until more results are published".[8]

NASA/JSC Advanced Propulsion Physics Laboratory (Eagleworks)

RF resonant tapered cavity thruster (EmDrive)

In July 2014, a NASA team at the Advanced Propulsion Physics Laboratory (informally known as Eagleworks)[25] located at the Johnson Space Center (JSC) and led by physicist Harold G. White, reported on an evaluation of a RF resonant tapered cavity similar to Shawyer's EmDrive, with positive results.[14]

Testing was performed on a low-thrust torsion pendulum that is capable of detecting force at a single-digit micronewton level, within a sealed stainless steel vacuum chamber, but at ambient atmospheric pressure, because the RF power amplifier used an electrolytic capacitor not capable of operating in hard vacuum.

NASA's tests of the tapered RF cavity were conducted at very low power (50 times less than Shawyer's 2002 experiment and 150 times less than the Chinese 2010 experiment) but a net mean thrust over five runs was measured at 91.2 µN at 17 W of input power. A net peak thrust was recorded at 116 µN at the same power level.[14]

In the coming months, Eagleworks plans to upgrade their equipment to higher power levels, use vacuum-capable RF amplifiers with power ranges of up to 125 W, and design a new tapered cavity analytically determined to be in the 0.1 N/kW region. Then, the test article will be shipped to other laboratories for independent verification and validation of the technology, at Glenn Research Center, the Jet Propulsion Laboratory and the Johns Hopkins University Applied Physics Laboratory.[14]

Cannae drive

The same NASA test campaign also evaluated another unconventional propulsion test article known as the Cannae drive (formerly Q-drive)[14] which is also an asymmetric but flatter resonant cavity invented by Guido P. Fetta, CEO of Cannae LLC,[26] a company located in Pennsylvania, who filed two patent applications[27][28] and presented a paper at the same conference.[29] Shawyer noted that the Cannae drive "operates along similar lines to EmDrive, except that the asymmetric force derives from a reduced reflection coefficient at one end plate" but also stated this design "degrades the Q and hence the specific thrust that can be obtained".[9]

Eagleworks tested two versions of the Cannae drive: a thruster test article with radial slots engraved along the bottom rim of the resonant cavity interior, as required by Fetta's theory to produce thrust;[26] and a "null" test article lacking those radial slots. Both drives were equipped with an internal dielectric.[14] Like the EmDrive tests, these took place at atmospheric pressure, not in a vacuum.

According to the technical report, both Cannae drives (the standard and the null test articles) produced net thrust. Some early media, quoting an abstract that did not detail the setup and existence of a third control test, at first considered this a possible flaw in the experiment, as the null test article had been expected to produce no thrust.[30][31] However in the complete paper, Eagleworks concluded this behavior proved "thrust production was not dependent upon the slotting", suggesting Fetta's attempt to explain the unbalance force generated by his drive would be incomplete at least. The paper referred to a possible interaction with "quantum vacuum virtual plasma".[14]

Theory

Any apparent reactionless drive is treated with skepticism by the physics community, because such a drive (apparently) violates the principle of conservation of momentum. Shawyer claims that his drive does not violate conservation of momentum.[10] Shawyer has published an updated theory paper (version 9.4) for the EmDrive.[32]

Should the EmDrive produce a real thrust, various conjectures have been made to explain the underlying physics. Shawyer claims the thrust would be caused by radiation pressure imbalance between the two faces of the cavity caused by the action of group velocity in different frames of reference, within the framework of special relativity.[33] Yang from NWPU predicts a resulting net force using classical electromagnetism.[13] Harold G. "Sonny" White, who investigates field propulsion at Eagleworks, NASA's Advanced Propulsion Physics Laboratory, notes that such resonant cavities may operate by creating a virtual plasma toroid that would realize net thrust using magnetohydrodynamics upon quantum vacuum fluctuations.[34] Dr. Fernando Minotti, a researcher at CONICET, in a 2013 paper published in a peer reviewed scientific journal noted that the thrust attributed to the EmDrive may be explained by certain theories of gravity.[35]

See also

References

  1. ^ "EmDrive.com". Satellite Propulsion Research Ltd (SPR) web site. Roger Shawyer / SPR Ltd.
  2. ^ "Satellite Propulsion Research". Aerospace Member Directory. ADS Group.
  3. ^ Mullins, Justin (8 September 2006). "Relativity drive: The end of wings and wheels?". New Scientist (2568): 30–34.
  4. ^ a b Hambling, David (24 September 2008). "Chinese Say They're Building 'Impossible' Space Drive". Wired. Wired.
  5. ^ Hambling, David (2 October 2008). "Video: 'Impossible' Space Drive In Action?". Wired. Wired.
  6. ^ a b Hambling, David (29 October 2009). "'Impossible' Device Could Propel Flying Cars, Stealth Missiles". WIred. Wired.
  7. ^ a b Hambling, David (5 November 2012). "Propellentless Space Propulsion Research Continues". Aviation Week & Space Technology.
  8. ^ a b c Hambling, David (6 February 2013). "EmDrive: China's radical new space drive". Wired UK. Wired UK.
  9. ^ a b c Hambling, David (31 July 2014). "Nasa validates 'impossible' space drive". Wired UK. Wired UK. Retrieved 31 July 2014.
  10. ^ a b "EmDrive FAQ". SPR Ltd. Retrieved 24 July 2011.
  11. ^ a b YANG, Juan; YANG, Le; ZHU, Yu; MA, Nan. "Applying Method of Reference 2 to Effectively Calculating Performance of Microwave Radiation Thruster" (PDF). Journal of Northwestern Polytechnical University. 28 (6): 807–813.
  12. ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.7498/aps.61.110301, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.7498/aps.61.110301 instead.
  13. ^ a b c Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1088/1674-1056/22/5/050301, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1088/1674-1056/22/5/050301 instead.
  14. ^ a b c d e f g Brady, David A.; White, Harold G.; March, Paul; Lawrence, James T.; Davies, Franck J. (30 July 2014). Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum. 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. American Institute of Aeronautics and Astronautics. doi:10.2514/6.2014-4029. Retrieved 31 July 2014. {{cite conference}}: Unknown parameter |laydate= ignored (help); Unknown parameter |laysource= ignored (help); Unknown parameter |layurl= ignored (help)
  15. ^ Fisher, Richard (5 November 2004). "Defying gravity: UK team claims engine based on microwaves could revolutionise spacecraft propulsion". The Engineer. 293 (7663). London: 8.
  16. ^ Fisher, Richard (1 September 2006). "Microwave engine gets a boost". The Engineer. London.
  17. ^ "80 Ton Lifter Possible in 6 Years: Interview with EmDrive Inventor". BTE Blog. BuildTheEnterprise. 27 February 2013.
  18. ^ "Fly by light". Contact Center Solutions, TMCnet. Technology Marketing Corporation (TMC). 8 September 2006.
  19. ^ a b Shawyer, Roger (September 2006). "A Theory of Microwave Propulsion for Spacecraft (Theory paper v.9.3)" (PDF). New Scientist.
  20. ^ Webb, Jeremy (3 October 2006). "Emdrive on trial". New Scientist Publisher's blog.
  21. ^ a b Egan, Greg (19 September 2006). Baez, John C. (ed.). "A Plea to Save New Scientist". The n-Category Café (a group blog on math, physics and philosophy).
  22. ^ Cite error: The named reference costella was invoked but never defined (see the help page).
  23. ^ ZHU, Yu; YANG, Juan; MA, Nan (September 2008). "The Performance Analysis of Microwave Thrust Without Propellant Based On The Quantum Theory". Journal of Astronautics (in Chinese). 29 (5): 1612–1615.
  24. ^ YANG, Juan; et al. "Figure 4: Different microwave output power range thrust measurement results. Output power ranging from 300-2500W" (PDF). {{cite web}}: Explicit use of et al. in: |author= (help)
  25. ^ White, Harold; March, Paul; Nehemiah, Williams; O'Neill, William (5 December 2011). Eagleworks Laboratories: Advanced Propulsion Physics Research. NASA Technical Reports Server (NTRS) (Technical report). NASA. JSC-CN-25207.
  26. ^ a b "Cannae Drive". Cannae LLC website. Retrieved 31 July 2014.
  27. ^ WO application 2007089284, Fetta, Guido Paul, "Resonating cavity propulsion system", published 2007-11-15, assigned to Fetta, Guido Paul 
  28. ^ US application 2014013724, Fetta, Guido P., "Electromagnetic thruster", published 2014-01-16, assigned to Cannae LLC 
  29. ^ Fetta, Guido P. (30 August 2014). Numerical and Experimental Results for a Novel Propulsion Technology Requiring no On-Board Propellant. 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. American Institute of Aeronautics and Astronautics. doi:10.2514/6.2014-3853. Retrieved 31 July 2014.
  30. ^ Nelsen, Eleanor (31 July 2014). "Improbable Thruster Seems to Work by Violating Known Laws of Physics". Nova. PBS. Retrieved 1 August 2014.
  31. ^ Timmer, John (1 August 2014). "Don't buy stock in impossible space drives just yet". Ars Technica. Ars Technica. Retrieved 2 August 2014.
  32. ^ Shawyer, Roger (March 2007). "A Theory of Microwave Propulsion for Spacecraft (Theory paper v.9.4)" (PDF). SPR Ltd.
  33. ^ Shawyer, Roger (29 September–3 October 2008). Microwave Propulsion - Progress in the EmDrive Programme (PDF). 59th International Astronautical Congress (IAC 2008). Glasgow, U.K.: International Astronautical Federation. {{cite conference}}: Check date values in: |date= (help)
  34. ^ Harold "Sonny" White (2013). "Eagleworks Laboratories WARP FIELD PHYSICS" (PDF). NASA Technical Reports Server (NTRS). NASA.
  35. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1134/S0202289313030080, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1134/S0202289313030080 instead.
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=EmDrive&oldid=620059344"