Editing Field propulsion

{{Short description|Hypothetical spacecraft propulsion concept using external force fields momentum for transportation}}
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'''Field propulsion''' is the concept of [[spacecraft propulsion]] where no [[propellant]] is necessary but instead [[momentum]] of the [[spacecraft]] is changed by an interaction of the spacecraft with external [[Field (physics)|force fields]], such as [[Gravitational field|gravitational]] and [[Magnetic field|magnetic fields]] from stars and planets. Proposed drives that use field propulsion are often called a [[Reactionless drive|reactionless or propellantless drive]].

== Types ==

===Practical methods===

Although not presently in wide use for space, there exist proven terrestrial examples of "field propulsion", in which electromagnetic fields act upon a conducting medium such as seawater or plasma for propulsion, is known as [[magnetohydrodynamics]] or MHD. MHD is similar in operation to electric motors, however rather than using moving parts or metal conductors, fluid or plasma conductors are employed. The EMS-1 and more recently the [[Yamato 1]]<ref>{{cite journal|url=http://www.ovaltech.ca/pdfss/mhddesign.pdf|title=Optimal Design of Thruster System for Superconducting Electromagnetic Propulsion Ship| first1=Shinsuke |last1=AKAGI|first2=Kikuo|last2=FUJITA |first3=Kazuo |last3=SOGA|journal=Proceedings of the 5th International Marine Design Conference |date=May 27, 1994|access-date=November 30, 2022}}</ref> are examples of such electromagnetic Field propulsion systems, first described in 1994.<ref>{{Cite patent|country=US|number=5333444|pubdate=1994-08-02|title=Superconducting electromagnetic thruster|assign1=[[United States Secretary of the Navy]]|inventor1-last=Meng|inventor1-first=James C. S.}}</ref> There is potential to apply MHD to the space environment such as in experiments like NASA's [[electrodynamic tether]], [[Lorentz transformation|Lorentz Actuated Orbits]],<ref>{{cite web|url=http://www.ovaltech.ca/pdfss/Lorentz_Actuated_Orbits_1385Peck.pdf|title=Lorentz-Actuated Orbits: Electrodynamic Propulsion without a Tether|first=Mason A. |last=Peck|access-date=November 30, 2022}}</ref> the [[Wingless Electromagnetic Air Vehicle|wingless electromagnetic air vehicle]], and [[magnetoplasmadynamic thruster]] (which does use propellant).

[[Electrohydrodynamics]] is another method whereby electrically charged fluids are used for propulsion and boundary layer control such as [[ion propulsion]]{{citation needed|date=January 2014}}

Other practical methods which could be loosely considered as field propulsion include: The [[gravity assist]] trajectory, which uses planetary [[gravity]] fields and orbital momentum; [[Solar sails]] and [[magnetic sails]] use respectively the [[radiation pressure]] and [[solar wind]] for spacecraft thrust; [[aerobraking]] uses the atmosphere of a planet to change relative velocity of a spacecraft. The last two actually involve the exchange of momentum with physical particles and are not usually expressed as an interaction with fields, but they are sometimes included as examples of field propulsion since no spacecraft propellant is required. An example is the [[Magnetic Sail#Magsail (MS)|Magsail]] magnetic sail design.<ref>{{Cite journal |last1=Zubrin |first1=Robert M. |last2=Andrews |first2=Dana G. |date=March 1991 |title=Magnetic sails and interplanetary travel |url=https://arc.aiaa.org/doi/10.2514/3.26230 |journal=Journal of Spacecraft and Rockets |language=en |volume=28 |issue=2 |pages=197–203 |doi=10.2514/3.26230 |bibcode=1991JSpRo..28..197Z |issn=0022-4650}}</ref>{{Rp|location=Sec. VIII}}

===Speculative methods===
Other concepts that have been proposed are speculative, using "frontier physics" and concepts from [[modern physics]]. So far none of these methods have been unambiguously demonstrated, much less proven practical.

The [[Woodward effect]] is based on a controversial concept of [[inertia]] and certain solutions to the equations for [[General Relativity]]. Experiments attempting to conclusively demonstrate this effect have been conducted since the 1990s.

In contrast, examples of proposals for field propulsion that rely on physics outside the present paradigms are various schemes for [[faster-than-light]], [[warp drive]] and [[antigravity]], and often amount to little more than catchy descriptive phrases, with no known physical basis{{citation needed|date=August 2014}}.  Until it is shown that the conservation of energy and momentum break down under certain conditions (or scales), any such schemes worthy of discussion must rely on energy and momentum transfer to the spacecraft from some external source such as a local force field, which in turn must obtain it from still other momentum and/or energy sources in the cosmos (in order to satisfy conservation of both energy and momentum).{{citation needed|date=January 2014}}

Several people have speculated that the [[Casimir effect]] could be used to create a propellantless drive, often described as the "''Casimir Sail"'', or a "''Quantum Sail''".<ref>{{Cite web |last= |title=Running on empty |url=https://www.newscientist.com/article/mg15821315-100-running-on-empty/ |access-date=2023-08-06 |website=New Scientist |language=en-US}}</ref><ref>{{Cite journal |last=DeBiase |first=R. L. |date=2010-01-28 |title=A Light Sail Inspired Model to Harness Casimir Forces for Propellantless Propulsion |url=https://www.osti.gov/biblio/21370934 |journal=AIP Conference Proceedings |language=English |volume=1208 |issue=1 |pages=153–167 |doi=10.1063/1.3326244 |bibcode=2010AIPC.1208..153D |osti=21370934 |issn=0094-243X}}</ref><ref>{{Cite journal |last=DeBiase |first=R. L. |date=2010-01-01 |title=A Light Sail Inspired Model to Harness Casimir Forces for Propellantless Propulsion |journal=Space |series=AIP Conference Proceedings |url=https://ui.adsabs.harvard.edu/abs/2010AIPC.1208..153D |volume=1208 |issue=1 |pages=153–167 |doi=10.1063/1.3326244|bibcode=2010AIPC.1208..153D }}</ref><ref>{{Cite book |title=Zero: the biography of a dangerous idea |date=2000 |publisher=Viking |isbn=978-0-14-029647-1 |editor-last=Seife |editor-first=Charles |edition=1. publ |series=A New York Times Notable Book |location=New York |pages=187–188}}</ref>

===Field propulsion based on physical structure of space===

This concept is based on the general relativity theory and the [[Quantum Field Theory|quantum field theory]] from which the idea that space has a physical structure can be proposed. The macroscopic structure is described by the general relativity theory and the microscopic structure by the quantum field theory.
The idea is to deform space around the space craft. By deforming the space it would be possible to create a region with higher pressure behind the space craft than before it. Due to the [[Pressure-gradient force|pressure gradient]] a force would be exerted on the space craft which in turn creates thrust for propulsion.<ref name=book>{{cite book|last1=Musha|first1=Takaaki|title=Field Propulsion System for Space Travel: Physics of Non-Conventional Propulsion Methods for Interstellar Travel|date=15 February 2018|publisher=Bentham Books|isbn=978-1-60805-566-1|pages=20–37}}</ref> Due to the purely theoretical nature of this propulsion concept it is hard to determine the amount of thrust and the maximum velocity that could be achieved. Currently there are two different concepts for such a field propulsion system one that is purely based on the general relativity theory and one based on the quantum field theory.<ref name=ref1>{{cite journal|last1=Minami|first1=Yoshinari|last2=Musha|first2=Takaaki|title=Field propulsion systems for space travel|journal=Acta Astronautica|date=February 2013|volume=82|issue=2|pages=215–20|doi=10.1016/j.actaastro.2012.02.027|bibcode = 2013AcAau..82..215M }}</ref>

In the '''general relativistic field propulsion system''' space is considered to be an elastic field similar to rubber which means that space itself can be treated as an infinite elastic body. If the [[space-time]] curves, a normal inwards surface stress is generated which serves as a pressure field. By creating a great number of those curve surfaces behind the space craft it is possible to achieve a unidirectional surface force which can be use for the acceleration of the space craft.<ref name=ref1 />

For the '''quantum field theoretical propulsion system''' it is assumed, as stated by the quantum field theory and [[quantum Electrodynamics]], that the [[quantum vacuum]] consists out of a zero-radiating electromagnetic field in a non-radiating mode and at a [[zero-point energy|zero-point energy state]], the lowest possible energy state. It is also theorized that matter is composed out of elementary primary charged entities, [[Parton (particle physics)|parton]]s, which are bound together as elementary oscillators. By applying an electromagnetic zero point field a [[Lorentz force]] is applied on the partons. Using this on a [[dielectric]] material could affect the inertia of the mass and that way create an acceleration of the material without creating stress or strain inside the material.<ref name=ref1 />

===Conservation Laws===
Conservation of momentum is a fundamental requirement of propulsion systems because in experiments momentum is always conserved.<ref>Ho-Kim, Quang; Kumar, Narendra; Lam, Harry C. S. (2004). Invitation to Contemporary Physics (illustrated ed.). World Scientific. p. 19. {{ISBN|978-981-238-303-7}}. Extract of page 19</ref> This conservation law is implicit in the published work of Newton and Galileo, but arises on a fundamental level from the spatial translation symmetry of the laws of physics, as given by [[Noether's theorem]].  In each of the propulsion technologies, some form of energy exchange is required with momentum directed backward at the speed of light 'c' or some lesser velocity 'v' to balance the forward change of momentum. In absence of interaction with an external field, the power 'P' that is required to create a thrust force 'F' is given by <math>F = P/v</math> when mass is ejected or <math>F=P/c</math> if mass-free energy is ejected.

For a photon rocket the efficiency is too small to be competitive.<ref>There will be no photon rocket, by V. Smilga http://www.dtic.mil/dtic/tr/fulltext/u2/611872.pdf {{Webarchive|url=https://web.archive.org/web/20170517115350/http://www.dtic.mil/dtic/tr/fulltext/u2/611872.pdf |date=2017-05-17 }}</ref> Other technologies may have better efficiency if the ejection velocity is less than speed of light, or a local field can interact with another large scale field of the same type residing in space, which is the intent of field effect propulsion.

===Advantages===
The main advantage of a field propulsion systems is that no propellant is needed, only an energy source. This means that no propellant has to be stored and transported with the space craft which makes it attractive for long term [[interplanetary spaceflight|interplanetary]] or even [[interstellar travel|interstellar]] [[Human spaceflight|crewed missions]].<ref name=ref1 /> With current technology a large amount of fuel meant for the way back has to be brought to the destination which increases the [[payload]] of the overall space craft significantly.  The increased payload of fuel, thus requires more force to accelerate it, requiring even more fuel which is the primary drawback of current rocket technology.  Approximately 83% of a Hydrogen-Oxygen powered rocket, which can achieve orbit, is fuel.<ref>{{cite web|last1=Pettit|first1=Don|title=The Tyranny of the Rocket Equation|url=https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html|website=NASA|access-date=2016-11-04|archive-date=2016-10-29|archive-url=https://web.archive.org/web/20161029230045/http://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html|url-status=dead}}</ref>

===Limits===
The idea that with field propulsion no fuel tank would be required is technically inaccurate. The energy required to reach the high speeds involved begins to be non-neglectable for [[interstellar travel]]. For example, a 1-[[tonne]] spaceship traveling at 1/10 of the [[speed of light]] carries a [[kinetic energy]] of 4.5 × 10<sup>17</sup> [[joule]]s, equal to 5 [[kilogram|kg]] according to the [[mass–energy equivalence]]. This means that for accelerating to such speed, no matter how this is achieved, the spaceship must have converted at least 5&nbsp;kg of [[Mass–energy equivalence|mass/energy]] into momentum, imagining 100% efficiency. Although such mass has not been "expelled" it has still been "disposed".

==See also==
{{col-list|colwidth=25em|
* [[Advanced Space Propulsion Investigation Committee]]
* [[Breakthrough Propulsion Physics Program]]
* [[Bussard ramjet]]
* [[Reactionless drive]]
* [[United States gravity control propulsion research]]
*[[Rocket propulsion technologies (disambiguation)]]
}}

== References ==
{{reflist}}

==External links==
*[http://www.ovaltech.ca/spctrvl/thryop3.html Examples of current field propulsion systems for ships.] 
*[http://www.ovaltech.ca/spctrvl/oneinddrv.html Example of a possible field propulsion system based on existing physics and links to papers on the topic.] broken link
*{{cite book|author=Stoyan Sarg|title=Field Propulsion by Control of Gravity: Theory and Experiments|url=https://books.google.com/books?id=01d9QgAACAAJ|year=2009|publisher=CreateSpace Independent Publishing Platform|isbn=978-1-4486-9308-5}}
*[http://www.bis-space.com/ Y. Minami., An Introduction to Concepts of Field Propulsion, JBIS,56,350-359(2003).]
*[http://www.npo-astro.org/index-e.html Minami Y., Musha T., Field Propulsion Systems for Space Travel, the Seventh IAA Symposium on Realistic Near-Term Advanced Scientific Space Missions, 11–13 July 2011, Aosta, Italy]
*[http://www.benthamscience.com/ebooks/index.htm Ed.T.Musha, Y.Minami, Field Propulsion System for Space Travel: Physics of Non-Conventional Propulsion Methods for Interstellar Travel, 2011] {{ISBN|978-1-60805-270-7}}.
*[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800010907.pdf Field Resonance Propulsion Concept - NASA]
*[http://www.asps.it ASPS]
*[https://www.linkedin.com/pulse/dope-gravity-creating-unnatural-asymmetric-angular-jeffrey-krause/ Biasing Nature's Omni-Vector Tensors via Dense, Co-aligned, Asymmetric Angular-Acceleration of Energy]
{{Spacecraft propulsion}}

[[Category:Spacecraft propulsion]]
[[Category:Science fiction themes]]
[[Category:Hypothetical technology]]