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Field propulsion comprisesproposed and researched concepts andproduction technologies of terrestrial andspacecraft propulsion in whichthrust is generated bycoupling a vehicle to externalfields or ambientmedia rather than byexpelling onboardpropellant. In this broad sense, field propulsion schemes are thermodynamicallyopen systems that exchangemomentum orenergy with their surroundings; for example, a field propulsion system may couple itself tophoton streams,radiation,magnetized plasma, or planetarymagnetospheres. Familiar exemplars includesolar sails,electrodynamic tethers, andmagnetic sails. By contrast, hypotheticalreactionless drives areclosed systems that would claim to produce net thrust without any external interaction, widely regarded as violating thelaw of conservation of momentum and theStandard Model ofphysics.
Withinaerospace engineering research, the label spans both established and proposed approaches that "push off" external reservoirs:photonic pressure fromsunlight (sails),charged particle streams such as thesolar wind (magsails and relatedmagnetic structures), and interactions with planetarymagnetospheres andionospheric environments (electrodynamic tethers). In narrower usage, the term also covers efforts to engineer field–matter coupling usingelectromagnetic propulsion (e.g.,electrohydrodynamics andmagnetohydrodynamics) as well as speculative mechanisms that draw ongeneral relativity,quantum field theory, orzero-point energy ideas to alter effectiveinertia or to couple directly to non-particulatefields of space.
Several elements of field-coupled propulsion have been successfully demonstrated in thelaboratory, field tests, and inlow Earth orbit—most notably, sails and tethers. No field propulsion method has yet been validated as a practical primary propulsion system forinterplanetary orinterstellar missions, and are currently known to be limited to orbital operations. Even so, the prospect of exchanging momentum with external energy or matter reservoirs (and thereby reducing carriedrocket propellant cost, mass, and weight) continues to motivate exploratory work. The topic remains active in targeted programs such asNASA's formerBreakthrough Propulsion Physics Program as well as in studies by nationalspace agencies, academic research groups, andindustry organizations that investigatepropellantless or externally powered alternatives to conventionalrocket engines andelectric propulsion systems.
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The termfield propulsion, sometimes calledfield resonance propulsion,[1]: 15 refers topropellant-lesspropulsion systems in whichthrust arises frominteractions with externalfields or ambientmedia, rather than from thesustained expulsion of onboardreaction mass or reliance on solidchemical fuels.[2] Examples includesolar sails,magnetic sails, andelectrodynamic tethers, which couple with externalphoton,plasma, ormagnetic fields instead of expellingonboard propellant.[3]: 1–2 Various types of field propulsion concepts include mechanisms where motion results from environmental coupling rather than from carrying and ejecting propellant.[4]: 215–216 Field propulsion is not a single technology but a spectrum of approaches, ranging from mature concepts that have beentested in flight tohighly speculative theoretical constructs.[5]: 2 "Field" refers broadly to approaches that might exchange momentum or energy with external reservoirs, such as plasmas, magnetic fields, or directed energy sources, and therefore contrasted with both conventional rockets and nuclear-thermal designs.[6]: 26
Examples include systems that attempt to draw on thephoton field of sunlight, thecharged particles of thesolar wind, or themagnetic fields of planetary environments.[3]: 1–2 Broad definitions often include solar sail systems such as theJapan Aerospace Exploration Agency's (JAXA)IKAROS mission, which demonstrated propulsion by harnessingradiation pressure from sunlight.[7][8]: 3 Magnetic sail concepts proposed by Dana Andrews andRobert Zubrin envisioned the use of large magnetic fields to couple with the solar wind and thereby transfer momentum to the spacecraft.[3]: 1–2 [9]: 197 Narrower definitions, however, focus on experimentalelectromagnetic propulsion mechanisms, includingelectrohydrodynamics (EHD)[10]: 2 andmagnetohydrodynamics (MHD), as well as more speculative proposals that invokegeneral relativity,quantum field theory, orzero-point energy as possible pathways to modifyinertia or couple directly to thestructured quantum vacuum.[4]: 215–216, 219 By interacting with such external reservoirs, a spacecraft can "push off" the surrounding medium, converting environmental energy or momentum intoacceleration.[4]: 216–217 In contrast, conventionalrockets achieve motion by expelling mass.[11]: 5–6 Most commonly, this is thecombustion output fromchemical propellants to generate thrust viaNewton's third law, which is the familiarrocket launch withexplosive flame and smoke beneath it.[11]: 5–6
Momentum conservation is the fundamental boundary on all propulsion concepts.[5]: 2 Conservation of momentum is a fundamental requirement of propulsion systems because momentum is always conserved. This conservation law is implicit in the published work ofIsaac Newton andGalileo Galilei, but arises on a fundamental level from the spatialtranslation symmetry of the laws of physics, as given byNoether's theorem.[12] Open systems comply with theconservation of momentum by transferring it to or from the surrounding environment.[4]: 216–217 For instance, MHD drives accelerateconductive fluids usingelectromagnetic fields, resulting inthrust through theLorentz force, with momentum conserved via interaction with external media, such as theinterplanetary orinterstellar media, or solar winds.[10]: 2 Environment-coupled approaches such as sails, tethers, or plasma-wave coupling remain possible if the method of external coupling is strong enough.[3]: 1–2, 11–12
Some field propulsionreviews note thatopen systems exchangemomentum or energy with external media and that proposals ofclosed-system 'reactionless drive' propulsion are viewed with skepticism because they conflict with thermodynamic laws and establishedscientific principles.[5]: 2 [4]: 216–217 Any propulsion method that claims to generate net thrust in a closed system without external interaction challenges physical law and is considered untenable under theStandard Model of physics,[a] and would requirephysics beyond the Standard Model to be viable.[16]: 9
Traditional rocketry has dominatedaerospace propulsion in the 20th and early 21st centuries.[17] In 1928, J. Navascués ofLeón, Spain described a field coupleddynamo-electric machine concept "producing translatory motion of machine by current reaction with earth's field", in which "Propulsion is caused by cutting with a closed conducting turn the earth'smagnetic flux".[18]: 7231 The Franklin Institute's astronautics lecture series in 1958 included a section explicitly titled 'Field Propulsion', describing propulsion 'by the use of fields' as a way to avoid anexhaust jet,[19]: 46–47 and U.S. Air Force general Donald L. Putt predicted that upcoming spacecraft would deploy "photo or ion field-type propulsion".[20]: 6 United Press International reported that in 1964 there was a proposal from theWestinghouse Air Brake Company to linkYoungstown, Ohio withPittsburgh via a "super conductor magnetic field propulsion"transit system.[21]: 9 Beginning in the 1960s as spaceflight programs expanded, contractor studies for theU.S. Air Force andNASA organized advanced and theorized advanced propulsion concepts under three main headings: Thermal, Field, and Photon, so that unconventional ideas for spaceflight could be compared within a common framework.[6]: 26 In 1980, theChicago Tribune reported on early NASA advocacy of field propulsion, called then "field resonance propulsion", and noted some research ofmagnetohydrodynamics began in 1971, as an extension of training astronauts onsolar physics.[1]: 15 Early research treated field propulsion concepts as long-range prospects rather than near-term flight systems, but they kept the terminology of "field" propulsion alive in successive planning cycles.[6]: 25
During the 1960s through the 1990s, electric and electromagnetic propulsion matured experimentally, with some systems flying in limited operational roles even as they continued to rely on propellant despite their strong field components.[22]: 1–2 [11]: 10–11, 623 By contrast, the more speculative end of the spectrum such as concepts that couple to the environment without carrying reaction mass, remained in the research phase.[5]: 1–2 [4]: 215–216 A 1972 report from theAir Force Rocket Propulsion Laboratory, followed by Jet Propulsion Laboratory studies in 1975 and 1982, formalized this division by publishing roadmaps that again divided advanced concepts into the same Thermal, Field, and Photon classes as prior 1960s research had.[6]: 25–26 These reports emphasized "infinite specific impulse" systems would obtain energy or working fluid from the ambient environment and suggested new advances in lasers and superconductors could breathe new life into earlier discarded concepts such as laser propulsion or ramjets.[6]: 25–26, 406 In 1980, theHuntsville Times reported on a program byTRW Inc.'s Defense and Space Systems Group researchingmagnetic field based field propulsion, called "force field propulsion", for vehicle launch applications.[23]: 4 That year, NASA scientist Al Holt was quoted by theChicago Tribune in his advocacy of field propulsion: "One of the most important things to me is to help break down the inhibiting mental attitude that space-time field interactions will remain in the realm ofscience fiction for hundreds of years."[1]: 18
By the late 1990s, NASA'sBreakthrough Propulsion Physics Project (BPP) framed research around the goals of propulsion with no propellant mass, maximum physically possible transit speeds, breakthrough energy sources, and emphasized empirical testability.[5]: 1, 3–4 It also raised the question of whether any propellantless effects could exist without violating conservation of momentum and energy.[5]: 6 LaterNASA Institute for Advanced Concepts (NIAC) studies continued in the same mold, examining whether Alfvén wave coupling or other plasma interactions might provide quasi-propellantless thrust.[3]: 1–2 Across all of these efforts, surveys at the physics frontier acknowledged the conceptual appeal of field propulsion but also stressed the unresolved consistency issues that arise when no clear external momentum channel can be identified.[5]: 2 TheBritish National Space Centre andSociety of British Aerospace Companies began organizing an annual field propulsion research conference in 2001, inaugurated inBrighton at theInstitute of Development Studies, with initial delegates includingHarry Kroto.[24][25]: 13 BySTS-75 in 1996[26] andLightSail 1 andLightSail 2 between 2015 and 2019, functional field propulsion systems were active inouter space.[27][28]
Published technical surveys and program documents use "field" or field-adjacent language in different ways. Contractor studies for NASA grouped "advanced" options under headings such as Thermal Propulsion, Field Propulsion, and Photon Propulsion, with "field" covering externally powered and field-interactive concepts beyond conventional rocketry.[6]: 26 BPP's research goals at NASA explicitly included "propulsion that requires no propellant mass," maximum physically possible transit speeds, and breakthrough energy methods to power such devices, framing the field propulsion question in terms of fundamental physics limits and testable claims.[5]: 1 Framed with an emphasis on empirical testability, the BPP stated three goals: propulsion that requires no propellant mass, transit at the maximum speeds physically possible, and energy sources to power such devices.[5]: 1, 3–4 Separately, NIAC funded studies on using ambient plasmas and magnetic fields (e.g., solar wind, magnetospheres) to generate thrust without expelling onboard propellant, including Alfvén-wave coupling concepts.[3]: 1–2
In practice, the viability of any open field-coupled concept depends on coupling strength to the surrounding environment. For example, momentum exchange with the solar wind or a magnetosphere scales with local plasma density, magnetic-field magnitude, and wave/field interaction efficiency; in weak or highly variable environments, thrust and control authority are correspondingly limited.[3]: 7–10 These constraints contrast with classical chemical and conventionalelectric rockets, whose performance is governed primarily by onboard propellant and its energy, reflecting fundamentalengineering limits on achievableexhaust velocity andenergy density.[11]: 39–40 Electromagnetic propulsion reviews describe solid-propellant pulsed plasma, magnetoplasmadynamic systems, and pulsed inductive thrusters as electromagnetic spaceflight technologies.[22]: 1 Later NIAC work examined momentum exchange with ambient plasmas and magnetic fields as propellantless or quasi-propellantless mechanisms.[3]: 1–2 Hypothetical field propulsion systems, in contrast, are framed in the literature as propellantless but encounter dependence on external media and unresolved consistency with conservation laws.[5]: 2
Beamed-energy propulsion sends power from a remote source directly to a spacecraft propulsion system, using directed-energy technologies such as lasers, microwaves, or relativistic charged-particle beams, so that the propulsion power source remains independent of the spacecraft.[6]: iii, II-1 A NASA contractor report,Advanced Beamed-Energy and Field Propulsion Concepts, surveyedbeamed-energy and field propulsion concepts, seeking improvements beyond chemical rocket propulsion to achieve large gains in payload, range, and terminal velocity, and focused on systems where power is beamed to the vehicle by laser, microwave, orrelativisticcharged particle beams so that the power source remains independent of the spacecraft.[6]: I-2, II-1 The NASA report organized prospects into thermal, field, and photon classes and identified enabling technologies (e.g., higher-current superconductors, potential room-temperature superconductors,metallic hydrogen) as then-potential paths to field propulsion prospects.[6]: I-2 It also described large swings in advanced propulsion funding over the previous decades, and highlighted significant studies by AFRPL (1972) and JPL (1975, 1982) as part of that history.[6]: I-1 The study emphasized a return to the unrestricted creativity and "free-thinking" that characterized propulsion research in the late 1950s and early 1960s.[6]: I-2
The AFRPL study concluded that propulsion researchers should focus on "infinite specific impulse" (Isp) concepts that draw both working fluid and energy from the ambient environment, because of their implications for outstanding performance.[6]: I-2 Some approaches use atmospheric or environmental material as working fluid or interaction medium, drawing reaction mass or momentum exchange from the ambient environment rather than from onboard propellant.[6]: I-2, IX-14–IX-15 Proposals also include advanced electrostatic and MHD-based concepts that could leverage charged particle interactions with atmospheric fields or ionospheric plasmas and geomagnetic fields to produce directed motion.[6]: IX-14–15, IX-33, XIII-1–3 The study suggested improvements in technologies like high-power lasers or new energy transfer methods could revitalize previously discarded propulsion ideas, including laser propulsion and infinite-Isp ramjets.[6]: I-2 TheChicago Tribune in 1980 highlightedsolar electric propulsion as a possible field propulsion option under research.[1]
Forward (1984) extended beamed-sail studies to the interstellar scale, suggesting that phased solar-system lasers could impart sustained acceleration to ultralight sails across astronomical distances.[29]: 187 He calculated that such a system might accelerate a probe to ~0.11 c and reach Alpha Centauri in about four decades, bringing the timescale of an interstellar flyby to within a human lifetime.[29]: 187, 193
The 1964Zond 2 mission toMars from theSoviet Union marked the first planetary use of electric propulsion, followed by successive U.S. deployments culminating in theNova satellite series.[22]: 1 A NASA electromagnetic-propulsion review identified three main types of electromagnetic propulsion systems:pulsed plasma thrusters (PPTs),magnetoplasmadynamic thrusters (MPD), andpulsed inductive thrusters (PIT).[22]: 1 The review noted benefits of using electromagnetic thrusters include their ability to provide precision for satellite positioning, high specific impulse, robustness, high power processing capability, and simplicity; pulsed thrusters also permit relatively simple system level scaling with available spacecraft power.[22]: 1
PPTs are the only electromagnetic thrusters used on operational satellites, though both PPT and MPD thrusters have been flown in space.[22]: 1 These efforts culminated in first flights of solid propellant pulsed plasma thrusters in the Soviet Union in 1964 and in the United States in 1968.[22]: 1 Developed in the late 1960s, these thrusters initiate an arc discharge across a solid fluorinated polymer bar, ablating a small amount of propellant and accelerating it by the Lorentz body force.[22]: 2 PPTs had already flown for attitude/drag makeup; MPD devices had space heritage in experimental regimes; and PITs sought to reduce electrode-erosion limits by inductive coupling.[22]: 1, 8 Unlike later concepts relying on inductive or steady-state operation, PPTs utilize compact, low-power, pulsed configurations suitable for satellite positioning and drag compensation.[22]: 1, 4
MPDs are another major class of electromagnetic propulsion systems investigated for both quasi-steady and steady-state spaceflight applications.[22]: 5 MPDs operate through the Lorentz force generated by the interaction of discharge currents with self-induced or externally applied magnetic fields.[22]: 5
PITs are a form of electromagnetic propulsion developed to overcome the erosion and lifetime limitations of electrode-based systems.[22]: 8 By inducing plasma currents through time-varying magnetic fields, PITs accelerate neutral propellants without requiring physical contact between conductors and plasma.[22]: 8 The concept originated in the late 1960s and evolved through successive experimental designs focused on performance scaling, circuit optimization, and propellant compatibility.[22]: 7 Although no PIT system has flown in space, the thruster class remains of interest due to its potential for high-efficiency, long-duration propulsion with minimal material degradation, particularly in missions requiring flexible propellant selection and reduced contamination risk.[22]: 7
A NIAC Phase I study evaluated "ambient plasma wave propulsion," focusing on wave-mediated interactions with existing space environments including solar wind and magnetospheres.[3]: 1–2 The study highlighted the appeal of no onboard reaction mass requirements for the method, combined with limits such as technical immaturity and shortfall of such concepts for significant maneuvering capabilities.[3]: 11–12
NASA's Breakthrough Propulsion Physics (BPP) memo framed research questions at the limits of physics—no-propellant propulsion, ultimate transit speeds, and breakthrough energy production—explicitly to sort physically testable ideas from non-viable claims.[5]: 1 Minami and Musha in their 2012 study reviewed proposals that treat space as having a substantial physical structure, described at macroscopic scales by general relativity and at microscopic scales by quantum field theory.[4]: 215–216 They outline mechanisms such as vacuum polarization, engineered spacetime curvature, and zero-point field interactions.[4]: 219 Their study frames the topic for this branch of field propulsion as theoretical as of 2012, and point to engineering that would excite localized regions of space.[4]: 220 This dual framework places field propulsion concepts at the intersection of general relativity, which treats spacetime as a dynamic geometry, and quantum field theory, where the vacuum hosts fluctuating fields and latent energy.[4]: 218–219 Several mechanisms have been theorized to achieve such coupling, including spacetime-curvature effects in general relativity and interactions with electromagnetic zero-point fields in quantum field theory.[4]: 216, 218–219
Vacuum-fluctuation phenomena such as theCasimir effect have been measured in many precision experiments and are reviewed extensively in the mainstream literature.[30]: 1827, 1829–1830 However, attempts to obtain net thrust or a gravity coupling from static electromagnetic configurations (often framed as "electrogravitic" effects) have not produced reproducible anomalous forces in controlled tests.[31]: 2, 15 [32]: 315, 318 British Aerospace was confirmed in 2001 to have initiated a research program called "Project Greenglow" to research "the possibility of the control of gravitational fields."[33][25]: 13
A wide range of space propulsion methods have been proposed or demonstrated that fit within broad definitions of field propulsion. One group of field propulsion concepts comprises environment-coupled systems that utilize their surroundings to produce thrust, including solar sails, magnetic sails, and, with certain restrictions, electrodynamic tethers, which use the solar wind or ambient magnetic fields to generate thrust; in an example design, a magnetic sail uses a loop of superconducting cable to create a magnetic field that deflects solar wind plasma and imparts momentum to the attached spacecraft.[3]: 1–2 [9]: 197 Electrically driven electromagnetic propulsion systems use strong electromagnetic fields to accelerate propellant plasma.[22]: 1 A further and more speculative class invokes direct interactions with a structured vacuum or with spacetime geometry, proposing thrust without any expulsion of mass, an idea surveyed in the general relativity and quantum field theory literature but not empirically validated.[4]: 215, 218–219
This layered taxonomy reflects the way that contractor reports and program reviews organized the subject during the late twentieth century.[6]: 26 Most space propulsion concepts carry propellant to produce momentum and many advanced systems use electric and/or magnetic fields to accelerate ionized propellant.[3]: 2 Pulsed plasma thrusters (PPT), magnetoplasmadynamic thrusters (MPD), and pulsed inductive thrusters (PIT) are electromagnetic thrusters that accelerate propellant, and like most electric propulsion systems fall within electric-propulsion development lineages.[22]: 1 [8]: 3 Academic surveys distinguish environment-coupled concepts from electric-propulsion devices that expel carried propellant, separating speculative field-coupled ideas from near-term electric technologies.[3]: 1–2 [22]: 1–2
Microwave electrothermal thrusters use microwave energy—potentially externally supplied—to heat a fluid propellant. When powered externally, it falls under beamed-energy propulsion with mass acceleration via directed fields.Laser ablation propulsion: uses pulsed laser energy to ablate onboard material to produce plasma and thrust. Though it expels mass, the energy source is external, placing it within the domain of beamed field-accelerated propulsion systems. No spaceflights to date; research has been limited to laboratory testing and subscale atmosphericLightcraft demonstrations, with orbital proposals remaining unflown.Photonic laser thrusters are a photon-pressure system that relies on externally beamed lasers instead of sunlight.
Several devices central to electromagnetic propulsion rely on strong fields yet remain conventional in the momentum sense because they accelerate carried propellant.[11]: 647–649 Representative families include pulsed plasma thrusters (PPTs), magnetoplasmadynamic thrusters (MPD), and pulsed-inductive thrusters (PIT), each with distinct trade-offs in lifetime, efficiency, and power scaling; PPTs have flown for attitude and drag makeup, MPD has flight heritage in experimental regimes, and PIT remains ground-tested.[22]: 1–2
Within the electric-propulsion family, these devices illustrate how strong fields can dominate the internal acceleration physics while momentum closure still proceeds through exhaust.[22]: 5–8 In programmatic roadmaps, these technologies frequently serve as baselines for comparison with environment-coupled concepts, anchoring expectations for power-to-thrust ratios, lifetime, and system mass at mission-relevant scales.[11]: 648–649 [22]: 5–8 Electron cyclotron resonance thrusters (ECR) use electron cyclotron resonance toionize and accelerate a gaseous propellant (commonly xenon), particularly in ionospheric or high-altitude environments. ECRs usingelectron cyclotron resonance withmicrowave discharge have flown in space, most notably as the μ10ion engine system on JAXA'sHayabusa andHayabusa2 asteroid missions.[34]: 2 [35]: 2
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These systems generate thrust by exchanging momentum with external fields (magnetic, plasma, or photon), without expelling onboard reaction mass. Solar sails are a propellant-less propulsion method that produces thrust from solar photon pressure (solar radiation pressure), rather than by expelling reaction mass.[2][8]: 4, 5 As with other environment coupled concepts, sail performance depends on local solar photon pressure: the Interstellar Probe concept uses a very close solar flyby to take advantage of "increased solar flux" and the resultant "increased solar photon pressure", and scaling to a 160,000 m2 sail would require advances in sail materials, deployment, and attitude control systems.[8]: 4 TheChicago Tribune in 1980 highlightedsolar electric propulsion as a possible field propulsion option under research.[1]
Sailcraft engineering couples ultra-light structures to stringent pointing and thermal constraints.[36]: 2990, 2995 [29]: 188 Square and heliogyro designs use thin film sails on deployable booms; reliable deployment of large, low-mass structures and thin films is a key challenge.[36]: 2991, 3004–3005 Typical sail films have reflective front coats and high-emissivity back coats; wrinkling and billowing reduce efficiency.[36]: 2993–2995 Once deployed, thrust is almost normal to the sail, so small attitude changes steer the thrust vector.[36]: 2990–2991 Performance evolves with materials science and control: lower areal density directly increases acceleration,[29]: 188 and bycanting the sail the small continuous thrust can be steered for precise trajectory shaping.[36]: 2990 Forward (Journal of Spacecraft and Rockets, 1984) outlined a proposed method of how solar-system-based laser systems and a ~1,000 km diameterFresnel zone "para-lens" could propel thin-film sails to ~0.11 c, enabling an unmanned flyby of Alpha Centauri in approximately 40 years.[29]: 187, 193 In Forward's proposal, a two-stage sail system in which a massive ring sail reflects laser light back onto a detached payload sail, enabling the unmanned spacecraft to rendezvous and brake within the Alpha Centauri system.[29]: 193–194
Magnetic sails couple a spacecraft-supported magnetic field to the solar wind, producing thrust through solar-wind deflection.[9]: 197 Analyses of magnetic sail concepts indicate thrust arises from deflecting the solar wind around a spacecraft-supported magnetic field, with performance set by the stand-off distance at which solar-wind dynamic pressure balances the sail's magnetic pressure; larger effective magnetic cross-sections increase momentum transfer but require large-radius, high-current superconducting coils.[9]: 197–199 Key engineering challenges include the mass and size of the superconducting loop and the constraints imposed by achievable superconducting currents and magnetic fields.[9]: 197–199
Mission studies of magnetic sails show that they can perform heliocentric transfers between circular orbits by using the solar wind for outbound acceleration and inbound braking.[9]: 197–199 Magsails have also been proposed for interstellar missions, where interaction with the interstellar medium provides propellantless terminal deceleration into a destination solar system.[9]: 201–203 The design tradeoffs emphasize achieving a large effective magnetic cross-section for the superconducting loop while keeping its mass low.[9]: 199 Magnetospheric plasma propulsion (M2P2) is a NIAC proposal byRobert Winglee, in which plasma injection inflates a magnetic bubble that couples with the solar wind. It is considered a variant of magnetic sails.[37][38]
The most studied examples are electrodynamic tethers (EDT), which generate Lorentz-force-based drag or thrust by coupling a long current-carrying conductor to a planetary magnetic field, thereby exchanging momentum with a planetary magnetosphere or ionosphere to enable propellantless drag or thrust in suitable environments (e.g., low Earth orbit), fall under broad definitions of field propulsion due to their use of external fields for momentum exchange, and have been deployed in severalspace tether missions, including theTSS-1,TSS-1R, andPlasma Motor Generator (PMG) experiments.[3]: 1 [39]: 136–138 [40]: 153–155, 83–84 As open systems, they conserve momentum by reaction with the ambient plasma and magnetic field.[40]: 188, 153–155 In operation, a conductive tether moving through a planetary magnetic field experiences a motional electromotive force; closing the circuit through the ambient ionosphere allows current to flow, and the resulting Lorentz force can provide either drag (for deorbit) or, with external power injection, thrust along specific orbital geometries.[40]: 137, 146–147 Electrodynamic tethers can also generate electrical power at the expense of orbital energy.[40]: 151
NIAC studies proposed "ambient plasma wave propulsion" in which RF energy is coupled into ambient plasma using a spacecraft antenna, generating Alfvén waves that travel along ambient magnetic field lines; the report describes the wave as adding momentum to the antenna and spacecraft and thereby providing thrust as a "truly propellantless propulsion system".[3]: 1–2 The 2011 Phase I assessment found the approach technically immature but potentially enabling if sensitivity and power challenges can be overcome.[3]: 1, 25–26 Magnetohydrodynamic interaction concepts extending magnetohydrodynamics (MHD) to space plasma propose generating thrust by exchanging momentum with ambient charged particles via Lorentz-force coupling. If the interacting plasma is external (e.g., ionospheric or solar wind), the system qualifies as field propulsion. If the plasma is internally supplied and expelled, it instead falls under electromagnetic or electrothermal propulsion.
Atmosphere-breathing electric propulsion is a concept where spacecraft collect ambient particles in low orbit, ionize them, and accelerate them using electromagnetic fields. It avoids onboard propellant but still involves mass acceleration. Ground prototypes have been tested (ESASitael, ABEP, JAXA), but not yet flown in space. Closest heritage areion thrusters andHall-effect thrusters, which have flown widely (Deep Space 1,Dawn,SMART-1,BepiColombo) and demonstrate the same field-acceleration principle with onboard propellant. These systems accelerate onboard or environmental particles using electromagnetic, electrostatic, or directed energy fields. Some may still require onboard mass or atmospheric medium.
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, known collectively as magnetohydrodynamics (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 theYamato 1[41]: 562 are examples of such electromagnetic field-propulsion systems, first described in 1994.[42] Electrohydrodynamics (EHD) is another method where electrically charged fluids are accelerated for propulsion and flow control; laboratory and flight demonstrations includedevices driven by corona discharge.[10]: 2 [43]: 532–535
In 1990, theDaily Telegraph reported on Japanese development work toward a magnetohydrodynamic propulsion ship, including plans to install the magnetic propulsion equipment and conduct at-sea testing.[44]: 11 By 1991–1992, the Ship & Ocean Foundation's experimental shipYamato 1 had been completed and successfully propelled by superconducting MHD thrusters during trials inKobe Harbor.[45]: 402 A 1992 harbor demonstration ofYamato 1 was completed using a superconducting magnetic propulsion system.[46]
Magnetic levitation (maglev) ground transport systems are another terrestrial example of propulsion via externally generated fields: maglev employs magnetic forces to lift, guide, and propel a vehicle over a guideway, with propulsion typically provided by a linear motor whose traveling magnetic field pulls or pushes the vehicle along the track.[47][48]: 2342 In 1992, theNew York Times described U.S. investment inmaglev development, noting that maglev trains would be lifted on magnetic cushions and propelled along a guideway by alternating magnetic fields that create a "magnetic wave".[49]: 9 The report said Congress had authorized a six-year, $700 million demonstration program and noted existing demonstration systems in Germany and Japan, including a reported speed record of 273 miles per hour on a test track.[49]: 9
Minami and Musha frame field propulsion at the physics frontier as interaction with a "substantial physical structure" of space, drawing ongeneral relativity atmacroscopic scales andquantum field theory at microscopic scales.[4]: 215–216 They conclude that future engineering technologies for space travel will most likely require some form of field propulsion toexcite properties oflocalized regions in space.[4]: 220 A 1979NASA technical memorandum outlined a speculative field resonance propulsion concept that hypothesized thrust from a resonance between coherent pulsedelectromagnetic field waveforms and gravitational waveforms associated with spacetime metrics, framed as potentially enabling galactic travel without prohibitive travel times.[50]: ii
The study described a notional spacecraft approach that would combine magnetic fieldline merging, hydromagnetic wave effects,free-electron lasers, and laser generation ofmegagauss fields, along with special structural and containment metals, as candidate enabling elements for the concept.[50]: ii It proposed that if a spacecraft could generate an electrohydromagnetic field configuration that is a harmonic of the spacetime metrics of a distant spacetime point and resonant with them, forces would act to move the spacecraft toward that spacetime point, likened to tuning a radio station.[50]: 5 The report cautioned that the concept depended on two assumptions not yet proven and on unverified magnetohydrodynamic processes, and that the spacecraft system described would require extensive modification or complete revamping after initial research activity and feasibility studies.[50]: 9 The concept depended on two assumptions: that space-time is a projection of ahigher-dimensional space analogous to ahologram, and that electromagnetic or hydromagnetic fields are related to gravitational fields such that aunified field theory could be developed.[50]: 1
Potential concepts studied by NASA and other parties have included vacuum polarization, engineered spacetime curvature, and zero-point-field interactions; none have been experimentally validated, and all face unresolved consistency issues with momentum conservation.[5]: 2 Minami and Musha distinguish between two field propulsion concepts: one framed in terms of general relativity and one in terms of quantum field theory.[4]: 215–220 In the general relativistic field propulsion system, space-time is considered to be an elastic field similar to rubber, which means space itself can be treated as an infinite elastic body.[51]: 20–21 In Minami and Musha's framing, propulsive force arises from interaction with a physical structure of space instead of from expelling reaction mass.[4]: 216–217 According to quantum field theory andquantum electrodynamics, thequantum vacuum is modeled as a nonradiating electromagnetic background, existing in a zero-point state, the minimum energy allowed by the theory.[51]: 24–25 Using this on adielectric material could, via the resulting Lorentz force on bound charges, affect the inertia of the mass and that way create an acceleration of the material without creating stress or strain inside the material.[4]: 216–219
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'One of the most important things to me', Holt says, 'is to help break down the inhibiting mental attitude that space-time field interactions will remain in the realm of science fiction for hundreds of years.'
{{cite news}}: CS1 maint: url-status (link)Propellant-less propulsion systems generate thrust via interaction with the surrounding environment (e.g., solar photon pressure, planetary magnetic fields, solar wind and ionospheric plasma pressures, and planetary atmospheres). By contrast, chemical and electric propulsion systems generate thrust by expulsion of reaction mass (i.e., propellant). Four propellant-less propulsion technologies have undergone in-space demonstrations to date, including solar sails, tethers, electric sails (and plasma brakes), and aerodynamic drag devices.
JAXA began a series of deployment test flights in 2004, leading to the successful flight of the Interplanetary Kite-craft Accelerated by Radiation Of the Sun (IKAROS) in 2010. The IKAROS is the first deep-space demonstration of solar sailing. The IKAROS verified solar radiation pressure effects on the sail and performing in-flight guidance and navigation techniques using the solar sail.
spatial translations ↔ conservation of momentum
In other words, translation invariance implies momentum conservation, and vice versa. Momentum and energy are conserved because the laws of physics are invariant under translations in space and time, respectively. We will explain this again in a more sophisticated way very soon. In general, the fact that symmetries imply conservation laws is called Noether's Theorem.
A typical expectation is that the induced forces would just act between the vehicle's field-inducing device and the rest of the vehicle, like blowing in your own sails, or trying to move a car by pushing on it from the inside. In such cases all the forces act internally and there would be no net motion of the vehicle. For reference, this issue can be called the net external force requirement. The net external force requirement is closely related to conservation of momentum. Conservation of momentum requires that the momentum imparted to the vehicle must be equal and opposite to the momentum imparted to a reaction mass. In the case of a field drive, there is no obvious reaction mass for the vehicle to push against.
According to this novel approach, apart from leading to a change in theWeltbild of physics by extending the general theory of relativity, gravitational engineering may eventually become a technological reality and lead to a novel era of spaceflight, i.e., propellantless propulsion. As a further consequence for physics, this theoretical view would force major extensions of both the standard model of cosmology and particle physics by providing a mechanism for the existence of dark matter and dark energy as well as novel fundamental particles.
...producing translatory motion of machine by current reaction with earth's field. Propulsion is caused by cutting with a closed conducting turn the earth's magnetic flux...
Putt prophesized that there would be 'undreamed-of' strides in the field of propulsion with vehicles boosted away from the earth with million-pound rocket engines which could continue with photo or ion field-type propulsion, and this should cover our solar system.
Further away but possibly the ultimate answer in moving large numbers of people in safety are compressed air propulsion and super conductor magnetic field propulsion. Super conductor magnetic field propulsion will need a major research project before it is feasible. But there has been a proposal for such a magnetic line linking Youngston, Ohio, with Pittsburgh.
{{cite news}}: CS1 maint: url-status (link)This WORKSHOP was called as the European response to the establishment of the NASA 'Breakthrough Propulsion Physics' workshops, & is open to all International participants, on a Global basis. Following recent coverage in the Public and scientific media, with regard to emerging experimental and engineering results in the field of 'Propellentless propulsion', and theoretical and experimental work on the 'Electrogravitics' hypothesis, it was decided that a European focus for this area was needed, external to NASA and the United States, and also International in character.
{{cite news}}: CS1 maint: url-status (link)LightSail® is a crowdfunded project from The Planetary Society to demonstrate that solar sailing is a viable means of propulsion for CubeSats — small, standardized spacecraft that are part of a global effort to lower the cost of space exploration. Our LightSail 2 spacecraft, which launched on June 25, 2019 and reentered Earth's atmosphere on Nov. 17, 2022, used sunlight alone to change its orbit.
The cathode-less electron cyclotron resonance ion engines, μ10, propelled the Hayabusa asteroid explorer, launched in May 2003, which is focused on demonstrating the technology needed for a sample return from an asteroid.
An ion thruster consists of an ion source and a neutralizer both of which utilize microwave discharge with electron cyclotron resonance at a frequency of 4.25 GHz.
Developed by a team at the University of Washington, the Mini-Magnetospheric Plasma Propulsion system, or M2P2, has a maximum speed of 180,000 miles per hour, or 4.3 million miles a day, about ten times the speed of a space shuttle. The brainchild of geophysicist Robert Winglee, the M2P2 system employs a huge plasma field around a satellite. The field catches solar wind, like an enormous electromagnetic sail.
Electrically conducting tethers will couple to the Earth's magnetic field. In low Earth orbit (LEO) there is sufficient plasma density to allow large currents to flow through the tether and close the loop efficiently through the plasma. The interaction between the current and the magnetic field produces a force that propels the tether... without expending propellant.
{{cite news}}: CS1 maint: url-status (link)The Ship & Ocean Foundation set up a research and development committee for MHD ship propulsion in 1985 and started an extensive R & D studies, and to construct an experimental ship to demonstrate that a ship can really be propelled by MHD thrusters with all the necessary machinery and equipments on board. The experimental ship, named the YAMATO 1, was completed in the fall of 1991 and was actually propelled successfully by MHD thrusters in the summer of 1992 in KOBE harbour.
{{cite journal}}: CS1 maint: url-status (link){{cite web}}: CS1 maint: url-status (link){{cite news}}: CS1 maint: url-status (link)| Specialties and interdisciplinarity |
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