Field propulsion

Field propulsion refers to spacecraft propulsion proposed and researched concepts and production technologies in which thrust is generated by coupling a vehicle to external fields or ambient media rather than by expelling onboard propellant. In this broad sense, field propulsion schemes are thermodynamically open systems that exchange momentum or energy with their surroundings; for example, a field propulsion system may couple itself to photon streams, radiation, magnetized plasma, or planetary magnetospheres. Familiar exemplars include solar sails, electrodynamic tethers, and magnetic sails. By contrast, hypothetical reactionless drives are closed systems that would claim to produce net thrust without any external interaction, widely regarded as violating the law of conservation of momentum and the standard model of physics.

Within aerospace engineering research, the label spans both established and proposed approaches that "push off" external reservoirs: photonic pressure from sunlight (sails), charged particle streams such as the solar wind (magsails and related magnetic structures), and interactions with planetary magnetospheres and ionospheric environments (electrodynamic tethers). In narrower usage, the term also covers efforts to engineer field–matter coupling using electromagnetic propulsion (e.g., electrohydrodynamics and magnetohydrodynamics) as well as speculative mechanisms that draw on general relativity, quantum field theory, or zero-point energy ideas to alter effective inertia or to couple directly to non-particulate fields of space.

Several elements of field-coupled propulsion have been successfully demonstrated in the laboratory, field tests, and in low Earth orbit—most notably, sails and tethers. No field propulsion method has yet been validated as a practical primary propulsion system for interplanetary or interstellar 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 carried rocket propellant cost, mass, and weight) continues to motivate exploratory work. The topic remains active in targeted programs such as NASA’s former Breakthrough Propulsion Physics Program as well as in studies by national space agencies, academic research groups, and industry organizations that investigate propellantless or externally powered alternatives to conventional rocket engines and electric propulsion systems.

Definition

The broad definition of field propulsion refers to propulsion systems in which thrust arises from interactions with external fields or ambient media, rather than from the sustained expulsion of onboard reaction mass or reliance on solid chemical fuels. In this framing, familiar exemplars include solar sails, magnetic sails, and electrodynamic tethers, which couple with external photon, plasma, or magnetic fields instead of expelling onboard propellant.^[1]^: 1–2 Some field propulsion reviews note that open systems exchange momentum or energy with external media and that proposals of closed-system 'reactionless drive' propulsion are viewed with skepticism because they conflict with conservation of momentum.^[2]^: 2 In contrast, conventional rockets achieve motion by expelling mass.^[3]^: 5–6 Most commonly, this is the combustion output from chemical propellants to generate thrust via Newton's third law, which is the familiar rocket launch with explosive flame and smoke beneath it.^[3]^: 5–6 That method has dominated aerospace propulsion since the advent of gunpowder in ancient warfare during the 11th century, initial rocketry concepts in the 14th century, and the internal combustion engine for aviation in the 20th century.^[3]

Field propulsion is not a single technology but a spectrum of approaches, ranging from relatively mature concepts that have been tested in flight to highly speculative theoretical constructs. Broad definitions often include solar sail systems, such as the Japan Aerospace Exploration Agency’s (JAXA) IKAROS mission, which demonstrated propulsion by harnessing radiation pressure from sunlight.^[1] In a similar spirit, magnetic sail concepts proposed by Dana Andrews and Robert Zubrin envision the use of large magnetic fields to couple with the solar wind and thereby transfer momentum to the spacecraft.^[1]^: 1–2^[4] Narrower definitions, however, focus on experimental electromagnetic propulsion mechanisms—including electrohydrodynamics (EHD) and magnetohydrodynamics (MHD)—as well as more speculative proposals that invoke general relativity, quantum field theory, or zero-point energy as possible pathways to modify inertia or couple directly to the structured quantum vacuum.^[5]^{: 215–216, 219}

The category of various types of field propulsion concepts investigate mechanisms where motion results from environmental coupling rather than from carrying and ejecting propellant.^[5]^{: 215–216} Examples include systems that attempt to draw on the photon field of sunlight, the charged particles of the solar wind, or the magnetic fields of planetary environments.^[1]^: 1–2 By interacting with such external reservoirs, a spacecraft could in principle "push off" the surrounding medium, converting environmental energy or momentum into acceleration.^[5]^{: 216–217} Meanwhile, hypothetical reactionless drives and related unproven constructs occupy a set of more controversial spaces: they are framed as closed systems that would claim to generate thrust without any identifiable external interaction.^[2] Because they lack a counter-momentum reservoir (a reaction mass, or something to "push off" from), they are widely regarded in the scientific literature as violating myriad physical laws of science.^[2]

Although various terrestrial and laboratory-scale systems have provided partial demonstrations, such as solar sail experiments, no field propulsion method had been validated as a reliable, primary propulsion system for practical spaceflight as of 2011.^[1]^: 11–12 Nonetheless, the topic continues to attract research attention, both because of the theoretical challenges it raises and because of the potential benefits if even one class of these systems could be made viable.^[2] Exploratory programs have included the former Breakthrough Propulsion Physics Program at NASA, as well as studies conducted under the auspices of other national space agencies, academic laboratories, space-related organizations, and private industry.^[6] Concurrently, options related to non-rocket spacelaunch are also under research.

Open versus closed systems

Open systems comply with the conservation of momentum by transferring it to or from the surrounding environment.^[5]^{: 216–217} For instance, MHD drives accelerate conductive fluids using electromagnetic fields, resulting in thrust through the Lorentz force, with momentum conserved via interaction with external media, such as the interplanetary or interstellar media, or the solar wind.^[7]^[1]

In contrast, reactionless drives are hypothetical closed systems that claim to produce thrust without exchanging momentum with an external entity, thereby violating the conservation of momentum, and are widely regarded as inconsistent with established scientific principles.^[5]^{: 216–217} 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.^[8] Any propulsion system that purports to generate net thrust in a closed system without external interaction challenges this principle and is considered physically untenable under the Standard Model of physics, and would likely require physics beyond the Standard Model to be viable.^[8] 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.^[1]^: 7–10 These constraints contrast with classical chemical and conventional electric rockets, whose performance is governed primarily by onboard propellant and its energy, reflecting fundamental engineering limits on achievable exhaust velocity and energy density.^[3]^: 39–40 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.^[2]^: 2

Conservation Laws

Building on this distinction between open and closed systems, conservation laws frame the boundary conditions for what types of propulsion are physically viable and which remain speculative or untenable. Conservation of momentum is a fundamental requirement of propulsion systems because in experiments momentum is always conserved. The conservation of momentum is a fundamental principle arising from spatial translation symmetry.^[8] Reviews of field propulsion concepts emphasize that any open system must exchange momentum with an external medium such as photons, plasma, or magnetic fields, while closed-system "reactionless" claims conflict with this framework.^[5]^[1]^[2]

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 $F=P/v$ when mass is ejected or $F=P/c$ if mass-free energy is ejected. For a photon rocket the efficiency is too small to be competitive.^[9] 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.

A practical implication is that devices which exchange momentum with slow external media (e.g., plasma or magnetic fields) can, in principle, achieve higher thrust per unit input power than pure photon emission (where $F=P/c$ ), albeit only within environments that provide sufficient coupling strength.^[9]^[1]^{[citation needed]}

History of research and programs

Discussion of field propulsion in the aerospace literature has rarely been isolated to a single technology; instead, it has appeared most often in surveys and roadmaps that attempted to organize non-chemical propulsion concepts into recurring categories. Beginning in the 1960s, when chemical rockets were reaching their theoretical limits, contractor reports for the Air Force and NASA began grouping alternatives under three headings—Thermal, Field, and Photon—so that exotic schemes could be compared within a common framework.^[6] Within this taxonomy, "field" referred 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. These early surveys tended to treat such 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]

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.^[7]^[3] By contrast, the more speculative end of the spectrum—concepts that sought to "push off" against the environment without carrying reaction mass—remained in the research phase. A 1972 Air Force Rocket Propulsion Laboratory report, followed by Jet Propulsion Laboratory studies in 1975 and 1982, formalized this division by publishing roadmaps that again divided advanced concepts into Thermal, Field, and Photon classes.^[6] These reports emphasized "infinite specific impulse" systems that would obtain energy or working fluid from the ambient environment, and suggested that new advances in lasers and superconductors might breathe new life into earlier discarded concepts such as laser propulsion or ramjets.^[6]

By the late 1990s, this style of classification had been taken up by NASA’s Breakthrough Propulsion Physics program, which explicitly asked whether propellantless propulsion could be made consistent with conservation laws and whether momentum exchange with ambient plasmas or fields could substitute for mass ejection.^[2]^[1] Later NIAC studies continued in the same mold, examining whether Alfvén-wave coupling or other plasma interactions might provide quasi-propellantless thrust.^[1]^: 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.^[2]^: 2

Scope and terminology in sources

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] Electromagnetic propulsion surveys treat plasma/ion engines (including pulsed plasma, magnetoplasmadynamic, and pulsed-inductive thrusters) as electric propulsion, some of which employ strong electromagnetic fields but still expel reaction mass.^[7] Physics-frontier program statements define an aspirational target class as "propulsion that requires no propellant mass," motivating studies of momentum exchange via ambient fields and other non-chemical pathways.^[2]

Programmatic efforts

NASA's Breakthrough Propulsion Physics (BPP) effort (established 1996) set research goals that 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.^[2] Separately, the NASA Institute for Advanced Concepts (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.^[1]^: 1–2 Framed explicitly as a way to separate testable physics from non-viable claims, the BPP articulated three headline goals—propulsion with no propellant mass, maximum physically possible transit speeds, and breakthrough energy sources—and used those goals to scope candidate studies across sails, tethers, and more speculative field-interaction ideas.^[2]

Beamed-energy and field-interactive concepts (Myrabo, 1983)

A NASA contractor survey of beam-powered propulsion in "Advanced Beamed-Energy and Field Propulsion Concepts" argued that emerging missions would require propulsion capabilities exceeding chemical rockets and examined systems where power is transmitted to the vehicle (laser/microwave/particle beams), decoupling onboard energy from thrust production.^[6] The report organized prospects into thermal, field, and photon classes and identified enabling technologies (e.g., higher-current superconductors, potential room-temperature superconductors) as potential gates to field-interactive designs.^[6] It also noted historic funding swings and prior AFRPL/JPL surveys, situating "field" concepts within long-running advanced propulsion roadmapping rather than near-term flight systems.^[6] Although nuclear-electric and solar-electric propulsion systems are advancing and may see application before 1990, they are insufficient for large-scale industrial use of lunar or asteroidal materials.^[6] Demonstrating plausible, efficient advanced propulsion systems may catalyze the next wave of major space activities, potentially serving as the trigger rather than the outcome of such expansion.^[6]

Advanced propulsion systems may overcome the limitations of chemical rockets by accessing more energetic physical principles, particularly those involving directed-energy and field interactions.^[6] Beamed-energy propulsion concepts eliminate the need for onboard energy sources by transmitting power from remote stations using lasers, microwaves, or particle beams to induce thrust remotely.^[6] Such systems decouple the vehicle from traditional propellant constraints and enable the possibility of high specific impulse with relatively high thrust-to-weight ratios.^[6] Theoretical development includes mechanisms for transferring momentum via electromagnetic coupling or by interacting with the physical structure of the vacuum, a line of reasoning that parallels field propulsion concepts.^[6] Some approaches explore the utilization of atmospheric or ambient materials as virtual reaction mass or interaction medium, pushing beyond the limitations of mass ejection propulsion.^[6] Proposals also include advanced electrostatic and MHD-based concepts that could leverage charged particle interactions with atmospheric fields to produce directed motion.^[6]

Funding for advanced propulsion research saw major swings from the 1960s to early 1980s, with initial surges during the 1960s and early 1970s, followed by sharp reductions post-1975.^[6] Notable reports on advanced propulsion during this funding trough include studies by the Air Force Rocket Propulsion Laboratory in 1972 and the Jet Propulsion Laboratory in 1975 and 1982.^[6] A 1972 Air Force Rocket Propulsion Laboratory (AFRPL) study was conducted to explore transitions beyond chemical propulsion and stimulate development of more advanced performance systems by the end of the 20th century.^[6] The AFRPL report categorized advanced propulsion into three domains: Thermal Propulsion, Field Propulsion, and Photon Propulsion, each evaluated for performance potential.^[6] The study emphasized a return to the unrestricted creativity and "free-thinking" that characterized propulsion research in the late 1950s and early 1960s.^[6]

Among its primary conclusions, the AFRPL report noted that more intensive energy sources—such as nuclear—offer performance improvements up to five orders of magnitude greater than chemical sources.^[6] It proposed that propulsion researchers should prioritize "infinite specific impulse" (Isp) systems that obtain both working fluid and energy from the ambient environment, offering exceptional performance potential.^[6] For field propulsion, specific technological breakthroughs such as higher current density superconductors, metallic hydrogen, or room temperature superconductors were identified as potentially enabling innovations.^[6] The study argued that 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]

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.^[10] 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.^[10]

Electromagnetic propulsion status (Myers, 1993)

A NASA electromagnetic-propulsion review by Myers identifies three main types of electromagnetic propulsion systems: pulsed plasma thrusters (PPTs), magnetoplasmadynamic thrusters (MPD), and pulsed-inductive thrusters (PIT). 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.^[7] The review emphasized benefits (high specific impulse, precise impulse bits, robustness) alongside unresolved issues (efficiency, cathode wear, spacecraft power/integration), presenting these as electric-propulsion architectures that still accelerate propellant even when strong fields are central to their operation.^[7]

Pulsed plasma thrusters (PPTs) represent the earliest class of electromagnetic propulsion systems to achieve operational deployment in space.^[7] Developed in the 1960s, these thrusters generate thrust by ablating solid propellant with an arc discharge and accelerating the resulting plasma via Lorentz forces.^[7] Unlike later concepts relying on inductive or steady-state operation, PPTs utilize compact, low-power, pulsed configurations suitable for satellite positioning and drag compensation.^[7] The Soviet Zond-2 Mars mission in 1964 marked the first planetary use of electric propulsion, followed by successive U.S. deployments culminating in the Nova satellite series.^[7] PPTs remain relevant for low-mass spacecraft requiring precise impulse bits, though scalability to higher power levels has presented technical challenges.^[7]

Magnetoplasmadynamic thrusters (MPDTs) are another major class of electromagnetic propulsion systems investigated for both quasi-steady and steady-state spaceflight applications.^[7] Operating through the Lorentz force generated by the interaction of discharge currents with self-induced or externally applied magnetic fields, MPD thrusters were among the first electric propulsion devices to fly in space.^[7] Initial experimental campaigns explored both self-field and applied-field configurations, with development advancing through international programs aimed at supporting high-power planetary missions.^[7] While technological challenges remain—including efficiency optimization and cathode erosion—MPD thrusters continue to serve as a key pathway toward scalable, high-thrust, long-duration propulsion architectures.^[7]

Pulsed inductive thrusters (PITs) are a form of electromagnetic propulsion developed to overcome the erosion and lifetime limitations of electrode-based systems.^[7] By inducing plasma currents through time-varying magnetic fields, PITs accelerate neutral propellants without requiring physical contact between conductors and plasma.^[7] The concept originated in the late 1960s and evolved through successive experimental designs focused on performance scaling, circuit optimization, and propellant compatibility.^[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.^[7]

Physics-frontier framing (Millis 1998; Minami & Musha 2012)

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.^[2]^: 1 Minami and Musha survey a class of proposals that posit a "substantial physical structure" of spacetime/vacuum (macroscopic in GR, microscopic in QFT) and investigate whether asymmetries in massless fields or vacuum-medium interactions could yield thrust without mass expulsion; they report that such systems remained theoretical and controversial, with ongoing but inconclusive experiments and consistency concerns with momentum conservation.^[5]

This dual framework situates 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.^[5] Several mechanisms have been theorized to achieve such coupling, including vacuum polarization, spacetime curvature manipulation, and asymmetrical force distributions generated by interactions with massless fields.^[5] Though none have been experimentally validated, laboratory-scale studies have sought force generation analogs such as zero-point energy fluctuations and electrogravitic interactions, with results remaining inconclusive and difficult to replicate.^[5] A central theoretical challenge is the reconciliation of these concepts with conservation of momentum, since without a clearly identified external momentum exchange medium such mechanisms would violate fundamental physical laws.^[5]

Ambient-environment coupling (Gilland & Williams, 2011)

A NIAC Phase I study evaluated "ambient plasma wave propulsion," focusing on momentum exchange with existing space environments (solar wind, magnetospheres) via waves such as Alfvén modes, alongside sails and electrodynamic tethers, as candidates for propellantless or quasi-propellantless thrust.^[1]^: 1–2 The authors highlight both the appeal (no onboard reaction mass) and the limits (technical immaturity, power/sensitivity shortfalls) of such concepts for significant maneuvering.^[1]^: 11–12

Conservation and performance context

Across these sources, conventional rocket and electric systems remain the baseline for operational missions, with performance bounded by energy and momentum balances described in standard propulsion texts.^[3] Field-coupled approaches that exchange momentum with external photon/plasma/magnetic reservoirs are consistent with conservation laws when the external medium provides the counter-momentum; claims of net thrust in closed systems without such exchange conflict with the momentum-conservation framework emphasized in physics-frontier reviews.^[1]^[2]^[5]

A complementary way to frame performance is through mission energetics rather than hardware categories, which shifts the emphasis from individual devices to the balance between energy, mass, and external coupling.^[3]^[2] In this view, field-coupled systems trade carried propellant mass for dependence on ambient fluxes and on the vehicle’s ability to couple power into those fluxes.^[1]^[2] Solar sails, for example, scale their acceleration with irradiance and sail area-to-mass ratio,^[1] meaning that sails reward extreme areal-density reductions and precise attitude control,^[1] but offer little thrust authority in deep shadow or far from the Sun, where flux drops with the square of heliocentric distance.^[1] Magnetic or magnetospheric sail concepts similarly scale with the dynamic pressure of the impinging plasma and with the effective stand-off distance of the vehicle’s field structure,^[4] leading to a design space dominated by coil mass, current, and magnetic-topology control in variable plasma conditions.^[4]

Another recurring theme is that open systems can move the "propellant problem" into the environment or into the ground segment.^[6]^[1] Beamed-energy concepts, for instance, externalize the power plant to a transmitter,^[6] while the vehicle mainly provides an absorber/converter and steering,^[6] reducing carried mass but imposing line-of-sight and infrastructure constraints,^[6] and introducing beam-riding guidance and safety considerations.^[6] In contrast, conventional electric propulsion internalizes both energy conversion and propellant handling,^[7]^[3] which simplifies operations in sparse environments at the price of carrying reaction mass and significant power-processing hardware.^[7]^[3]

Momentum conservation is the fundamental boundary on all propulsion concepts. Devices that attempt to produce thrust without propellant or any other exchange of momentum are “not consistent with known physics.”^[2]^: 2 Academic reviews echo this conclusion, stating that propulsion systems which generate thrust without reaction mass or interaction with external fields are regarded as inconsistent with the present framework of physics.^[5]^{: 215–216, 219} Environment-coupled approaches such as sails, tethers, or plasma-wave coupling remain possible if the method of external coupling is strong enough.^[1]^{: 1–2, 11–12}

Types

Field propulsion concepts are usually grouped into broad classes that distinguish how momentum exchange is achieved and whether propellant is carried onboard. In the most frequently cited taxonomy, one category encompasses environment-coupled systems that draw upon external reservoirs—such as solar sails that push against photon flux, magnetic or magnetospheric sails that couple with the solar wind, and electrodynamic tethers that interact with planetary magnetic fields.^[1]^[4] A second category covers electrically driven devices in which strong electromagnetic fields dominate the acceleration physics, but in which momentum closure still proceeds through exhaust of a carried propellant; representative examples include pulsed plasma thrusters (PPTs), magnetoplasmadynamic thrusters (MPD), and pulsed-inductive thrusters (PIT).^[7] 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.^[5] Finally, some historical NASA surveys also grouped beamed-energy propulsion into "field" or field-adjacent categories, because the energy supply is external to the vehicle and power is transmitted by laser, microwave, or particle beams rather than carried onboard.^[6]

This layered taxonomy reflects the way that contractor reports and program reviews organized the subject during the late twentieth century. Air Force Rocket Propulsion Laboratory and Jet Propulsion Laboratory roadmaps in the 1970s and 1980s placed advanced systems into three headings—Thermal, Field, and Photon—explicitly separating concepts that drew energy or momentum from their environments from those that remained tethered to onboard propellant stores.^[6] Within that scheme, "field propulsion" was deliberately used as an umbrella for externally powered or environment-coupled designs, not as an endorsement of reactionless claims. This usage carried into later Breakthrough Propulsion Physics framing at NASA, where "propellantless" propulsion was treated as a research question at the boundary of physics rather than a mature technology.^[2]

In contemporary technical reviews it is common to reserve the term "field propulsion" for schemes that exchange momentum with external reservoirs, since those remain consistent with conservation of momentum when an identifiable medium supplies the counterforce. By contrast, devices such as PPT, MPD, and PIT thrusters—although dominated by internal electromagnetic fields—are placed within the broader family of electric propulsion because their exhaust streams provide the reaction mass that enforces momentum balance.^[7]^[1] This careful delineation has become standard in academic surveys, both to clarify what is physically admissible under current theory and to distinguish between near-term electric technologies and more speculative field-coupled approaches.^[3]

Field-adjacent: beamed-energy propulsion

Historical roadmaps also considered beamed-energy propulsion "field-adjacent," since power is supplied from outside the vehicle (laser, microwave, or particle beams) and converted to thrust onboard, decoupling energy supply from carried mass.^[6] Such schemes are not propellantless if they ablate or heat onboard reaction mass, but the externalization of power places them near "field" concepts in advanced-propulsion surveys.^[6]^{[citation needed]}

Beyond simple ablation or thermal boost,^[6] roadmaps examined hybrid schemes in which a vehicle carries a small amount of working fluid that is heated or photodesorbed by a remote beam,^[6] allowing thrust throttling while still decoupling most of the energy supply from onboard mass.^[6] Such studies typically trade transmitter complexity and pointing requirements against vehicle mass and thermal limits;^[6] mirrors, rectennas, or absorber cavities must survive high power densities while maintaining optical figure or RF efficiency across long ranges.^[6] Mission analyses in this class often treat the beaming infrastructure as reusable capital equipment, amortized across multiple flights,^[6] whereas the vehicles are lightweight, short-lived stages optimized for acceleration corridors.^[6]

Electric/magnetic thrusters that still expel propellant

Several devices central to electromagnetic propulsion rely on strong fields yet remain conventional in the momentum sense because they accelerate carried propellant.^[7] 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/drag makeup, MPD has flight heritage in experimental regimes, and PIT remains ground-tested.^[7]

Within the electric-propulsion family, these devices illustrate how strong fields can dominate the internal acceleration physics while momentum closure still proceeds through exhaust.^[7] PPTs offer exceptionally small impulse bits and simple architectures at the cost of limited efficiency and erosion;^[7] MPD devices promise higher thrust densities at high power but face cathode life and plume-divergence challenges;^[7] and PIT concepts remove electrodes via inductive coupling while introducing pulsed-power and coil-standoff design trades.^[7] In programmatic roadmaps, these technologies frequently serve as baselines for comparison with environment-coupled concepts,^[3]^[7] anchoring expectations for power-to-thrust ratios, lifetime, and system mass at mission-relevant scales.^[3]^[7]

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^[12] are examples of such electromagnetic Field propulsion systems, first described in 1994.^[13]

There is potential to apply MHD to the space environment such as in experiments like NASA's electrodynamic tether^[1], Lorentz Actuated Orbits,^[14] the wingless electromagnetic air vehicle, and magnetoplasmadynamic thruster (which does use propellant).^[7] A NASA Institute for Advanced Concepts study in 2011 evaluated "ambient plasma wave propulsion," in which spacecraft generate Alfvén waves in surrounding plasma or magnetospheric fields to exchange momentum without expelling onboard propellant.^[1] The report noted such systems are technically immature but could enable new classes of exploration missions if developed.^[1] In space contexts, related "field-coupled" approaches include photon sails, magnetic/magnetospheric sails, and electrodynamic tethers that exchange momentum with external photon, plasma, or magnetic reservoirs instead of expelling onboard propellant.^[1]^[4]

Electrohydrodynamics (EHD) is another method whereby electrically charged fluids are accelerated for propulsion and flow control; laboratory demonstrations include so-called "ionocraft" devices driven by corona discharge.^[3]

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^[1]; 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 Magsail magnetic sail design.^[4]

Ambient plasma–wave coupling

NIAC studies have examined using radio-frequency waves (e.g., Alfvén waves) launched from a vehicle to couple with ambient plasma and magnetic fields, transferring momentum to the environment and producing propellantless thrust. The 2011 Phase I assessment found the approach technically immature but potentially enabling if sensitivity and power challenges can be overcome.^[1]

Early sketches of plasma-wave momentum exchange noted that even modest wave–particle coupling coefficients could integrate to useful Δv over long dwell times,^[1] if the vehicle can sustain transmission and maintain favorable geometry relative to the background magnetic field.^[1] The principal hurdles are power generation,^[1] antenna or coil size relative to the targeted wavelengths,^[1] and unambiguous measurement of tiny forces in a variable plasma environment.^[1] NIAC assessments therefore emphasized incremental demonstrations—first characterizing coupling in controlled plasma chambers and then evaluating low-Earth-orbit opportunities near strong geomagnetic gradients—before any attempt at deep-space application.^[1]

Electrodynamic tethers

Electrodynamic tethers exchange momentum with a planetary magnetosphere/ionosphere via Lorentz forces on a long current-carrying conductor, enabling drag or thrust without propellant in suitable environments (e.g., low Earth orbit).^[1] As open systems, they conserve momentum by reaction with the ambient plasma and magnetic field.^[1] 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.^[1] Beyond orbit changes, tethers can also be used for in-situ power generation at the expense of orbital energy, though practical systems must address current collection (e.g., plasma contactors), arcing, attitude control, and vulnerability to micrometeoroids or space debris.^[1]

Design studies for long-lived tethers converge on a handful of recurring subsystems: robust conductors with high current capacity per unit mass;^[1] end-body plasma contactors for efficient current collection and emission;^[1] power-processing electronics to govern current and polarity;^[1] and attitude-control strategies that manage gravity-gradient torques and Lorentz torques concurrently.^[1] Operationally, deorbit modes exploit drag to dissipate orbital energy,^[1] while boost modes require external power injection to drive current against the motional EMF, converting electrical input into mechanical energy of the orbit.^[1] Both modes must manage arcing risk at terminators and in auroral zones,^[1] suggesting operational envelopes that avoid known space-weather hazards where practical.^[1]

Magnetic and magnetospheric sails

Magnetic sails (including variants such as magnetospheric plasma concepts) generate thrust by coupling a spacecraft-supported magnetic field to the solar wind, transferring momentum from the ambient charged particle flow to the vehicle.^[4] Such systems are included in field propulsion taxonomies because they push against an external plasma/magnetic reservoir instead of expelling propellant.^[1] Analyses of magnetic sail concepts indicate thrust arises from deflecting the supersonic solar wind around a spacecraft-supported magnetic field, with performance set by the stand-off distance and the dynamic pressure of the flow; larger effective magnetic cross-sections increase momentum transfer but demand lightweight, high-current coils or plasma-inflated magnetic structures.^[4] Anticipated advantages include propellantless cruise and braking in the heliosphere, while challenges include coil mass, cryogenic or superconducting requirements, and control of magnetic topology in a variable plasma environment.^[4]

Mission sketches using magnetic sails typically fall into two categories: heliocentric cruises that exploit the quasi-steady solar wind for outbound acceleration and inbound braking,^[4] and planetary-magnetosphere operations that use local field topology for station-keeping or slow orbit changes.^[4] The common design thread is maximizing effective magnetic cross-section per unit mass.^[4] Options include high-current coils made from lightweight conductors^[4] and "inflatable" magnetospheres in which injected plasma maintains an extended magnetic obstacle to the flow.^[4] Control is effected by modulating current or by biasing the field geometry,^[4] at the expense of additional power and thermal-management complexity.^[4]^[1]

Solar sails

Solar sails produce continuous, low-thrust acceleration by exchanging momentum with incident photons from the Sun; because the counter-momentum is supplied by the external photon field, they fall under broad definitions of field-coupled propulsion rather than reaction-mass ejection.^[1] As with other environment-coupled concepts, performance depends on the available flux—in this case solar irradiance and sail reflectivity—and falls with distance from the Sun, motivating large, lightweight structures and precise attitude control schemes.^[1]

Sailcraft engineering couples ultra-light structures to stringent pointing and thermal constraints.^[1] Square or heliogyro architectures, reflective coatings, boom materials, and deployment mechanisms must all survive launch loads yet unfurl with minimal wrinkling or creep.^[1] Once deployed, the sail must hold attitude to within tight tolerances,^[1] since thrust vectoring derives from minute changes in sail normal relative to the Sun line.^[1]

Performance therefore evolves with materials science and control algorithms: lower areal density directly increases acceleration,^[1] while better attitude control turns weak continuous thrust into precise trajectory shaping.^[1] Forward (Journal of Spacecraft and Rockets, 1984) outlined a proposed method of how solar-system-based laser systems and a ~1,000 km diameter Fresnel zone "para-lens" could propel thin-film sails to ~0.11 c, enabling an unmanned flyby of Alpha Centauri in approximately 40 years.^[10] 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.^[10]

Field propulsion based on physical structure of space

Minami and Musha frame field propulsion at the physics frontier as interaction with a "substantial physical structure" of space, drawing on general relativity at macroscopic scales and quantum field theory at microscopic scales.^[5]^{: 215–216} They conclude that future engineering technologies for space travel will most likely require some form of field propulsion to excite properties of localized regions in space.^[5]^: 220 Surveyed mechanisms include 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] This concept is based on the general relativity theory and the 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 a force would be exerted on the space craft which in turn creates thrust for propulsion.^[15] 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. Minami and Musha distinguish between two field propulsion concepts: one framed in terms of general relativity and one in terms of quantum field theory.^[5]^{: 215–220}

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.^[5]

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 state, the lowest possible energy state. It is also theorized that matter is composed out of elementary primary charged entities, partons, 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.^[5]

Technologies

Magnetic waves, called Alfvén S-waves, flow from the base of black hole jets.

A wide range of space propulsion methods have been proposed or demonstrated that fit within broad definitions of field propulsion. These systems do not rely on conventional chemical rockets, but instead seek to generate thrust by interacting with external media or applying directed energy fields. The following list highlights representative concepts.

Electromagnetic propulsion

Electromagnetic systems use electric and magnetic fields to accelerate plasma or ions.

Electrodynamic propulsion: Electrodynamic propulsion systems interact with ambient magnetic or plasma fields to generate thrust without conventional propellant. The most studied examples are electrodynamic tethers, which generate Lorentz-force-based drag or thrust by coupling with a planetary magnetic field. Electrodynamic propulsion falls under broad definitions of field propulsion due to their use of external fields for momentum exchange. These systems have been deployed and used in space on a number of space tether missions, including the TSS-1, TSS-1R, and Plasma Motor Generator (PMG) experiments.

Electron cyclotron resonance (ECR) thrusters: ECR thrusters use electron cyclotron resonance to ionize and accelerate ambient plasma, particularly in ionospheric or high-altitude environments. These systems can, in principle, generate thrust by coupling to environmental plasma, qualifying as a field propulsion mechanism when onboard mass is not expelled. They are an example of field propulsion. ECRs using electron cyclotron resonance with microwave discharge have flown in space, most notably as the μ10 ion engine system on JAXA's Hayabusa and Hayabusa2 asteroid missions.^[16]^: 2^[17]^: 2

Field-accelerated mass systems

These systems accelerate onboard or environmental particles using electromagnetic, electrostatic, or directed energy fields. Some may still require onboard mass or atmospheric medium.

Atmosphere-breathing electric propulsion: 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 (ESA Sitael ABEP, JAXA), but not yet flown in space. Closest heritage are ion thrusters and Hall-effect thrusters, which have flown widely (Deep Space 1, Dawn, SMART-1, BepiColombo) and demonstrate the same field-acceleration principle with onboard propellant.
Lightcraft: Beamed-energy propulsion is considered a form of field propulsion in NASA-sponsored research on advanced aerospace systems.
Laser ablation propulsion: A system where pulsed laser energy ablates 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 atmospheric Lightcraft demonstrations, with orbital proposals remaining unflown.
Microwave electrothermal thruster: A thruster using 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.

Field-momentum exchange systems

These systems generate thrust by exchanging momentum with external fields (magnetic, plasma, or photon), without expelling onboard reaction mass.

Alfvén wave / RF-driven plasma wave propulsion: A proposed propulsion method that uses radio-frequency-driven Alfvén waves to couple with ambient magnetic and plasma fields, generating thrust without expelling onboard reaction mass. These waves propagate along magnetic field lines and can transfer momentum to space plasma, making the system a candidate for propellantless thrust.^[1]
Electrodynamic tethers: Electrodynamic tethers are a distinct form of space propulsion that generate thrust by exchanging momentum with ambient magnetic fields or plasma, usually in low Earth orbit.^[1] They are a subset of the broader category of space tethers, which includes non-propulsive applications such as momentum exchange and orbital stabilization.
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.
Magnetospheric plasma propulsion (M2P2): A NASA Institute for Advanced Concepts proposal by Robert Winglee, in which plasma injection inflates a magnetic bubble that couples with the solar wind. It is considered a variant of magnetic sails.
Magnetic sail: Magnetic sails are a broader class of concepts that generate thrust by interacting with the solar wind or interplanetary magnetic fields, rather than expelling onboard reaction mass.^[1]
Photonic laser thruster: A photon-pressure system that relies on externally beamed lasers instead of sunlight. It shares the basic physics of solar sails but provides higher energy density and directional control.^[6]
Plasma magnet sail: Another concept proposed by Winglee, in which a plasma-driven magnetic field expands outward to form a virtual sail that interacts with the solar wind.
Solar sail: Solar sails rely on natural sunlight for propulsion, using photon pressure to generate thrust. They are the most developed form of sail-based field propulsion.

References

This article incorporates public domain material from websites or documents of the United States government.

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am ^an ^ao ^ap ^aq ^ar ^as ^at ^au ^av ^aw ^ax ^ay ^az ^ba ^bb ^bc ^bd ^be ^bf ^bg ^bh Gilland, James H.; Williams, George J. (2011). The Potential for Ambient Plasma Wave Propulsion (PDF) (Report). NASA Institute for Advanced Concepts (NIAC). Archived from the original (PDF) on 2024-06-12. Retrieved 2025-06-06.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q Millis, Marc G. (June 1998). NASA Breakthrough Propulsion Physics Program (PDF) (Report). NASA Technical Memorandum. Cleveland, OH: NASA Lewis Research Center. Archived from the original (PDF) on 2021-06-23. Retrieved 2025-06-13.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Sutton, George P.; Biblarz, Oscar (2017). Rocket Propulsion Elements (PDF) (9th ed.). Wiley. ISBN 9781118753651. Archived from the original (PDF) on 2022-06-12.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p Zubrin, Robert M.; Andrews, Dana G. (March 1991). "Magnetic sails and interplanetary travel". Journal of Spacecraft and Rockets. 28 (2): 197–203. Bibcode:1991JSpRo..28..197Z. doi:10.2514/3.26230. ISSN 0022-4650.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t Minami, Yoshinari; Musha, Takaaki (January 2012). "Field propulsion systems for space travel". Acta Astronautica. 81 (1). Elsevier: 59–66. doi:10.1016/j.actaastro.2012.02.027. ISSN 0094-5765. Archived from the original on 2025-09-18. Retrieved 2025-09-17.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am ^an ^ao ^ap ^aq Myrabo, Leik N. (May 31, 1983). Advanced Beamed-Energy and Field Propulsion Concepts (Contractor Report). NASA Contractor Report Series. McLean, Virginia: BDM Corporation for the California Institute of Technology and Jet Propulsion Laboratory. BDM/W-83-225-TR; NAS 1.26:176108; Accession 85N33186. Archived from the original (PDF) on 2021-12-14. Retrieved 2025-06-03.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae Myers, Roger M. (February 1993). Electromagnetic Propulsion for Spacecraft: Presented at the 1993 Aerospace Design Conference, Irvine, California, February 15–18, 1993 (PDF) (Contractor Report). NASA Contractor Report Series. Brook Park, Ohio: Sverdrup Technology, Inc. for the NASA John H. Glenn Research Center at Lewis Field. AIAA-93-1086; NASA-CR-191186; Accession 94N26441. Archived from the original (PDF) on 2023-06-10. Retrieved 2025-06-05.
^ ^a ^b ^c 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
^ ^a ^b There will be no photon rocket, by V. Smilga http://www.dtic.mil/dtic/tr/fulltext/u2/611872.pdf Archived 2017-05-17 at the Wayback Machine
^ ^a ^b ^c ^d Forward, Robert L. (March–April 1984). "Roundtrip interstellar travel using laser-pushed lightsails" (PDF). Journal of Spacecraft and Rockets. 21 (2): 187–195. Bibcode:1984JSpRo..21..187F. doi:10.2514/3.8632. ISSN 0022-4650. Archived from the original on 2013-12-21.
^ Warren, J. W. (1979). Understanding force: an account of some aspects of teaching the idea of force in school, college and university courses in engineering, mathematics and science. London: Murray. pp. 28–29. ISBN 978-0-7195-3564-2.
^ AKAGI, Shinsuke; FUJITA, Kikuo; SOGA, Kazuo (May 27, 1994). "Optimal Design of Thruster System for Superconducting Electromagnetic Propulsion Ship" (PDF). Proceedings of the 5th International Marine Design Conference. Retrieved November 30, 2022.
^ US 5333444, Meng, James C. S., "Superconducting electromagnetic thruster", published 1994-08-02, assigned to United States Secretary of the Navy
^ Peck, Mason A. "Lorentz-Actuated Orbits: Electrodynamic Propulsion without a Tether" (PDF). Retrieved November 30, 2022.
^ Musha, Takaaki (15 February 2018). Field Propulsion System for Space Travel: Physics of Non-Conventional Propulsion Methods for Interstellar Travel. Bentham Books. pp. 20–37. ISBN 978-1-60805-566-1.
^ Kuninaka, H. (2009). Overview and Research Status of Microwave Discharge Ion Thruster System (PDF). 31st IEPC; American Institute of Aeronautics and Astronautics. International Electric Propulsion Conference (IEPC). p. 1. Archived from the original (PDF) on 2024-04-15. 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.
^ Nishiyama, K. (2011). The Ion Engine System for Hayabusa2 (PDF). 32nd IEPC; American Institute of Aeronautics and Astronautics. International Electric Propulsion Conference (IEPC). p. 2. Archived from the original (PDF) on 2024-04-15. 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.

External links

[Gilland_NIAC_Plasma_2011-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am ^an ^ao ^ap ^aq ^ar ^as ^at ^au ^av ^aw ^ax ^ay ^az ^ba ^bb ^bc ^bd ^be ^bf ^bg ^bh Gilland, James H.; Williams, George J. (2011). The Potential for Ambient Plasma Wave Propulsion (PDF) (Report). NASA Institute for Advanced Concepts (NIAC). Archived from the original (PDF) on 2024-06-12. Retrieved 2025-06-06.

[Millis_BPPP_NASA_1998-2] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q Millis, Marc G. (June 1998). NASA Breakthrough Propulsion Physics Program (PDF) (Report). NASA Technical Memorandum. Cleveland, OH: NASA Lewis Research Center. Archived from the original (PDF) on 2021-06-23. Retrieved 2025-06-13.

[Sutton_Rockets_2017-3] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Sutton, George P.; Biblarz, Oscar (2017). Rocket Propulsion Elements (PDF) (9th ed.). Wiley. ISBN 9781118753651. Archived from the original (PDF) on 2022-06-12.

[ZubrinAndrews1991-4] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p Zubrin, Robert M.; Andrews, Dana G. (March 1991). "Magnetic sails and interplanetary travel". Journal of Spacecraft and Rockets. 28 (2): 197–203. Bibcode:1991JSpRo..28..197Z. doi:10.2514/3.26230. ISSN 0022-4650.

[Minami_Musha_Field_Acta_Astronautica_2012-5] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t Minami, Yoshinari; Musha, Takaaki (January 2012). "Field propulsion systems for space travel". Acta Astronautica. 81 (1). Elsevier: 59–66. doi:10.1016/j.actaastro.2012.02.027. ISSN 0094-5765. Archived from the original on 2025-09-18. Retrieved 2025-09-17.

[Myrabo_NASA_JPL_Beam/Field_Concepts_1983-6] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am ^an ^ao ^ap ^aq Myrabo, Leik N. (May 31, 1983). Advanced Beamed-Energy and Field Propulsion Concepts (Contractor Report). NASA Contractor Report Series. McLean, Virginia: BDM Corporation for the California Institute of Technology and Jet Propulsion Laboratory. BDM/W-83-225-TR; NAS 1.26:176108; Accession 85N33186. Archived from the original (PDF) on 2021-12-14. Retrieved 2025-06-03.

[Myers_NASA_Electromagnetic_Propulsion_1993-7] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae Myers, Roger M. (February 1993). Electromagnetic Propulsion for Spacecraft: Presented at the 1993 Aerospace Design Conference, Irvine, California, February 15–18, 1993 (PDF) (Contractor Report). NASA Contractor Report Series. Brook Park, Ohio: Sverdrup Technology, Inc. for the NASA John H. Glenn Research Center at Lewis Field. AIAA-93-1086; NASA-CR-191186; Accession 94N26441. Archived from the original (PDF) on 2023-06-10. Retrieved 2025-06-05.

[Kim_et_al_Physics_WS-8] 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

[auto-9] There will be no photon rocket, by V. Smilga http://www.dtic.mil/dtic/tr/fulltext/u2/611872.pdf Archived 2017-05-17 at the Wayback Machine

[Forward_lightsails_1984-10] Forward, Robert L. (March–April 1984). "Roundtrip interstellar travel using laser-pushed lightsails" (PDF). Journal of Spacecraft and Rockets. 21 (2): 187–195. Bibcode:1984JSpRo..21..187F. doi:10.2514/3.8632. ISSN 0022-4650. Archived from the original on 2013-12-21.

[11] Warren, J. W. (1979). Understanding force: an account of some aspects of teaching the idea of force in school, college and university courses in engineering, mathematics and science. London: Murray. pp. 28–29. ISBN 978-0-7195-3564-2.

[12] AKAGI, Shinsuke; FUJITA, Kikuo; SOGA, Kazuo (May 27, 1994). "Optimal Design of Thruster System for Superconducting Electromagnetic Propulsion Ship" (PDF). Proceedings of the 5th International Marine Design Conference. Retrieved November 30, 2022.

[13] US 5333444, Meng, James C. S., "Superconducting electromagnetic thruster", published 1994-08-02, assigned to United States Secretary of the Navy

[14] Peck, Mason A. "Lorentz-Actuated Orbits: Electrodynamic Propulsion without a Tether" (PDF). Retrieved November 30, 2022.

[Musha_FP-15] Musha, Takaaki (15 February 2018). Field Propulsion System for Space Travel: Physics of Non-Conventional Propulsion Methods for Interstellar Travel. Bentham Books. pp. 20–37. ISBN 978-1-60805-566-1.

[Kuninaka_IEPC_2009-16] Kuninaka, H. (2009). Overview and Research Status of Microwave Discharge Ion Thruster System (PDF). 31st IEPC; American Institute of Aeronautics and Astronautics. International Electric Propulsion Conference (IEPC). p. 1. Archived from the original (PDF) on 2024-04-15. 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.

[Nishiyama_IEPC_2011-17] Nishiyama, K. (2011). The Ion Engine System for Hayabusa2 (PDF). 32nd IEPC; American Institute of Aeronautics and Astronautics. International Electric Propulsion Conference (IEPC). p. 2. Archived from the original (PDF) on 2024-04-15. 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.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]