Anti-gravity

Idea of creating a place or object that is free from the force of gravity

Artistic depiction of a fictional anti-gravity vehicle

Anti-gravity (also known as non-gravitational field) is the phenomenon of creating a place or object that is free from the force of gravity. It does not refer to either the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift. Anti-gravity is a recurring concept in science fiction.

"Anti-gravity" is often used to refer to devices that look as if they reverse gravity even though they operate through other means, such as lifters, which fly in the air by moving air with electromagnetic fields.[1][2]

## Historical attempts at understanding gravity

[edit]

Main article: History of gravitational theory

The possibility of creating anti-gravity depends upon a complete understanding and description of gravity and its interactions with other physical theories, such as general relativity and quantum mechanics; however, no quantum theory of gravity has yet been found.

During the summer of 1666, Isaac Newton observed an apple falling from the tree in his garden, thus realizing the principle of universal gravitation.[3] Albert Einstein in 1915 considered the physical interaction between matter and space, where gravity occurs as a consequence of matter causing a geometric deformation of spacetime which is otherwise flat.[4][5][6] Einstein, both independently and with Walther Mayer, attempted to unify his theory of gravity with electromagnetism using the work of Theodor Kaluza[7] and James Clerk Maxwell to link gravity and quantum field theory.[8]

Theoretical quantum physicists have postulated the existence of a quantum gravity particle, the graviton. Various theoretical explanations of quantum gravity have been created, including superstring theory, loop quantum gravity, E8 theory and asymptotic safety theory amongst many others.

## Probable solutions

[edit]

In Newton's law of universal gravitation, gravity was an external force transmitted by unknown means. In the 20th century, Newton's model was replaced by general relativity where gravity is not a force but the result of the geometry of spacetime. Under general relativity, anti-gravity is impossible except under contrived circumstances.[9][10][11]

### Gravity shields

[edit]

A monument at Babson College dedicated to Roger Babson for research into anti-gravity and partial gravity insulators

Main article: Gravitational shielding

In 1948 businessman Roger Babson (founder of Babson College) formed the Gravity Research Foundation to study ways to reduce the effects of gravity.[12] Their efforts were initially somewhat "crankish", but they held occasional conferences that drew such people as Clarence Birdseye, known for his frozen-food products, and helicopter pioneer Igor Sikorsky.[citation needed] Over time the Foundation turned its attention away from trying to control gravity, to simply better understanding it. The Foundation nearly disappeared after Babson's death in 1967. However, it continues to run an essay award, offering prizes of up to $4,000. As of 2017, it is still administered out of Wellesley, Massachusetts, by George Rideout Jr., son of the foundation's original director.[13] Winners include California astrophysicist George F. Smoot (1993), who later won the 2006 Nobel Prize in Physics, and Gerard 't Hooft (2015) who previously won the 1999 Nobel Prize in Physics.[14]

### General relativity research in the 1950s

[edit]

Main article: United States gravity control propulsion research

General relativity was introduced in the 1910s, but development of the theory was greatly slowed by a lack of suitable mathematical tools.[clarification needed] It appeared that anti-gravity was outlawed under general relativity.

It is claimed the US Air Force also ran a study effort throughout the 1950s and into the 1960s.[15] Former Lieutenant Colonel Ansel Talbert wrote two series of newspaper articles claiming that most of the major aviation firms had started gravity control propulsion research in the 1950s. However, there is no outside confirmation of these stories, and since they take place in the midst of the policy by press release era, it is not clear how much weight these stories should be given.

It is known that there were serious efforts underway at the Glenn L. Martin Company, who formed the Research Institute for Advanced Study.[16][17] Major newspapers announced the contract that had been made between theoretical physicist Burkhard Heim and the Glenn L. Martin Company. Another effort in the private sector to master understanding of gravitation was the creation of the Institute for Field Physics, University of North Carolina at Chapel Hill in 1956, by Gravity Research Foundation trustee Agnew H. Bahnson.

Military support for anti-gravity projects was terminated by the Mansfield Amendment of 1973, which restricted Department of Defense spending to only the areas of scientific research with explicit military applications. The Mansfield Amendment was passed specifically to end long-running projects that had no results.

Under general relativity, gravity is the result of following spatial geometry (change in the normal shape of space) caused by local mass-energy. This theory holds that it is the altered shape of space, deformed by massive objects, that causes gravity, which is actually a property of deformed space rather than being a true force. Although the equations cannot normally produce a "negative geometry", it is possible to do so by using "negative mass". The same equations do not, of themselves, rule out the existence of negative mass.

Both general relativity and Newtonian gravity appear to predict that negative mass would produce a repulsive gravitational field. In particular, Sir Hermann Bondi proposed in 1957 that negative gravitational mass, combined with negative inertial mass, would comply with the strong equivalence principle of general relativity theory and the Newtonian laws of conservation of linear momentum and energy. Bondi's proof yielded singularity-free solutions for the relativity equations.[18] In July 1988, Robert L. Forward presented a paper at the AIAA/ASME/SAE/ASEE 24th Joint Propulsion Conference that proposed a Bondi negative gravitational mass propulsion system.[19]

Bondi pointed out that a negative mass will fall toward (and not away from) "normal" matter, since although the gravitational force is repulsive, the negative mass (according to Newton's law, F=ma) responds by accelerating in the opposite of the direction of the force. Normal mass, on the other hand, will fall away from the negative matter. He noted that two identical masses, one positive and one negative, placed near each other will therefore self-accelerate in the direction of the line between them, with the negative mass chasing after the positive mass.[18] Notice that because the negative mass acquires negative kinetic energy, the total energy of the accelerating masses remains at zero. Forward pointed out that the self-acceleration effect is due to the negative inertial mass, and could be seen induced without the gravitational forces between the particles.[19]

The Standard Model of particle physics, which describes all currently known forms of matter, does not include negative mass. Although cosmological dark matter may consist of particles outside the Standard Model whose nature is unknown, their mass is ostensibly known – since they were postulated from their gravitational effects on surrounding objects, which implies their mass is positive. The proposed cosmological dark energy, on the other hand, is more complicated, since according to general relativity the effects of both its energy density and its negative pressure contribute to its gravitational effect.

### Unique force

[edit]

Under general relativity any form of energy couples with spacetime to create the geometries that cause gravity. A longstanding question was whether or not these same equations applied to antimatter. The issue was considered solved in 1960 with the development of CPT symmetry, which demonstrated that antimatter follows the same laws of physics as "normal" matter, and therefore has positive energy content and also causes (and reacts to) gravity like normal matter (see gravitational interaction of antimatter).

For much of the last quarter of the 20th century, the physics community was involved in attempts to produce a unified field theory, a single physical theory that explains the four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. Scientists have made progress in unifying the three quantum forces, but gravity has remained "the problem" in every attempt. This has not stopped any number of such attempts from being made, however.

Generally these attempts tried to "quantize gravity" by positing a particle, the graviton, that carried gravity in the same way that photons (light) carry electromagnetism. Simple attempts along this direction all failed, however, leading to more complex examples that attempted to account for these problems. Two of these, supersymmetry and the relativity related supergravity, both required the existence of an extremely weak "fifth force" carried by a graviphoton, which coupled together several "loose ends" in quantum field theory, in an organized manner. As a side effect, both theories also all but required that antimatter be affected by this fifth force in a way similar to anti-gravity, dictating repulsion away from mass. Several experiments were carried out in the 1990s to measure this effect, but none yielded positive results.[20]

In 2013 CERN looked for an antigravity effect in an experiment designed to study the energy levels within antihydrogen. The antigravity measurement was just an "interesting sideshow" and was inconclusive.[21]

### Breakthrough Propulsion Physics Program

[edit]

During the close of the twentieth century NASA provided funding for the Breakthrough Propulsion Physics Program (BPP) from 1996 through 2002. This program studied a number of "far out" designs for space propulsion that were not receiving funding through normal university or commercial channels. Anti-gravity-like concepts were investigated under the name "diametric drive". The work of the BPP program continues in the independent, non-NASA affiliated Tau Zero Foundation.[22]

## Empirical claims and commercial efforts

[edit]

There have been a number of attempts to build anti-gravity devices, and a small number of reports of anti-gravity-like effects in the scientific literature. None of the examples that follow are accepted as reproducible examples of anti-gravity.

### Gyroscopic devices

[edit]

A "kinemassic field" generator from U.S. patent 3,626,605: Method and apparatus for generating a secondary gravitational force field

Gyroscopes produce a force when twisted that operates "out of plane" and can appear to lift themselves against gravity. Although this force is well understood to be illusory, even under Newtonian models, it has nevertheless generated numerous claims of anti-gravity devices and any number of patented devices. None of these devices has ever been demonstrated to work under controlled conditions, and they have often become the subject of conspiracy theories as a result.

Another "rotating device" example is shown in a series of patents granted to Henry Wallace between 1968 and 1974. His devices consist of rapidly spinning disks of brass, a material made up largely of elements with a total half-integer nuclear spin. He claimed that by rapidly rotating a disk of such material, the nuclear spin became aligned, and as a result created a "gravitomagnetic" field in a fashion similar to the magnetic field created by the Barnett effect.[23][24][25] No independent testing or public demonstration of these devices is known.

In 1989, it was reported that a weight decreases along the axis of a right spinning gyroscope.[26] A test of this claim a year later yielded null results.[27] A recommendation was made to conduct further tests at a 1999 AIP conference.[28]

### Thomas Townsend Brown's gravitator

[edit]

Further information: Biefeld-Brown effect, Electrogravitics, and United States gravity control propulsion research § Brown's gravitator

In 1921, while still in high school, Thomas Townsend Brown found that a high-voltage Coolidge tube seemed to change mass depending on its orientation on a balance scale. Through the 1920s Brown developed this into devices that combined high voltages with materials with high dielectric constants (essentially large capacitors); he called such a device a "gravitator". Brown made the claim to observers and in the media that his experiments were showing anti-gravity effects. Brown would continue his work and produced a series of high-voltage devices in the following years in attempts to sell his ideas to aircraft companies and the military. He coined the names Biefeld–Brown effect and electrogravitics in conjunction with his devices. Brown tested his asymmetrical capacitor devices in a vacuum, supposedly showing it was not a more down-to-earth electrohydrodynamic effect generated by high voltage ion flow in air.

Electrogravitics is a popular topic in ufology, anti-gravity, free energy, with government conspiracy theorists and related websites, in books and publications with claims that the technology became highly classified in the early 1960s and that it is used to power UFOs and the B-2 bomber.[29] There is also research and videos on the internet purported to show lifter-style capacitor devices working in a vacuum, therefore not receiving propulsion from ion drift or ion wind being generated in air.[29][30]

Follow-up studies on Brown's work and other claims have been conducted by R. L. Talley in a 1990 US Air Force study, NASA scientist Jonathan Campbell in a 2003 experiment,[29] and Martin Tajmar in a 2004 paper.[31] They have found that no thrust could be observed in a vacuum and that Brown's and other ion lifter devices produce thrust along their axis regardless of the direction of gravity consistent with electrohydrodynamic effects.

### Gravitoelectric coupling

[edit]

In 1992, the Russian researcher Eugene Podkletnov claimed to have discovered, whilst experimenting with superconductors, that a fast rotating superconductor reduces the gravitational effect.[32] Many studies have attempted to reproduce Podkletnov's experiment, always to negative results.[33][34][35][36]

Douglas Torr, of the University of Alabama in Huntsville proposed how a time-dependent magnetic field could cause the spins of the lattice ions in a superconductor to generate detectable gravitomagnetic and gravitoelectric fields in a series of papers published between 1991 and 1993.[37][38][39] In 1999, a Miss Li appeared in Popular Mechanics, claiming to have constructed a working prototype to generate what she described as "AC Gravity." No further evidence of this prototype has been offered.[40][41]

Douglas Torr and Timir Datta were involved in the development of a "gravity generator" at the University of South Carolina.[42] According to a leaked document from the Office of Technology Transfer at the University of South Carolina and confirmed to Wired reporter Charles Platt in 1998, the device would create a "force beam" in any desired direction and the university planned to patent and license this device. No further information about this university research project or the "Gravity Generator" device was ever made public.[43]

## Göde Award

[edit]

The Institute for Gravity Research of the Göde Scientific Foundation has tried to reproduce many of the different experiments which claim any "anti-gravity" effects. All attempts by this group to observe an anti-gravity effect by reproducing past experiments have been unsuccessful thus far. The foundation has offered a reward of one million euros for a reproducible anti-gravity experiment.[44]

## In fiction

[edit]

The existence of anti-gravity is a common theme in science fiction.[45] The Encyclopedia of Science Fiction lists Francis Godwin's posthumously-published 1638 novel The Man in the Moone, where a "semi-magical" stone has the power to make gravity stronger or weaker, as the earliest variation of the theme.[45] The first story to use anti-gravity for the purpose of space travel, as well as the first to treat the subject from a scientific rather than supernatural angle, was George Tucker's 1827 novel A Voyage to the Moon.[45][46][47]

### Apergy

[edit]

Apergy is a term for a fictitious form of anti-gravitational energy first used by Percy Greg in his 1880 sword and planet novel Across the Zodiac.[48] The term was later adopted by other fiction authors such as John Jacob Astor IV in his 1894 science fiction novel A Journey in Other Worlds, and it also appeared outside of explicit fiction writing.[45][48]

## See also

[edit]

* Area 51
* Aerodynamic levitation
* Artificial gravity
* Burkhard Heim
* Casimir effect
* Clinostat
* Electrostatic levitation
* Exotic matter
* Gravitational interaction of antimatter
* Gravitational shielding
* Gravitational wave
* Ion-propelled aircraft
* Heim theory
* Magnetic levitation
* Nazi UFOs
* Optical levitation
* Reactionless drive
* Tractor beam

## References

[edit]

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2. ^ "On the Verge of Antigravity". About.com. Archived from the original on 23 February 2017. Retrieved 23 July 2010.
3. ^ Department of Physics A Brief History of Isaac Newton's Apple Tree, University of York, Retrieved 2019-07-20
4. ^ Papachristou, Costas J. (2016). "Electromagnetic waves, gravitational waves and the prophets who predicted them". arXiv:1603.00871 [physics.pop-ph].
5. ^ Albert Einstein Grundgedanken der allgemeinen Relativitätstheorie und Anwendung dieser Theorie in der Astronomie (Preussische Akademie der Wissenschaften, Sitzungsberichte, 1915 (teil 1), 31), Zur allgemeinen Relativitätstheorie (Preussische Akademie der Wissenschaften, Sitzungsberichte, 1915 (teil 2), 778–786, 799–80) Retrieved 2019-06-16
6. ^ Charles W. Misner, Kip S. Thorne, John Archibald Wheeler Gravitation, p. 1231, Princeton University Press, 24 October 2017 ISBN 0691177791, ISBN 9780691177793, Retrieved 2019-06-16
7. ^ Kaluza, Theodor (1921). "Zum Unitätsproblem in der Physik". Sitzungsber. Preuss. Akad. Wiss. Berlin. (Math. Phys.): 966–972\. Bibcode:1921SPAW.......966K. https://archive.org/details/sitzungsberichte1921preussi
8. ^ Einstein, Albert (1879-1955). Autograph manuscript, comprising calculations and arguments from the Einheitliche theorie von Gravitation un Elektrizitt Christie's Retrieved 2019-06-16
9. ^ Peskin, M and Schroeder, D.; An Introduction to Quantum Field Theory (Westview Press, 1995) ISBN 0-201-50397-2
10. ^ Wald, Robert M. (1984). General Relativity. Chicago: University of Chicago Press. ISBN 978-0-226-87033-5.
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15. ^ Goldberg, J. M. (1992). US air force support of general relativity: 1956–1972. In, J. Eisenstaedt & A. J. Kox (Ed.), Studies in the History of General Relativity, Volume 3 Boston, Massachusetts: Center for Einstein Studies. ISBN 0-8176-3479-7
16. ^ Mallan, L. (1958). Space satellites (How to book 364). Greenwich, CT: Fawcett Publications, pp. 9–10, 137, 139. LCCN 58-001060
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18. ^ a b Bondi, H. (1957). "Negative mass in general relativity". Reviews of Modern Physics. 29 (3): 423–428\. Bibcode:1957RvMP...29..423B. doi:10.1103/revmodphys.29.423.
19. ^ a b Forward, R. L. (1990). "Negative matter propulsion". Journal of Propulsion and Power. 6 (1): 28–37\. doi:10.2514/3.23219.; see also commentary Landis, G.A. (1991). "Comments on Negative Mass Propulsion". Journal of Propulsion and Power. 7 (2): 304. doi:10.2514/3.23327.
20. ^ Supergravity and the Unification of the Laws of Physics, by Daniel Z. Freedman and Peter van Nieuwenhuizen, Scientific American, February 1978
21. ^ Jason Palmer, Antigravity gets first test at Cern's Alpha experiment, bbc.co.uk, 30 April 2013
22. ^ Tau Zero Foundation
23. ^ U.S. patent 3,626,606
24. ^ U.S. patent 3,626,605
25. ^ U.S. patent 3,823,570
26. ^ Hayasaka, H. & Takeuchi, S. (1989). "Anomalous weight reduction on a gyroscope's right rotations around the vertical axis on the Earth". Physical Review Letters. 63 (25): 2701–2704\. Bibcode:1989PhRvL..63.2701H. doi:10.1103/PhysRevLett.63.2701. PMID 10040968.
27. ^ Nitschke, J. M. & Wilmath, P. A. (1990). "Null result for the weight change of a spinning gyroscope". Physical Review Letters. 64 (18): 2115–2116\. Bibcode:1990PhRvL..64.2115N. doi:10.1103/PhysRevLett.64.2115. PMID 10041587.
28. ^ Iwanaga, N. (1999). "Reviews of some field propulsion methods from the general relativistic standpoint". AIP Conference Proceedings. Vol. 458\. pp. 1015–1059\. doi:10.1063/1.57497.
29. ^ a b c Thompson, Clive (August 2003). "The Antigravity Underground". Wired Magazine.
30. ^ Thomas Valone, Electrogravitics II: Validating Reports on a New Propulsion Methodology, Integrity Research Institute, page 52-58
31. ^ Tajmar, M. (2004). "Biefeld-Brown Effect: Misinterpretation of Corona Wind Phenomena". AIAA Journal. 42 (2): 315–318\. Bibcode:2004AIAAJ..42..315T. doi:10.2514/1.9095.
32. ^ Podkletnov, E; Nieminen, R (10 December 1992). "A possibility of gravitational force shielding by bulk YBa2Cu3O7−x superconductor". Physica C. 203 (3–4): 441–444\. Bibcode:1992PhyC..203..441P. doi:10.1016/0921-4534(92)90055-H.3–4&rft.pages=441-444&rft.date=1992-12-10&rft_id=info:doi/10.1016/0921-4534(92)90055-H&rft_id=info:bibcode/1992PhyC..203..441P&rft.aulast=Podkletnov&rft.aufirst=E&rft.au=Nieminen,+R&rfr_id=info:sid/en.wikipedia.org:Anti-gravity" class="Z3988">
33. ^ N. Li; D. Noever; T. Robertson; R. Koczor; et al. (August 1997). "Static Test for a Gravitational Force Coupled to Type II YBCO Superconductors". Physica C. 281 (2–3): 260–267\. Bibcode:1997PhyC..281..260L. doi:10.1016/S0921-4534(97)01462-7.2–3&rft.pages=260-267&rft.date=1997-08&rft_id=info:doi/10.1016/S0921-4534(97)01462-7&rft_id=info:bibcode/1997PhyC..281..260L&rft.au=N.+Li&rft.au=D.+Noever&rft.au=T.+Robertson&rft.au=R.+Koczor&rft.au=W.+Brantley&rfr_id=info:sid/en.wikipedia.org:Anti-gravity" class="Z3988">
34. ^ Woods, C.; Helme, J.; Cooke, S.; Caldwell, C. (2001). "Gravity modification by high-temperature superconductors". 37th Joint Propulsion Conference and Exhibit. doi:10.2514/6.2001-3363.
35. ^ Hathaway, G.; Cleveland, B.; Bao, Y. (2003). "Gravity modification experiment using a rotating superconducting disk and radio frequency fields". Physica C: Superconductivity. 385 (4): 488–500\. Bibcode:2003PhyC..385..488H. doi:10.1016/S0921-4534(02)02284-0.
36. ^ Tajmar, M.; De Matos, C.J. (2003). "Gravitomagnetic field of a rotating superconductor and of a rotating superfluid". Physica C: Superconductivity. 385 (4): 551–554\. arXiv:gr-qc/0203033. Bibcode:2003PhyC..385..551T. doi:10.1016/S0921-4534(02)02305-5.
37. ^ Li, Ning; Torr, DG (1 September 1992). "Gravitational effects on the magnetic attenuation of superconductors". Physical Review. B46 (9): 5489–5495\. Bibcode:1992PhRvB..46.5489L. doi:10.1103/PhysRevB.46.5489. PMID 10004334.
38. ^ Li, Ning; Torr, DG (15 January 1991). "Effects of a gravitomagnetic field on pure superconductors". Physical Review. D43 (2): 457–459\. Bibcode:1991PhRvD..43..457L. doi:10.1103/PhysRevD.43.457. PMID 10013404.
39. ^ Li, Ning; Torr, DG (August 1993). "Gravitoelectric-electric coupling via superconductivity". Foundations of Physics Letters. 6 (4): 371–383\. Bibcode:1993FoPhL...6..371T. doi:10.1007/BF00665654. S2CID 122075917.
40. ^ Wilson, Jim (1 October 2000). "Taming Gravity". Popular Mechanics. Archived from the original on 5 November 2012. Retrieved 5 January 2014.
41. ^ Cain, Jeanette. "Gravity Conquered?". light-science.com. Archived from the original on 6 July 2013. Retrieved 5 January 2014.
42. ^ "Patent and Copyright Committee List of Disclosures Reviewed Between July 1996 and June 1997 - USC ID". Archived from the original on 2 May 2014. Retrieved 2 May 2014.
43. ^ Platt, Charles (1 March 1998). "Breaking the Law of Gravity". Wired. Retrieved 10 May 2025.
44. ^ "The Göde award - One Million Euro to overcome gravity". Institute of Gravity Research. Archived from the original on 28 April 2015. Retrieved 2 January 2014.
45. ^ a b c d Sudbery, Tony; Langford, David; Nicholls, Peter (2020). "Antigravity". In Clute, John; Langford, David; Sleight, Graham (eds.). The Encyclopedia of Science Fiction (4th ed.). Retrieved 20 December 2024.
46. ^ Bailey, James Osler (1972) [1947]. "Chapter Three: Down Alph the Sacred River: Scientific Fiction, 1817–1870—C. The Wonderful Journey—3. To Other Planets". Pilgrims Through Space and Time: Trends and Patterns in Scientific and Utopian Fiction. Greenwood Press. p. 45\. ISBN 978-0-8371-6323-9.
47. ^ Roberts, Adam (2016). "SF 1850–1900: Mobility and Mobilisation". The History of Science Fiction. Palgrave Histories of Literature (2nd ed.). Palgrave Macmillan. p. 156\. doi:10.1057/978-1-137-56957-8_7. ISBN 978-1-137-56957-8. OCLC 956382503.
48. ^ a b Langford, David (2017). "Apergy". In Clute, John; Langford, David; Sleight, Graham (eds.). The Encyclopedia of Science Fiction (4th ed.). Retrieved 20 December 2024.

## Bibliography

[edit]

Criteria:

* "Newtons discovery of the apple law"
* "Newtons principle of gravitation" > "Newtons principle of gravitation apple falls" (google > google books)

## Further reading

[edit]

* Bly, Robert W. (2005). "Antigravity". The Science in Science Fiction: 83 SF Predictions That Became Scientific Reality. Consulting Editor: James Gunn. BenBella Books. pp. 21–26\. ISBN 978-1-932100-48-8.
* Cady, W. M. (15 September 1952). "Thomas Townsend Brown: Electro-Gravity Device" (File 24–185). Pasadena, CA: Office of Naval Research. Public access to the report was authorized on 1 October 1952.

## External links

[edit]

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Spacecraft propulsion

Concepts|

* Rocket
* Rocket engine
* Reaction engine
* Reaction mass
* Thrust
* Specific impulse
* Delta-v
* Staging
* Rocket equation
* Thermal rocket

Physical propulsion|

* Cold gas thruster
* Water rocket
* Steam rocket
* Solar sail
* Diffractive
* Electric sail
* Magnetic sail
* Solar thermal rocket
* Photon rocket
* WINE

Chemical propulsion|

| State|

* Liquid-propellant rocket
* Solid-propellant rocket
* Hybrid-propellant rocket

|

Propellants|

* Liquid propellant
* Cryogenic
* Hypergolic
* Monopropellant
* Bipropellant
* Tripropellant

Power cycles|

* Staged combustion cycle
* Expander cycle
* Gas-generator cycle
* Tap-off cycle

Intake mechanisms|

* Pressure-fed engine
* Pump-fed engine
* Electric-pump-fed engine

Electrical propulsion|

| Electrostatic|

* Colloid thruster
* Ion thruster
* Gridded
* Hall-effect thruster
* Field-emission electric propulsion

|

Electromagnetic|

* Pulsed inductive thruster
* Magnetoplasmadynamic thruster
* Electrodeless plasma thruster
* Plasma magnet

Electrothermal|

* Pulsed plasma thruster
* Vacuum arc thruster
* Helicon double-layer thruster
* Arcjet rocket
* Resistojet rocket
* Microwave electrothermal thruster
* VASIMR

Other|

* Atmosphere-breathing electric propulsion
* High Power Electric Propulsion
* MagBeam
* Mass driver

Nuclear propulsion|

| Closed system|

* Direct Fusion Drive
* Nuclear electric rocket
* Nuclear thermal rocket
* Radioisotope
* Salt-water
* Gas core
* "Lightbulb"
* Nuclear photonic rocket

|

Open system|

* Nuclear pulse propulsion
* Antimatter-catalyzed
* Pulsed nuclear thermal rocket‎
* Fusion rocket
* Bussard ramjet
* Fission-fragment rocket
* Fission sail

External power|

* Beam-powered propulsion
* Tethers

Related concepts|

* Orbital mechanics
* Orbital maneuver
* Gravity assist
* Aerogravity assist
* Oberth effect
* Space launch
* Non-rocket spacelaunch
* Aerobraking
* Aerocapture
* Atmospheric entry
* Reactionless drive
* Field propulsion
* Warp drive
* Alcubierre drive

Spaceflight portal

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