Reactionless drive

Reactionless drive

A reactionless drive (also known by many other names, such as an inertial propulsion engine, reactionless thruster, reactionless engine, bootstrap drive or inertia drive) is a fictional or theorized method of propulsion where thrust is generated without any need for any outside force or net momentum exchange to produce linear motion. The name comes from Newton's Third Law of Motion, usually expressed as: "For every action, there is an equal and opposite reaction". Such a drive would necessarily violate the conservation of momentum, a fundamental principle of all current understandings of physics. In addition it can be shown that conservation of energy is violated.

In spite of their physical impossibility, such devices are a staple of science fiction, particularly for space propulsion, and as with perpetual motion machines have been proposed as working technologies.



Oscillation thruster

An oscillation thruster (also known as a stiction drive, internal drive or slip-stick drive) proposes to use the motion of internal masses to create a net thrust. These thrusters include either vibrational or rotating masses, in which one portion of the cyclical motion is high-speed, and the other low-speed, or alternately high and low impulse. The actual result is that for some of the motion a high force is generated, enough to overcome friction. However on the "return stroke" the force is not high enough, and any motion occurring in the first portion is not reset. In this way the devices "steal" working mass from their supporting surface, a fact that may not be apparent to casual observation.

Basically, an oscillation thruster works just like walking does, one mass is "thrown" backward, "thrusting" the device forward according to conservation of momentum (like a person taking a step forward), then the mass is more slowly brought forward to its initial position (like the person using their step to pull the rest of their body forward). The thruster is allowed to move forward in the first step because the mass is "thrown" back with large enough force to overcome static friction. The "thruster" doesn't move backward in the second step because static friction provides an outside force that overcomes the step (like the ground does when you're walking).

Although there have been many versions proposed, all oscillation thrusters have the following common components:

  • Chassis to support a system of masses,
  • Conveyor that moves the masses through an asymmetric cycle,
  • Power source for the conveyor.

A primary feature is that these internal masses go through some sort of cyclic motion where the motion in one direction is quicker than in the return direction.

Inventors of oscillation thrusters extrapolate its behavior to mean that it can work in a vacuum in zero gravity.

One of the most famous proposed reactionless drives was the Dean drive. Although Dean himself gave few indications of how his "reactionless drive" was supposed to work, it appears to be an attempt at an oscillation thruster. Other examples of oscillation thrusters are the Thornson Inertial Engine[1] and Henry Bull’s Impulse Engine of 1935.[2]

Quantum vacuum

Magnetoelectric materials can be electrically polarized by magnetic fields; the quantum vacuum contains randomly fluctuating magnetic fields. A sufficiently small piece of magnetoelectric material can be placed in the quantum vacuum and then rotated 180 degrees. The random magnetic fields can induce a change in electric polarization in the block of material. It has been proposed that this change causes the combined electric and magnetic fields to push the block in one direction while they (the fields themselves, or more technically, the bosons of which these fields are composed) get pushed in the other direction. The trick doesn't work if the magnetoelectric block is too large but curiously it should work if there's a grid of many tiny blocks working together. This mechanism was first suggested in December 2009 and has not been tested. The author of the original paper suggested that the mechanism could be used would be powerful enough to reorient satellites if a material with a magnetoelectric constant ten times higher than the strongest such materials known today could be found.[3]

Physical impossibility

Reactionless drives are impossible as "breaking the law of conservation of momentum shatters the entire mathematical framework" of physics.[4] These devices by their very nature violate the law of conservation of momentum—if a ship with such a drive existed, then any motion of that ship, unaccompanied by the motion of any other material, would cause the center of gravity of the universe to move with it.

Furthermore, the total energy of the universe becomes reference frame dependent—energy can only be conserved in the presence of a reactionless drive in (at most) one reference frame, because in all other reference frames the change in kinetic energy of the ship differs from the power expended by the ship. Given that these two laws—the conservation of momentum and the principle of relativity—are so well established (and thoroughly verified) in physics, any ordinary mechanical system purporting to violate the laws is generally dismissed outright.[5]

Alternative approaches

Although the basic tenet of reactionless propulsion is physically impossible, hypothetical cases have been put forward which would create the same effect without evidently violating either Newton's Third Law or conservation of energy:

  • General relativity allows a hypothetical astronaut to "swim" in curved space without using reaction mass, cf. In other words, if spacetime is flat, then an astronaut can change his or her orientation in space through certain body movements (in the same manner as a falling cat can orient itself so that it hits the ground feet-first), but no amount of this sort of exertion will change the position of his center of mass. However, if local spacetime is curved, a similar trick can be used to take advantage of this curvature; mass held in the astronaut's outstretched hands moves in a slightly different path through curved spacetime than mass at the astronaut's feet, and the resulting "force" on the astronaut can change his position. While this concept is allowed by the currently accepted laws of physics, it is not clear how or even if this effect could provide a useful means of accelerating an actual space vehicle.[6]
  • Electrodynamic tethers do not expel reaction mass like a rocket;[7] however, as electromagnetic fields can carry energy and momentum,[8] tethers do have a mechanism for momentum transfer and hence are not reactionless.


Dean drive

The Dean drive, invented by Norman L. Dean, is a device intended to be a reactionless thruster. According to Dean his models were able to demonstrate this effect. He received two patents for related devices that are known to be unable to generate a uni-directional force, but he occasionally demonstrated devices that were different.[9][10] Dean's claims of reactionless thrust generation have subsequently been shown to be in error; the thrust generated is understood to be reliant on friction with the surface on which the device is resting.[11][12]

Gyroscopic Inertial Thruster (GIT)

The Gyroscopic Inertial Thruster is a proposed reactionless engine which uses entirely mechanical principles. The concept involves various methods of leverage against the supports of a large gyroscope.[13] Scottish inventor Sandy Kidd, a former RAF radar technician, investigated the possibility without success in the 1980s.[14] He posited that a gyroscope set at various angles could provide a lifting force, defying gravity.[15] In the 1990s, several people sent suggestions to NASA's Space Exploration Outreach Program (SEOP) recommending that NASA study gyroscopic inertial drive, especially the developments of American inventor Robert Cook, and Canadian inventor Roy Thornson.[13] In the '90s and 2000s, enthusiasts attempted building and testing GIT machines.[citation needed]

See also


  1. ^
  2. ^ "Henry Bull's Impulse Engine of 1935". Retrieved 2011-06-21. 
  3. ^ A magneto-electric quantum wheel. Accessed 2010-04-12.
  4. ^ Chung, Winchell D. jr. (2011-05-30). "Reactionless Drives". Atomic Rockets. Retrieved 2011-06-21. 
  5. ^ "Sean Carroll, The Alternative Science Checklist". Retrieved 2011-06-21. 
  6. ^ Gu, Eduardo. "Eduardo Guéron, Scientific American, August 2009, retrieved 2010-09-01". Retrieved 2011-06-21. 
  7. ^ Tethers | Macmillan Space Sciences. Accessed 2008-05-04.
  8. ^ "Special Projects Group via Internet Archive. Accessed 2008-05-04". 2002-11-13. Retrieved 2011-06-21. 
  9. ^ "Engine With Built-in Wings". Popular Mechanics. Sept 1961. 
  10. ^ "Detesters, Phasers and Dean Drives". Analog. June 1976. 
  11. ^ Mills, Marc G.; Thomas, Nicholas E. (July 2006). "Responding to Mechanical Antigravity". 42nd Joint Propulsion Conference and Exhibit. NASA. 
  12. ^ Goswami, Amit (2000). The Physicists' View of Nature. Springer. pp. 60. ISBN 0306464500. 
  13. ^ a b LaViolette, Paul A. (2008). Secrets of Antigravity Propulsion: Tesla, UFOs, and Classified Aerospace Technology. Inner Traditions / Bear & Co. p. 384. ISBN 159143078X. 
  14. ^ New Scientist 148: 96. 1995. 
  15. ^ Childress, David Hatcher (1990). Anti-Gravity & the Unified Field. Lost Science. Adventures Unlimited Press. p. 178. ISBN 0932813100. 

External links

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